SIP Working Group W. Marshall Internet Draft AT&T Document: <draft-ietf-sip-call-auth-01.txt> K. Ramakrishnan TeraOptic Networks E. Miller G. Russell CableLabs B. Beser Pacific Broadband M. Mannette K. Steinbrenner 3Com D. Oran F. Andreasen Cisco J. Pickens Com21 P. Lalwaney Nokia J. Fellows Copper Mountain Networks D. Evans D. R. Evans Consulting K. Kelly NetSpeak February, 2001 SIP Extensions for Media Authorization 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 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." SIP Extensions for Media Authorization February 2001 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. The distribution of this memo is unlimited. It is filed as <draft-ietf- sip-call-auth-01.txt>, and expires August 31, 2001. Please send comments to the authors. 1. Abstract This document describes the need for call authorization and offers a mechanism for call authorization that can be used for admission control and against denial of service attacks. 2. Conventions used in this 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 [2]. 3. Background and Motivation The current IP Telephony systems consider a perfect world in which there is unlimited amount of bandwidth and network layer QoS comes free. The reality is that bandwidth is neither unlimited nor free. Enhanced quality of service, as required for high-grade voice communication, needs special authorization for better than `best-effort' service. Without such a capability, it is possible that a single berserk IP telephony device can cause denial of service to a significant number of others. 4. Overview Integration of Media Authorization and Call Signaling architecture consists of User Agents (UAs) which are considered untrusted, and SIP- Proxy which authorizes the call that is initiated by UA. The SIP-Proxy authorizes the Media data flow to/from the UA and returns to the UA a Media-Authorization-Token, which is to be used for authorization when bandwidth is requested for the data-stream. When the UA is ready to send the media data-stream to the other end- point, it first requests bandwidth, using the Authorization-Token it received from its SIP-Proxy. 5. Changes to SIP to Support Media Authorization This document extends SIP in support of an authorization scheme. In this architecture the SIP-Proxy supplies the UA an Authorization-Token which is to be used for bandwidth requests. The extension defined allows network resources to be authorized by the SIP-Proxy. The following syntax specification uses the augmented Backus-Naur Form (BNF) as described in RFC-2234 [3]. SIP Extensions for Media Authorization February 2001 5.1 SIP Header Extension The Media-Auth-Token general header conveys an identifier of the local Gate to a UA. This information is used for authorizing the Media Stream. Media-Auth = "Media-Authorization" ":" Media-Authorization-Token Media-Authorization-Token = 1*hex 5.2 SIP Procedures This section defines a SIP [4] profile for usage in Media Authorization compatible systems from the point of view of Authorizing Calls. The initial SIP INVITE message, as well as mid-call resource change messages and mid-call changes in call destination should be authorized. These SIP messages are sent through the proxies to receive this authorization. 5.2.1. User Agent Client (UAC) The Media-Auth-Token, contained in the Media-Authorization header, is included in the first response message sent by the SIP-Proxy to the UAC. The UAC SHOULD use the Media-Authorization-Token when requesting bandwidth for Media data stream during initiation and retaining of the bandwidth. The UAC converts the string of hex digits into binary, and utilizes the result as a Policy-Element as defined in RFC2750[8]. This Policy-Element would typically contain the authorizing entity and credentials, and be used in an RSVP request for media data stream resources. 5.2.2. User Agent Server (UAS) The User Agent Server receives the Media-Authorization-Token in the INVITE message from SIP-Proxy. The UAS SHOULD use the Media-Authorization-Token when requesting bandwidth for media data stream during initiation and retaining of the bandwidth. The UAS converts the string of hex digits into binary, and utilizes the result as a Policy-Element as defined in RFC2750[8]. This Policy-Element would typically contain the authorizing entity and credentials, and be used in an RSVP request for media data stream resources. 5.2.3. Originating Proxy (OP) The Originating Proxy (OP) authenticates the caller, and verifies the caller is authorized to receive the requested level of QoS. In cooperation with originating Policy Decision Point (PDP-o), the OP obtains and/or generates a Media-Authorization-Token that contains sufficient information for the UAC to get the authorized bandwidth for the media streams. The Media-Authorization-Token is formatted as a SIP Extensions for Media Authorization February 2001 Policy-Element, as defined in RFC2750[8], and converted to a string of hex digits. The Originating Proxy MUST insert the Media-Authorization header in the response message that it sends to UAC. 5.2.4. Destination Proxy (DP) The Destination Proxy (DP) authenticates the called party, and verifies the called party is authorized to receive the requested level of QoS. In cooperation with termination Policy Decision Point (PDP-t), the DP obtains and/or generates a Media-Authorization-Token that contains sufficient information for the destination server to get the authorized bandwidth for the media streams. The Media-Authorization-Token is formatted as a Policy-Element, as defined in RFC2750[8], and converted to a string of hex digits. The Destination Proxy MUST insert the Media-Authorization header in the INVITE message that it sends to the UAS. 6. Examples 6.1. Requesting Bandwidth via RSVP messaging Resource Reservation Protocol (RSVP) is the end-to-end Layer 3 reservation protocol that is widely used [7]. 6.1.1. User Agent Client Side Figure 1 presents a high-level overview of a basic call flow with Media Authorization from the viewpoint of the UAC. It is assumed that the SIP- Proxy has a previously established authentication relationship with the client. When a user goes off-hook and dials a telephone number, the UAC collects the dialed digits and sends the initial INVITE message to Originating SIP-Proxy. The Originating SIP-Proxy (OP) authenticates UAC and forwards the INVITE message to the proper SIP-proxy. Assuming that the call is not forwarded, the other end-point sends a 183 response to the initial INVITE, forwarded back to OP. Included in this response is the negotiated bandwidth requirement for the connection. When OP receives the 183, it has sufficient information regarding the end-points, bandwidth and characteristics of the media exchange. It initiates a Policy-Setup message to POP-o. The PDP-o stores the authorized Media description in its local store generates an Authorization-Token that points to this description and returns the Authorization-Token to OP. SIP Extensions for Media Authorization February 2001 UAC ER-o PDP-o OP | Invite | | | Client Authentication |------------------------------------------->| and Call Authorization | | | | Invite | | | |--------------> | | | | 180/3 | | | Auth. Profile |<-------------- | | |<--------------| | | | Auth. Token | | | |-------------->| Auth. Token put into | | | 180/3 | Media-Authorization header |<-------------------------------------------| extension. |Copies the RSVP policy object | |from the Media-Authorization | | RSVP-PATHo | | | |----------->| REQ | | | |-------------->| Using the Auth-Token and Authorized | | DEC | Profile that is set by the SIP Proxy | |<--------------| the PDP makes the decision | | | | RSVP-PATHo | |------------------------------------------------> | | | | RSVP-PATHt |<-------------------------------------------------------------- |Copies the RSVP policy object | |from the Media-Authorization | | RSVP-RESVt | | | |----------->| REQ | | | |-------------->| Using the Auth-Token and Authorized | | DEC | Profile that is set by the SIP Proxy | |<--------------| the PDP makes the decision | | | | RSVP-RESVt | |---------------------------------------------------> | | | | RSVP-RESVo |<---------------------------------------------------------------- | | | | RSVP-RESVCONFo |----------------------------------------------------------------> | | | | RSVP-RESVCONFt |<---------------------------------------------------------------- | | | | 200 OK |<-------------------------------------------|<------------------ | | | | MEDIA |<===============================================================> | | | | ACK |----------------------------------------------------------------> Figure 1 SIP Extensions for Media Authorization February 2001 The OP includes the Authorization-Token in the Media-Auth-Token header extension of the 183 message. The UAC upon reception stores the Media-Authorization-Token inside the Media-Auth-Token header extension. Before sending the Media stream, the UAC requests bandwidth using an RSVP-PATH message which includes the Session info that describes the Media data-stream and TSpec that describes the bandwidth requested along with Authorization information that was stored in Media-Authorization- Token. ERo, upon reception of the RSVP-PATHo message checks the authorization through a PDP-o COPS message exchange. The PDPo checks the authorization using the stored authorized Media description that was linked to Authorization-Token that it returned to OP. If authorization is successful PDPo returns an "install" Decision. ERo checks the admissibility for the call and if admission succeeds, it forwards the RSVP-PATHo message. Once UAC receives the RSVP-PATHt message it sends RSVP-RESVt message to reserve the bandwidth. ERo, upon reception of the RSVP-RESVt message checks the authorization through a PDPo COPS message exchange. The PDPo checks the authorization using the stored authorized Media description that was linked to Authorization-Token that it returned to OP. If authorization is successful PDPo returns an "install" Decision. ERo checks the admissibility for the call and if admission succeeds, it forwards the RSVP-RESVt message. Upon reception of RSVP-RESVo message the UAC sends RSVP-RESVCONFo message to indicate that the reservation completed for one direction. Upon reception of both RSVP-RESVCONFt and 200OK the UAC returns ACK message. 6.1.2. User Agent Server Side Figure 2 presents a high-level overview of a call flow with Media Authorization from the viewpoint of the UAS. It is assumed that the SIP- Proxy has a previously established authentication relationship with the client. Since the Destination SIP-Proxy (DP) has sufficient information regarding the end-points, bandwidth and characteristics of the media exchange, it initiates a Policy-Setup message to the termination Policy Decision Point (PDPt). SIP Extensions for Media Authorization February 2001 UAS ERt PDPt DP | | | | Invite | | | |<-------------- | | | | Proxy Authentication | | | Auth. Profile | and Call Authorization | | |<--------------| | | | Auth. Token | | | |-------------->| Auth. Token put into | | | Invite | Media-Authorization header |<------------------------------------------| extension | 180/3 | | | |------------------------------------------>| 180/3 |Copies the RSVP policy object |--------------> |from the Media-Authorization | | RSVP-PATHt| | | |---------->| REQ | | | |-------------->| Using the Auth-Token and Authorized | | DEC | Profile that is set by the SIP Proxy | |<--------------| the PDP makes the decision | | | | RSVP-PATHt | |--------------------------------------------------> | | | | RSVP-PATHo |<-------------------------------------------------------------- |Copies the RSVP policy object | |from the Media-Authorization | | RSVP-RESVo| | | |---------->| | | | | REQ | | | |-------------->| Using the Auth-Token and Authorized | | DEC | Profile that is set by the SIP Proxy | |<--------------| the PDP makes the decision | | | | RSVP-RESVo | |---------------------------------------------------> | | | | RSVP-RESVt |<--------------------------------------------------------------- | | | | RSVP-RESVCONFt |---------------------------------------------------------------> | | | | RSVP-RESVCONFo |<--------------------------------------------------------------- | | | | 200 OK |-----------------------------------------> |-------------------> | | | | ACK |<---------------------------------------------------------------- Figure 2 SIP Extensions for Media Authorization February 2001 The PDP-t stores the authorized Media description in its local store generates an Authorization-Token that points to this description and returns the Authorization-Token to DP. Assuming that the call is not forwarded, the UAS sends a 183 response to the initial INVITE message, which is forwarded back to UAC. At the same time UAS sends RSVP-PATHt message for Media data-stream that includes the Session info that describes the Media data-stream and TSpec that describes the bandwidth requested along with Authorization information that was stored in Media-Authorization-Token. ERt, upon reception of the RSVP-PATHt message checks the authorization through a PDPt COPS message exchange. The PDPt checks the authorization using the stored authorized Media description that was linked to Authorization-Token that it returned to DP. If authorization is successful PDPt returns an "install" Decision. ERt checks the admissibility for the call and if admission succeeds, it forwards the RSVP-PATHt message. Once the UAS receives the RSVP-PATHo message, it sends RSVP-RESVo message to reserve the bandwidth. ERt, upon reception of the RSVP-RESVo message, checks the authorization through a PDPt COPS message exchange. The PDPt checks the authorization using the stored authorized Media description that was linked to Authorization-Token that it returned to DP. If authorization is successful PDPt returns an "install" Decision. ERt checks the admissibility for the call and if admission succeeds, it forwards the RSVP-RESVo message. Upon reception of RSVP-RESVo message the UAS sends RSVP-RESVCONFt message to indicate that the reservation completed for one direction. Upon reception of both RSVP-RESVCONFo and 200OK the UAS returns ACK message. 6.2. Requesting Bandwidth via DOCSIS MAC messaging The DOCSIS MAC layer [5] QoS Set-Up the call flows are different in the sense that the Authorization token is a simple 32bit number [6], encoded as a Policy-Element. DSA-REQ, DSA-RSP, and DSA-ACK are layer 2 messages that are specific to and optimized for the Cable environment which simplifies/reduces delays for the embedded client implementation [6]. SIP Extensions for Media Authorization February 2001 UAC ER/CMTSo OP | Invite | | |------------------------------------------->| Client Authentication | | |and Call Authorization | | | | | | Invite | | |-----------> | | | | | | 180/3 OK | | |<------------ | | | | | Gate-Setup | | |<--------------------- | | | Gate-Setup-Ack | | |---------------------> | | | | GateID put into | | | Media-Authorization header | | | extension | | 180/3 OK | |<-------------------------------------------| |Copies the GAteID object | |from the Media-Authorization | | | | | DSA-REQ | | |------------------->| | | | Using the GateID and the Profile | | communicated during Gate-Setup | | the CMTS honors the request and creates | DSA-RSP | a scheduler with appropriate settings |<-------------------| | | | | | DSA-ACK | | |------------------->| | | | | Figure 3 6.2.1. User Agent Client Side Figure 3 presents a high-level overview of a call flow with Media Authorization from the viewpoint of the UAC. It is assumed that the SIP- Proxy has a previously established authentication relationship with the client. When a user goes off-hook and dials a telephone number, the originating SIP Client (UAC) collects the dialed digits and sends the initial INVITE message to Originating SIP-Proxy. The Originating SIP-Proxy (OP) authenticates UAC and forwards the INVITE message to the proper destination SIP-proxy. Assuming that the call is not forwarded, the other end-point sends a 183 response to the initial INVITE, forwarded back to OP. Included in this response is the negotiated bandwidth requirement for the connection. SIP Extensions for Media Authorization February 2001 When OP receives the 183, it has sufficient information regarding the end-points, bandwidth and characteristics of the media exchange. It sends a Gate-Setup message to ER/CMTSo containing Media data-stream description and bandwidth characteristics. The ER/CMTSo returns a 32 bit index value that inside ER/CMTSo points to Media definition that OP send out. UAC sends DSA-REQ message asking for bandwidth, which includes the 32 bit index value. ER/CMTSo, upon reception of the RSA-REQ message uses the index value to find the authorized media description. Checks the requested media link against authorized if the both authorization and admission succeeds it starts a layer 2 link for Media data-stream on the Cable Access link and returns DSA-RSP, which is acknowledged by UAC via DSA-ACK message. Upon reception of 200OK the UAC returns ACK message. 6.2.2. User Agent Server Side Figure 4 presents a high-level overview of a basic call flow with Media Authorization from the viewpoint of the UAS. It is assumed that the Destination SIP-Proxy (DP) has a previously established authentication relationship with the UAS. When DP receives the INVITE message, it has sufficient information regarding the end-points, bandwidth and characteristics of the media exchange. It sends a Gate-Setup message to ER/CMTSt containing Media data-stream description and bandwidth characteristics. The ER/CMTSt returns a 32 bit index value that inside ER/CMTSt points to Media definition that DP send out. The DP includes the 32 bit index value in the Media-Auth-Token header extension that its including into the INVITE message. The UAS sends a 183 response to the initial INVITE, which is forwarded back to UAC. At the same time UAS sends DSA-REQ message asking for bandwidth which includes the 32 bit index value. ER/CMTSt, upon reception of the RSA-REQ message uses the index value to find the authorized media description. Checks the requested media link against authorized if the both authorization and admission succeeds it starts a layer 2 link for Media data-stream on the Cable Access link and returns DSA-RSP, which is acknowledged by UAC via DSA-ACK message. Upon reception of DSA-RSP the UAS returns ACK message. SIP Extensions for Media Authorization February 2001 UAS ER/CMTSt DP | | | | | | Invite | | |<----------- | | | Proxy Authentication | | | and Call Authorization | | Gate-Setup | | |<----------------------| | | Gate-Setup-Ack | | |---------------------->| | | | GateID put into | | | Media-Authorization header | | | extension | Invite | | |<-------------------------------------------| | | | | | 180/3 | |------------------------------------------->| | | | 180/3 | | |------------> |Copies the GateID object | |from the Media-Authorization | | | | | DSA-REQ | |------------------->| | | Using the GateID and the Profile | | communicated during Gate-Setup | | the CMTS honors the request and creates | DSA-RSP | a scheduler with appropriate settings |<-------------------| | | | DSA-ACK | | |------------------->| | | | | | | 200 OK | |------------------------------------------->| | | | 200 OK | | |------------> Figure 4 SIP Extensions for Media Authorization February 2001 7. Advantages of the Proposed Approach The use of call authorization makes it possible to control the utilization of network resources. This in turn makes IP Telephony more robust against denial of service attacks and various kinds of service frauds. Using the authorization capability, the service provider can control the number of flows, the amount of bandwidth, and the end-point reached making the IP Telephony system dependable in the presence of scarce resources. 8. Security Considerations Media Authorization Tokens sent from a SIP-Proxy to a UAC/UAS MUST be protected from eavesdropping, through a mechanism such as IPSec. 9. Notice Regarding Intellectual Property Rights AT&T may seek patent or other intellectual property protection for some or all of the technologies disclosed in the document. If any standards arising from this disclosure are or become protected by one or more patents assigned to AT&T, AT&T intends to disclose those patents and license them on reasonable and non-discriminatory terms. Future revisions of this draft may contain additional information regarding specific intellectual property protection sought or received. 3COM may seek patent or other intellectual property protection for some or all of the technologies disclosed in the document. If any standards arising from this disclosure are or become protected by one or more patents assigned to 3COM, 3COM intends to disclose those patents and license them on reasonable and non-discriminatory terms. Future revisions of this draft may contain additional information regarding specific intellectual property protection sought or received. 10. Reference 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 Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, Internet Mail Consortium and Demon Internet Ltd., November 1997 4 M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP: session initiation protocol,"Request for Comments (Proposed Standard) 2543, Internet Engineering Task Force, Mar. 1999. SIP Extensions for Media Authorization February 2001 5 CableLabs, "Data-Over-Cable Service Interface Specifications, Radio Frequency Interface Specification, SP-RFIv1.1-I04-000407", April 2000. 6 PacketCable, Dynamic Quality of Service Specification, pkt-sp-dqos- i01-991201, December 1, 1999. 7 Wroclawski, J, RFC 2210, The Use of RSVP with IETF Integrated Services, RFC2210, September 1997. 8 Herzog, S, RSVP Extensions for Policy Control, RFC2750, January 2000. 11. Acknowledgments The Distributed Call Signaling work in the PacketCable project is the work of a large number of people, representing many different companies. The authors would like to recognize and thank the following for their assistance: John Wheeler, Motorola; David Boardman, Daniel Paul, Arris Interactive; Bill Blum, Jon Fellows, Jay Strater, Jeff Ollis, Clive Holborow, Motorola; Doug Newlin, Guido Schuster, Ikhlaq Sidhu, 3Com; Jiri Matousek, Bay Networks; Farzi Khazai, Nortel; John Chapman, Bill Guckel, Michael Ramalho, Cisco; Chuck Kalmanek, Doug Nortz, John Lawser, James Cheng, Tung- Hai Hsiao, Partho Mishra, AT&T; Telcordia Technologies; and Lucent Cable Communications. 13. Author's Addresses Bill Marshall AT&T Florham Park, NJ 07932 Email: wtm@research.att.com K. K. Ramakrishnan TeraOptic Networks Summit, NJ 07901 Email: kk@teraoptic.com Ed Miller CableLabs Louisville, CO 80027 Email: E.Miller@Cablelabs.com Glenn Russell CableLabs Louisville, CO 80027 Email: G.Russell@Cablelabs.com Burcak Beser Pacific Broadband Communications San Jose, CA Email: Burcak@pacband.com Mike Mannette SIP Extensions for Media Authorization November 2000 3Com Rolling Meadows, IL 60008 Email: Michael_Mannette@3com.com Kurt Steinbrenner 3Com Rolling Meadows, IL 60008 Email: Kurt_Steinbrenner@3com.com Dave Oran Cisco Acton, MA 01720 Email: oran@cisco.com Flemming Andreasen Cisco Edison, NJ Email: fandreas@cisco.com John Pickens Com21 San Jose, CA Email: jpickens@com21.com Poornima Lalwaney Nokia San Diego, CA 92121 Email: poornima.lalwaney@nokia.com Jon Fellows Copper Mountain Networks San Diego, CA 92121 Email: jfellows@coppermountain.com Doc Evans D. R. Evans Consulting Boulder, CO 80303 Email: n7dr@arrl.net Keith Kelly NetSpeak Boca Raton, FL 33587 Email: keith@netspeak.com SIP Working Group Expiration 5/31/01 14 SIP Extensions for Media Authorization November 2000 Full Copyright Statement "Copyright (C) The Internet Society (date). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implmentation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." Expiration Date This memo is filed as <draft-ietf-sip-call-auth- 01.txt>, and expires August 31, 2001. SIP Working Group Expiration 5/31/01 15
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