CDMA2000 Wireless Data Requirements for AAA

Status of this Memo

This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.

Copyright Notice

Copyright © The Internet Society (2001). All Rights Reserved.

Abstract

This memo specifies cdma2000 wireless data AAA (Authentication, Authorization, Accounting) requirements associated with third generation wireless architecture that supports roaming among service providers for traditional PPP and Mobile IP services.

1. Introduction

The architecture is designed for use with a cellular network as an access medium. Sections 1, 2, present a brief high level review of the cdma2000 wireless data architecture. Section 3 presents cdma2000 AAA requirements.

This document specifies AAA requirements associated with a third generation cdma2000 wireless architecture that supports roaming among service providers for traditional PPP and Mobile IP services. The architecture is designed for use with a cellular network as an access medium.

   Sections 1 and 2 present a brief, high level review of the cdma2000
   wireless  data architecture as an aid to interested AAA WG members.
   Section 3 presents cdma2000 AAA requirements, and is self contained
   relative to the architecture review.

1.1. Requirements language

In this document, the key words "MAY", "MUST, "MUST NOT", "optional", "recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as described in [RFC2119].

Please note that the requirements specified in this document are to be used in evaluating AAA protocol submissions. As such, the requirements language refers to capabilities of these protocols; the protocol documents will specify whether these features are required, recommended, or optional. For example, requiring that a protocol support confidentiality is NOT the same thing as requiring that all protocol traffic be encrypted.

A protocol submission is not compliant if it fails to satisfy one or more of the MUST or MUST NOT requirements for the capabilities that it implements. A protocol submission that satisfies all the MUST, MUST NOT, SHOULD and SHOULD NOT requirements for its capabilities is said to be "unconditionally compliant"; one that satisfies all the MUST and MUST NOT requirements but not all the SHOULD or SHOULD NOT requirements for its protocols is said to be "conditionally compliant."

1.2. General Service Requirements

• Provide service during subscriber visiting between wireless networks systems while maintaining a formal customer-service provider relation with only one wireless service provider.

• Support Traditional PPP and Mobile IP services:

         o  Support dynamic and static home address assignments for
            Mobile IP
         o  Support a Home Agent in the mobile's home wireless network,
            home ISP, or private network.
         o  Support IP Security on the Mobile IP tunnel between Foreign
            Agent and Home Agent, in order to avoid the overhead of a
            voluntary tunnel on the radio interface.

• Provide robust authentication, authorization and accounting services (AAA):

         o  Provide separation of airlink resource AAA services and data
            resource AAA services.
         o  Authenticate and authorize a mobile based on an IMSI and an
            NAI.  The architecture allows for a carrier to determine if
            billing is based on the IMSI or the NAI.
         o  Support optional AAA broker services between wireless
            carriers and between wireless carriers and other external
            data networks.
         o  Allow for distribution of specific Mobile IP security key
            information to support home agent assignment, fast handoff,
            and fast HA-FA authentication assignment during
            registration.

• Provide QoS

2. High Level Architecture

The high level architecture is shown in Figure 1. The six major entities that compose the network are the Home Agent, the PDSN, the AAA Server, the Radio Network, the HLR/VLR, and Mobile Client.

            Visited Access              Home Access
            Provider Network           Provider Network
              +--------+                 +--------+
              |        |      SS7        |        |
              |  VLR   |-----------------|  HLR   |
              |        |                 |        |
              +--------+                 +--------+
                  |
                  |
                  |  Visited Access      Broker        Home IP
                  |  Provider Network    Network       Network
                  |     +--------+      +--------+   +--------+
                  |     |        |      |        |   |        |
                  |     |  AAA   |------|  AAA   |---|  AAA   |
                  |     |        |      |        |   |        |
                  |     +--------+      +--------+   +--------+
                  |             \                \       |
                  |              \                \      |
                  |               \                \     |
                  |                \                \    |
                  |                 \                \   |
              +---------+       +---------+       +---------+
              |         |       |         |       |         |
              |   RN    |-------|  PDSN   |-------|  HA     |
              |         |       |         |       |         |
              +---------+       +---------+       +---------+
                  |
                  |   Visited Access            Home Network
                  |  Provider Network           -Private
            Mobile|                             -Visited Provider
              IP  |                             -Home Provider
                  |                             -Home ISP
               +--------+
               | Mobile |
               | Node   |
               +--------+

Figure 1: General cdma2000 Wireless IP Architecture

2.1. PDSN

      o  Acts as a Foreign Agent;
      o  Establish, maintain, and terminate link layer to the mobile
         client;
      o  Initiate the authentication, authorization and accounting for
         the mobile client;
      o  Optionally, securely tunnel using IP security to the Home
         Agent;
      o  Receives service parameters from AAA for mobile client;
      o  Collect usage data for accounting purposes to be relayed to
         AAA;
      o  Routes packets to external packet data networks or to the HA in
         the case of reverse tunneling;
      o  Maps home address and Home Agent address to a unique link layer
         identifier used to communicate with Radio Network.

2.2. Authentication, Authorization, and Accounting Server

      o  Interact with the Foreign Agent and other AAA servers to
         authorize, authenticate and perform accounting for the mobile
         client;
      o  Provides mechanism to support security association between
         PDSN/FA and HA and between the MN and PDSN/FA;
      o  For dynamic Home Agent assignment, dynamically identify an HA
         and assign a MN on that HA, and provide the security
         association between the MN and HA;
      o  Provide QoS information to the PDSN;
      o  Optionally, assign dynamic home address.

2.3. Radio Network

      o  Maps Mobile Client identifier reference to a unique link layer
         identifier used to communicate with PDSN;
      o  Validates Mobile Station for access service;
      o  Manages physical layer connection to the Mobile Client;
      o  Maintain state of reachability for packet service between the
         access radio network and the mobile station;
      o  Buffers packets arriving from the PDSN, when radio resources
         are not in place or are insufficient to support the flow from
         the PDSN;
      o  Relays packets between the mobile station and the PDSN.

2.4. Location Registers (VLR/HLR)

• Stores authentication and authorization information for the radio network.

2.5. Home Agent

o Maintains user registration and redirects packets to the PDSN; o Optionally, establish an IP secure tunnel to the PDSN/FA; o Supports the dynamic Home Agent assignment;
o Optionally, assigns dynamic home address;
o Support reverse tunneling.

2.6. Mobile Node

      o  Support PPP;
      o  Can act as a Mobile IP Node; and support Foreign Agent
         Challenge and NAI;
      o  Interacts with the Radio Network to obtain appropriate radio
         resources from the network for the exchange of packets;
      o  Maintains knowledge of status of radio resources (e.g., active,
         standby, dormant);
      o  Buffers packets when radio resources are not in place or are
         insufficient to support the flow to the network.

3. AAA Requirements

3.1. Core AAA Requirements

The following is a summary of cdma2000 AAA specific requirements. In these requirements, the serving network and home network may or may not have a direct business relationship. In such cases in which there is not a direct business relationship, service may be supported indirectly via broker.

      o  Authenticate and authorize a user NAI in a roaming environment.
         The NAI is obtained via CHAP (for traditional PPP service) or a
         Foreign Agent Challenge (for Mobile IP service).  A shared
         secret exists between the mobile and its HAAA.  The FAC will
         typically be computed in a manner  consistent with CHAP.
      o  Transport wireless data attributes from the home network to the
         Serving network.  This may often take the form of a user
         profile.
      o  Encrypt or sign one or more AVPs in an AAA message between
         home, serving network, or some broker across multiple AAA
         server hops.
      o  Support a reliable AAA transport mechanism.
         o  This transport mechanism will be able indicate to an AAA
            application that a message was delivered to the next peer
            AAA application or that a time out occurred.
         o  Retransmission is controlled by the reliable AAA transport
            mechanism, and not by lower layer protocols such as TCP.
      
         o  Even if the AAA message is to be forwarded, or the message's
            options or semantics do not conform with the AAA protocol,
            the transport mechanism will acknowledge that the peer
            received the AAA message.  However, if the message fails to
            pass authentication, it will not be acknowledged.
         o  Acknowledgements should be allowed to be piggybacked in AAA
            messages
         o  The reliable transport mechanism features shall have the
            capability to detect silent failures of the AAA peer or path
            to the AAA peer, to manage failure on a proactive basis.
         o  Transport a digital certificate in an AAA message, in order
            to minimize the number of round trips associated with AAA
            transactions.  Note: This requirement applies to AAA
            applications and not mobile stations.
         o  Support both proxy and non-proxy brokers, where non-proxy
            brokers imply the broker terminates an entire request and
            initiates a new request.  AAA brokers should have the
            capability to modify certain parts of AAA messages whereby
            to operate to in non-proxy or proxy environments.
         o  Provide message integrity and identity authentication on a
            per hop (AAA node) basis.
         o  Support replay protection and optional non-repudiation
            capabilities for all authorization and accounting messages.
            The AAA protocol must provide the capability for accounting
            messages to be matched with prior authorization messages.
         o  Support accounting via both bilateral arrangements and via
            broker AAA servers providing accounting clearinghouse and
            reconciliation between serving and home networks.  There is
            an explicit agreement that if the private network or home
            ISP authenticates the mobile station requesting service,
            then the private network or home ISP network also agrees to
            reconcile charges with the home service provider or broker.
            Real time accounting must be supported.
         o  Provides security between AAA servers, and between AAA
            server and PDSN or HA via IP security.

3.2. Mobile IP Specific Requirements and AAA

3.2.1. Mobile IP Security Discussion

Three Mobile IP security extensions are defined in RFC 2002:

        . HA - FA
        . MN - FA
        . HA - MN

Therefore, Mobile IP and IPsec security models differ in that Mobile IP provides its own authentication mechanisms calculated within the Mobile IP registration procedures whereas IPsec uses IPsec AH.

The keys and SPIs associated with the MN-FA and HA-FA extensions need to be dynamically established in a roaming wireless carrier environment. The MN-FA extension is useful for allowing a new FA (PDSN) to quickly authenticate a mobile using the previous foreign agent extension. The HA-FA extension is useful for the HA to ensure that only FAs from carrier's with roaming agreements access the HA. The MN-HA is usually provisioned, but for dynamic Home Agent assignment, this security association must be dynamically created.

It is possible to use IPsec AH between MN and FA, FA and HA, and MN and HA. IKE may be used to establish security associations between these entities. However, use of IKE may pose a problem for smaller mobiles and may introduce unacceptable delays for certain applications (e.g., Voice Over IP). The following three sections outline Mobile IP specific functions that benefit from AAA based key distribution.

3.2.2. Dynamic Home Agent Assignment

A visited or home AAA server will optionally be able perform dynamic HA assignment. For dynamically assigned HA, the visited AAA server will indicate to the home AAA server whether it supports dynamic HA assignment in those cases in which the mobile node requests dynamic assignment. If so indicated, the home AAA server may choose to allow the visited AAA server to perform the HA assignment. Otherwise, the home AAA assigns the HA.

3.2.3. Fast Handoff

To achieve a faster handoff, the mobile may attempt to avoid an AAA transaction with the home AAA server. To accomplish this, the mobile may send the PDSN the Previous FA address in the RRQ message from the mobile, along with the MN-FA authentication extension. The new PDSN passes the Previous FA address and MN-FA authentication extension to the visited AAA server. If the visited AAA server is able authenticate the MN-FA authentication extension for the mobile, then the visited AAA may be able to avoid an actual transaction to the home AAA server.

3.2.4. HA-FA Authentication

To achieve a fast registration for the case of a mobile station with a Home Agent, the PDSN and HA may receive from the AAA mechanism a HA-FA key and SPI that is used to authenticate the PDSN and the HA to each other.

3.2.5. Key Distribution

These functions are primarily useful in a wireless environment in which handoffs may occur rapidly (implying a need for low latency), or where mobile devices have limited computing power. To achieve these functions, AAA will be used to securely pass keys and SPIs between the serving network and target network in encrypted form. These keys are then used for the specific functions outlined in this document.

3.3. IKE and AAA

The use of IKE in the cdma2000 wireless architecture requires the use of certificates. However, the AAA servers may be able to distribute a pre- shared key to the Mobile IP Agents for use during Phase 1 ISAKMP exchanges. This may lessen the need for on-line revocation checks.

3.4. Interoperability with RADIUS

Users with a home AAA server based on RADIUS may desire to roam into a wireless carrier network that uses "new" AAA servers based on the requirements in this document, and vice verse. The AAA protocol should be designed in a way so as to make conversions to and from RADIUS messages straight forward. This will allow for the development of gateway processes to aid in interoperability. Note: The features of the new AAA protocols which are beyond the feature set of the RADIUS protocol will not be available for users while on home or serving networks based on RADIUS.

4. References

   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

5. Security Considerations

This document is very much about security. These requirements do not require the serving and home networks to not be in the same domain nor must they have a direct relationship. The serving network requires authorization from the home network so that the serving network obtains proof it will get paid for services rendered to the mobile. This implies the home network must authenticate the user. AAA functions must be performed in a secure manner. The requirements contained in section 2 outline the security required.

Mobile IP supports authentication mechanisms outside IP Security. These mechanism may be enhanced in a cellular wireless environment by allowing a home AAA server to distribute keys to the serving network. Additionally, the home AAA server may be able to send a pre-shared key to be used in Phase 1 ISAKMP security association establishment between FA and HA. These keys would sent in encrypted form from the home network to the serving network. As supported in the requirements contained in section 2, the encryption could be handled via public cryptography and certificates.

6. IANA Considerations

This document does not create any new number spaces for IANA administration.

7. Acknowledgements

The authors are active members of the TIA TR45.6 committee.

8. Authors' Addresses

Pat R. Calhoun
Network and Security Research Center, Sun Labs
Sun Microsystems, Inc.
15 Network Circle
Menlo Park, CA 94025
USA

   Phone: (650) 786-7733
   EMail: pcalhoun@eng.sun.com

Ed Campbell
CommWorks Corporation, A 3Com Company
3800 Golf Road
Rolling Meadows, IL 60008

   Phone: (847)262-2325
   E-Mail: ed_campbell@commworks.com

Gopal Dommety
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
USA

EMail:

          gdommety@cisco.com

Tom Hiller
Rm 2F-218
263 Shuman Dr.
Lucent Technologies
Naperville, IL
USA

   Phone: (630) 979-7673
   EMail: tom.hiller@lucent.com

Raymond T. Hsu
Qualcomm Inc.
6455 Lusk Blvd.
San Diego, CA 92121
USA

   Phone: (619) 651-3623
   EMail: rhsu@qualcomm.com
   
   Mark A. Lipford
   Sprint PCS
   15405 College Blvd.
   Lenexa, KS  66219
   
   Phone:  (913) 890-4248
   EMail: mlipfo01@sprintspectrum.com
   
   Serge Manning
   Award Solutions, Inc.
   800 E. Campbell Rd., Suite 120
   Richardson, TX  75081
   
   Phone: (972) 664-0727 x350
   EMail: serge@awardsolutions.com

Peter J. McCann
Lucent Technologies
Rm 2Z-305
263 Shuman Blvd
Naperville, IL 60566
USA

   Phone: (630) 713 9359
   EMail: mccap@lucent.com

Mark Munson
1371 Winding Branch Circle
Atlanta, Georgia 30338
USA

   Phone: (678) 339-4439
   EMail: mmunson@gte.net

Haeng Koo
Samsung Telecommunications America, Inc.
1130 E. Arapaho Road
Richardson, TX 75081
USA

   Phone: (972)761-7755
   EMail: hskoo@sta.samsung.com

Pat Walsh
Lucent Technologies
263 Shuman Blvd.
1F-545
Naperville, IL

   Phone: +1 630-713-5063
   EMail: walshp@lucent.com

Yingchun Xu
WaterCove Networks
One Century Centre, Suite 550
1750 E. Golf Road
Schaumburg, IL

   Phone: +1 847-477-9280
   EMail: yxu@watercove.com

Brent Hirschman
1501 Shure Dr.
Arlington Heights, IL 60006
USA

   Phone: (847) 632-1563
   EMail: qa4053@email.mot.com

Eric Jaques
Vodafone
2999 Oak Road, MS-750
Walnut Creek, CA 94596
USA

   Phone: +1-925-210-3900
   EMail: ejaques@akamail.com

Sanjeevan Sivalingham
Ericsson Wireless Communications Inc.,
Rm Q-356C
6455 Lusk Blvd
San Diego, CA 92126
USA

   Phone: (858) 332-5670
   EMail:  s.sivalingham@ericsson.com

Xing Chen
Alcatel USA
1000 Coit Road
Plano, TX 75075
USA

   Phone: 972-519-4142
   Fax:   +1 972-519-3300
   EMail: xing.chen@usa.alcatel.com
   
   Byung-Keun Lim
   LG Electronics Inc.
   533, Hogye-dong, Donan-Ku, Anyang-shi, Kyungki-do, 431-080,
   Korea
   
   Phone: +82-31-450-7199
   Fax:   +82-31-450-7050
   EMail: bklim@lge.com

Hajime Shiino
Lucent Technologies Japan Ltd.
25 Mori Bldg. 1-4-30 Roppongi,
Minato-ku Tokyo
Japan

   Phone: +81-3-5561-3695
   EMail: hshiino@lucent.com

Shinichi Baba
Toshiba America Research, Inc.
PO Box 136,
Convent Station, NJ 07961-0136
USA

   Phone: (973) 829-4795
   EMail: sbaba@tari.toshiba.com

Takahiro Ayaki
DDI corporation
Ichibancho FS Bldg.
8, Ichibancho, Chiyoda-ku Tokyo
Japan

   Phone: +81-3-3221-9682
   EMail: ayaki@ddi.co.jp

Alan Hameed
Fujitsu
2801 Telecom Parkway
Richardson, Texas 75082
USA

Phone:

          (972) 479-2089
   
   Charles N. Lo
   Vodafone AirTouch
   2999 Oak Rd
   Walnut Creek, CA  94596
   USA
   
   Phone: (925) 210-3460
   EMail: Charles.Lo@vodafone-us.com

Takuo Seki
IDO Corporation
Gobancho YS Bldg.
12-3, Gobancho, Chiyoda-ku Tokyo
Japan

   Phone: +81-3-3263-9660
   EMail: t-seki@kddi.com

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