Mipshop Working Group Youngsong Mun Internet-Draft Seonggeun Ryu Expires: August, 2009 Soongsil University February, 2009 Enhanced Fast Handover for Mobile IPv6 based on IEEE 802.11 Network draft-mun-mipshop-efh-fast-mipv6-03.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. 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 August 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract In MIPv6 [1], whenever a mobile node changes its attached point, handover process should be followed to inform its home agent and S. Ryu, et al. Expires August, 2009 [Page 1] Internet-Draft Enhanced Fast Handover February 2008 correspondent of a MN's current location. The handover process is decomposed into layer 2 and layer 3 handovers again, and these two handovers are accomplished sequentially, which causes long latency problem. This problem is a critical issue in MIPv6. To make up for this, we propose an enhanced Fast Handover scheme to reduce the overall latency on handover, revising the Fast Handover [2]. Especially, several messages in layer 3 are sent in one frame during layer 2 handover. Table of Contents 1. Introduction.....................................................3 2. Terminology......................................................3 3. Background Information...........................................5 3.1. IEEE 802.11 Network 3.2. Fast Handover for Mobile IPv6 3.3. A scheme using Fast Handover based on IEEE 802.11 4. Proposed Protocol Details........................................7 5. Message Formats..................................................9 6. Security Considerations..........................................9 7. Conclusions......................................................9 8. References.......................................................9 9. Authors' Addresses..............................................10 S. Ryu, et al. Expires August, 2009 [Page 2] Internet-Draft Enhanced Fast Handover February 2008 1. Introduction As the advancement of wireless communication, requirements on the wireless Internet and mobility support are increasing. To support mobility, Mobile IPv6 (MIPv6) [1] has been proposed by the Internet Engineering Task Force (IETF). In MIPv6, when a mobile node (MN) moves to other subnetwork, it needs certain process, a handover, which causes long latency problem. There have been many researches to reduce the handover latency in MIPv6, such as a Fast Handover [2] and a hierarchical MIPv6 [3]. Still, aforementioned mechanisms are not appropriate to satisfy real-time traffic. We propose a enhanced fast handover scheme (EFH) to reduce the handover latency, modified from the Fast Handover scheme based on IEEE 802.11 [4]. In the Fast Handover, handover latency is smaller than the one of MIPv6, and packets from a CN to the MN are not lost during the handover because a tunnel is formed between a previous access router (PAR) and a new access router (NAR) before the layer 2 handover, and the NAR will buffer packets destined to the MN through the tunnel. The Fast Handover scheme, however, needs more signal packets and buffering. In the EFH, handover latency and signal packets are reduced than the Fast Handover due to multiple signal packets in one frame. 2. Terminology This document borrows all of the terminology from Mobile IPv6 [1] and Mobile IPv6 Fast Handovers [2], with the following additional terms from the 802.11 specification [4]. Mobile Node (MN) A Mobile IPv6 host. Correspondent Node (CN) A IPv6 host communicating with MN. Access Point (AP) A Layer 2 device connected to an IP subnet that offers wireless connectivity to a MN. An Access Point Identifier (AP-ID) refers the AP's L2 address. Sometimes, AP-ID is also referred to as a Base Station Subsystem ID (BSSID). Access Router (AR) The MN's default router. Previous Access Router (PAR) The MN's default router prior to its handover. S. Ryu, et al. Expires August, 2009 [Page 3] Internet-Draft Enhanced Fast Handover February 2008 New Access Router (NAR) The MN's anticipated default router subsequent to its handover. Previous CoA (PCoA) The MN's Care of Address valid on PAR's subnet. New CoA (NCoA) The MN's Care of Address valid on NAR's subnet. Handover A process of terminating existing connectivity and obtaining new IP connectivity. Layer 2 handover Movement of a MN's point of Layer 2 connection from one wireless access point to another. Layer 3 handover Movement of a MN between FAs which involves changing the care-of address (CoA) at Layer 3. Router Solicitation for Proxy Advertisement (RtSolPr) A message from the MN to the PAR requesting information for a potential handover. Proxy Router Advertisement (PrRtAdv) A message from the PAR to the MN that provides information about neighboring links facilitating expedited movement detection. The message also acts as a trigger for network-initiated handover. Fast Binding Update (FBU) A message from the MN instructing its PAR to redirect its traffic (towards NAR). Fast Binding Acknowledgment (FBack) A message from the PAR in response to FBU. Fast Neighbor Advertisement (FNA) A message from the MN to the NAR to announce attachment, and to confirm use of NCoA when the MN has not received FBACK. Handover Initiate (HI) A message from the PAR to the NAR regarding a MN's handover. Handover Acknowledge (HAck) A message from the NAR to the PAR as a response to HI. S. Ryu, et al. Expires August, 2009 [Page 4] Internet-Draft Enhanced Fast Handover February 2008 3. Background Information 3.1. IEEE 802.11 IEEE 802.11 wireless LAN is the layer 2 protocol and supports mobility in a link layer level. IEEE 802.11 handover takes place when a MN changes its association from one access point (AP) to another and its process consists of a search phase and an execution phase. This handover process simply consists of the following steps [5]: a. The MN realizes that a handoff is necessary due to degrading radio transmission environment for the current AP. b. Search Phase The MN performs a scan to see what APs are available. The result of the scan is a list of APs together with physical layer information, such as signal strength. The MN chooses one of the APs and performs a join to synchronize its physical and MAC layer timing parameters with the selected AP. c. Execution Phase 1. Authentiation phase The MN requests authentication with the new AP. For an "Open System", such authentication is a single round-trip message exchange with null authentication. 2. Association phase The MN requests association or reassociation with the new AP. A reassociation request contains the MAC layer address of the old AP, while a plain association request does not. At the association(reassociation) phase, the MN's link layer is really connected to the NAP. In some 802.11 implementations, the scan performs far in advance of the handover and perhaps in advance of any realtime traffic. [5] 3.2. Fast Handover In MIPv6, when a MN moves from one subnet to another subnet, a certain process is needed such as a handover. The handover consists of layer 2 and layer 3 handovers which are physical and logical handovers, respectively. In the Fast Handover, two handovers are interleaved to reduce a handover latency. The Fast Handover is a scheme which improves MIPv6 handover. In the Fast Handover, there are two modes, such as predictive and reactive mode. In this draft, we only explain and use the predictive mode. In the Fast Handover, several portions of the layer 3 handover are S. Ryu, et al. Expires August, 2009 [Page 5] Internet-Draft Enhanced Fast Handover February 2008 performed prior to the layer 2 handover. In other words, the MN performs the layer 3 handover while it connected to a PAR, and in this case, the PAR must have information about destined AR. The PAR establishes a tunnel between itself and a NAR and verifies MN's NCoA through exchanging a handover initiate (HI) message and a handover acknowledge (HAck) message. Packets that arrive at previous care-of address (PCoA) are sent to the NAR through an established tunnel during the handover. The tunnel is kept until MN's NCoA is registered to a HA. MN PAR NAR HA CN | | | | | |---RoSolPr--->| | | | |<--PrRrAdv----| | | | | | | | | |------FBU---->| | | | | |------HI----->| | | | |<----HAck---- | | | |<---FBack---- |-----FBack--->| | | --- --- | | Layer 2 Handover | | --- --- | | |-------------FNA------------>| | | |----Binding Update to HA--------------->| | | | | | |<-------------Return Routability--------------->| | | | | |----Binding Update to CN----------------------->| | | | | Fig. 1. MIPv6 fast handover Scheme (FMIPv6) - Predictive mode Fig. 1 shows the Fast Handover scheme. The MN initiates the Fast Handover scheme when a layer 2 trigger take places. The MN sends an RtSolPr message to the PAR and receives a PrRtAdv messages for information of the NAR. The MN creates the NCoA and sends a FBU message with the NCoA. The PAR receives the FBU message, then sends a HI message and receives a HAck message to verify the NCoA in the NAR and to establish a tunnel between the PAR and the NAR. The PAR sends FBack messages to the MN and the NAR, respectively after verification of the NCoA. The MN performs the layer 2 handover when it receives the FBack message. The MN sends a FNA message to NAR to inform its movement after the layer 2 handover. Then the MN exchanges a BU and a BA with the HA to register the NCoA. A Return Routability procedure is performed between the MN and the CN to establish security association, and then the MN sends Binding Update message to the CN. S. Ryu, et al. Expires August, 2009 [Page 6] Internet-Draft Enhanced Fast Handover February 2008 After registration, the handover is finished. 3.3. A scheme using Fast Handover based on IEEE 802.11 The Fast Handover based on IEEE 802.11 wireless LAN has been studied. [5] shows a order that layer 2 and layer 3 handover processes are performed when the layer 2 protocol is the IEEE 802.11 wireless LAN and the layer 3 protocol is the MIPv6 Fast Handover. [7] has been proposed by Y. Mun and J. Kim to improve the Fast Handover. They thought a scheme that mingles the layer 3 handover with the layer 3 handover, and propose that a MN encapsulates a BU message to HA in a layer 2 frame during layer 2 handover to reduce the handover latency. In this scheme, APs and a MN must have ability which can encapsulate and decapsulate an information element (IE) [6]. 4. Enhanced Fast Handover (EFH) Details When a MN moves into another network, a handover process should be followed not to lose connectivity. The handover process consists of a layer 2 and a layer 3 handovers. The layer 2 handover processes a scan phase, authentication phase and association phase. The layer 3 handover is decomposed into creating, verifying and registering a new address. The layer 2 and layer 3 handovers are performed sequentially in MIPv6 while several messages related to layer 3 handover are exchanged prior the layer 2 handover and the rest of the layer 3 handover in the Fast Handover. To perform the Fast Handover, several signal messages are needed. These additional messages make network traffic and use node's resources. In the EFH, the MN sends one frame containing several signal messages related to layer 3 handover during the layer 2 handover. Therefore, the EFH can register a new address to HA and CN more quickly than the Fast Handover. Figure 1 shows messages of the EFH. We assume that the MN must be able to encapsulate a BU destined to HA,a HoTI and a CoTI messages to an 802.11 reassociation request frame. A NAP is assumed to decapsulate the 802.11 reassociation request frame and to forward the BU message to HA, the HoTI and the CoTI messages to CN. The EFH only can be performed when the fast handover is the predictive mode. Otherwise, the MN performs a MIPv6 handover (or the reactive mode of the Fast Handover). IPsec mechanism is employed between the MN and the HA, using current security association (SA) when the MN sends the BU message to HA and the HoTI message to CN. S. Ryu, et al. Expires August, 2009 [Page 7] Internet-Draft Enhanced Fast Handover February 2008 MN PAP PAR NAP NAR HA CN | | | | | | | |---RoSolPr---->| | | | | |<--PrRrAdv-----| | | | | | | | | | | | |------FBU----->| | | | | | | |-------HI----->| | | | | |<-----HAck---- | | | |<---FBack----- |------FBack--->| | | ----| | | | | | | ^ |----Auth. Request----->| | | | L2 |<---Auth. Response-----| | | | Hand |--Reassociatoin Req.-->| | | | over |<--Reassociation Res.--|--MIPv6 BU to HA->| | ----| | | |------HoTI------->|------>| | | | |------CoTI--------------->| |----------FNA----------------->| | | | | | | | | | |<---Binding Acknowledgement from HA-------| | |<---HoTI from CN--------------------------|<------| |<---CoTI from CN----------------------------------| | | | | | | | |----Binding Update to CN------------------------->| | | | | | | | Figure 1: The enhanced fast handover scheme (EFH) The EFH detail is as follows: Once authentication phase in the layer 2 handover is completed successfully, reas-sociation phase starts. A MN sends an 802.11 reassociation request frame, which contains three messages that are performed after the layer 2 handover; a BU, a home test init (HoTI) and a care-of test init (CoTI) messages. Source address of layer 3 handover messages is a NCoA. Once a NAP receives the reassociation request frame, it decapsulates that frame and forwards three messages. Finally the BU message gets to the HA via the NAR and HoTI and CoTI messages get to CN via the NAR. The rest of handover process is very similar to the Fast Handover. S. Ryu, et al. Expires August, 2009 [Page 8] Internet-Draft Enhanced Fast Handover February 2008 5. Message Formats To be defined. 6. Security Considerations In this draft, the security between a MN and a AR does not specify any particular mechanism to convey information between the MN and AR the set of information identified in the following internet draft, can be conveyed between the MN and the AR in a different suitable manner outside the scope of this document (e.g. ICMP, the protocol defined by the PANA WG, etc.). 7. Conclusions In the MIPv6, handover latency is a critical issue. To solve this problem, R. Koodli has proposed the Fast Handover which reduces handover latency in the MIPv6. Still, this scheme is not appropriate to satisfy real-time traffic, since . We propose an enhanced fast handover scheme (EFH) to reduce the overall latency on the handover, revising the Fast Handover. Especially, several messages related to the layer 3 handover are sent in one frame during layer 2 handover. Currently, the Fast Handover scheme is being standardized in IETF, and then will soon be a RFC document. The EFH scheme improves the Fast Handover, using layer 2 handover frame. Therefore, if EFH scheme is used with the Fast Handover sheme, a handover performance will be improved. 8. References [1] D. Johnson, C. E. Perkins, and J. Arkko, "Mobility Support in IPv6", Request for Comments (Proposed Standard) 3775, Internet Engineering Task Force, June 2004. [2] R. Koodli, (editor), "Fast Handovers for Mobile IPv6", Request for Comments (Experimental) 4068, Internet Engineering Task Force, July 2005. [3] H. Soliman, C. Catelluccia, K. Malki, L. Bellier, "Hierarchical Mobile IPv6 mobility management (HMIPv6)", Request for Comments (Experimental) 4140, Internet Engineering Task Force, August 2005. [4] "Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications", ANSI/IEEE Std 802.11, 1999 Edition. S. Ryu, et al. Expires August, 2009 [Page 9] Internet-Draft Enhanced Fast Handover February 2008 [5] P. McCann, "Mobile IPv6 Fast Handovers for 802.11 Networks", draft-ietf-mipshop-80211fh-03.txt, October 2004. Work In Progress. [6] Y. Mun, J. Park, "Layer 2 Handoff for Mobile-IPv4 with 802.11", draft-mun-mobileip-layer2-handoff-mipv4-01.txt, September 2003. Work In Progress. [7] J. Kim, Y. Mun, "A Study on Handoff Performance Improvement Scheme for Mobile IPv6 over IEEE 802.11 Wireless LAN", Septeber 2003, Work In Progress. [8] M. Ergen, "IEEE 802.11 Tutorial", June 2002. 9. Authors' Addresses Seonggeun Ryu Soongsil University Seoul Korea Email: sgryu@sunny.ssu.ac.kr Youngsong Mun Soongsil University Seoul Korea Email: mun@computing.ssu.ac.kr S. Ryu, et al. Expires August, 2009 [Page 10] Internet-Draft Enhanced Fast Handover February 2008 S. Ryu, et al. Expires August, 2009 [Page 11]