SIP Working Group W. Marshall Internet Draft K. Ramakrishnan Document: <draft-dcsgroup-sip-call-auth-01.txt> AT&T Category: Informational E. Miller G. Russell CableLabs B. Beser M. Mannette K. Steinbrenner 3Com D. Oran F. Andreasen Cisco J. Pickens Com21 P. Lalwaney J. Fellows Motorola D. Evans Secure Cable Solutions K. Kelly NetSpeak March, 2000 SIP Extensions for Media Authorization Status of this Memo This document is an Internet-Draft and is NOT offered in accordance with Section 10 of RFC2026 [1], and the author does not provide the IETF with any rights other than to publish as an Internet-Draft. 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. DCS Group Category Informational - Expiration 9/30/00 1 SIP Extensions for Media Authorization March 2000 The distribution of this memo is unlimited. It is filed as <draft- dcsgroup-sip-call-auth-01.txt>, and expires September 30, 2000. 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 SIP Clients which are considered untrusted, and SIP Proxy Agents which authorizes the call that is initiated by the SIP Client. The Sip Proxy Agent authorizes the Media data flow to/from the SIP Client and returns to the Client a Media-Authorization-Token, which is to be used for authorization when bandwidth is requested for the data-stream. When the Client 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 client 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]. DCS Group Category Informational - Expiration 9/30/00 2 SIP Extensions for Media Authorization March 2000 5.1 SIP Header Extension The Media-Auth-Token general header conveys an identifier of the local Gate to a SIP Client. 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 DCS 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. Originating 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 Client SHOULD use the Media-Auth-Token when requesting bandwidth for Media data stream during initiation and retaining of the bandwidth. 5.2.2. Destination Server (UAS) The Destination Server receives the Media-Auth-Token in the INVITE message from SIP-Proxy. The Media-Authorization-Token information included MUST be stored. The Server SHOULD use the Media-Auth-Token when requesting bandwidth for Media data stream during initiation and retaining of the bandwidth. 5.2.3. Originating Proxy Behavior The Originating Proxy authenticates the caller, and verifies the caller is authorized to receive the requested level of QoS. In cooperation with a policy-decision-point, they generate a Media-Auth-Token that contains sufficient information for the originating client to get the authorized bandwidth for the media streams. The Originating Proxy MUST insert the Media-Authorization header in the response message that it sends to MTA-o. 5.2.4. Destination Proxy Behavior DCS Group Category Informational - Expiration 9/30/00 3 SIP Extensions for Media Authorization March 2000 The Destination Proxy authenticates the called party, and verifies the called party is authorized to receive the requested level of QoS. In cooperation with a policy-decision-point, they generate a Media-Auth- Token that contains sufficient information for the destination servier to get the authorized bandwidth for the media streams. The Destination Proxy MUST insert the Media-Authorization header in the INVITE message that it sends to MTA-d. 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 [5]. 6.1.1. Originating Client Side Figure 1 presents a high-level overview of a basic MTA-to-MTA call flow with Media Authorization from the viewpoint of Originating SIP Client. It is assumed that the SIP-Proxy has a previously established authentication relationship with the MTA. When a user goes off-hook and dials a telephone number, the originating SIP Client (MTA-o) collects the dialed digits and sends the initial INVITE message to its SIP-Proxy. The originating SIP-Proxy (DP-o) authenticates MTA-o and f o r wards the INVITE message to the proper destination proxy. Assuming that the call is not forwarded, the other end-point sends a 183 response to the initial INVITE, forwarded back to DP-o. Included in this response is the negotiated bandwidth requirement for the connection. When DP-o 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 PDP-o. The PDP-o stores the authorized Media description in its local store generates a Authorization-Token that points to this description and returns the Authorization-Token to DP-o. DCS Group Category Informational - Expiration 9/30/00 4 SIP Extensions for Media Authorization March 2000 MTA-o ER-o PDP-o DP-o | 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 DCS Group Category Informational - Expiration 9/30/00 5 SIP Extensions for Media Authorization March 2000 The DP-o includes the Authorization-Token in the Media-Auth-Token header extension that its including into the 183 message. MTA-o upon reception stores the Media-Authorization-Token inside the Media-Auth-Token header extension. Before sending the Media stream, MTA-o and MTA-t each request bandwidth using 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. ER-o, upon reception of the RSVP-PATHo message checks the authorization through PDP-o COPS message exchange. The PDP-o checks the authorization using the stored authorized Media description that was linked to Authorization-Token that it returned to DP-o. If authorization is successful PDP-o returns install Decision. ER-o checks the admissibility for the call and if admission succeeds, it forwards the RSVP-PATHo message. Once MTA-o receives the RSVP-PATH-t message it sends RSVP-RESVt message to reserve the bandwidth. ER-o, upon reception of the RSVP-RESVt message checks the authorization through PDP-o COPS message exchange. The PDP-o checks the authorization using the stored authorized Media description that was linked to Authorization-Token that it returned to DP-o. If authorization is successful PDP-o returns install Decision. ER-o checks the admissibility for the call and if admission succeeds, it forwards the RSVP- RESVt message. Upon reception of RSVP-RESVo message the MTA-o sends RSVP-RESVCONFo message to indicate that the reservation completed for one direction. Upon reception of both RSVP-RESVCONFt and 200OK the MTA-o returns ACK message. 6.1.2. Terminating Client Side Figure 2 presents a high-level overview of a basic MTA-to-MTA call flow with Media Authorization from the viewpoint of Terminating SIP Client (MTA-t). It is assumed that the SIP-Proxy has a previously established authentication relationship with the MTA. The destination SIP-Proxy (DP-t) upon reception of the Invite message. Since it has sufficient information regarding the end-points, bandwidth and characteristics of the media exchange. It initiates a Policy-Setup message to PDP-t. DCS Group Category Informational - Expiration 9/30/00 6 SIP Extensions for Media Authorization March 2000 MTA-t ER-t PDP-t DP-t | | | | 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 DCS Group Category Informational - Expiration 9/30/00 7 SIP Extensions for Media Authorization March 2000 The PDP-t stores the authorized Media description in its local store generates a Authorization-Token that points to this description and returns the Authorization-Token to DP-t. Assuming that the call is not forwarded, the MTA-t sends a 183 response to the initial INVITE, which is forwarded back to MTA-o. At the same time MTA-t 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. ER-t, upon reception of the RSVP-PATHt message checks the authorization through PDP-t COPS message exchange. The PDP-t checks the authorization using the stored authorized Media description that was linked to Authorization-Token that it returned to DP-t. If authorization is successful PDP-t returns install Decision. ER-t checks the admissibility for the call and if admission succeeds, it forwards the RSVP-PATHd message. Once MTA-t receives the RSVP-PATHo message it sends RSVP-RESVo message to reserve the bandwidth. ER-t, upon reception of the RSVP-RESVo message checks the authorization through PDP-t COPS message exchange. The PDP-t checks the authorization using the stored authorized Media description that was linked to Authorization-Token that it returned to DP-t. If authorization is successful PDP-t returns install Decision. ER-t checks the admissibility for the call and if admission succeeds, it forwards the RSVP- RESVo message. Upon reception of RSVP-RESVd message the MTA-t sends RSVP-RESVCONFt message to indicate that the reservation completed for one direction. Upon reception of both RSVP-RESVCONFo and 200OK the MTA-t returns ACK message. 6.2. Requesting Bandwidth via DOCSIS MAC messaging The DOCSIS MAC layer QoS Set-Up the call flows are different in the sense that the Authorization token is a simple 32bit number. And DSA-REQ, DSA- RSP, and DSA-ACK are layer 2 messages that are specific to and optimized for Cable environment which simplifies/reduces delays for the embedded client implementation. DCS Group Category Informational - Expiration 9/30/00 8 SIP Extensions for Media Authorization March 2000 MTA-o ER/CMTS-o DP-o | Invite | | |------------------------------------------->| Client Authentication | | |and Call Authorization | | | | | | Invite | | |-----------> | | | | | | 180/3 OK | | |<------------ | | | | | Gate-Setup | | |<--------------------- | | | Gate-Setup-Ack | | |---------------------> | | | | GateID put into | | | Media-Authorization header | | | extensiom | | 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. Originating Client Side Figure 3 presents a high-level overview of a basic MTA-to-MTA call flow with Media Authorization from the viewpoint of Originating SIP Client (MTA-o). It is assumed that the SIP-Proxy has a previously established authentication relationship with the MTA. When a user goes off-hook and dials a telephone number, the originating SIP Client (MTA-o) collects the dialed digits and sends the initial INVITE message to its SIP-Proxy. The originating SIP-Proxy (DP-o) authenticates MTA-o and forwards the INVITE message to the proper destination proxy. DCS Group Category Informational - Expiration 9/30/00 9 SIP Extensions for Media Authorization March 2000 Assuming that the call is not forwarded, the other end-point sends a 183 response to the initial INVITE, forwarded back to DP-o. Included in this response is the negotiated bandwidth requirement for the connection. When DP-o 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/CMTS-t containing Media data-stream description and bandwidth characteristics. The ER/CMTS-t returns a 32 bit index value that inside ER/CMTS-t points to Media definition that DP-o send out. MTA-t sends DSA-REQ message asking for bandwidth which includes the 32 bit index value. ER/CMTS-t, 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 MTA-o via DSA-ACK message. Upon reception of 200OK the MTA-t returns ACK message. 6.2.2. Terminating Client Side Figure 4 presents a high-level overview of a basic MTA-to-MTA call flow with Media Authorization from the viewpoint of Terminating SIP Client (MTA-t). It is assumed that the SIP-Proxy has a previously established authentication relationship with the MTA. When DP-t receives the Invite, it has sufficient information regarding the end-points, bandwidth and characteristics of the media exchange. It sends a Gate-Setup message to ER/CMTS-t containing Media data-stream description and bandwidth characteristics. The ER/CMTS-t returns a 32 bit index value that inside ER/CMTS-t points to Media definition that DP-t send out. The DP-t includes the 32 bit index value in the Media-Auth-Token header extension that its including into the Invite message. The MTA-t sends a 183 response to the initial INVITE, which is forwarded back to MTA-o. At the same time MTA-t sends DSA-REQ message asking for bandwidth which includes the 32 bit index value. ER/CMTS-t, 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 MTA-o via DSA-ACK message. Upon reception of DSA-RSP the MTA-t returns ACK message. DCS Group Category Informational - Expiration 9/30/00 10 SIP Extensions for Media Authorization March 2000 MTA-t ER/CMTS-t DP-t | | | | | | 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 DCS Group Category Informational - Expiration 9/30/00 11 SIP Extensions for Media Authorization March 2000 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 proxy to a UAC/UAS MUST be protected from eavesdropping, through a mechanism such as IPSec. 9. 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. 5 RFC 2210, The Use of RSVP with IETF Integrated Services by J. Wroclawski, September 1997. 10. 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. DCS Group Category Informational - Expiration 9/30/00 12 SIP Extensions for Media Authorization March 2000 13. Author's Addresses Bill Marshall AT&T Florham Park, NJ 07932 Email: wtm@research.att.com K. K. Ramakrishnan AT&T Florham Park, NJ 07932 Email: kkrama@research.att.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 3Com Rolling Meadows, IL 60008 Email: Burcak_Beser@3com.com Mike Mannette 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 DCS Group Category Informational - Expiration 9/30/00 13 SIP Extensions for Media Authorization March 2000 Email: jpickens@com21.com Poornima Lalwaney Motorola San Diego, CA 92121 Email: plalwaney@gi.com Jon Fellows Motorola San Diego, CA 92121 Email: jfellows@gi.com Doc Evans Secure Cable Solutions Westminster, CO 30120 Email: drevans@securecable.com Keith Kelly NetSpeak Boca Raton, FL 33587 Email: keith@netspeak.com DCS Group Category Informational - Expiration 9/30/00 14 SIP Extensions for Media Authorization March 2000 Full Copyright Statement "Copyright (C) The Internet Society (date). 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