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Versions: 00 01 02                                                      
Mobile IP Working Group              Eva Gustafsson, Ericsson, Editor
INTERNET-DRAFT                                              June 1999
Expires December 1999
                                             Annika Jonsson, Ericsson
                                             Elisabeth Hubbard, Telia
                                               Jonas Malmkvist, Telia
                                                   Anders Roos, Telia

        Requirements on Mobile IP from a Cellular Perspective

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@standards.nortelnetworks.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
working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at

The list of Internet-Draft Shadow Directories can be accessed at


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
gather 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.

<draft-ietf-mobileip-cellular-requirements-02.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. Addresses.......................................................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 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 Cdma 2000, are such IMT-2000 systems.

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. In the following,
the term Mobile IP refers to both Mobile IPv4 [20] and Mobile IPv6 [18].

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

<draft-ietf-mobileip-cellular-requirements-02.txt>            [Page 2]

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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, Mobile IP
functionality shall be independent of the access network technology. For
Mobile IP to be deployed in future cellular networks, it needs to
interwork with, or operate in co-existence with, existing protocols in
the cellular networks.

Considering a migration from Mobile IPv4 to Mobile IPv6, there may be
mobile nodes which are upgraded and mobile nodes which are not.
Similarly, there may be home and/or visited networks supporting Mobile
IPv4, and others supporting Mobile IPv6. Such a scenario must be
supported. Mobile nodes supporting Mobile IPv6 must also be able to
communicate with mobile nodes supporting Mobile IPv4.

Mobile IP provides authentication of the signalling messages [18][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. In Mobile IPv4, 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 IPv4,
as suggested in [27]. For Mobile IPv6, use of IPSec is included in the
protocol [18].

Emerging Internet quality-of-service (QoS) mechanisms are expected to
enable 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 QoS 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 QoS for mobile users, particularly
in case of handover and route optimization [23]. The differences between
stationary and mobile nodes making use of QoS mechanisms should also be
minimized, and network operators should not need to employ different QoS
platforms for stationary and mobile users. The emerging QoS
architectures, Differentiated Services and Integrated Services
[4][5][24][25], do not consider mobile nodes. Additions or changes may
be needed.

<draft-ietf-mobileip-cellular-requirements-02.txt>            [Page 3]

QoS mechanisms enforce a differentiated sharing of bandwidth among
services and users. Thus, there must be mechanisms available to identify
traffic flows with different QoS attributes, and to make it possible to
charge the users accordingly.

It is well known that mobile nodes are more complex to handle than
stationary ones. Even so, 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)
QoS and policy control; and (iii) directory services and gateway
services like IP telephony.

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, 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
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: (i) full or initial
authentication; and (ii) 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
when a mobile node changes its point of attachment, within or between
administrative domains, 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 [18][20]. However, additional solutions and
extensions, mainly to Mobile IPv4, have introduced identification and
authentication based on the Network Access Identifier (NAI)
[1][2][8][9][10][11][12][21]. Basing the authentication on the IP
address means that it is the host that is authenticated, while

<draft-ietf-mobileip-cellular-requirements-02.txt>            [Page 4]

authentication based on the NAI enables authentication of the mobile
user. The latter alternative would lessen 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 is subscribed. Such
authentication procedures have been suggested for Mobile IPv4 in
[8][10], and may, for instance, be performed through AAA functionality.
Full authentication may not be performed at the home agent, since the
home agent may be dynamically allocated.

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 is independent of the access
network technology, Mobile IP authentication should be independent of
the authentication for the access medium, 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 or binding updates 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 AAA infrastructure as stationary
Internet nodes.

<draft-ietf-mobileip-cellular-requirements-02.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 its
network access point/foreign agent could be handled by lower-level
functionality in the access network. Then, the access point/foreign
agent could generate a registration request or binding update on behalf
of the mobile node. This was described for Mobile IPv4 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/binding updates generated on
behalf of a mobile node provide such a solution. They also provide a
means to minimize the signalling over the radio link. Lastly, secure
full and subsequent authentication for registration requests/binding
updates 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 for Mobile IPv4 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.
Another solution for IP mobility support across routing realms is
suggested in [26]. Lastly, 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-02.txt>            [Page 6]

The requirements for support of private networks are:

 1. Support of private address spaces MUST be included in Mobile IPv4.

 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 or binding updates 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 IPv4 protocol, as specified in [20], is built on the concept
of triangular routing. Reverse tunnelling has been suggested as an
addition to Mobile IPv4, to support topologically correct reverse
tunnels [19]. Reverse tunnelling may also be valuable to provide
location privacy, both for Mobile IPv4 and Mobile IPv6. 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 or binding updates 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 between the mobile node, or foreign agent, and the home agent.

The requirements for reverse tunnelling are:

 1. It MUST be possible to employ reverse tunnelling together with Mobile

 2. For Mobile IPv4, a network operator MUST be able to refuse mobile
nodes, or agents generating registration requests/binding updates 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 IPv4
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
[23][22]. In order to minimize the delay, and to optimize the
utilization of network resources, it must be possible for an operator

<draft-ietf-mobileip-cellular-requirements-02.txt>            [Page 7]

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. For Mobile IPv6, route optimization is
included in the protocol.

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 available for the
traffic. Integrated and differentiated services [4][5][24][25] 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

8. Dynamic home address assignment

In many IPv4 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]. The latter requirement applies
to Mobile IPv6 as well as to Mobile IPv4. A solution for dynamic home
address assignment for Mobile IPv4 was proposed in [11][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 [18][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
and signalling delay, would be to have a home agent dynamically assigned
in the visited network.

<draft-ietf-mobileip-cellular-requirements-02.txt>            [Page 8]

It must be possible for a mobile node, or an agent generating
registration requests/binding updates 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.

The requirements for a temporary home solution are:

 1. It MUST be possible for a mobile node, or an agent generating
registration requests/binding updates on behalf of a mobile node, to
request and be assigned a dynamic home agent in the home network.

 2. It SHOULD be possible for a mobile node, or an agent generating
registration requests/binding updates on behalf of a mobile node, to
request and be assigned a dynamic home agent in the visited network.

 3. 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 IPv4, as specified in [20], does not guarantee seamless/loss-less
handover between different foreign agents within the same administrative
domain. The existing solution may be acceptable for 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][13][14][15][23].
However, the handover performance still needs to be improved in order
to support real-time applications, or to support loss-less handover.

When a mobile node supporting Mobile IPv6 changes care-of address, it
is able to generate binding updates to its home agent, to its previous
default router and to its correspondent nodes [18]. However, the radio
is a scarce resource, and transmission of multiple simultaneous binding
updates may not be feasible.

11. Conclusions

This draft provides a list of requirements on Mobile IP 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.

<draft-ietf-mobileip-cellular-requirements-02.txt>            [Page 9]

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.

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, Conny Larsson and
Georg Chambert at Ericsson and Thomas Eklund at SwitchCore 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] Y. Bernet, et al.: "A Framework for Differentiated Services",
Internet draft (work in progress), draft-ietf-diffserv-framework-02,
February 1999.

[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.

<draft-ietf-mobileip-cellular-requirements-02.txt>            [Page 10]

[7] S. Bradner: "The Internet Standards Process -- Revision 3", RFC
2026, October 1996.

[8] P.R. Calhoun, G. Montenegro, C.E. Perkins: "Mobile IP Regionalized
Tunnel Management", Internet draft (expired), 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 (expired), draft-calhoun-diameter-mobileip-01.txt,
November 1998.

[11] P.R. Calhoun, C.E. Perkins: "Mobile IP Dynamic Home Address
Allocation Extension", Internet draft (expired), draft-ietf-mobileip-
home-addr-alloc-00.txt, November 1998.

[12] P.R. Calhoun, C.E. Perkins: "Mobile IP Network Access Identifier
Extension", Internet draft (work in progress), draft-ietf-mobileip-mn-
nai-02.txt, May 1999.

[13] M. Chuah, A. Yan, Y. Li: "Distributed Registrations Enhancements
to Mobile IP", Internet draft (expired), draft-chuali-mobileip-dremip-
00.txt, October 1997.

[14] K. El Malki, N.A. Fikouras: "Fast Handoff Method for Real-Time
Traffic over Scaleable Mobile IP Networks", Internet draft (work in
progress), draft-elmalki-mobileip-fast-handoffs-00.txt, March 1999.

[15] S.F. Foo, K.C. Chua: "Regional Aware Foreign Agent (RAFA) for Fast
Local Handoffs", Internet draft (expired), 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 (expired), 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 (expired), draft-ietf-mobileip-ipv6-07.txt, November 1998.

<draft-ietf-mobileip-cellular-requirements-02.txt>           [Page 11]

[19] G. Montenegro: "Reverse Tunneling for Mobile IP", RFC 2344, May

[20] C. Perkins, Editor: "IP Mobility Support", RFC 2002, October 1996.

[21] C.E. Perkins, P.R. Calhoun: "Mobile IP Challenge/Response
Extensions", Internet draft (work in progress), draft-ietf-mobileip-
chal-02.txt, May 1999.

[22] C. Perkins, D.B. Johnson: "Registration Keys for Route
Optimization", Internet draft (expired), draft-ietf-mobileip-regkey-
00.txt, November 1997.

[23] C. Perkins, D.B. Johnson: "Route Optimization in Mobile IP",
Internet draft (work in progress), draft-ietf-mobileip-optim-08.txt,
February 1999.

[24] S. Shenker, J. Wroclawski: "General Characterization Parameters for
Integrated Service Network Elements", RFC 2215, September 1997.

[25] S. Shenker, J. Wroclawski: "Network Element Service Specification
Template", RFC 2216, September 1997.

[26] W.T. Teo, Y. Li: "Mobile IP extension for Private Internets Support
(MPN), Internet draft (work in progress), draft-teoyli-mobileip-mvpn-
02.txt, February 1999.

[27] J.K. Zao, M. Condell: "Use of IPSec in Mobile IP", Internet draft
(expired), draft-ietf-mobileip-ipsec-use-00.txt, November 1997.

15. Addresses

The working group can be contacted via the current chairs:

Erik Nordmark                    Basavaraj Patil
Sun Microsystems, Inc.           Nortel Networks Inc.
17 Network Circle                2201 Lakeside Blvd.
Menlo Park, California 94025     Richardson, TX. 75082-4399
USA                              USA

nordmark@sun.com                 bpatil@nortelnetworks.com

<draft-ietf-mobileip-cellular-requirements-02.txt>           [Page 12]

Questions about this memo can be directed to:

Eva Gustafsson, Annika Jonsson
Ericsson Radio Systems AB
Network and Systems Research
SE-164 80 Stockholm

{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

{elisabeth.a.hubbard | jonas.x.malmkvist | anders.g.roos}@telia.se

<draft-ietf-mobileip-cellular-requirements-02.txt>           [Page 12]

                        Expires December 1999