SIPPING Working Group S. Niccolini
Internet-Draft NEC
Intended status: Informational S. Salsano
Expires: August 27, 2007 Univ. of Rome Tor Vergata
L. Veltri
Univ. of Parma
February 23, 2007
Requirements for vertical handover of multimedia sessions using SIP
draft-niccolini-sipping-siphandover-01
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Abstract
This document analyses the issue of handling vertical handovers among
different network technologies using SIP.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Scenario for vertical handover . . . . . . . . . . . . . . . . 4
3. Requirements for Vertical Handovers . . . . . . . . . . . . . 5
4. Taxonomy of possible approaches . . . . . . . . . . . . . . . 7
5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Security considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Informative References . . . . . . . . . . . . . . . . . . . . 11
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14
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1. Introduction
Let us consider a terminal (hereafter named "Mobile Host" or MH),
possibly equipped with different network interfaces (i.e. a subset of
WiFi, Bluetooth, GPRS, 3G, fixed Ethernet, WiMax). Each interface
will receive an IP address from the corresponding Access Network
(AN). Therefore the mobile host will have a set of different IP
addresses and will have to select which one to use when running
multimedia sessions with correspondent terminals. While the mobile
host moves, the "selected" interface may become not available due to
loss of signal, or could suffer high packet loss or packet delay.
Under these circumstances, the MH would like to switch to another
interface (using a different IP address) keeping the running sessions
active. Even with a single interface the connected access network
can become not available anymore and the terminal could connect to
another Access Network (in this case on the same technology), which
provides a different IP address. If the switch to the new AN is fast
enough, the MH could also be interested in keeping the running
session active.
This problem has been addressed with different approaches. One
approach is based on "network level" mobility solutions like Mobile
IP or MobileIPv6. Another approach is based on "application level"
mobility solution. The main advantage of application level mobility
solutions is that they do not require any support at the network
level from the different access networks, which only needs to provide
plain IP connectivity. This document details the issues and the
requirements regarding an "application level" mobility solution, in
particular considering the solution that exploits the SIP protocol.
The aim of SIP based application level mobility is to keep active a
multimedia session that has been established with SIP, while the
terminal switches from one network interface to another or it changes
IP address on the same interface.
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2. Scenario for vertical handover
The figure below shows a Mobile Host that wants to communicate with a
"Correspondent Host" (CH). The Mobile Host can connect to different
Access Networks (AN1, AN2, AN3 are represented in the figure). The
different ANs could have different wireless or wired techologies and
the Mobile Host could be connected to more than one Access Network at
the same time if it has more than one physical network interface.
Note that the Access Networks can provide public or private addresses
to the mobile host (in most typical scenarios the Access Networks are
likely to provide private IP addresses). For example in the figure
below AN 1 and AN 3 provide a private address (as shown by the NAT
box), while AN2 provides a public address. Similarly, the
Correspondent Host can have a public address (like CH 1 in the
figure) or a private IP address (like CH 2 in the figure).
+-------+
| AN1 |-----+
----| | NAT | +--------+
/ +-------+-----+ |Corresp.|
+-------+ __________ | Host 1 |
| Mobile| +-------+ / \ +--------+
| Host | | AN2 | / \
+-------+ ----| | | INTERNET |
+ - - - + \ /
\__________/
\ +-------+ +--------+
----| AN3 |-----+ +-----|Corresp.|
| | NAT | | NAT | Host 2 |
+-------+-----+ +-----+--------+
The goal of the handover mechanism is to let the MH roam among
different Access Networks in a seamless way. The mobility management
mechanism should consider the roaming of the MH both "off call" and
during an active call. The MH should be able to dinamically choose
among the available ANs the one that better suits its needs (e.g.
perceived quality of media flows and cost) in a given moment. It is
important to notice that this draft does not address the criteria and
tools for selection of the "best" access network, it only details the
issues and the requirements regarding the mobility management and
handover execution mechanims.
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3. Requirements for Vertical Handovers
In this session we discuss a set of requirements that a mobility
management solution based on SIP should have.
o The solution should be as fast as possible. The goal is to
provide a "seamless" handover with no perception from the user
point of view. If it is not possible to provide a truly seamless
solution, the impairment should be minimized.
o The solution should support a "forward handover" (i.e. in which
all the procedure is performed on the new target Access Network).
This is important if the connection on the old Access Network is
suddenly broken. If possible (i.e. if the connection with the old
access network does not break suddenly) the solution could exploit
the communication on the old access network in order to better
control the handover procedure. Soft handovers (i.e. where the
two active connections can be exploited in the same moment to send
the session data) could be exploited.
o The handover solution should be compatible with NATted networks,
i.e. it should interoperate gracefully with NAT traversal
mechanisms for SIP signaling and for session media flows.
o The handover solution should not require a support in the
different access network. The access networks are only required
to provide IP connectivity (either with public or private
addresses) for the forwarding of signalling SIP packets and media
RTP packets.
o The switch of the "active" interface during a SIP transaction
should be supported. As an example the terminal should be able to
send (receive) an INVITE on the currenlty active interface, switch
to another interface and receive (send) the 200 OK on the other
interface.
o An optional desirable requirement is to allow the decoupling of
"user level" registration and mobility and "terminal level"
mobility. As an example a user with AOR "sip:user@domain.com"
should be allowed to use different terminals (i.e. Mobile Hosts
supporting the handover solutions as well as normal SIP
terminals). These terminals can be used in sequence or at the
same time depending on the capability of his own "home" registrar/
proxy server, and this is independent of the vertical handover
solution which takes care of the mobility of only one specific
Mobile Host. A concrete example for this requirement is to
support a user "sip:user@domain.com" who owns three Mobile Hosts
(one could be his phone, one his PDA, one his laptop) and two
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fixed terminals (his desktop and his home VoIP phone). The
vertical handover solution takes care of the mobility of the
phone, PDA and laptop as three separate Mobile Hosts (which can
also be all active in the same time).
o An optional desirable requirement is to provide privacy with
respect to user location and user movements.
o Another desirable feature is that existing user agents should
inter-work with the handover procedure without the need to be
updated. This requirement applies especially to the
"Correspondent Hosts" (which in general are not moving, but they
are communicating with a moving terminal). If this requirement is
not fulfilled there is the need to change all SIP terminals to
support the handovers of Mobile Host. To a lesser extent this
requirements also applies to the Mobile Host itself: it would be
desirable to reuse existing SIP clients (User Agents) without
updating them to support the terminal mobility.
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4. Taxonomy of possible approaches
The application level mobility solutions based on SIP can be
classified in "Correspondent host based" or "Intermediate Element
based".
o Correspondent Host based solutions
RFC 3261 [1] has a built in mechanism for mobility management. The
"off-call" mobility management consists in the Registration process.
The "on-call" handover is performed using RE-INVITE messages towards
the Corresponding Node. No intermediate entities are directly
involved in the handover process. This has the advantage that no
additional procedure for the handover needs to be implemented in
network elements, and that there is no additional load in the
networks due to the handovers. On the other hand, the procedure
requirese that the Corresponding Node (which in general is not a
mobile host) supports the RE-INVITE mechanism. A second drawback is
that the handover delay is directly proportional to the end-to-end
delay, and this could be higher with respect to the delay occurring
between a mobile node and an intermediate entity.
o Intermediate Element based solutions
In order to overcome the drawbacks of the Correspondent Host based
solutions, "intermediate" entities that take an active role in the
handover can be introduced. Several proposals can be found in the
literature, but to our knowledge no internet draft has been proposed
in this respect. Hereafter we mention some of the existing
proposals. In [2] intermediate entities are used only to speed up
the handover process, but the handover procedure still involves the
Corresponding Node as well. A similar approach is followed in [4],
which also deals with location based selection of the "optimal"
intermediate entity and of wireless access points. In [3] the
intermediate entities fully handle the user mobility, hiding the
mobility to the Corresponding Nodes.
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5. Conclusions
As a concluding remark, we believe that it is important to consider a
new solution for vertical handover that meets the set of requirements
that has been analysed. This solution will help providing seamless
handover to SIP based application with a better performance and
overcoming some shortcomings of the current solution based on [1].
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6. Security considerations
The security considerations should be taken into account in the
design of the handover solution, so that no new additional security
issues will be introduced.
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7. IANA Considerations
This document does not require IANA actions.
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8. Informative References
[1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[2] N. Banerjee et al., "Seamless SIP-Based Mobility for Multimedia
Applications", IEEE Network , March/April 2006.
[3] S. Salsano et al., "Architecture and testbed implementation of
vertical handovers based on SIP Session Border Controllers", to
appear in Wireless Personal Communications, Springer , 2007.
[4] S. Tsiakkouris, I. Wassell, "PROFITIS: architecture for
location-based vertical handovers supporting real-time
applications", 25th IEEE International Performance, Computing,
and Communications Conference, IPCCC 2006, Phoenix, Arizona,
April 10-12, 2006 .
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Appendix A. Acknowledgments
The authors would like to thank Chiara Mingardi (Univ. of Padova/NEC)
and Andrea Polidoro (Univ. of Rome Tor Vergata) for their support in
the identification of the requirements and the fruitful discussions
about possible solutions.
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Authors' Addresses
Saverio Niccolini
Network Laboratories, NEC Europe Ltd.
Kurfuersten-Anlage 36
Heidelberg 69115
Germany
Phone: +49 (0) 6221 43 42 118
Email: saverio.niccolini@netlab.nec.de
URI: http://www.netlab.nec.de
Stefano Salsano
DIE, University of Rome "TorVergata"
Via Politecnico, 1
Rome 00156
Italy
Phone: +39 06 7259 7770
Email: stefano.salsano@uniroma2.it
URI: http://netgroup.uniroma2.it/Stefano_Salsano
Luca Veltri
DII, University of Parma
Parco Area delle Scienze 181/A
Parma 43100
Italy
Phone: +39 0521 90 5768
Email: luca.veltri@unipr.it
URI: http://www.tlc.unipr.it/veltri
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