No Specific Working Group T. Ernst Internet-Draft WIDE at Keio University Expires: August 9, 2004 N. Montavont LSIIT - ULP R. Wakikawa Keio University E. Paik Seoul National University C. Ng Panasonic Singapore Labs K. Kuladinithi University of Bremen T. Noel LSIIT - ULP February 9, 2004 Goals and Benefits of Multihoming draft-multihoming-generic-goals-and-benefits-00 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 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 9, 2004. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document attempts to define the goals and benefits of Ernst, et al. Expires August 9, 2004 [Page 1] Internet-Draft Goals and Benefits of Multihoming February 2004 multihoming for fixed and mobile hosts and routers. Those goals and benefits are illustrated with a set of real-life scenarios. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Goals and Benefits of Multihoming . . . . . . . . . . . . . . 4 4. Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Configurations . . . . . . . . . . . . . . . . . . . . . . . . 9 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 12 Intellectual Property and Copyright Statements . . . . . . . . 15 Ernst, et al. Expires August 9, 2004 [Page 2] Internet-Draft Goals and Benefits of Multihoming February 2004 1. Introduction New equipments shipped on the market now often integrate several wireless technologies. The main purpose of this integration is to federate all means of communications in order to access the Internet ubiquitously (from everywhere and at any time) since a permanent Internet connectivity is now required by some applications. Unfortunately, there is no network interfaces assuring global scale connectivity. Nodes must thus use various type of network interfaces to obtain wide area network connectivity [8]. New equipments also integrate several access technologies in order to increase bandwidth availability or to select the technology the most appropriate according to the type of flow or choices of the user. Basically, each network interface has different cost, performance, bandwidth, access range, and reliability. Users should thus be able to select the most appropriate set of network interface(s) depending on the network environment, particularly in wireless networks which are mutable and less reliable than wired networks. Users should also be able to select the most appropriate interface per communication type or to combine a set of interfaces to get sufficient bandwidth. The purpose of this document is to show real-life scenarios in order to illustrate the goals and benefits of multihoming for fixed and mobile hosts and routers in a generic fashion, i.e. without focusing on issues pertaining to hosts, or routers, or mobility. Specific mobility issues pertaining to mobile nodes and mobile networks are discussed in companion drafts [6], [5] and [7]. This document is organized as follows: we first define the terms used in the document before emphasizing the goals and benefits of multihoming. Next follows a differentiation between cases where a multihomed node has a single interface and the cases where it has multiple interfaces. Then, we describe some real-life scenarios to illustrate the goals and benefits of multihoming and we conclude with the description of possible configurations at the network layer. 2. Terminology In this section we define terms related to multihoming: Interface (from [2]) A node's attachment to a link Ernst, et al. Expires August 9, 2004 [Page 3] Internet-Draft Goals and Benefits of Multihoming February 2004 Multihomed Node A node (either a host or a router) is multihomed when it has several IPv6 addresses to choose between, i.e. in the following cases when it is: multi-prefixed: multiple prefixes are advertised on the link(s) the node is attached to. multi-interfaced: the node has multiple interfaces to choose between, on the same link or not. Multihomed Network From the above definition, it follows that a network is multihomed when either the network is simultaneously connected to the Internet via more than one router, or when a router is multi-prefixed or multi-interfaced. 3. Goals and Benefits of Multihoming We cannot distinguish the goals of multihoming from the benefits of being multihomed, but we can identify several situations where it is either advisable or beneficial to be multihomed: Ubiquitous Access: To provide an extended coverage area. Multiple interfaces bound to distinct technologies can be used to ensure a permanent connectivity is offered. Redundancy/Fault-Recovery: To act upon failure of one point of attachment, i.e. the functions of a network are assumed by secondary system components when the primary component becomes unavailable (e.g. failure). Connectivity is guaranteed as long as at least one connection to the Internet is maintained. Load Sharing: To spread network traffic load among several routes. This is achieved when traffic load is distributed simultaneously among different connections between the node and the Internet [4]. Ernst, et al. Expires August 9, 2004 [Page 4] Internet-Draft Goals and Benefits of Multihoming February 2004 Load Balancing: To balance load between multiple point of attachments (simultaneously active or not), usually chosing the lest loaded connection. Bi-casting: Bi-casting (n-casting) duplicates a particular flow for simultaneous transmission through different routes. It minimizes packet loss typically for real-time communication and burst traffic. It also minimizes delay of packet delivery caused by congestions and achieves more reliable real-time communication than single-casting. For mobile computing, bi-casting is useful not to drop packets when a mobile node changes its interface during communication [1]. Preference Settings: To provide the user or the application or the ISP the ability to choose the preferred transmission technology or access network for matters of cost, efficiency, politics, bandwidth requirement, delay, etc. When considering these goals/benefits, one has to consider whether these goals can be achieved with transparency or without transparency. Transparency is achieved when switching to a different point of attachment does not cause on-going sessions to break. For instance, ubiquity with transparency is achieved when switching between two different access mechanism does not cause on-going sessions to be disrupted. In order to achieve transparency, a necessary (may or may not be sufficient) condition is for the end-point addresses to remain unchanged. This is in-view of the large amount of Internet traffic today are carried by TCP, which unlike SCTP, cannot handle multiple end-point address pairs. 4. Cases From the definition of a multihomed node it follows that a multihomed node has several IPv6 addresses to choose between. In order to expose the goals and benefits to manage multihomed nodes, we propose to distinguish two main cases: either the node has only one interface, or the node has several interfaces. A rough analysis of these two cases is detailed below. Ernst, et al. Expires August 9, 2004 [Page 5] Internet-Draft Goals and Benefits of Multihoming February 2004 Case 1: One Interface The node has one interface. It is multihomed when several prefixes are advertised on its interface. The node must therefore configure several IPv6 addresses. An address selection mechanism is needed. This multihomed configuration may yield the following benefits for the node: * Load sharing can be performed in the network * Redundancy: In case of failure of one IPv6 prefix, one of the address of the node will not be valid anymore. The fact that the node has another address built with other prefixes should allow it to recover this sort of failure, however transparency may not achieved since on-going sessions using the invalid address would have to be terminated, and restarted using the new address. It is also to be noted that all sessions on the node will be disrupted if all prefixes fail to be announced (e.g. all were announced by the same router and this router broke down). * Preference: the source address can be chosen according to preferences set up by the user, or according to preferences set up in the network (such as with the default router preferences option introduced in Router Advertisement [3], or by ISP. Case 2: Several Interfaces The node has more than one interface. The node must therefore configure several IPv6 addresses (one on each interface). An address selection mechanism is needed. This multihomed configuration may yield the following benefits for the node: * Load balancing: between the interfaces * Redundancy: another interface can be used if one fails * Ubiquity: it is more likely to have access to another technology if a technology cannot be used * Preferences: interface and address selection is required. The problem can be seen exactly as in the first case (the node has only one interface) if we consider that the interface preference is a parameter for the address selection. Therefore in this case, the interface selection/preference is a Ernst, et al. Expires August 9, 2004 [Page 6] Internet-Draft Goals and Benefits of Multihoming February 2004 supplementary parameter in the address selection algorithm. 5. Scenarios The following scenarios highlight the usage of several interfaces and the benefit of such configuration. Each scenario usually yields more than one benefit. The first scenario focuses on using two wireless interfaces for the purpose of balancing the load while second shows the usage of preference settings. The third is a combination of the first two. The fourth and fifth illustrate how multiple connections can provide ubiquitous Internet access and how load can be balanced according to some preferences. The last one illustrates redundancy and bi-casting. Scenario 1: Load Balancing Alice is at the airport waiting to board the plane. She receives a call from her husband. This audio communication is received via a wireless local area link realized over one of the available hot-spots. She knows this is going to be a long flight and wishes to catch up on some work. Alice uses a wireless LAN connection to download the necessary data. However, there is not enough time and Alice decides to accelerate the download. Her notebook is equipped with an additional wireless local area network interface. Alice decides to distribute the different download flows between the wireless interfaces to accelerate the download. Scenario 2: Preference Settings and Transparent Flow Handoffs Mr. Smith is on his way to work waiting at a train station. He uses this opportunity and the presence of a wireless LAN hot-spot to download the news from his favorite on-line news channel. His train is announced. Mr. Smith decides to buy a ticket. However, the ticket reservation service is only available via a wide area cellular link of a specific provider. While Mr. Smith is downloading the news and accessing the train ticket reservation service, he receives a phone call over a wide area cellular link. Mr. Smith decides he wishes to initiate a video flow for this communication. The bandwidth and traversal delay of the wide area cellular link is not adequate for the video conference, so both flows (video/audio) are transferred to a wireless local area link via a hot-spot. This transfer occurs transparently and without affecting any other active flows. Scenario 3: Preference Settings for House Networking Ernst, et al. Expires August 9, 2004 [Page 7] Internet-Draft Goals and Benefits of Multihoming February 2004 Mr. Vernes works at home for a publishing company. He has an in-house network and get access to the Internet via ADSL, a public 802.11b WLAN from the street and satellite. The satellite link he has access to is only downward but is extremely cheap for TV broadcasting. He chooses to send requests for joining the TV broadcasting via ADSL rather the 802.11b although 802.11b in the street is free. He has noticed the 802.11b is unreliable at some point in time during the day. On the other hand, he has configured his network to use the 802.11b link at night to publish web content comprising video. Once a week, he communicate with overseas peer staff by videoconferencing. Voice being the most important, he has configured his VoIP session over ADSL. Video is sent at maximum rate when 802.11b is working fine, otherwise one picture every 5 sec over ADSL. Scenario 4: Ubiquitous Access, Load Balancing, Preference Setting An ambulance is called at the scene of a car accident. A paramedic initiates a communication to a hospital via a wide area cellular link for the relay of low bit-rate live video from the site of the crash to assess the severity of the accident. It is identified that one of the passengers has suffered a severe head injury. The paramedic decides to consult a specialist via video conferencing. This session is initiated from the specialist via the same wide area cellular link. Meanwhile, the paramedic requests for the download of the patient medical records from the hospital servers. The paramedic decides in mid-session that the wide area cellular link is too slow for this download and transfers the download to the ambulance satellite link. Even though this link provides a significantly faster bit rate it has a longer traversal delay and only down-link is available. For this, only the down-stream of the download is transferred while up-stream proceeds over the wide area cellular link. Connectivity with the ambulance is managed over a wireless local area link between the paramedic and the ambulance. Even though the paramedic has performed a partial hand-off for the transfer of the download down-stream to the satellite link, the upstream and the video conferencing session remains on the wide area cellular link. This serves best the time constraint requirements of the real time communication. Scenario 5: Ubiquitous Access and Load Sharing Jules drives his car to a new place and constantly keeps some sort of Internet access through one the access technology. His car navigator downloads road information from the internet and his car-audio serves on-line audio streaming. When his car passes an area where both high-data-rate WLAN and low-data-rate cellular network available, it distributes load to WLAN and cellular Ernst, et al. Expires August 9, 2004 [Page 8] Internet-Draft Goals and Benefits of Multihoming February 2004 connection. When his car passes an area where only wide-coverage-range cellular network is available, it maintains its connection via the cellular network. When Bob passes an area where even cellular networks can not be reached, he can switch to the expensive satellite network with multiple interfaces that his car support. Scenario 6: Redundancy and Bi-Casting Catherine performs an operation via long-distance medical system. She watches a patient in a battle field over the screen which delivers real-time image of the patient. Sensors on her arms deliver her operational action and a robot performs her operation in the battle field. Since the operation is critical, the delivery of patient image and Catherine's action is done by bi-casting from/to multiple interface. So in case of one of the interface failed, Catherine can continue her long-distance operation. 6. Configurations This section details the possible network configurations that are considered important. Possible configurations may involve either a fixed host, a mobile host, a fixed router or a mobile router. Case 1: One Interface A typical case of this scenario is a node with an IEEE 802.11 interface, connected to an access point. The access point is connected trough an Ethernet link to two access routers. Each access router is configured to send Router Advertisement on the link and can be used as default router. Several reasons may lead to the fact that two access routers are on the same link: for instance, the access points may be shared between different ISPs, or two access routers may be used for redundancy or load sharing purposes. In that case, the node will build two global IPv6 addresses on its interface. When the node establishes an IPv6 communication (e.g. open a TCP connection), it has to choose which address to use. This choice can be influenced by many parameters: user preference, different price on prefixes, preference flag in Router Advertisement, destination prefix... The critical points that can be highlighted here are the following: * Choice of the router: each access router the node is be Ernst, et al. Expires August 9, 2004 [Page 9] Internet-Draft Goals and Benefits of Multihoming February 2004 connected to might have different capacity. As an example, if the node is inside a mobile network and is connected to two mobile routers, each mobile router may implement different technology on their egress interface. This would have a strong impact on the node traffic. * Load Sharing: This benefit is mainly for the network side: if different access routers or routes can be used to forward the node traffic, it will share the traffic load on the network. * Lost of a prefix: If the node looses one of its prefix, it can not use the corresponding address anymore. So the node needs a recovery mechanism allowing to remove all current communication to one of its other IPv6 address. The time needed for the detection of the prefix failure and the time to redirect communications to one of its other addresses is considered as critical. * Mobility of the node: If the node moves to a new point of attachment in another subnet, it will need to change its IPv6 addresses. In order to maintain all its previous communication, it will need to redirect the flows to its new location, whatever the old address used for the flow. The scalability of the redirection can also be considered here. Case 2: Multiple Interfaces The typical case of this scenario is a node that has two interfaces, each on a different technology, in order to benefit a better coverage area (ubiquitous access) and the capacity and specification of each technology. Such an example is to have a WLAN interface (e.g. IEEE 802.11b) and a 3GPP interface (e.g. GPRS). In this case, the node may use its two interfaces either alternatively or simultaneously. If it alternatively uses its two interfaces, the node falls into case one (multiple prefixes and one interface) and is multihomed or the node is not multihomed. In the following, we thus consider that the node simultaneously uses its two interfaces. In this case, the node will have one or several addresses per interface according to the number of prefixes announced on the link(s) it is connected to. Also, the two interfaces can be connected to the same link as well as to different link. When considering such a multihoming management, it might imply different issues. Once more this node will have to make a choice between its different addresses, but the interface on which the address is bound to will be a supplementary parameter in the address selection. The different characteristics of each interface Ernst, et al. Expires August 9, 2004 [Page 10] Internet-Draft Goals and Benefits of Multihoming February 2004 may help to decide first which interface to use. The critical points that can be highlighted here are the following: * Choice of the router: each access router the node is be connected to might have different capacity. As an example, if the node is inside a mobile network and is connected to two mobile routers, each mobile router may implement different technology on their egress interface. This would have a strong impact on the node traffic. * Load Balancing: As the node has several available interfaces at the same time, it is interesting to simultaneously use them for different flows. To do so, the node must be able to choose a different interface for each new communication (through the address selection). * Load Sharing: This benefit is mainly for the network side: if different access routers or routes can be used to forward the node traffic, it will share the traffic load on the network. * Lost of a prefix: If the node looses one of its prefix, it can not use the corresponding address anymore. So the node needs a recovery mechanism allowing to remove all current communication to one of its other IPv6 address. The time needed for the detection of the prefix failure and the time to redirect communications to one of its other addresses is considered as critical. * Interface failure: If one of the used interface breaks down (lost of network connection of access router is not reachable anymore), the node must be able to redirect all its flows from that interface to one of the alive interface. The time needed to discover the failure and to redirect each flow has to be considered. The scalability of such a solution is also an issue. * Mobility of the node: If the node moves to a new point of attachment in another subnet, it will need to change its IPv6 addresses. In order to maintain all its previous communication, it will need to redirect the flows to its new localization, whatever the old address used for the flow. The scalability of the redirection can also be considered here. Ernst, et al. Expires August 9, 2004 [Page 11] Internet-Draft Goals and Benefits of Multihoming February 2004 7. Acknowledgments References [1] Elmalki, K. and H. Soliman, "Simultaneous Bindings for Mobile IPv6 Fast Handovers", draft-elmalki-mobileip-bicasting-v6-05.txt (work in progress), October 2003. [2] Manner, J. and M. Kojo, "Mobility Related Terminology", draft-ietf-seamoby-terminology-04 (work in progress), April 2003. [3] Draves, R. and D. Thaler, "Default Router Preferences, More-Specific Routes, and Load Sharing", draft-ietf-ipv6-router-selection-03 (work in progress), December 2003. [4] Hinden, R. and D. Thaler, "IPv6 Host to Router Load Sharing", draft-ietf-ipv6-host-load-sharing-01 (work in progress), January 2004. [5] Ng, C., "Multihoming Issues in Network Mobility Support", draft-xxx-nemo-multihoming-00 (work in progress), Feb 2004. [6] Montavont, N., "Analysis of Multihoming in Mobile IPv6", draft-xxx-nemo-multihoming-00 (work in progress), Feb 2004. [7] Fikouras, N., "Mobile IPv4 Flow Mobility", draft-nomad-mip4-flow-mobility-problem-statement-00.txt (work in progress), Feb 2004. [8] Stemm, M. and R. Katz, "Vertical Handoffs in Wireless Overlay Networks", Journal Mobile Networks and Applications, vol. 3, number 4, pages 335-350, 1998. Ernst, et al. Expires August 9, 2004 [Page 12] Internet-Draft Goals and Benefits of Multihoming February 2004 Authors' Addresses Ernst Thierry WIDE at Keio University Jun Murai Lab., Keio University. K-square Town Campus, 1488-8 Ogura, Saiwa-Ku Kawasaki, Kanagawa 212-0054 Japan Phone: +81-44-580-1600 Fax: +81-44-580-1437 EMail: ernst@sfc.wide.ad.jp URI: http://www.sfc.wide.ad.jp/~ernst/ Nicolas Montavont LSIIT - Univerity Louis Pasteur Pole API, bureau C444 Boulevard Sebastien Brant Illkirch 67400 FRANCE Phone: (33) 3 90 24 45 87 EMail: montavont@dpt-info.u-strasbg.fr URI: http://www-r2.u-strasbg.fr/~montavont/ Wakikawa Ryuji Keio University Jun Murai Lab., Keio University. 5322 Endo Fujisawa, Kanagawa 252-8520 Japan Phone: +81-466-49-1100 Fax: +81-466-49-1395 EMail: ryuji@sfc.wide.ad.jp URI: http://www.mobileip.jp/ Ernst, et al. Expires August 9, 2004 [Page 13] Internet-Draft Goals and Benefits of Multihoming February 2004 Paik, Eun Kyoung Seoul National University Multimedia Communications Lab., Seoul National Univ. Shillim-dong, Kwanak-gu Seoul 151-744 Korea Phone: +82-2-880-1832 Fax: +82-2-872-2045 EMail: eun@mmlab.snu.ac.kr URI: http://mmlab.snu.ac.kr/~eun/ Chan-Wah Ng Panasonic Singapore Laboratories Pte Ltd Blk 1022 Tai Seng Ave #06-3530 Tai Seng Industrial Estate Singapore 534415 SG Phone: +65 65505420 EMail: cwng@psl.com.sg Koojana Kuladinithi University of Bremen ComNets-ikom,University of Bremen. Otto-Hahn-Allee NW 1 Bremen, Bremen 28359 Germany Phone: +49-421-218-8264 Fax: +49-421-218-3601 EMail: koo@comnets.uni-bremen.de URI: http://www.comnets.uni-bremen.de/~koo/ Thomas Noel LSIIT - Univerity Louis Pasteur Pole API, bureau C444 Boulevard Sebastien Brant Illkirch 67400 FRANCE Phone: (33) 3 90 24 45 92 EMail: noel@dpt-info.u-strasbg.fr URI: http://www-r2.u-strasbg.fr/~noel/ Ernst, et al. 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