RFC 5164
Mobility Services Transport: Problem Statement
RFC 5164: Mobility Services Transport: Problem Statement 🎀
Okay bestie, the title block first 🦋. This one is by T. Melia, Ed. from Cisco Systems, it came out in March 2008, and it's in the Informational category, so it's giving "here's some info" and not a standard 💅. It was published through the Network Working Group, and its header has no Obsoletes or Updates line, so it doesn't replace or change any other RFC ✨.
Status of This Memo ✨
Okay so this memo is just information for the Internet community 🫶. It does not specify an Internet standard of any kind, and distribution of it is unlimited 🌈.
Abstract 🦋
Okay the networking community is literally obsessed with building solutions that help with IP handover between heterogeneous wired and wireless access systems 🔥. IEEE 802.21 is one of them, but it's not the only one 💅. Intelligent access selection takes link-layer attributes into account, and that means a bunch of different information types need to get delivered to the terminal from different sources in 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's at least one common piece of the signalling problem that's squarely in IETF territory 🫶. This document presents a problem statement for that core problem 💖.
Table of Contents 🌸
1. Introduction ....................................................2
2. Terminology .....................................................3
2.1. Requirements Language ......................................3
3. Definition of Mobility Services .................................4
4. Deployment Scenarios for MoS ....................................4
4.1. End-to-End Signalling and Transport over IP ................5
4.2. End-to-End Signalling and Partial Transport over IP ........5
4.3. End-to-End Network-to-Network Signalling ...................6
5. MoS Transport Protocol Splitting ................................7
5.1. Payload Formats and Extensibility Considerations ...........8
5.2. Requirements on the Mobility Service Transport Layer .......8
6. Security Considerations ........................................11
7. Conclusions ....................................................12
8. Acknowledgements ...............................................13
9. References .....................................................13
9.1. Normative References ......................................13
9.2. Informative References ....................................13
Contributors ......................................................141. Introduction ✨
Okay so this document is a problem statement for exchanging information to support handover in heterogeneous link environments 🦋 [1]. This mobility support service makes more sophisticated handover operations possible by making information available about network characteristics, neighboring networks and their characteristics, indications that a handover should take place, and suggestions for suitable target networks to hand over to 💅. The mobility support services are complementary to 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 🎀:
- The Information: the information elements being exchanged. The messages could be of a different nature, such as information, commands to perform an action, or events informing of a change, potentially being defined following a common structure.
- 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] 🧚. It's not bound to any specific link layer, and it can operate over more that one network-layer hop 🌈. The solution should be flexible to accommodate evolution in the MIH standard 🫶, and it should also be applicable for other new mobility signalling protocols that 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 6 provides security considerations. Section 7 summarizes the conclusions and open issues 👑.
2. Terminology 🌸
Okay so these are the abbreviations used in the document 💅:
- 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, the 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.
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 [2] 💜.
3. Definition of Mobility Services 🧚
As mentioned in the Introduction, mobility (handover) support in heterogeneous wireless environments needs functional components, either in the mobile terminal or in the network, to exchange information and eventually make decisions based on that exchange 💖. For instance, traditional host-based handover solutions could be complemented with more sophisticated network-centric solutions 🔥. Also, neighborhood discovery, which can be a complex operation in heterogeneous wireless scenarios, can become a simpler step if it's implemented with a unified interface towards the access network 🫶.
In this document, the different supporting functions for Media Independent Handover (MIH) management are generally referred to as Mobility Services (MoS), which have different requirements for the transport protocol 🎀. These requirements and their associated functionalities are the focus of this document ✨. Speaking 802.21 terminology, MoS can be regarded as Information Services (IS), Event Services (ES), and 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 so you can understand the overall problem of transporting the 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 delivering information for Mobility Services only for the latter case 💅.
4.1. End-to-End Signalling and Transport over IP 💖
Okay so 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 🌸
Same vibe as before: the Information Exchange runs end-to-end between the MN and the second NN 🦋. However, in this scenario, some transport other than IP is used from the MN to the first NN, and transport over IP is only used 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 Remote Authentication Dial-In User Service (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 Network-to-Network Signalling 🍓
In this case, NN-to-NN signalling is envisioned 🌈. This model should allow different network components to gather information from each other 💜. It's useful, for instance, in conditions where network components need to make decisions and instruct mobile terminals about operations to be executed 👑.
+------+ +------+
| NN | | NN |
| (EP) | | (EP) |
+------+ +------+
Information Exchange
------------------->
<-------------------
/----------------\
< Transport >
\----------------/Figure 3: Information Exchange between Different NNs
Network nodes exchange information about the status of connected terminals 🫶.
5. MoS Transport Protocol Splitting ✨
okay so this section is about splitting things up, and bestie, the layering is so clean 🧚 Figure 4 shows a model where each Information Exchange is handled by a signalling protocol that's specific to one mobility service. Those messages then get relayed over a generic transport layer, which is called the Mobility Service Transport Layer.
+----------------+ ^
|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 IPThe Mobility Service Transport Layer gives the higher-layer mobility support services certain functionality (outlined in Section 5.2) so they can swap information between the communicating Mobility Service functions 💌 It's basically a container capability. It also handles any required transport and security operations needed for the communication, and it doesn't care about the protocol semantics or the data inside the specific Mobility Services. Main character energy for the transport layer, honestly 💅
The Mobility Support Services can also define their own protocol exchanges for sending service-specific information elements. Ngl, the meaning and significance of those information elements will probably be handled by standards bodies other than the IETF 🙈 Some example Mobility Services are the Information Services, Event Services, and Command Services.
5.1. Payload Formats and Extensibility Considerations
Here's how the Mobility Service Transport Protocol (MSTP) is laid out 🎀
+----------------+----------------------------------------+
|Mobility Service| Opaque Payload |
|Transport Header| (Mobility Support Service) |
+----------------+----------------------------------------+
Figure 5: Protocol StructureThis figure shows the case for an MIH message that's smaller than the MTU of the path to the destination. Bigger payloads might need the transport protocol to transparently fragment and reassemble the MIH message, which is so fun to think about 🦋
The opaque payload holds the Mobility Support Service (MSTP) information that's being transported. The definition of the Mobility Service Transport Header is something that's best handled within the IETF 🫶 And MSTP doesn't inspect the payload at all, so whatever info is needed will be supplied by the MSTP users. It's giving privacy and separation of concerns, periodt 👑
5.2. Requirements on the Mobility Service Transport Layer ✨
Okay bestie, this section lists the general transport requirements the Mobility Service Transport Protocol should support 💅 The authors figured at least the following need to be taken into account 🧚
Discovery: MNs need to be able to either discover nodes that support certain services, or discover services provided by a certain node 🔍 Service discovery can be handled with messages defined in [1]. This section refers to node-discovery in either scenario. There are no assumptions about where these Mobility Service nodes sit in the network, so the discovery mechanism needs to work across administrative boundaries 🌸 Speed of discovery, protection against spoofing, when discovery needs to happen, and how long the discovery information stays valid all need to be considered 💜 Approaches include:
- Hard coding information into the MN, either the IP address of the NN, or information about the NN that can be resolved to an IP address. The configuration could be managed dynamically, but this assumes the NN is independent of the access network the MN is currently attached to.
- Pushing information to the MN, where it's delivered as part of other configuration operations, for example via DHCP or a Router Discovery exchange. The benefit is that no additional exchanges with the network are required, but limitations associated with modifying these protocols may limit how applicable the solution is.
- MN dynamically requesting information about a node, which may require both MN and NN support for a particular service discovery mechanism. This may need extra support from the access network (e.g., multicast or anycast), even when the access network doesn't support the service directly itself.
Numerous directory and configuration services already exist, so reusing these mechanisms may be appropriate 🎀 There's an open question about whether multiple discovery methods would be needed, and whether NNs would also need to discover other NNs 🤔 The definition of a service also needs to be pinned down, including how granular the description is. For example, IEEE 802.21 specifies three different types of Mobility Services (Information Services, Command Services, and Event Services) that can be located in different portions of the network. So an MN could run a discovery procedure for any service running in the (home or visited) network, or it could run a discovery procedure for one specific service 🦋
Information from a trusted source: The MN uses Mobility Service information to decide what steps to take next, so it is essential that there is some way to make sure the information comes from a trustworthy source 🫶 This requirement should reuse trust relationships that are already established in the network. For example, the relationships set up by the Authentication, Authorization, and Accounting (AAA) infrastructure after a mutual authentication, or the certificate infrastructure required to support SEND [10]. Section 6 provides a more complete analysis.
Security association management: A common security association negotiation method, independent of any specific MSTP user, should be implemented between the endpoints of the MSTP. The solution must also work in the case of MN mobility 🔐
Secure delivery: The Mobility Service information must be delivered securely (integrity and confidentiality) between trusted peers, even though the transport may pass through untrusted intermediate nodes and networks 🛡️ The Mobility Service information should also be protected against replay attacks and denial-of-service attacks 💀
Low latency: Some Mobility Services generate time-sensitive information, so the information needs to be delivered over quite short timescales, and the required lifetime of a connection might be quite short-lived ⏱️ As an example, the frequency of messages defined in [1] varies according to the MIH service type. Events and Commands messages are expected to arrive at an interval of hundreds of milliseconds, so they can capture quick changes in the environment and/or process handover commands ⚡ Information Service messages, on the other hand, are mainly exchanged each time a new network is visited, which may be on the order of hours or days 🌙 For reliable delivery, short-lived connections could be set up as needed, although there is a connection setup latency associated with this approach. Alternatively, a long-lived connection could be used, but this requires advance warning that it's 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 may be essential for some Mobility Services, but it's really hard to trade this off against the low latency requirement 😭 It's also quite difficult to design a robust, high-performance mechanism that can operate in heterogeneous environments, especially one where link characteristics can vary quite dramatically. There are two main approaches that could be adopted:
- 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 the MIH level) to allow communicating endpoints to acknowledge receipt of information.
- Assume the underlying transport will provide reliable delivery. In this case there is no need to provide reliability at the MIH level.
Guidelines provided in [3] are being considered while this document is being written 📚
Congestion Control: A Mobility Service may want to transfer small or large amounts of data, which places different congestion control requirements on the transport 📦 As an example, the MIH message [1] size varies widely: from about 30 bytes (for a broadcast capability discovery request) to normally less than 64 KB, but it may be greater than 64KB (for an IS MIH_Get_Information response primitive). A typical MIH message size for the Events and Commands Services ranges between 50 to 100 bytes. The solution should consider different congestion control mechanisms depending on the amount of data generated by the application (MIH), as suggested in [3] 🌈
Fragmentation and reassembly: ES and CS messages are small, are sent frequently, and may want to trade off reliability to meet the tight latency requirements 🏃♀️ IS messages, on the other hand, are more forgiving when it comes to latency constraints, and some long IS messages could exceed the MTU of the path to the destination 📏 Depending on the choice of transport protocol, different fragmentation and reassembly strategies are required 🧩
Multihoming: For some Information Services exchanged with the MN, the request and response messages could be carried over two different links. For example, a handover command request could be on the current link while the response is delivered on the new link 🦋 The transport protocol is expected to be capable of receiving information via multiple links. The MSTP user is also expected to combine information belonging to the same session/transaction. When mobility is applied, the underlying IP mobility mechanism should provide session continuity 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 🌐
6. Security Considerations 🚨
Network-supported Mobility Services aim to improve 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 on the content of the message payload, which is handled by the handover services application. Regardless of how big the effect is, message delivery mechanisms need to provide protection against tampering, spoofing, and replay attacks 🚫
Sensitive and identifying information about a mobile device may be exchanged during handover-service message exchange. Since handover decisions are made based on message exchanges, it may be possible to trace a user's movement between cells, or predict future movements, by inspecting handover service messages. To prevent such tracking, message confidentiality and message integrity should be available. This is especially important because many mobile devices are associated with only one user, so divulging this information may violate the user's privacy 🙈 Identifying information may also be exchanged during security association construction. Since this information may be used to trace users across cell boundaries, identity protection should be available, if possible, when establishing source addresses (SAs) 🔒
In addition, the user should not have to disclose their identity to the network (anymore than it needed to during authentication) in order to access the Mobility Support Services 🎭 For example, if the local network is only 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 to access the Mobility Support Services available locally 🧚
Finally, the NNs themselves will potentially be subject to denial-of-service attacks from MNs, and these problems will be made worse if operating 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, and service-specific protocol exchange) denial-of-service prevention or mitigation should be built in 🛡️
7. Conclusions ✨
okay so this section is the wrap-up bestie 🎀 It says this document laid out a broad problem statement for signalling information elements across a network to support Mobility Services. To make that kind of signalling service work, we need a generic transport solution that has certain transport and security properties. The whole motivation came from work in IEEE 802.21, but the goal is that solutions here work for a wider range of Mobility Services, not just that one 🦋
It would be super valuable to set realistic performance goals for this shared problem (so the transport and security parts) using experience from earlier IETF work and what deployments are actually feasible 📊 That info could then help other standards bodies design Mobility Services with performance requirements that are doable 💅
Lowkey, a lot of what's needed is already available from existing IETF protocols, or a combination of them 🧚 This document doesn't pick a side on whether an existing protocol can be adapted or whether we need brand new protocol development. Either way, the skills to develop protocols in this area live in the IETF 👑 iykyk
8. Acknowledgements 🫶
Thanks to Subir Das, Juan Carlos Zuniga, Robert Hancock, and Yoshihiro Ohba for their input 💖 Thanks also to the IEEE 802.21 chair, Vivek Gupta, for coordinating the work and supporting the IETF liaison ✨ And thank you to all the IEEE 802.21 WG folks who contributed to this document indirectly 🌸
9. References 📚
9.1. 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 Levels", BCP 14, RFC 2119, March 1997.9.2. Informative References
[3] Eggert, L. and G. Fairhurst, "UDP Usage Guidelines for
Application Designers", Work in Progress.
[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., Ed., "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., Ed., "Fast Handovers for Mobile IPv6", RFC 4068,
July 2005.
[10] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.Contributors' Addresses 🌈
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
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.comAuthors' Addresses 🦋
Telemaco Melia, Editor
Cisco Systems International Sarl
Avenue des Uttins 5
1180 Rolle
Switzerland (FR)
Phone: +41 21 822718
EMail: tmelia@cisco.comFull Copyright Statement 🔥
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📦 where this page comes from
- ietf: rfc5164 2008-03
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