Internet Engineering Task Force Mike Pierce INTERNET DRAFT Artel Expires October, 2002 Don Choi DISA April 2002 Architecture for Assured Service Capabilities in Voice over IP draft-pierce-sipping-assured-service-arch-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 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 a http://www.ietf.org/ietf/lid-abstracts.text The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Copyright Notice Copyright (c) Internet Society 2002. All rights reserved. Pierce Expires October 2002 Page 1 Internet Draft Architecture for Assured Service in VoIP April 2002 Reproduction or translation of the complete documents, but not of extracts, including this notice, is freely permitted. Abstract Assured Service refers to the set of capabilities used to ensure that mission critical communications are setup and remain connected. This memo describes the architecture required to meet the requirements detailed in [Pierce1]. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . 2 2. Architectures . . . . . . . . . . . . . . . . . . . . . . 3 2.1 End-to-end Architecture . . . . . . . . . . . . . . . . . 3 2.2 Service Provider Network Architecture . . . . . . . . . . 3 3. Required Architecture . . . . . . . . . . . . . . . . . . 4 4. Required Procedures . . . . . . . . . . . . . . . . . . . 4 4.1 Authentication . . . . . . . . . . . . . . . . . . . . . 4 4.2 Function of Proxy . . . . . . . . . . . . . . . . . . . . 5 4.3 Session Control . . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . 6 6. References . . . . . . . . . . . . . . . . . . . . . . . 6 7. Authors' Addresses . . . . . . . . . . . . . . . . . . . 6 Full Copyright Statement . . . . . . . . . . . . . . . . . . . 7 1. Introduction The requirements for Assured Service are given in [Pierce1]. Many other drafts and RFCs have addressed the assumed architecture for the provision of SIP-based services. A lot of consideration has been given to continued reliance on the pure peer-to-peer model on which the Internet (and especially HTTP) has been based vs. migration to centralized control models in which dedicated proxies perform specific functions for the control of telephony services. This would include, possibly, full knowledge of the state of each call. While there is an wide-spread desire to maintain the peer-to-peer architecture, there has been increasing admissions in various drafts that centralized control or intelligent "middleboxes" are required in many cases. This list will likely continue to grow. Some examples are: 1. The revision to RFC 2543 [SIP-2543bis] defines the notion of a "Call Stateful proxy", which "retains state for a dialog from the initiating INVITE to the terminating BYE request", i.e., for the duration of a call. However, no use of this state has been included in the current version of SIP [SIP-2543bis]. Pierce Expires October 2002 Page 2 Internet Draft Architecture for Assured Service in VoIP April 2002 2. Draft-ietf-sipping-cc-framework-00 includes the concept of a "central control" signaling model (although its reference to 3pcc indicates that the actual concept is not "centralized" but rather a specialized end-user performing control for other users.) 3. The abstract for draft-ietf-sipping-service-examples-00 recognizes that "some [services] require the assistance of a SIP Proxy", but that "most ... shown in this document are implemented in the SIP User Agents". However, it then states that the flows shown assume "a network of proxies, registrars, PSTN gateways, and other SIP servers that have a pre-established trust relationship with each other... User agents wishing to use the services in this network are required to authenticate themselves with an edge proxy..." 4. The draft for identity and privacy [SIP-IDENTITY] states that, in order for an originating device to achieve privacy concerning its identity related information, one must "assume an architecture where the caller initiates a session to the callee via a trusted entity in its network. The callee in turn receives the session initiation via a trusted entity". It further states that the "trusted entity ... belongs to and is controlled by the Network". 2. Architectures Various discussions and memos have identified two potential network architectures for the provision of SIP services. They are briefly: 2.1 End-to-end Architecture All service provision is between and under control of the calling and called party, referred to as "User Agent Client (UAC)" and "User Agent Server (UAS)", respectively. This terminology of "client" and "server" are based on the HTTP model from which this model is derived and have no real significance to this model. Either end can initiate a transaction. There is no device in between which provides service support, only routers for packets. (If a specialized back-to-back user agent (B2BUA) is used for some defined capability, that B2BUA simply acts as the termination point of two distinct sessions. There is no additional "network" function which associates the two sessions.) 2.2 Service Provider Network Architecture A Service Provider maintains and controls network elements which play an active role in the provision of services to end users. These network elements may be referred to as back-to-back user agents (B2BUA), proxies, servers, or middleboxes, but they all have the common characteristic of being provided by a Service Provider. These elements terminate SIP messages, perform service control, and send new or modified SIP messages to other network elements or to the other user. Pierce Expires October 2002 Page 3 Internet Draft Architecture for Assured Service in VoIP April 2002 3. Required Architecture In order to provide the security and feature control required for Assured Service, it is necessary to utilize the Service Provider Network Architecture in which proxies are used to support call origination and termination for each user involved in the service. The architecture is the "trapezoid" described in [SIP-2543bis] and [SIP-IDENTITY] as follows (copied from draft-ietf-sip-srv-06): ......................... .......................... . . . . . +-------+ . . +-------+ . . | | . (2) . | | . . | Proxy |----------------- | Proxy | . . | 1 | . . | 2 | . . | | . . | | . . +-------+ . . +-------+ . . / . . \ . . / (1) . . \ (3) . . / . . \ . . / . . \ . . +-------+ . . +-------+ . . | | . (4) . | | . . | UA 1 |------------------------------------| UA 2 | . . | | . . | | . . +-------+ . . +-------+ . . Domain A . . Domain B . ......................... .......................... Interfaces: (1) Originating UA 1 to Proxy 1: Authentication and all SIP messages to/from UA 1 (2) Proxy 1 to Proxy 2 (and to other devices such as policy servers): SIP messages and policy actions (3) Proxy 2 to terminating UA 2: Authentication and all SIP messages to/from U 2 (4) Originating UA 1 to terminating UA 2: Voice packets 4. Required Procedures 4.1 Authentication Each UA which might use the Assured Service capability must authenticate with a designated proxy before any service activation is attempted. Normally, this would be at the time the device is powered on, connected to the network, or is initialized, or it might be done at pre-determined time intervals. Whether or not this authentication requires a user interaction (human entry of a password, iris scan, etc.) is not important and depends on the application. Such an authentication may be very time consuming, with password verification and policy data-base look-ups. After this authentication, this proxy Pierce Expires October 2002 Page 4 Internet Draft Architecture for Assured Service in VoIP April 2002 must handle all session establishment, both to and from this UA. This authentication function may be performed when the user attempts the first session setup, for example, when an individual is allowed to use a common device by first "logging on" with their identity and password. In fact, this is still an "authentication" function performed before the session setup is attempted. However, in this case, it must be understood that there may be an additional delay due to the authentication process before a call can be placed. This authentication process is not unique to the provision of the Assured Service capability. It is also required for many other services which are to be provided by the service provider's proxy based on pre-established authorizations. 4.2 Function of Proxy Besides the processing of the authentication, each proxy is responsible for a number of functions important to the provision of Assured Service (as well as other services) and the handling of interactions, where required, between different services. This includes (for Assured Service): - maintaining state of all existing sessions, including their priority, which exist on the UA (both proxies). - maintaining knowledge of other services being used by the UA which might need to be taken into consideration when applying the Assured Service capabilities (both proxies). - verifying that the originating UA is allowed to establish the session at the precedence level requested (originating proxy). - establish permission at the access router for it to handle the precedence marked packets from the UA (both proxies). - performing the timing function to control the diversion service (terminating proxy). - deciding when to preempt the end user and sending the appropriate preempt messages to the other party (both proxies). - maintaining records of the use of the service, whether for accounting or auditing purposes (both proxies). 4.3 Session Control Session establishment and release should follow the same message sequence as defined in SIP and its extensions for non-Assured Service calls. There should not be any additional messages. The only additional requirements are the inclusion of: Pierce Expires October 2002 Page 5 Internet Draft Architecture for Assured Service in VoIP April 2002 - the priority level as defined in [Resource-priority] in the INVITE - security related information in every message which would consist of an authentication header (AH) using cryptographic techniques to allow the receiving end (user or proxy) to validate the authenticity of the message before acting on it. (This requirement is not unique to Assured Service, but is also required to secure other capabilities.) 5. Security Considerations This memo mostly deals with the architectural requirements to provide the necessary security. While it does not attempt to define the actual security mechanisms used for authentication and authorization, it establishes the service architecture required. 6. References [SIP-CALL-AUTH] draft-ietf-sip-call-auth-04, "SIP Extension for Media Authorization", February 2002. [SIP-2543bis] draft-ietf-sip-rfc2543bis-09, "SIP: Session Initiation Protocol" (revision), February 2002. [SIP-IDENTITY] draft-ietf-sip-privacy-04, "SIP extensions for Network-asserted Caller Identity and Privacy within Trusted Networks", February 2002. [Baker] draft-baker-ieprep-requirements-00, "IEPS Requirement Statement", February 2002. [Pierce1] draft-pierce-sipping-assured-service-02, "Requirements for Assured Service Capabilities in Voice over IP", April 2002. [Pierce2] draft-pierce-sipping-pref-treat-examples-00, "Examples for Provision of Preferential Treatment in Voice over IP", April 2002. 7. Authors' Addresses Michael Pierce Artel 1893 Preston White Drive Reston, VA 20191 Phone: +1 410.817.4795 Email: pierce1m@ncr.disa.mil Don Choi DISA 5600 Columbia Pike Falls Church, VA 22041-2717 Phone: +1 703.681.2312 Email: choid@ncr.disa.mil Pierce Expires October 2002 Page 6 Internet Draft Architecture for Assured Service in VoIP April 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). 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 implementation 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 are provided on an "AS IS" basis and THE INTERNET SOCIETY and THE INTERNET ENGINEERING TASK FORCE disclaim 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. Internet Draft Architecture for Assured Service in VoIP April 2002