Internet Engineering Task Force J. Loughney INTERNET-DRAFT Nokia Date: November 17, 2000 Expires: May 17, 2001 Seamless Mobility Concerns draft-loughney-seamoby-concerns-00.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 . This draft expires on 14 May 2001 Abstract As a mobile node moves in a network, existing mobility mechanisms may not be sufficient to achieve performance as expected by the user. Seamless mobility can be said to be achieved when a mobile node suffers little to no disruption of service. This document presents an overview of requirements and functions needed for Seamless Mobility and their impact. Internet Draft Seamless Mobility Concerns November 17, 2000 1 Introduction........................................................3 1.2 Terminology .....................................................3 1.3 Basic Requirements ..............................................4 2 Services ...........................................................4 2.1 Paging...........................................................4 2.2 Micromobility....................................................4 2.3 Context Transfer.................................................5 2.3.1 QoS ..........................................................5 2.3.2 Header Compression State .....................................5 2.3.3 Security .....................................................5 2.3.4 Buffering ....................................................5 3 Requirements........................................................6 3.1 Mobile IP based solution ........................................6 3.2 IPv6 Based ......................................................6 3.3 Split in micro- and macro-mobility regions. .....................7 3.4 Layer 2 Information Should Not Be Relied Upon ...................7 3.5 Minimize Air Interface Signaling ................................8 3.6 Interworking Between IP and Radio Specific Mobility Management. .8 3.7 Idle Mode Support ...............................................8 3.8 Handover Performance ............................................8 3.9 Security requirements must be met ...............................8 3.9.1 User Identity ...............................................8 3.9.2 Location Protection ..........................................9 4 Acknowledgements....................................................9 5 References.........................................................9 6 Author's Address...................................................10 Copyright Statement..................................................10 Loughney, John [Page 2] Internet Draft Seamless Mobility Concerns November 17, 2000 1 Introduction In a general sense, seamless mobility can be considered from the end-user's perspective: on-going sessions and services should not suffer due to the mobility of the end-terminal. This document outlines some requirements and techniques for achieving seamless mobility. 1.1 Basic Handover Model The following figure presents a basic IP handover. I +------------+ +-+ | Previous | < | | ---------- | Router | ------ > ----\ +-+ | (Prtr) | < \ MN | | \ | +------------+ +---------------+ | ^ IP | Correspondent | | | Network | Node | V | +---------------+ v / I +------------+ / +-+ | New | < / | | ---------- | Router | ------ > ----/ +-+ | (Nrtr) | < MN | | +------------+ 1.2 Terminology Mobile Node (MN) - A user terminal with an IP client. Also called the Mobile Terminal or Mobile Station. Access Node - Node which the mobile node attaches to (on the IP layer) Fast Handover - A handover procedure which does not result in any excessive packet transfer delay. This procedure should not introduce any noticeable extra delays which can cause degraded performance of service. To put it succinctly, low delay. Smooth Handover - A handover procedure which does not result in any packet loss. This procedure should not lose user data and is tolerant to some delay in the procedure execution. To put it succinctly, low loss. Seamless Handover - A handover procedure which does not result in any degradation of service noticeable by a user. This procedure has Loughney, John [Page 3] Internet Draft Seamless Mobility Concerns November 17, 2000 strict timing requirement for the execution and is tolerant to some packet loss. To put it succinctly, seamless handover = fast handover + smooth handover. 1.3 Basic Requirements Listed below are the major requirement areas : * Mobile IP based solution * IPv6 Based * Split in micro- and macro-mobility regions * Layer 2 Information Should Not Be Relied Upon * Minimize Air Interface Signaling * Interworking between IP and Radio specific Mobility Management * Idle Mode Support * Handover Performance * Security Requirements 2 Services 2.1 Paging In cellular networks the concept of "paging area" (or location area/routing area) is defined. Paging areas are used to locate an MN in idle mode in order to deliver incoming calls. The MN in idle mode keeps the network informed of its location at the level of location/routing area, i.e. indicates its current location/routing area to the network any time there is a change in the location/routing area. A location/routing area usually encompasses more than a base-station area, so that the MN does not drain its battery out by performing frequent location/routing area updates. At the same time, the size of paging areas shall be such that the signaling load resulting from paging is minimized. Paging area size is calculated by optimizing the trade off between the two aspects described above. The challenge is to manage paging area with involving as little radio/layer 2 specific functions as possible. 2.2 Micromobility Loughney, John [Page 4] Internet Draft Seamless Mobility Concerns November 17, 2000 Micromobility is the ability for a mobile node to move without notifying its home agent. For the purposes of this draft, macromobility is when the mobile node's home agent is notified of any movement, or simply conventional Mobile IP. There are a number of protocols and architectures seeking to provide micromobility, including hierarchical mobile IP [8]. These micromobility solutions seek to speed handovers while meeting performance goals. 2.3 Context Transfer In order to achieve seamless handovers, target access nodes may need certain things. These are discussed below. 2.3.1 QoS During a handover, the target access node should be able to provide the minimum QoS that the mobile node expects. In the event where more than one access node is available as the target for a handover, the access node providing closest the expected QoS should be selected. 2.3.2 Header Compression State Header compression may be needed for IP transport over wireless links. IP headers can add a significant overhead compared to the radio frames which are sent over tradition cellular air interfaces. This problem is being solved by developing header compression schemes [2]. For seamless handovers, the new node must have appropriate compression state. The failure to possess this state could result in discarding the uplink packets and transmission of uncompressed packets in the downlink. [5] It is important to select header compression schemes which can sustain the air interface characteristics of errors and packet loss. The scheme should also be spectrum efficient during the handovers. 2.3.3 Security Security is always a concern, and even more so for mobile nodes. It should be possible that the access nodes involved in a handover can exchange security credentials so that AAA process does not need to be performed again. 2.3.4 Buffering In some cases a number of methods are used to improve the performance data flows, such as packet buffering. If the previous Loughney, John [Page 5] Internet Draft Seamless Mobility Concerns November 17, 2000 access node has supported such a method or methods then the target access node should also support the method(s) or otherwise make sure that the service does not degrade visibly due to lack of those methods. For example, some non standards-track methods may deploy TCP acknowledgement manipulation at the access node, i.e. buffering of ACKs or modification of acknowledgements. In seamless handovers, the target access node should either be able to start to support the method by receiving the state or otherwise be able to compensate the loss of the method, for example by providing higher bandwidth for the flow. 3 Requirements 3.1 Mobile IP based solution Mobile IP [1] as developed within the Mobile IP working group is the de-facto standard for IP level mobility. All Seamless Mobility solutions should work with Mobile IP, without adding additional requirements to Mobile IP. Extensions to the Mobile IP header are acceptable, though. 3.2 IPv6 Based "The Case for IPv6" [9] lays out detailed and compelling arguments for IPv6. IPv6 [7] also introduces many mobility improvements compared to IPv4, so all work should be designed with IPv6 as a baseline. "Mobility Support in IPv6" [1] discusses the support for mobility in IPv6. In general, IPv6 supports Mobile IP better than IPv4. Some of the benefits listed include: * Support for what is known in Mobile IPv4 as "Route Optimization." * Support is also integrated into Mobile IPv6 for allowing mobile nodes and Mobile IP to coexist efficiently with routers that perform "ingress filtering". * The use of the care-of address as the Source Address in each packet's IP header also simplifies routing of multicast packets sent by a mobile node. * There is no longer any need to deploy special routers as "foreign agents" as are used in Mobile IPv4. * Mobile IPv6 utilizes IP Security (IPsec) for all security requirements (sender authentication, data integrity protection, and replay protection) for Binding Updates (which serve the role of both registration Loughney, John [Page 6] Internet Draft Seamless Mobility Concerns November 17, 2000 * Most packets sent to a mobile node while away from home in Mobile IPv6 are sent using an IPv6 Routing header rather than IP encapsulation. * Mobile IPv6 defines an Advertisement Interval option on Router Advertisements (equivalent to Agent Advertisements in Mobile IPv4), allowing a mobile node to decide for itself how many Router Advertisements (Agent Advertisements) it is willing to miss before declaring its current router unreachable. * The use of IPv6 destination options allows all Mobile IPv6 control traffic to be piggybacked on any existing IPv6 packets. Additionally, IPv4 has limited addressing capacity. It is assumed the growth of the wireless internet will cause an exhaustion of IPv4 addresses, thus it would not be sensible to design to IPv4. Some regions and administrative boundaries are currently facing a shortage of IPv4 addresses, due to the original allocation scheme of IP addresses. They will face the exhaustion first. It is highly unlikely that they will be satisfied with IPv4 based solutions. That being said, interworking with IPv4 networks will be a reality for some time, so that solutions should be IPv4 compatible as well. 3.3 Split in micro- and macro-mobility regions. An access node manages the physical layer connection to the mobile node, including frequently occurring handovers between cells (micro- mobility). The handovers can be assumed to occur less frequently at the Core Network level (macromobility). By splitting mobility into micromobility and macromobility, signaling can be reduced; latency can be reduced; packet loss can be reduced thus increasing performance. 3.4 Layer 2 Information Should Not Be Relied Upon Interaction between layer 2 (radio) and layer 3 (IP Protocols) should be minimized. The Internet has a requirement that link layer should be transparent to IP Bearer traffic. That being said, certain information may be provided by a specific layer 2 that can assist in seamless mobility. It should be possible to take advantage of this information, when available. Changes in radio specific layer 2 level mobility functions should be limited only to IP Transport Control functions. Loughney, John [Page 7] Internet Draft Seamless Mobility Concerns November 17, 2000 3.5 Minimize Air Interface Signaling Bandwidth and frequency spectrum of an air interface may be a limited and expensive resource, thus it is important to have radio resource management optimized for an efficient use of the available spectrum. In the existing cellular radio networks the optimization is performed in many ways. For instance, by assigning radio resource after terrestrial resource assignment in a call setup, by performing call audit between the base station and the call processing agent to release any stuck radio resources, etc. The signaling burden, in general, should be minimized, as it may compete with user data. 3.6 Interworking Between IP and Radio Specific Mobility Management. There are many devices using radio specific mobility management functions (layer 2). It would be desirable to consider the interworking between layer 2 and layer 3 mobility management. A Seamless Mobility proxy may be needed in order to achieve this. This should be studied in further detail. 3.7 Idle Mode Support As mobile nodes may be power-constrained, it is likely that they may enter some idle mode when not active. In order to support services, it should be possible to page the mobile node when the node is idle. 3.8 Handover Performance The implications of seamless mobility on network requirements depend on the service itself. For example, the delay and packet loss requirements during seamless handover for e-mail transfer are obviously much less demanding than those of Voice over IP service. For some services Seamless handover may be achieved only with smooth handovers or fast handovers, with some other services Seamless handovers are required. Moreover, the quantitative requirements of smooth or fast handover may vary from service to service. For realtime services, handover performance should be no worse than for cellular system voice service. During inter-system handover, the source system adapts to the target system. 3.9 Security requirements must be met 3.9.1 User Identity During session initiation, there is a period during which the MN has Loughney, John [Page 8] Internet Draft Seamless Mobility Concerns November 17, 2000 identified itself with the network but the network has not yet verified the credentials received from the MT. At this point, no security mechanism can be applied to protect the exchange of information between the MN and the network. The MN has to identify itself to the network with its subscriber identity using unencrypted message. A third-party could possibly eavesdrop and listen to this identity, gaining privileged information. In the existing cellular systems, the MN hides its real identity by using a temporary identity provided by the network during previous interactions, thus avoiding identification by third parties. 3.9.2 Location Protection For security and privacy reasons, users may wish to have their location from corresponding nodes. During roaming and handovers, the location of an MN should be kept securely in the network and not revealed to the correspondent nodes. 4 Acknowledgements The author would like to thank Roland Wolker, Sanna Maenpaa, Jussi Ruutu and Kimmo Raatikainen for their comments. 5 References [1] Johnson, D- and Perkins, C.; "Mobility Support in IPv6"; draft-ietf-mobileip-ipv6-12.txt; Work in Progress; April 2000. [2] Le, K., et. al., Adaptive Header ComprEssion (ACE) for Real- Time Multimedia, draft-ietf-rohc-rtp-ace- 00.txt; Work in Progress); May 2000. [3] Kempf, J., et. al., "IP Mobility and the CDMA Radio Access Network: Applicability Statement for Soft Handover soft handover a statement", draft-kempf- cdma-appl-00.txt; work in progress; May 2000. [4] Koodli, R., et. al., "Header Compression State Relocation in IP Mobile Networks", draft-koodli-rohc- hc-relocate-00.txt; Work In Progress; July 2000. [5] Koodli, R. and Perkins, C. "A Framework for Smooth Handovers with Mobile IPv6" (work in progress). draft-ietf-koodli-smoothv6-00.txt, July 2000. Loughney, John [Page 9] Internet Draft Seamless Mobility Concerns November 17, 2000 [6] Saifullah, Y. and Faccin, S.; " Common Radio Access Protocols Issues and Requirements"; draft-saifullah- craps-issues-req-00.txt; Work In Progress; July 2000. [7] Deering, S., and Hinden, R. (Editors); "Internet Protocol, Version 6 (IPv6) Specification"; RFC 2460, December 1998. [8] Soliman, H.; "Hierarchical MIPv6 mobility management"; ; Work In Progress; October 2000. [9] King, S., et. al; "The Case for IPv6"; draft-iab- case-for-ipv6-06.txt; Work In Progress; July 2000. 6 Author's Address John Loughney Nokia Research Center PO Box 407 FIN-00045 Nokia Group Finland EMail: john.loughney@nokia.com Copyright Statement 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. Loughney, John [Page 10]