Network Working Group T. Melia, Ed. Request for Comments: 5677 Alcatel-Lucent Category: Standards Track G. Bajko Nokia S. Das Telcordia Technologies Inc. N. Golmie NIST JC. Zuniga InterDigital Communications, LLC December 2009 IEEE 802.21 Mobility Services Framework Design (MSFD) Abstract This document describes a mobility services framework design (MSFD) for the IEEE 802.21 Media Independent Handover (MIH) protocol that addresses identified issues associated with the transport of MIH messages. The document also describes mechanisms for Mobility Services (MoS) discovery and transport-layer mechanisms for the reliable delivery of MIH messages. This document does not provide mechanisms for securing the communication between a mobile node (MN) and the Mobility Server. Instead, it is assumed that either lower- layer (e.g., link-layer) security mechanisms or overall system- specific proprietary security solutions are used. Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. IESG Note As described later in this specification, this protocol does not provide security mechanisms. In some deployment situations lower- layer security services may be sufficient. Other situations require proprietary mechanisms or as yet incomplete standard mechanisms, such as the ones currently considered by IEEE. For these reasons, the specification recommends careful analysis before considering any deployment. Melia, et al. Standards Track [Page 1] RFC 5677 MSFD December 2009 The IESG emphasizes the importance of these recommendations. The IESG also notes that this specification deviates from the traditional IETF requirement that support for security in the open Internet environment is a mandatory part of any Standards Track protocol specification. An exception has been made for this specification, but this should not be taken to mean that other future specifications are free from this requirement. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust’s Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License. Melia, et al. Standards Track [Page 2] RFC 5677 MSFD December 2009 Table of Contents 1. Introduction ....................................................4 2. Terminology .....................................................4 2.1. Requirements Language ......................................7 3. Deployment Scenarios ............................................7 3.1. Scenario S1: Home Network MoS ..............................8 3.2. Scenario S2: Visited Network MoS ...........................8 3.3. Scenario S3: Third-Party MoS ...............................9 3.4. Scenario S4: Roaming MoS ...................................9 4. Solution Overview ..............................................10 4.1. Architecture ..............................................11 4.2. MIHF Identifiers (FQDN, NAI) ..............................12 5. MoS Discovery ..................................................12 5.1. MoS Discovery When MN and MoSh Are in the Home Network (Scenario S1) .....................................13 5.2. MoS Discovery When MN and MoSv Both Are in Visited Network (Scenario S2) .....................................14 5.3. MoS Discovery When MIH Services Are in a Third-Party Remote Network (Scenario S3) ..................14 5.4. MoS Discovery When the MN Is in a Visited Network and Services Are at the Home Network (Scenario S4) ........15 6. MIH Transport Options ..........................................15 6.1. MIH Message Size ..........................................16 6.2. MIH Message Rate ..........................................17 6.3. Retransmission ............................................17 6.4. NAT Traversal .............................................18 6.5. General Guidelines ........................................18 7. Operation Flows ................................................19 8. Security Considerations ........................................21 8.1. Security Considerations for MoS Discovery .................21 8.2. Security Considerations for MIH Transport .................21 9. IANA Considerations ............................................22 10. Acknowledgements ..............................................23 11. References ....................................................23 11.1. Normative References .....................................23 11.2. Informative References ...................................23 Melia, et al. Standards Track [Page 3] RFC 5677 MSFD December 2009 1. Introduction This document proposes a solution to the issues identified in the problem statement document [RFC5164] for the layer 3 transport of IEEE 802.21 MIH protocols. The MIH Layer 3 transport problem is divided into two main parts: the discovery of a node that supports specific Mobility Services (MoS) and the transport of the information between a mobile node (MN) and the discovered node. The discovery process is required for the MN to obtain the information needed for MIH protocol communication with a peer node. The information includes the transport address (e.g., the IP address) of the peer node and the types of MoS provided by the peer node. This document lists the major MoS deployment scenarios. It describes the solution architecture, including the MSFD reference model and MIHF identifiers. MoS discovery procedures explain how the MN discovers Mobility Servers in its home network, in a visited network or in a third-party network. The remainder of this document describes the MIH transport architecture, example message flows for several signaling scenarios, and security issues. This document does not provide mechanisms for securing the communication between a mobile node and the Mobility Server. Instead, it is assumed that either lower layer (e.g., link layer) security mechanisms, or overall system-specific proprietary security solutions, are used. The details of such lower layer and/or proprietary mechanisms are beyond the scope of this document. It is RECOMMENDED against using this protocol without careful analysis that these mechanisms meet the desired requirements, and encourages future standardization work in this area. The IEEE 802.21a Task Group has recently started work on MIH security issues that may provide some solution in this area. For further information, please refer to Section 8. 2. Terminology The following acronyms and terminology are used in this document: Media Independent Handover (MIH): the handover support architecture defined by the IEEE 802.21 working group that consists of the MIH Function (MIHF), MIH Network Entities, and MIH protocol messages. Melia, et al. Standards Track [Page 4] RFC 5677 MSFD December 2009 Media Independent Handover Function (MIHF): a switching function that provides handover services including the Event Service (ES), Information Service (IS), and Command Service (CS), through service access points (SAPs) defined by the IEEE 802.21 working group [IEEE80221]. MIHF User: An entity that uses the MIH SAPs to access MIHF services, and which is responsible for initiating and terminating MIH signaling. Media Independent Handover Function Identifier (MIHFID): an identifier required to uniquely identify the MIHF endpoints for delivering mobility services (MoS); it is implemented as either a FQDN or NAI. Mobility Services (MoS): composed of Information Service, Command Service, and Event Service provided by the network to mobile nodes to facilitate handover preparation and handover decision, as described in [IEEE80221] and [RFC5164]. MoSh: Mobility Services provided by the mobile node’s Home Network. MoSv: Mobility Services provided by the Visited Network. MoS3: Mobility Services provided by a third-party network, which is a network that is neither the Home Network nor the current Visited Network. Mobile Node (MN): an Internet device whose location changes, along with its point of connection to the network. Mobility Services Transport Protocol (MSTP): a protocol that is used to deliver MIH protocol messages from an MIHF to other MIH-aware nodes in a network. Information Service (IS): a MoS that originates at the lower or upper layers of the protocol stack and sends information to the local or remote upper or lower layers of the protocol stack. The purpose of IS is to exchange information elements (IEs) relating to various neighboring network information. Event Service (ES): a MoS that originates at a remote MIHF or the lower layers of the local protocol stack and sends information to the local MIHF or local higher layers. The purpose of the ES is to report changes in link status (e.g., Link Going Down messages) and various lower layer events. Melia, et al. Standards Track [Page 5] RFC 5677 MSFD December 2009 Command Service (CS): a MoS that sends commands from the remote MIHF or local upper layers to the remote or local lower layers of the protocol stack to switch links or to get link status. Fully Qualified Domain Name (FQDN): a complete domain name for a host on the Internet, showing (in reverse order) the full delegation path from the DNS root and top-level domain down to the host name (e.g., myexample.example.org). Network Access Identifier (NAI): the user ID that a user submits during network access authentication [RFC4282]. For mobile users, the NAI identifies the user and helps to route the authentication request message. Network Address Translator (NAT): a device that implements the Network Address Translation function described in [RFC3022], in which local or private network layer addresses are mapped to routable (outside the NAT domain) network addresses and port numbers. Dynamic Host Configuration Protocol (DHCP): protocols described in [RFC2131] and [RFC3315] that allow Internet devices to obtain respectively IPv4 and IPv6 addresses, subnet masks, default gateway addresses, and other IP configuration information from DHCP servers. Domain Name System (DNS): a protocol described in [RFC1035] that translates domain names to IP addresses. Authentication, Authorization, and Accounting (AAA): a set of network management services that respectively determine the validity of a user’s ID, determine whether a user is allowed to use network resources, and track users’ use of network resources. Home AAA (AAAh): an AAA server located on the MN’s home network. Visited AAA (AAAv): an AAA server located in a visited network that is not the MN’s home network. MIH Acknowledgement (MIH ACK): an MIH signaling message that an MIHF sends in response to an MIH message from a sending MIHF. Point of Service (PoS): a network-side MIHF instance that exchanges MIH messages with an MN-based MIHF. Melia, et al. Standards Track [Page 6] RFC 5677 MSFD December 2009 Network Access Server (NAS): a server to which an MN initially connects when it is trying to gain a connection to a network and that determines whether the MN is allowed to connect to the NAS’s network. User Datagram Protocol (UDP): a connectionless transport-layer protocol used to send datagrams between a source and a destination at a given port, defined in RFC 768. Transmission Control Protocol (TCP): a stream-oriented transport- layer protocol that provides a reliable delivery service with congestion control, defined in RFC 793. Round-Trip Time (RTT): an estimation of the time required for a segment to travel from a source to a destination and an acknowledgement to return to the source that is used by TCP in connection with timer expirations to determine when a segment is considered lost and should be resent. Maximum Transmission Unit (MTU): the largest size of an IP packet that can be sent on a network segment without requiring fragmentation [RFC1191]. Path MTU (PMTU): the largest size of an IP packet that can be sent on an end-to-end network path without requiring IP fragmentation. Transport Layer Security Protocol (TLS): an application layer protocol that primarily assures privacy and data integrity between two communicating network entities [RFC5246]. Sender Maximum Segment Size (SMSS): size of the largest segment that the sender can transmit as per [RFC5681]. 2.1. 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 [RFC2119]. 3. Deployment Scenarios This section describes the various possible deployment scenarios for the MN and the Mobility Server. The relative positioning of the MN and Mobility Server affects MoS discovery as well as the performance of the MIH signaling service. This document addresses the scenarios listed in [RFC5164] and specifies transport options to carry the MIH protocol over IP. Melia, et al. Standards Track [Page 7] RFC 5677 MSFD December 2009 3.1. Scenario S1: Home Network MoS In this scenario, the MN and the services are located in the home network. We refer to this set of services as MoSh as shown in Figure 1. The MoSh can be located at the access network the MN uses to connect to the home network, or it can be located elsewhere. +--------------+ +====+ | HOME NETWORK | |MoSh| +--------------+ +====+ /\ || \/ +--------+ | MN | +--------+ Figure 1: MoS in the Home Network 3.2. Scenario S2: Visited Network MoS In this scenario, the MN is in the visited network and mobility services are provided by the visited network. We refer to this as MoSv as shown in Figure 2. +--------------+ | HOME NETWORK | +--------------+ /\ || \/ +====+ +-----------------+ |MoSv| | VISITED NETWORK | +====+ +-----------------+ /\ || \/ +--------+ | MN | +--------+ Figure 2: MoSv in the Visited Network Melia, et al. Standards Track [Page 8] RFC 5677 MSFD December 2009 3.3. Scenario S3: Third-Party MoS In this scenario, the MN is in its home network or in a visited network and services are provided by a third-party network. We refer to this situation as MoS3 as shown in Figure 3. (Note that MoS can exist both in home and in visited networks.) +--------------+ | HOME NETWORK | +====+ +--------------+ +--------------+ |MoS3| | THIRD PARTY | <===> /\ +====+ +--------------+ || \/ +-----------------+ | VISITED NETWORK | +-----------------+ /\ || \/ +--------+ | MN | +--------+ Figure 3: MoS from a Third Party 3.4. Scenario S4: Roaming MoS In this scenario, the MN is located in the visited network and all MIH services are provided by the home network, as shown in Figure 4. +====+ +--------------+ |MoSh| | HOME NETWORK | +====+ +--------------+ /\ || \/ +-----------------+ | VISITED NETWORK | +-----------------+ /\ || \/ +--------+ | MN | +--------+ Figure 4: MoS Provided by the Home While in Visited Melia, et al. Standards Track [Page 9] RFC 5677 MSFD December 2009 Different types of MoS can be provided independently of other types and there is no strict relationship between ES, CS, and IS, nor is there a requirement that the entities that provide these services should be co-located. However, while IS tends to involve a large amount of static information, ES and CS are dynamic services and some relationships between them can be expected, e.g., a handover command (CS) could be issued upon reception of a link event (ES). This document does not make any assumption on the location of the MoS (although there might be some preferred configurations), and aims at flexible MSFD to discover different services in different locations to optimize handover performance. MoS discovery is discussed in more detail in Section 5. 4. Solution Overview As mentioned in Section 1, the solution space is being divided into two functional domains: discovery and transport. The following assumptions have been made: o The solution is primarily aimed at supporting IEEE 802.21 MIH services -- namely, Information Service (IS), Event Service (ES), and Command Service (CS). o If the MIHFID is available, FQDN or NAI’s realm is used for mobility service discovery. o The solutions are chosen to cover all possible deployment scenarios as described in Section 3. o MoS discovery can be performed during initial network attachment or at any time thereafter. The MN may know the realm of the Mobility Server to be discovered. The MN may also be pre-configured with the address of the Mobility Server to be used. In case the MN does not know what realm / Mobility Server to query, dynamic assignment methods are described in Section 5. The discovery of the Mobility Server (and the related configuration at MIHF level) is required to bind two MIHF peers (e.g., MN and Mobility Server) with their respective IP addresses. Discovery MUST be executed in the following conditions: o Bootstrapping: upon successful Layer 2 network attachment, the MN MAY be required to use DHCP for address configuration. These procedures can carry the required information for MoS configuration in specific DHCP options. Melia, et al. Standards Track [Page 10]