IETF Mobile IP Working Group E. Njedjou Internet Draft P. Bertin Document: draft-njedjou-inter-an-handoffs-00.txt France Telecom R&D P. Reynolds Orange SA June 2003 Motivation for Network Controlled Handoffs using IP mobility between heterogeneous Wireless Access Networks 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 Internet Draft will expire on December 2003 Copyright Notice Copyright (c) The Internet Society (2003). All rights reserved. Abstract In the near future, multi-interfaces Mobile Nodes will be used for connecting to the Internet by way of a multitude of Radio Access Networks including 802.11 based WLANs, GPRS, CDMA2000 and 3G based cellular networks. Ensuring the non-disrupted flow of real-time applications data, as well as adhering to subscribed service profiles while the Mobile Node moves between Access Networks of different technologies, is an issue that needs to be addressed. It is assumed that a unified and external IP core network is used to support such a Njedjou Expires December 2003 [Page 1] Internet Draft Motivation for Network Controlled June 2003 Inter-AN Handoffs using IP mobility multitude of Access Networks. This will probably be the case for a mobile network operator intending to benefit its subscribers with its own hot-spots broadband internet access. Consequently, the need arises to define managed handoff mechanisms between heterogeneous attachment networks, while providing service continuity to the Mobile Node. As such, information necessary for the Mobile Node to performing a judicious handoff across Wireless Access Networks, will have to be gathered from the involved Access Networks, transferred across the IP network that interconnects them, to the operators home network. This document discusses the desirability of a network controlled handoff process for optimizing inter-Access Network Mobile Node mobility. The approach presented provides the means for the operator home network to achieve the best possible selection of the Mobile Node target Access Network for handoff, on the basis of information gathered on the most relevant nodes. It introduces a new function located in the operator network and referred to as a Mobility Manager. It also introduces the concepts for implementing such a handoff process to make it compatible with Mobile IPv6. Other documents will be needed to specify the protocol structures that are intended for handling the handoff process hereafter described. Table of Content 1. Introduction...............................................2 2. Terminology................................................3 2.1. General Terms..............................................4 2.2. Specific terms.............................................5 3. Motivation for a Network Controlled Handoff................5 4. Proposed Concept...........................................7 4.1. Architectural Considerations...............................7 4.2. Protocol Considerations....................................8 5. Scenarios..................................................9 5.1. Scenario 1.................................................9 5.2. Scenario 2................................................10 5.3. Scenario 3................................................10 6. Performances Considerations...............................10 7. Security Considerations...................................11 8. References................................................11 9. Acknowledgments...........................................12 10. Author's Addresses........................................12 11. Intellectual Property Statement...........................12 1. Introduction Njedjou Expires December 2003 [Page 2] Internet Draft Motivation for Network Controlled June 2003 Inter-AN Handoffs using IP mobility Next generation multi-interfaces Mobile Nodes (MN) will be able to gain connectivity to the Internet over a multitude of Access Networks (AN) including 802.11 based WLANs, GPRS, CDMA2000 and 3G based cellular networks. Ensuring seamless flow of real-time application traffic as well as adhering to Mobile Node subscribed service profiles whilst in handoff between such heterogeneous access links is the challenge. Currently, one way to handle the Layer 3 (L3) mobility of nodes is to make use of such protocols as [MIPV4] or [MIPV6]. These protocols are mainly concerned with describing how a MN can maintain its connectivity to the Internet after a change of its IP point of attachment as a result of its mobility. Using these protocols, the MN is able to attach itself to a variety of ANs regardless of the underlying link technology. The MN then needs to be efficiently assisted in choosing or detecting among several available, the one attachment link suitable for its needs, in the case where a handoff might be unavoidable to achieve a seamless transfer of the sessions features. [FMIPV6] [FMIPV4] provide the means to optimize the L3 handoff procedures by taking benefit from timely information available at link-layer, namely Layer 2 (L2) triggers, to anticipate the change of the MN's Access Router (AR) of attachment before the loss of current link connectivity. In this way, handoff delays can be reduced as well as service context information transferred from old to new default router before the MN connects to the new subnet. Prior to performing this Fast Handoff procedure to the new AR, it might be useful to first select the AN where it is better for the MN to attach to, with respect to the criteria that most satisfy its requirements. Effectively, in [FMIPV6], for either mobile or network initiated handoff modes, the handoff management is performed within the ANs edge, be it in the MN or in the ARs (previous and candidate). Still, in some situations, from a MN as well as from an AR perspective, the view of the network might not be large and comprehensive enough to make the most pertinent decision about the opportunity for the mobile Node to perform a handoff to a particular AR. It then might appear more effective to convey the link layer trigger information (or any other information relevant to take the handoff decision) into the provider external IP network. In this way, the decision to move the terminal to a new link could be made relatively to information, events or situations for which the AN edge would not have had the knowledge. 2. Terminology The keywords "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. Njedjou Expires December 2003 [Page 3] Internet Draft Motivation for Network Controlled June 2003 Inter-AN Handoffs using IP mobility The terminology used in this document is in conformance with that given in [TERM]. The definitions of some of the terms are recalled and some additional terms are defined. 2.1. General Terms Access Point (AP) An Access Point is a layer 2 device that is connected to the wired Network and offers the wireless link connection to the MN. Access Network Router (ANR) An IP router in the Access Network. An Access Network Router may include Access Network specific functionalities as QoS. Access Router (AR) An Access Network Router residing on the edge of an Access Network and connected to one or more APs. An AR offers IP connectivity to Mobile Node. Access Network (AN) An IP network which includes one or more Access Network routers Access Network Gateway (ANG) An ANR that separates an Access Network from other IP networks. Capability of AR A characteristic of the service offered by an AR that may be of interest to a MN when the AR is being considered as a handoff candidate. Candidate AR (CAR) An AR to which MN has a choice of performing IP-level handoff. This means that MN has the right radio interface to connect to an AP that is served by this AR. GGSN Gateway GPRS Support Node. A router between the GPRS network and an external network (i.e, the Internet). The GGSN is an example of an Access Network Gateway. Layer 2 Handoff (L2 Handoff) A process of terminating existing link layer connectivity and obtaining new one. This handoff alone is transparent to the routing at the IP layer. Layer 3 Handoff (L3 Handoff) A process of terminating existing network layer connectivity and obtaining new one. Link Layer Trigger (L2 Trigger) Njedjou Expires December 2003 [Page 4] Internet Draft Motivation for Network Controlled June 2003 Inter-AN Handoffs using IP mobility Information from L2 that informs L3 of the detailed events involved in handoff sequencing at L2. L2 triggers are not specific to any particular L2, but rather represent generalizations of L2 information available from a wide variety of L2 protocols Mobile Node (MN) An IP node capable of changing its point of attachment to the network. Inter-AN Handoff This handoff occurs when the MN moves to a new AN. This requires some sort of host mobility across ANs, which typically is provided by the external IP core. Intra-AN Handoff This handoff occurs when the MN changes ARs inside the same AN. 2.2. Specific terms Network Controlled Handoff (NCH) In this handoff, the decision is taken by an external network element Inter-AN Network Controlled Handoff A Network Controlled Handoff where the Mobile Node moves to a new AN Mobility Manager (MM) A function that serves for the management of inter-AN mobility of hosts. 3. Motivation for a Network Controlled Handoff Integrating several access technologies to a single IP based core network requires efficient management of mobility and resources among heterogeneous ANs. In the following, it is assumed that each AN relies on a given access technology at L2. Further, inter-AN handoffs is considered as the main issue to be optimized even if the presented concepts may be further applied to intra-AN handoffs. In the near future, Mobile Nodes will be able to integrate and manage different radio access technologies. Using alternatively, or even simultaneously, those different radio access technologies will require to provide new services able to dynamically adapt their features to the capacities of available technologies and resources in any area. Thus it is necessary to manage, efficiently, seamless mobility among heterogeneous ANs in a transparent manner for the end user. This leads one to consider two main issues: Njedjou Expires December 2003 [Page 5] Internet Draft Motivation for Network Controlled June 2003 Inter-AN Handoffs using IP mobility . to manage efficiently handoff schemes at the IP layer. . to provide means to select the appropriate AN when at least two distinct ANs are available for a given Mobile Node. These ANs can be based on the same or different L2 technologies. For the first issue, the Mobile IP [MIPV4][MIPV6] protocols provide an efficient solution to perform IP based handoff applicable over heterogeneous networks. Mobile IP efficiency can be optimized with the implementation of Fast Handoff Schemes described in [FMIPV4], [FMIPV6] and hierarchical approach described in [HMIPV6]. For the second issue, the use of L2 triggers [REQ] needs to be considered in order to provide the MN with information on current access attachment availability and capabilities. As defined in [REQ], L2 triggers can be implemented within a MN or an Access Router and can be carried within L3 protocols. Thus handoff triggering is performed either in the MN or the AN, whereas the handoff process involves several entities located in both the AN and the Home Network, especially for inter-AN handoffs. Indeed, with Mobile IP the MN needs to update its association in the Home Agent located in the Home network. It can be noted that Mobile IP Home Agent can be either located in Local Area Networks (for example, corporate LANs), ISP platforms or operators IP core networks. In the last two cases (the ones considered here), the MN will never attach itself to its Home network but move among different Visited Networks that provide AN facilities. When managed in the MN and/or AR, AN selection for handoff triggering can be made only with locally available information such as MN radio signal strength and link quality on one or several Interfaces, and AR load and/or capabilities. However, other information registered in the Home Network can be relevant for making such selection: for example, user profiles, global load of Access Networks (acquired for example from ANGs), user preferences, operator policy, peering agreements between access and service providers. Then, it appears that AN information, being restricted to the MN and AR knowledge, provides only a limited view that may lead to a non-optimal AN selection. Such optimal selection can be obtained only when mixing different kinds of parameters available locally and remotely in the home network. This leads to the consideration of performing handoff triggering in a specific network handoff control function taking care of several types of parameters as mentioned above. This specific function could be, for example, implemented in a home Network element like a Home Agent (but this is not mandatory) and provided with remote ANs information reported by the MN, ARs and/or ANGs. Such information can Njedjou Expires December 2003 [Page 6] Internet Draft Motivation for Network Controlled June 2003 Inter-AN Handoffs using IP mobility be reported through a protocol able also to transport handoff triggering messages giving the MN the optimal target AN to handoff to. In the following, the entity responsible for network handoff assistance function is called the Mobility Manager (MM). Hence, MNs can periodically report such information as link quality to the MM which, based on information received from different MNs as well as several parameters registered in a central database such as user profiles and operator policy, evaluates for each MN when triggering inter-AN handoff. It is also necessary to consider in which way communication can be made possible between ARs or ANGs and the MM to help in handoff decision by providing complementary information such as the AR or global AN load. Moreover, as the MM by performing AN selection, anticipates the MN movement and potentially the next attachment point, it is able to provide this information to the relevant entity in AN or Home Network for preparing changes in path updates. Such optimization would support planned handoff limiting packet losses. Finally, it should be outlined that when handoff need evaluation and decision are completely managed by the MNs, the computation of overloading information is required and may be limited by MN processing capabilities, especially for smart mobile devices. Hence, a Network Controlled handoff scheme limits the computation to be done by the Mobile Nodes. 4. Proposed Concept 4.1. Architectural Considerations The considered reference architecture for an AN is taken from [TERM]. It can be noted that depending on the access technology, some of the considered entities may be present or not. Typically: . in a GPRS based AN, the ANG can be considered being implemented at the GGSN so that the rest of the network is viewed as a L2 technology from both the MN and GGSN point of views. Thus, neither AR nor ANR are present and intra-AN mobility is managed at L2. . in a 802.11 based AN, all the networking elements (AR, ANR and ANG) can be present and allow to manage inter-AR mobility at L3 whether intra-AR mobility is done in L2. However, this reference architecture permits the hiding of AN entities from the rest of the external network (IP core and Home Network), which allows the management of inter-AN mobility between AN based on the same or even different L2 technologies. Njedjou Expires December 2003 [Page 7] Internet Draft Motivation for Network Controlled June 2003 Inter-AN Handoffs using IP mobility --- ------ ------- | --- | <--> | | -------| AR | -------------------| | | | |--[] --- /------ \ /| ANG |--| --- AP / \ / | | | MN / \ / ------- | (+ mobile --- / ------- | device(s)) | |---- | ANR | | --- ------- | AP / \ | / \ ------- | --- ------ / \| | | | |-------| AR |---------------------| ANG |--| --- ------ | | | AP ------- | | Access Network (AN) 1 | | Figure 1: Reference Access Network Architecture The complete reference architecture for managing mobility among several ANs is given hereafter. --------------- -------- ----------- | ----- | ( ) | Home | | | ANG || ( ) | Agent | | ----- | ( ) | (HA) | | AN 1 | ( ) ------------ | --- | --------------- ( INTERNET ) | Mobility |---- | |--[] ( OR )| Manager | --- --------------- ( IP CORE NETWORK ) | (MM) | | ----- | ( ) ------------ | | ANG || ( ) | ----- | ( ) | AN 2 | ( ) --------------- --------- Figure 2: Reference Architecture for inter-AN Mobility Management 4.2. Protocol Considerations As already introduced, the considered scheme for inter-AN Mobility Management relies on a protocol between the MN and the MM. It is also considered that communication could be provided between ANs and MM for optimizing network selection with additional information. The general requirements for such a protocol to support are: . reporting of locally available information from MN (and maybe AR) to the MM responsible for handoff control. The reported Njedjou Expires December 2003 [Page 8] Internet Draft Motivation for Network Controlled June 2003 Inter-AN Handoffs using IP mobility information may include radio link quality measured by the MN on different ANs through one or several interfaces as well as capabilities of the ARs, or they may be simple abstracted values for example ôcan see - cant seeö. In order to avoid unnecessary signaling, these reports can be sent only when the MN identifies that current radio link quality is degrading or when new Access Networks become available. . delivering of handoff triggering messages from the MM to the MN when the MM identifies the need for such a handoff to occur. These trigger messages should include new AN selection information from the MM to the MN. . awareness about handoff triggering from the MM to other logical entity involved in the handoff process such as HA (and maybe AR or ANG) for making them able to prepare the handoff, for example, by reserving adequate resources, establishing relevant tunnels between ARs). . transporting said information in standard Mobile IP within newly defined extensions. 5. Scenarios The following scenarios illustrate some advantages of a Network Controlled approach compared to the basic scenarios assuming MN or AR control. In these scenarios, one makes the assumption that the MN belongs to a mobile network operator which also provide 802.11 based WLAN access services in hot Spot areas, a situation likely to be encountered in the near future. The 802.11 access is always supposed to be better in terms of access speed. One also considers a multi-interface smart MN, for example, notebook, PDA, etc. 5.1. Scenario 1 Consider the case of such a MN that has been under 802.11 coverage for a while. The user of the MN has registered a profile with broadband Internet access preference. Over time, MNs number increases within the AN, leading to saturation of the ANG. With a handoff scheme managed from within the AN edge i.e. between MN and AR, as long as the load and QoS capabilities of the current AR are satisfactory to maintain the MN attachment, no handoff need would be detected. However, a Mobility Manager located, for instance, inside the external IP core network of the operator (IP core serving multiple ANs), could get information that the 802.11 AN overall load, and IP QoS, are in a critical state and, having an overall visibility of the situation, decide that the MN should handoff to the GPRS Access Njedjou Expires December 2003 [Page 9] Internet Draft Motivation for Network Controlled June 2003 Inter-AN Handoffs using IP mobility Network because the capabilities measured on that AN could help maintain a service level that match its profile. 5.2. Scenario 2 Consider the MN is currently attached to a GPRS AN, and is moving inside 802.11 coverage. One further assumes that sufficient MNs are present in the AR serving the coverage area, for it to be overloaded. A handoff process operated with an AN edge visibility would not permit the MN to gain attachment to the 802.11 AN because of the saturation at the AR. However, A Mobility Manager knowing the profiles priorities of the MNs currently attached to the 802.11 AR (as they would have been stored in a home network register), could decide to instruct some of those MNs with lower demanding needs, to handoff to the GPRS access, giving capacity for the MN to attach to that AR. In this way, the MN having higher demanding profiles would be able to benefit from the WLAN facility. 5.3. Scenario 3 Consider the MN is currently attached to a GPRS network and assume that it is moving into 802.11 coverage hosting an AN provided by a service provider having peering agreements with the mobile operator. The MN will have knowledge from layer 2 triggers information (acquired from its own or from its current AR) that a 802.11 link is becoming available. A handoff procedure managed between MN and AR edge could then prompt the MN to handoff to a target AR of the 802.11 coverage on the sole basis of these L2 triggers information combined to the capabilities of the ARs. In the case where the link layer triggers information, and/or capabilities of the ARs, were reported to a Mobility Manager these information could be matched to other features like mobile operator handoff policy, before prompting the terminal to handoff to the 802.11 AN or not. 6. Performances Considerations The concept introduced below is targeted at optimizing inter-AN handoff scenarios and is not meant to provide any alternative to existing related work as done in [FMIPV6]: it is intended to complement the previous approach with a specific focus on handoff involving the crossing between heterogeneous AN technologies. Network Controlled inter-AN handoff as presented here can effectively be implemented so as to co-exist with Fast Handoffs. In which case, once the selection of the candidate AN can be indicated by the MM to the MN, a Fast Handoff process could be initiated with the intent to Njedjou Expires December 2003 [Page 10] Internet Draft Motivation for Network Controlled June 2003 Inter-AN Handoffs using IP mobility reduce the latency caused by the Mobile IP protocols operation. Furthermore, it can be noted that the Network Controlled scheme always applies even when such features as Fast Handoffs are not supported at the edge of the access network. However, in this situation, such information as AR capabilities available with [FMIPV6] might not be profitable in the AN candidate choice. 7. Security Considerations It is acknowledged that there are new security threats associated with the handoff management concept presented above. Authentication of the local information from MN (L2 triggers, capabilities of ARs, etc.) needed to MM to assist in handoff decision needs to be ensured. This will guard against malicious MN pretending to belong to the home network and requesting unauthorized handoff services. The MN reports could contain information on ARs that should be hidden from third parties as eavesdropper could make use of such information to perform denial of service attacks on these sensitive network elements. Handoff decision from MM to MN will have to be authenticated as well to prevent against false MMs pretending to assist the MN in its handoff process. This information needs to be encrypted in order to keep the MN location hidden to any eavesdropper, as the handoff instruction message will reveal the identification of the next AN where the MN will handoff to. Integrity protection is necessary because of the sensitiveness of the information exchanged between the MM in the home network and the MN. A modified report on AN characteristics could compromise any targeted seamless handoff. There also might be other specific security requirements to be fulfilled that are not identified in this document. It should therefore be observed that the architecture and protocols extensions to be defined with the objective to implement the concept have to follow the general mechanisms and guidelines available from IETF security solutions and protocols. 8. References [MIPV4] "IP Mobility Support", C. Perkins (Editor), RFC 2002, October 1996. [MIPV6] "Mobility Support in IPv6", D. Johnson, C. Perkins, and Jari Arkko, draft-ietf-mobileip-ipv6-21.txt, work in progress, February 2003. Njedjou Expires December 2003 [Page 11] Internet Draft Motivation for Network Controlled June 2003 Inter-AN Handoffs using IP mobility [FMIPV6] "Fast Handoffs for Mobile IPv6", MIPv6 handoff Design Team, draft-ietf-mobileip-fast-mipv6-06.txt, work in progress, March 2003. [HMIPV6] "Hierarchical Mobile IPv6 mobility management", H Soliman, C Castellucia, K El-Maki, L Bellier, draft-ietf-mobileip-hmipv6-07.txt, work in progress, October 2002. [REQ] "Requirements for Layer 2 Protocols to Support Optimized Handoff for IP Mobility" J Kempf Ed, draft-manyfolks-l2-mobilereq- 00.txt, work in progress, January 2000. [TERM] "Mobility Related Terminology", J. Manner, M. Kojo, draft- ietf-seamoby-mobility-terminology-01.txt, work in progress, November 2002. 9. Acknowledgments 10. Author's Addresses Eric Njedjou France Telecom R & D 4, Rue du Clos Courtel 35512 CESSON SEVIGNE Phone: +33 2 99 12 48 78 Email: eric.njedjou@france.telecom.com Philippe Bertin France Telecom R & D 4, Rue du Clos Courtel 35512 CESSON SEVIGNE Phone: +33 2 99 12 41 57 Email: philippe.bertin@france.telecom.com Paul Reynolds Orange SA Bradley Stoke Bristol BS32 4QJ Phone: +44 7973 746 050 Email: paul.reynolds@orange.co.uk 11. Intellectual Property Statement France Telecom is the owner of pending patent applications that may relate to this Internet Draft. See France Telecom's notice Regarding Intellectual Property Rights: http://www.ietf.org/ietf/IPR/FRANCE- TELECOM.txt Njedjou Expires December 2003 [Page 12]