No Specific Working Group T. Ernst Internet-Draft WIDE at Keio University Expires: January 17, 2005 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 July 19, 2004 Goals and Benefits of Multihoming draft-ernst-generic-goals-and-benefits-00 Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. 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 January 17, 2005. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Ernst, et al. Expires January 17, 2005 [Page 1] Internet-Draft Goals and Benefits of Multihoming July 2004 Abstract This document attempts to define the goals and benefits of 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. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Classification and Resulting Issues . . . . . . . . . . . . . 8 5.1 Case 1: One Interface, Multiple Prefixes . . . . . . . . . 8 5.2 Case 2: Several Interfaces . . . . . . . . . . . . . . . . 10 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13 Intellectual Property and Copyright Statements . . . . . . . . 16 Ernst, et al. Expires January 17, 2005 [Page 2] Internet-Draft Goals and Benefits of Multihoming July 2004 1. Introduction New equipments shipped on the market now often integrate several access technologies (both wired and wireless). 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) as no single technology can be expected to be deployed everywhere. Flows may thus need to be redirected from one interface to the other due to the loss of connectivity or change of the network conditions. Several access technologies are also integrated 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 demonstrate 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. The readers should note that we implicitly assumed multihoming in an IPv6 enviroment when describing the goals and benefits, though some of them may be applicable to IPv4 as well. Issues pertaining to site multihoming in fixed networks are discussed in [3]. Mobility issues pertaining to mobile nodes and mobile networks are respectively discussed in companion drafts [7] and [6]. The readers may refer to [8] for a description of the problem specific to Mobile IPv4. This document is organized as follows: we first define the terms used in the document before emphasizing the goals and benefits of multihoming. Then, we describe some real-life scenarios to illustrate 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 and we conclude with the description of possible configurations at the network layer. 2. Terminology This draft is based on the terminology defined in [2]. For the purpose of clarity, we remind the definition of interface. Terms related to multihoming are not known to be defined in existing IETF Ernst, et al. Expires January 17, 2005 [Page 3] Internet-Draft Goals and Benefits of Multihoming July 2004 RFCs. Interface (from [2]) A node's point of attachment to a link. 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 either: multi-prefixed: multiple prefixes are advertised on the link(s) the node is attached to, or. 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 from the benefits of multihoming, but there are several situations where it is either advisable or beneficial to be multihomed: Permanent and Ubiquitous Access To provide an extended coverage area via distinct access technologies. 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 system component 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. Ernst, et al. Expires January 17, 2005 [Page 4] Internet-Draft Goals and Benefits of Multihoming July 2004 Load Sharing: To spread network traffic load among several routes. This is achieved when traffic load is distributed among different connections between the node and the Internet [5]. Load Balancing: To balance load between multiple point of attachments (simultaneously active or not), usually chosing the less loaded connection or according to preferences on the mapping between flows and interfaces. Bi-casting (n-casting): To duplicate a particular flow simultaneously through different routes. This minimizes packet loss typically for real-time communication and burst traffic. It also minimizes delay of packet delivery caused by congestion 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. Increased Bandwidth To provide the user or the application with more bandwidth than is available with any one interface. Multiple interfaces connected to different links can increase the total availble bandwith. 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 between interfaces does not cause the disruption of on-going sessions. 4. Scenarios The following real-life scenarios highlight the benefits of multihoming. Each scenario usually yields more than one of the benefits outlined in the above section. All scenarios focus on wireless technologies though no mobility management may be involved (one can use wireless access at office). Ernst, et al. Expires January 17, 2005 [Page 5] Internet-Draft Goals and Benefits of Multihoming July 2004 The first scenario focuses on using two wireless interfaces for the purpose of increasing bandwidth while the 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, Increased Bandwidth (no mobility) 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 network (WLAN) 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 WLAN 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 WLAN interface. Alice decides to use this additional WLAN interface to connect to another access point, and distribute the different download flows between the wireless interfaces to accelerate the download. Scenario 2: Preference Settings and Transparent Flow Handoffs (with mobility) Mr. Smith is on his way to work waiting at a train station. He uses this opportunity and the presence of a WLAN 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 the WLAN link provided by the hot-spot. This transfer occurs transparently and without affecting any other active flows. Scenario 3: Preference Settings for House Networking (fixed) Mr. Verne 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 has noticed the 802.11b is unreliable at some point in time during the day, so he chooses to send requests and Ernst, et al. Expires January 17, 2005 [Page 6] Internet-Draft Goals and Benefits of Multihoming July 2004 periodic refreshments for joining the TV broadcasting via ADSL rather the 802.11b although 802.11b in the street is free. 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 a picture is periodically refreshed over ADSL. Scenario 4: Load Balancing, Preference Settings, Increased Bandwidth (no mobility) 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 WLAN 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 (with mobility) Jules drives his car to a new place and constantly keeps some sort of Internet access through one access technology. His car navigator downloads road information from the Internet and his car-audio plays on-line audio streaming. When his car passes an area where both high-data-rate WLAN and low-data-rate cellular network are available, it distributes load to the WLAN access and the cellular network access. When his car passes an area where only a wide coverage-range cellular network is available, it maintains its connection via the cellular network. Ernst, et al. Expires January 17, 2005 [Page 7] Internet-Draft Goals and Benefits of Multihoming July 2004 Scenario 6: Redundancy and Bi-Casting (with no mobility) Dr. Catherine performs an operation via long-distance medical system. She watches a patient in a battle field over the screen which delivers real-time images 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 images and Catherine's action is done by bi-casting from/to multiple interfaces. So in case one of the interface fails, the long-distance operation can be continued. 5. Classification and Resulting Issues 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. 5.1 Case 1: One Interface, Multiple Prefixes The single-interfaced node is multihomed when several prefixes are advertised on its interface. The node must therefore configure several IPv6 addresses. The node has to choose which address to use when an IPv6 communication is established (e.g. open a TCP connection). This choice can be influenced by many parameters: user preference, different price on prefixes, preference flag in Router Advertisement, destination prefix, etc. An address selection mechanism is needed. A typical example 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 Advertisements 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. The node will then build two global IPv6 addresses on its interface. This multihomed configuration may yield different issues / benefits to the node. We now analyse the benefits and the process needed on this node: o Ubiquitous Access Ubiquitous access cannot be guaranteed when the node looses Ernst, et al. Expires January 17, 2005 [Page 8] Internet-Draft Goals and Benefits of Multihoming July 2004 Internet connectivity through its sole interface (e.g. the node is going outside the coverage area of its access point). o 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 be achieved since on-going sessions using the invalid address would have to be terminated, and restarted using the new address. To avoid this, the node needs a recovery mechanism allowing to redirect 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. o Load sharing Load Sharing can be performed in the network, according to the address used by the node. The choice of the address used by the node and the router selection can be influenced by the load sharing rules. 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. o Load balancing As the node has only one interface, load balancing (share traffic between node's interface) cannot be performed. o Bi-casting Bi-casting can be performed to ensure the delivery of packets on the node. To do so, more than one IPv6 address must be used simultaneously for one flow. Although packets can not be distributed to different interfaces on the node, bi-casting would allow the node to seamlessly change the address used on the node if such a protocol is used to change address of on-going flow. Time synchronization can be an issue in this case. If we use different access technologies or routes for each casting, the round trip time (RTT) can differ from casting to casting. Thus the receiver will receive the same contents in different time. o Preference The source address can be chosen according to preferences set up by the user, or according to preferences set up in the network Ernst, et al. Expires January 17, 2005 [Page 9] Internet-Draft Goals and Benefits of Multihoming July 2004 (such as with the default router preferences option introduced in Router Advertisement [4], or by the ISP. o Increased Bandwidth With only one interface connected to a link, the node generally will not be able to enjoy increased bandwidth with multiple prefixes. However, this benefit might be gained indirectly. For instance, by alternating between different addresses, the total throughput may be higher (eg. due to load sharing). Also, some web and file transfer servers limit transfer bandwidths based on the client's address. By using different addresses to connect to the same server, the node may also see an increase in file transfer rate. 5.2 Case 2: Several Interfaces The node may use its multiple interfaces either alternatively or simultaneously. If it alternatively uses its interfaces, the node is either multihomed if multiple prefixes are advertised on its current link (case 1, one interface), or not multihomed if only one prefix is advertised on its current link. We will thus consider that the node uses multiple interfaces simultaneously. The node must thus configure at least one IPv6 address per interface (or several addresses per interface if several prefixes are announced on the link(s) it is connected to). Also, multiple interfaces can be connected to the same link as well as to different links. These configurations will imply different issues. An address selection mechanism is also needed, but this time the interface on which the address is bound to will be a supplementary parameter in the address selection. The different characteristics of each interface may help to decide first which interface to use. A typical example is a node with two interfaces, each one on a different technology (e.g. a WLAN IEEE 802.11b interface and a 3GPP GPRS interface), in order to benefit from a better coverage area (ubiquitous access) and the capacity and specification of each technology. This multihomed configuration may yield different benefits to the node. We now analyse the benefits and the process needed on this node: o Ubiquitous Access It is easier to guarantee ubiquitous access when the node has Ernst, et al. Expires January 17, 2005 [Page 10] Internet-Draft Goals and Benefits of Multihoming July 2004 multiple interfaces since several technologies may be available at the same time. However, the node must be able to use all technologies at the same time and to maintain Internet connectivity while a technology can not be used. It is obvious that the node must have the choice to use any of the available technologies, and that this choice must not prevent the node to redirect a communication to another interface/address. o Redundancy Two levels of redundancy can be seen in this case: either one address of one interface is not valid anymore (e.g. because the corresponding prefix is not advertised on the link), or the node can lose its internet connectivity through one interface. In the former case, the fact that another IPv6 address is available on the interface would allow the node to switch addresses for on-going flows. In the latter case, the fact that the node has another connection to the internet through another interface would allow it to redirect on-going flow from the previous interface to the new one. Either case, the node needs to change the IPv6 address for on-going session from the no longer valid address to one of the address available on the target interface. The redirection will trigger a decision process to choose the best target interface to redirect the flow. In both cases, transparency of the addressses switching is an important issue. Loss of a prefix: If the node loses one of its prefix, it can no longer use the corresponding address anymore. So the node needs a recovery mechanism that allows it to transfer all current communications to one of its other IPv6 address(es). The time needed for the detection of the prefix failure and the time to redirect communications to one of its other addresses may be critical. Interface failure: If one of the used interface breaks down (loss of network connection or 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 communications, it will need to redirect the flows to its new point of attachment, whatever the old address used for the flow. The scalability of the redirection can also be considered here. Ernst, et al. Expires January 17, 2005 [Page 11] Internet-Draft Goals and Benefits of Multihoming July 2004 o Load Sharing This benefit is mainly for the network side: if different access routers or routes can be used to forward traffic going into and out of the node, they can share the traffic load on the network. If the node uses several addresses at the same time for its on-going sessions, load sharing can be performed in the network. This goal can be a parameter that helps the source address selection. o Load balancing Load balancing can be achieved on the node if several interfaces are used simultaneously. Several interfaces can be used to spread the traffic load on the node. This implies the choice of the IPv6 address to use for each flow and the ability to choose a different addresss for each flow. o Bi-casting Bi-casting might be used to ensure the packets delivery on the node. It also allow seamless redirection between two addresses / interfaces with zero packets loss. Bi-casting can be performed if several IPv6 addresses can be simultaneously used for one flow. One entity between the CN (included) and the node (excluded) must duplicate the traffic to the destination node. o 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 supplementary parameter in the address selection algorithm. o Increased Bandwidth With multiple interface connected to a link, the node generally will be able to enjoy increased bandwidth. 6. Acknowledgments 7 References [1] Malki, K. and H. Soliman, "Simultaneous Bindings for Mobile IPv6 Ernst, et al. Expires January 17, 2005 [Page 12] Internet-Draft Goals and Benefits of Multihoming July 2004 Fast Handovers", draft-elmalki-mobileip-bicasting-v6-05 (work in progress), November 2003. [2] Manner, J. and M. Kojo, "Mobility Related Terminology", RFC 3753, June 2004. [3] Abley, J., Black, B. and V. Gill, "Goals for IPv6 Site-Multihoming Architectures", RFC 3582, August 2003. [4] Draves, R. and D. Thaler, "Default Router Preferences and More-Specific Routes", draft-ietf-ipv6-router-selection-04 (work in progress), June 2004. [5] Hinden, R., "IPv6 Host to Router Load Sharing", draft-ietf-ipv6-host-load-sharing-02 (work in progress), May 2004. [6] Ng, C., Paik, E. and T. Ernst, "Analysis of Multihoming in Network Mobility Support", draft-ietf-nemo-multihoming-issues-00 (work in progress), July 2004. [7] Montavont, N., Wakikawa, R. and T. Ernst, "Analysis of Multihoming in Mobile IPv6", draft-montavont-mobileip-multihoming-pb-statement-01 (work in progress), Feb 2004. [8] Fikouras, N., "Mobile IPv4 Flow Mobility Problem Statement", draft-nomad-mip4-flow-mobility-pb-00.txt (work in progress), Feb 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/ Ernst, et al. Expires January 17, 2005 [Page 13] Internet-Draft Goals and Benefits of Multihoming July 2004 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/ Paik, Eun Kyoung Seoul National University Multimedia and Mobile 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 Ernst, et al. Expires January 17, 2005 [Page 14] Internet-Draft Goals and Benefits of Multihoming July 2004 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. Expires January 17, 2005 [Page 15] Internet-Draft Goals and Benefits of Multihoming July 2004 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. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Ernst, et al. Expires January 17, 2005 [Page 16]