Mobile IP Working Group Eva Gustafsson, Ericsson, Editor
INTERNET-DRAFT April 1999
Expires October 1999
Annika Jonsson, Ericsson
Elisabeth Hubbard, Telia
Jonas Malmkvist, Telia
Anders Roos, Telia
Requirements on Mobile IP from a Cellular Perspective
<draft-ietf-mobileip-cellular-requirements-01.txt>
Status of this memo
This document is a submission by the Mobile IP Working Group of the
Internet Engineering Task Force (IETF). Comments should be submitted
to the mobile-ip@smallworks.com mailing list. Distribution of this
memo is unlimited.
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
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Abstract
The increasing interest in Mobile IP as a potential macro-mobility
solution for cellular networks leads to new solutions and extensions
to the existing protocol. As part of this work, there is a need to put
together the requirements on Mobile IP from a cellular perspective.
This draft lists a set of requirements on Mobile IP for use in cellular
networks, for instance IMT-2000, and relates the requirements to
proposed solutions. These requirements consider Mobile IPv4, but the
list will be extended for Mobile IPv6 as well.
<draft-ietf-mobileip-cellular-requirements-01.txt> [Page 1]
Table of contents
1. Introduction......................................................2
2. General considerations............................................3
3. Authentication....................................................4
4. Registration requests generated on behalf of a mobile node........5
5. Private networks..................................................6
6. Reverse tunnelling................................................7
7. Route optimization................................................7
8. Dynamic home address assignment...................................8
9. Temporary home....................................................8
10. Handover performance.............................................9
11. Conclusions......................................................9
12. Intellectual property considerations............................10
13. Acknowledgements................................................10
14. References......................................................10
15. Author's address................................................12
1. Introduction
Recently, there has been an increasing interest in Mobile IP as a
potential future mobility standard, common to cellular systems and the
Internet as a whole [3][16][17]. The benefits of adopting a common
mobility solution would include independence of access network
technologies and common solutions for fixed and wireless networks.
The purpose of this document is to state a first version of the
requirements on Mobile IP as a potential macro-mobility solution for
future cellular networks. In particular, we consider third generation
mobile systems fulfilling the requirements from ITU for International
Mobile Telecommunications - 2000 (IMT-2000). The Universal Mobile
Telecommunication System (UMTS) and the Enhanced Data rates for GSM
Evolution (EDGE), which both evolve from the GSM/GPRS standard, as well
as Cdma2000, are such IMT-2000 systems. One important aspect when
considering Mobile IP for cellular networks, is to provide interworking
with existing solutions.
Parts of the requirements presented in this document are specific for
Mobile IP in cellular networks, while others consider mobile users in
general. However, we have chosen to include all kinds of requirements
necessary for a cellular operator to deploy Mobile IP. The requirements
in this document mainly refer to Mobile IPv4 [20], but will be extended
for Mobile IPv6 [18] as well.
<draft-ietf-mobileip-cellular-requirements-01.txt> [Page 2]
We start in Section 2 with some general, system-level requirements for
IP mobility in cellular networks. Then we list more specific
requirements in Section 3 through Section 10. Section 11 concludes the
document.
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 [6].
2. General considerations
This section describes some general considerations and requirements on
a system using Mobile IP. Note that these requirements are not specific
requirements on the Mobile IP protocol, but point out important aspects
on a system level.
To allow Mobile IP to be a mobility solution which supports many
different kinds of access networks/technologies, the Mobile IP
functionality shall be independent of the access network technology. For
Mobile IP to be deployed in future cellular networks, it also needs to
provide interworking with existing protocols.
Mobile IP provides authentication of the signalling messages [20]. For
security reasons, such as keeping the current location of a user unknown
to other users, it should also be possible to provide encryption of the
Mobile IP signalling. This may be implemented through, for instance,
IPSec tunnels and security associations established on a permanent basis
inside and between different administrative domains. It should also be
possible to provide encryption of the traffic. A solution is to employ
IPSec together with Mobile IP, as suggested in [25].
As emerging Internet quality-of-service mechanisms are expected to
enable a wide-spread use of real-time services between stationary nodes,
for instance voice over IP and videoconferencing, there will be a demand
for using the same kind of services when being mobile. Promising a
certain level of quality of service to a mobile user is generally
difficult, since there may not be enough resources available in the part
of the network that the mobile node is moving into. However, when network
resources allow, there should be mechanisms to handle quality of service
for mobile users, particularly in case of handover and route
optimization. The differences between stationary and mobile nodes making
use of quality-of-service mechanisms should also be minimized, and
network operators should not need to employ different quality of service
platforms for stationary and mobile users. The emerging quality-of-
service architectures, Differentiated Services and Integrated Services
[4][5][23][24], do not consider mobile nodes. Additions or changes may
be needed.
<draft-ietf-mobileip-cellular-requirements-01.txt> [Page 3]
Quality-of-service mechanisms enforce a differentiated sharing of
bandwidth among different services and different users. Thus, there must
be mechanisms available to identify traffic flows with different
quality-of-service attributes, and to make it possible to charge the
different users accordingly.
It is well known that mobile nodes are more complex to handle than
stationary ones. Anyway, the extra handling of mobile nodes should be
based on the same basic mechanisms as the stationary ones, rather than
on separate mechanisms. Among these basic mechanisms are (i) an
Authentication, Authorization, Accounting (AAA) infrastructure; (ii)
quality of service and policy control; and (iii) directory services and
gateway services like IP telephony.
Lastly, as more and more users become mobile, the need for a uniform
service delivery across various access technologies increases.
Ultimately, the user should not need to know what kind of access
technology is in use at a particular moment. When bandwidth and other
network capabilities allow, IP-based services should appear the same way
independently of the access technology. Moreover, a normal user will try
to employ the most efficient access, considering capacity and cost,
which means that changes of access technology can be expected during
active sessions. Thus, the change of access technology should be as
smooth and as transparent to the user as possible.
These are general considerations and requirements; some of them may
apply to Mobile IP and some may be fulfilled through other protocols and
solutions. The following sections address more specific requirements on
Mobile IP, in order to provide solutions satisfactory for operators as
well as end users.
3. Authentication
The authentication of a mobile node or user can be performed at different
locations and be based upon different parameters. We may also consider
two phases of the authentication procedure: full or initial
authentication and subsequent authentications. Full authentication is
performed when the existing security associations are insufficient, for
instance at initial registration, or when a mobile node requests a new
home agent. Subsequent authentications are performed at handover, that
is, when a mobile node changes its point of attachment within the same
administrative domain, or to renew bindings before they are timed out.
The Mobile IP protocol specifies authentications to be performed at the
home agent, and the identifications to be based on the home IP address
of the mobile node [20]. However, additional solutions and extensions
to Mobile IP have introduced identification and authentication based on
the Network Access Identifier (NAI) [1][2][8][9][10][11][12][13].
Basing the authentication on the IP address means that it is the host
that is authenticated, while authentication based on the NAI results in
<draft-ietf-mobileip-cellular-requirements-01.txt> [Page 4]
authentication of the mobile user. The latter alternative would
alleviate the connection between a specific user and a specific host,
and provide a secure way for dynamic allocation of IP addresses. Thus,
the full authentication must be based on a unique user identity, for
example the NAI.
For reasons of subscription handling and charging, the full
authentication must always be performed at the home domain or by the
home operator, that is, where the user has its subscription. Such
authentication procedures have been suggested in [8][10], and may, for
instance, be performed through AAA functionality. The full
authentication should not be performed at the home agent, since the home
agent may be dynamically allocated.
However, once a mobile node is connected to a visited network,
performing subsequent authentications at the home domain could result
in significant signalling delay. To minimize the signalling delay, and
to reduce the signalling between the visited and the home network, it
should be possible to perform subsequent authentications in the visited
network, as described in [8].
Finally, since the Mobile IP protocol shall allow independence of the
access network technology, the Mobile IP authentication should be
independent of the authentication for the access, for instance the radio
resources. A separation of the authentication procedures is motivated
by the fact that radio resources are scarce, and an access network
operator may not want to allow Mobile IP signalling until the access
network in itself has accepted to provide resources for a mobile node.
Also, different access networks with, for instance, radio-based or fixed
access, experience different types of security threats, and may address
them differently.
The requirements for the authentication procedure are:
1. There MUST be a generic Mobile IP authentication procedure,
specifying full and subsequent authentication, as well as authentication
for registration requests generated on behalf of a mobile node.
2. Full authentication MUST be performed with the home network, the
home administrative domain or with the home operator of the mobile user.
3. There MUST be a unique user identity for full authentication.
4. It SHOULD be possible to perform subsequent authentication locally
at the visited network.
5. Mobile IP SHOULD use the same authentication infrastructure as
stationary Internet nodes.
<draft-ietf-mobileip-cellular-requirements-01.txt> [Page 5]
4. Registration requests generated on behalf of a mobile node
There may be cases when a mobile node does not support Mobile IP
signalling. If so, the signalling between the mobile node and the
foreign agent could be handled by lower-level functionality in the
access network. Then, the foreign agent could generate a registration
request on behalf of the mobile node. This was described in [9] as
surrogate registrations.
For reasons of backward compatibility with existing systems, it must be
possible to implement Mobile IP without introducing Mobile IP signalling
in the terminal. Registration requests generated by the foreign agent
on behalf of a mobile node provide such a solution. They also provide a
means to minimize the signalling over the radio link, and shall be
included in Mobile IP. Lastly, secure full and subsequent authentication
for registration requests generated on behalf of a mobile node must be
ensured according to the generic authentication procedure for Mobile IP.
The requirements for registration requests generated on behalf of a
mobile node are:
1. It MUST be possible to employ Mobile IP in a network without
introducing Mobile IP signalling in the terminal.
5. Private networks
Since private networks are an important part of the communication
network structure, Mobile IP must support private networks and private
address spaces. A proposed solution is to support private address spaces
through proxy home and foreign agents [8]. This solution also supports
hierarchical foreign agents within a network. Such a hierarchy may be
valuable in order to improve handover performance. It may also be
important for security reasons, since it allows the existence of agents
without direct connection to external agents, that is, agents external
to for instance a private network. Since most private networks are
protected by firewalls, Mobile IP must provide a means for signalling
and traffic to pass these firewalls.
Larger private networks may provide their own home agents, but there is
also the case where one operator provides a home agent which is shared
by several smaller private networks. Then, a mobile node may want access
to a private network which is not its home network. In this case, we
recognize a need for, for instance, the VPN Identifier Extension in the
registration request [9]. The NAI of a mobile user points out the home
network of the user and the VPN Identifier Extension points out the final
destination of the tunnel.
<draft-ietf-mobileip-cellular-requirements-01.txt> [Page 6]
The requirements for support of private networks are:
1. Support of private address spaces MUST be included in Mobile IP.
2. Mobile IP MUST provide a means for signalling and traffic to pass
through firewalls.
3. Mobile IP MUST provide a means for a mobile node, or an agent
generating registration requests on behalf of a mobile node, to request
access to a network which is not the home network of the mobile node.
6. Reverse tunnelling
The Mobile IP protocol, as specified in [20], is built on the concept
of triangular routing. Reverse tunnelling has been suggested as an
addition to Mobile IP, to support topologically correct reverse tunnels
[19]. For reasons of security and charging, it must be possible for a
network operator to employ reverse tunnelling, and to refuse mobile
nodes, or agents generating registration requests on behalf of mobile
nodes, which do not request reverse tunnelling when required. It must
also be possible to employ encryption of the traffic with reverse
tunnelling. Lastly, it should be possible to choose how to employ
reverse tunnelling: all the way to the home agent, or to a firewall or
gateway somewhere between the foreign agent and the home agent.
The requirements for reverse tunnelling are:
1. It MUST be possible to employ reverse tunnelling together with Mobile
IP.
2. A network operator MUST be able to refuse mobile nodes, or agents
generating registration requests on behalf of mobile nodes, which do not
request reverse tunnelling.
7. Route optimization
New access techniques are expected to give users significantly more
bandwidth than today, which will lead to more traffic in the backbone
networks. Thus, it is important to minimize the load on the backbone,
as well as the delay, through efficient routing. In the Mobile IP
protocol, datagrams destined to a mobile node are sent to its home
address and are tunnelled by the home agent to the current care-of
address [20]. Route optimization is a suggested addition, which allows
correspondent nodes to send datagrams directly to a mobile node
[22][21]. In order to minimize the delay, and to optimize the
utilization of network resources, it must be possible for an operator
to employ route optimization. Especially, this would improve the
performance for two mobile nodes located in a visited network, which are
communicating with each other.
<draft-ietf-mobileip-cellular-requirements-01.txt> [Page 7]
The authentication procedure for route optimization must be according
to the generic authentication procedure for Mobile IP, and there must
be a secure way to distribute information of the current address of a
mobile node. If requested, encryption must also be ensured for the
traffic. Integrated and differentiated services [4][5][23][24] do not
always handle the change from triangular to optimized routing in a
smooth way, and Mobile IP extensions or changes may be needed. Lastly,
choosing the optimal route, with respect to the number of hops, may
result in a lower level of quality of service. In order to maintain a
negotiated quality of service, the quality-of-service mechanisms may
need to interact with the route optimization mechanisms.
The requirements for route optimization are:
1. It MUST be possible to employ route optimization together with Mobile
IP.
8. Dynamic home address assignment
In many networks, including home networks of mobile nodes, addresses are
assigned dynamically. Dynamic address assignment provides a means to
better utilize the IP addresses in a network. It must be possible to
assign an address to a mobile node, which belongs to a home network that
usually employs dynamic address assignment. Furthermore, if the home
agent is dynamically assigned, the home address needs to be dynamically
assigned as well, since the home address must belong to the same sub-
network as the home agent [20]. A solution for dynamic home address
assignment was proposed in [12].
The requirements for dynamic home address assignment are:
1. Dynamic home address assignment MUST be included in Mobile IP.
9. Temporary home
According to Mobile IP, as specified in [20], the home agent is allocated
in the home network. However, mobile users may have a need for a
temporary home, not necessarily through a home agent assigned in the
home network. The need could be to have an anchor point for some period
of time, and the most optimal solution, considering routing performance,
would be to have a home agent dynamically assigned in the visited
network.
It must be possible for a mobile node, or an agent generating
registration requests on behalf of a mobile node, to request and obtain
a dynamically assigned home agent in the home network or in the visited
network. It should also be possible for a mobile node which has obtained
a dynamically assigned home agent in a visited network, to keep this
home agent when moving to another network. A solution for dynamic home
agent assignment, fulfilling these requirements, has been suggested in
[13].
<draft-ietf-mobileip-cellular-requirements-01.txt> [Page 8]
The requirements for a temporary home solution are:
1. It MUST be possible for a mobile node, or an agent generating
registration requests on behalf of a mobile node, to request and be
assigned a dynamic home agent either in the home network or in the
visited network.
2. A mobile node which has been assigned a dynamic home agent in a
visited network SHOULD be able to keep this home agent when moving to
another network.
10. Handover performance
Mobile IP, as specified in [20], does not provide seamless/loss-less
handover between different foreign agents within the same administrative
domain. The existing solution may be acceptable for certain non-delay-
sensitive and loss-tolerant applications, but needs to be improved in
order to support for instance real-time applications.
There have been suggestions on how to improve the handover performance,
in terms of making the signalling procedure faster [8][14][15][22].
However, the handover performance still needs to be improved in order
to support for instance real-time applications, or to support loss-less
handover.
11. Conclusions
This draft provides a list of requirements on Mobile IPv4 for use in
cellular networks. Beside the general requirements on functionality and
security, there are specific requirements on authentication, address
assignment, routing and issues providing interworking with existing
cellular solutions.
All the requirements provided in this draft may not be necessary in a
first step of introducing Mobile IP in cellular networks. However, we
believe that they all need to be considered to eventually support all
various demands from different operators and end users. The requirements
list will also be extended for Mobile IPv6.
<draft-ietf-mobileip-cellular-requirements-01.txt> [Page 9]
12. Intellectual property considerations
Ericsson has a patent US 5708655 which might be relevant to the issues
considered in this document. If access to this patent should become
necessary for implementing any standard or standards proposal based on
this document, Ericsson is willing to license this patent and any
foreign counterparts on fair and reasonable terms and conditions to
anybody for such use. If somebody asking for such a license from Ericsson
owns or controls a patent also necessary for implementing the standard,
Ericsson consider fair and reasonable terms and conditions to include a
grant back license on such patent and any foreign counterparts. For the
avoidance of doubt Ericsson supports the handling of IPR issues
according to RFC 2026 [7].
13. Acknowledgements
The authors would like to thank Henrik Basilier, Martin Korling, Lars
Westberg, Anders Herlitz, Yuri Ismailov, Ulf Olsson, Thomas Eklund and
Georg Chambert at Ericsson for their valuable comments.
14. References
[1] B. Aboba: "Support for Mobile IP in Roaming", Internet draft
(expired), draft-ietf-roamops-mobileip-01.txt, March 1998.
[2] B. Aboba, M. Beadles: "The Network Access Identifier", RFC 2486,
January 1999.
[3] C.B. Becker, B. Patil, E. Qaddoura: "IP Mobility Architecture
Framework", Internet draft (work in progress), draft-ietf-mobileip-ipm-
arch-00, February 1999.
[4] S. Blake, Editor: "A Framework for Differentiated Services",
Internet draft (work in progress), draft-ietf-diffserv-framework-01,
October 1998.
[5] S. Blake, Editor: "An Architecture for Differentiated Services", RFC
2475, December 1998.
[6] S. Bradner: "Key words for use in RFCs to Indicate Requirements
Levels", RFC 2119, March 1997.
[7] S. Bradner: "The Internet Standards Process -- Revision 3", RFC
2026, October 1996.
<draft-ietf-mobileip-cellular-requirements-01.txt> [Page 10]
[8] P.R. Calhoun, G. Montenegro, C.E. Perkins: "Mobile IP Regionalized
Tunnel Management", Internet draft (work in progress), draft-ietf-
mobileip-reg-tunnel-00.txt, November 1998.
[9] P.R. Calhoun, G. Montenegro, C.E. Perkins: "Tunnel Establishment
Protocol", Internet draft (expired), draft-ietf-mobileip-calhoun-tep-
01.txt, March 1998.
[10] P.R. Calhoun, C.E. Perkins: "DIAMETER Mobile IP Extensions",
Internet draft (work in progress), draft-calhoun-diameter-mobileip-
01.txt, November 1998.
[11] P.R. Calhoun, C.E. Perkins: "Mobile IP Challenge/Response
Extensions", Internet draft (work in progress), draft-ietf-mobileip-
chal-01.txt, February 1999.
[12] P.R. Calhoun, C.E. Perkins: "Mobile IP Dynamic Home Address
Allocation Extension", Internet draft (work in progress), draft-ietf-
mobileip-home-addr-alloc-00.txt, November 1998.
[13] P.R. Calhoun, C.E. Perkins: "Mobile IP Foreign Agent
Challenge/Response Extension", Internet draft (work in progress),
draft-ietf-mobileip-challenge-00.txt, November 1998.
[14] M. Chuah, A. Yan, Y. Li: "Distributed Registrations Enhancements
to Mobile IP", Internet draft (work in progress), draft-chuali-mobileip-
dremip-02.txt, November 1998.
[15] S.F. Foo, K.C. Chua: "Regional Aware Foreign Agent (RAFA) for Fast
Local Handoffs", Internet draft (work in progress), draft-chuafoo-
mobileip-rafa-00.txt, November 1998.
[16] E. Gustafsson, A. Herlitz, A. Jonsson, M. Korling: "UMTS/IMT-2000
and Mobile IP/DIAMETER Harmonization", Internet draft (work in
progress), draft-gustafsson-mobileip-imt-2000-00.txt, November 1998.
[17] T. Hiller, Editor: "3G Wireless Data Provider Architecture Using
Mobile IP and AAA", Internet draft (work in progress), draft-hiller-
3Gwireless-00.txt, March 1999.
[18] D.B. Johnson, C. Perkins: "Mobility Support in IPv6", Internet
draft (work in progress), draft-ietf-mobileip-ipv6-07.txt, November
1998.
[19] G. Montenegro: "Reverse Tunneling for Mobile IP", RFC 2344, May
1998.
<draft-ietf-mobileip-cellular-requirements-01.txt> [Page 11]
[20] C. Perkins, Editor: "IP Mobility Support", RFC 2002, October 1996.
[21] C. Perkins, D.B. Johnson: "Registration Keys for Route
Optimization", Internet draft (expired), draft-ietf-mobileip-regkey-
00.txt, November 1997.
[22] C. Perkins, D.B. Johnson: "Route Optimization in Mobile IP",
Internet draft (work in progress), draft-ietf-mobileip-optim-08.txt,
February 1999.
[23] S. Shenker, J. Wroclawski: "General Characterization Parameters for
Integrated Service Network Elements", RFC 2215, September 1997.
[24] S. Shenker, J. Wroclawski: "Network Element Service Specification
Template", RFC 2216, September 1997.
[25] J.K. Zao, M. Condell: "Use of IPSec in Mobile IP", Internet draft
(expired), draft-ietf-mobileip-ipsec-use-00.txt, November 1997.
15. Author's address
Eva Gustafsson, Annika Jonsson
Ericsson Radio Systems AB
Network and Systems Research
SE-164 80 Stockholm
SWEDEN
{eva.m.gustafsson | annika.jonsson}@era.ericsson.se
Elisabeth Hubbard, Jonas Malmkvist, Anders Roos
Telia Research AB
Network Research
Vitsandsgatan 9
SE-123 86 Farsta
SWEDEN
{elisabeth.a.hubbard | jonas.x.malmkvist | anders.g.roos}@telia.se
<draft-ietf-mobileip-cellular-requirements-01.txt> [Page 12]
Expires October 1999
