One document matched: draft-ietf-mobileip-cellular-requirements-00.txt

Mobile IP Working Group              Eva Gustafsson, Ericsson, Editor
INTERNET-DRAFT                                          February 1999
Expires August 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-00.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 
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 
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at 
http://www.ietf.org/shadow.html.


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. There is also a need to put together the 
demands on Mobile IP, from a cellular perspective, in order to 
harmonize the evolution of Mobile IP and the existing mobility 
solutions in cellular networks.

This draft lists a first 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.


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Table of contents

1. Introduction......................................................2
2. General requirements..............................................3
3. Authentication....................................................4
4. Surrogate registrations...........................................5
5. Private networks..................................................6
6. Reverse tunnelling................................................6
7. Route optimization................................................7
8. Dynamic home address assignment...................................8
9. Dynamic home agent assignment.....................................8
10. Handover performance.............................................8
11. Conclusions......................................................9
12. Acknowledgements.................................................9
13. References.......................................................9
14. Author's address................................................11





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 [11]. The benefits of adopting a common mobility 
solution would include independence of access network technologies, 
common solutions for fixed and wireless networks, and ultimately a 
world-wide acknowledged mobility standard.

The purpose of this document is to state a first version of the 
requirements on Mobile IP as a potential macro-mobility solution for 
cellular networks. The requirements in this document mainly refer to 
Mobile IPv4 [14] and its extension drafts, but the list of requirements 
will be extended for Mobile IPv6 [12] as well.

One important aspect on the requirements is the compatibility with 
existing solutions, for instance the GPRS Tunnelling Protocol (GTP). The 
General Packet Radio Service (GPRS) will be deployed in GSM cellular 
mobile systems starting 1999, giving IP mobility service to potentially 
hundreds of millions of users. The GSM/GPRS standard is evolving into 
the third generation systems: Universal Mobile Telecommunication System 
(UMTS) and the Enhanced Data rates for GSM Evolution (EDGE). These will, 
like Cdma2000, fulfil the ITU requirements for third generation mobile 
systems, IMT-2000.

We start in Section 2 by describing some general requirements for IP 
mobility in cellular networks. Then we list more specific requirements 
in Section 3 through Section 10. Section 11 concludes the document.





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2. General requirements

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 compatibility with existing protocols, for instance GTP.

Mobile IP provides authentication of the signalling messages [14]. 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 [19].

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 reverse tunnelling, route 
optimization and handover. The differences between stationary and mobile 
nodes making use of quality-of-service mechanisms should also be 
minimized. An application requesting a quality-of-service level should 
not need to be mobile aware, and network operators should not need to 
employ different quality of service platforms for stationary and mobile 
users. The emerging quality-of-service architectures, Integrated 
Services and Differentiated Services [3][4][17][18], do not consider 
mobile nodes. Additions or changes may be needed.

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.



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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 the general requirements; some of them apply to Mobile IP and 
some may be fulfilled through other protocols and solutions. The 
following sections address more specific requirements on Mobile IP for 
use in a cellular environment, 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: initial or full 
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 registrations to be performed at the 
home agent, and to be based on the home IP address of the mobile node 
[14]. However, additional solutions and extensions to Mobile IP have 
introduced identification and authentication based on the Network Access 
Identifier (NAI) [1][2][5][6][7][8][9]. Basing the authentication on 
the IP address means that it is the host that is authenticated, while 
authentication based on the NAI results in 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. Therefore, we advocate the full 
authentication to be based on a unique user identity, for example the 
NAI. 

Furthermore, the full authentication should not be performed at the home 
agent, since the home agent may be dynamically allocated. Instead, it 
should be performed at the home network or home administrative domain 
as suggested in [5][7], for instance through AAA functionality.

For reasons of subscription handling and charging, the full 
authentication should always be performed at the home domain or by the 
home operator, that is, where the user has its subscription. However, 
once a mobile node is connected to a visited network, performing 
subsequent authentications at the home domain could result in



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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 [5].

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. It should be possible to perform Mobile IP authentication without 
interaction with the access network / radio resources.

 2. There must be a generic Mobile IP authentication procedure, 
specifying full and subsequent authentication, as well as authentication 
for surrogate registrations.

 3. Full authentication must be performed with the home network, the 
home administrative domain or with the home operator of the mobile user.

 4. There must be a unique user identity for full authentication, for 
instance the NAI [2].

 5. It should be possible to perform subsequent authentication locally 
at the visited network.

 6. Mobile IP should use the same authentication infrastructure as 
stationary Internet nodes.


4. Surrogate registrations

In access networks that have sufficient lower-level signalling, Mobile 
IP registrations between the mobile node and the foreign agent are 
unnecessary. Such situations are supported by surrogate registrations 
as described in [6].

For reasons of backward compatibility with existing systems, it must be 
possible to implement Mobile IP, for instance in GPRS networks, without 
introducing Mobile IP signalling in the terminal. Surrogate 
registrations provide such a solution. They also provide a means to 
minimize the signalling over the radio link, and shall therefore be 
included in Mobile IP.



<draft-ietf-mobileip-cellular-requirements-00.txt>            [Page 5]



The requirements for surrogate registrations are:

 1. It must be possible to employ Mobile IP in a network without 
introducing Mobile IP signalling in the terminal.

 2. Secure full and subsequent authentication for surrogate 
registrations must be ensured according to the generic authentication 
procedure for Mobile IP.


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 [5]. 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 the VPN Identifier Extension in the registration 
request [6]. 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.

The requirements for support of private networks are:

 1. Support of private address spaces must be included in Mobile IP.

 2. Mobile IP must support proxy agents and hierarchical agents.

 3. Mobile IP must provide a means for signalling and traffic to pass 
through firewalls.

 4. The VPN Identifier Extension must be supported in Mobile IP.


6. Reverse tunnelling

The Mobile IP protocol, as specified in [14], 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




<draft-ietf-mobileip-cellular-requirements-00.txt>            [Page 6]


[13]. For reasons of security and charging, it must be possible for a 
network operator to employ reverse tunnelling, and to refuse mobile 
nodes, or surrogate agents, which do not request reverse tunnelling when 
required. It must also be possible to employ encryption of the traffic 
with reverse tunnelling. In the case of private networks, it should be 
possible to choose how to employ reverse tunnelling: all the way to the 
home agent, to the proxy home agent, or only to the proxy foreign 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 surrogate 
agents, which do not request reverse tunnelling when required.

 3. With private networks, it should be possible to employ reverse 
tunnelling to the home agent, to the proxy home agent or to the proxy 
foreign agent.


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 
through efficient routing. In the Mobile IP protocol, datagrams destined 
to a mobile node are sent to its home address and are tunnelled by its 
home agent to the current care-of address [14]. Route optimization is a 
suggested addition to Mobile IP, which allows correspondent nodes to 
send datagrams directly to a mobile node [16][15]. In order to minimize 
the delay, and to optimize the utilization of network resources, it 
shall 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.

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 [3][4][17][18] do not 
always handle the change from triangular to optimized routing in a 
smooth way. 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.


<draft-ietf-mobileip-cellular-requirements-00.txt>            [Page 7]


 2. It should be possible to employ quality-of-service mechanisms 
together with route optimization.


8. Dynamic home address assignment

A solution for dynamic home address assignment is proposed in [8]. 
Dynamic assignment of the home address provides a means to better 
utilize the IP addresses at the home sub-network. Moreover, in case 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 [14]. The dynamic assignment of home 
addresses is in conflict with the use of the home address as the mobile 
node identifier in [14], and a different identifier is required. In [8], 
the NAI is employed for identification.

The requirements for dynamic address assignment are:

 1. Dynamic home address assignment must be included in Mobile IP.


9. Dynamic home agent assignment

In addition to dynamically assigned home addresses, there is a need for 
dynamic allocation of the home agent. A dynamically allocated home agent 
in the visited network can, for instance, improve the routing 
performance. It shall be possible for a mobile node, or a surrogate 
agent, to request and obtain a dynamically assigned home agent in the 
home network or in the visited network. It shall 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 [9].

The requirements for dynamic home agent assignment are:

 1. Dynamic home agent assignment must be included in Mobile IP.

 2. It must be possible for a mobile node, or a surrogate agent, to 
request and be assigned a dynamic home agent either in the home network 
or in the visited network.

 3. A mobile node which has been assigned a dynamic home agent in a 
visited network must be able to keep this home agent when moving to 
another network.








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10. Handover performance

Mobile IP, as specified in [14], 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 [5][10][16]. However, 
the handover performance still needs to be improved in order to support 
for instance real-time applications, or to support loss-less handover.

The requirements for handover are:

 1. The handover performance, in terms of loss and delay, must be 
improved to support real-time and loss-sensitive applications.


11. Conclusions

This draft provides a first list of requirements on Mobile IPv4 for use 
in cellular networks, such as IMT-2000. Beside the general requirements 
on functionality and security, there are specific requirements on 
authentication, address assignment, routing and issues providing 
backward compatibility to existing solutions, for instance GTP.

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.


12. 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.


13. 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.





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[3] S. Blake, Editor: "A Framework for Differentiated Services", 
Internet draft (work in progress), draft-ietf-diffserv-framework-01, 
October 1998.

[4] S. Blake, Editor: "An Architecture for Differentiated Services", RFC 
2475, December 1998.

[5] 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.

[6] P.R. Calhoun, G. Montenegro, C.E. Perkins: "Tunnel Establishment 
Protocol", Internet draft (expired), draft-ietf-mobileip-calhoun-tep-
01.txt, March 1998.

[7] P.R. Calhoun, C.E. Perkins: "DIAMETER Mobile IP Extensions", 
Internet draft (work in progress), draft-calhoun-diameter-mobileip-
01.txt, November 1998

[8] 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. 

[9] 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.

[10] 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. 

[11] 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.

[12] D.B. Johnson, C. Perkins: "Mobility Support in IPv6", Internet 
draft (work in progress), draft-ietf-mobileip-ipv6-07.txt, November 
1998.

[13] G. Montenegro: "Reverse Tunneling for Mobile IP", RFC 2344, May 
1998.

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





<draft-ietf-mobileip-cellular-requirements-00.txt>            [Page 10]



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

[16] C. Perkins, D.B. Johnson: "Route Optimization in Mobile IP", 
Internet draft (expired), draft-ietf-mobileip-optim-07.txt, November 
1997.

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

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

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


14. 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













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Expires August 1999