RE: [802.21] IETF draft on problem statement
Title: Vice Chair candidate
Hello,
Here
is a draft version of the internet-draft that is due on 6th March to the IETF
that contains the 802.21 problem
statement encompassing all MIH services. Your comments are most
welcome.
Regards,
Srini
MIPSHOP E. Hepworth
Internet-Draft Siemens Roke Manor Research
Expires: August 29, 2006 G. Daley
Panasonic
S. Sreemanthula
S. Faccin
Nokia Research Center
G. Vivek
Intel
February 25, 2006
Problem Statement: Media Independent Handover Signalling
draft-hepworth-mipshop-mih-problem-statement-01
Status of this Memo
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This Internet-Draft will expire on August 29, 2006.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
There are on-going activities in the networking community to develop
solutions for handover between heterogeneous wired and wireless
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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. 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. Entities . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. End-to-End Signalling and Transport over IP . . . . . . . 4
2.2. End-to-End Signalling and Partial Transport over IP . . . 4
2.3. End-to-End Signalling with a Proxy . . . . . . . . . . . . 5
3. Solution Components . . . . . . . . . . . . . . . . . . . . . 7
3.1. Payload Formats and Extensibility Considerations . . . . . 8
4. Requirements on the Mobility Service Transport Layer . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. Conclusions and Open Issues . . . . . . . . . . . . . . . . . 13
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 14
Appendix B. Relationship to IEEE 802.21 . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . . . 17
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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, neighbouring networks and associated
characteristics, indications that a handover should take place, and
suggestions for suitable target networks to which to handover.
There are two key attributes to the handover support service problem:
1. The Information and Information Exchange mechanism: this includes
the information elements that describe the information, and any
signalling exchanges that are required to support the transfer of
these Information Elements.
2. The Underlying Transport: this supports the 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 security issues, 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 authors, and does not represent the official view of IEEE
802.21.
The structure of this document is as follows. Section 2 provides a
simple model for the entities involved in the signalling and their
possible relationships. Section 3 describes a decomposition of the
signalling problem into service specific parts and a generic
transport part. Section 4 describes more detailed requirements for
the transport component. Section 5 provides security considerations,
and Section 6 summarises the conclusions and open issues.
2. Entities
The following section provides an overview of the network entities
that are expected to be involved in the signalling exchanges to
support the handover operation. The following abbreviations are used
in this section:
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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.
The deployment sceanrios 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.
2.1. 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
2.2. 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 a upper-
layer multihop protocol such as RADIUS used as a backhaul transport
protocol between an Access Point and the Authentication Server.
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+------+ +------+ +------+
| MN | | NN | | NN |
| | | (EP) | | (EP) |
+------+ +------+ +------+
Information Exchange
<------------------------------------>
(Transport over /------------------\
<--------------->< Transport over IP >
e.g. L2) \------------------/
Figure 2: Partial Transport
2.3. 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.
o Information Exchange Approach
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 Approack
The Proxy NN processes all layers of the protocol suite in the
same way as an ordinary EP.
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o Redirection Approach
In this case, the redirection NN processes enough of the
Information Exchange to forward the message to the correct
ultimate NN for that MN and service type. Subsequent Information
Exchanges take place between the MN and NN.
+------+ +----------+ +------+
| MN | | Redirect | | NN |
| (EP) | | NN | | (EP) |
+------+ +----------+ +------+
Information Exchange
------------------> ------------------->
[------Minimal Transport/Security------]
Information Exchange
<-------------------------------------->
/--------------------------------------\
< Transport >
\--------------------------------------/
Figure 4: Redirection Approach
The initial messages are assumed to have minimal transport
requirements. The main information exchange takes place directly
between the endpoints.
o Directory Approach
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In this scenario, the MN (EP) carries out an Information Exchange
with a Directory node in the network to determine which NN should
be used for subsequent Information Exchanges.
+------+ +------------+ +------+
| MN | | Directory | | NN |
| (EP) | | (EP) | | (EP) |
+------+ +------------+ +------+
Information Exchange
------------------->
<-------------------
[Minimal Transport/Security]
Information Exchange
<------------------------------------->
/--------------------------------------\
< Transport >
\--------------------------------------/
Figure 5: Directory Approach
The Information Exchange with the Directory requires only minimal
processing, just enough to determine the appropriate NN for the MN
to use. Transport and security requirements for the lookup phase
are typically very limited. This option provides one approach to
supporting initial node discovery, where subsequent Information
Exchanges are carried out directly between two peers.
The question as to which of these proxy options should be considered
is still open.
3. Solution Components
Figure 6 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).
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+----------------+ ^
|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 6: Handover Services over IP
The Mobility Service Transport Layer provides certain functionality
(outlined in Section 4) 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 discovery, transport and security operations required to
provide communication.
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 Media Independent Information
Service [1], and the Media Independent Command and Event Services
[2].
3.1. Payload Formats and Extensibility Considerations
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The format of the Mobility Service Transport Protocol is as follows:
+----------------+----------------------------------------+
|Mobility Service| Opaque Payload |
|Transport Header| (Mobility Support Service) |
+----------------+----------------------------------------+
Figure 7: Protocol Structure
The opaque payload encompasses the Mobility Support Service
information that is to be transported. The definition of the
Mobility Service Trabsport Header is something that is best addressed
within the IETF.
The Mobility Support Service payload format also includes a header,
which could vary depending on the definition of each Mobility Support
Service.
+----------------+-------------------------------+
Mobility Support | Header | Payload |
Service 1 (IS) | |(Mobility Support Service Data)|
+----------------+-------------------------------+
+--------+---------------------------------------+
Mobility Support | Header | Payload |
Service 2 (other) | | (Mobility Support Service Data) |
+--------+---------------------------------------+
Figure 8: Protocol Structure
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.
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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.
4. 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 within IEEE 802.21 has suggested that
at least the following need to be taken into account:
Discovery: MNs need the ability to locate nodes that support
particular mobility services in the network. There are no
assumptions about the location of these mobility services within
the network, therefore the discovery mechanism needs to operate
across administrative boundaries. Issues such as speed of
discovery, when discovery needs to take place, and the length of
time over which the discovery information may remain valid all
need to be considered. Similar discovery requirements may apply
to general NN discovery in the network.
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 includes cases where
trusted proxies along the path have access to, and may modify,
parts of the Mobility Service information. 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.
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
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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).
Option 1 has a number of diasadvantges associated with it, namely
that ultimately the protocol design ends up re-inventing a lot of
the functionality already avaialble in lower layers at a higher
layer where access to information about what is going on in the
network is restricted. For example, how will the higher layer
determine the cause of the error, if a message is lost due to
network congestion, it is pointless sending the message again. It
also adds to the complexity of the higher layer protocol, and
makes successful deployment less certain (the protocol will have
to be trialled in a number of network situations instead of re-
using a protocol that has already been tested).
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
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etc.).
Secure delivery: The Mobility Service information must be delivered
securely between trusted peers, where the transport may pass
though untrusted intermediate nodes and networks.
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
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.
Further information about transport requirements related to specific
Mobility Services can be found in [1] and [2].
5. 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
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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 a 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.
6. 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 was outlined. Whilst the
motivation for considering this problem has come form 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.
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One important open issue is the question of how much Mobility Service
specific functionality (with respect to the structure shown in [])
should be seen as part of the common problem within IETF scope. One
option is that the problem scope is limited strictly to message
transport requirements, the other extreme is that the full mobility
service protocols should be defined. An intermediate stage would be
to consider message sequences and use cases for different mobility
services but leave the details of Information Elements by other
bodies, but potentially including IETF working groups.
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 lies in the IETF.
7. References
[1] Faccin, S., "Some Requirements for a Handover Information
Service", draft-faccin-mih-infoserv-01 (work in progress),
October 2005.
[2] Sreemanthula, S., "A Problem Statement for Event Services and
Command Services for Media Independent Handovers",
draft-sreemanthula-es-cs-problem-statement-00 (work in
progress), October 2005.
[3] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko,
"Diameter Base Protocol", RFC 3588, September 2003.
Appendix A. Acknowledgements
Thanks to Robert Hancock, Andrew McDonald and Jari Arkko for their
inputs.
Appendix B. Relationship to IEEE 802.21
The following Appendix provides some further information on the
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relationship of this problem statement to the work being carried out
by IEEE 802.21.
IEEE 802.21 has identified three Mobility Support Services to enable
better inter-technology handover decisions. These are:
1. the Event Service (ES) which provides indications from lower
layers about changes in the connectivity state. This is
particularly relevant to wireless interfaces.
2. the Command Service (CS) which provides a mechanism for
controlling handovers. This includes the establishment,
redirection, or removal of state in either the network or the
mobile terminal, so that handovers occur smoothly.
3. the Information Service (IS) which provides additional handover-
related information. This allows the network or host to make
informed decisions of which handover operations to undertake
either in response to an event, or when planning controlled or
commanded handovers.
Something about formats?
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Authors' Addresses
Eleanor Hepworth
Siemens Roke Manor Research
Roke Manor
Romsey, SO51 5RE
UK
Email: eleanor.hepworth@roke.co.uk
Greg Daley
Panasonic Digital Networking Laboratory
2 Research Way
Princeton, New Jersey 08540
USA
Phone: +1 609 734 7334
Email: greg.daley@research.panasonic.com
Srivinas Sreemanthula
Nokia Research Center
6000 Connection Dr.
Irving, TX 75028
USA
Email: srinivas.sreemanthula@nokia.com
Stefano Faccin
Nokia Research Center
6000 Connection Dr.
Irving, TX 75229
USA
Email: stefano.faccin@nokia.com
Vivek Gupta
Intel Corporation
Vivek's Address
Vivek's Address 00
USA
Phone: +1 000 000 0000
Email: vivek.g.gupta@intel.com
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