MIPSHOP E. Hepworth Internet-Draft Siemens Roke Manor Research Expires: December 28, 2006 S. Sreemanthula Nokia S. Faccin Intel Y. Ohba Toshiba June 26, 2006 Media Independent Handovers: Problem Statement draft-hepworth-mipshop-mih-problem-statement-02 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 December 28, 2006. Copyright Notice Copyright (C) The Internet Society (2006). 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 Hepworth, et al. Expires December 28, 2006 [Page 1] Internet-Draft MIH Problem Statement June 2006 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction to IEEE 802.21 . . . . . . . . . . . . . . . . . 4 2.1. Information Services . . . . . . . . . . . . . . . . . . . 4 2.2. Event Services . . . . . . . . . . . . . . . . . . . . . . 4 2.3. Command Services . . . . . . . . . . . . . . . . . . . . . 4 3. Protocol Entities . . . . . . . . . . . . . . . . . . . . . . 5 4. Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 5 4.1. End-to-End Signalling and Transport over IP . . . . . . . 5 4.2. End-to-End Signalling and Partial Transport over IP . . . 6 4.3. End-to-End Signalling with a Proxy . . . . . . . . . . . . 6 5. Solution Components . . . . . . . . . . . . . . . . . . . . . 7 5.1. Payload Formats and Extensibility Considerations . . . . . 8 5.2. Official IEEE 802.21 Requirements for IP-based transport . . . . . . . . . . . . . . . . . . . . . . . . 10 5.3. Other Considerations on the Mobility Service Transport Layer . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5.4. Security Considerations . . . . . . . . . . . . . . . . . 12 5.5. Conclusions and Open Issues . . . . . . . . . . . . . . . 13 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Appendix A. Enabling Event and Command Services . . . . . . . . . 14 A.1. Explicit Signaling for Remote Event/Command Services . . . 14 A.2. Mitigation of Security Issues and Validation of Transported Indications . . . . . . . . . . . . . . . . . 15 A.3. Mapping of Identifiers . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 Intellectual Property and Copyright Statements . . . . . . . . . . 19 Hepworth, et al. Expires December 28, 2006 [Page 2] Internet-Draft MIH Problem Statement June 2006 1. Introduction This Internet Draft provides a problem statement for the exchange of information to support handover in heterogeneous link environments. This mobility support service allows more sophisticated handover operations by making available information about network characteristics, neighbouring 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 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 and Information Exchange mechanism: this includes the information elements or data that describe the information, and any signalling exchanges that are required to support the transfer of this data. IEEE 802.21 WG has undertaken this problem of defining the protocol semantics, data formats in a manner that is independent of transport which carries this information. 2. The Underlying Transport: this supports the above Information Exchange between devices in the network. The requirements on this transfer mechanism include transport issues, because of the volume of data to be sent, as well as discovery and security issues for this transport, as the signalling may cross administrative boundaries and is interdependent with AAA aspects. This draft has been motivated by on-going work within IEEE 802.21, but the following description intentionally describes the problem from a more general perspective. This document represents the views of the IEEE 802.21 WG and presents official requirements for an IP transport to support the Information Exchange discussed above. The structure of this document is as follows. Section 2 provides a brief overview of the mobility handover services as defined in IEEE 802.21. 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 5.4 provides security considerations, and Section 5.5 summarizes the conclusions and open issues. Hepworth, et al. Expires December 28, 2006 [Page 3] Internet-Draft MIH Problem Statement June 2006 2. Introduction to IEEE 802.21 At this time, three broad classes of services for handover assistance, particularly aiming at improving the inter-technology, are under consideration within the IEEE 802.21 Working Group [1]. They require passing of information within hosts, locally and between different hosts, remotely. The services are Information Services (IS), Event Services (ES) and Command Services (CS). 2.1. Information Services Information Services (IS) are one part of handover services used to provide network related information about the current or neighboring networks with same or different access link technology. This allows the network or host to make informed decisions of which network to handover to or handover operations to undertake either in response to certain events, or when planning controlled or commanded handovers. The IS work complementary to the mobility management protocols in the capacity that they are utilized before making decisions for handovers in the aspect of network selection. 2.2. Event Services Event Services (ES) provide indications from one layer or one functionality to another about status changes in the connectivity state. This is particularly relevant to wireless interfaces. It should be noted that the events of one link technology can be carried over current or another link technology. Remote event service is a protocol exchange mechanism between two different network nodes to inform of ES. The event notification can originate either from a mobile node or a node in the network. Receipt and processing of an event belonging to the ES may generate a reaction in the receiving node (e.g. trigger IP layer mobility). 2.3. Command Services Command Services (CS) provide mechanisms for controlling handovers or functions aiding handovers either locally or between two functions. They provide mechanisms to establish, redirect, or remove state in either the network or mobile node, so that handovers occur smoothly. Remote command service is a protocol exchange mechanism between network nodes to instruct the recipient network nodes to execute a specific function. Execution of a command service at the mobile node or a node in the network may result in loss of current link connectivity and/or change in the network point of attachment. Receipt and processing of a command belonging to the CS generates an expected response in the receiving node (e.g. create a new link layer connection, disconnect a link layer connection, etc). Hepworth, et al. Expires December 28, 2006 [Page 4] Internet-Draft MIH Problem Statement June 2006 3. Protocol Entities The following section provides an overview of the network entities that is expected to be involved in the signalling exchanges to support the handover operation. The following abbreviations are used in this section: o MN: mobile node o 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). o EP: endpoint, intended to represent the terminating endpoints of the transport protocol used to support the signalling exchanges between nodes. o MME: A Mobility Management Entity implements network selection and handover decision algorithms and utilizes mobility signaling protocols and other protocols that aid in mobility functions. 4. Deployment Scenarios 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, and are out-of-scope. The following scenarios are discussed for understanding the overall problem of transporting MIH protocol and is not intended to show the scenarios are part of the requirements in the transport design. 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 Hepworth, et al. Expires December 28, 2006 [Page 5] Internet-Draft MIH Problem Statement June 2006 +------+ +------+ | 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 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 4.3. End-to-End Signalling with a Proxy In the final case, a number of proxies are inserted along the path between the two transport endpoints. The use of proxies is possible in both cases 1 and 2 above, but distinguished here as there are a number of options as to how the proxy may behave with regard to the transport and end-to-end signalling exchange. Hepworth, et al. Expires December 28, 2006 [Page 6] Internet-Draft MIH Problem Statement June 2006 In this case, the proxy performs some processing on the Information Exchange before forwarding the information on. This can be viewed as concatenating signalling exchanges between a number of EPs. +------+ +---------+ +------+ | MN | | ProxyNN | | NN | | (EP) | | (EP) | | (EP) | +------+ +---------+ +------+ Information Exchange ------------------> -------------------> <------------------- <------------------ /---------------\ /----------------\ < Transport > < Transport > \---------------/ \----------------/ Figure 3: Information Exchange Approach The Proxy NN processes all layers of the protocol suite in the same way as an ordinary EP. There is a possibility for realizing other proxy scenarios. 5. Solution Components 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). Hepworth, et al. Expires December 28, 2006 [Page 7] Internet-Draft MIH Problem Statement June 2006 +----------------+ ^ |Mobility Support| | | Service 2 | | +----------------+ | (e.g. ES) | | Mobility Service |Mobility Support| +----------------+ | Signaling | Service 1 | +----------------+ | Layer | (e.g. IS) | |Mobility Support| | +----------------+ | Service 3 | | | (other) | | +----------------+ 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 Hepworth, et al. Expires December 28, 2006 [Page 8] Internet-Draft MIH Problem Statement June 2006 The format of the Mobility Service Transport Protocol is as follows: +----------------+----------------------------------------+ |Mobility Service| Opaque Payload | |Transport Header| (Mobility Support Service) | +----------------+----------------------------------------+ Figure 5: Protocol Structure The opaque payload encompasses the Mobility Support Service information that is to be transported. The definition of the Mobility Service Transport Header is something that is best addressed within the IETF. There are a number of issues with regard to the Mobility Support Service header and payload definition. These include: 1. Responsibility for defining the header: where should the contents of the Mobility Support Service header be defined, and should there be one or multiple header definitions (i.e. will a common header definition for all mobility support services be adequate?). Where there are commonalities, it may indicate that these aspects should actually be included in the Mobility Service Transport Header. 2. Payload Format: the format or the Mobility Support Service Data payload could be represented in a number of formats, e.g. TLV, ASN/1, XML or text. Ideally, a single payload representation should be defined, as support for multiple formats leads to unnecessary complexity. It is expected that a set of Data Objects will be defined for the Mobility Support Services to exchange. 3. Sharing of Data Objects: which refers to sharing the definitions of Data Objects between Mobility Support Services, e.g. if a Capabilities object is defined that is used by multiple Mobility Support Services, should the same definition be used by all of them. If this is the case, then a common identifier space is needed to identify the different Data Objects. There is a question about where the definition of Data Objects and the management of the identifier space should take place. The answers to some of the above issues may in part depend on how many standards groups are interested in defining their own Mobility Support Services. Hepworth, et al. Expires December 28, 2006 [Page 9] Internet-Draft MIH Problem Statement June 2006 5.2. Official IEEE 802.21 Requirements for IP-based transport o The transport protocol must work regardless of the network location of the MIH Protocol Entity e.g. on the same subnet, or deep in the network belonging to same or different IP administrative domain. o The transport protocol must be capable to support both IPv4 and IPv6 versions. o The transport protocol must be capable of delivering time- sensitive MIH information. o The transport protocol must enable Network address Translation (NAT) traversal for IPv4 networks. o The transport protocol must enable Firewall pass-through for IPv4 and IPv6 networks. o The discovery protocol must work regardless of the network location of the MIH Protocol Entity e.g. on the same subnet, or deep in the network belonging to same or different IP administrative domain. o The discovery protocol must work for IPv4 and IPv6 hosts. o The discovery protocol must allow for more than one MIH Protocol Entity to be discovered at a time. o The discovery protocol must enable Network Address Translator (NAT) traversal for IPv4 networks. o The discovery protocol must enable Firewall pass-through for IPv4 and IPv6 networks. o The security mechanism must provide a common security association (SA) negotiation method regardless of the network location of the MIH Protocol Entity e.g. on the same subnet, or deep within the network. o The security mechanism must provide mutual authentication of MIH end nodes. o The security mechanism may provide one way authentication of either of MIH end nodes. o The security mechanism must provide integrity protection for MIH Protocol exchanges. Hepworth, et al. Expires December 28, 2006 [Page 10] Internet-Draft MIH Problem Statement June 2006 o The security mechanism may provide confidentiality for the MIH Protocol exchanges. o The security mechanism must protect against replay attacks. o The security mechanism may protect MIH service entities and discovery resources against denial of service o attacks. o The security mechanism must not be dependent on the MIH protocol. o The security mechanism may provide means to reuse or fast reestablishment the SA due to host mobility. 5.3. Other Considerations on the Mobility Service Transport Layer The following section outlines some of other considerations for design of the Mobility Service Transport Protocol. Analysis within IEEE 802.21 has suggested that at least the following need to be taken into account: Congestion Control: A Mobility Service may wish to transfer large amounts of data, placing a requirement for congestion control in the transport. There is an interaction between this requirement and that of the requirement for low latency since ways to deal with timely delivery of smaller asynchronous messages around the larger datagrams is required (mitigation of head of line blocking etc.). Multiplexing: The transport service needs to be able to support different mobility services. This may require multiplexing and the ability to manage multiple discovery operations and peering relationships in parallel. 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. Depending on the IP mobility mechanism, there is some impact on the transport option for the mobility information services. This may potentially have some associated latency and security issues, for example, if the transport is over IP there is some transparency but Mobile IP may introduce additional delay and both TCP and UDP must use the permanent address of the MN. In addition to the above, it may be necessary for the transport to Hepworth, et al. Expires December 28, 2006 [Page 11] Internet-Draft MIH Problem Statement June 2006 support multiple applications (or modes of operation) to support the particular requirements of the Information Exchange being carried out between nodes. This may require the ability to multiplex multiple information exchanges into a single transport exchange. 5.4. Security Considerations Network supported mobility services aim at improving decision making and management of dynamically connected hosts. The control and maintenance of mobile nodes becomes challenging where authentication and authorization credentials used to access a network are unavailable for the purpose of bootstrapping a security association for handover services. Information Services may not require authorization of the client, but both event and command services must 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 operatorXYX.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. Hepworth, et al. Expires December 28, 2006 [Page 12] Internet-Draft MIH Problem Statement June 2006 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 consider at what stage (e.g. discovery, transport layer establishment, service specific protocol exchange) denial of service prevention or mitigation should be built in. 5.5. Conclusions and Open Issues This Internet draft outlined a broad problem statement for the signalling of information elements across a network to support media independent handover 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. 6. Acknowledgements Thanks to Greg Daley and Subir Das for engaging in good discussions. Thanks to Robert Hancock, Andrew McDonald and Jari Arkko for their inputs. Thanks to the IEEE 802.21 chair, Vivek Gupta for coordinating the work and supporting the IETF liaison. 7. References [1] "Draft IEEE Standard for Local and Metropolitan Area Networks: Media Independent Handover Services", IEEE LAN/MAN Draft IEEE P802.21/D01.00, March 2006. [2] Adoba, B., "Architectural Implications of Link Indications Hepworth, et al. Expires December 28, 2006 [Page 13] Internet-Draft MIH Problem Statement June 2006 draft-iab-link-indications-03.txt", June 2005. Appendix A. Enabling Event and Command Services This section analyzes the feasibility of remote events and commands, and describes a set of requirements to enable remote ES and CS. The section discusses some potential solutions to solve some issues typically associated with remote events and explicit signaling. However, such solutions are discussed just to provide example of how drawbacks and limitations identified e.g. in [2] can be overcome. This draft does not propose any specific solutions. [2] contains a set of observations on requirements that solutions need to fulfill to justify and enable transport of events between peer entities over the media (e.g. wireless link). This section addresses these observations in order to assess the feasibility of remote ES and CS. A.1. Explicit Signaling for Remote Event/Command Services [2] indicates that alternatives not requiring explicit signaling are preferred, and that explicit signaling proposals must prove that existing explicit signaling mechanisms are inadequate. Implicit signaling (e.g. path change processing and link-aware routing metrics) has been considered for the scenarios described in this draft. However, implicit signaling may not work in several cases of inter-technology handover. As an example, in certain scenarios the handover is executed but the mobile node does not move between subnets (e.g. in 3GPP networks where the GGSN and the PDG are located in the same subnet). In other scenarios, explicit signaling is required between the mobile node and a network node to report events related to an access link different from the one currently being used by the mobile node (e.g. a mobile node using a 3GPP link detects the availability of a WLAN link). Such events would not be visible to the network node without explicit signaling. Various wireless technologies already have defined mobility management solutions that deploy explicit signaling to support handover (e.g. 3GPP, 3GPP2, IEEE 802.16, etc.), or are at present developing new solutions (e.g. IEEE 802.11 Fast BSS Transition). However, such solutions are clearly defined for intra-technology handover (e.g. 3GPP solutions apply to handover between 3GPP technologies). However, none of these wireless technologies has defined a solution that is applicable to inter-technology handover (e.g. between different IEEE 802 access links, or between a 3GPP access link and an IEEE 802 access link). Hepworth, et al. Expires December 28, 2006 [Page 14] Internet-Draft MIH Problem Statement June 2006 A.2. Mitigation of Security Issues and Validation of Transported Indications The validity of the information delivered through explicit signaling in the Remote Event Service and the Remote Command Service is essential to guarantee that the mobile node or the network node make handover decision and perform handover based on valid conditions. In [2] the issue of validity of the indications is correctly raised, since in a generic model the receiver of the indication (e.g. the mobile node) may not have the ability to verify if the indication has e.g. been sent by a host off the actual path in use, and therefore possibly not capable of providing accurate indications. With the specific model for Remote Event Services and Remote Command Services briefly described in this document and IEEE 802.21 [1], a "relationship" is generated between the mobile node and an MME through a process of discovery and registration. Authentication can be part of such process (possibly mutual authentication), as described in the security considerations. Considering this specific model, information in Remote Event Service and Remote Command Service are generated by a node with which the recipient of the Remote Event Service and Remote Command Service has setup a relationship before hand. It is up to the recipient to ensure during the discovery and registration process that the source of Remote Event Service and Remote Command Service is reputable and can provide accurate information. An example of how this can be achieved is based on authentication mechanisms and the adoption of a trust model similar to those adopted in current networks for authentication of roaming users. The mobile node can authenticate with a home domain/network based on a subscription with such domain/network. If the MME is located e.g. in the home network, the MME can authenticate with the MME based on credentials the mobile node possesses as a result of the subscription. If the MME is e.g. in the visited domain, a transitive trust model can be adopted, where the mobile node authenticates with the home domain/network based on a subscription and through the visited domain. As a result, a security association is established between the mobile node and the MME. A model similar to the one adopted in AAA can be adopted. Hepworth, et al. Expires December 28, 2006 [Page 15] Internet-Draft MIH Problem Statement June 2006 Mobile Node Network |-------------------------------------| |---------| +----------+ +--------+ +--------+ +-------+ | Appl./ | | | | | | | | Transp./ | |MIHF(ES/| | Link | | MME | | Network | | CS) | | Layers | | | | Layers | | | | | | | +----------+ +--------+ +--------+ +-------+ | | | | +---------------------------------+ | | +-----------------+ | | | | Mapping of | | | | |Local Identifiers| | | | +-----------------+ | | +---------------------------------+ | | | | | +--------------------------------------------------------+ | Discovery | +--------------------------------------------------------+ | | | | +--------------------------------------------------------+ | Registration | | +----------------------------------------------------+ | | | Authentication | | | +----------------------------------------------------+ | | | +--------------------------------------------------------+ | | | | | Security Association | |<==============================================>| | | | | | Media Independent Host ID | |<==============================================>| | | | | +----------+ +--------+ +--------+ +-------+ |-------------------------------------| |---------| Legend: ===== shared between Fig.12 Mobile Node - MME Relationship and Mapping of Identifiers. A.3. Mapping of Identifiers [2] raises a legitimate issue regarding the fact that typically the IP layer, the link layer, the transport layer and the application layer use different identifiers, and therefore reporting of information regarding these layers to a remote node may require matching the various identifiers. Hepworth, et al. Expires December 28, 2006 [Page 16] Internet-Draft MIH Problem Statement June 2006 When local event services generate indications within a host (e.g. the mobile node), the host has detailed knowledge of the various identifiers used at the different layers (e.g. the IP address, the MAC addresses for the various IEEE 802 accesses, etc.). As depicted in figure 12, an MIHF located in the mobile node can maintain a local mapping of the various identifiers. When the mobile node discovers and registers with another network node (e.g. an MME), an identifier specific to Remote Event Services and Remote Command Services can be adopted to uniquely identify the mobile node , e.g. a Media Independent Host Identifier. The Media Independent Host Identifier can be e.g. assigned to the mobile node by the home network as part of a set of subscription credentials. The Media Independent Host Identifier could be a new identifier, or an existing identifier could be reused (e.g. NAI). Subsequently, all the remote even notifications and remote command exchanges can be based on the Media Independent Host Identifier, therefore limiting the need to maintain the mapping between different identifiers at different layers local to the host. Hepworth, et al. Expires December 28, 2006 [Page 17] Internet-Draft MIH Problem Statement June 2006 Authors' Addresses Eleanor Hepworth Siemens Roke Manor Research Roke Manor Romsey, SO51 5RE UK Email: eleanor.hepworth@roke.co.uk Srinivas Sreemanthula Nokia 6000 Connection Dr. Irving, TX 75028 USA Email: srinivas.sreemanthula@nokia.com Stefano Faccin Intel 2200 Mission College Blvd Santa Clara, CA 95054 USA Email: stefano.faccin@intel.com Yoshihiro Ohba Toshiba America Research, Inc. 1 Telcordia Drive Piscateway NJ 08854 USA Email: yohba@tari.toshiba.com Hepworth, et al. Expires December 28, 2006 [Page 18] Internet-Draft MIH Problem Statement June 2006 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. Hepworth, et al. Expires December 28, 2006 [Page 19]