Network Working Group G. Ash Internet Draft AT&T Labs Category: Informational October, 2001 Expires: April 2002 Traffic Engineering & QoS Methods for IP-, ATM-, & TDM-Based Multiservice Networks STATUS OF THIS MEMO: This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Distribution of this memo is unlimited. ABSTRACT This is an informational document submitted in response to a request from the IETF Traffic Engineering Working Group (TEWG) for service provider uses, requirements, and desires for traffic engineering best current practices. As such, the work sets a direction for routing and traffic performance management in networks based on traffic engineering (TE) and QoS best current practices and operational experience, such as used in the AT&T dynamic routing/class-of-service network. Analysis models are used to demonstrate that these currently operational TE/QoS methods and best current practices are extensible to Internet TE and packet networks in general. The document describes, analyzes, and recommends TE methods which control a network's response to traffic demands and other stimuli, such as link failures or node failures. These TE methods include: a) traffic management through control of routing functions, which include call routing, connection routing, QoS resource management, routing table management, and dynamic transport routing. b) capacity management through control of network design, including routing design. c) TE operational requirements for traffic management and capacity management, including forecasting, performance monitoring, and short-term network adjustment. ***************************************************************************** NOTE: A PDF VERSION OF THIS DRAFT (WITH FIGURES & TABLES) IS AVAILABLE AT http://www.research.att.com/~jrex/jerry/ ***************************************************************************** ----------------------------------------------------------------------------- TABLE OF CONTENTS ABSTRACT 1.0 Introduction 2.0 Definitions 3.0 Traffic Engineering Model 4.0 Traffic Models 5.0 Traffic Management Functions 6.0 Capacity Management Functions 7.0 Traffic Engineering Operational Requirements 8.0Traffic Engineering Modeling & Analysis 9.0 Conclusions/Recommendations 9.1 Conclusions/Recommendations on Call Routing & Connection Routing Methods (ANNEX 2) 9.2 Conclusions/Recommendations on QoS Resource Management (ANNEX 3) 9.3 Conclusions/Recommendations on Routing Table Management Methods & Requirements (ANNEX 4) 9.4 Conclusions/Recommendations on Dynamic Transport Routing Methods (ANNEX 5) 9.5 Conclusions/Recommendations on Capacity Management Methods (ANNEX 6) 9.6 Conclusions/Recommendations on TE Operational Requirements (ANNEX 7) 10.0 Recommended TE/QoS Methods for Multiservice Networks 10.1 Recommended Application-Layer IP-Network-Based Service-Creation Capabilities 10.2 Recommended Call/IP-Flow Control Layer Capabilities 10.3 Recommended Connection/Bearer Control Layer Capabilities 10.4 Recommended Transport Routing Capabilities 10.5 Recommended Network Operations Capabilities 10.6 Benefits of Recommended TE/QoS Methods for Multiservice Networks 11.0 Security Considerations 12.0 Acknowledgements 13.0 Authors' Addresses 14.0 Copyright Statement ANNEX 1. Bibliography ANNEX 2. Call Routing & Connection Routing Methods 2.1 Introduction 2.2 Call Routing Methods 2.3 Connection (Bearer-Path) Routing Methods 2.4 Hierarchical Fixed Routing (FR) Path Selection 2.5 Time-Dependent Routing (TDR) Path Selection 2.6 State-Dependent Routing (SDR) Path Selection 2.7 Event-Dependent Routing (EDR) Path Selection 2.8 Interdomain Routing 2.9 Modeling of Traffic Engineering Methods 2.9.1 Network Design Comparisons 2.9.2 Network Performance Comparisons 2.9.3 Single-Area Flat Topology versus Multi-Area Hierarchical Network Topology 2.9.4 Network Modeling Conclusions 2.10 Conclusions/Recommendations ANNEX 3. QoS Resource Management Methods 3.1 Introduction 3.2 Class-of-Service Identification, Policy-Based Routing Table Derivation, & QoS Resource Management Steps 3.2.1 Class-of-Service Identification 3.2.2 Policy-Based Routing Table Derivation 3.2.3 QoS Resource Management Steps 3.3 Dynamic Bandwidth Allocation, Protection, and Reservation Principles 3.4 Per-Virtual-Network Bandwidth Allocation, Protection, and Reservation 3.4.1 Per-VNET Bandwidth Allocation/Reservation - Meshed Network Case 3.4.2 Per-VNET Bandwidth Allocation/Reservation - Sparse Network Case 3.5 Per-Flow Bandwidth Allocation, Protection, and Reservation 3.5.1 Per-Flow Bandwidth Allocation/Reservation - Meshed Network Case 3.5.2 Per-Flow Bandwidth Allocation/Reservation - Sparse Network Case 3.6 Packet-Level Traffic Control 3.7 Other QoS Resource Management Constraints 3.8 Interdomain QoS Resource Management 3.9 Modeling of Traffic Engineering Methods 3.9.1 Performance of Bandwidth Reservation Methods 3.9.2 Multiservice Network Performance: Per-VNET vs. Per-Flow Bandwidth Allocation 3.9.3 Multiservice Network Performance: Single-Area Flat Topology vs. Multi-Area 2-Level Hierarchical Topology 3.9.4 Multiservice Network Performance: Need for MPLS & DiffServ 3.10 Conclusions/Recommendations ANNEX 4. Routing Table Management Methods & Requirements 4.1 Introduction 4.2 Routing Table Management for IP-Based Networks 4.3 Routing Table Management for ATM-Based Networks 4.4 Routing Table Management for TDM-Based Networks 4.5 Signaling and Information Exchange Requirements 4.5.1 Call Routing (Number Translation to Routing Address) Information-Exchange Parameters 4.5.2 Connection Routing Information-Exchange Parameters 4.5.3 QoS Resource Management Information-Exchange Parameters 4.5.4 Routing Table Management Information-Exchange Parameters 4.5.5 Harmonization of Information-Exchange Standards 4.5.6 Open Routing Application Programming Interface (API) 4.6 Examples of Internetwork Routing 4.6.1 Internetwork E Uses a Mixed Path Selection Method 4.6.2 Internetwork E Uses a Single Path Selection Method 4.7 Modeling of Traffic Engineering Methods 4.8 Conclusions/Recommendations ANNEX 5. Transport Routing Methods 5.1 Introduction 5.2 Dynamic Transport Routing Principles 5.3 Dynamic Transport Routing Examples 5.4 Reliable Transport Routing Design 5.4.1 Transport Link Design Models 5.4.2 Node Design Models 5.5 Modeling of Traffic Engineering Methods 5.5.1 Dynamic Transport Routing Capacity Design 5.5.2 Performance for Network Failures 5.5.3 Performance for General Traffic Overloads 5.5.4 Performance for Unexpected Overloads 5.5.5 Performance for Peak-Day Traffic Loads 5.6 Conclusions/Recommendations ANNEX 6. Capacity Management Methods 6.1 Introduction 6.2 Link Capacity Design Models 6.3 Shortest Path Selection Models 6.4 Multihour Network Design Models 6.4.1 Discrete Event Flow Optimization (DEFO) Models 6.4.2 Traffic Load Flow Optimization (TLFO) Models 6.4.3 Virtual Trunking Flow Optimization (VTFO) Models 6.5 Day-to-day Load Variation Design Models 6.6 Forecast Uncertainty/Reserve Capacity Design Models 6.7 Meshed, Sparse, and Dynamic-Transport Design Models 6.8 Modeling of Traffic Engineering Methods 6.8.1 Per-Virtual-Network vs. Per-Flow Network Design 6.8.2 Integrated vs. Separate Voice/ISDN & Data Network Designs 6.8.3 Multilink vs. 2-Link Network Design 6.8.4 Single-area Flat vs. 2-Level Hierarchical Network Design 6.8.5 EDR vs. SDR Network Design 6.8.6 Dynamic Transport Routing vs. Fixed Transport Routing Network Design 6.9 Conclusions/Recommendations ANNEX 7. Traffic Engineering Operational Requirements 7.1 Introduction 7.2 Traffic Management 7.2.1 Real-time Performance Monitoring 7.2.2 Network Control 7.2.3 Work Center Functions 7.2.3.1 Automatic controls 7.2.3.2 Code Controls 7.2.3.3 Reroute Controls 7.2.3.4 Peak-Day Control 7.2.4 Traffic Management on Peak Days 7.2.5 Interfaces to Other Work Centers 7.3 Capacity Management---Forecasting 7.3.1 Load forecasting 7.3.1.1 Configuration Database Functions 7.3.1.2 Load Aggregation, Basing, and Projection Functions 7.3.1.3 Load Adjustment Cycle and View of Business Adjustment Cycle 7.3.2 Network Design 7.3.3 Work Center Functions 7.3.4 Interfaces to Other Work Centers 7.4 Capacity Management---Daily and Weekly Performance Monitoring 7.4.1 Daily Congestion Analysis Functions 7.4.2 Study-week Congestion Analysis Functions 7.4.3 Study-period Congestion Analysis Functions 7.5 Capacity Management---Short-Term Network Adjustment 7.5.1 Network Design Functions 7.5.2 Work Center Functions 7.5.3 Interfaces to Other Work Centers 7.6 Comparison of Off-line (TDR) versus On-line (SDR/EDR) TE Methods 7.7 Conclusions/Recommendations 1.0 Introduction This is an informational document submitted in response to a request from the IETF Traffic Engineering Working Group (TEWG) for service provider uses, requirements, and desires for traffic engineering best current practices. As such, the work sets a direction for routing and traffic performance management in networks based on traffic engineering (TE) and QoS best current practices and operational experience, such as used in the AT&T dynamic routing/class-of-service network [A98]. Analysis models are used to demonstrate that these currently operational TE/QoS methods and best current practices are extensible to Internet TE and packet networks in general. TE is an indispensable network function which controls a network's response to traffic demands and other stimuli, such as network failures. TE encompasses * traffic management through control of routing functions, which include number/name translation to routing address, connection routing, routing table management, QoS resource management, and dynamic transport routing. * capacity management through control of network design. Current and future networks are rapidly evolving to carry a multitude of voice/ISDN services and packet data services on internet protocol (IP), asynchronous transfer mode (ATM), and time division multiplexing (TDM) networks. The long awaited data revolution is occurring, with the extremely rapid growth of data services such as IP-multimedia and frame-relay services. Within these categories of networks and services supported by IP, ATM, and TDM protocols have evolved various TE methods. The TE mechanisms are covered in the document, and a comparative analysis and performance evaluation of various TE alternatives is presented. Finally, operational requirements for TE implementation are covered. The recommended TE methods are meant to apply to IP-based, ATM-based, and TDM-based networks, as well as the interworking between these network technologies. Essentially all of the methods recommended are already widely applied in operational networks worldwide, particularly in PSTN networks employing TDM-based technology. However, the TE methods are shown to be extensible to packet-based technologies, that is, to IP-based and ATM-based technologies, and it is important that networks which evolve to employ these packet technologies have a sound foundation of TE methods to apply. Hence, it is the intent that the recommended TE methods in this document be used as a basis for requirements for TE methods, and, as needed, for protocol development in IP-based, ATM-based, and TDM-based networks to implement the TE methods. Hence the TE methods encompassed in this document include: * traffic management through control of routing functions, which include call routing (number/name translation to routing address), connection routing, QoS resource management, routing table management, and dynamic transport routing. * * capacity management through control of network design, including routing design. * * TE operational requirements for traffic management and capacity management, including forecasting, performance monitoring, and short-term network adjustment. Results of analysis models are presented which illustrate the tradeoffs between various TE approaches. Based on the results of these studies as well as established practice and experience, TE methods are recommended for consideration in network evolution to IP-based, ATM-based, and/or TDM-based technologies. We begin this document with a general model for TE functions, which include traffic management and capacity management functions responding to traffic demands on the network. We then present a traffic-variations model which these TE functions are responding to. Next we outline traffic management functions which include call routing (number/name translation to routing address), connection or bearer-path routing, QoS resource management, routing table management, and dynamic transport routing. These traffic management functions are further developed in ANNEXES 2, 3, 4, and 5. We then outline capacity management functions, which are further developed in ANNEX 6. Finally we briefly summarize TE operational requirements, which are further developed in ANNEX 7. In ANNEX 2, we present models for call routing, which entails number/name translation to a routing address associated with service requests, and also compare various connection (bearer-path) routing methods. In ANNEX 3, we examine QoS resource management methods in detail, and illustrate per-flow versus per-virtual-network (or per-traffic-trunk or per-bandwidth-pipe) resource management and the realization of multiservice integration with priority routing services. In ANNEX 4, we identify and discuss routing table management approaches. This includes a discussion of TE signaling and information exchange requirements needed for interworking across network types, so that the information exchange at the interface is compatible across network types. In ANNEX 5 we describe methods for dynamic transport routing, which is enabled by the capabilities such as optical cross-connect devices, to dynamically rearrange transport network capacity. In ANNEX 6 we describe principles for TE capacity management, and in ANNEX 7 we present TE operational requirements. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. 2.0 Definitions Alternate Path Routing: a routing technique where multiple paths, rather than just the shortest path, between a source node and a destination node are utilized to route traffic, which is used to distribute load among multiple paths in the network; Autonomous System: a routing domain which has a common administrative authority and consistent internal routing policy. An AS may employ multiple intradomain routing protocols and interfaces to other ASs via a common interdomain routing protocol; Blocking: refers to the denial or non-admission of a call or connection-request, based for example on the lack of available resources on a particular link (e.g., link bandwidth or queuing resources); Call: generic term to describe the establishment, utilization, and release of a connection (bearer path) or data flow; Call Routing: number (or name) translation to routing address(es), perhaps involving use of network servers or intelligent network (IN) databases for service processing; Circuit Switching denotes the transfer of an individual set of bits within a TDM time-slot over a connection between an input port and an output port within a given circuit-switching node through the circuit-switching fabric (see Switching) Class of Service characteristics of a service such as described by service identity, virtual network, link capability requirements, QoS & traffic threshold parameters; Connection: bearer path, label switched path, virtual circuit, and/or virtual path established by call routing and connection routing; Connection Admission a process by which it is determined whether a link or a node has sufficient resources Control (CAC) to satisfy the QoS required for a connection or flow. CAC is typically applied by each node in the path of a connection or flow during set-up to check local resource availability; Connection Routing: connection establishment through selection of one path from path choices governed by the routing table; Crankback a technique where a connection or flow setup is backtracked along the call/connection/flow path up to the first node that can determine an alternative path to the destination node; Destination Node: terminating node within a given network; Flow: bearer traffic associated with a given connection or connectionless stream having the same originating node, destination node, class of service, and session identification; GoS (grade of service) a number of network design variables used to provide a measure of adequacy of a group of resources under specified conditions (e.g., GoS variables may be probability of loss, dial tone delay, etc.) GoS standards parameter values assigned as objectives for GoS variables Integrated Services: a model which allows for integration of services with various QoS classes, such as key-priority, normal-priority, & best-effort priority services; Link: a bandwidth transmission medium between nodes that is engineered as a unit; Logical Link: a bandwidth transmission medium of fixed bandwidth (e.g., T1, DS3, OC3, etc.) at the link layer (layer 2) between 2 nodes, established on a path consisting of (possibly several) physical transport links (at layer 1) which are switched, for example, through several optical cross-connect devices; Node: a network element (switch, router, exchange) providing switching and routing capabilities, or an aggregation of such network elements representing a network; Multiservice Network a network in which various classes of service share the transmission, switching, queuing, management, and other resources of the network; O-D pair: an originating node to destination node pair for a given connection/bandwidth-allocation request; Originating Node: originating node within a given network; Packet Switching denotes the transfer of an individual packet over a connection between an input port and an output port within a given packet-switching node through the packet-switching fabric (see Switching) Path: a concatenation of links providing a connection/bandwidth-allocation between an O-D pair; Physical Transport Link:a bandwidth transmission medium at the physical layer (layer 1) between 2 nodes, such as on an optical fiber system between terminal equipment used for the transmission of bits or packets (see transport); Policy-Based Routing network function which involves the application of rules applied to input parameters to derive a routing table and its associated parameters; QoS (quality of service)a set of service requirements to be met by the network while transporting a Connection or flow; the collective effect of service performance which determine the Degree of satisfaction of a user of the service QoS Resource network functions which include class-of-service Management identification, routing table derivation, connection admission, bandwidth allocation, bandwidth protection, Bandwidth reservation, priority routing, and priority queuing; QoS Routing see QoS Resource Management; QoS Variable any performance variable (such as congestion, delay, etc.) which is perceivable by a user Route: a set of paths connecting the same originating node-destination node pair; Routing the process of determination, establishment, and use of routing tables to select paths between an input port at the ingress network edge and output port at the egress network edge; includes the process of performing both call routing and connection routing (see call routing and connection routing) Routing Table: describes the path choices and selection rules to select one path out of the route for a connection/bandwidth-allocation request; Switching denotes connection of an input port to an output port within a given node through the switching fabric Traffic Engineering encompasses traffic management, capacity management, traffic measurement and modeling, network modeling, and performance analysis; Traffic Engineering network functions which support traffic engineering Methods and include call routing, connection routing, QoS resource management, routing table management, and capacity management; Traffic Stream: a class of connection requests with the same traffic characteristics; Traffic Trunk: an aggregation of traffic flows of the same class which are routed on the same path (see logical link) Transport refers to the transmission of bits or packets on the physical layer (layer 1) between 2 nodes, such as on an optical fiber system between terminal equipment (note that this definition is distinct from the IP-protocol terminology of transport as end-to-end connectivity at layer 4, such as with the Transport Control Protocol (TCP)) Via node: an intermediate node in a path within a given network; 3.0 Traffic Engineering Model Figure 1.1 illustrates a model for network traffic engineering. The central box represents the network, which can have various architectures and ----------------------------------------------------------------------------- Figure 1.1 Traffic Engineering Model (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- configurations, and the routing tables used within the network. Network configurations could include metropolitan area networks, national intercity networks, and global international networks, which support both hierarchical and nonhierarchical structures and combinations of the two. Routing tables describe the path choices from an originating node to a terminating node, for a connection request for a particular service. Hierarchical and nonhierarchical traffic routing tables are possible, as are fixed routing tables and dynamic routing tables. Routing tables are used for a multiplicity of traffic and transport services on the telecommunications network. The functions depicted in Figure 1.1 are consistent with the definition of TE employed by the Traffic Engineering Working Group (TEWG) within the Internet Engineering Task Force (IETF): Internet Traffic Engineering is concerned with the performance optimization of operational networks. It encompasses the measurement, modeling, characterization, and control of Internet traffic, and the application of techniques to achieve specific performance objectives, including the reliable and expeditious movement of traffic through the network, the efficient utilization of network resources, and the planning of network capacity. Terminology used in the document, as illustrated in Figure 1.2, is that a link is a transmission medium (logical or physical) which connects two nodes, a ----------------------------------------------------------------------------- Figure 1.2 Terminology (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- path is a sequence of links connecting an origin and destination node, and a route is the set of different paths between the origin and destination that a call might be routed on within a particular routing discipline. Here a call is a generic term used to describe the establishment, utilization, and release of a connection, or data flow. In this context a call can refer to a voice call established perhaps using the SS7 signaling protocol, or to a web-based data flow session, established perhaps by the HTTP and associated IP-based protocols. Various implementations of routing tables are discussed in ANNEX 2. Traffic engineering functions include traffic management, capacity management, and network planning. Traffic management ensures that network performance is maximized under all conditions including load shifts and failures. Capacity management ensures that the network is designed and provisioned to meet performance objectives for network demands at minimum cost. Network planning ensures that node and transport capacity is planned and deployed in advance of forecasted traffic growth. Figure 1.1 illustrates traffic management, capacity management, and network planning as three interacting feedback loops around the network. The input driving the network ("system") is a noisy traffic load ("signal"), consisting of predictable average demand components added to unknown forecast error and load variation components. The load variation components have different time constants ranging from instantaneous variations, hour-to-hour variations, day-to-day variations, and week-to-week or seasonal variations. Accordingly, the time constants of the feedback controls are matched to the load variations, and function to regulate the service provided by the network through capacity and routing adjustments. Traffic management functions include a) call routing, which entails number/name translation to routing address, b) connection or bearer-path routing methods, c) QoS resource management, d) routing table management, and e) dynamic transport routing. These functions can be a) decentralized and distributed to the network nodes, b) centralized and allocated to a centralized controller such as a bandwidth broker, or c) performed by a hybrid combination of these approaches. Capacity management plans, schedules, and provisions needed capacity over a time horizon of several months to one year or more. Under exceptional circumstances, capacity can be added on a shorter-term basis, perhaps one to several weeks, to alleviate service problems. Network design embedded in capacity management encompasses both routing design and capacity design. Routing design takes account of the capacity provided by capacity management, and on a weekly or possibly real-time basis adjusts routing tables as necessary to correct service problems. The updated routing tables are provisioned (configured) in the switching systems either directly or via an automated routing update system. Network planning includes node planning and transport planning, operates over a multiyear forecast interval, and drives network capacity expansion over a multiyear period based on network forecasts. The scope of the TE methods includes the establishment of connections for narrowband, wideband, and broadband multimedia services within multiservice networks and between multiservice networks. Here a multiservice network refers to one in which various classes of service share the transmission, switching, management, and other resources of the network. These classes of services can include constant bit rate (CBR), variable bit rate (VBR), unassigned bit rate (UBR), and available bit rate (ABR) traffic classes. There are quantitative performance requirements that the various classes of service normally are required to meet, such as end-to-end blocking, delay, and/or delay-jitter objectives. These objectives are achieved through a combination of traffic management and capacity management. Figure 1.3 illustrates the functionality for setting up a connection from an originating node in one network to a destination node in another network, ----------------------------------------------------------------------------- Figure 1.3 Example of Multimedia Connection Across TDM-, ATM-, and IP-Based Networks (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- using one or more routing methods across networks of various types. The Figure illustrates a multimedia connection between two PCs which carries traffic for a combination of voice, video, and image applications. For this purpose a logical point-to-point connection is established from the PC served by node a1 to the PC served by node c2. The connection could be a CBR ISDN connection across TDM-based network A and ATM-based network C, or it might be a VBR connection via IP-based network B. Gateway nodes a3, b1, b4, and c1 provide the interworking capabilities between the TDM-, ATM-, and IP-based networks. The actual multimedia connection might be routed, for example, on a path consisting of nodes a1-a2-a3-b1-b4-c1-c2, or possibly on a different path through different gateway nodes. We now briefly describe the traffic model, the traffic management functions, the capacity management functions, and the TE operational requirements, which are further developed in ANNEXES 2-7 of the document. 4.0 Traffic Models In this section we discuss load variation models which drive traffic engineering functions, that is traffic management, capacity management, and network planning. Table 1.1 summarizes examples of models that could be used to represent the different traffic variations under consideration. Traffic models for both voice and data traffic need to be reflected. Work has been done on measurement and characterization of data traffic, such as web-based traffic [FGLRRT00, FGHW99, LTWW94]. Some of the analysis suggests that web-based traffic can be self-similar, or fractal, with very large variability and extremely long tails of the associated traffic distributions. Characterization studies of such data traffic have investigated various traditional models, such as the Markov modulated Poisson Process (MMPP), in which it is shown that MMPP with two parameters can suitably capture the essential nature of the data traffic [H99, BCHLL99]. Modeling work has been done to investigate the causes of the extreme variability of web-based traffic. In [HM00], the congestion-control mechanisms for web-based traffic, such as window flow control for transport-control-protocol (TCP) traffic appear to be at the root cause of its extreme variability over small time scales. [FGHW99] also shows that the variability over small time scales is impacted in a major way by the presence of TCP-like flow control algorithms which give rise to burstiness and clustering of IP packets. However, [FGHW99] also finds that the self-similar behavior over long time scales is almost exclusively due to user-related variability and not dependent on the underlying network-specific aspects. Regarding the modeling of voice and date traffic in a multiservice model, [HM00] suggests that the regular flow control dynamics are more useful to model than the self-similar traffic itself. Much of the traffic to be modeled is VBR traffic subject to service level agreements (SLAs), which is subject to admission control based on equivalent bandwidth resource requirements and also to traffic shaping in which out-of-contract packets are marked for dropping in the network queues if congestion arises. Other VBR traffic, such as best-effort internet traffic, is not allocated any bandwidth in the admission of session flows, and all of its packets would be subject to dropping ahead of the CBR and VBR-SLA traffic. Hence, we can think of the traffic model consisting of two components: * the CBR and VBR-SLA traffic that is not marked for dropping constitute less variable traffic subject to more traditional models * the VBR best-effort traffic and the VBR-SLA traffic packets that are marked and subject to dropping constitute a much more variable, self-similar traffic component. Considerable work has been done on modeling of broadband and other data traffic, in which two-parameter models that capture the mean and burstiness of the connection and flow arrival processes have proven to be quite adequate. See [E.716] for a good reference on this. Much work has also been done on measurement and characterization of voice traffic, and two-parameter models reflecting mean and variance (the ratio of the variance to the mean is sometimes called the peakedness parameter) of traffic have proven to be accurate models. We model the large variability in packet arrival processes in an attempt to capture the extreme variability of the traffic. Here we reflect the two-parameter, multiservice traffic models for connection and flow arrival processes, which are manageable from a modeling and analysis aspect and which attempt to capture essential aspects of data and voice traffic variability for purposes of traffic engineering and QoS methods. In ANNEX 2 we introduce the models of variability in the packet arrival processes. ----------------------------------------------------------------------------- Table 1.1 Traffic Models for Load Variations of Connection/Flow Arrival Processes (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- For instantaneous traffic load variations, the load is typically modeled as a stationary random process over a given period (normally within each hourly period) characterized by a fixed mean and variance. From hour to hour, the mean traffic loads are modeled as changing deterministically; for example, according to their 20-day average values. From day to day, for a fixed hour, the mean load can be modeled, for example, as a random variable having a gamma distribution with a mean equal to the 20-day average load. From week to week, the load variation is modeled as a random process in the network design procedure. The random component of the realized week-to-week load is the forecast error, which is equal to the forecast load minus the realized load. Forecast error is accounted for in short-term capacity management. In traffic management, traffic load variations such as instantaneous variations, hour-to-hour variations, day-to-day traffic variations, and week-to-week variations are responded to in traffic management by appropriately controlling number translation/routing, path selection, routing table management, and/or QoS resource management. Traffic management provides monitoring of network performance through collection and display of traffic and performance data, and allows traffic management controls, such as destination-address per-connection blocking, per-connection gapping, routing table modification, and path selection/reroute controls, to be inserted when circumstances warrant. For example, a focused overload might lead to application of connection gapping controls in which a connection request to a particular destination address or set of addresses is admitted only once every x seconds, and connections arriving after an accepted call are rejected for the next x seconds. In that way call gapping throttles the calls and prevents overloading the network to a particular focal point. Routing table modification and reroute control are illustrated in ANNEXES 2, 3, 5, and 7. Capacity management must provide sufficient capacity to carry the expected traffic variations so as to meet end-to-end blocking/delay objective levels. Here the term blocking refers to the denial or non-admission of a call or connection request, based for example on the lack of available resources on a particular link (e.g., link bandwidth or queuing resources). Traffic load variations lead in direct measure to capacity increments and can be categorized as (1) minute-to-minute instantaneous variations and associated busy-hour traffic load capacity, (2) hour-to-hour variations and associated multihour capacity, (3) day-to-day variations and associated day-to-day capacity, and (4) week-to-week variations and associated reserve capacity. Design methods within the capacity management procedure account for the mean and variance of the within-the-hour variations of the offered and overflow loads. For example, classical methods [e.g., Wil56] are used to size links for these two parameters of load. Multihour dynamic route design accounts for the hour-to-hour variations of the load and, hour-to-hour capacity can vary from zero to 20 percent or more of network capacity. Hour-to-hour capacity can be reduced by multihour dynamic routing design models such as the discrete event flow optimization, traffic load flow optimization, and virtual trunking flow optimization models described in ANNEX 6. As noted in Table 1.1, capacity management excludes non-recurring traffic such as caused by overloads (focused or general overloads), or failures. This process is described further in ANNEX 7. It is known that some daily variations are systematic (for example, Monday morning business traffic is usually higher than Friday morning); however, in some day-to-day variation models these systematic changes are ignored and lumped into the stochastic model. For instance, the traffic load between Los Angeles and New Brunswick is very similar from one day to the next, but the exact calling levels differ for any given day. This load variation can be characterized in network design by a stochastic model for the daily variation, which results in additional capacity called day-to-day capacity. Day-to-day capacity is needed to meet the average blocking/delay objective when the load varies according to the stochastic model. Day-to-day capacity is nonzero due to the nonlinearities in link blocking and/or link queuing delay levels as a function of load. When the load on a link fluctuates about a mean value, because of day-to-day variation, the mean blocking/delay is higher than the blocking/delay produced by the mean load. Therefore, additional capacity is provided to maintain the blocking/delay probability grade-of-service objective in the presence of day-to-day load variation. Typical day-to-day capacity required is 4--7 percent of the network cost for medium to high day-to-day variations, respectively. Reserve capacity, like day-to-day capacity, comes about because load uncertainties---in this case forecast errors---tend to cause capacity buildup in excess of the network design that exactly matches the forecast loads. Reluctance to disconnect and rearrange link and transport capacity contributes to this reserve capacity buildup. At a minimum, the currently measured mean load is used to adjust routing and capacity design, as needed. In addition, the forecast-error variance component in used in some models to build in so-called protective capacity. Reserve or protective capacity can provide a cushion against overloads and failures, and generally benefits network performance. However, provision for reserve capacity is not usually built into the capacity management design process, but arises because of sound administrative procedures. These procedures attempt to minimize total cost, including both network capital costs and operations costs. Studies have shown that reserve capacity in some networks to be in the range of 15 to 25 percent or more of network cost [FHH79]. This is further described in ANNEXES 5 and 6. 5.0 Traffic Management Functions In ANNEXES 2-5, traffic management functions are discussed: a) Call Routing Methods (ANNEX 2). Call routing involves the translation of a number or name to a routing address. We describe how number (or name) translation should result in the E.164 ATM end-system addresses (AESA), network routing addresses (NRAs), and/or IP addresses. These addresses are used for routing purposes and therefore must be carried in the connection-setup information element (IE). b) Connection/Bearer-Path Routing Methods (ANNEX 2). Connection or bearer-path routing involves the selection of a path from the originating node to the destination node in a network. We discuss bearer-path selection methods, which are categorized into the following four types: fixed routing (FR), time-dependent routing (TDR), state-dependent routing (SDR), and event-dependent routing (EDR). These methods are associated with routing tables, which consist of a route and rules to select one path from the route for a given connection or bandwidth-allocation request. c) QoS Resource Management Methods (ANNEX 3). QoS resource management functions include class-of-service derivation, policy-based routing table derivation, connection admission, bandwidth allocation, bandwidth protection, bandwidth reservation, priority routing, priority queuing, and other related resource management functions. d) Routing Table Management Methods (ANNEX 4). Routing table management information, such as topology update, status information, or routing recommendations, is used for purposes of applying the routing table design rules for determining path choices in the routing table. This information is exchanged between one node and another node, such as between the ON and DN, for example, or between a node and a network element such as a bandwidth-broker processor (BBP). This information is used to generate the routing table, and then the routing table is used to determine the path choices used in the selection of a path. e) Dynamic Transport Routing Methods (ANNEX 5). Dynamic transport routing combines with dynamic traffic routing to shift transport bandwidth among node pairs and services through use of flexible transport switching technology, such as optical cross-connects (OXCs). Dynamic transport routing offers advantages of simplicity of design and robustness to load variations and network failures, and can provide automatic link provisioning, diverse link routing, and rapid link restoration for improved transport capacity utilization and performance under stress. OXCs can reconfigure logical transport capacity on demand, such as for peak day traffic, weekly redesign of link capacity, or emergency restoration of capacity under node or transport failure. MPLS control capabilities are proposed for the setup of layer 2 logical links through OXCs [ARDC99]. 6.0 Capacity Management Functions In ANNEX 6, we discuss capacity management methods, as follows: a) Link Capacity Design Models. These models find the optimum tradeoff between traffic carried on a shortest network path (perhaps a direct link) versus traffic carried on alternate (longer, less efficient) network paths. b) Shortest Path Selection Models. These models enable the determination of shortest paths in order to provide a more efficient and flexible routing plan. c) Multihour Network Design Models. Three models are described including i) discrete event flow optimization (DEFO) models, ii) traffic load flow optimization (TLFO) models, and iii) virtual trunking flow optimization (VTFO) models. DEFO models have the advantage of being able to model traffic and routing methods of arbitrary complexity, for example, such as self-similar traffic. d) Day-to-day Load Variation Design Models. These models describe techniques for handling day-to-day variations in capacity design. e) Forecast Uncertainty/Reserve Capacity Design Models. These models describe the means for accounting for errors in projecting design traffic loads in the capacity design of the network. 7.0 Traffic Engineering Operational Requirements In ANNEX 7, we discuss traffic engineering operational requirements, as follows: a) Traffic Management. We discuss requirements for real-time performance monitoring, network control, and work center functions. The latter includes automatic controls, manual controls, code controls, cancel controls, reroute controls, peak-day controls, traffic management on peak days, and interfaces to other work centers. b) Capacity Management - Forecasting. We discuss requirements for load forecasting, including configuration database functions, load aggregation, basing, and projection functions, and load adjustment cycle and view of business adjustment cycle. We also discuss network design, work center functions, and interfaces to other work centers. c) Capacity Management - Daily and Weekly Performance Monitoring. We discuss requirements for daily congestion analysis, study-week congestion analysis, and study-period congestion analysis. d) Capacity Management - Short-Term Network Adjustment. We discuss requirements for network design, work center functions, and interfaces to other work centers. e) Comparison of off-line (TDR) versus on-line (SDR/EDR) TE methods. We contrast off-line TE methods, such as in a TDR-based network, with on-line TE methods, such as in an SDR- or EDR-based network. 8.0 Traffic Engineering Modeling & Analysis In ANNEXES 2-6 we use network models to illustrate the traffic engineering methods developed in the document. The details of the models are presented in each ANNEX in accordance with the TE functions being illustrated. In the document, a full-scale 135-node national network node model is used together with a multiservice traffic demand model to study various TE scenarios and tradeoffs. Typical voice/ISDN traffic loads are used to model the various network alternatives. These voice/ISDN loads are further segmented in the model into eight constant-bit-rate (CBR) virtual networks (VNETs), including business voice, consumer voice, international voice in and out, key-service voice, normal and key-service 64-kbps ISDN data, and 384-kbps ISDN data. The data services traffic model incorporates typical traffic load patterns and comprises three additional VNET load patterns. These include a) a variable bit rate real-time (VBR-RT) VNET, representing services such as IP-telephony and compressed voice, b) a variable bit rate and credit card check, and c) an unassigned bit rate (UBR) VNET, representing best-effort services such as email, voice mail, and file transfer multimedia applications. The cost model represents typical switching and transport costs, and illustrates the economies-of-scale for costs projected for high capacity network elements in the future. Many different alternatives and tradeoffs are examined in the models, including: 1. centralized routing table control versus distributed control 2. off-line, pre-planned (e.g.,TDR-based) routing table control versus on-line routing table control (e.g., SDR- or EDR-based) 3. per-flow traffic management versus per-virtual-network (or per-traffic-trunk or per-bandwidth-pipe) traffic management 4. sparse logical topology versus meshed logical topology 5. FR versus TDR versus SDR versus EDR path selection 6. multilink path selection versus two-link path selection 7. path selection using local status information versus global status information 8. global status dissemination alternatives including status flooding, distributed query for status, and centralized status in a bandwidth-broker processor Table 1.2 summarizes brief comparisons and observations, based on the modeling, in each of the above alternatives and tradeoffs (further details are contained in ANNEXES 2-6). ----------------------------------------------------------------------------- Table 1.2 Tradeoff Categories and Comparisons (Based on Modeling in ANNEXES 2-6) (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- 9.0 Conclusions/Recommendations Following is a summary of the main conclusions/recommendations reached in the document. 9.1 Conclusions/Recommendations on Call Routing & Connections Routing Methods (ANNEX 2) * TE methods are recommended to be applied, and in all cases of the TE methods being applied, network performance is always better and usually substantially better than when no TE methods are applied * Sparse-topology multilink-routing networks are recommended and provide better overall performance under overload than meshed-topology networks, but performance under failure may favor the 2-link STT-EDR/DC-SDR meshed-topology options with more alternate routing choices. * Single-area flat topologies are recommended and exhibit better network performance and, as discussed and modeled in ANNEX 6, greater design efficiencies in comparison with multi-area hierarchical topologies. As illustrated in ANNEX 4, larger administrative areas can be achieved through use of EDR-based TE methods as compared to SDR-based TE methods. * Event-dependent-routing (EDR) TE path selection methods are recommended and exhibit comparable or better network performance compared to state-dependent-routing (SDR) methods. a. EDR TE methods are shown to an important class of TE algorithms. EDR TE methods are distinct from the TDR and SDR TE methods in how the paths (e.g., MPLS label switched paths, or LSPs) are selected. In the SDR TE case, the available link bandwidth (based on LSA flooding of ALB information) is typically used to compute the path. In the EDR TE case, the ALB information is not needed to compute the path, therefore the ALB flooding does not need to take place (reducing the overhead). b. EDR TE algorithms are adaptive and distributed in nature and typically use learning models to find good paths for TE in a network. For example, in a success-to-the-top (STT) EDR TE method, if the LSR-A to LSR-B bandwidth needs to be modified, say increased by delta-BW, the primary LSP-p is tried first. If delta-BW is not available on one or more links of LSP-p, then the currently successful LSP-s is tried next. If delta-BW is not available on one or more links of LSP-s, then a new LSP is searched by trying additional candidate paths until a new successful LSP-n is found or the candidate paths are exhausted. LSP-n is then marked as the currently successful path for the next time bandwidth needs to be modified. The performance of distributed EDR TE methods is shown to be equal to or better than SDR methods, centralized or distributed. c. While SDR TE models typically use available-link-bandwidth (ALB) flooding for TE path selection, EDR TE methods do not require ALB flooding. Rather, EDR TE methods typically search out capacity by learning models, as in the STT method above. ALB flooding can be very resource intensive, since it requires link bandwidth to carry LSAs, processor capacity to process LSAs, and the overhead can limit area/autonomous system (AS) size. Modeling results show EDR TE methods can lead to a large reduction in ALB flooding overhead without loss of network throughput performance [as shown in ANNEX 4]. d. State information as used by the SDR options (such as with link-state flooding) provides essentially equivalent performance to the EDR options, which typically used distributed routing with crankback and no flooding. e. Various path selection methods can interwork with each other in the same network, as required for multi-vendor network operation. * Interdomain routing methods are recommended which extend the intradomain call routing and connection routing concepts, such as flexible path selection and per-class-of-service bandwidth selection, to routing between network domains. 9.2 Conclusions/Recommendations on QoS Resource Management Methods (ANNEX 3) * QoS resource management is recommended and is shown to be effective in achieving connection-level and packet-level GoS objectives, as well as key service, normal service, and best effort service differentiation. * Admission control is recommended and is the basis that allows for applying most of the other controls described in this document. * Per-VNET bandwidth allocation is recommended and is essentially equivalent to per-flow bandwidth allocation in network performance and efficiency. Because of the much lower routing table management overhead requirements, as discussed and modeled in ANNEX 4, per-VNET bandwidth allocation is preferred to per-flow allocation. * Both MPLS QoS and bandwidth management and DiffServ priority queuing management are recommended and are important for ensuring that multiservice network performance objectives are met under a range of network conditions. Both mechanisms operate together to ensure QoS resource allocation mechanisms (bandwidth allocation, protection, and priority queuing) are achieved. 9.3 Conclusions/Recommendations on Routing Table Management Methods & Requirements (ANNEX 4) * Per-VNET bandwidth allocation is recommended and is preferred to per-flow allocation because of the much lower routing table management overhead requirements. Per-VNET bandwidth allocation is essentially equivalent to per-flow bandwidth allocation in network performance and efficiency, as discussed in ANNEX 3. * EDR TE methods are recommended and can lead to a large reduction in ALB flooding overhead without loss of network throughput performance. While SDR TE methods typically use ALB flooding for TE path selection, EDR TE methods do not require ALB flooding. Rather, EDR TE methods typically search out capacity by learning models, as in the STT method. ALB flooding can be very resource intensive, since it requires link bandwidth to carry LSAs, processor capacity to process LSAs, and the overhead can limit area/autonomous system (AS) size. * EDR TE methods are recommended and lead to possible larger administrative areas as compared to SDR-based TE methods because of lower routing table management overhead requirements. This can help achieve single-area flat topologies which, as discussed in ANNEX 3, exhibit better network performance and, as discussed in ANNEX 6, greater design efficiencies in comparison with multi-area hierarchical topologies. 9.4 Conclusions/Recommendations on Transport Routing Methods (ANNEX 5) * Dynamic transport routing is recommended and provides greater network throughput and, consequently, enhanced revenue, and at the same time capital savings should result, as discussed in ANNEX 6. a. Dynamic transport routing network design enhances network performance under failure, which arises from automatic inter-backbone-router and access logical-link diversity in combination with the dynamic traffic routing and transport restoration of logical links. b. Dynamic transport routing network design is recommended and improves network performance in comparison with fixed transport routing for all network conditions simulated, which include abnormal and unpredictable traffic load patterns. * Traffic and transport restoration level design is recommended and allows for link diversity to ensure a minimum level of performance under failure. * Robust routing techniques are recommended, which include dynamic traffic routing, multiple ingress/egress routing, and logical link diversity routing; these methods improve response to node or transport failures. 9.5 Conclusions/Recommendations on Capacity Management Methods (ANNEX 6) * Discrete event flow optimization (DEFO) design models are recommended and are shown to be able to capture very complex routing behavior through the equivalent of a simulation model provided in software in the routing design module. By this means, very complex routing networks have been designed by the model, which include all of the routing methods discussed in ANNEX 2 (FR, TDR, SDR, and EDR methods) and the multiservice QoS resource allocation models discussed in ANNEX 3. * Sparse topology options are recommended, such as the multilink STT-EDR/DC-SDR/DP-SDR options, which lead to capital cost advantages, and more importantly to operation simplicity and cost reduction. Capital cost savings are subject to the particular switching and transport cost assumptions. Operational issues are further detailed in ANNEX 7. * Voice and data integration is recommended and a. can provide capital cost advantages, and b. more importantly can achieve operational simplicity and cost reduction, and c. if IP-telephony takes hold and a significant portion of voice calls use voice compression technology, this could lead to more efficient networks. * Multilink routing methods are recommended and exhibit greater design efficiencies in comparison with 2-link routing methods. As discussed and modeled in ANNEX 3, multilink topologies exhibit better network performance under overloads in comparison with 2-link routing topologies; however the 2-link topologies do better under failure scenarios. * Single-area flat topologies are recommended and exhibit greater design efficiencies in termination and transport capacity, but higher cost, and, as discussed and modeled in ANNEX 3, better network performance in comparison with multi-area hierarchical topologies. As illustrated in ANNEX 4, larger administrative areas can be achieved through use of EDR-based TE methods as compared to SDR-based TE methods. * EDR methods are recommended and exhibit comparable design efficiencies to SDR. This suggests that there is not a significant advantage for employing link-state information in these network designs, especially given the high overhead in flooding link-state information in SDR methods. * Dynamic transport routing is recommended and achieves capital savings by concentrating capacity on fewer, high-capacity physical fiber links and, as discussed in ANNEX 5, achieves higher network throughput and enhanced revenue by their ability to flexibly allocate bandwidth on the logical links serving the access and inter-node traffic. 9.6 Conclusions/Recommendations on TE Operational Requirements (ANNEX 7) * Monitoring of traffic and performance data is recommended and is required for traffic management, capacity forecasting, daily and weekly performance monitoring, and short-term network adjustment. * Traffic management is recommended and is required to provide monitoring of network performance through collection and display of real-time traffic and performance data and allow traffic management controls such as code blocks, connection request gapping, and reroute controls to be inserted when circumstances warrant. * Capacity management is recommended and is required for capacity forecasting, daily and weekly performance monitoring, and short-term network adjustment. * Forecasting is recommended and is required to operate over a multiyear forecast interval and drive network capacity expansion. * Daily and weekly performance monitoring is recommended and is required to identify any service problems in the network. If service problems are detected, short-term network adjustment can include routing table updates and, if necessary, short-term capacity additions to alleviate service problems. Updated routing tables are sent to the switching systems * Short-term capacity additions are recommended and are required as needed, but only as an exception, whereas most capacity changes are normally forecasted, planned, scheduled, and managed over a period of months or a year or more. * Network design, which includes routing design and capacity design, is recommended and is required within the capacity management function. * Network planning is recommended and is required for longer-term node planning and transport network planning, and operates over a horizon of months to years to plan and implement new node and transport capacity. 10. Recommended TE/QoS Methods for Multiservice Networks In summary, TE methods are recommended in this Section for consideration in network evolution. These recommendations are based on * results of analysis models presented in ANNEXES 2-6, which illustrate the tradeoffs between various TE approaches, * results of operational comparison studies presented in ANNEXES 2-6, * established best current practices and experience. 10.1 Recommended Application-Layer IP-Network-Based Service-Creation Capabilities As discussed in ANNEX 4, these capabilities are recommended for application-layer service-creation capabilities: * Parlay API (application programming interface) * call processing language (CPL) & common gateway interface (CGI) * SIP/IN (intelligent network) interworking 10.2 Recommended Call/IP-Flow Control Layer Capabilities As discussed in ANNEXES 2 and 4, these capabilities are recommended for name translation, call signaling, and split gateway control: * ENUM/DNS-based name to IP-address translation * SIP-based distributed call signaling (DCS) * MGCP/MEGACO for split gateway control 10.3 Recommended Connection/Bearer Control Layer Capabilities In this Section we summarize the findings in ANNEXES 2, 3, and 4 which give rise to a recommendation for a TE/QoS admission control method for connection/flow admission, which incorporates dynamic Qos routing connection/bearer layer control. The analysis considered in ANNEXES 2, 3, and 4 investigates bandwidth allocation for the aggregated case ("per traffic-trunk" or per-VNET (virtual network)) versus the per-flow bandwidth allocation. The following recommendations are made on QoS resource management, topology, and connection layer control: * virtual-network traffic allocation for multiservice network * MPLS-based virtual-network based QoS resource management & dynamic bandwidth reservation methods * DiffServ-based priority queuing * per-virtual-network (per-traffic-trunk) bandwidth allocation for lower routing table management overhead * sparse-topology multilink routing for better performance & design efficiency * single-area flat topology (as much as possible, while retaining edge-core architecture) for better performance & design efficiency * MPLS and DiffServ functionality to meet TE/QoS requirements * success-to-the-top (STT) event-dependent-routing (EDR) TE path selection methods for better performance & lower overhead These TE admission control and dynamic QoS routing methods will ensure stable/efficient performance of TE methods and help manage resources for and differentiate key service, normal service, & best effort service, and are now briefly summarized. Figure 1.4 illustrates the recommended QoS resource management methods. As illustrated in the Figure, in the ----------------------------------------------------------------------------- Figure 1.4 Use MPLS/Diffserv/Virtual-Network-Based QoS Resource Management with Dynamic Bandwidth Reservation Methods (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- multi-service, QoS resource management network, bandwidth is allocated to the individual VNETs (high-priority key services VNETs, normal-priority services VNETs, and best-effort low-priority services VNETs). The Figure also illustrates the use of virtual-network traffic allocation for multiservice networks and the means to differentiate key service, normal service, & best effort service. High-priority and normal-priority traffic connections/flows are subject to admission control based on equivalent bandwidth allocation techniques. However, best-effort services are allocated no bandwidth, and all best-effort traffic is subject to dropping in the queuing/scheduling discipline under congestion conditions. This allocated bandwidth is protected by bandwidth reservation methods, as needed, but otherwise shared. Each ON monitors VNET bandwidth use on each VNET CRLSP, and determines when VNET CRLSP bandwidth needs to be increased or decreased. Bandwidth changes in VNET bandwidth capacity are determined by ONs based on an overall aggregated bandwidth demand for VNET capacity (not on a per-connection demand basis). Based on the aggregated bandwidth demand, these ONs make periodic discrete changes in bandwidth allocation, that is, either increase or decrease bandwidth on the CRLSPs constituting the VNET bandwidth capacity. For example, if connection requests are made for VNET CRLSP bandwidth that exceeds the current CRLSP bandwidth allocation, the ON initiates a bandwidth modification request on the appropriate CRLSP(s). For example, this bandwidth modification request may entail increasing the current CRLSP bandwidth allocation by a discrete increment of bandwidth denoted here as delta-bandwidth (DBW). DBW is a large enough bandwidth change so that modification requests are made relatively infrequently. Also, the ON periodically monitors CRLSP bandwidth use, such as once each minute, and if bandwidth use falls below the current CRLSP allocation the ON initiates a bandwidth modification request to decrease the CRLSP bandwidth allocation by a unit of bandwidth such as DBW. Therefore the recommendation is to do "per-VNET", or per traffic trunk, bandwidth allocation, and not call by call, or "per flow" allocation, as , as discussed in Sections 3.4 and 3.5. This kind of per-VNET bandwidth allocation also applies in the case of multi-area TE, as discussed in Sections 2.8 and 3.8. Therefore some telephony concepts, such as call-by-call set up, are not needed in VoIP/TE. That is, there are often good reasons not to make things look like the PSTN. On the other hand, some principles do still apply to VoIP/TE, but are not used as yet, and should be. The main point about bandwidth reservation is related to both admission control and queue management. That is, if a flow is to be admitted on a longer path, that is, not the primary path (which is preferred and tried first, but let us assume did not have the available bandwidth on one or more links/queues), then there needs to be a minimum level of available bandwidth, call in RESBW (reserved bandwidth), available on each link and in each queue in addition to the requested bandwidth (REQBW). That is, one needs to have RESBW + BEWBW available on each link and queue before admitting the flow on the longer path. On the primary path RESBW is not required. The simulation results given in ANNEX 3 are for an MPLS network, and the results show the effect of using bandwidth reservation, and what happens if you do not use bandwidth reservation (see Tables 3.4 and 3.5). Bandwidth allocation and management is done according to the traffic priority (i.e., key, normal, and best effort), as described in ANNEX 3, and is an additional use of bandwidth reservation methods beyond the use in path selection, as in the example above. Bandwidth allocation in the queues is done according to traffic priority, as discussed in Section 3.6. These principles put forth in the document do not depend on whether the underlying technology is IP/MPLS-based, ATM/PNNI-based, or TDM/E.351-based, they apply to all technologies, as is demonstrated by the models. In the models the per-VNET method compares favorably with the per-flow method, which is all feasible within the current MPLS protocol specification and is therefore recommended for the TE admission control and dynamic QoS routing methods. Furthermore, we find that a distributed event-dependent-routing (EDR)/STT method of LSP management works just as well or better than the state-dependent-routing (SDR) with flooding. An example of the EDR/STT method: Figure 1.5 illustrates the recommended STT EDR path selection method and the use of a sparse, single-area topology. ----------------------------------------------------------------------------- Figure 1.5 Use Success-to-the-Top (STT) Event-Dependent-Routing (EDR) TE Path Selection Methods in a Sparse, Single-Area Topology (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- The EDR/STT method is fully distributed, reduces flooding, and a larger perhaps even a single backbone area could be used as a result. Edge-router (ER) to backbone-router (BR) hierarchy is also modeled. We modeled an MPLS/DiffServ ER-BR resource management, although it is sometimes claimed that DiffServ alone would suffice on the ER-BR links. The problem there is what happens when bandwidth is exhausted for the connection-oriented voice, ISDN, IP-telephony, etc. services versus the best-effort services. One needs a TE admission control mechanism to reject connection requests when need be. In the ER/BR hierarchy modeled, there is a mesh of LSPs in the backbone, but separate LSPs ("big pipes") for each ER to the backbone BRs, that is, for each ER-BR area (i.e., there is no ER-ER LSP mesh in this case). Some example VNET definitions are given in Figure 1.6 along with example Service Identity components, as well traffic allocation characteristics such as service priority and bandwidth characteristics. ----------------------------------------------------------------------------- Figure 1.6 Use Virtual-Network Traffic Allocation for Multiservice Network Differentiate Key Service, Normal Service, & Best Effort Service (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- 10.4 Recommended Transport Routing Capabilities As discussed in ANNEX 5, the following recommendations are made for transport routing: * dynamic transport routing for better performance & design efficiency * traffic and transport restoration level design, which allows for link diversity to ensure a minimum level of performance under failure 10.5 Recommended Network Operations Capabilities As discussed in ANNEXES 5 and 6, the following recommendations are made for network operations and design: * monitor traffic & performance data for traffic management & capacity management Figure 1.1 illustrates the monitoring of network traffic and performance data to support traffic management and capacity management functions. * traffic management methods to provide monitoring of network performance and implement traffic management controls such as code blocks, connection request gapping, and reroute controls Figure 1.7 illustrates the recommended traffic management functions. ----------------------------------------------------------------------------- Figure 1.7 Employ Traffic Management Methods to Provide Monitoring of Network Performance and Implement Traffic Management Controls (such as code blocks, connection request gapping, and reroute controls) (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- * capacity management methods to include capacity forecasting, daily and weekly performance monitoring, and short-term network adjustment Figure 1.8 illustrates the recommended capacity management functions. ----------------------------------------------------------------------------- Figure 1.8 Employ Capacity Management Methods to Include Capacity Forecasting, Daily and Weekly Performance Monitoring, and Short-Term Network Adjustment (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- * discrete event flow optimization (DEFO) design models to capture complex routing behavior and design multiservice TE networks Figure 1.9 illustrates the recommended DEFO design models. The greatest advantage of the DEFO model is its ability to capture very complex routing ----------------------------------------------------------------------------- Figure 1.9 Use Discrete Event Flow Optimization (DEFO) Design Models to Capture Complex Routing Behavior & Design Multiservice TE Networks (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- behavior through the equivalent of a simulation model provided in software in the routing design module. By this means, very complex routing networks have been designed by the model, which include all of the routing methods discussed in ANNEX 2, TDR, SDR, and EDR methods, and the multiservice QoS resource allocation models discussed in ANNEX 3. Complex traffic processes, such as self-similar traffic, can also be modeled with DEFO methods. 10.6 Benefits of Recommended TE/QoS Methods for Multiservice Integrated Networks The benefits of recommended TE/QoS Methods for IP-based multiservice integrated network are as follows: * IP-network-based service creation (Parlay API, CPL/CGI, SIP-IN) * lower operations & capital cost * improved performance * simplified network management The IP-network-based service creation capabilities are discussed in ANNEX 4, the operations and capital cost impacts in ANNEXES 2 and 6, and improved performance impacts in ANNEXES 2 and 3. Simplified network management comes about because of the following impacts of the recommended TE admission control and dynamic QoS routing methods: * distributed control, as discussed in ANNEX 2 * eliminate available-link-bandwidth flooding, as discussed in ANNEX 4 * larger/fewer areas, as discussed in ANNEX 4 * automatic provisioning of topology database, as discussed in ANNEX 3 * fewer links/sparse network to provision, as discussed in ANNEX 2 11. Security Considerations This document does not introduce new security issues beyond those inherent in MPLS and may use the same mechanisms proposed for this technology. It is, however, specifically important that manipulation of administratively configurable parameters be executed in a secure manner by authorized entities. 12. Acknowledgements The author is indebted to many people for much help and encouragement in the course of developing this work. In the IETF I'd like to especially thank Dan Awduche of Movaz, Jim Boyle of Level 3 Communications, Angela Chiu of Celion Networks, and Tom Scott of Vedatel for all their helpful comments, assistance, and encouragement. Within AT&T I'd like to especially thank Chuck Dvorak, Bur Goode, Wai Sum Lai, and Jennifer Rexford for the excellent support and on-going discussions. In the ITU I'd like to particularly thank Anne Elvidge of BT, Tommy Petersen of Ericsson, Bruce Pettitt of Nortel, and Jim Roberts of France Telecom for the valuable help throughout the course of this work. I'd also like to thank Professor Lorne Mason of INRS/University of Quebec for his many insights, discussions, and comments in the course of this work. 13. Authors' Addresses Gerald R. Ash AT&T Labs Room MT D5-2A01 200 Laurel Avenue Middletown, NJ 07748 Phone: 732-420-4578 Fax: 732-368-8659 Email: gash@att.com 14. Full Copyright Statement Copyright (C) The Internet Society (1998). All Rights Reserved. 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This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. ANNEX 1. Bibliography [A98] Ash, G. R., Dynamic Routing in Telecommunications Networks, McGraw-Hill, 1998. [A99a] Awduche, D. O., MPLS and Traffic Engineering in IP Networks, IEEE Communications Magazine, December 1999. [A99b] Awduche, D. O., MPLS and Traffic Engineering in IP Networks, IEEE Communications Magazine, December 1999. [A99d] Apostolopoulos, G., On the Cost and Performance Trade-offs of Quality of Service Routing", Ph.D. thesis, University of Maryland, 1999. [A00] Armitage, G., Quality of Service in IP Networks: Foundations for a Multi-Service Internet, Macmillan, April 2000. 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R., Maunder, A., QoS Resource Management in ATM Networks, AF-99-, Rome Italy, April 1999. [ARDC99] Awduche, D. O., Rekhter, Y., Drake, J., Coltun, R., Multiprotocol Lambda Switching: Combined MPLS Traffic Engineering Control with Optical Crossconnects, Work in Progress. [ATM950013] ATM Forum Technical Committee, B-ISDN Inter Carrier Interface (B-ICI) Specification Version 2.0 (Integrated), af-bici-0013.003, December 1995. [ATM960055] ATM Forum Technical Committee, Private Network-Network Interface Specification Version 1.0 (PNNI 1.0), af-pnni-0055.000, March 1996. [ATM960056] ATM Forum Technical Committee, Traffic Management Specification Version 4.0, af-tm0056.000, April 1996. [ATM960061] ATM Forum Technical Committee, ATM User-Network Interface (UNI) Signaling Specification Version 4.0, af-sig-0061.000, July 1996. [ATM980103] ATM Forum Technical Committee, Specification of the ATM Inter-Network Interface (AINI) (Draft), ATM Forum/BTD-CS-AINI-01.03, July 1998. 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[B00a] Bernet, Y., The Complementary Rles of RSVP and Differentiated Services in the Full-Service QoS Network, IEEE Communications Magazine, February 2000. [B91] Brunet, G., Optimisation de L'acheminement Sequentiel Non-hierarchique par Automattes Intelligents, M. Sc. Thesis, INRS-Telecommunications, 1991. [BCHLL99] Bolotin, V., Coombs-Reyes, Heyman, D., Levy, Y., Liu, D., IP Traffic Characterization for Planning and Control, Teletraffic Engineering in a Competitive World, P. Key and D. Smith (Eds.), Elsevier, Amsterdam, 1999. [Bur61] Burke, P. J., "Blocking Probabilities Associated with Directional Reservation," unpublished memorandum, 1961. [C90] Callon, R., Use of OSI IS-IS for Routing in TCP/IP and Dual Environments, RFC1195, December 1990. [C97] Crovella, M. E., Self-Similarity in WWW Traffic: Evidence and Possible Causes, IEEE Transactions on Networking, December 1997. [CED91] Chao, C-W., Eslambolchi, H., Dollard, P., Nguyen, L., Weythman, J., "FASTAR---A Robust System for Fast DS3 Restoration," Proceedings of GLOBECOM 1991, Phoenix, Arizona, December 1991, pp. 1396--1400. [CHY00] Chaudhuri, S., Hjalmtysson, G., Yates, J., Control of Lightpaths in an Optical Network, work in progress. [CST00] Chiu, A., Strand, J., Tkach, R., Unique Features and Requirements for The Optical Layer Control Plane, work in progress. [COM 2-39-E] ANNEX, Draft New Recommendation E.ip, Report of Joint Meeting of Questions 1/2 and 10/2, Torino, Italy, July 1998. [CW00] Cherukuri, R., Walsh, T., Proposal for Work Item to Support Voice over MPLS (VoMPLS), MPLS Forum Technical Committee Contribution, Dublin, Ireland, June 2000. [D99] Dvorak, C., IP-Related Impacts on End-to-End Transmission Performance, ITU-T Liaison to Study Group 2, Temporary Document TD GEN-22, Geneva Switzerland, May 1999. [Dij59] Dijkstra, E. W., "A Note on Two Problems in Connection with Graphs," Numerical Mathematics, Vol. 1, 1959, pp. 269--271. [DN99] Dianda, R. B., Noorchashm, M., Bandwidth Modification for UNI, PNNI, AINI, and BICI, ATM Forum Technical Working Group, April 1999. [DPW99] Doverspike, R. D., Phillips, S., Westbrook, J. R., Future Transport Network Architectures, IEEE Communications Magazine, August 1999. [DR00] Davie, B. S., Rekhter, Y., MPLS: Technology and Applications, Morgan Kaufmann Publishers, May 2000. [DY00] Doverspike, R., Yates, J., Challenges for MPLS Protocols in the Optical Network Control Plane, submitted for publication. [E.41IP] ITU-T Recommendation, Framework for the Traffic Management of IP-Based Networks, March 2000. [E.106] ITU-T Recommendation, Description of International Emergency Preference System (IEPS). [E.164] ITU-T Recommendation, The International Telecommunications Numbering Plan. [E.170] ITU-T Recommendation, Traffic Routing. [E.177] ITU-T Recommendation, B-ISDN Routing. [E.191] ITU-T Recommendation, B-ISDN Numbering and Addressing, October 1996. [E.350] ITU-T Recommendation, Dynamic Routing Interworking. [E.351] ITU-T Recommendation, Routing of Multimedia Connections Across TDM-, ATM-, and IP-Based Networks. [E.352] ITU-T Recommendation, Routing Guidelines for Efficient Routing Methods. [E.353] ITU-T Recommendation, Routing of Calls when Using International Network Routing Addresses [E.412] ITU-T Recommendation, Network Management Controls. [E.490] ITU-T Recommendation, Traffic measurement and evaluation - General survey, June 1992. [E.491] ITU-T Recommendation, Traffic Measurement by destination, May 1997. [E.492] ITU-T Recommendation, Traffic reference period, February 1996. [E.493] ITU-T Recommendation, Grade of service (GOS) monitoring, February 1996. [E.500] ITU-T Recommendation, Traffic intensity measurement principles, November 1998. [E.501] ITU-T Recommendation, Estimation of traffic offered in the network, May 1997. 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[E.523] ITU-T Recommendation, Standard traffic profiles for international traffic streams, November 1988. [E.524] ITU-T Recommendation, Overflow approximations for non-random inputs, May 1999. [E.525] ITU-T Recommendation, Designing networks to control grade of service, June 1992. [E.526] ITU-T Recommendation, Dimensioning a circuit group with multi-slot bearer services and no overflow inputs, March 1993. [E.527] ITU-T Recommendation, Dimensioning a circuit group with multi-slot bearer services and overflow traffic, March 2000. [E.528] ITU-T Recommendation, Dimensioning of digital circuit multiplication equipment (DCME) systems, February 1998. [E.529] ITU-T Recommendation, Network Dimensioning using End-to-End GOS Objectives, May 1997. [E.600] ITU-T Recommendation, Terms and Definitions of Traffic Engineering, March 1993. [E.651] ITU-T Recommendation, Reference Connections for Traffic Engineering of IP Access Networks. [E.716] User Demand Modeling in Broadband-ISDN, October 1996. [E.731] ITU-T Recommendation, Methods for dimensioning resources operating in circuit-switched mode, October 1992. [E.733] ITU-T Recommendation, Methods for dimensioning resources in Signalling System No. 7 networks, November 1998. [E.734] ITU-T Recommendation, Methods for Allocation and Dimensioning Intelligent Network (IN) Resources, October 1996. [E.735] ITU-T Recommendation, Framework for traffic control and dimensioning in B-ISDN, May 1997. [E.736] ITU-T Recommendation, Methods for cell level traffic control in B-ISDN, March 2000. [E.737] ITU-T Recommendation, Dimensioning methods for B-ISDN, May 1997. [E.743} ITU-T Recommendation, Traffic measurements for SS No. 7 dimensioning and planning, April 1995. [E.745] ITU-T Recommendation, Cell Level Measurement Requirements for the B-ISDN, March 2000. [E.800] ITU-T Recommendation, Terms and Definitions Related to Quality of Service and Network Performance Including Dependability, August 1994. [E.TE] ITU-T Draft Recommendation, QoS Routing & Related Traffic Engineering Methods for IP-, ATM- and TDM-Based Multiservice Networks, September 2001. [ETSIa] ETSI Secretariat, Telecommunications and Internet Protocol Harmonization over Networks (TIPHON); Naming and Addressing; Scenario 2, DTS/TIPHON-04002 v1.1.64, 1998 [ETSIb] ETSI STF, Request for Information (RFI): Requirements for Very Large Scale E.164 -> IP Database, TD35, ETSI EP TIPHON 9, Portland, September 1998. [ETSIc] TD290, ETSI Working Party Numbering and Routing, Proposal to Study IP Numbering, Addressing, and Routing Issues, Sophia, September 1998. [FCTS00] Requirements for support of Diff-Serv-aware MPLS Traffic Engineering, work in progress. [FGHW99] Feldman, A., Gilbert, A., Huang, P., Willinger, W., Dynamic of IP Traffic: A Study of the Role of Variability and the Impact of Control, Proceedings of the ACM SIGCOMM, September 1999. [FGLRRT00] Feldman, A., Greenberg, A., Lund, C., Reingold, N., Rexford, J., True, F., Deriving Traffic Demands for Operational IP Networks: Methodology and Experience, work in progress. [FGLRR99] Feldman, A., Greenberg, A., Lund, C., Reingold, N., Rexford, J., True, F., Netscope: Traffic Engineering for IP Networks, IEEE Network Magazine, March 2000. [FH98] Ferguson, P., Huston, G., Quality of Service: Delivering QoS on the Internet and in Corporate Networks, John Wiley & Sons, 1998. [FHH79] Franks, R. L., Heffes, H., Holtzman, J. M., Horing, S., Messerli, E. J., "A Model Relating Measurements and Forecast Errors to the Provisioning of Direct Final Trunk Groups," Bell System Technical Journal, Vol. 58, No. 2, February 1979. [FI00] Fujita, N., Iwata, A., Traffic Engineering Extensions to OSPF Summary LSA, work in progress. [FJ93] Floyd, S., Jacobson, V., Random Early Detection Gateways for Congestion Avoidance, IEEE/ACM Transactions on Networking, August 1993. [FO00] Folts, H., Ohno, H., Functional Requirements for Priority Services to Support Critical Communications, work in progress. [FRC98] Feldman, A., Rexford, J., Caceres, R., Efficient Policies for Carrying Web Traffic Over Flow-Switched Networks, IEEE/ACM Transactions on Networking, December 1998. [FT00] Fortz, B., Thorup, M., Internet Traffic Engineering by Optimizing OSPF Weights, Proceedings of IEEE INFOCOM, March 2000. [G.723.1] ITU-T Recommendation, Dual Rate Speech Coder for Multimedia Communications Transmitting at 5.3 and 6.3 kbit/s, March 1996. [G99a] Glossbrenner, K., Elements Relevant to Routing of ATM Connections, ITU-T Liaison to Study Group 2, Temporary Document 1/2-8, Geneva Switzerland, May 1999. [G99b] Glossbrenner, K., IP Performance Studies, ITU-T Liaison to Study Group 2, Temporary Document GEN-27, Geneva Switzerland, May 1999. [GDW00] Ghani, N., Duxit, S., Wang, T., On IP-Over-WDM Integration, IEEE Communications Magazine, March 2000. [GJFALF99] Ghanwani, A., Jamoussi, B., Fedyk, D., Ashwood-Smith, P., Li, L., Feldman, N., Traffic Engineering Standards in IP Networks using MPLS, IEEE Communications Magazine, December 1999. [GT00] Grossglauser, M., Tse, D., A Time-Scale Decomposition Approach to Meansurement-Based Admission Control, submitted for publication, August 2000. [GR99] Greene, N., Ramalho, M., Media Gateway Control Protocol Architecture and Requirements,work inprogress. [H95] Huitema, C., Routing in the Internet, Prentice Hall, 1995. [H97] Halabi, B., Internet Routing Architectures, Cisco Press, 1997. [H99] Heyman, D. P., Estimation of MMPP Models of IP Traffic, unpublished work. [H.225.0] ITU-T Recommendation, Media Stream Packetization and Synchronization on Non-Guaranteed Quality of Service LANs, November 1996. [H.245] ITU-T Recommendation, Control Protocol for Multimedia Communication, March 1996. [H.246] Draft ITU-T Recommendation, Interworking of H.Series Multimedia Terminals with H.Series Multimedia Terminals and Voice/Voiceband Terminals on GSTN and ISDN, September 1997. [H.323] ITU-T Recommendation, Visual Telephone Systems and Equipment for Local Area Networks which Provide a Non-Guaranteed Quality of Service, November 1996. [HCC00] Huston, G., Cerf, V. G., Chapin, L., Internet Performance Survival Guide: QoS Strategies for Multi-Service Networks, John Wiley & Sons, February 2000. [HiN76] Hill, D. W., Neal, S. R., "The Traffic Capacity of a Probability Engineered Trunk Group," Bell System Technical Journal, Vol. 55, No. 7, September 1976. [HL96] Heyman, D. P., Lakshman, T. V., What are the Implications of Long-Range Dependence for VBR-Video Traffic Engineering?, IEEE Transactions on Networking, June 1996. [HSMOA00] Huang, C., Sharma, V., Makam, S., Owens, K., A Path Protection/Restoration Mechanism for MPLS Networks, work in progress. [HM00] Heyman, D. P., Mang, X., Why Modeling Broadband Traffic is Difficult, and Potential Ways of Doing It, Fifth INFORMS Telecommunications Conference, Boca Raton, FL, March 2000. [HSMO00] Huang, C., Sharma, V., Makam, S., Owens, K., A Path Protection/Restoration Mechanism for MPLS Networks, work in progress. [HSMOA00] Huang, C., Sharma, V., Makam, S., Owens, K., Akyol, B., Extensions to RSVP-TE for MPLS Path Protection, work in progress. [HY00] Hjalmtysson, G., Yates, J., Smart Routers - Simple Optics, An Architecture for the Optical Internet, submitted for publication. [I.211] ITU-T Recommendation, B-ISDN Service Aspects, March 1993. [I.324] ITU-T Recommendation, ISDN Network Architecture, 1991. [I.327] ITU-T Recommendation, B-ISDN Functional Architecture, March 1993. [I.356] ITU-T Recommendation, B-ISDN ATM Layer Cell Transfer Performance, October 1996. [IFAF01] Iwata, A., Fujita, N., Ash, G., Farrel, A., Crankback Routing Extensions for MPLS Signaling, work in progress. [IYBKQ00] Isoyama, K., Yoshida, M., Brunner, M., Kind, A., Quittek, J., Policy Framework QoS Information Model for MPLS, work in progress. [J00] Jamoussi, B., Editor, Constraint-Based LSP Setup using LDP, work in progress. [JSHPG00] Juttner, A., Szentesi, A., Harmatos, J., Pioro, M., Gajowniczek, P., On Solvability of an OSPF Routing Problem, 15th Nordic Teletraffic Seminar, Lund, 2000. [K99] Kilkki, K., Differentiated Services for the Internet, Macmillan, 1999. [Kne73] Knepley, J. E., "Minimum Cost Design for Circuit Switched Networks," Technical Note Numbers 36--73, Defense Communications Engineering Center, System Engineering Facility, Reston, Virginia, July 1973. [KR00] Kurose, J. F., Ross, K. W., Computer Networking, A Top-Down Approach Featuring the Internet, Addison-Wesley, 2000. [KR00a] Kompella, K., Rekhter, Y., LSP Hierarchy with MPLS TE, work in progress. [KR00b] Kompella, K., Rekhter, Y., Multi-area MPLS Traffic Engineering, work in progress. [Kru37] Kruithof, J., "Telefoonverkeersrekening," De Ingenieur, Vol. 52, No. 8, February 1937. [Kru79] Krupp, R. S., "Properties of Kruithof's Projection Method," Bell System Technical Journal, Vol. 58, No. 2, February 1979. [Kru82] Krupp, R. S., "Stabilization of Alternate Routing Networks," IEEE International Communications Conference, Philadelphia, Pennsylvania, 1982. [L99] Li, T., MPLS and the Evolving Internet Architecture, IEEE Communications Magazine, December 1999. [LCGGA00] Lee, C., Celer, A., Gammage, N., Ganti, S., Ash, G., Distributed Route Exchangers, work in progress. [LG00] Lee, C., Ganti, S., Path Request and Path Reply Message, work in progress. [LNCTS00] Le Faucheur, F., Nadeau, T. D., Chiu, A., Townsend, W., Skalecki, D., Extensions to IS-IS, OSPF, RSVP and CR-LDP for support of Diff-Serv-aware MPLS Traffic Engineering, work in progress. [LRACJ00] Luciani, J., Rajagopalan, B., Awduche, D., Cain, B., Jamoussi, B., IP over Optical Networks - A Framework, work in progress. [LS00] Lazer, M., Strand, J., Some Routing Constraints, Optical Interworking Forum contribution OIF2000.109, May 2000. [LTWW94] Leland, W., Taqqu, M., Willinger, W., Wilson, D., On the Self-Similar Nature of Ethernet Traffic, IEEE/ACM Transactions on Networking, February 1994. [LDVKCH00] Le Faucheur, F., Davari, S., Vaananen, P., Krishnan, R., Cheval, P., Heinanen, J., MPLS Support of Differentiated Services, work in progress. [M85] Mason, L. G., Equilibrium Flows, Routing Patterns and Algorithms for Store-and-Forward Networks, North-Holland, Large Scale Systems, Vol. 8, 1985. [M98] Metz, C., IP Switching: Protocols and Architecture, McGraw-Hill, 1998. [M98a] Ma, Q., Quality-of-Service Routing in Integrated Services Networks, Ph.D. Thesis, Carnegie Mellon University, Pittsburgh, PA, 1998. [M99] Moy, J., OSPF: Anatomy of an Internet Routing Protocol, Addison Wesley, 1999. [M99a] McDysan, D., QoS and Traffic Management in IP and ATM Networks, McGraw-Hill, 1999. [M00] Makam, s., et. al., Framework for MPLS-based Recovery, work in progress. [MRMRBMSOAPLFEK00] Marshall, W., Ramakrishnan, K., Miller, E., Russell, G., Beser, B., Mannette, M., Steinbrenner, K., Oran, D., Andreasen, F., Pickens, J., Lalwaney, P., Fellows, J., Evans, D., Kelly, K., Architectural Considerations for Providing Carrier Class Telephony Services Utilizing SIP-based Distributed Call Control Mechanisms, work in progress. [MRMRBMSOAPLFEK00a] Marshall, W., Ramakrishnan, K., Miller, E., Russell, G., Beser, B., Mannette, M., Steinbrenner, K., Oran, D., Andreasen, F., Pickens, J., Lalwaney, P., Fellows, J., Evans, D., Kelly, K., SIP Extensions for supporting Distributed Call State, work in progress. [MRMRBMSOAPLFEK00b] Marshall, W., Ramakrishnan, K., Miller, E., Russell, G., Beser, B., Mannette, M., Steinbrenner, K., Oran, D., Andreasen, F., Pickens, J., Lalwaney, P., Fellows, J., Evans, D., Kelly, K., Integration of Resource Management and SIP, work in progress. [MS97] Ma, Q., Steenkiste, P., On Path Selection for Traffic with Bandwidth Guarantees, Proceedings of IEEE International Conference on Network Protocols, October 1997. [MS97a] Ma, Q., Steenkiste, P., Quality-of-Service Routing for Traffic with Performance Guarantees, Proceedings of IFIP Fifth International Workshop on Quality of Service, May 1997. [MS98] Ma, Q., Steenkiste, P., Routing Traffic with Quality-of-Service Guarantees, , Proceedings of Workshop on Network and Operating Systems Support for Digital Audio and Video, July 1998. [MS99] Ma, Q., Steenkiste, P., Supporting Dynamic Inter-Class Resource Sharing: A Multi-Class QoS Routing Algorithm, Proceedings of IEEE INFOCOM '99, March 1999. [MS00] Ma, T., Shi, B., Bringing Quality Control to IP QoS, Network Magazine, November 2000. [Mum76] Mummert, V. S., "Network Management and Its Implementation on the No. 4ESS," International Switching Symposium, Japan, 1976. [NaM73] Nakagome, Y., Mori, H., "Flexible Routing in the Global Communication Network," Proceedings of the Seventh International Teletraffic Congress, Stockholm, Sweden, 1973. [NWM77] Narendra, K. S., Wright, E. A., Mason, L. G., Application of Learning Automata to Telephone Traffic Routing and Control, IEEE Transactions on Systems, Man and Cybernetics, Vol. SMC-7, No. 11, November 1977. [NWRH99] Neilson, R., Wheeler, J., Reichmeyer, F., Hares, S., A Discussion of Bandwidth Broker Requirements for Internet2 Qbone Deployment, August 1999. [PARLAY] Parlay API Specification 1.2, September 10, 1999. [PaW82] Pack, C. D., Whitaker, B. A., "Kalman Filter Models for Network Forecasting," Bell System Technical Journal, Vol. 61, No. 1, January 1982. [PSHJGK00] On OSPF Related Network Optimization Problems, IFIPATM IP 2000, Ilkley, July 2000. [PW00] Park, K., Willinger, W., Self-Similar Network Traffic and Performance Evaluation, John Wiley & Sons, August 2000. [Q.71] ITU-T Recommendation, ISDN Circuit Mode Switched Bearer Services. [Q.765.5] ITU-T Recommendation, Application Transport Mechanism - Bearer Independent Call Control (BICC), December 1999. [Q.1901] ITU-T Recommendation, Bearer Independent Call Control Protocol, February 2000. [Q.2761] ITU-T Recommendation, Broadband Integrated Services Digital Network (B-ISDN) Functional Description of the B-ISDN User Part (B-ISUP) of Signaling System Number 7. [Q.2931] ITU-T Recommendation, Broadband Integrated Services Digital Network (B-ISDN) - Digital Subscriber Signalling System No. 2 (DSS 2) - User-Network Interface (UNI) Layer 3 Specification for Basic Call/Connection Control, February 1995. [R99] Roberts, J. W., Engineering for Quality of Service, Chapter appearing in [PW00]. [R01] Roberts, J. W., Traffic Theory and the Internet, IEEE Communications Magazine, January 2001. [RFC1633] Braden, R., Clark, D., Shenker, S., Integrated Services in the Internet Architecture: an Overview, June 1994. [RFC1889] Schulzrinne, H., Casner, S., Frederick, R., Jacobson, V., RTP: A Transport Protocol for Real-Time Applications, January 1996. [RFC1940] Estrin, D., Li, T., Rekhter, Y., Varadhan, K., Zappala, D., Source Demand Routing: Packet Format and Forwarding Specification (Version 1), May 1996. [RFC1992]Castineyra, I., Chiappa, N., Steenstrup, M., The Nimrod Routing Architecture, August 1996. [RFC2205] Bradem. R., Zhang, L., Berson, S., Herzog, S., Jamin, S., Resource ReSerVation Protocol (RSVP) - Version 1 Functional Specification, September 1997. [RFC2328] Moy, J, OSPF Version 2, April 1998. [RFC2332] Luciani, J., Katz, D., Piscitello, D., Cole, B., Doraswamy, N., NBMA Next Hop Resolution Protocol (NHRP), April 1998. [RFC2370] Coltun, R., The OSPF Opaque LSA Option, July 1998. [RFC2386] Crawley, E., Nair, R., Rajagopalan, B., Sandick, H., A Framework for QoS-based Routing in the Internet, August 1998. [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., Weiss, W., An Architecture for Differentiated Services, December 1998. [RFC2543] Handley, M., Schulzrinne, H., Schooler, E. Rosenberg, J. SIP: Session Initiation Protocol, March 1999. [RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., McManus, J. Requirements for Traffic Engineering over MPLS, September 1999. [RFC2722] Brownlee, N., Ruth, G., Traffic Flow Measurement: Architecture, October 1999. [RFC2805] Greene, N., Ramalho, M., Rosen, B., Media Gateway Control Protocol Architecture and Requirements, April 2000. [RFC2916] Faltstrom, P., E.164 Number and DNS, September 2000. [RFC3031] Rosen, E., Viswanathan, A., Callon, R., Multiprotocol Label Switching Architecture, January 2001. [RFC3036] Anderson, L., Doolan, P., Feldman, N., Fredette, A., Thomas, B., LDP Specification, January 2001. [RL00] Rekhter, Y., Li, T., A Border Gateway Protocol 4 (BGP-4), Work in Progress. [RO00] Roberts, J. W., Oueslati-Boulahia, S., Quality of Service by Flow Aware Networking, work in progress. [S94] Stevens, W. R., TCP/IP Illustrated, Volume 1, The Protocols, Addison-Wesley, 1994. [S95] Steenstrup, M., Editor, Routing in Communications Networks, Prentice-Hall, 1995. [S99] Swallow, G., MPLS Advantages for Traffic Engineering, IEEE Communications Magazine, December 1999. [SAHG00] Slutsman, L., Ash, G., Haerens, F., Gurbani, V. K., Framework and Requirements for the Internet Intelligent Network (IIN), work in progress. [SC00] Strand, J., Chiu, A. L., What's Different About the Optical Layer Control Plane?, submitted for publication. [SCT01] Strand, J., Chiu, A., Tkach, R., Issues for Routing in the Optical Layer, IEEE Communications Magazine, February 2001. [SL99] Schwefel, H-P., Lipsky, L., Performance Results for Analytic Models of Traffic in Telecommunication Systems, Based on Multiple ON-OFF Sources with Self-Similar Behavior, 16th International Teletraffic Congress, Edinburgh, June 1999. [ST98] Sikora, J., Teitelbaum, B., Differentiated Services for Internet2, Internet2: Joint Applications/Engineering QoS Workshop, Santa Clara, CA, May 1998. [ST99] Sahinoglu, Z., Tekinay, S., On Multimedia Networks: Self-Similar Traffic and Network Performance, IEEE Communication Magazine, January 1999. [STB99] Suryaputra, S., Touch, J. D., Bannister, J., Simple Wavelength Assignment Protocol, USC Information Sciences Institute ISC/ISI RR-99-473, October 1999. [SX01] Strand, J., Xue, Y., Routing for Optical Networks With Multiple Routing Domains, oif2001.046 (for a copy send an email request to jls@research.att.com). [TRQ3000] Supplement to ITU-T Recommendation Q.1901, Operation of the Bearer Independent Call Control (BICC) Protocol with Digital Subscriber Signaling System No. 2 (DSS2), December 1999. [TRQ3010] Supplement to ITU-T Recommendation Q.1901, Operation of the Bearer Independent Call Control (BICC) Protocol with AAL Type 2 Signaling Protocol (CS1), December 1999. [TRQ3020] Supplement to ITU-T Recommendation Q.1901, Operation of the Bearer Independent Call Control (BICC) Protocol with Broadband ISDN User Part (B-ISUP) Protocol for AAL Type 1 Adaptation, December 1999. [Tru54] Truitt, C. J., "Traffic Engineering Techniques for Determining Trunk Requirements in Alternate Routed Networks," Bell System Technical Journal, Vol. 31, No. 2, March 1954. [V99] Villamizar, C., MPLS Optimized Multipath, work in progress. [VD00] Venkatachalam, S., Dharanikota, S., A Framework for the LSP Setup Across IGP Areas for MPLS Traffic Engineering, work in progress. [VDN00] Venkatachalam, S., Dharanikota, S., Nadeau, T. "OSPF, IS-IS, RSVP, CR-LDP extensions to support inter-area traffic engineering using MPLS TE,", work in progress. [Wal00] Walsh, T., Multiprotocol Label Switching (MPLS) in BICC, ITU-T Study Group 11 Contribution, Melbourne, Australia, May 2000. [WBP00] Wright, G., Ballarte, S., Pearson, T., CR-LDP Extensions for Interworking with RSVP-TE, work in progress. [Wei63] Weintraub, S., Tables of Cumulative Binomial Probability Distribution for Small Values of p, London: Collier-Macmillan Limited, 1963. [WE99] Widjaja, I., Elwalid, A., MATE: MPLS Adaptive Traffic Engineering, work in progress. [WHJ00] Wright, S., Herzog, S., Jaeger, R., Requirements for Policy Enabled MPLS, work in progress. [Wil56] Wilkinson, R. I., "Theories of Toll Traffic Engineering in the U.S.A.," Bell System Technical Journal, Vol. 35, No. 6, March 1956. [Wil58] Wilkinson, R. I., "A Study of Load and Service Variations in Toll Alternate Route Systems," Proceedings of the Second International Teletraffic Congress, The Hague, Netherlands, July 1958, Document No. 29. [Wil71] Wilkinson, R. I., "Some Comparisons of Load and Loss Data with Current Teletraffic Theory," Bell System Technical Journal, Vol. 50, October 1971, pp. 2807--2834. [XHBN00] Xiao, X., Hannan, A., Bailey, B., Ni, L. M., Traffic Engineering with MPLS in the Internet, IEEE Network Magazine, March/April 2000. [XN99] Xiao, X., Ni, L. M., Internet QoS: A Big Picture, IEEE Network Magazine, March/April, 1999. [Yag71] Yaged, B., Jr., "Long Range Planning for Communications Networks," Polytechnic Institute of Brooklyn, Ph.D. Thesis, 1971. [Yag73] Yaged, B., "Minimum Cost Design for Circuit Switched Networks," Networks, Vol. 3, 1973, pp. 193--224. [YR99] Yates, J. M., Rumsewicz, M. P. Lacey, J. P. R., Wavelength Converters in Dynamically-Reconfigurable WDM Networks, IEEE Communications Society Survey Paper, 1999. [ZSSC97] Zhang, Sanchez, Salkewicz, Crawley, Quality of Service Extensions to OSPF or Quality of Service Route First Routing (QOSPF), work in progress. ANNEX 2 Call Routing & Connection Routing Methods Traffic Engineering & QoS Methods for IP-, ATM-, & TDM-Based Multiservice Networks 2.1 Introduction In the document we assume the separation of "call routing" and signaling for call establishment from "connection (or bearer-path) routing" and signaling for bearer-channel establishment. Call routing protocols primarily translate a number or a name, which is given to the network as part of a call setup, to a routing address needed for the connection (bearer-path) establishment. Call routing protocols are described for example in [Q.2761] for the Broadband ISDN Used Part (B-ISUP) call signaling, [ATM990048] for bearer-independent call control (BICC), or virtual trunking, call signaling, [H.323] for H.323 call signaling, [GR99] for the media gateway control [RFC2805] call signaling, and in [HSSR99] for the session initiation protocol (SIP) call signaling. Connection routing protocols include for example [Q.2761] for B-ISUP signaling, [ATM960055] for PNNI signaling, [ATM960061] for UNI signaling, [DN99] for switched virtual path (SVP) signaling, and [J00] for MPLS constraint-based routing label distribution protocol (CRLDP) signaling. A specific connection or bearer-path routing method is characterized by the routing table used in the method. The routing table consists of a set of paths and rules to select one path from the route for a given connection request. When a connection request arrives at its originating node (ON), the ON implementing the routing method executes the path selection rules associated with the routing table for the connection to determine a selected path from among the path candidates in the route for the connection request. In a particular routing method, the path selected for the connection request is governed by the connection routing, or path selection, rules. Various path selection methods are discussed: fixed routing (FR) path selection, time-dependent routing (TDR) path selection, state-dependent routing (SDR) path selection, and event-dependent routing (EDR) path selection. 2.2 Call Routing Methods Call routing entails number (or name) translation to a routing address, which is then used for connection establishment. Routing addresses can consist, for example, of a) E.164 ATM end system addresses (AESAs) [E.191], b) network routing addresses (NRAs) [E.353], and/or c) IP addresses [S94]. As discussed in ANNEX 4, a TE requirement is the need for carrying E.164-AESA addresses, NRAs, and IP addresses in the connection-setup information element (IE). In that case, E.164-AESA addresses, NRAs, and IP addresses become the standard addressing method for interworking across IP-, ATM-, and TDM-based networks. Another TE requirement is that a call identification code (CIC) be carried in the call-control and bearer-control connection-setup IEs in order to correlate the call-control setup with the bearer-control setup [Q.1901, ATM990048]. Carrying these additional parameters in the Signaling System 7 (SS7) ISDN User Part (ISUP) connection-setup IEs is referred to as the bearer independent call control (BICC) protocol. Number (or name) translation, then, should result in the E.164-AESA addresses, NRAs, and/or IP addresses. NRA formats are covered in [E.353], and IP-address formats in [S94]. The AESA address has a 20-byte format as shown in Figure 2.1a below [E.191]. ----------------------------------------------------------------------------- Figure 2.1a AESA Address Structure (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- The IDP is the initial domain part and the DSP is the domain specific part. The IDP is further subdivided into the AFI and IDI. The IDI is the initial domain identifier and can contain the 15-digit E.164 address if the AFI is set to 45. AFI is the authority and format identifier and determines what kind of addressing method is followed, and based on the 1 octet AFI value, the length of the IDI and DSP fields can change. The E.164-AESA address is used to determine the path to the destination endpoint. E.164-AESA addressing for B-ISDN services is supported in ATM networks using PNNI, through use of the above AESA format. In this case the E.164 part of the AESA address occupies the 8 octet IDI, and the 11 octet DSP can be used at the discretion of the network operator (perhaps for sub-addresses). The above AESA structure also supports AESA DCC (data country code) and AESA ICD (international code designator) addressing formats. Within the IP network, routing is performed using IP addresses. Translation databases, such as based on domain name system (DNS) technology [RFC2916], are used to translate the E.164 numbers/names for calls to IP addresses for routing over the IP network. The IP address is a 4-byte address structure as shown below: ----------------------------------------------------------------------------- Figure 2.1b IP Address Structure (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- There are five classes of IP addresses. Different classes have different field lengths for the network identification field. Classless inter-domain routing (CIDR) allows blocks of addresses to be given to service providers in such a manner as to provide efficient address aggregation. This is accompanied by capabilities in the BGP4.0 protocol for efficient address advertisements [RL00, S94]. 2.3 Connection (Bearer-Path) Routing Methods Connection routing is characterized by the routing table used in the method and rules to select one path from the route for a given connection or bandwidth-allocation request. When a connection/bandwidth-allocation request is initiated by an ON, the ON implementing the routing method executes the path selection rules associated with the routing table for the connection/bandwidth-allocation to find an admissible path from among the paths in the route that satisfies the connection/bandwidth-allocation request. In a particular routing method, the selected path is determined according to the rules associated with the routing table. In a network with originating connection/bandwidth-allocation control, the ON maintains control of the connection/bandwidth-allocation request. If crankback/bandwidth-not-available is used, for example, at a via node (VN), the preceding node maintains control of the connection/bandwidth-allocation request even if the request is blocked on all the links outgoing from the VN. Here we are discussing network-layer connection routing (sometimes referred to as "layer-3" routing), as opposed to the link-layer logical-transport-link ("layer-2") routing or physical-layer ("layer-1") routing. In the document the term "link" will normally mean "logical-link." In ANNEX 5 we address logical-link routing. The network-layer (layer-3) connection routing methods addressed include those discussed in * Open Shortest Path First (OSPF), Border Gateway Protocol (BGP), and Multiprotocol Label Switching (MPLS) for IP-based routing methods, * User-to-Network Interface (UNI), Private Network-to-Network Interface (PNNI), ATM Inter-Network Interface (AINI), and Bandwidth Modify for ATM-based routing methods, and * Recommendations E.170, E.350, and E.351 for TDM-based routing methods. In an IP network, logical links called traffic trunks can be defined which consist of MPLS label switched paths (LSPs) between the IP nodes. Traffic trunks are used to allocate the bandwidth of the logical links to various node pairs. In an ATM network, logical links called virtual paths (VPs) (the equivalent of traffic trunks) can be defined between the ATM nodes, and VPs can be used to allocate the bandwidth of the logical links to various node pairs. In a TDM network, the logical links consist of trunk groups between the TDM nodes. A sparse logical link network is typically used with IP and ATM technology, as illustrated in Figure 2.2, and FR, TDR, SDR, and EDR can be used in combination with multilink shortest path selection. ----------------------------------------------------------------------------- Figure 2.2 Sparse Logical Network Topology with Connections Routed on Multilink Paths (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- A meshed logical-link network is typically used with TDM technology, but can be used also with IP or ATM technology as well, and selected paths are normally limited to 1 or 2 logical links, or trunk groups, as illustrated in Figure 2.3. ----------------------------------------------------------------------------- Figure 2.3 Mesh Logical Network Topology with Connections Routed on 1- and 2-Link Paths (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- Paths may be set up on individual connections (or "per flow") for each call request, such as on a switched virtual circuits (SVC). Paths may also be set up for bandwidth-allocation requests associated with "bandwidth pipes" or traffic trunks, such as on switched virtual paths (SVPs) in ATM-based networks or constraint-based routing label switched paths (CRLSPs) in IP-based networks. Paths are determined by (normally proprietary) algorithms based on the network topology and reachable address information. These paths can cross multiple peer groups in ATM-based networks, and multiple autonomous systems (ASs) in IP-based networks. An ON may select a path from the routing table based on the routing rules and the QoS resource management criteria, described in ANNEX 3, which must be satisfied on each logical-link in the path. If a link is not allowed based on the QoS criteria, then a release with crankback/bandwidth-not-available parameter is used to signal that condition to the ON in order to return the connection/bandwidth-allocation request to the ON, which may then select an alternate path. In addition to controlling bandwidth allocation, the QoS resource management procedures can check end-to-end transfer delay, delay variation, and transmission quality considerations such as loss, echo, and noise. When source routing is used, setup of a connection/bandwidth-allocation request is achieved by having the ON identify the entire selected path including all VNs and DN in the path in a designated-transit-list (DTL) or explicit-route (ER) parameter in the connection-setup IE. If the QoS or traffic parameters cannot be realized at any of the VNs in the connection setup request, then the VN generates a crankback (CBK)/bandwidth-not-available (BNA) parameter in the connection-release IE which allows a VN to return control of the connection request to the ON for further alternate routing. In ANNEX 4, the DTL/ER and CBK/BNA elements are identified as being required for interworking across IP-, ATM-, and TDM--based networks. As noted earlier, connection routing, or path selection, methods are categorized into the following four types: fixed routing (FR), time-dependent routing (TDR), state-dependent routing (SDR), and event-dependent routing (EDR). We discuss each of these methods in the following paragraphs. Examples of each of these path selection methods are illustrated in Figures 2.4a and 2.4b and discussed in the following sections. ----------------------------------------------------------------------------- Figure 2.4a TDR Dynamic Path Selection Methods (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- ----------------------------------------------------------------------------- Figure 2.4b EDR & SDR Dynamic Path Selection Methods (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- Dynamic routing allows routing tables to be changed dynamically, either in an off-line, preplanned, time-varying manner, as in TDR, or on-line, in real time, as in SDR or EDR. With off-line, pre-planned TDR path selection methods, routing patterns contained in routing tables might change every hour or at least several times a day to respond to measured hourly shifts in traffic loads, and in general TDR routing tables change with a time constant normally greater than a call/traffic-flow holding time. A typical TDR routing method may change routing tables every hour, which is longer than a typical voice call/traffic-flow holding time of a few minutes. Three implementations of TDR dynamic path selection are illustrated in Figure 2.4a, which shows multilink path routing, 2-link path routing, and progressive routing. TDR routing tables are preplanned, preconfigured, and recalculated perhaps each week within the capacity management network design function. Real-time dynamic path selection does not depend on precalculated routing tables. Rather, the node or centralized bandwidth broker senses the immediate traffic load and if necessary searches out new paths through the network possibly on a per-traffic-flow basis. With real-time path selection methods, routing tables change with a time constant on the order of or less than a call/traffic-flow holding time. As illustrated in Figure 2.4b, on-line, real-time path selection methods include EDR and SDR. 2.4 Hierarchical Fixed Routing (FR) Path Selection Hierarchical fixed routing (FR) is an important routing topology employed in all types of networks, including IP-, ATM-, and TDM-based networks. In IP-based networks, there is often a hierarchical relationship among different "areas", or sub-networks. Hierarchical multi-domain (or multi-area or multi-autonomous-system) topologies are normally used with IP routing protocols (OSPF, BGP) and ATM routing protocols (PNNI), as well as within almost all TDM-based network routing topologies. For example, in Figure 2.4c, BB1 and BB2 could be backbone nodes in a "backbone area", and AN1 and AN2 could be access nodes in separate "access ----------------------------------------------------------------------------- Figure 2.4c Hierarchical Fixed Routing Path Selection Methods (2-Level Hierarchical Network) (A PDF version of this document with Figures & Tables is availble at http://www.research.att.com/~jrex/jerry/) ----------------------------------------------------------------------------- areas" distinct from the backbone area. Routing between the areas follows a hierarchical routing pattern, while routing within an area follows an interior gateway protocol (IGP), such as OSPF plus MPLS. Similarly, in ATM-based networks the same concept exists, but here the "areas" are called "peer-groups", and for example, the IGP used within peer-groups could be PNNI. In TDM-based networks, the routing between sub-networks, for example, metropolitan-area-networks and long-distance networks, is normally hierarchical, as in IP- and ATM-based networks, and the IGP in TDM-based networks could be either hierarchical or dynamic routing. We now discuss more specific attributes and methods for hierarchical FR path selection. In a FR method, a routing pattern is fixed for a connection request. A typical example of fixed routing is a conventional, TDM-based, hierarchical alternate routing pattern where the route and route selection sequence are determined on a preplanned basis and maintained over a long period of time. Hierarchical FR is illustrated below. FR is more efficiently applied, however, when the network is nonhierarchical, or flat, as compared to the hierarchical structure [A98]. The aim of hierarchical fixed routing is to carry as much traffic as is economically feasible over direct links between pairs of nodes low in the hierarchy. This is accomplished by application of routing procedures to determine where sufficient load exists to justify high-usage logical-links, and then by application of alternate-routing principles that effectively pool the capacities of high-usage links with those of final links, to the end that all traffic is carried efficiently. The routing of connection requests in a hierarchical network involves an originating ladder, a terminating ladder, and links interconnecting the two ladders. In a two-level network, for example, the originating ladder is the final link from lower level-1 node to the upper level-2 node, and the terminating ladder is the final link from upper level-2 node to the lower level-1 node. Links AN1-BB2, AN2-BB1, and BB1--BB2 in Figure 2.4c are examples of interladder links. The identification of the proper interladder link for the routing of a given connection request identifies the originating ladder "exit" point and the terminating ladder "entry" point. Once these exit and entry points are identified and the intraladder links are known, a first-choice path from originating to terminating location can be determined. Various levels of traffic concentration are used to achieve an appropriate balance between transport and switching. The generally preferred routing sequence for the AN1 to AN2 connections is 1. A connection request involving no via nodes: path AN1-AN2 (if the link existed). 2. A connection request involving one via node: path AN1-BB2-AN2, AN1-BB1-AN2, in that order. 3. A connection request involving two via nodes: path AN1-BB1-BB2-AN2 This procedure provides only the first-choice interladder link from AN1 to AN2. Connection requests from AN2 to AN1 often route differently. To determine the AN2-to-AN1 route requires reversing the diagram, making AN2-BB2 the originating ladder and AN1-BB1 the terminating ladder. In Figure 2.4c the preferred path from AN2 to AN1 is AN2-AN1, AN2-BB1-AN1, AN2-BB2-AN1, and AN2-BB2-BB1-AN1, in that order. The alternate path for any high-usage link is the path the node-to-node traffic load between the nodes would follow if the high-usage link did not exist. In Figure 2.4c, this is AN2-BB1-AN1. 2.5 Time-Dependent Routing (TDR) Path Selection TDR methods are a type of dynamic routing in which the routing tables are altered at a fixed point in time during the day or week. TDR routing tables are determined on an off-line, preplanned basis and are implemented consistently over a time period. The TDR routing tables are determined considering the time variation of traffic load in the network, for example based on measured hourly load patterns. Several TDR time periods are used to divide up the hours on an average business day and weekend into contiguous routing intervals sometimes called load set periods. Typically, the TDR routing tables used in the network are coordinated by taking advantage of noncoincidence of busy hours among the traffic loads. In TDR, the routing tables are preplanned and designed off-line using a centralized bandwidth broker, which employs a TDR network design model. Such models are discussed in ANNEX 6. The off-line computation determines the optimal routes from a very large number of possible alternatives, in order to maximize network throughput and/or minimize the network cost. The designed routing tables are loaded and stored in the various nodes in the TDR network, and periodically recomputed and updated (e.g., every week) by the bandwidth broker. In this way an ON does not require additional network information to construct TDR routing tables, once the routing tables have been loaded. This is in contrast to the design of routing tables on-line in real time, such as in the SDR and EDR methods described below. Paths in the TDR routing table may consist of time varying routing choices and use a subset of the available paths. Paths used in various time periods need not be the same. Paths in the TDR routing table may consist of the direct link, a 2-link path through a single VN, or a multiple-link path through multiple VNs. Path routing implies selection of an entire path between originating and terminating nodes before a connection is actually attempted on that path. If a connection on one link in a path is blocked (e.g., because of insufficient bandwidth), the connection request then attempts another complete path. Implementation of such a routing method can be done through control from the originating node, plus a multiple-link crankback capability to allow paths of two, three, or more links to be used. Crankback is an information-exchange message capability that allows a connection request blocked on a link in a path to return to the originating node for further alternate routing on other paths. Path-to-path routing is nonhierarchical and allows the choice of the most economical paths rather than being restricted to hierarchical paths. Path selection rules employed in TDR routing tables, for example, may consist of simple sequential routing. In the sequential method all traffic in a given time period is offered to a single route, and lets the first path in the route overflow to the second path which overflows to the third path, and so on. Thus, traffic is routed sequentially from path to path, and the route is allowed to change from hour to hour to achieve the preplanned dynamic, or time varying, nature of the TDR method. Other TDR path selection rules can employ probabilistic techniques to select each path in the route and thus influence the realized flows. One such method of implementing TDR multilink path selection is to allocate fractions of the traffic to routes and to allow the fractions to vary as a function of time. One approach is cyclic path selection, illustrated in Figure 2.4a, which has as its first route (1, 2, ..., M), where the notation (i, j, k) means that all traffic is offered first to path i, which overflows to path j, which overflows to path k. The second route of a cyclic route choice is a cyclic permutation of the first route: (2, 3, ..., M, 1). The third route is likewise (3, 4, ..., M, 1, 2), and so on. This approach has computational advantages because its cyclic structure requires considerably fewer calculations in the design model than does a general collection of paths. The route congestion level of cyclic routes are identical; what varies from route to route is the proportion of flow on the various links. Two-link TDR path selection is illustrated in Figure 2.4a. An example implementation is 2-link sequential TDR (2S-TDR) path selection. By using the crankback signal, 2S-TDR limits path connections to at most two links, and, in meshed network topologies, such TDR 2-link sequential path selection allows nearly as much network utilization and perfo