draft-satish-l2-mobilereq-01.txt Informational Satish Jamadagni Tata Consultancy Services Internet Draft Document: draft-satish-l2-mobilereq-01.txt July 2003 L2 considerations for optimized IP mobility Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. This is an individual draft for consideration by the seamoby Working Group. 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 IP mobility protocols have traditionally been designed to be independent of any L2 considerations. A critical factor in achieving good performance for IP mobility protocols is its closeness to an L2 handover. Handover occurs when a Mobile Node moves from one radio access Point to another. If the new radio access point is associated with a new subnet, the routing reachability change will have to reflect at the access routers. Better synchronization between L2 handover and L3 handover are still more important when supporting fast handoff between two wireless domains. This draft discusses the L2 handover steps and the possible coupling of L2 and L3 layers to support optimize layer 3 handover. This draft also explores the location information as a possible L2 trigger to support optimized L3 handover. Also an L2 trigger message format is defined which can be handled at L3 independent of other protocol considerations. Satish [Page 1] Internet Draft L2 considerations for.. July 2003 It is emphasized that the L2 considerations for optimized IP mobility work should serve well the objectives of 4G (All IP wireless) as well as Software Defined Radio (SDR) or the multi mode handover scenarios. Table of Contents 1.0 Introduction 2.0 Terminology 3.0 The meaning of an L2 trigger 4.0 Decomposition of the L2 handoff process to identify L2 triggers 4.1. L2 handoff Initiation stage 4.2. L2 handoff decision stage 4.3. L2 handoff execution stage 4.4. Information in an L2 trigger 5.0 Location trigger as an L2 Trigger 6.0 Using L2 Triggers in combination with application triggers 7.0 The L2 message format considerations 8.0 Summary 9.0 References 10.0 Author's Addresses 1.0 Introduction An important consideration in the design of IP mobility protocols is handover. A moving Mobile Node (MN) may irregularly need to change the radio Access Point (AP) with which it is communicating. The change in L2 connectivity to a new AP may cause a change in IP routing reachability change and this requires updation of routing information at the access routers (ARs). Even if no change in subnet occurs, the Aps may still need to communicate the change in on-link reachability to the local AR. For a handover to occur, candidate APs must be identified and a target AP must be selected. Once the initial identification and decision are complete, the handover process can begin. Several protocol designs have been advanced for Mobile IP that seek to reduce the amount of handover latency at L3. These protocols depend on timely information from the L2 protocol about the progress of L2 handover. L2 handover progress information also affects context transfer [11] and candidate access router discovery [12]. Context transfer involves moving context information (QoS, header compression, authentication, etc.) from the old AR to the new AR. By moving such context information, the ARs can avoid requiring the MN to set up all the context information from scratch. This considerably reduces the amount of time necessary to set up basic network service on the new subnet. Synchronization between L2 & L3 can happen as the L2 handover progresses. If handover progress information is available from L2, all L3 activities including context transfer and handover process can be Satish [Page 2] Internet Draft L2 considerations for.. July 2003 pipelined instead of waiting for crisp L2 events. This document discusses requirements on underlying systems for supporting optimized IP mobility. Apart from the possible L2 triggers listed in [7], this draft suggests location information as a serious potential L2 trigger in bringing about optimized IP mobility as emerging 3G & WLAN stds support location measurements at L2. 2.0 Terminology The following terms are used in this document. Access Point (AP): A Layer 2 (L2) access entity, e.g. wireless base transceiver stations. Its primary function is to provide Mobile Nodes (MNs) an L2 wireless link. Access Router (AR): A Layer 3 (L3) IP router, residing in an access network. An AR is the first hop router for a MN. L2 Handover: Change of MN's link layer connection from one AP to another. L3 Handover: Change of MN's routable address from one AR to another. 3.0 The meaning of an L2 trigger Theoretically speaking L2 and L3 can be loosely or tightly coupled. The IP layer has emerged independent of L2 considerations. L2 triggers in the context of this document are still in the scope of a loosely coupled interaction between L2 and L3 with L3 supporting a few additional L2 trigger handling capabilities and the L3 handover mechanisms also (along with the regular MIP related mechanisms) on these triggers. A tight coupling can be defined as both L2 and L3 being reflective or a single handover entity controlling both the L2 and L3 handovers with a possible non-compliance to existing (as we know of it today) L2 and L3 handover mechanisms (cross-layer control). Such a tight coupling will be relevant in the future within the scope of the all IP wireless (4G) with inter-technology support when a L2 trigger from one mode can possibly be consumed by another mode within a handheld terminal or may be within a network. The information carried & the consumption of L2 triggers can vary depending on the nature of handover control i.e. whether the handover is a Mobile Controlled (MCHO), Network Controlled (NCHO), Mobile Assisted (MAHO) or a Network Assisted (NCHO) handover. The relevance or Satish [Page 3] Internet Draft L2 considerations for.. July 2003 importance of L2 triggers is much greater for a soft handover scenario (make before break scenario) than for a hard handover (break before make scenario). The nature of L2 considerations being discussed for optimized IP mobility should include 1. possible location based handovers when possible location information is available in a network, example: in 3G terminals with location measurement and reporting capability as well as L3s which are location aware [9] [10] 2. Inter-technology handover scenarios with the L2 trigger generated in one mode is consumed by another mode (or a mode controller with a subsequent reaction in another mode). 4.0 Decomposition of the L2 handoff process for identifying L2 triggers This section deals with decomposing the L2 handoff process to understand the L2 triggers that can facilitate better L3 handover. An initial set of L2 triggers has been identified in [7] and the set of triggers provided in this draft can be seen as a continuation of that work. Three steps are identified in the L2 handoff process and appropriate triggers are defined: 1.The L2 handoff initiation stage, 2.The L2 handoff decision stage and 3.The L2 handoff execution stage. The above decomposition specifies three L2 triggers that go beyond the basic L2 "Link-Up" and "Link-down" notifications. The identification of intermediate states in L2 handoff provides for notifications which can help pipeline the L3 handover process. The time span between a L2 handoff initiation and an actual L2 handoff (execution) can be substantial and depends on the actual theresholding (number of beacons from a target access point before which a handover decision is arrived at) or any Quality of Service based algorithms that might be used for L2 handover. L2 trigger | When generated | L3 followup | Parameters -----------|----------------------|---------------|----------------- L2 handoff | | | Handoff Initiation initiation | | | cause | QoS degradation |Ex:L3 candidate| Ex: QoS degradation | with active | access router | at the MN L2 | signal or beacon |scanning & | | measurement | table updation| | | | ---------------------------------------------------------------------- L2 handoff | | | decision | | identify | | L2 handover decision | appropriate | | to a specific AP | Target router | Satish [Page 4] Internet Draft L2 considerations for.. July 2003 | | | ---------------------------------------------------------------------- L2 handoff | Reassociation start | possible L3 | execution | with possible | auth & | | authorization & | authorization | | authentication | procedures | | | | | | | ----------------------------------------------------------------------- 4.1. L2 handoff Initiation stage The Initiation phase identifies the need for handover and subsequently initiates it. L2 handover initiation triggers can originate from an MN or the AP. The MN L2 initiation may be due to a perceived degradation in QoS. The AP initiation may be to serve any time dependent load factors. The reasons for a handover initiation can be any of the following: Availability, Congestion, Effective S/R, Emergency service, Interference, Loading, Macro/Micro/Pico - Operator policy like handover slow moving users to a pico cell and fast moving users to larger cells, Security levels, Network forced maintained, QoS (delay, delay variation), location etc. L2 handoff initiation triggers can be used by L3 for fast handoff initiation. L3 fast handoff initiation may include identification of Candidate Access Routers (CARs) for handoff. Here L2 handoff initiation trigger is a notification to L3 sent at the start of the L2 handoff initiation. This trigger can be indicative of the L2 handoff threshold crossing. 4.2. L2 handoff decision stage The L2 handover decision phase compares information from a variety of sources with recorded user preferences and network policy. It also involves a playoff between options to identify the best available handover option taking into consideration user preference and network policy. It then notifies the handoff execution module for an L2 handoff execution. L2 decision trigger can be used by the L3 to proceed from a to CAR discovery phase to a Target Access Router (TAR) identification phase. 4.3. L2 handoff Execution stage The objective of the handover execution phase is to change mode (in a multi mode scenario) or network conforming to the details resolved to in the decision phase. This stage typically involves authorization or reauthorization and authentication as well as connection change or radio access node change. Further it also involves control point transfer signaling and security related signaling. Satish [Page 5] Internet Draft L2 considerations for.. July 2003 The L2 handoff execution trigger can be used by the L3 to complete any L3 authorization and authentication formalities. It can also act as a conformation to any L3 pre-registration [REFERENCE] that might have been initiated. This signal can also act as a time reference to take a decision on whether to fall back on the pre-registration and opt for a post registration in case of the combined fast handoff method. 5. Location trigger as an L2 trigger Recently there has been much interest in location tracking and usage of such information for a host of applications. The 3GPP forum is specifying location measurements and location-based services. [10] specifies a Location Configuration Information (LCI) format under control of the end device. Location information interpretation logic could reside at the terminal or at a server for retrieval by the end device. An important feature of the LCI is its inclusion of a resolution parameter for each of the dimensions of location. The LCI includes latitude, longitude and altitude with resolution indicators for each, as well as for the datum of the location. Location or service location based handovers are a serious possibility in a multi-mode or heterogeneous access service area. Handovers based on location information will use location information for handover initiations. Typically such location measurements will be achieved by a L2 entity (The RRC in a 3G terminal). Such information can be used by the L3 to optimize handovers. An L2 trigger should thus have provision to accommodate location information. The location information will be part of the L2 handover initiation trigger if the L2 handover was initiated based on the location. This location information will be used by a L3 component (location aware) to converge on a target access router faster. 6.0 Using L2 Triggers in combination with application triggers In a heterogeneous wireless access environment, the L2 handoff causes can be very many. In such a scenario it is always advantageous to provide as elaborate an L2 trigger as possible. This is the primary motivation for suggesting additional L2 triggers as detailed in the previous sections. For example if the time interval between an L2 initiation trigger and a decision trigger is large such time can be used by the MN to achieve a CAR updation. Apart from L2 triggers the preliminary set of multimode handsets that are being made available commercially are provided with a simple user programmable interface to specify which mode to use. Such a simple interface can be made sophisticated to include greater programmability by specifying location information where a specified mode could be used. In such a scenario the L2 triggers will be used with some application or user specified logic. Satish [Page 6] Internet Draft L2 considerations for.. July 2003 A better handshake between L2 & L3 can be visualized when a set of QoS parameters can be exchanged to achieve a coordinated handover for a specified QoS objective for example L3 location triggers [9] could be used to force a L2 link handover. It is asserted in this draft that the L2 triggers will have to be as comprehensive as possible with considerations & thoughts to the emerging all IP wireless handover scenarios. An elaboration of such considerations will be part of future work. 7.0 The L2 trigger message type considerations Primarily 2 message types will have to be defined 1. One which registers the scope of an L3 interest or capabilities in handling the details provided in an L2 trigger 2. The other would be a message format describing the set of L2 trigger parameters which includes message type, QoS parameters, location information and formats etc. 8.0. Summary Current trends in wireless networking suggest a trend towards and all IP networks consisting of a variety of heterogeneous wireless Access points. A change in wireless AP, either between an AP supporting one wireless link technology and an AP supporting another, or between two APs supporting the same wireless technology, necessarily results in a change in the on-subnet reachability. In this draft three new L2 triggers are suggested with the primary idea of facilitating pipelining of L2 and L3 handovers for example the L2 decision stage trigger can ease the L3 decision process i.e. the target access router can be indicated in the L2 decision stage trigger. The need for a finer granularity of L2 triggers for L3 handover support is also motivated by Candidate access router discovery and context transfer issues. Candidate access router discovery is an important issue for fast handoff initiation [12]. L2 triggers can be used to initiate the Candidate access router discovery. An L2 decision handoff notification with the decision information (which carries the domain address to which the handover has to occur) can allow L3 handover to proceed with out the CAR discovery process. An L2 initiation trigger can be used as an initiation for CAR discovery operation. A finer L2 trigger granularity can also facilitate sensible context caching algorithms. Context transfer (CT) is aimed at supporting seamless mobility between two ARs that provide access to a mobile node. Approaches toward a CT framework are well described in [11]. Conceptually, CT can take place before, during, or after handover. Exactly when CT takes place is highly dependent on some available triggers and L2 triggers makes up for the lack of any other form of triggers. Satish [Page 7] Internet Draft L2 considerations for.. July 2003 8.0 References 1. Perkins, C., ed., "IP Mobility Support," RFC 2002, October, 1996. 2. El-Malki, K., et. al., "Low Latency Handoff in Mobile IPv4," draft-ietf-mobileip-lowlatencyhandoffs-v4-01.txt, a work in progress. 3. Tsirtsis, G., et. al. "Fast Handovers for Mobile IPv6," draft-ietf-mobileip-fast-mipv6-01.txt, a work in progress. 4. N Montavone et al, MIPv6 for multiple interfaces, draft-montavont-mobileip-mmi-0o.txt, work in progress. 5. "Recommended Practice for Multi-Vendor Access Point Interoperability via an Inter-Access Point Protocol Across Distribution Systems Supporting IEEE 802.11 Operation," IEEE Std 802.11f/D1, DRAFT. 6 Kamel Baba et al, Fast Handoff l2 Trigger API, draft-singh-l2trigger-api-00.txt, a work in progress 7 Alper E. Yegin, et. al., "Supporting Optimized handover for IP mobility Requirements for underlying systems, "draft-manyfolks-l2-mobilereq-02.txt, a work in progress. 8. R.J Jayabal, Context transfer and fast Mobile Ipv6 Interactions in a layer-2 source triggered anticipative handover, draft-rjaya-ct-fmip6 -l2st-ant-ho-00.txt, a work in progress. 9. M. Ylianttila, et. al., "Considerations on IP Spatial Location Protocol Requirements, " draft-ylianttila-isl-prot-req-00.txt",a work in progress. 10. J. Polk et al, Location Configuration Information for GEOPRIV, draft-ietf-geopriv-dhcp-lci-option-01.txt, a work in progress. 11. Sayed, H., et. al., "General Requirements for a Context Transfer Framework," draft-hamid-seamoby-ct-reqs-01.txt, a work in progress. 12. Trossen, D., et. al., "Issues in Candidate Access Router Discovery for Seamless IP Handoffs," draft-ietf-seamoby-CARdiscovery-issues-00.txt, a work in progress. Satish [Page 8] Internet Draft L2 considerations for.. July 2003 9.0 Author's Addresses Satish Jamadagni, Tata Consultancy Services 11th Floor, "INNOVATOR", ITPL Sadaramangala Industrial Area, Whitefield Road, Bangalore - 560066 Ph: +91-80-8410085 Ext : 320 Fax:+91-80-8410114 Email: satish_jamadagni@blore.tcs.co.in Internet Draft L2 considerations for.. July 2003