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AAA Working Group                                             John Wang
                                                               Motorola
Internet Draft                                                Rong Wang
Document: <draft-wang-aaa-cel-req-00.txt>                      Motorola

Expire: April 20, 2000                                 October 20, 1999

     Cellular Network Authentication, Authorization, and Accounting
                              Requirements
                      <draft-wang-aaa-cel-req-00.txt>

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
      all provisions of Section 10 of RFC2026 [1].

   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
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   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.

   This document is a submission by the AAA Working Group of the
   Internet Engineering Task Force (IETF).  Comments should be
   submitted to the aaa-wg@merit.edu mailing list.

   Distribution of this memo is unlimited.

1. Abstract

   The AAA Working group is currently looking at defining the
   requirements for Authentication, Authorization and Accounting. This
   document contains the requirements that should be supported within
   AAA to aid in providing next generation cellular services.

2. Conventions used in this document

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   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 [2].

3. Background

   There is a trend in the cellular industry to support next generation
   cellular services based on IP technology.

   The current IP network is designed for stationary or portable
   commuting. There are fundamental differences between portable
   commuting and cellular applications. In cellular industry the
   following issues are of great concern: the limited over-the-air
   capacity, the restricted computing power and power supply of Mobile
   Station (MS), the latency consideration for real time applications,
   and the mobility behavior of MS etc. These lead to some stringent
   requirements on the IP network as a whole.

   Next generation cellular applications will raise the requirements on
   IP network even higher. There are two fundamental factors that
   clearly differentiate the new generation from the current cellular
   applications: global coverage and multi-mode MS with integrated
   service.

   AAA functionality, among with others such as mobility management and
   call control, is an integral part of system management. To ensure
   efficient system implementation, the architecture and functionality
   of the overall system management functions must be compatible.

   This document defines AAA requirements for the next generation
   cellular services targeting an integrated system management
   architecture with high quality and overall system efficiency.

4. Terminology

   Access Network
                 The access network provides the basic transmission,
                 local control and management functions needed for the
                 terminal device to access the resources of the Core
                 Network.

   Core Network
                 The next generation core network should provide the
                 transmission, switching, control and management
                 functions needed to connect the Access Network to
                 other networks. The intent is that Core Network hide
                 all nuances specific to a given network technology
                 from the Access Network.

   Foreign Agent (FA)
                 A router on a mobile node's visited network which
                 provides routing services to the mobile node while

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                 registered.  The foreign agent de-tunnels and delivers
                 datagrams to the mobile node. For datagrams sent by a
                 mobile node, the foreign agent may serve as a default
                 router for registered mobile nodes.

   Home Agent (HA)
                 A router on a mobile node's home network which, when
                 the mobile node is away from home, receives traffic
                 for the mobile node, tunnels these datagrams for
                 delivery to the mobile node, and maintains current
                 location information for the mobile node.

   Home Location Register (HLR)
                 The functional entity that provides the primary
                 database repository of subscriber information used to
                 provide control and intelligence in cellular and
                 wireless networks.

   Integrated Service
                 A service that is capable of supporting multiple
                 access technologies in a resource, cost and latency
                 efficient way.

   Mobile Node (MN)
                 A host that changes its point of attachment from one
                 network or sub-network to another.

   Mobile Station (MS)
                 The mobile of portable subscriber radio-telephone
                 equipment.

   Multi-mode MS
                 MS capable of accessing multiple access networks
                 (possible simultaneously).

   5. Utilization of AAA Functions in Current Cellular Networks

   In cellular network, authentication is a set of functions used to
   prevent fraudulent access to cellular networks by devices illegally
   programmed with counterfeit Mobile Identification Number (MIN) and
   Electronic Serial Number (ESN) information [3]. A successful mobile-
   to-network authentication occurs when the MS demonstrates its
   possession of assigned secret authentication information to network.
   This can be achieved by showing calculation results based on the
   authentication information in such a way that the network can verify
   its correctness. A centralized Authentication Center (AC) is
   the primary functional entity in the current cellular network
   responsible for managing the authentication information, although
   the serving system may also be allocated certain responsibilities.

   The authentication process can be invoked by many events. It is
   performed most often in the following situations:

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   - Registration
   - Call Origination
   - Call Termination

6. AAA Considerations in Next Generation Cellular Network

   As cellular networks migrate to an integrated architecture, there
   are new situations that must be considered when designing the AAA
   solution.

6.1 Integrated Mobility Management and AAA

   Mobile IP [3] enables a mobile node to change its attachment point
   on the Internet while maintaining its IP address as well as network
   connectivity. As a mobility management protocol, Mobile IP is
   suitable for portable computing but it is not efficient enough for
   cellular applications. Tromboning is one major issue in Mobile IP
   when used in a cellular network [4].

   There have been many efforts to make Mobile IP more efficient. Some
   of the leading efforts include the route optimization [5] and Mobile
   IP regional tunnel management [6] techniques. These technologies are
   based on a hierarchical location database architecture to provide
   ways to update the MN location information and to make it possible
   to connect a call based on local information rather than reference
   to the Home Agent(HA).

   The mobility management functions (e.g. registration, handoff
   functions) tie directly with the AAA functions. It is preferable
   that AAA and mobility management functions are integrated together.

6.2 Integrated AAA Architecture for Integrated Access Networks

   Currently, each access network technology has its own authentication
   and authorization process. For example, access
   authentication/authorization in a cellular network is carried out
   through messages between MS, its Home Location Register (HLR) and a
   centralized Authentication Center. Meanwhile, access
   authentication/authorization in Mobile IP is done through messaging
   between the Mobile Node (MN), its HA, Foreign Agent (FA) and AAA
   server(s).

   An integrated AAA architecture cross access technology provides an
   opportunity for creating a unified AAA interface for integrated
   services.

6.3 Addressing

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   To function properly in an integrated network, it is indispensable
   to have an unique address to identify the end user or the customer
   device.

   It is a general practice in existing cellular industry to adopt a
   topology dependent address that is directly routable without
   consulting any centralized global database. It is of crucial
   importance for IP network to maintain this feature for cellular or
   other real time applications due to efficiency and latency
   considerations. Consequently, AAA solution must be able to support
   topology dependent address as well.

6.4 Independent of Radio Access Technologies

   Multiple radio access technologies (e.g. Global System for Mobile
   Communication and Code-Division Multiple Access) exist in the
   cellular network. AAA functions should be independent of the air
   interface protocol used to access the network.

7. Cellular Service Requirements on AAA

   Based on the above scenarios of cellular networks/services,
   the following specific requirements for AAA can be ascertained.

   - The AAA server SHOULD be able to support mobility management with
     a layered and distributed architecture efficiently.

   - AAA SHOULD be able to work in an integrated mobility management
     and AAA framework to offer the most efficient solution.

   - AAA SHOULD be able to offer an integrated and efficient solution
     for a customer with multi-mode capable MS.

   - AAA MUST be able to provide mutual authentication functionality
     for MS and the network(s). And the AAA solution MUST be scalable.

   - AAA MUST support mutual authenticated key agreement to provide
     keys for message privacy and integrity.

   - AAA MUST be able to work with the topology dependent address.

   - AAA MUST support message privacy and integrity.

   - The AAA solution MUST be able to support device roaming.

   - The AAA solution SHOULD be able to support user roaming.

   - AAA MUST support the option for AC to share some temporary secret
     information about a MS or subscriber with serving system in a
     secure and efficient way.

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   - AAA SHOULD provide flexible period key update.

   - There SHOULD NOT be any assumptions on the access network
     technologies for AAA solutions.

8. Security Considerations

   This draft defines the AAA requirements for the next generation
   cellular services. As AAA is security driven, most of this document
   addresses the security considerations AAA must make on behalf of
   cellular services.

9. References

   1  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
      9, RFC 2026, October 1996.

   2  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997

   3  Perkins, C., editor, "IP mobility support", RFC 2002, October
      1996

   4  Gallagher M. and Snyder R., "Mobile Telecommunications Networking
      with IS-41", McGraw-Hill, 1997

   5  Perkins, C. et. al., "draft-ietf-mobileip-optim-08.txt:
      Route Optimization in Mobile IP", Internet Draft, February 1999

   6  Gustafsson, E. et. al., "draft-ietf-mobileip-reg-tunnel-01.txt:
      Mobile IP Regional Tunnel Management", Internet Draft, August
      1999

10. Acknowledgement

   Many thanks to Phil Roberts, Dan Brown and Lily Chen at Motorola for
   their valuable comments and support.

11. Author's Addresses

   John Wang
   Motorola Inc.
   1501 W. Shure Dr.
   Arlington Heights, IL 60004, USA
   Phone: (847) 435-2710
   Email: ezw001@email.mot.com

   Rong Wang
   Motorola Inc.

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   1501 W. Shure Dr.
   Arlington Heights, IL 60004, USA
   Phone: (847) 632-2647
   Email: rwang1@email.mot.com

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