Detecting Network Attachment WG S. Aust (editor) INTERNET DRAFT N. A. Fikouras Expires: August 15, 2004 C. Goerg ComNets-IKOM, Uni. Bremen C. Pampu Siemens AG February 15, 2004 Policy Based Mobile IPv6 Handover Decision (POLIMAND) draft-iponair-dna-polimand-01.txt 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. Abstract A handover is the process during which a mobile node is handed over between access routers. Handovers occur as a consequence of lower layer (i. e., link-layer) handovers that signify a switch of the physical connection to a new location. In IP based networks the handover can be performed on IP layer by using MIPv6. For the duration of a Mobile IPv6 handover, a mobile node is unable to send or receive traffic. The length of this disruption is considered critical because it affects the performance of the communication. An additional factor is the access router selection. It implies the selection of the most suitable access router from which a mobile node should receive services. With the help of link layer information it is possible on one side to provide proactive Mobile IPv6 handover decisions and on the other side to select the best access router. This draft describes a method that allows seamless Mobile IPv6 handovers and optimal access router selection based on link layer information. POLIMAND Expires August 2004 1 Table of Contents 1. Introduction....................................................2 2. Conventions used in this document...............................2 3. Terminology.....................................................3 4. Mobile IPv6 Handovers in wireless Networks û Problem Overview...3 5. Reactive/Proactive Mobile IPv6 Handover Decision................6 5.1 Reactive Handover Decision.....................................6 5.2 Proactive Handover Decision....................................7 6. Mobile IPv6 Handovers based on Link Layer Information...........7 7. Mobile IPv6 Handover Enhancements...............................8 7.1 Link Layer Parameters for enhanced Handover Decision...........9 7.2 Handover Decision Enhancement Function.........................9 8. Interaction between enhanced Handover Decision and Mobile IPv6..9 8.1 Control of Router Advertisements..............................10 8.2 Sending Router Solicitations..................................10 8.3 Sending Mobile IPv6 Handover Triggers.........................10 9. Security Considerations........................................10 10. References....................................................10 Authors' Addresses................................................11 Acknowledgements..................................................11 Intellectual Property Statement...................................11 Full Copyright Statement..........................................12 1. Introduction In cellular and wireless networks, Mobile IPv6 handover decision making can benefit from link layer information for the support of seamless roaming which leads to low packet loss during handovers. This draft describes a method that considers the aforementioned link layer information that are indicative of the status of any underlying bearer technology to determine the terms of each handover. Due to the wide range of wireless bearer systems with different characteristics, this draft defines an intermediate layer between Mobile IPv6 and any bearer system. This layer gathers and evaluates information from the various link layers generating hints towards Mobile IPv6. It can monitor the changes of the link layer parameters, determining tendencing or forecasting upcoming changes in link state. Moreover, it can monitor the link characteristic for each of the underlying bearer system separatelly. This leads to effective Mobile IPv6 handover decisions making without the need for major changes in the Mobile IPv6 protocol. 2. Conventions used in this document POLIMAND Expires August 2004 2 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 RFC-2119 [1]. 3. Terminology This document uses the following terms: Domain A collection of networks sharing a common network administration. Home Agent (HA) As defined in [2]. Correspondent Node (CN) As defined in [2]. Mobile Node (MN) As defined in [2]. Neighbor Discovery (ND) As defined in [3]. Neighbor Unreachablility Detection As defined in [3]. Router Advertisement (RA) As defined in [3]. Router Solicitation (RS) As defined in [3]. Multicast As defined in [3]. Router As defined in [4]. Host As defined in [4]. Link As defined in [4]. Address As defined in [4]. Multicast Address As defined in [4]. Stateful/Stateless IPv6 Address Autoconfiguration As described in [4]. 4. Mobile IPv6 Handovers in wireless Networks û Problem Overview Mobile IPv6 handovers in heterogeneous wireless networks are based on movement detection that forces handovers from the previous network to the new network (see fig. 1). Movement detection for Mobile IPv6 is POLIMAND Expires August 2004 3 described in [2] and is used by mobile nodes to detect whether an access router is reachable for data transmission or not. An optimization of movement detection is described in [5] and contains an overview about possible movement detection in Mobile IPv6. Movement detection can be used as a basis for an enhanced handover decision to establish Mobile IPv6 handovers between different networks (see fig. 1) before the previous link breaks. Movement detection which is described in [2] is based on Neighbor Discovery/Neighbor Unreachablility Detection [3] and on router advertisements which are frequently broadcast by the access routers. The following statements have to be considered to determine whether the movement detection in [2] is appropriate for seamless handovers in heterogeneous and overlay networks or not. ôGeneric movement detection uses Neighbor Unreachability Detection to detect when the default router is no longer bi- directional reachable, in which case the mobile node must discover a new default router (usually on a new link). However, this detection only occurs when the mobile node has packets to send, and in the absence of frequent Router Advertisements or indications from the link-layer, the mobile node might become unaware of an L3 handover that occurred. Therefore, the mobile node should supplement this method with other information whenever it is available to the mobile node (e.g., from lower protocol layers).ô [2]. ôRouters generate Router Advertisements frequently enough that hosts will learn of their presence within a few minutes, but not frequently enough to rely on an absence of advertisements to detect router failure; a separate Neighbor Unreachability Detection algorithm provides failure detection.ö [3]. ôThis limitation, however, is not suitable to providing timely movement detection for mobile nodes.ö [2]. In [2] it is described how often the router advertisements have to be broadcast by access routers to support movement detection in heterogeneous networks, so-called unsolicited router advertisements. ôOne method which can provide for faster movement detection is to increase the rate at which unsolicited Router Advertisements are sent. Mobile IPv6 relaxes this limit such that routers may send unsolicited multicast Router Advertisements more frequently. This method can be applied where the router is expecting to provide service to visiting mobile nodes (e.g., wireless network interfaces), or on which it is serving as a home agent to one or more mobile nodes (who may return home and need to hear its Advertisements).Routers supporting mobility should be able to be configured with a smaller MinRtrAdvInterval value and MaxRtrAdvInterval value to allow sending of unsolicited multicast Router Advertisements more often. The minimum allowed values are: MinRtrAdvInterval 0.03 seconds MaxRtrAdvInterval 0.07 seconds.ö [2]. POLIMAND Expires August 2004 4 ôIn the case where the minimum intervals and delays are used, the mean time between unsolicited multicast router advertisements is 50ms.ö [2]. This method can be applied by access routers which expect visiting mobile nodes within their access networks which are roaming between previous networks and new networks. Movement detection which is based on Neighbor Unreachability Detection is not appropriate for seamless mobility due to the fact that the previous link breaks before the handover is performed. This causes too long service disruptions, because the Neighbor Unreachability Detection detects that the link cannot be used for further communication only after the previous link breaks. It has to be understood that all statements in [2] and [3] describe movement detection and neighbor unreachability detection after the previous link breaks. Movement detection considered in this draft is based on router advertisements which are frequently broadcast by access routers (described in [2] as movement detection for mobile nodes). The following describes how the handover decision can be enhanced by using so-called proactive Mobile IPv6 handovers in heterogeneous networks without major changes in the Mobile IPv6 protocol. +-----+ +--+ | | +--+ |CN|------|Inter|------|HA| +--+ | net | +--+ | | +-----+ | | | | previous ---------- ---------- new network | * * | network | * * | +-------+ * * +-------+ | AR(n) | ** |AR(n+1)| +-------+ ** +-------+ . ** . Link(n) . * * . Link(n+1) +--+ * * +--+ |MN| ==*======*=> |MN| +--+ *movement* +--+ AR(n) coverage * * AR(n+1) coverage area * * area * * * * * * * * * * Figure 1: Mobile IPv6 handover scenario from Link(n) to Link (n+1). POLIMAND Expires August 2004 5 5. Reactive/Proactive Mobile IPv6 Handover Decision There are two different handover decisions which have an impact of the packet loss during handovers: reactive and proactive handover decision. The reactive Mobile IPv6 handover allows an active link connection to the previous access router until the previous link breaks. Afterwards it establishes an active link to the new access router. For the proactive Mobile IPv6 handover the mobile node has an active link connection to the new access router before the link breaks and can maintain the previous link even when the handover from the previous access router to the new access router has been established. In that case the handover can be established before the previous link breaks. The proactive handover from one access router to another may be forced by a link layer hint that is based on link layer information about the link conditions. A list of link layer parameters which are available in different bearer systems is given in [6]. In the following the reactive handover decision and the proactive handover decision based on link layer information are described to show the advantages on the proactive handover decision to reduce packet loss during Mobile IPv6 handovers. 5.1 Reactive Handover Decision In fig.2 the mobile node roams between (n) different access networks (see also fig.1). Link(n) is the connection to the router in network(n) and Link(n+1) is the connection to the router in network(n+1). While Link(n) is permanently reliable, Link(n+1) changes its link characteristics (good/bad link layer conditions). After the link conditions have been changed the link breaks (bad conditions). When the previous link has been broken the mobile node starts the stateful/stateless IPv6 address autoconfiguration [4] if it is required. When the address configuration has been successfully finished, the new IPv6 address can be used by the interface of the mobile node for data transmission. The handover duration between the previous link and the new link is named link disruption. Link disruption is the reason for packet loss during handovers between the previous network and the new network. It has to be reduced to minimize packet loss during Mobile IP handovers. Active Link(n) Link(n) |---------------------------------------------------- Active Link(n+1) Link(n+1) broken | Link(n+1) |----------|----------| | Good Bad | Conditions Conditions Lifetime Addr. Link(n) | expires config. active | |--------|-------|------------- | Handover Link | Link(n+1)/Link(n) disruption \|/ |----------------| POLIMAND Expires August 2004 6 Figure 2: Mobile IPv6 handover from Link(n+1) to Link (n) based on a reactive handover scenario. In [7] a reactive handover design is described which is based on link layer hints for Mobile IPv6 handovers after the previous link breaks. It forces an IPv6 address autoconfiguration during Mobile IP handover to the new access router after the previous link has been lost by the mobile node. 5.2 Proactive Handover Decision For the proactive Mobile IPv6 handover decision the mobile node has a link connection to a new network before the link of the previous network breaks. Thus, the proactive handover decision differs from the reactive scenario that has no link connection during the handover. In fig. 3 the characteristic of Link(n+1) has changed and a hint can be used to establish a Mobile IPv6 handover. The hint contains information about the link characteristic and may be used to control Mobile IPv6 handovers. After the hint has been occurred, the router advertisements can be controlled for movement detection of the mobile node. How the router advertisements may be controlled is described in chapter 8 of this draft. The hint should trigger an anticipated IPv6 (stateful/stateless) address configuration [4] if this is required (see fig.3). When the new IPv6 address is available and can be used by the mobile node interface (Link(n+1)), the handover can be established and the new link can be used for data transmission. Active Link(n) Link(n) |---------------------------------------------------- Active Link(n+1) Link(n+1) broken | Link(n+1) |----------|----------| | Good Bad | Conditions|Conditions | | | Link(n+1) Hint |Lifetime Addr. Link(n) | \|/expires config. active | |--------|-------|------------------------ | Hanover Link | Link(n+1)/Link(n) disruption \|/ |-----| Figure 3: Mobile IPv6 handover from Link(n+1) to Link(n) based on a proactive handover scenario. The proactive handover decision reduces link disruption to a minimum because a new link will be established for ongoing data transmission while the previous link is still used. It reduces furthermore the packet loss during handovers and can be used in anticipated handover scenarios. 6. Mobile IPv6 Handovers based on Link Layer Information There are different bearer systems available which provide different link layer information. Different bearer systems like IEEE POLIMAND Expires August 2004 7 802.11a/b/g, hiperLAN2, GSM, GPRS and UMTS are currently available and may be used by Mobile IPv6 networks. These bearer systems use various link layers with different types of link layer information. Different link layer information requires a generic platform which combines link layer information from different link layer systems. However, a list of different link layer parameters from various network systems is required that simplifies the control of Mobile IPv6 handovers between different access domains. Link layer parameters can be divided several classes, e.g. in Link Information, Environment Information, Neighborhood Information, and Link Layer Management Information. 7. Mobile IPv6 Handover Enhancements This draft proposes a so-called ôHandover decision enhancement functionö. It is a proactive Mobile IPv6 handover decision method, which is the basis for zero or less packet loss during vertical handovers in heterogeneous and overlay networks. This method forces Mobile IPv6 handovers before the previous link breaks. This so-called anticipated handover has the advantage that a more suitable link can be used instead of the previous link, which may not provide adequate link conditions. It minimizes packet loss and provides seamless and reliable link connectivity of the mobile node. This method provides a uniform interface for a range of heterogeneous bearer systems for the interaction with Mobile IPv6. It should interact with Mobile IPv6 and indicates when and how a Mobile IPv6 handover should occur. It may be able to even force a handover. The control Mobile IPv6 handovers based on link layer information is handled by an enhanced handover decision. It uses link layer information to decide if there is a handover required from the previous network to a new network (handover decision). Fig. 4 shows the control of Mobile IPv6 handovers based on link layer information. +---------------------+ | OSI Layer 4-7 | +---------------------+ | Network Layer (MIP) | +---------------------+ /|\ | +---------------------+ | Handover decision | |enhancement function | +---------------------+ /|\ | +---------------------+ | Data Link Layer | +---------------------+ | Physical Layer | +---------------------+ POLIMAND Expires August 2004 8 Figure 4: Interaction between the handover decision enhancement function and network layer to control Mobile IPv6 handovers based on link layer information. The handover decision enhancement function establishes Mobile IPv6 handovers from the previous network to the new network when the link characteristic is no longer adequate for data transmission. Thus, a decision is required when the handover has to be forced. The decision should be based on a combination of different link layer information to control Mobile IPv6 handovers. +--------------------------------------+ | Network Layer | +--------------------------------------+ |Handover decision enhancement function| +------------+------------+------------+ |802.11 a/b/g| GSM/GPRS | 3G | | Ad hoc | | UMTS | +------------+------------+------------+ Figure 5: Interaction of the handover decision enhancement function between link layer and network layer with respect of current bearer access systems. The handover decision enhancement function should consider the functionality of hierarchical Mobile IP approaches (Hierarchical Mobile IPv6) that is described in [8] and fast Mobile IP handovers (Fast Mobile IPv6) that is described in [9]. HMIPv6 and FMIPv6 may use an enhanced handover decision to reduce link disruption and to minimize packet loss during vertical handovers in heterogeneous and overlay networks. 7.1 Link Layer Parameters for enhanced Handover Decision Different link layer parameters [6] can be used for an enhanced handover decision to determine Mobile IPv6 handovers between different bearer systems. The following link layer information should be helpful to decide when a handover has to be established. TBD 7.2 Handover Decision Enhancement Function TBD 8. Interaction between enhanced Handover Decision and Mobile IPv6 The handover decision enhancement function uses link layer information to define when a Mobile IPv6 handover has to be established. There are three different approaches: - Control of router advertisements - Sending router solicitations - Sending triggers for Mobile IP handoffs POLIMAND Expires August 2004 9 8.1 Control of Router Advertisements Router advertisements are needed for movement detection of the mobile node. Movement detection and its various algorithms are described in [10]. When a mobile node does not detect router advertisements of the network where it is currently attached, the mobile node forces a handover to a new network which sends unknown router advertisements. This is mainly based on receiving router advertisements for movement detection, especially for Lazy Cell Switching (LCS) and Eager Cell Switching (ECS) which are also described in [10]. The handover decision enhancement function may control router advertisements of the previous link. The control of router advertisements may forces the mobile node to establish a handover from the previous network to the new network due to the fact that router advertisements of the previous network are no longer visible. 8.2 Sending Router Solicitations TBD 8.3 Sending Mobile IPv6 Handover Triggers TBD 9. Security Considerations The implementation of the enhanced handover decision should guarantee that all link layer information which have to be considered by the handover decision are generated by the link layer of the mobile node. 10. References [1] S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. RFC 2119, IETF, March 1997. [2] D. Johnson, C. Perkins, J. Arkko. Mobility Support in IP6. Internet Draft (work in progress), July 2003. [3] T. Narten, E. Nordmark, W. Simpson. Neighbor Discovery for IP Version 6 (IPv6). RFC 2461, December 1998. [4] S. Thomson, T. Narten. IPv6 Stateless Address Autoconfiguration. RFC 2462, December 1998. [5] G. Daley, J. Choi. Movement Detection Optimization in Mobile IPv6. Internet Draft (work in progress), May 2003. [6] P. Bertin, T. Noel, N. Montavont. Parameters for Link Hints. Internet Draft (work in progress), August 2003. [7] S. D. Park, E. Njedjou, N. Montavont. L2 Triggers Optimized Mobile IPv6 Vertical Handover. Internet Draft (work in progress), January 2004. [8] H. Soliman, C. Castelluccia, K. El-Malki, L. Bellier. Hierarchical Mobile IPv6 Mobility Management (HMIPv6). Internet Draft (work in progress), June 2003. [9] R. Koodli. Fast Handovers for Mobile IPv6. Internet Draft (work in progress), October 2003. [10] N. A. Fikouras, C. G÷rg. A Complete Comparison of Algorithms for Mobile IP Hand-offs with Complex Movement Patterns and Internet POLIMAND Expires August 2004 10 Audio. In the proceedings of WPMC 2001, Aalborg, Denmark, September 2001 [11] J. Kempf, M. M. Khalil, B. Pentland. IPv6 Fast Router Advertisement. Internet Draft (work in progress), October 2003. Authors' Addresses Stefan Aust Department of Communication Networks (ComNets) Center for Information and Communication Technology (ikom) University of Bremen Phone: +49-421-218-8264 D-28219 Bremen, Germany Email: aust@comnets.uni-bremen.de Niko A. Fikouras Department of Communication Networks (ComNets) Center for Information and Communication Technology (ikom) University of Bremen Phone: +49-421-218-3339 D-28219 Bremen, Germany Email: niko@comnets.uni-bremen.de Carmelita Goerg Department of Communication Networks (ComNets) Center for Information and Communication Technology (ikom) University of Bremen Phone: +49-421-218-2277 28219, Bremen, Germany Email: cg@comnets.uni-bremen.de Cornel Pampu Siemens AG ICM N PG SP RC PN Siemensdamm 62 D-13623 Berlin Phone: +49-30-386-20265 Germany Email: Cornel.Pampu@siemens.com Acknowledgements This work was done within the framework of the IPonAir project which is partly funded by the German Ministry of Education and Research (BMB+F), http://www.iponair.de Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property 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; neither does it represent that it has made any effort to identify an such rights. Information on the IETFÆs procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication 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 Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice POLIMAND Expires August 2004 11 this standard. Please address the information to the IETF Executive Director. Full Copyright Statement Copyright (C) The Internet Society (2004). All Rights Reserved. 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