Network Working Group P. Kim Internet-Draft Korea Polytechnic University Expires: April 12, 2006 Oct 13, 2005 A Fast Handover Scheme for Mobile IPv6 Based Wireless Networks draft-pskim-mipv6-fasthandover-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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 April 12, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This draft proposes a new fast handover scheme for Mobile IPv6 based wireless networks. To implement the proposed scheme, the beacon message used in L2 is defined newly by adding a specific subfield to the capability information field. In addition, Router Information Request/Reply messages used in L3 are defined newly. The proposed scheme provides the faster acquisition of new access router's network information than the existing one, which might be advantageous for the low handover latency. In addition, the proposed scheme might reduce amount of traffic in comparison with the existing one, which might be remarkable when there are many mobile nodes that are now connecting to current access router. Moreover, in the proposed scheme, a mobile node can know whether it changes access router or access point, which can remove redundant traffic of the existing one. Kim A Fast Handover Scheme for Mobile IPv6 [Page 1] Internet-Draft A Fast Handover Scheme for Mobile IPv6 Oct 2005 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Network Configuration and Router Information Table . . . . . . 4 4. New Fast handover Scheme . . . . . . . . . . . . . . . . . . . 4 4.1 Beacon Message Format . . . . . . . . . . . . . . . . . . . 4 4.2 Router Information Request/Reply Message Formats . . . . . . 5 5. Basic Operation Procedure of Proposed Scheme . . . . . . . . . 7 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 9 Intellectual Property and Copyright Statements . . . . . . . . 10 Kim A Fast Handover Scheme for Mobile IPv6 [Page 2] Internet-Draft A Fast Handover Scheme for Mobile IPv6 Oct 2005 1. Introduction In future Mobile IPv6 based wireless networks, the need to communicate efficiently on the move and to minimize to packet loss caused by a handover is becoming increasingly important because a handover latency would be unacceptable for real-time Internet services. Thus, in recent, a fast handover scheme [1]-[3] has been proposed for Mobile IPv6 as a way to reduce a L3 handover latency. In this draft, a new fast handover scheme is proposed to reduce the L3 handover latency for Mobile IPv6 based wireless networks where there are several access routers (ARs) connected by access points (APs). To implement the proposed scheme, the beacon message used in L2 is defined newly by adding a specific subfield to the existing reserved field. Using this message, a MN can know whether it changes AR or AP. In addition, Router Information Request/Reply messages used in L3 are defined newly. Using these messages, the MN can acquire network information about all ARs in ESS, such as ARs' IP addresses, prefix lengths, and identities, which is performed once only at the booting time and isn't performed in real-time communication. In real-time communication, this network information allows the MN to formulate a new care-of address and to be able to communicate immediately when the MN changes its point of attachment from the current AR (CAR) to the new AR (NAR). That is, the proposed scheme can omit a Router Solicitation for a Proxy message and a Proxy Router Advertisement message used in the existing one [1]-[3], in real-time communication. This means that the proposed scheme provides the faster acquisition of NAR's network information than the existing one, which might be remarkable for low L3 handover latency. In addition, the omission of above two messages might reduce amount of traffic when there are many MNs that are now connecting to the CAR. Moreover, in the proposed scheme, the MN can know whether it changes AR or AP while the existing one cannot. Thus, when the MN changes AP, the proposed scheme can remove redundant traffic of the existing one. 2. Requirements The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Kim A Fast Handover Scheme for Mobile IPv6 [Page 3] Internet-Draft A Fast Handover Scheme for Mobile IPv6 Oct 2005 3. Network Configuration and Router Information Table This draft considers an IEEE 802.11 wireless network where there are serveral access routers (ARs). All access points (APs) connected to ARs and mobile nodes (MNs) are considered to belong to the same Extended Service Set (ESS), and thus have same ESS identity (ESSID). For example, buildings such as offices, banks and hospitals can be considered. These buildings have several floors where there is one AR for each floors. Mobile hosts such as laptop computers and handheld PCs used by resident people within the building are considered as MNs. Usually, these MNs would not go out the building, but would move within the building. As shown in [1]-[3], all ARs in this wireless network share each other's network information, such as ARs' IP addresses, prefix lengths, and identities, and thus may have information table that will be called the Router Information Table (RIT). Note that the AP can know its AR's identity (ARID) by a system administrator's presetting. Note that a change of AP on same subnet does not require a change of AR because AR is link-layer reachable from the MN connected to any APs. This case is outside the scope of L3 handover schemes. However, a change of AP between different subnets require a change of AR, because the MN would be attaching to a different subnet. In this case, a L3 handover scheme would need to be invoked in order to provide low handover latency between the two ARs. Therefore, it should be required to know whether the MN changes AP or AR. Note that this draft borrows all of the terminology from the existing scheme [1]-[3] and the IEEE 802.11 specification [4]. 4. New Fast handover Scheme In this section, a new fast handover scheme is proposed for the Mobile IPv6 based IEEE 802.11 wireless network with serveral access routers. Firstly, Router Information Request/Reply messages are defined newly to implement the proposed scheme. Secondly, the operation procedure of the proposed scheme is described and the comparison with the existing one [1]-[3] is shown. Lastly, several advantages of the proposed scheme over the existing one is described. 4.1 Beacon Message Format In order to implement the proposed scheme, the beacon message defined recently in [5] is used. The beacon message contains information such as timestamp, beacon interval, capability information, SSID, etc [4]. In [5], the capability information field is modified by adding the specific subfield "ARID". Since this field uses the existing Kim A Fast Handover Scheme for Mobile IPv6 [Page 4] Internet-Draft A Fast Handover Scheme for Mobile IPv6 Oct 2005 reserved field, other fields are not affected. Using this beacon message, the MN can know whether it changes AR or AP, which will be explained later. 4.2 Router Information Request/Reply Message Formats In order to implement the proposed scheme, Router Information Request/Reply messages used in L3 are defined newly. These messages are made from the Internet Control Message Protocol for IPv6 (ICMPv6) in [6]. Then, using these messages, the MN performs the Router Information Request/Reply at its booting time. Fig. 1 shows the Router Information Request message. This message is used by the MN to request network information about all ARs from one of them. The description of each fields are as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Identifier | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Fig.1 Router Information Request Message Formats o Type : 160 (or any available value) o Code : 0 o Identifier : MUST be set by the sender so that replies can be matched to this request. o Reserved : MUST be set to zero by the sender and ignored by the receiver. In the IP header of this message, the source address is an IP address assigned to the sending interface and the destination address is the address of the all routers multicast address. Fig. 2 shows the Router Information Reply message that is used to acknowledge receipt of a Router Information Request. Kim A Fast Handover Scheme for Mobile IPv6 [Page 5] Internet-Draft A Fast Handover Scheme for Mobile IPv6 Oct 2005 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Identifier | Number of ARs | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ARID | Prefix Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + AR's IPv6 Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . . . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ARID | Prefix Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + AR's IPv6 Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Fig.2 Router Information Reply Message Formats o Type : 161 (or any available value) o Code : 0 o Checksum : The ICMP checksum. o Identifier : Copied from Router Information Request. o Number of ARs : The number of ARs' addresses. o ARID : ARs' identity. o Prefix Length : The prefix length of AR's address. o AR's IP Address : IPv6 Address of AR In the IP header of this message, the source address is an IP address assigned to the sending interface and the destination address is the Source Address of an invoking Router Information Request. Kim A Fast Handover Scheme for Mobile IPv6 [Page 6] Internet-Draft A Fast Handover Scheme for Mobile IPv6 Oct 2005 5. Basic Operation Procedure of Proposed Scheme The operation procedure of the proposed scheme is described and the comparison with the existing one [1]-[3] is shown. According to the specification of IEEE 802.11 wireless network [4], it is required that the MN sets the ESSID before operation. At the same time, in this draft, it is required that the MN sets a flag additionally to determine whether it conforms to the proposed scheme. That is, if its ESS supports the proposed scheme, the MN sets the flag and conforms the proposed scheme. Otherwise, the MN will not set the flag and can conform the existing one in [1]-[3]. When the MN is booting, it sends a Router Information Request message using all routers multicast address to current subnet in order to acquire network information about all ARs in ESS, ARs' IP addresses, prefix lengths, and identities. In response to Router Information Request message, the current AR (CAR) on the current subnet sends a Router Information Reply message using the RIT. Then, the MN receives this reply message and caches the RIT in this reply message. Note that this Router Information Reqeust/Reply is performed once only at the booting time and thus isn't performed in real-time communication. Assume that the MN communicates with the corresponding node (CN). In real-time communication, when the MN moves, the "trigger" may arrive from specific L2 events that might determine the need for handover. In this draft, this trigger itself is not specified in detail. Since this trigger is based on the beacon message given by AP, the MN can know the ARID of its AP from the trigger. Then, the MN checks this ARID using the RIT cached previously, in order to determine whether the MN changes AP or AR. If the MN changes AP, it continues real-time communication via the CAR. Otherwise, the MN finds the new AR (NAR) corresponding to ARID from the RIT, and formulates a new care-of address (NCoA) using the prefix of the NAR's address. On the other hand, in the existing scheme [1]-[3], when the trigger containing the AP's identity arrives from specific L2 events, the MN sends a Router Solicitation for a Proxy (RtSolPr) message to the CAR in order to acquire network information of the NAR in real-time communication. This message contains the identity of its prospective AP. To response to RtSolPr message, the CAR finds the network information about the NAR corresponding to AP's identity from the RIT, and sends a Proxy Router Advertisement (PrRtAdv) message with the network information about the NAR to the MN. Note that these RtSolPr and PrRtAdv are performed even if the MN changes AP without change of AR. Then, the MN receives this reply message and determines whether the MN changes AP or AR. If the MN changes AP, it continues real-time communication via the CAR. Otherwise, the MN formulates a NCoA using the prefix of the NAR's address. Kim A Fast Handover Scheme for Mobile IPv6 [Page 7] Internet-Draft A Fast Handover Scheme for Mobile IPv6 Oct 2005 After then, in both the proposed scheme and the existing one, the MN associates its current CoA (CCoA) with NAR's IP address for forwarding purposes using a Fast Binding Update (FBU). Then, the CAR sends a Fast Binding Acknowledgment (FBACK) message to the MN and the NAR. The FBACK message confirms whether NCoA could be used, only after which the MN must use NCoA on the new subnet. At this time, the CAR sends a Handover Initiate (HI) message to NAR, after looking up the IP address corresponding to ARID supplied by the MN using its RIT. This FBU/FBACK and HI/HACK allows that packets arriving at the CAR can be tunneled to the NAR. When the MN has confirmed its NCoA and then completes the Binding Update procedure with its CN, the MN continues real-time communication with the CN using NCoA as its source IP address via the NAR. 6. Advantages over Existing Scheme The proposed scheme provides several advantages over the existing one in [1]-[3]. As mentioned in Section 5, the proposed scheme can omit RtSolPr/PrRtAdv messages used in the existing one, in real-time communication. The proposed scheme provides the faster acquisition of NAR's network information than the existing one, which might be advantageous for the low L3 handover latency. In addition, the omission of above two messages might reduce amount of traffic in comparison with the existing one, which might be remarkable when there are many mobile nodes that are now connecting to the CAR. Moreover, in the proposed scheme, the MN can know whether it changes AR or AP, while the existing one cannot. Thus, when the MN changes AP, the proposed scheme can remove redundant traffic of the existing one. However, when there are many ARs on the IEEE 802.11 wireless network, the size of the RIT may increase. Then, the more memory is required for the MN to cache the RIT, which may be a weak point of the proposed scheme. Kim A Fast Handover Scheme for Mobile IPv6 [Page 8] Internet-Draft A Fast Handover Scheme for Mobile IPv6 Oct 2005 7. References [1] Kempf, J., Wood, J., Fu, G. "Fast mobile ipv6 handover packet loss performance: measurement for emulated real time traffic" In: 2003 IEEE Wireless Communications and Networking, 2003. [2] McCann, P. "Mobile IPv6 Fast Handovers for 802.11 Networks", IETF Draft:draftietf-mipshop-80211fh-04.txt, Feb 2005. [3] Koodli, R. "Fast Handovers for Mobile IPv6", IETF RFC 4068, Jul 2005. [4] ISO/ICE: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. ANSI/IEEE Std 802.11, 1999. [5] IEEE 802.11 MAC and PHY to support InterWorking with External Networks. IEEE 802.11u PAR, 2005. [6] Conta, A., Deering, S. "Internet Control message Protocol (ICMP) for the Internet Protocol Version 6 (IPv6) Specification", IETF RFC 2463, December 1998 Authors' Addresses Pyungsoo Kim Department of Electronics Engineering, Korea Polytechnic University, 2121 Jungwang-Dong, Shiheung City, Gyeonggi-Do 429-793 KOREA Phone: +82 31 496 8413 EMail: pskim@kpu.ac.kr Kim A Fast Handover Scheme for Mobile IPv6 [Page 9] Internet-Draft A Fast Handover Scheme for Mobile IPv6 Oct 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Kim A Fast Handover Scheme for Mobile IPv6 [Page 10]