MIPSHOP T. Melia Internet-Draft NEC Intended status: Informational E. Hepworth Expires: May 15, 2008 Siemens Roke Manor Research S. Sreemanthula Nokia Research Center Y. Ohba Toshiba G. Vivek Intel J. Korhonen TeliaSonera R. Aguiar IT S. Xia HUAWEI November 12, 2007 Mobility Services Transport: Problem Statement draft-ietf-mipshop-mis-ps-04 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 15, 2008. Copyright Notice Melia, et al. Expires May 15, 2008 [Page 1] Internet-Draft Mobility Services Transport November 2007 Copyright (C) The IETF Trust (2007). Abstract There are on-going activities in the networking community to develop solutions that aid in IP handover mechanisms between heterogeneous wired and wireless access systems including, but not limited to, IEEE 802.21. Intelligent access selection, taking into account link layer attributes, requires the delivery of a variety of different information types to the terminal from different sources within the network and vice-versa. The protocol requirements for this signalling have both transport and security issues that must be considered. The signalling must not be constrained to specific link types, so there is at least a common component to the signalling problem which is within the scope of the IETF. This draft presents a problem statement for this core problem. Requirements Language 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 [2] Melia, et al. Expires May 15, 2008 [Page 2] Internet-Draft Mobility Services Transport November 2007 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Definition of Mobility Services . . . . . . . . . . . . . . . 5 4. Deployment Scenarios for MoS . . . . . . . . . . . . . . . . . 5 4.1. End-to-End Signalling and Transport over IP . . . . . . . 6 4.2. End-to-End Signalling and Partial Transport over IP . . . 6 4.3. End-to-End Network-to-Network Signalling . . . . . . . . . 7 5. MoS Transport Protocol Splitting . . . . . . . . . . . . . . . 7 5.1. Payload Formats and Extensibility Considerations . . . . . 8 5.2. Requirements on the Mobility Service Transport Layer . . . 9 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 8. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 13 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 10.1. Normative References . . . . . . . . . . . . . . . . . . . 13 10.2. Informative References . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . . . . 17 Melia, et al. Expires May 15, 2008 [Page 3] Internet-Draft Mobility Services Transport November 2007 1. Introduction This Internet Draft provides a problem statement for the exchange of information to support handover in heterogeneous link environments [1] . This mobility support service allows more sophisticated handover operations by making available information about network characteristics, neighboring networks and associated characteristics, indications that a handover should take place, and suggestions for suitable target networks to which to handover. The mobility support services work complementarily with IP mobility mechanisms [4], [5], [6], [7], [8], [9] to enhance the overall performance and usability perception. There are two key attributes to the handover support service problem for inter-technology handovers: 1. The Information: the information elements being exchanged. The messages could be of different nature, such as information, commands to perform an action, or events informing of a change, potentially being defined following a common structure. 2. The Underlying Transport: the transport mechanism to support exchange of the information elements mentioned above. This transport mechanism includes information transport, discovery of peers, and the securing of this information over the network. The initial requirement for this protocol comes from the need to provide a transport for the Media Independent Handover (MIH) protocol being defined by IEEE 802.21[1] which is not bound to any specific link layer and can operate over more that one network-layer hop. The solution should be flexible to accommodate evolution in the MIH standard, and should also be applicable for other new mobility signalling protocols which have similar message patterns and discovery and transport requirements. The structure of this document is as follows. Section 3 defines mobility services. Section 4 provides a simple model for the protocol entities involved in the signalling and their possible relationships. Section 5 describes a decomposition of the signalling problem into service specific parts and a generic transport part. Section 5.2 describes more detailed requirements for the transport component. Section 7 provides security considerations, and Section 8 summarizes the conclusions and open issues. 2. Terminology The following abbreviations are used in the document: Melia, et al. Expires May 15, 2008 [Page 4] Internet-Draft Mobility Services Transport November 2007 MIH: media independent handover MN: mobile node NN: network node, intended to represent some device in the network (the location of the node e.g. in the access network, home network is not specified, and for the moment it is assumed that they can reside anywhere). EP: endpoint, intended to represent the terminating endpoints of the transport protocol used to support the signalling exchanges between nodes. 3. Definition of Mobility Services As mentioned in the introduction mobility (handover) support in heterogeneous wireless environments requires functional components located either in the mobile terminal or in the network to exchange information and eventually to take decisions upon this information exchange. For instance traditional host-based handover solutions could be complemented with more sophisticated network-centric solutions. Also, neighborhood discovery, potentially a complex operation in heterogeneous wireless scenarios, can result in a simpler step if implemented with an unified interface towards the access network. In this document the different supporting functions for media independent handover (MIH) management are generally referred as Mobility Services (MoS) having different requirements for the transport protocol. These requirements and associated functionalities are the focus of this document. Speaking 802.21 terminology MoS can be reagarded as Infomation Services (IS), Event Services (ES), Command Service (CS). 4. Deployment Scenarios for MoS The deployment scenarios are outlined in the following sections. Note: while MN-to-MN signalling exchanges are theoretically possible, these are not currently being considered. The following scenarios are discussed for understanding the overall problem of transporting MIH protocol. Although these are all possible scenarios and MIH services can be delivered through link- layer specific solutions and/or through a "layer 3 or above" protocol, this problem statement focuses on the delivery of information for mobility services for the latter case only. Melia, et al. Expires May 15, 2008 [Page 5] Internet-Draft Mobility Services Transport November 2007 4.1. End-to-End Signalling and Transport over IP In this case, the end-to-end signalling used to exchange the handover information elements (the Information Exchange) runs end-to-end between MN and NN. The underlying transport is also end-to-end +------+ +------+ | MN | | NN | | (EP) | | (EP) | +------+ +------+ Information Exchange <------------------------------------> /------------------------------------\ < Transport over IP > \------------------------------------/ Figure 1: End-to-end Signalling and Transport 4.2. End-to-End Signalling and Partial Transport over IP As before, the Information Exchange runs end-to-end between the MN and the second NN. However, in this scenario, some other transport means than IP is used from the MN to the first NN, and the transport over IP is used only between NNs. This is analogous to the use of EAP end-to-end between Supplicant and Authentication Server, with an upper-layer multihop protocol such as RADIUS used as a backhaul transport protocol between an Access Point and the Authentication Server. +------+ +------+ +------+ | MN | | NN | | NN | | | | (EP) | | (EP) | +------+ +------+ +------+ Information Exchange <------------------------------------> (Transport over /------------------\ <--------------->< Transport over IP > e.g. L2) \------------------/ Figure 2: Partial Transport Melia, et al. Expires May 15, 2008 [Page 6] Internet-Draft Mobility Services Transport November 2007 4.3. End-to-End Network-to-Network Signalling In this case NN to NN signalling is envisioned. Such model should allow different network components to gather information from each other. This is useful for instance in conditions where network components need to take decisions and instruct mobile terminals of operation to be executed. +------+ +------+ | NN | | NN | | (EP) | | (EP) | +------+ +------+ Information Exchange -------------------> <------------------- /----------------\ < Transport > \----------------/ Figure 3: Information Exchange between different NN Network nodes exchange information about connected terminals status. 5. MoS Transport Protocol Splitting Figure 4 shows a model where the Information Exchanges are implemented by a signalling protocol specific to a particular mobility service, and these are relayed over a generic transport layer (the Mobility Service Transport Layer). Melia, et al. Expires May 15, 2008 [Page 7] Internet-Draft Mobility Services Transport November 2007 +----------------+ ^ |Mobility Support| | | Service 2 | | +----------------+ | | | Mobility Service |Mobility Support| +----------------+ | Signaling | Service 1 | +----------------+ | Layer | | |Mobility Support| | +----------------+ | Service 3 | | | | | +----------------+ V ================================================ +---------------------------------------+ ^ Mobility Service | Mobility Service Transport Protocol | | Transport +---------------------------------------+ V Layer ================================================ +---------------------------------------+ | IP | +---------------------------------------+ Figure 4: Handover Services over IP The Mobility Service Transport Layer provides certain functionality (outlined in Section 5.2) to the higher layer mobility support services in order to support the exchange of information between communicating mobility service functions. The transport layer effectively provides a container capability to mobility support services, as well as any required transport and security operations required to provide communication without regard to the protocol semantics and data carried in the specific mobility services. The Mobility Support Services themselves may also define certain protocol exchanges to support the exchange of service specific Information Elements. It is likely that the responsibility for defining the contents and significance of the Information Elements is the responsibility of other standards bodies other than the IETF. Example mobility services include the Information Services, Event and Command services. 5.1. Payload Formats and Extensibility Considerations Melia, et al. Expires May 15, 2008 [Page 8] Internet-Draft Mobility Services Transport November 2007 The format of the Mobility Service Transport Protocol (MSTP) is as follows: +----------------+----------------------------------------+ |Mobility Service| Opaque Payload | |Transport Header| (Mobility Support Service) | +----------------+----------------------------------------+ Figure 5: Protocol Structure The opaque payload encompasses the Mobility Support Service (MSTP) information that is to be transported. The definition of the Mobility Service Transport Header is something that is best addressed within the IETF. MSTP does not inspect the payload and any required information will be provided by the MSTP users. 5.2. Requirements on the Mobility Service Transport Layer The following section outlines some of the general transport requirements that should be supported by the Mobility Service Transport Protocol. Analysis has suggested that at least the following need to be taken into account: Discovery: MNs need the ability to either discover nodes that support certain services, or discover services provided by a certain node. The service discovery can be dealt with messages as defined in [1]. This section refers to node-discovery in either scenario. There are no assumptions about the location of these mobility services node within the network, therefore the discovery mechanism needs to operate across administrative boundaries. Issues such as speed of discovery, protection against spoofing, when discovery needs to take place, and the length of time over which the discovery information may remain valid all need to be considered. Approaches include: * Hard coding information into the MN, indicating either the IP address of the NN, or information about the NN that can be resolved onto an IP address. The configuration information could be managed dynamically, but assumes that the NN is independent of the access network to which the MN is currently attached. * Pushing information to the MN, where the information is delivered to the MN as part of other configuration operations, for example, via DHCP or Router Discovery exchange. The benefit of this approach is that no additional exchanges with the network would be required, but the limitations associated with modifying these protocols may limit applicability of the Melia, et al. Expires May 15, 2008 [Page 9] Internet-Draft Mobility Services Transport November 2007 solution. * MN dynamically requesting information about a node, which may require both MN and NN support for a particular service discovery mechanism. This may require additional support by the access network (e.g. multicast or anycast) even when it may not be supporting the service directly itself. Numerous directory and configuration services already exist, and reuse of these mechanisms may be appropriate. There is an open question about whether multiple methods of discovery would be needed, and whether NNs would also need to discover other NNs. The definition of a service also needs to be determined, including the granularity of the description. For example IEEE 802.21 specifies three different type of Mobility services (Indormation Services, Command Services and Event Services) that can be located in different portion of the network. A MN could therefore run a discovery procedure of any service running in the (home or visited) network or could run a discovery procedure for a specific service. Information from a trusted source: The MN uses the Mobility Service information to make decisions about what steps to take next. It is essential that there is some way to ensure that the information received is from a trustworthy source. This requirement should reuse trust relationships that have already been established in the network, for example, on the relationships established by the AAA infrastructure after a mutual authentication, or on the certificate infrastructure required to support SEND [10]. Section 7 provides a more complete analysis. Security association management: A common security association negotiation method, independent of any specific MSTP user, should be implemented. The solution must also work in case on MN mobility. Secure delivery: The Mobility Service information must be delivered securely (integrity and confidentiality) between trusted peers, where the transport may pass though untrusted intermediate nodes and networks. The Mobility Service information should also be protected against replay attacks and denial of service attacks. Low latency: Some of the Mobility Services generate time sensitive information. Therefore, there is a need to deliver the information over quite short timescales, and the required lifetime of a connection might be quite short lived. For reliable delivery, short-lived connections could be set up as and when needed, although there is a connection setup latency associated Melia, et al. Expires May 15, 2008 [Page 10] Internet-Draft Mobility Services Transport November 2007 with this approach. Alternatively, a long-lived connection could be used, but this requires advanced warning of being needed and some way to maintain the state associated with the connection. It also assumes that the relationships between devices supporting the mobility service are fairly stable. Another alternative is connectionless operation, but this has interactions with other requirements such as reliable delivery. Reliability: Reliable delivery for some of the mobility services may be essential, but it is difficult to trade this off against the low latency requirement. It is also quite difficult to design a robust, high performance mechanism that can operate in heterogeneous environments, especially one where the link characteristics can vary quite dramatically. There are two main approaches that could be adopted: 1. Assume the transport cannot be guaranteed to support reliable delivery. In this case, the Mobility Support Service itself will have to provide a reliability mechanism (at MIH level) to allow communicating endpoints to acknowledge receipt of information. 2. Assume the underlying transport will provide reliable delivery. There is no need in this case to provide reliability at MIH level. Congestion Control: A Mobility Service may wish to transfer small or large amounts of data, placing different requirements for congestion control in the transport. The solution should consider different congestion control mechanisms depending on the amount of data generated by the application (MIH) as suggested in [3] Multihoming: For some information services exchanged with the MN, there is a possibility that the request and response messages can be carried over two different links e.g. a handover command request is on the current link while the response could be delivered on the new link. It is expected that the transport protocol is capable of receiving information via multiple links and to combine information beloning to the same session/ transaction. When mobility is applied the undelaying IP mobility mechanism should provide session continuty when required. IPv4 and IPv6 support: The MSTP must support both IPv4 and IPv6 including NAT traversal for IPv4 networks and firewall pass- through for IPv4 and IPv6 networks. Melia, et al. Expires May 15, 2008 [Page 11] Internet-Draft Mobility Services Transport November 2007 6. IANA Considerations This document makes no request of IANA. 7. Security Considerations Network supported mobility services aim at improving decision making and management of dynamically connected hosts. Information Services may not require authorization of the client, but both event and command services may authenticate message sources, particularly if they are mobile. Network side service entities will typically need to provide proof of authority to serve visiting devices. Where signalling or radio operations can result from received messages, significant disruption may result from processing bogus or modified messages. The effect of processing bogus messages depends largely upon the content of the message payload, which is handled by the handover services application. Regardless of the variation in effect, message delivery mechanisms need to provide protection against tampering, and spoofing. Sensitive and identifying information about a mobile device may be exchanged during handover service message exchange. Since handover decisions are to be made based upon message exchanges, it may be possible to trace an user's movement between cells, or predict future movements, by inspecting handover service messages. In order to prevent such tracking, message confidentiality should be available. This is particularly important since many mobile devices are associated with only one user, as divulgence of such information may violate the user's privacy. Additionally, identifying information may be exchanged during security association construction. As this information may be used to trace users across cell boundaries, identity protection should be available if possible, when establishing SAs. In addition, the user should not have to disclose its identity to the network (any more than it needed to during authentication) in order to access the Mobility Support Services. For example, if the local network is just aware that an anonymous user with a subscription to "example.com" is accessing the network, the user should not have to divulge their true identity in order to access the Mobility Support Services available locally. Finally, the network nodes themselves will potentially be subject to denial of service attacks from MNs and these problems will be exacerbated if operation of the mobility service protocols imposes a heavy computational load on the NNs. The overall design has to Melia, et al. Expires May 15, 2008 [Page 12] Internet-Draft Mobility Services Transport November 2007 consider at what stage (e.g. discovery, transport layer establishment, service specific protocol exchange) denial of service prevention or mitigation should be built in. 8. Conclusions This Internet draft outlined a broad problem statement for the signalling of information elements across a network to support mobility services. In order to enable this type of signalling service, a need for a generic transport solution with certain transport and security properties were outlined. Whilst the motivation for considering this problem has come from work within IEEE 802.21, a desirable goal is to ensure that solutions to this problem are applicable to a wider range of mobility services. It would be valuable to establish realistic performance goals for the solution to this common problem (i.e. transport and security aspects) using experience from previous IETF work in this area and knowledge about feasible deployment scenarios. This information could then be used as an input to other standards bodies in assisting them to design mobility services with feasible performance requirements. Much of the functionality required for this problem is available from existing IETF protocols or combination thereof. This document takes no position on whether an existing protocol can be adapted for the solution or whether new protocol development is required. In either case, we believe that the appropriate skills for development of protocols in this area lie in the IETF. 9. Acknowledgements Thanks to Subir Das, Juan Carlos Zuniga, Robert Hancock and Yoshihiro Ohba for their inputs. Thanks to the IEEE 802.21 chair Vivek Gupta for coordinating the work and supporting the IETF liaison. Thanks to all IEEE 802.21 WG folks who indirectly contributed to this document. 10. References 10.1. Normative References [1] "Draft IEEE Standard for Local and Metropolitan Area Networks: Media Independent Handover Services", IEEE LAN/MAN Draft IEEE P802.21/D07.00, July 2007. [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Melia, et al. Expires May 15, 2008 [Page 13] Internet-Draft Mobility Services Transport November 2007 Levels", RFC 2119, March 2007. 10.2. Informative References [3] Eggert, L. and G. Fairhurst, "UDP Usage Guidelines for Application Designers", draft-ietf-tsvwg-udp-guidelines-03 (work in progress), September 2007. [4] 3GPP, "3GPP system architecture evolution (SAE): Report on technical options and conclusions", 3GPP TR 23.882 0.10.1, February 2006. [5] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, August 2002. [6] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. [7] Moskowitz, R. and P. Nikander, "Host Identity Protocol (HIP) Architecture", RFC 4423, May 2006. [8] Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)", RFC 4555, June 2006. [9] Koodli, R., "Fast Handovers for Mobile IPv6", RFC 4068, July 2005. [10] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005. Authors' Addresses Telemaco Melia NEC Europe Network Laboratories Kufuerstenanlage 36 Heidelberg 69115 Germany Phone: +49 6221 90511 42 Email: telemaco.melia@netlab.nec.de Melia, et al. Expires May 15, 2008 [Page 14] Internet-Draft Mobility Services Transport November 2007 Eleanor Hepworth Siemens Roke Manor Research Roke Manor Romsey, SO51 5RE UK Email: eleanor.hepworth@roke.co.uk Srivinas Sreemanthula Nokia Research Center 6000 Connection Dr. Irving, TX 75028 USA Email: srinivas.sreemanthula@nokia.com Yoshihiro Ohba Toshiba America Research, Inc. 1 Telcordia Drive Piscateway NJ 08854 USA Email: yohba@tari.toshiba.com Vivek Gupta Intel Corporation 2111 NE 25th Avenue Hillsboro, OR 97124 USA Phone: +1 503 712 1754 Email: vivek.g.gupta@intel.com Jouni Korhonen TeliaSonera Corporation. P.O.Box 970 FIN-00051 Sonera FINLAND Phone: +358 40 534 4455 Email: jouni.korhonen@teliasonera.com Melia, et al. Expires May 15, 2008 [Page 15] Internet-Draft Mobility Services Transport November 2007 Rui L.A. Aguiar Instituto de Telecomunicacoes Universidade de Aveiro Aveiro 3810 Portugal Phone: +351 234 377900 Email: ruilaa@det.ua.pt Sam(Zhongqi) Xia Huawei Technologies Co.,Ltd HuaWei Bld., No.3 Xinxi Rd. Shang-Di Information Industry Base 100085 Hai-Dian District Beijing, P.R. China Phone: +86-10-82836136 Email: xiazhongqi@huawei.com Melia, et al. Expires May 15, 2008 [Page 16] Internet-Draft Mobility Services Transport November 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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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. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Melia, et al. Expires May 15, 2008 [Page 17]