MIP4 Working Group N. A. Fikouras
INTERNET DRAFT K. Kuladinithi
Expires: August 2004 C. Goerg
ComNets-ikom, Uni. Bremen
C. Bormann
TZI, Uni. Bremen
May 2004
Mobile IPv4 Flow Mobility Problem Statement
draft-nomad-mip4-flow-mobility-pb-00.txt
Status of this Memo
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Abstract
Internet capable mobile or portable devices are already a modern
commodity while it is becoming all the more common that such devices are
hosts to more then one wireless interface. The aim of this document is
to show that a mobile user may make best use of this property by using
multiple wireless interfaces in parallel. This would incline that the
mobile user can distribute active flows across the available wireless
interfaces and is able to seamlessly transfer them between the wireless
interfaces in mid-session without interruption.
Table of Contents
1. Introduction....................................................2
3. Scenarios for multiple interface management and flow mobility...3
3.1 Scenario 1......................................................3
3.2 Scenario 2......................................................3
3.3 Scenario 3......................................................4
4. Related Work....................................................4
4.1 Mobile IP.......................................................4
4.2 Stream Control Transmission Protocol............................5
4.3 Resource reservation Protocol...................................5
4.4 Filters for Mobile IP...........................................6
References.........................................................6
Authors' Addresses.................................................7
Intellectual Property Statement....................................7
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1. Introduction
It is forecasted that by 2005 an increasing portion of Internet users
will be using wireless devices such as web-enabled cell phones and
PDAs to go online as the number of worldwide Internet users will
nearly triple to 1.17 billion [1]. As a response to the explosive
growth of mobile Internet users, operators have urged for the
deployment of packet services in wide-area cellular networks. This
was accompanied by a rollout of standards for license free personal
and local area communication networks. The increasing availability of
a range of heterogeneous wireless technologies is a strong indication
that future mobile Internet communication systems will be built upon
wireless overlay networks [2]. It is understood that in order to make
best use of this property one must be able to selectively and
intelligently utilise in parallel any number of wireless networks in
his/her vicinity while dynamically distributing active flows across
the available wireless network links. The benefits of taking
advantage of this property can be grouped in three main areas,
namely:
o The aggregation of network resources available over a selection of
the wireless networks.
o The matching of individual flows and wireless network links with
respect to attributes such as cost, quality of service parameters
or a specific service.
o Achieving loss-less handoffs with minimal effect to active
communications.
The purpose of this draft is to:
o Raise awareness on the opportunities aroused by the increasing
availability of multi-interfaced mobile nodes.
o Articulate the problems of simultaneously using multiple wireless
network links with existing protocols.
o Argument that a solution can best be provided with an extension of
the Mobile IP protocol.
2 Problem Overview
In homogeneous networks, a hand-off is initiated only when a mobile
unit eludes the boundaries of an administered domain and enters
another. However, in heterogeneous networks, a mobile unit does not
need to move in order to initiate a hand-off. Algorithms for hand-
offs between heterogeneous networks are different from those for
homogeneous networks. Any hand-off decision is bound to affect a
range of active communications with different attributes and
requirements, benefiting some while degrading the performance of
others. The simultaneous use of multiple wireless network links
reduces the effect of this problem by a factor equivalent to the
number of network connections. To that end, the mobile node should be
able to move individual flows between network links with respect to
the requirements of the flow and the users preferences. The
management of flows should require minimal interaction with
communication peers while the differentiation of flows should take
place as close to the mobile node as possible. This will allow for
fast reaction times while restricting the amount of signaling that
traverses the core network fabric.
The requirements for any proposed solution aim at providing support
for multiple wireless interface management and flow mobility include:
o solution should operate in a transparent fashion to higher layer
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protocols and applications.
o solution should involve a minimum amount of signaling that should
be restricted to the mobile nodes vicinity and not communicated to
the Internet.
o solution should dictate a minimum amount of alterations to nodes
other than the mobile node and the mobility management support
infrastructure.
o solution should not compromise the security of involved nodes.
o solution should be backwards compatible, i.e. remain functional
even in environments where their operational requirements are not
supported.
3. Scenarios for multiple interface management and flow mobility
The following scenarios describe a tactical application and two
everyday life situations aimed at highlighting the need for
simultaneous use of multiple wireless links and flow mobility.
3.1 Scenario 1
An ambulance is called at the scene of a car accident. A paramedic
initiates a communication to a hospital via a wide area cellular link
for the relay of low bit-rate live video from the site of the crash
to assess the severity of the accident. It is identified that one of
the passengers has suffered a severe head injury. The paramedic
decides to consult a specialist via video conferencing. This session
is initiated from the specialist via the same wide area cellular
link. Meanwhile, the paramedic requests for the download of the
patients medical records from the hospitals servers. The paramedic
decides in mid-session that the wide area cellular link is too slow
for this download and transfers the download to the ambulance
satellite link. Even though this link provides a significantly faster
bit rate it has a longer traversal delay and only down-link is
available. For this, only the down-stream of the download is
transferred while up-stream proceeds over the wide area cellular
link. Connectivity with the ambulance is managed over a wireless
local area link between the paramedic and the ambulance. Even though
the paramedic has performed a partial hand-off for the transfer of
the download down-stream to the satellite link, the upstream and the
video conferencing session remains on the wide area cellular link.
This serves best the time constraint requirements of the real time
communication.
3.2 Scenario 2
Mr. Smith is on his way to work waiting at a train station. He uses
this opportunity and the presence of a wireless LAN hot-spot to
download the news from his favorite on-line news channel. His train
is announced and Mr. Smith decides to buy a ticket. However, the
ticket reservation service is only available via a wide area cellular
link of a specific provider. While Mr. Smith is downloading the news
and accessing the train ticket reservation service he receives a
phone call. This connection is receives over a separate wide area
cellular link. Mr. Smith answers the call to be informed that a
colleague is also at the train station and would like to travel with
him. Mr. Smith decides he wishes to initiate a video flow for this
communication. The bandwidth and traversal delay of the wide area
cellular link is not adequate for the video conference, so both flows
(video/audio) are transferred to a wireless local area link via a
hot-spot. This transfer occurs transparently and without affecting
any other active flows.
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In order to cater for the communication means of the modern man,
communication devices should be equipped with a range of
heterogeneous wireless interfaces providing with several points of
attachment to the global Internet.
3.3 Scenario 3
Alice is at the airport waiting to board the plane. She receives a
call by her husband. This audio communication is received via a
wireless local area link realized over one of the available hot-
spots. She knows this is going to be a long flight and wishes to
catch up on some work. Alice uses a wireless LAN connection to
download the necessary data. However, there is not enough time and
Alice decides to accelerate the download. Her notebook is equipped
with an additional wireless local area network interface. Alice
decides to distribute the different download flows between the
multiple interfaces to accelerate the download.
This scenario illustrates the capacity of mobile nodes with multiple
points of attachment not just to distribute and transfer whole flows
between the wireless links.
The scenarios illustrate several requirements of day-to-day as well
as tactical applications, namely:
1) The seamless interoperability of heterogeneous wireless networks
that allows for vertical mobility across the various layers of the
wireless overlay network. These will include wide area cellular
networks for the connectivity of units on the move as well as local
area wireless networks for connectivity either via hot-spots or
mobile ad-hoc networks.
2) Access for all mobile users to resources on the global Internet
and more importantly reachability on a globally unique, permanent
identity.
3) Policy based selection of the type of communication network for
different types of communications. The high correlation between type
of mobility, position, reposition and type of communication/service
that a mobile user may request or receive must be reflected in this
policy.
4) Simultaneous use of multiple wireless networks. Without this
feature these scenarios would not be feasible as mobile units would
be required to switch between available wireless networks in order to
more efficiently communicate with others or to access specific
services. As awareness is raised for the opportunities made possible
by multi-interfaced mobile nodes, policy based routing will gain
importance.
The following section gives a discussion of existing solutions to the
problem of mobility, flow and multiple interface management and
explains the shortcoming of each such solution.
4. Related Work
4.1 Mobile IP
The Mobile IP [3] is currently the dominant solution for the
provision of Internet mobility management. However, Mobile IP has
been designed with a focus on mobile nodes with a single wireless
link to the Internet. Mobile IP introduces the notion of Internet
layer hand-offs that are initiated every time that a mobile node
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moves across Internet administrative domains. Mobile IP Mobility
Agents are unable to distinguish between individual flows and with
every subsequent Mobile IP hand-off all active flows are redirected
to the most recently registered location. This behavior restricts
mobile nodes with multiple access interfaces that in order to take
advantage of that property should be able to determine on a per flow
basis how to have them distributed across the available wireless
links.
A solution to the problem of simultaneous multiple access interface
management can be provided with the combination of multi-homing and
Mobile IP route optimization. By sharing acquired care-of addresses
and home IP addresses between the available access interfaces, it is
possible with route optimization to distribute flows from different
communication peers between the access interfaces. However, such a
solution would require that for every change of state signaling
information would have to be relayed to the corresponding
communication peer. In addition, it would be impossible to
differentiate between incoming flows from the same source and
addressed to the same home IP address. Furthermore, multi-homing is
based on the high availability of Internet addresses, several of
which would be allocated to each mobile node, globally. Even though
this might be feasible for IPv6 it is not possible for IPv4 where
Internet addresses are scarce. It is considered that capability to
simultaneously use multiple access interfaces and to move flows
between them should be available to IPv4 and IPv6 mobile nodes alike.
[4] highlights the goals and benefits of multi-homing in IPv6.
4.2 Stream Control Transmission Protocol
The same problem could be resolved with the help of transport layer
protocols such as the SCTP [5]. The SCTP is like TCP a reliable
transport service. Similar to TCP, SCTP is a session-oriented
mechanism, meaning that a relationship between the endpoints of an
SCTP communication is negotiated prior to data transmission. SCTP
includes native support for multi-homing but only for redundancy
purposes. This means that, SCTP endpoints exchange lists of addresses
during initiation of the association while a single one is chosen for
the SCTP data transmission. Should that IP address become unavailable
or when demonstrating high packet loss, the communication will fall-
back to another home IP address until the first becomes again
available. In combination with Mobile IP, SCTP could guarantee the
reachability of the mobile node on any one of those home IP
addresses. This behavior resembles the requirement for flow mobility
but is only initiated for redundancy purposes and not otherwise
controlled by the mobile node. Even if renegotiation of communication
parameters was possible in mid-session it would involve exchanging
signaling information between communication peers that would
propagate through the Internet fabric. A final argument against the
use of SCTP for the realization of multiple access interface
management and flow mobility is that the support of SCTP in the
existing Internet infrastructure is minimal.
4.3 Resource reservation Protocol
A key issue in flow mobility is the capacity to differentiate between
individual flows destined for a particular mobile node. The RSVP [6]
has been designed specifically for hosts to request specific
qualities of service from the network for particular flows. However,
RSVP does not perform its own routing; instead it uses underlying
routing protocols to determine where it should carry reservation
requests and subsequently flows. Consequently, a mobile node that
wishes to move a flow between two access interfaces would be able to
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use RSVP to identify a flow but would not be able to alter routing in
order to have the flow delivered to selected access interface.
4.4 Filters for Mobile IP
Filters for Mobile IPv4 bindings [7] enables mobile nodes to
associate one or more Filters with mobility bindings during
registration. Flows that match a Filter will be processed as defined
by the Filter. In this manner, it is possible for a mobile node to
distribute flows among available wireless links, or to request that
such flows are dropped before reaching the mobile node.
Filters for Mobile IP does not introduce any additional signaling, it
dictates that filters and filtering management extensions should be
piggybacked by registration signaling. This protocol extension to
Mobile IP does not introduce any security requirements as existing
security considerations are adequate. Filters for Mobile IP is
compatible with hierarchical Mobile IP organizations that enables the
localized management of flow mobility and restricts signaling from
reaching communication peers. Even in this absence of hierarchical
Mobile IP considerations, filtering information is terminated at the
Home Agent and is not propagated further. This extension inherits the
property of the basic Mobile IP to operate transparently to active
communications. As such filtering occurs in a manner transparent to
transport layer protocols and applications. For the deployment of
Filters for Mobile IP no changes are required to Correspondent Nodes
while any alterations affect only the mobile node requesting for
filtering services and the Mobile IP infrastructure that wishes to
provide this service. Filters for Mobile IP is backwards compatible
with standard Mobile IP and can be deployed in conjunction with
multi-homing; for every home IP address separately. There are
currently several proposals aimed at introducing filters in Mobile IP
[7-10]. [7] has been successfully implemented and experimentally
evaluated [11] proving the feasibility of this approach.
References
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[1] eTForecasts, "Internet Users Will Surpass 1 Billion in 2005,"
http://www.etforecasts.com/pr/pr201.htm.
[2] R. H. Katz and E. A. Brewer, "The Case for Wireless Overlay
Networks," in Mobile Computing, T. Imielinski and H. F. Korth,
Eds.: Kluwer Academic Publishers, 1996, pp. 621-650.
[3] C. E. Perkins, "IP Mobility Support for IPv4," IETF RFC3344, August
2002.
[4] T. Ernst, N. Montavont, R. Wakikawa, C. Ng, T. Noel, E. Paik, and
K. Kuladinithi, "Goals and Benefits of Multihoming," IETF
http://www.ietf.org/internet-drafts/draft-ernst-generic-
multihoming-pb-statement-00.txt, February 2004.
[5] L. Ong and J. Yoakum, "An Introduction to the Stream Control
Transmission Protocol (SCTP)," IETF RFC3286, May 2002.
[6] R. Braden, L. Zhang, S. Berson, S. Herzog, and S. Jamin, "Resource
ReSerVation Protocol (RSVP) - Version 1 Functional Specification,"
IETF RFC2205, September 1997.
[7] N. A. Fikouras, A. Udugama, K. Kuladinithi, C. Görg, and W. Zirwas,
"Filters for Mobile IP Bindings (NOMAD)," IETF
http://www.ietf.org/internet-drafts/draft-nomad-mobileip-filters-
05.txt, October 2003.
[8] K. Kuladinithi, N. A. Fikouras, and C. Görg, "Filters for Mobile
IPv6 Bindings (NOMADv6)," IETF http://www.ietf.org/internet-
drafts/draft-nomadv6-mobileip-filters-01.txt, October 2003.
[9] N. Montavont and T. Noel, "Home Agent Filtering for Mobile IPv6,"
IETF http://www.ietf.org/internet-drafts/draft-montavont-mobileip-
ha-filtering-v6-00.txt, 1/2004 2004.
[10] H. Soliman, K. Malki, and C. Castelluccia, "Per-flow movement in
MIPv6," IETF http://www.ietf.org/internet-drafts/draft-soliman-
mobileip-flow-move-03.txt, 7/2003 2003.
[11] N. A. Fikouras, A. Udugama, C. Görg, W. Zirwas, and J. M.
Eichinger, "Experimental Evaluation of Load Balancing for Mobile
Internet Real-Time Communications," presented at Proceedings of the
Sixth International Symposium on Wireless Personal Multimedia
Communications (WPMC), Yokosuka, Kanagawa, Japan, 2003.
Authors' Addresses
Niko A. Fikouras
Departmnt of Communication Networks (ComNets)
Center for Information and Communication Technology (ikom)
University of Bremen Phone: +49-421-218-3339
D-28219 Bremen, Germany Email: niko@comnets.uni-bremen.de
Koojana Kuladinithi
Department of Communication Networks (ComNets)
Center for Information and Communication Technology (ikom)
University of Bremen Phone: +49-421-218-8264
D-28219 Bremen, Germany Email: koo@comnets.uni-bremen.de
Carmelita Goerg
Department of Communication Networks (ComNets)
Center for Information and Communication Technology (ikom)
University of Bremen Phone: +49-421-218-2277
D-28219, Bremen, Germany Email: cg@comnets.uni-bremen.de
Carsten Bormann
Technologie-Zentrum Informatik (TZI)
University of Bremen Phone: +49-421-218-7024
D-28219, Bremen, Germany Email: cabo@informatik.uni-bremen.de
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