Internet Draft XiPeng Xiao Document: draft-ietf-pwe3-requirements-04.txt Riverstone Networks Expires: June 2003 Danny McPherson TCB Prayson Pate Overture Networks Editors Requirements for Pseudo-Wire Emulation Edge-to-Edge (PWE3) draft-ietf-pwe3-requirements-04.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. 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. Abstract This document describes base requirements for the Pseudo-Wire Emulation Edge to Edge Working Group (PWE3 WG). It provides guidelines for other working group documents that will define mechanisms for providing pseudo-wire emulation of Ethernet, ATM, Frame Relay, raw HDLC, and MPLS. Requirements for pseudo-wire emulation of TDM (i.e. "synchronous bit streams at rates defined by ITU G.702") are defined in another document. It should be noted that the PWE3 WG standardizes mechanisms that can be used to provide PWE3 services, but not the services themselves. Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 Co-Authors The following are co-authors of this document: Vijay Gill AOL Time Warner, Inc. Kireeti Kompella Juniper Networks, Inc. Thomas D. Nadeau Cisco Systems Craig White Level 3 Communications, LLC. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Expires 06/03 Xiao/McPherson/Pate [Page 2] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 Table of Contents 1 Terminology .................................................. 4 2 Introduction ................................................. 4 2.1 What Are Pseudo Wires? ..................................... 4 2.2 Background and Motivation .................................. 5 2.3 Current Network Architecture ............................... 5 2.4 PWE3 as a Path to Convergence .............................. 6 2.5 Suitable Applications for PWE3 ............................. 6 2.6 Summary .................................................... 6 3 Reference Model of PWE3 ...................................... 7 4 Packet Processing ............................................ 8 4.1 Encapsulation .............................................. 8 4.2 Frame Ordering ............................................. 9 4.3 Frame Duplication .......................................... 9 4.4 Segmentation and Reassembly ................................ 9 4.5 Handling Control Messages of the Native Services ........... 9 4.6 Consideration of Per-PSN Packet Overhead ................... 10 5 Maintenance of Emulated Services ............................. 10 5.1 Setup and Teardown of Pseudo-Wires ......................... 10 5.2 Status Monitoring .......................................... 10 5.3 Notification of Status Changes ............................. 11 5.4 Keep-alive ................................................. 12 6 Management of Emulated Services .............................. 12 6.1 MIBs ....................................................... 12 6.2 General MIB Requirements ................................... 12 6.3 Configuration and Provisioning ............................. 13 6.4 Performance Monitoring ..................................... 13 6.5 Fault Management and Notifications ......................... 13 6.6 Pseudo-Wire Connection Verification and Traceroute ........ 13 7 Faithfulness of Emulated Services ............................ 13 7.1 Characteristics of an Emulated Service ..................... 14 7.2 Service Quality of Emulated Services ....................... 14 8 Non-Requirements ............................................. 14 9 Quality of Service (QoS) Considerations ...................... 15 10 Inter-domain Issues ......................................... 16 11 Security Considerations ..................................... 16 12 Acknowledgments ............................................. 16 13 References .................................................. 16 14 Authors' Addresses .......................................... 17 15 Full Copyright Section ...................................... 19 Expires 06/03 Xiao/McPherson/Pate [Page 3] Expires 06/03 Xiao/McPherson/Pate [Page 3] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 1. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALLNOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. Some terms used throughout this document are listed below. Customer Edge A device where one end of a service originates and/or terminates. The CE is not aware that it is using an emulated service rather than a native service. Packet Switched Network A network using IP or MPLS as the mechanism for packet forwarding Provider Edge A device that provides PWE3 to a CE. Pseudo Wire A mechanism that carries the essential elements of an emulated service from one PE to one or more other PEs over a PSN. Pseudo Wire Emulation Edge to Edge A mechanism that emulates the essential attributes of a service (such as a T1 leased line or Frame Relay) over a PSN. Pseudo Wire PDU A PDU sent on the PW that contains all of the data and control information necessary to emulate the desired service. PSN Tunnel A tunnel across a PSN inside which one or more PWs can be carried. 2. Introduction 2.1. What Are Pseudo Wires? Pseudo Wire Emulation Edge-to-Edge (PWE3) is a mechanism that emulates the essential attributes of a service over a Packet Switched Network (PSN). The required functions of PWs include encapsulating service-specific PDUs arriving at an ingress port, and carrying them across a path or tunnel, managing their timing and order, and any other operations required to emulate the behavior and characteristics of the service as faithfully as possible. Expires 06/03 Xiao/McPherson/Pate [Page 4] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 From the customer perspective, the PW is perceived as an unshared link or circuit of the chosen service. However, there may be deficiencies that impede some applications from being carried on a PW. These limitations should be fully described in the appropriate service-specific documents and Applicability Statements. 2.2. Background and Motivation The following sections give some background on where networks are today and why they are changing. It also talks about the motivation to provide converged networks while continuing to support existing services. Finally it discusses how PWs can be a solution for this dilemma. 2.3. Current Network Architecture 2.3.1. Multiple Networks For any given service provider delivering multiple services, the current infrastructure usually consists of parallel or "overlay" networks. Each of these networks implements a specific service, such as Frame Relay, Internet access, etc. This is expensive, both in terms of capital expense and operational costs. Furthermore, the presence of multiple networks complicates planning. Service providers wind up asking themselves these questions: - Which of my networks do I build out? - How many fibers do I need for each network? - How do I efficiently manage multiple networks? A converged network helps service providers answer these questions in a consistent and economical fashion. 2.3.2. Transition to a Packet-Optimized Converged Network In order to maximize return on their assets and minimize their operating costs, service providers often look to consolidate the delivery of multiple service types onto a single networking technology. As packet traffic takes up a larger and larger portion of the available network bandwidth, it becomes increasingly useful to optimize public networks for the Internet Protocol. However, many service providers are confronting several obstacles in engineering packet-optimized networks. Although Internet traffic is the fastest growing traffic segment, it does not generate the highest revenue per bit. For example, Frame Relay traffic currently generates higher revenue per bit than native IP services do. Private line TDM services still generate even more revenue per bit than does Frame Expires 06/03 Xiao/McPherson/Pate [Page 5] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 Relay. In addition, there is a tremendous amount of legacy equipment deployed within public networks that does not communicate using the Internet Protocol. Service providers continue to utilize non-IP equipment to deploy a variety of services, and see a need to interconnect this legacy equipment over their IP-optimized core networks. 2.4. PWE3 as a Path to Convergence How do service providers realize the capital and operational benefits of a new packet-based infrastructure, while leveraging the existing equipment and also protecting the large revenue stream associated with this equipment? How do they move from mature Frame Relay or ATM networks, while still being able to provide these lucrative services? One possibility is the emulation of circuits or services via PWs. Circuit emulation over ATM and interworking of Frame Relay and ATM have already been standardized. Emulation allows existing services to be carried across the new infrastructure, and thus enables the interworking of disparate networks. Implemented correctly, PWE3 can provide a means for supporting today's services over a new network. 2.5. Suitable Applications for PWE3 What makes an application suitable (or not) for PWE3 emulation? When considering PWs as a means of providing an application, the following questions must be considered: - Is the application sufficiently deployed to warrant emulation? - Is there interest on the part of service providers in providing an emulation for the given application? - Is there interest on the part of equipment manufacturers in providing products for the emulation of a given application? - Are the complexities and limitations of providing an emulation worth the savings in capital and operational expenses? If the answer to all four questions is "yes", then the application is likely to be a good candidate for PWE3. Otherwise, there may not be sufficient overlap between the customers, service providers, equipment manufacturers and technology to warrant providing such an emulation. 2.6. Summary To maximize the return on their assets and minimize their operational costs, many service providers are looking to consolidate the delivery of multiple service offerings and traffic types onto a single IP- optimized network. Expires 06/03 Xiao/McPherson/Pate [Page 6] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 In order to create this next-generation converged network, standard methods must be developed to emulate existing telecommunications formats such as Ethernet, Frame Relay, and ATM over IP-optimized core networks. This document describes requirements for accomplishing this goal. 3. Reference Model of PWE3 A pseudo-wire (PW) is a connection between two provider edge (PE) devices which connects two pseudo-wire end-services (PWESs). In this document, A PWES is either: - an Ethernet link or a VLAN link between two ports, or - an ATM VC or VP, or - a Frame Relay VC, or - a raw HDLC circuit, or - an MPLS LSP between a customer edge (CE) device and a PE (See Figure 1). |<------- Pseudo Wire ------>| | | | |<-- PSN Tunnel -->| | PW V V V V PW End Service+----+ +----+ End Service +-----+ | | PE1|==================| PE2| | +-----+ | |----------|............PW1.............|----------| | | CE1 | | | | | | | | CE2 | | |----------|............PW2.............|----------| | +-----+ | | |==================| | | +-----+ ^ +----+ +----+ | ^ | Provider Edge 1 Provider Edge 2 | | | |<-------------- Emulated Service ---------------->| Customer Customer Edge 1 Edge 2 Figure 1: PWE3 Reference Model During the setup of a PW, the two PEs will be configured or will automatically exchange information about the service to be emulated so that later they know how to process packets coming from the other end. After a PW is set up between two PEs, frames received by one PE from a PWES are encapsulated and sent over the PW to the remote PE, where native frames are re-constructed and forwarded to the other CE. For a detailed PWE3 architecture overview, readers should refer to the PWE3 architecture document [PWE3_ARCH]. Expires 06/03 Xiao/McPherson/Pate [Page 7] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 This document does not assume that a particular type of PWs (e.g. [L2TPv3] sessions or [MPLS] LSPs) is used. Instead, it describes generic requirements that apply to all PWs, for all services including Ethernet, ATM, Frame Relay, raw HDLC and MPLS. 4. Packet Processing This section describes forwarding plane requirements for PWE3. 4.1. Encapsulation Every PE MUST provide service interfaces for encapsulating PDUs from the PWESs. It should be noted that the PDUs to be encapsulated may or may not contain L2 header information. This is service specific. Every PWE3 service MUST specify what the PDU is. A PW header consists of all the header fields in a PW PDU that are used by the PW egress to determine how to process the PDU. The PSN tunnel header is not considered as part of the PW header. Specific requirements on PDU encapsulation are listed below. 4.1.1. Conveyance of Necessary L2 Header Information The egress of a PW needs some information, e.g. which native service the PW PDUs belong to, and possibly some L2 header information, in order to know how to process the PDUs received. A PWE3 encapsulation approach MUST provide some mechanism for conveying such information from the PW ingress to the egress. It should be noted that not all such information must be carried in the PW header of the PW PDUs. Some information (e.g. service type of a PW) can be stored as state information at the egress during PW setup. 4.1.2. Support of Variable Length PDUs A PWE3 approach MUST accommodate variable length PDUs, if variable length PDUs are allowed by the native service. For example, a PWE3 approach for Frame Relay MUST accommodate variable length frames. 4.1.3. Support of Multiplexing and Demultiplexing If a service in its native form is capable of grouping multiple circuits into a "trunk", e.g. multiple ATM VCs in a VP or multiple Ethernet VLANs in a port, some mechanism SHOULD be provided so that a single PW can be used to connect two end-trunks. From encapsulation perspective, sufficient information MUST be carried so that the egress of the PW can demultiplex individual circuits from the PW. Expires 06/03 Xiao/McPherson/Pate [Page 8] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 4.2. Frame Ordering When packets carrying the PW PDUs traverse a PW, they may arrive at the egress out of order. For some services, the frames (either control frames only or both control and data frames) must be delivered in order. For such services, some mechanism MUST be provided for ensuring in-order delivery. Providing a sequence number in the PW header for each packet is one possible approach. 4.3. Frame Duplication In rare cases, packets traversing a PW may be duplicated. For some services, frame duplication is not allowed. For such services some mechanism MUST be provided to ensure that duplicated frames will not be delivered. The mechanism may or may not be the same as the mechanism used to ensure in-order frame delivery. 4.4. Segmentation and Reassembly It is desirable to avoid packet Segmentation and Reassembly (SAR). One way to do thus is to ensure that the combined size of the payload and its associated PWE3 and PSN headers do not exceed the PSN path MTU. If SAR cannot be completely avoided, at a PW ingress, if the length of a packet resulted from encapsulation exceeds the PSN path MTU, the PDU MAY be dropped. In this case, the management plane of the ingress PE MAY be notified. Alternatively, a segmentation mechanism MAY be defined and used. At a PW egress, if the length of a L2 frame that is restored from a PW PDU exceeds the MTU of destination PWES, it MUST be dropped. In this case, the management plane of the egress PE MAY be notified. 4.5. Handling Control Messages of the Native Services Some native services use control messages for maintaining the circuits. These control messages may be in-band, e.g. Ethernet flow control or ATM performance management, or out-of-band, e.g. the signaling VC of an ATM VP. It is desirable that the PEs participate as little as possible in the signaling and maintenance of the native services. However, it is up to each specific PWE3 approach to specify what the PEs MUST do in this regard. For an emulated service, it is possible that some control messages (e.g. OAM) are processed at the PEs while others (e.g. keep-alive) are passed through transparently like data messages to the remote CE. If control messages are passed through, it MAY be desirable to provide higher reliability for them. The mechanisms for providing the high reliability NEED NOT be defined in the PWE3 WG. Expires 06/03 Xiao/McPherson/Pate [Page 9] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 4.6. Consideration of Per-PSN Packet Overhead For ATM emulation, if each packet carries one cell, the PSN tunnel header overhead is relatively large. In order to reduce overhead, multiple cells MAY be concatenated before a PSN tunnel header is added. Each encapsulated cell still carries its own PW header so that the egress of the PW knows how to process it. However, the benefit of concatenating multiple cells for header efficiency should be weighed against the resulting increase in delay, jitter and the larger penalty incurred by packet loss. In some cases, it may be appropriate to perform silence suppression or other compression. 5. Maintenance of Emulated Services This section describes control plane requirements for PWE3. 5.1. Setup and Teardown of Pseudo-Wires A PW must be set up before an emulated service can be established, and must be torn down when an emulated service is no longer needed. Setup and teardown of a PW can be triggered by a CLI command from the management plane of a PE, or by signaling (i.e. setup or teardown) of a PWES, e.g., an ATM SVC, or by an auto-discovery mechanism. Every PWE3 approach MUST define some setup mechanism for establishing the PWs. During the setup process, the PEs need to exchange some information (e.g. learn each other's capability). The setup mechanism MUST enable the PEs to exchange all necessary information. For example, both endpoints must agree on methods for encapsulating PDUs and handling frame ordering. Which signaling protocol to use and what information to exchange are service specific. Every PWE3 approach MUST specify them. Manual configuration of PWs can be considered as a special kind of signaling and is allowed. Sessions in a L2TPv3 tunnel or MPLS LSPs can be used as PWs. Selection of a particular type of PWs is carrier-dependent and is outside scope of the PWE3 WG. 5.2. Status Monitoring Some native services have mechanisms for status monitoring. For example, ATM supports OAM for this purpose. For such services, the corresponding emulated services MUST specify how to perform status monitoring. The mechanisms NEED NOT be defined in this WG. Some status monitoring mechanisms defined in other WGs, e.g. [LSPPING], may be leveraged. Expires 06/03 Xiao/McPherson/Pate [Page 10] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 5.3. Notification of Status Changes 5.3.1. Up/Down Notification If a native service is bi-directional, the corresponding emulated service can only be signaled up when the associated PWs and PSN tunnels in both directions are functional. Because the two CEs of an emulated service are not adjacent, a failure may occur at a place such that one or both physical links between the CEs and PEs remain up. For example in Figure 1, if the physical link between CE1 and PE1 fails, the physical link between CE2 and PE2 will not be affected and will remain up. Unless CE2 is notified about the remote failure, it will continue to send traffic over the emulated service to CE1. Such traffic will be discarded at PE1. Some native services have failure notification so that when the services fail, both CEs will be notified. For such native services, the corresponding PWE3 service MUST provide a failure notification mechanism. Similarly, if a native service has notification mechanism so that when a network failure is fixed, all the affected services will change status from "Down" to "Up", the corresponding emulated service MUST provide a mechanism for doing so. 5.3.2. Misconnection and Payload Type Mismatch With PWE3, misconnection and payload type mismatch can occur. A PWE3 approach MAY define some mechanism for detecting and handling misconnection and payload type mismatch. 5.3.3. Packet Loss, Corruption, and Out-of-order Delivery A PW can incur packet loss, corruption, and out-of-order delivery. This can impact the working condition of an emulated service. For some payload types, packet loss, corruption, and out-of-order delivery can be mapped to either a bit error burst, or loss of carrier on the PW. If a native service has some mechanism to deal with bit error, the corresponding PWE3 service SHOULD provide a similar mechanism. 5.3.4. Other Status Notification A PWE3 approach MAY provide mechanism for other status notification, if any. 5.3.5. Collective Status Notification Expires 06/03 Xiao/McPherson/Pate [Page 11] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 Status of a group of emulated circuits may be affected identically by a single network incidence. For example, when the physical link between a CE and a PE fails, all the emulated circuits that go through that link will fail. It is likely that there exists a group of emulated circuits which all terminate at a remote CE. (There can be multiple such CEs). Therefore, it is desirable that a single notification message be used to notify failure of the whole group of emulated circuits. A PWE3 approach MAY provide some mechanism for notifying status changes of a group of emulated circuits. One possible approach is to associate each emulated circuit with a group ID when the PW for that emulated circuit is set up. Multiple emulated circuits can then be grouped by associating them with identical group ID. In status notification, that group ID can be used to refer to all the emulated circuits in that group. 5.4. Keep-alive If a native service has keep-alive mechanism, the corresponding emulated service MUST have keep-alive support. This can possibly be done by transparently transporting the native keep-alive messages across the PW. Alternatively, the keep-alive mechanism of the PW signaling protocol (e.g. L2TPv3), if it exists, can be utilized. 6. Management of Emulated Services Each PWE3 approach SHOULD provide some mechanisms for network operators to manage the emulated service. These mechanisms can be in the forms described below. 6.1. MIBs SNMP MIBs [SMIV2] MUST be provided for managing each emulated service as well as pseudo-wire in general. These MIBs SHOULD be created with the following requirements. 6.2. General MIB Requirements New MIBs MUST augment or extend where appropriate, existing tables as defined in other existing service-specific MIBs for existing services such as MPLS or L2TP. For example, the ifTable as defined in the Interface MIB [IFMIB] MUST be augmented to provide counts of out-of- order packets. A second example is the extension of the MPLS-TE-MIB [TEMIB] when emulating circuit services over MPLS. Rather than redefining the tunnelTable so that PWES can utilize MPLS tunnels, for example, entries in this table MUST instead be extended to add additional PWES-specific objects. Doing so facilitates a natural extension of those objects defined in the existing MIBs in terms of management, as well as leveraging existing agent implementations. Interfaces implementing a PWES MUST appear as an interface in the Expires 06/03 Xiao/McPherson/Pate [Page 12] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 ifTable. 6.3. Configuration and Provisioning MIB Tables MUST be designed to facilitate configuration and provisioning of the PWES. The MIB(s) MUST facilitate intra-PSN configuration and monitoring of PWES connections. 6.4. Performance Monitoring MIBs MUST collect statistics for performance and fault management. MIBs MUST provide a description of how existing counters are used for PW emulation and SHOULD not replicate existing MIB counters. 6.5. Fault Management and Notifications Notifications SHOULD be defined where appropriate to notify the network operators of any interesting situations, including faults detected in the PWES. Objects defined to augment existing protocol-specific notifications in order to add PWES functionality MUST explain how these notifications are to be emitted. 6.6. Pseudo-Wire Connection Verification and Traceroute For network management purpose, a connection verification mechanism SHOULD be supported by PWs. Connection verification as well as other alarming mechanisms can alert network operators that a PW has lost its remote connection. It is sometimes desirable to know the exact functional path of a PW for troubleshooting purpose, thus a traceroute function capable of reporting the path taken by data packets over the PW SHOULD be provided. 7. Faithfulness of Emulated Services An emulated service SHOULD be as similar to the native service as possible, but it is NOT REQUIRED that they are identical. The applicability statement of a PWE3 service MUST report limitations of the emulated service. Some basic requirements on faithfulness of an emulated service are described below. Expires 06/03 Xiao/McPherson/Pate [Page 13] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 7.1. Characteristics of an Emulated Service From the perspective of a CE, an emulated circuit is characterized as an unshared link or circuit of the chosen service, although service quality of the emulated service may be different from that of a native one. Specifically, the following requirements MUST be met: 1) It MUST be possible to define type (e.g. Ethernet, which is inherited from the native service), speed (e.g. 100Mbps), and MTU size for an emulated circuit, if it is possible to do so for a native circuit. 2) If the two endpoints CE1 and CE2 of emulated circuit #1 are connected to PE1 and PE2, respectively, and CE3 and CE4 of emulated circuit #2 are also connected to PE1 and PE2, then the PWs of these two emulated services may share the same physical paths between PE1 and PE2. But from each CE's perspective, its emulated circuit MUST appear as unshared. For example, CE1/CE2 MUST NOT be aware of existence of emulated circuit #2 or CE3/CE4. 3) If an emulated circuit fails (either at one of the PWESs or in the middle of the PW), both CEs MUST be notified in a timely manner, if they will be notified in the native service. The definition of "timeliness" is service-dependent. 4) If a routing protocol (e.g. IGP) adjacency can be established over a native circuit, it MUST be possible to be established over an emulated circuit as well. 7.2. Service Quality of Emulated Services It is NOT REQUIRED that an emulated service provide the same service quality as the native service. The PWE3 WG only defines mechanisms for providing PW emulation, not the services themselves. What quality to provide for a specific emulated service is a matter between a service provider (SP) and its customers, and is outside scope of the PWE3 WG. In fact, different SPs can use the same PWE3 approach with different QoS mechanisms to provide the same emulated service with different service quality. 8. Non-Requirements Some non-requirements are mentioned in various sections of this document. Those work items are outside scope of the PWE3 WG. They are summarized below: Expires 06/03 Xiao/McPherson/Pate [Page 14] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 - Service interworking; In Service Interworking, the IWF (Interworking Function) between two dissimilar protocols (e.g., ATM & MPLS, Frame Relay & ATM, ATM & IP, ATM & L2TP, etc.) terminates the protocol used in one network and translates (i.e. maps) its Protocol Control Information (PCI) to the PCI of the protocol used in other network for User, Control and Management Plane functions to the extent possible. - Selection of a particular type of PWs; - Striving to make the emulated services perfectly match their native services; - Defining mechanisms for signaling the PSN tunnels; - Defining how to perform traffic management on packets that carry PW PDUs; - Providing security for the PW PDUs; - Providing any multicast service that is not native to the emulated medium. To illustrate this point, Ethernet transmission to a multicast IEEE-48 address is considered in scope, while multicast services like [MARS] that are implemented on top of the medium are out of scope; 9. Quality of Service (QoS) Considerations In this document, QoS means satisfactory service quality. It should not be confused with QoS mechanisms such as Weighted Fair Queuing (WFQ) or Random Early Detection (RED). QoS is essential for ensuring that emulated services are similar (but not necessarily identical) to their native forms. It is up to network operators to decide how to provide QoS - They can choose to rely on over-provisioning and/or deploy some QoS mechanisms. In order to take advantage of QoS mechanisms defined in other working groups, e.g. the traffic management schemes defined in DiffServ WG, it is desirable that some mechanisms exists for differentiating the packets resulted from PDU encapsulation. These mechanisms NEED NOT be defined in the PWE3 approaches themselves. For example, if the packets are MPLS or IP packets, their EXP or DSCP fields can be used for marking and differentiating. A PWE3 approach MAY provide Expires 06/03 Xiao/McPherson/Pate [Page 15] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 guidelines for marking and differentiating, e.g. what fields in the original L2 headers should be used for determining the EXP/DSCP value. But the exact procedure of how to perform marking and differentiating, e.g. specifying the mapping function from Ethernet 802.1p field to EXP field, is out of scope. 10. Inter-domain Issues PWs are directly between the PW end-points. Whether a PSN tunnel is inter-domain or not is transparent to PWE3. Therefore, inter-domain issues caused by two PW end-points locating in different administrative domains are issues for PSN-tunnel setup protocols such as RSVP or LDP or L2TPv3, not for PWE3. 11. Security Considerations The PW end-point, PW demultiplexing mechanism, and the payloads of the native service can all be vulnerable to attack. PWE3 should leverage security mechanisms provided by the PW Demultiplexer or PSN Layers. Such mechanisms SHOULD protect PW end-point and PW Demultiplexer mechanism from denial-of-service (DoS) attacks and spoofing of the native data units. Controlling PSN access to the PW end-point is generally effective against DoS attacks and spoofing, and can be part of protection mechanism. Protection mechanisms SHOULD also address the spoofing of tunneled PW data. The validation of traffic addressed to the PW Demultiplexer end-point is paramount in ensuring integrity of PW encapsulation. Security protocols such as IPSec [RFC2401] can be used. 12. Acknowledgments The authors would like to acknowledge input from S. Bryant, R. Cohen, G. Heron, T. Johnson, A. Malis, L. Martini, E. Rosen, J. Rutemiller, T. So, Y. Stein and S. Vainshtein. 13. References [IFMIB] K. McCloghrie, and F. Kastenholtz, "The Interfaces Group MIB using SMIv2", RFC 2233, Nov. 1997. [L2TPv3] J. Lau, M. Townsley, A. Valencia, G. Zorn, I. Goyret, G. Pall, A. Rubens, B. Palter, "Layer Two Tunneling Protocol (L2TPv3)", , work in progress, Nov. 2002. [LSPPING] K. Kompella, P. Pan, N. Sheth, D. Cooper, G. Swallow, S. Wadhwa, and R. Bonica, "Detecting Data Plane Liveliness in MPLS", , work in progress, Oct. 2002. Expires 06/03 Xiao/McPherson/Pate [Page 16] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 [MARS] G. Armitage, "Support for Multicast over UNI 3.0/3.1 based ATM Networks", RFC2022, November 1996 [MPLS] E. Rosen, A. Viswanathan, and R. Callon, "Multiprotocol Label Switching Architecture", RFC3031, January 2001 [TEMIB] C. Srinivasan, A. Viswanathan, and T. Nadeau, "MPLS Traffic Engineering Management Information Base", , work in progress, Nov. 2002. [PWE3_ARCH] S. Bryant and P. Pate, et. al., "PWE3 Architecture", , work in progress, Nov. 2002. [RFC2401] S. Kent, R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, Nov. 1998. [RTP] H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", RFC1889, January 1996. [SMIV2] J. Case, K. McCloghrie, M. Rose, and S. Waldbusser, "Structure of Management Information for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1902, January 1996. 14. Authors' Addresses XiPeng Xiao Riverstone Networks 5200 Great America Parkway Santa Clara, CA 95054 Email: xxiao@riverstonenet.com Danny McPherson TCB.net Email: danny@tcb.net Prayson Pate Overture Networks P. O. Box 14864 RTP, NC, USA 27709 Email: prayson.pate@overturenetworks.com Vijay Gill AOL Time Warner EMail: vijaygill9@aol.com Kireeti Kompella Expires 06/03 Xiao/McPherson/Pate [Page 17] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 Juniper Networks, Inc. 1194 N. Mathilda Ave. Sunnyvale, CA 94089 Email: kireeti@juniper.net Thomas D. Nadeau Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA 01824 Email: tnadeau@cisco.com Craig White Level 3 Communications, LLC. 1025 Eldorado Blvd. Broomfield, CO, 80021 Email: Craig.White@Level3.com Expires 06/03 Xiao/McPherson/Pate [Page 18] Internet Draft draft-ietf-pwe3-requirements-04 Dec. 2002 15. Full Copyright Section Copyright (C) The Internet Society (2000). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. 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. Expires 06/03 Xiao/McPherson/Pate [Page 19]