Hyun-Kook Kahng Internet Draft Jin Woo Jung Document: draft-kahng-rss-mipv4-00.txt Jung Hoon Cheon Korea University Expires: 2002 July 2001 Redirect Subnet Switching in Mobile IPv4 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 except that the right to produce derivative works is not granted. 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. Abstract From a viewpoint of a layer architecture, a network layer should feature a mobility support. Then the users can enjoy their mobility whatever data-link devices and user applications they use. Mobile IP has been proposed for a solution to provide IP-layer handoffs between subnets served by different Foreign Agents. However, it still suffers an interruption of the communications for real-time applications. In certain cases, the latency involved in these handoffs can be above the threshold required the support of delay-sensitive or real-time services. The aim of this document is to present a move detection mechanism to achieve low-latency Mobile IP handoffs. The described techniques allow greater support for real-time services on a Mobile IPv4 network by minimizing the period of time when a Mobile Node is unable to send or receive IP packets due to the delay in the mobile IPv4 move detection. The next-generation of mobile communication networks will have higher transmission rates and radio frequencies, smaller cell sizes and a greater number of cells. When switching cells, mobile node(MN) must KOREA University [Page1] INTERNET-DRAFT Redirect Subnet Switching july 2001 have an efficient IP-based handoff scheme that handle switching between subnets of different characteristics. However, current wireless links and Mobile IPv4 protocols work independently, and this causes problems. Also, A subnet MAY contain several cells. For this case, the mobile node MUST not change its IP address. This document specifies the move detection on layer 3, which is independent of the move detection on layer 2. Table of Contents Status of this Memo................................................1 Abstract...........................................................1 1. Introduction....................................................3 1.1 Requirements...................................................4 1.2 Terminology....................................................4 1.3 Overview.......................................................5 1.4 Requirement Languages..........................................5 2. Redirect Subnet Switching Method................................6 2.1 General Redirect Subnet Switching Method.......................6 2.2 Problems.......................................................8 2.3 Combined the Redirect Subnet Switching with LCS(Lazy Cell Switching).........................................................8 3. Redirect Route Setup Message...................................11 References........................................................13 Author's Addresses................................................14 Korea University [Page2] INTERNET-DRAFT Redirect Subnet Switching july 2001 1. Introduction Mobile IPv4 has been proposed for a solution to provide IP-layer handoffs between subnets served by different Foreign Agents(FAs). However, it still suffers an interruption of the communications for real-time applications. In certain cases, the latency involved in these handoffs can be above the threshold required the support of delay-sensitive or real-time services. The aim of this document is to present a move detection mechanism to achieve low-latency Mobile IPv4 handoffs. The described techniques allow greater support for real-time services on a Mobile IPv4 network by minimizing the period of time when a Mobile Node is unable to send or receive IP packets due to the delay in the Mobile IP move detection. The next-generation of mobile communication networks will have higher transmission rates and radio frequencies, smaller cell sizes and a greater number of cells. When switching cells, Mobile Node(MN) must have an efficient IP-based handoff scheme that handle switching between subnets of different characteristics. However, current wireless links and Mobile IPv4 protocols work independently, and this causes problems. In the absence of a communication between the link and IP layers that would enable a Mobile Node to forecast an upcoming hand-off, Mobile IPv4 has to rely on alternative means to detect movement[1]. Specifically, every Mobility Agent is required to advertise its existence and all available care-of addresses in fixed period intervals. A Mobile Node entering a new subnet will detect its movement by receipt of an "unknown" advertisement. As such, a Mobile Node entering a network with multiple advertising agents may be prone to performing several handoffs prior to reestablishing network connectivity. In certain cased, the latency involved in these methods can be above the threshold required for the support of delay-sensitive or real-time services. This document specified the new method that provides the shortest move detection for faster handoff. The presented techniques allow greater support for real-time services on a Mobile IPv4 network by minimizing the period of time when a MN is unable to send or receive IP packets due to the delay in the Mobile IPv4 move detection. Proposed method is based on strict source route option of IP version 4[2]. The strict source route option provides a means for the source of IP datagram to supply routing information to be used by the gateways in forwarding the datagram to the destination. If datagarm is not passed specified route, Network Node sends ICMP error message to source node of IP dataram. Korea University [Page3] INTERNET-DRAFT Redirect Subnet Switching july 2001 1.1 Requirements The following requirements are applicable to low-latency handoff techniques and are supported by the methods in this document: - provide low-latency and low loss handoff for real time services, - have not dependence on a wireless layer 2 technology, - reduce the effect of TCP performance. - limit wireless bandwidth usage. 1.2 Terminology This section presents a few terms used through the document. Binding The association of a home address with a care-of address , along with the remaining lifetime of that association. CN Specified in RFC 2002[1]. COA Specified in RFC 2002[1]. Default Home Router(DHR) Router is nearest to MN on Home Network. Default Foreign Router(DFR) Router is nearest to MN on Foreign Network. Foreign Agent Specified in RFC 2002[1]. Home Agent Specified in RFC 2002[1]. Link-Layer Address The address used to identify an endpoint of some communication over a physical link. Typically, the Link-Layer address is an interface's Media Access Control(MAC) address. Modified Datagram Datagram with using the strict source route option. Node Host or Router. Redirect Subnet Switching(RSS) This method is based on the characteristic of IP option. Subnet Korea University [Page4] INTERNET-DRAFT Redirect Subnet Switching july 2001 MAY contain several Cells. 1.3 Overview Mobile IPv4 was originally designed without any assumptions about the underlying link layers over which it would operate so that it could have the widest possible applicability. This approach has the advantage of facilitating a clean separation between Layer 2 and Layer 3 of the protocol stack, but it has negative consequences for handoff latency. In the field of wireless communications, mobility is usually understood as low-level mobility, that is the movement of a mobile node between base stations(BSs) and the relative wireless handoff mechanism which occurs as a result. The term low-level mobility denotes node mobility that is handled by the MAC and its support for roaming. Its aim is to establish and maintain reliable link connectivity despite node movement and loss nature of the wireless medium. Low-level mobility would involve the mobile node leaving the region of coverage of the BS in subnet A, entering the region of coverage of the BS in subnet B and registering with it at link layer level. However, when considering a mobile IP network it is necessary to define another type of mobility, namely high-level mobility. High- level mobility occurs at the IP(i.e. Mobile IP)level. This involves the Mobile IPv4 move detection method, which enable a mobile node to take decisions on whether it should switch between agents. This is not normally dependent on low-level mobility, although low-level mobility must precede high-level mobility. This document assumed that the underlying link layer connection is already established, and the layer 3 cannot use the function of layer 2. Therefore, this document is specified under the assumption that the technique on layer 3 is independent of the technique on underlying layer 2 for providing move detection. Redirect Subnet Switching mechanism is based on the characteristic of strict source route option. When mobile node(MN) sends every packet to correspondent node(CN), MN's IP output function MUST always set up the strict source routing option. Therefore, when MN moves from one subnet to another subnet, the address of MN's default router is changed, and resulting in redirect route setup message sent to MN from network node. 1.4 Requirement Languages In this document, the key words "MAY", "MUST", "MUST NOT", "optional", "recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as described in [3]. Korea University [Page5] INTERNET-DRAFT Redirect Subnet Switching july 2001 2. Redirect Subnet Switching Method 2.1 General Redirect Subnet Switching Method The RSS method is based on the characteristic of the strict source route option. When MN sends every packet to correspondent node, MN's IP function has to always set up the strict source route option. Therefore, when MN moves from one subnet to another subnet, the address of default router is changed, and resulting in a redirect route setup message sent to MN. The MN performs move detection upon receipt of redirect route setup message and, if appropriate, it sends a Registration Request Message[1] to default foreign router requesting a simultaneous binding. The basic RSS mechanism is summarized in Figure 1: +------------------------------+---------------------------+ +----+| +---------------+ +----+ | +----------------+ | | CN || | Default Home | | MN | | |Default Foreign | | +--+-+| | Router (DHR) | +-+--+ |+----+ |Router (DFR) | | | | +-------+-------+ | || MN | +--------+-------+ | +--+--+---------+-----------+--+ |+-+--+ | | |Communicating with modified | | | | | |Datagram | | | | | +--+--+---------+-----------+--+ | | | | | | | | Moving | | | | | | | |--------+->| 1.Modified | | | | | | | | Datagram | | | | | | | |------------->| | | | | | | | 2.Redirect | | | | | | | | Route Setup | | | | | | | |<-------------| | | | | | | | | | | | | | | |3.Reg. Request| | | | | | | |------------->| | | | | Registrion| Request| | | | | | |<----------+--------+--+--------------| | | | | Registrion| Reply | | | | | | |-----------+--------+--+------------->| | | | | | | | Reg. Reply | | | | | | | |<-------------| | | Home Domain | Foreign Domain | +------------------------------+---------------------------+ Figure 1. General RSS Handoff Following steps provide more detail on this mechanism: 1. MN sends modified datagram with the strict source route option. 2. If Default Foreign Router is acts as Mobility Agent, Default Foreign Router sends a Redirect Route Setup Message to MN. 3. Then, the MN performs move detection upon receipt of the Redirect Route Setup Message and, if appropriate, it sends a Registration Korea University [Page6] INTERNET-DRAFT Redirect Subnet Switching july 2001 Request message[1] to Foreign Default Router requesting a simultaneous binding. Figure 1 specified the general RSS handoff. Because MN transmits packets, which involve strict source route option, the Foreign Default Router reply with a Redirect Router Setup Message. When MN receives this message from router that takes the place of mobile agent function, this message is similar to the agent advertisement message of Mobile IPv4. But, we modified the means of header fields in the Agent Advertisement message for RSS[1].: Redirect Route Setup Message(see Section 3). The MN that received redirect route setup message sends registration request message to the address of FA, which is extracted from the agent advertisement message. But, if Default Foreign Router does not act as mobility Agent, following procedures are adapted. When MN is received a redirect route setup message from router that does not take the place of agent function, this redirect route setup message does not contain the location information of agent: generic ICMP error message(see RFC 777[7]). The RSS mechanism for the case that Default Router dose not act mobile agent is summarized in Figure 2: +------------------------------+---------------------------+ +----+| +---------------+ +----+ | +----------------+ | | CN || | Default Home | | MN | | |Default Foreign | | +--+-+| | Router (DHR) | +-+--+ |+----+ |Router (DFR) | | | | +-------+-------+ | || MN | +--------+-------+ | +--+--+---------+-----------+--+ |+-+--+ | | | Communicating with modified | | | | | | Datagram | | | | | +--+--+---------+-----------+--+ | | | | | | | | Moving | | | | | | | |--------+->| Modified | | | | | | | | Datagram | | | | | | | |------------->| | | | | | | |Original ICMP | | | | | | | |Error Message | | | | | | | |<-------------| | | | | | | | Agnet | | | | | | | | Solicitation | | | | | | | | Message | | | | | | | |------------->| | | | | | | | Agent | | | | | | | | Advertisement| | | | | | | | Message | | | | | | | |<-------------| | | | | | | | Registration | | | | | | | | Request | | | | | Registrion| Request| | | | Korea University [Page7] INTERNET-DRAFT Redirect Subnet Switching july 2001 | | |<----------+--------+--+--------------| | | | | Registrion| Reply | | | | | | |-----------+--------+--+------------->| | | | | | | | Reg. Reply | | | | | | | |------------->| | | Home Domain | Foreign Domain | +------------------------------+---------------------------+ Figure 2. The case that Default Router dose not act mobile agent This method is useful in case that mobile agent does not exist on subnet after MN moves. In this case(does not exist FA), when MN receives a Original ICMP error message, MN may alternatively operate Foreign Agents by replacing them with a dynamic host configuration service(DHCP). Then, MN sends registration request message with using allocated CCOA to HA. Following steps provide more detail when dose not exist Foreign Agent: 1. MN sends modified datagram with strict source route option. 2. If Default Foreign Router does not act as Mobility Agent, Foreign Default Router sends ICMP error message to the MN. 3. The MN performs move detection upon receipt of ICMP error message and, if appropriate, it triggers the procedure by using DHCP. 4. If the MN obtains CCOA in successful, it sends registration request message with using allocated CCOA to HA. In this document, a agent advertisement message is sent by broadcasting, this method can compensate the move detection during MN does not send packet. But, any network which does not support broadcast cannot compensate the movement during MN does not send packet. For this case, this mechanism needs to additional method of upper layer(i.e. HeartBeat). 2.2 Problems General Redirect Subnet Switching has two critical problems: RSS have a overhead-per-datagram(i.e. for Ethernet link, 0.8 % overhead/datagram. 12/1500), and cannot achieve move detection when MN does not send datagram. The overhead-per-datagram can be reduced with limited RSS. The limited RSS specifies that the first datagram of full data only contains the strict source route option. 2.3 Combined the Redirect Subnet Switching with LCS(Lazy Cell Switching) In section 2.2, we specified two problems. In this section, we suggest improved RSS combined with LCS in Mobile IPv4[1] for solving the second problem of RSS. Korea University [Page8] INTERNET-DRAFT Redirect Subnet Switching july 2001 The LCS method for move detection is based upon the Lifetime field within the main body of the ICMP Router Advertisement portion of the agent advertisement. Therefore, this method relies on the interval of agent advertisement. Otherwise, RSS relies on the transmission rate of MN. So, we propose improved RSS, which is based on LCS for compensating the disadvantage of RSS The overall improved RSS move detection method is summarized in Figure 3: -------------------------------+--------------------------- +----+| +---------------+ +----+ | +----------------+ | | CN || | Default Home | | MN | | |Default Foreign | | +--+-+| | Router (DHR) | +-+--+ |+----+ |Router(DFR) | | | | +-------+-------+ | || MN | +--------+-------+ | +--+--+---------+-----------+--+ |+-+--+ | | |Communicating with modified | | | | | |Datagram | | | | | +--+--+---------+-----------+--+ | | 1.FDR's Agent| | | | | | | | Advertisement| | | | | | | |<-------------|<-+ | | | | | | | 2.Modified | | | | | | | | | Datagram | | | | | | | | |------------->| X | | | | | | | : | | | | | | | Moving | | 2.Modified | | | | | | |--------+->| Datagram | | | | | | | | |------------->|<-+ | | | | | | | 3. Redirect | | | | | | | | Route Setup | | | | | | | |<-------------| | | | | | | | Registration | | | | | | | | Request | | | | | | | |------------->| | | | | | | | Registration | | | | | | | | Request | | | | |<----------+--------+--+--------------| | | | | | | | Registration | | | | | | | | Reply | | | | |-----------+--------+--+------------->| | | | | | | | Registration | | | | | | | | Reply | | | | | | | |<-------------| | | | | | | | | | | Home Domain | Foreign Domain | +------------------------------+---------------------------+ X : The interval of Advertisement Message Figure 3. Improved RSS The procedure of combined RSS with LCS is divided following steps: 1. Default Foreign Router sends periodically an agent advertisement message. 2. When Mobile Node received the agent advertisements from any FA, MN SHOULD record the Lifetime received in any agent Korea University [Page9] INTERNET-DRAFT Redirect Subnet Switching july 2001 advertisements, until that Lifetime expires. Then, MN sends datagram with using the RSS method during the specified time(x of Figure3). If MN does not have any sending data, MN SHOULD send modified datagram with NULL data. 2b. If the MN fails to receive another advertisement from the same agent within the specified Lifetime, it SHOULD assume that it has lost contact with that agent. The MN SHOULD send datagram with using the RSS method during specified time. If MN does not have any sending data, MN SHOULD send modified datagram with NULL data. 3. When the MN receives Redirect Route Setup Message, it can achieve move detection. 4. If the MN has previously received an Agent Advertisement from another agent for which the Lifetime field has not yet expired, the mobile node MAY cache agent advertisement of the agent. Otherwise, the mobile node SHOULD extract a new agent from Redirect Route Setup Message. Because the mobility agents periodically send a advertisement message, The Default Router on the subnet can intercept the advertisement message, and MUST cache the location information of the mobility agent. Therefore, this procedure is required to modify the function of all network node(e.g., router, mobile node). Korea University [Page10] INTERNET-DRAFT Redirect Subnet Switching july 2001 3. Redirect Route Setup Message The Redirect Error Message is used to determine whether MN is currently connected to its home network or to a foreign network, and by which a mobile node can detect when it has moved from one network to another. In other words, because MN cannot directly send packets to default router, MN must register current location to previous agent. Redirect Error Message can be used for both error notification and agent advertisement. If the node sending Redirect Error Message does not know the location of agent, it only informs MN of MN's movement. Otherwise, the node sending Redirect Error Message sends the message that contains error reporting information and agent location information. The RSS extends ICMP Router Discovery[4] as its primary mechanism for move detection. The Redirect Route Setup Message is formed with including the modification of agent advertisement in an ICMP Router Advertisement message. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Num Addrs |Addr Entry Size| LifeTime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Agent or Router Address[1]...[n] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Preference Level[1]...[n] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extension ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Registration Lifetime |R|B|H|F|M|G|V| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Zero or more care-of address | | .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4. Redirect Route Setup Message The mobile node uses these Redirect Error Message to determine their current point of attachment to the Internet. Within an Redirect Error Message, ICMP Router Advertisement fields of the message are required to conform to the following additional specifications: - Link-Layer Fields Korea University [Page11] INTERNET-DRAFT Redirect Subnet Switching july 2001 Destination Address The link-layer destination address of mobile node that transmitted packets through incorrect route list MUST be set. - IP Fields TTL The TTL for all Redirect Route Setup Message MUST be set to 1. Destination Address as specified for ICMP Router Discovery [4], the IP destination address of an Redirect Route Setup message MUST be either the "all systems on this link" multicast address(224.0.0.1) or the "limited broadcast" address (255.255.255.255). The subnet-directed broadcast address of the form .<-1> cannot be used since mobile nodes will not generally know the prefix of the foreign network. - ICMP Fields Code The Code field of Redirect Route Setup Message is interpreted as follows: 1 The router only handles common traffic -- that is, it only acts as router for IP datagram not necessarily related to mobile nodes. Therefore, the Agent or Router Address Field[i] only contains router list. 32 The router acts as mobility agent -- that is, Agent or Router Address field contains the list of mobility agent on current subnet and the list of Default Router on current subnet. Lifetime Specified in RFC 2002. Agent or Router Address These fields MAY contain one or more router addresses. If the router acts as mobility agent, these fields MAY contain mobility agent address as the last field and contain router list on this subnet. Otherwise, these fields MAY contain the list of router on this subnet. Preference Level[i] If the router of Agent or Router Address acts as mobility agent, these fields MUST be set to 0. Otherwise, these fields MAY be set to the preferability of each Agent or Router Address[i] as a default router address, relative to other router addresses on the same subnet. The last part of Agent Advertisement is the same as specified in RFC 2002. Korea University [Page12] INTERNET-DRAFT Redirect Subnet Switching july 2001 References [1] C. Perkins, Editor, "IP Mobility Support", RFC 2002, October 1996. [2] J. Postel, Editor, "Internet Protocol", STD 5, RFC 791, September 1981. [3] S. Bradner, Editor, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14. RFC 2119. March 1997. [4] S. Deering, Editor, "ICMP Router Discovery Messages", RFC 1256, September 1991. [5] S. Deering, Editor, "Host Extensions for IP Multicasting", STD 5, RFC 1112, August 1989. [6] Droms, R., "Dynamic Host Configuration Protocol", RFC 1541, October 1993. [7] J. Postel, Editor, "Internet Control Message Protocol", RFC 777, April 1981. Korea University [Page13] INTERNET-DRAFT Redirect Subnet Switching july 2001 Author's Addresses Jin Woo Jung Korea University Electronic Information Engineering Phone: +82-41-860-1424 Seoul, Korea Email: grjjw@tiger.korea.ac.kr Hyun Kook Kahng Korea University Electronic Information Engineering Phone: +82-41-860-1424 Seoul, Korea Email: kahng@tiger.korea.ac.kr Jung Hoon Cheon Korea University Electronic Information Engineering Phone: +82-41-860-1424 Seoul, Korea Email: grcurly@tiger.korea.ac.kr Korea University [Page14]