Mobileip Working Group Karim El-Malki, Ericsson INTERNET-DRAFT Hesham Soliman, Ericsson Expires: March 2001 September,2000 Fast Handoffs in MIPv6 Status of this memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that Other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/lid-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This document is an individual submission to the IETF. Comments should be directed to the authors. Abstract This draft describes a method to achieve Fast Handoffs in Mobile IPv6. Fast Handoffs are required in Mobile IPv6 in order to limit the period of service disruption experienced by a wireless Mobile Node when moving between access routers. This requirement becomes even more important when supporting real-time services. Fast Handoffs involve anticipating the movement of MNs by sending multiple copies of the traffic to potential Mobile Node movement locations. Both flat and Hierarchical Mobile IPv6 models are El-Malki, Soliman [Page 1] INTERNET-DRAFT Fast Handoffs in MIPv6 September,2000 considered. The Hierarchical MIPv6 mobility Management model in [1] already offers improvements to Mobile IP handoffs by providing a local Mobility Anchor Point (MAP) functionality. Some additions are made to the operation of this existing Hierarchical model to achieve Fast Handoffs. TABLE OF CONTENTS 1. Introduction...............................................2 2. Fast Handoffs..............................................4 2.1 Initiating Fast Handoffs through the "previous" AR.........5 3. Fast Handoffs in Hierarchical MIPv6........................8 4. Acknowledgements...........................................14 5. References.................................................14 6. Addresses..................................................14 1. Introduction Fast Handoffs anticipate the movement of wireless Mobile Nodes (MNs) by utilizing simultaneous bindings in order to send multiple copies of the traffic to potential Mobile Node movement locations. In this way, Fast Handoffs coupled to layer 2 mobility can help in achieving seamless handoffs between Access Routers (ARs) by eliminating the delay period required to perform a Registration following a Mobile IP handoff. An alternative method to perform improved handoffs, namely Smooth Handoffs, is described in [2]. The method for Fast Handoff addresses the need to support services having strict delay bounds (i.e. real-time) which in certain cases may be hard to support if traffic has to be forwarded between ARs using Smooth Handoffs. Also, in the non-realtime case it may be possible that the new AR receives buffered traffic from the previous AR (smooth handoff)and traffic from the CN which could cause some out-of-order and delayed packets to be delivered to the MN. In some cases this may affect the performance of higher level protocols (i.e. TCP). This same situation will not arise using Fast Handoffs. This draft considers both the normal Mobile IPv6 model [2] and the hierarchical Mobile IPv6 model [1]. These are shown in Figure 1 where the Access Points (APs) or Radio Access Networks (RANs) are used to provide a MN with wireless L2 access. El-Malki, Soliman [Page 2] INTERNET-DRAFT Fast Handoffs in MIPv6 September,2000 Simultaneous bindings are described in this draft and may be achieved by setting a new, "B" flag in the BU sent by the MN to a MAP. In this way, the MAP will add a new binding for the MN without removing the existing entry. Hence packets arriving to the MAP will be tunnelled to both addresses in its BC. _________ __________ | | | | | HA |--------| (MAP) |________ |_________| |_________| \ / | \ \ \ ... ... ... \ \ ______/_ _\______ | | | | | | | AR2/MAP| | AR1/MAP| | |________| |________| | ____|___ ____|___ ____|___ | | | | | | |AP/RAN 2| |AP/RAN 1| |AP/RAN 3| |________| |________| |________| | ____|___ | | CN | MN | |________| Figure 1: Flat (HA only) and Hierarchical (HA and MAP) MIPv6 model The method to anticipate MN movement by interacting with the wireless L2 is described later in this draft. The Hierarchical Mobile IPv6 scheme introduced in [1] allows a Mobile Node to perform registrations locally with an MAP in order to reduce the number of signalling messages to the home network and CNs. This achieves a reduction in the signalling delay when a Mobile Node moves between ARs and therefore improves the performance of such handoffs. This draft describes Fast Handoffs in Hierarchical Mobile IPv6 (HMIPv6) using Regional Registrations. When considering a MIPv6 handoff, two different cases can be considered depending on the network architecture: - The previous and new AR are physically connected - The previous and new AR are connected via another node/network El-Malki, Soliman [Page 3] INTERNET-DRAFT Fast Handoffs in MIPv6 September,2000 The first case can be considered a subset of the more generic case. Hence the solution proposed will be addressing the generic (second) scenario. 2. Fast Handoffs Fast Handoffs address the need to achieve seamless Mobile IP Handoffs when the MN moves between ARs. This is done by "bicasting" traffic to the "previous" AR and "new" AR while the MN is moving between them. The anticipation of the MN's movement is achieved by tight coupling with Layer 2 functionality which is dependent on the type of access technology used. The coupling between L2 and L3 technologies may occur in the network nodes or the MNs, or both, depending on the access technology. "Bicasting" is achieved through simultaneous bindings, where the MN activates the "B" flag in the MAP registration. When a MAP Registration has the "B" flag set, the receiving MAP, which has an existing binding for the MN, will add the relevant new binding for the MN but will also maintain any existing binding it had for the MN. Two different handoff scenarios are considered in this draft: - A MN having to do a handoff between two different ARs with which it can be simultaneously data-connected (eg. Two different access technologies). In this case it may not be essential to request simultaneous bindings. The MN may simply continue using both COAs (on the old and new link) as specified in [2]. - A MN having to do a handoff between two access routers with which it can not be simultaneously data-connected. This is the more generic case and _bicasting_ can be used to achieve Fast Handofffs. When the MN has multiple active bindings with a MAP, it may or may not receive multiple copies of the same traffic directed to it. The use of simultaneous bindings does not necessarily mean that the MN is receiving packets contemporarily from multiple sources. This depends on the characteristics of the access (L2) technology. The "bicasting" of packets is used to anticipate the MN's movement and speed up handoffs by sending a copy of the data to the AR which the MN is moving to. Until the MN actually completes the L2 handoff to the new AR, the data "copy" reaching this AR may be discarded. In this way the total handoff delay is limited to the time needed to perform the L2 handoff. Thus, Fast Handoffs coupled to the L2 access potentially result in loss-less IP-layer mobility. As described in 2.1, depending on the L2 characteristics, it is also possible for an MN to initiate a Fast Handoff through the "previous" AR without having direct access to the "new" AR. El-Malki, Soliman [Page 4] INTERNET-DRAFT Fast Handoffs in MIPv6 September,2000 2.1 Initiating Fast Handoffs through the "previous" AR In the case in which the wireless L2 technology allows the MN tobe data-connected to multiple wireless access points simultaneously, the MN may solicit advertisements from ARs before completing handoffs. In this case "bicasting" may not be necessary. Some existing wireless L2 technologies and their implementations do not allow a MN to be data-connected to multiple wireless access points simultaneously. Thus, in order to perform a Fast Handoff it is necessary for some form of interworking between layers 2 and 3. It should be noted that the method by which an AR determines when a MN has initiated an L2 handoff is outside the scope of this draft and may involve interaction with L2 messaging. Also, the interaction between L2 and L3 should allow the Mobile Node to perform a L2 handoff only after having performed the L3 Fast Handoff described in this draft. That is, the L2 handoff may be performed after the MN's Registration with the "new" AR which produces a simultaneous binding at the MAP. This Registration may be transmitted more than once to reduce the probability that it is lost due to errors on the wireless link. Alternatively, the MN may choose to send a BU to the MAP with the _A_ flag set. A Fast Handoff in this case requires the MN to receive "new" router advertisements through the "old" wireless access points, and to perform a registration with the "new" FA through the "old" wireless access point. Two ways of performing this follow. I. Inter-AR Solicitation This solution assumes that the AR with which the MN is currently registered is aware of the IP address of the "new" AR which the MN is moving to and a physical connection exists between them (ie. they have a common link). The method by which the current AR is informed of this may depend on interaction with L2 and is outside the scope of this draft. Once the current AR is aware of the address of the AR which the MN will move to, it will send the "new" AR a router solicitation message. The "new" AR will reply to the current AR by sending it a router advertisement with appropriate extensions. The current AR will then send the router advertisement to the MN's address. As a consequence, the MN, being eager to perform new registrations, will send a registration request to the "new" AR through the "old" wireless access point served by the current AR. El-Malki, Soliman [Page 5] INTERNET-DRAFT Fast Handoffs in MIPv6 September,2000 II. Piggy-backing Advertisements on L2 messaging Let us take Figure 1 as an example, where a MN initiates an L2 handoff from AP/RAN1 to AP/RAN2 (Note that it may not be the MN which takes decisions on handoffs). It is assumed that when an L2 handoff is initiated, AP/RAN1 and AP/RAN2 perform L2 messaging procedures to negotiate the L2 handoff. Since the MN is not attached to AP/RAN2 yet, AR2 is unaware of the IP address of the MN and cannot send an advertisement to it. Therefore it is necessary for the L2 procedures to interwork with Mobile IP. Once a L2 handoff is initiated, such that AP/RAN2 and AP/RAN1 are in communication, it is possible for AP/RAN2 to solicit an advertisement from AR2 and transfer it to AP/RAN1. Once this is received by the MN, the MN can perform a registration directed to AR2 even though the MN has no data-connection to AP/RAN2 yet. The precise definition of such L2 procedures is outside the scope of Mobile IP. 3. Fast Handoffs in HMIPv6 HMIPv6 is described in [1]. Fast IP Handoffs can be achieved in a very simple and efficient manner. When the MN receives a router Advertisement including a MAP option, as specified in [1], it should perform actions according to the following movement detection mechanisms. In a Hierarchical Mobile IP network such as the one described in this draft, the MN MUST be: - "Eager" to perform new bindings - "Lazy" in releasing existing bindings The above means that the MN will perform Regional Registrations with any "new" MAP advertised by the AR (Eager). The method by which the MN determines whether the MAP is a "new" MAP is described in [1]. However the MN should not release existing bindings until it no longer receives its MAP option or the lifetime of its existing binding expires (Lazy). If the MN has at least one existing binding with a MAP, additional simultaneous regional registrations will be performed requesting a short lifetime. This is done in order to limit the lifetime of bindings which the MN only needs temporarily and therefore limit bandwidth usage. This is the case when the MN is moving between ARs and uses Fast Handoffs to achieve near loss-less IP mobility. The lifetime of additional "auxiliary" bindings needed for Fast Handoffs is thus limited. It should be noted that the method described above is applicable to hierarchical and flat architectures. As described in [1], a MAP can exist on any level in the hierarchy, including ARs. Hence, a El-Malki, Soliman [Page 6] INTERNET-DRAFT Fast Handoffs in MIPv6 September,2000 bicasting request can also be sent to a MAP located in the AR, in the case where no MAPs are located higher in the hierarchy. 4. Extensions to MIPv6 To allow bicasting from the MAP to take place, a new flag,_B_, is added to the BU message. Upon reception of a BU message with the _B_ flag set, a MAP SHOULD bicast all incoming packets addressed to the MN to its current COA as well as the new COA in the BU requesting the bicast. The new BU message is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |A|H|R|D|M|B|Res| Prefix Length | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-Options... +-+-+-+-+-+-+-+-+-+-+-+- Description of extensions to the BU option: B If set, it indicates a request for bicasting all traffic received for the MN to its current address as well as the new address in the BU. Res 2 bit reserved field 5. Fast Handoffs and DAD The use of DAD to verify the uniqueness of a statelessly configured IPv6 address may add delays to a MIPv6 handoff. The probability of an inteface identifier duplication on the same subnet can be considered very low. Hence, to avoid this delay, a MN may choose to continue sending and receiving traffic using its newly formed COA while performing DAD on the new subnet. In the case where a duplication exists, the MN MUST follow the rules in [4]. This issue is not specific to this proposal and may also be addressed in future revisions of [2]. 6. Notice Regarding Intellectual Property Rights Ericsson may seek patent or other intellectual property protection for some or all of the technologies disclosed in this document. If any standards arising from this disclosure are or become protected by one or more patents assigned to Ericsson, Ericsson intends to El-Malki, Soliman [Page 7] INTERNET-DRAFT Fast Handoffs in MIPv6 September,2000 disclose those patents and license them on reasonable and non- discriminatory terms. Future revisions of this draft may contain additional information regarding specific intellectual property protection sought or received. 7. References [1] H. Soliman, C. Castellucia, K. El Malki and L. Bellier "Hierarchical Mobile IPv6 and Fast Handoffs", draft-ietf-mobileip-hmipv6-00.txt (work in progress), September 2000 [2] D. Johnson and C. Perkins, "Mobility Support in IPv6", draft-ietf-mobileip-ipv6-12.txt, February 2000. [3] K. El Malki and H. Soliman " Fast Handoffs in Mobile IPv4". (work in progress) [4] S. Thomson and T. Narten "IPv6 Stateless Address Autoconfiguration". RFC 2462. 8. Acknowledgements The authors would like to thank the following members of the working group (in alphabetical order) for their comments and the interesting discussions about this draft: Gopal Dommety (Cisco), Dave Johnson (Rice University), Erik Nordmark (Sun), Mohan Parthasarathy (Sun), Carl Williams (Sun)and Alper Yegin (Sun). 9. Addresses The working group can be contacted via the current chairs: Basavaraj Patil Phil Roberts Nokia Corporation Motorola M/S M8-540 6000 Connection Drive 1501 West Shure Drive Irving, TX 75039 Arlington Heights, IL 60004 USA USA Phone: +1 972-894-6709 Phone: +1 847-632-3148 EMail: Raj.Patil@nokia.com EMail: QA3445@email.mot.com Fax : +1 972-894-5349 Questions about this memo can be directed to: Karim El Malki Ericsson Radio Systems AB Access Networks Research SE-164 80 Stockholm El-Malki, Soliman [Page 8] INTERNET-DRAFT Fast Handoffs in MIPv6 September,2000 SWEDEN Phone: +46 8 7573561 Fax: +46 8 7575720 E-mail: Karim.El-Malki@era.ericsson.se Hesham Soliman Ericsson Australia 61 Rigall St., Broadmeadows Melbourne, Victoria 3047 AUSTRALIA Phone: +61 3 93012049 Fax: +61 3 93014280 E-mail: Hesham.Soliman@ericsson.com.au El-Malki, Soliman [Page 9]