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Differences from draft-ietf-mipshop-mis-ps-01.txt
MIPSHOP T. Melia
Internet-Draft NEC
Intended status: Informational E. Hepworth
Expires: January 10, 2008 Siemens Roke Manor Research
S. Sreemanthula
Nokia Research Center
Y. Ohba
Toshiba
G. Vivek
Intel
J. Korhonen
TeliaSonera
R. Aguiar
IT
Sam(Zhongqi). Xia
HUAWEI
July 9, 2007
Mobility Services Transport: Problem Statement
draft-ietf-mipshop-mis-ps-02
Status of this Memo
By submitting this Internet-Draft, each author represents that any
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This Internet-Draft will expire on January 10, 2008.
Copyright Notice
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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.
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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 Signalling with a Proxy . . . . . . . . . . . . 7
4.4. End-to-End Network-to-Network Signalling . . . . . . . . . 7
5. MoS Transport Protocol Splitting . . . . . . . . . . . . . . . 8
5.1. Payload Formats and Extensibility Considerations . . . . . 9
5.2. Requirements on the Mobility Service Transport Layer . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . . . 18
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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, 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 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,
Command or Event, 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 MIH protocol being defined by IEEE
802.21[1] (specifically the IS/ES/CS components) 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 6 provides security considerations, and Section 7
summarizes the conclusions and open issues.
2. Terminology
The following abbreviations are used in the document:
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o MIH: media independent handover
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.
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 reducing terminal complexity. Also, neighborhood
discovery, potentially a complex operation in heterogeneous wireless
scenarios, can result in a more simple 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 IS, ES, 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.
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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
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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.
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 might process all layers of the protocol suite in the
same way as an ordinary EP.
There is a possibility for realizing other proxy scenarios.
4.4. 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.
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+------+ +------+
| NN | | NN |
| (EP) | | (EP) |
+------+ +------+
Information Exchange
------------------->
<-------------------
/----------------\
< Transport >
\----------------/
Figure 4: Information Exchange between different NN
Network nodes exchange information about connected terminals status.
5. MoS Transport Protocol Splitting
Figure 5 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).
+----------------+ ^
|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 5: Handover Services over IP
The Mobility Service Transport Layer provides certain functionality
(outlined in Section 5.2) to the higher layer mobility support
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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
The format of the Mobility Service Transport Protocol (MSTP) is as
follows:
+----------------+----------------------------------------+
|Mobility Service| Opaque Payload |
|Transport Header| (Mobility Support Service) |
+----------------+----------------------------------------+
Figure 6: 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,
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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, in a 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
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, should the MN
look for an "IS" service, or "IS-local information", and "IS-home
network information" services?).
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 [9]. The
security mechanism may provide mutual authentication of MN and NN
and it may provide one way authentication of either of MN and NN.
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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
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 some sort of reliability mechanism to
allow communicating endpoints to acknowledge receipt of
information.
2. Assume the underlying transport will deal with most error
situations, and provide a very basic acknowledgement mechanism
that (if no acknowledgement is received) will indicate that
something more serious has occurred than a packet drop (since
these other types of error conditions are dealt with at the
transport layer).
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Congestion Control: A Mobility Service may optionally 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.
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.
In addition to the above, it may be necessary for the transport to
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 (see figure
Figure 7) .
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+==================================+
| |
| +++++++++++++++++++++ |
| | MoS | |
| | (e.g. IS, ES, CS) | |
| +++++++++++++++++++++ |
| /\ | ..............
| ||_________________|_: MoS :
| || | :Multiplexing:
| \/ | :............:
| +++++++++++++++++++++ | | +---------+
| | MSTP | | | | MoS(1) |
| | Transport | | | |.........|
| +++++++++++++++++++++ | | | MSTP |
| /\ | | |.........|
| || | | _____| IP |
| || | | / +=========+
| || | | /
| \/ | ^+++++++++^ | / +---------+
| +++++++++++++++++++++ | / \ | / | MoS(2) |
| | IP |--------|--< Internet > '---- |.........|
| +++++++++++++++++++++ | \ / | \ |Transport|
| | v+++++++++v | \ |.........|
| | | \__| IP |
+==================================+ | +=========+
| :
| :
| +---------+
| | MoS(3) |
| |.........|
| |Transport|
| |.........|
|________| IP |
+=========+
Figure 7: Multiplexing examples
6. 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
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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
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.
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.
7. 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
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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.
8. References
[1] "Draft IEEE Standard for Local and Metropolitan Area Networks:
Media Independent Handover Services", IEEE LAN/MAN Draft IEEE
P802.21/D05.00, April 2007.
[2] Aboba, B., "Architectural Implications of Link Indications",
draft-iab-link-indications-10 (work in progress), March 2007.
[3] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
August 2002.
[4] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
[5] Moskowitz, R. and P. Nikander, "Host Identity Protocol (HIP)
Architecture", RFC 4423, May 2006.
[6] Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)",
RFC 4555, June 2006.
[7] 3GPP, "3GPP system architecture evolution (SAE): Report on
technical options and conclusions", 3GPP TR 23.882 0.10.1,
February 2006.
[8] Koodli, R., "Fast Handovers for Mobile IPv6", RFC 4068,
July 2005.
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[9] 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
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
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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,Hai-Dian District Beijing
100085
P.R. China
Phone: +86-10-82836136
Email: xiazhongqi@huawei.com
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