SIPPING Working Group V. Hilt Internet-Draft Bell Labs/Lucent Technologies Expires: January 13, 2006 G. Camarillo Ericsson J. Rosenberg Cisco Systems July 12, 2005 A Delivery Mechanism for Session-Specific Session Initiation Protocol (SIP) Session Policies draft-hilt-sipping-session-spec-policy-03 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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. This Internet-Draft will expire on January 13, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This specification defines a delivery mechanism for session-specific Session Initiation Protocol (SIP) sessions policies. Hilt, et al. Expires January 13, 2006 [Page 1] Internet-Draft Session-Specific Policies July 2005 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Overview of Operation . . . . . . . . . . . . . . . . . . . . 7 4.1 Offer in Request . . . . . . . . . . . . . . . . . . . . . 7 4.2 Offer in Response . . . . . . . . . . . . . . . . . . . . 9 5. UA/Policy Server Rendezvous . . . . . . . . . . . . . . . . . 10 5.1 UAC Behavior . . . . . . . . . . . . . . . . . . . . . . . 10 5.2 UAS Behavior . . . . . . . . . . . . . . . . . . . . . . . 12 5.3 Proxy Behavior . . . . . . . . . . . . . . . . . . . . . . 12 5.4 Header Definition and Syntax . . . . . . . . . . . . . . . 13 6. Policy Channel . . . . . . . . . . . . . . . . . . . . . . . . 14 6.1 Session Information . . . . . . . . . . . . . . . . . . . 14 6.2 Session Policies . . . . . . . . . . . . . . . . . . . . . 15 6.2.1 Event Header Parameters . . . . . . . . . . . . . . . 15 6.2.2 The Use of URIs . . . . . . . . . . . . . . . . . . . 16 6.2.3 Subscriber Behavior . . . . . . . . . . . . . . . . . 16 6.2.4 Notifier Behavior . . . . . . . . . . . . . . . . . . 16 6.2.5 Example . . . . . . . . . . . . . . . . . . . . . . . 16 7. Updating Policies . . . . . . . . . . . . . . . . . . . . . . 17 8. Security Considerations . . . . . . . . . . . . . . . . . . . 17 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 18 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 10.1 Normative References . . . . . . . . . . . . . . . . . . . 17 10.2 Informative References . . . . . . . . . . . . . . . . . . 18 A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19 Intellectual Property and Copyright Statements . . . . . . . . 20 Hilt, et al. Expires January 13, 2006 [Page 2] Internet-Draft Session-Specific Policies July 2005 1. Introduction Some domains have policies in place, which impact the sessions established using the Session Initiation Protocol (SIP) [4]. These policies are often needed to support the network infrastructure or the execution of services. For example, wireless networks usually have limited resources for media traffic. During periods of high activity, a wireless network provider wants to restrict the bandwidth that is available in a session. With session policies, the user agent is able to learn about the current bandwidth limit and can make an informed decision about the number of streams, the media types, and the codecs it can use in that session. Similarly, a user agent can be informed that certain codecs or media types are disallowed and may not be used in the current session. In another example, a SIP user agent is using a network which connects to the public Internet through a firewall or a network border device. The provider would like to tell the user agent to direct the media streams to the appropriate IP addresses and ports of that firewall or border device. Knowing this policy enables the user agent to setup sessions with other user agents across the firewall or the network border. In a third example, a domain wants to perform QoS marking and traffic shaping on media streams. This functionality is implemented in a media intermediary. With session policies, such a media intermediary can be inserted into the media path. In contrast to other methods, the use of session policies does not require the inspection or modification of SIP message bodies by intermediaries (a discussion of this and other design aspects can be found in [8]). Domains sometimes enforce policies they have in place. For example, a domain might have a configuration in which all packets containing a certain audio codec are dropped. Unfortunately, enforcement mechanisms usually do not inform the user about the policies they are enforcing and silently keep the user from doing anything against them. This may lead to the malfunctioning of devices that is incomprehensible to the user. With session policies, the user knows about the restricted codecs and can use a different codec or simply connect to a domain with less stringent policies. Session policies provide an important combination of consent coupled with enforcement. That is, the user becomes aware of the policy and needs to act on it, but the provider still retains the right to enforce the policy. Session-policies can be set up in two different ways: specifically for a session or independent of a session. Session-specific policies are created for one particular session, usually under consideration of certain aspects of this session (e.g. the IP addresses and ports Hilt, et al. Expires January 13, 2006 [Page 3] Internet-Draft Session-Specific Policies July 2005 that are used for media). Since session-specific policies are tailored to a session, they only apply to the session they are created for. These policies require a delivery mechanism that enables the exchange of session policy information at the time a session is established. This document defines such a delivery mechanism. It enables user agents to submit session details to a policy server and allows the policy server to provide policies for this session in response. Session-independent policies on the other hand are independent of a specific session and generally apply to the sessions set up by a user agent. An example is a policy which generally prohibits the use of high-bandwidth codecs. In principle, these policies could also be delivered to user agents individually for each session, using the session-specific delivery mechanism. However, since these policies apply to many sessions, it is more efficient to deliver them to user agents only when the user agent is initialized or a policy changes. The framework for session-independent policies [6] defines a delivery mechanism for session-independent policies. It also defines a minimal session policy format aimed at achieving interoperability between different user agents and policy servers. This policy format is independent of the policy delivery mechanism and can be used for session-independent as well as for session-specific policies. 2. Terminology In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119 [1] and indicate requirement levels for compliant implementations. Hilt, et al. Expires January 13, 2006 [Page 4] Internet-Draft Session-Specific Policies July 2005 3. Architecture +-------------+ /------| Proxy |----... +----+ / +-------------+ | |---/ +-------------+ | | | Policy | | UA |============| Server | | | +-------------+ | |**** +-------------+ +----+ * | Router w/ | *******| Policy |****... | Enforcement | +-------------+ --- SIP Signaling === Policy Channel *** Media Figure 1 The following entities are involved in setting up session-specific policies (see Figure 1): a user agent (UA), a proxy, a policy server and possibly a router with policy enforcement functionality. The proxy's role is to provide a rendezvous mechanism for UA and policy server. It conveys the URI of the policy server in its domain to UAs and ensures that UAs know where to retrieve policies from. It does not deliver the actual policies to UAs. The policy server is a separate logical entity that may be physically co-located with the proxy. Each domain has at most one policy server. The role of the policy server is to generate session policies for a session. It receives session information from a UA, generates a policy and returns that policy back to the UA. The way policies are generated is outside the scope of this specification. A policy server could, for example, use local rules, query external sources for additional information or retrieve policies from a separate policy infrastructure. A UA receives the URI of a policy server from the proxy. It uses this URI to establish a policy channel to the policy server. It provides information about the current session to the policy server and receives session policies in response. The UA may also receive policy updates from the policy server during the course of a session. A network may have a policy enforcement infrastructure in place. However, this specification does not make any assumptions about the Hilt, et al. Expires January 13, 2006 [Page 5] Internet-Draft Session-Specific Policies July 2005 enforcement of session policies and the mechanisms defined here are orthogonal a policy enforcement infrastructure. Their goal is to provide a means for the UA to convey session information to a policy server and to receive the policies that apply to this session in response. The protocol defined in this specification follows a separate channel model. SIP signaling is only used to rendezvous the UA with the policy server. From this point on, UA and policy server communicate directly with each other over a separate policy channel. This is opposed to a piggyback model, where the exchange of session and policy information between the user agent and the policy server is piggybacked onto SIP signaling messages exchanged between the two user agents. A disadvantage of the separate channel model is that it requires additional messages for the exchange of policy information. The advantages of using a separate policy channel is that it decouples the exchange of signaling messages between endpoints from the exchange of policy information between endpoint and policy server. This decoupling enables the use of encryption on the signaling path (to secure the communication between endpoints) and on the policy channel (to secure the communication between endpoint and policy server). Existing schemes for authorization, authentication, signing and encryption can be used on the policy channel. This is not possible if policies are piggybacked onto the signaling messages. Another advantage of the separate channel model is that policies do not travel along the signaling path possibly crossing may domains. If policy server and UA are in the same network, policy information never leaves this network. In addition, endpoints can specifically decide which aspects of a session they want to disclose to a certain policy server. Finally, a policy server does not rely on a SIP signaling message flowing by to provide a session policy to an endpoint. A policy server can use the separate channel at any time to update session policies as needed. The communication on the policy channel between a UA and a policy server involves two main operations: 1. The UA discloses information about the current session and the offer/answer exchange to the policy server. 2. The policy server sends policy instructions to the UA. Some types of policies do not involve sending policy instructions, but only information disclosure. Still, a general session-specific policy mechanism needs to support both operations. The same way, some policy servers only need to inspect the offer, but Hilt, et al. Expires January 13, 2006 [Page 6] Internet-Draft Session-Specific Policies July 2005 not the answer. Nevertheless, a general mechanism needs to consider policy servers which need to inspect both. Finally, some policy servers need to update the session policies that have been sent to a UA. Again, a general mechanism should provide this capability. 4. Overview of Operation This section provides example call flows to illustrate the establishment of session-specific policies. It does not contain a normative protocol definition. In the following scenario, there are two domains (domain A and domain B), which both have session-specific policies for UAs in their domain. Both domains do not provide policies to UAs outside of their domain. The two domains have a proxy (P A and P B) and a policy server (PS A and PS B). The policies in both domains involve the session description offer and answer. 4.1 Offer in Request The first call flow depicts an INVITE transaction with the offer in the request. It is assumed that the UAC does not have previous knowledge about the policy server in its domain. (1) UA A sends an INVITE to proxy P A. P A knows that policies apply to this session and (2) returns a 488 to UA A. P A includes the URI of PS A in the 488 response. (3) UA A contacts PS A, discloses the session description offer to PS A and (4) receives policies for the offer. (5) UA A reformulates the INVITE request under consideration of the received policies and includes a Policy-Id header to indicate that it has already contacted PS A. P A does not reject the INVITE this time and removes the Policy-Id header when forwarding the INVITE. P B adds a Policy-Contact header containing the URI of PS B. (6) UA B uses this URI to contact PS B and discloses the offer and the answer it is about to send. (7) UA B receives policies from PS B and applies them to the offer and answer respectively. (8) UA B returns the updated answer in the 200 OK. (9) UA A contacts PS A with the answer and (10) retrieves answer policies from PS A. Hilt, et al. Expires January 13, 2006 [Page 7] Internet-Draft Session-Specific Policies July 2005 UA A P A P B UA B | | | | | INVITE offer | | | |---------------->| | | (1) | 488 | | | | + Policy-Contact| | | |<----------------| | | (2) | ACK | | | |---------------->| | | | | PS A | | | | | | | PolicyChannel | | | | + InfoOffer | | | |------------------->| | | (3) | PolicyChannel | | | | + PolicyOffer | | | |<-------------------| | | (4) | | | | | | | | | INVITE offer' | INVITE offer' | INVITE offer | | + Policy-Id | | + Policy-Contact| |---------------->|--------------->|---------------->| (5) | | | | | | PS B | | | | | | | | | PolicyChannel | | | | + InfoOffer | | | | + InfoAnswer | | | |<-------------------| (6) | | | PolicyChannel | | | | + PolicyOffer | | | | + PolicyAnswer | | | |------------------->| (7) | | | | | | | | | OK answer | OK answer | OK answer | |<----------------|<---------------|<----------------| (8) | ACK | |--------------------------------------------------->| | | | | | | | | | PolicyChannel | | | | + InfoAnswer | | | |------------------->| | | (9) | PolicyChannel | | | | + PolicyAnswer | | | |<-------------------| | | (10) | | | | Hilt, et al. Expires January 13, 2006 [Page 8] Internet-Draft Session-Specific Policies July 2005 Figure 2 4.2 Offer in Response This call flow depicts an INVITE transaction with the offer in the response. Steps (1) - (8) are analogous to steps (1) - (8) in the above flow. An important difference is that in steps (9) and (10) UA A contacts PS A after receiving the offer in the 200 OK but before returning the answer in step (11). This enables UA A to return the final answer, which includes all applicable policies, in the ACK. However, it requires that PS A immediately returns a policy to avoid a delay in the transmission of the ACK. This is similar to Flow I in [7]. UA A P A P B UA B | | | | | INVITE | | | |---------------->| | | (1) | 488 | | | | + Policy-Contact| | | |<----------------| | | (2) | ACK | | | |---------------->| | | | | PS A | | | | | | | PolicyChannel | | | |------------------->| | | (3) | PolicyChannel | | | |<-------------------| | | (4) | | | | | | | | | INVITE | INVITE | INVITE | | + Policy-Id | | + Policy-Contact| |---------------->|--------------->|---------------->| (5) | | | | | | PS B | | | | | | | | | PolicyChannel | | | | + InfoOffer | | | |<-------------------| (6) | | | PolicyChannel | | | | + PolicyOffer | | | |------------------->| (7) | | | | | | | | | OK offer | OK offer | OK offer | Hilt, et al. Expires January 13, 2006 [Page 9] Internet-Draft Session-Specific Policies July 2005 |<----------------|<---------------|<----------------| (8) | | | | | | | | | PolicyChannel | | | | + InfoOffer | | | | + InfoAnswer | | | |------------------->| | | (9) | PolicyChannel | | | | + PolicyOffer | | | | + PolicyAnswer | | | |<-------------------| | | (10) | | | | | ACK answer | |--------------------------------------------------->| (11) | | | | | | | | | | | PolicyChannel | | | | + InfoAnswer | | | |<-------------------| (12) | | | PolicyChannel | | | | + PolicyAnswer | | | |------------------->| (13) | | | | Figure 3 5. UA/Policy Server Rendezvous The first step in setting up session-specific policies is to rendezvous the UAs with the relevant policy servers. This is achieved by providing the URIs of all policy servers relevant for a session to the UAs. 5.1 UAC Behavior When a UA compliant to this specification generates an INVITE or UPDATE request, it MUST include a Supported header field with the option tag "policy" in the request. A UAC may receive a 488 in response to an INVITE or UPDATE request, which contains a Policy-Contact header field. This is a new header that contains the URI of a policy server. A 488 response with this header is generated by a proxy to convey the URI of the local policy server to the UAC. The UAC SHOULD contact this URI to retrieve the session policies that apply to the current request. If the UAC decides to accept the received policies, it SHOULD apply them to the request and resend the updated request. Hilt, et al. Expires January 13, 2006 [Page 10] Internet-Draft Session-Specific Policies July 2005 If the UAC has applied session policies to a request, it MUST insert a Policy-Id header into that request. The Policy-Id header MUST include the URIs of all policy servers the UAC has contacted during the processing of that request. The Policy-Id header enables a proxy to determine whether the URI of its policy server is already known to the UAC (and thus the request can be passed through) or whether the URI still needs to be conveyed to the UAC in a 488 response. In some cases, a request may traverse multiple domains with session- policies in place. Each of these domains may return a 488 response containing a policy server URI. Since the UAC contacts the policy server URI received in a 488 response before it resends the request, session policies are always applied to a session in the order in which the request traverses through these domains. Policies of the local network are applied first (since the local proxy is the first proxy that responds with a 488 response), policies of the first policy-enabled transit network are applied next, and so on. The order in which policies are applied to a session may be significant, for example, if a policy inserts media intermediaries into the media path. Session policies may apply to the offer, the answer or both session descriptions. Depending on the requirements of the policy, a UAC may need to contact the policy server with the offer and with the answer. A UAC MUST always contact the same policy servers for the offer and the answer. If the UAC receives an answer in the response to an INVITE request (i.e. the request contained the offer), it MUST send the ACK before retrieving the policies for the answer from the policy server. If the UAC receives a response with an offer (i.e. the INVITE request did not contain an offer), the UAC MUST first contact the policy server to retrieve session policies and apply these policies before sending the answer in the ACK. The answer in the ACK will therefore already consider the relevant policies. This approach assumes that the policy server immediately responds to a policy request and does not require manual intervention to create a policy. A delay in the response from the policy server would delay the transmission of the ACK and could trigger retransmissions of the INVITE response (also see the recommendations for Flow I in [7]). A UAC SHOULD cache the URI of the local policy server. It receives this URI in a 488 from the proxy in the local domain. The UAC SHOULD use this URI to retrieve session policies for a new INVITE or UPDATE request before it is sent. Caching the local policy server URI avoids the retransmission of this URI for each new INVITE or UPDATE request. Some domains may want to prevent the UAC from caching the local policy server URI. For example, if the policy server does not Hilt, et al. Expires January 13, 2006 [Page 11] Internet-Draft Session-Specific Policies July 2005 need to be involved in all sessions or the policy server URI changes from session to session. A proxy can mark the URI of such a policy server as "non-cacheable". The UA SHOULD NOT cache a non-cacheable policy server URI and SHOULD remove the current URI from its cache when receiving such a URI. The UAC SHOULD NOT cache policy server URIs it has received from proxies outside of the local domain. These policy servers may not be relevant for subsequent sessions, which may go to a different destination and may traverse different domains. The UAC SHOULD maintain a list of policy server URIs for each dialog. This list SHOULD include all policy server URIs that were contacted for the initial INVITE that created the dialog. The UAC should keep this list until the dialog is terminated. The UAC SHOULD contact the policy server URIs in this list before sending an INVITE or UPDATE request within that dialog. This avoids the retransmission of policy server URIs for mid-dialog requests. Contacting policy servers for mid-dialog INVITE or UPDATE requests is needed to enable policy servers to keep track of the session description and to update policies accordingly. 5.2 UAS Behavior An incoming INVITE or UPDATE request may contain a Policy-Contact header with a list of policy server URIs. The UAS SHOULD use these URIs to retrieve session policies. The UAS MUST use the policy server URIs in the order in which they were contained in the Policy- Contact header, starting with the topmost value. If the UAS receives an ACK with an answer, it may need to contact the policy servers again depending on the policy. In this case, it MUST contact the same policy servers it has contacted for the offer. 5.3 Proxy Behavior A proxy may provide the URI of the local policy server to the UAC or the UAS when processing an INVITE or UPDATE request. If an INVITE or UPDATE request contains a Supported header field with the option tag "policy", the proxy MAY reject the request with a 488 response to provide the local policy server URI to the UAC. Before rejecting a request, the proxy MUST check whether the request has a Policy-Id header field that already contains this policy server URI. If the request does not have such a header or the local policy server URI is not present in that header, then the proxy MAY reject the request with a 488. The proxy MUST insert a Policy-Contact header in the 488 response that contains the URI of the local policy server. Hilt, et al. Expires January 13, 2006 [Page 12] Internet-Draft Session-Specific Policies July 2005 The proxy MAY add the header field parameter "non-cacheable" to prevent the UAC from caching this policy server URI. If the local policy server URI is already present in the Policy-Id header of an INVITE or UPDATE request, the proxy MUST NOT reject the request as described above. The proxy SHOULD remove this policy server URI from the Policy-Id header field before forwarding the request. The proxy MAY insert a Policy-Contact header field into an INVITE or UPDATE request in order to convey the policy server URI to the UAS. If the request already contains a Policy-Contact header field, the proxy MUST insert the URI before of all existing values at the beginning of the list. A proxy MUST NOT change the order of existing Policy-Contact header values. 5.4 Header Definition and Syntax The Policy-Id header field is inserted into an INVITE or UPDATE request by the UAC. It identifies all policy servers the UAC has contacted for the request. A Policy-Id header value is the URI of a policy server. The syntax of the Policy-Id header field is: Policy-Id = "Policy-Id" HCOLON absoluteURI *(COMMA absoluteURI) The Policy-Contact header field can be inserted into INVITE and UPDATE requests by a proxy. It contains an ordered list of policy server URIs that need to be contacted by the UAS. The UAS starts to process the header field at the topmost value of this list. New header field values are inserted at the top. The Policy-Contact header field effectively forms a stack. The "non-cacheable" header field parameter MUST NOT be used in a request. The Policy-Contact header field can also be inserted into a 488 response to an INVITE or UPDATE request by a proxy. It contains a policy server URI that needs to be contacted by the UAC. A proxy MAY add the "non-cacheable" header field parameter to indicate that the UAC should not cache the policy server URI. The syntax of the Policy-Contact header field is: Policy-Contact = "Policy-Contact" HCOLON policyURI *(COMMA policyURI) policyURI = absoluteURI [ SEMI "non-cacheable" ] Hilt, et al. Expires January 13, 2006 [Page 13] Internet-Draft Session-Specific Policies July 2005 The BNF for absoluteURI is defined in [4]. Table 1 is an extension of Tables 2 and 3 in [4]. The column 'UPD' is for the UPDATE method [3]. Header field where proxy ACK BYE CAN INV OPT REG UPD _______________________________________________________________ Policy-Id R rd - - - o - - o Policy-Contact R a - - - o - - o Policy-Contact 488 a - - - o - - o Table 1: Policy-Id and Policy-Contact Header Fields Figure 6 6. Policy Channel The policy channel is set up between the UA and the policy server. This channel is needed to accomplish two tasks: first, to convey information about the current session from the UA to the policy server and, second, to return the policies for that session from the policy server back to the UA. 6.1 Session Information OPEN ISSUE: Which method should be used to convey session information from the UA to the policy server? Use cases for session-specific policies that may help resolving this issue are discussed in [6]. The following proposals have been made: 1. SIP SUBSCRIBE: session information is conveyed to the policy server in the body of SUBSCRIBE requests. The UA subscribes to session policies for each session. Semantically, session information is a filter criteria that selects the policies, which apply to the current session from the pool of all available policies. This semantics may not be applicable to all policies, in particular, if they are generated dynamically based on session information. Also, session information can only be provided by the subscriber and not by a third party. 2. SIP PUBLISH: the UA submits session information to the policy server in the body of a SIP PUBLISH request. The policy server uses this information to generate policies and makes these policies available for subscriptions. The UA can subscribe to these policies and will receive all policies (new or updated) via NOTIFY requests. The subscription can be established at the same time the PUBLISH request is sent. The UA may even use a single subscription to receive the policies for all sessions it sets up. In this case, each NOTIFY would cover all policies from that Hilt, et al. Expires January 13, 2006 [Page 14] Internet-Draft Session-Specific Policies July 2005 server (content indirection may be used). 3. HTTP: Similar to PUBLISH. Instead of using a PUBLISH request, the UA submits session information in the body of a HTTP request. The policies are received through a subscription. The UA needs two policy server URIs: a SIP URI (for the subscription) and a HTTP URI (to upload session information). 4. XCAP: Similar to HTTP. Instead of using plain HTTP, XCAP is used to upload session information. OPEN ISSUE: Which information should be disclosed to the policy server. Is this policy specific? Or should the UA generally disclose the session description? 6.2 Session Policies The UA accesses the policies that apply to the current session through the policy server URIs it has received during session establishment (see Section 5). The UA subscribes to these URIs and receives the current session policies. The policies for a session may change while the session is in progress. The UA is notified about updates to policies through the subscription. The session policy documents may be contained directly in the body of a NOTIFY message or they may be retrieved from an URI contained in the NOTIFY via content indirection. The subscription to session-specific policies is based on the Framework for SIP User Agent Profile Delivery [2]. It uses the new profile-type 'policy', which is defined in this document. Defining a new profile type for session-policies enables the decoupling of session-specific policies from other sources of profile information, such as user, device, or local profiles. 'Policy' profiles are provided by domains that have session-specific policies in place. 6.2.1 Event Header Parameters The new token 'policy' is defined for the 'profile-type' event header parameter. This extends the syntax of the profile-type event header parameter [2] as follows: profile-types = "device" / "user" / "application" / "local" / "policy" A SUBSCRIBE request for the policy profile-type may contain the 'network-user' parameter with the user's AoR. This parameter may be needed since the subscription URI does not reveal the user's AOR. Knowing the user's AOR may help a policy server to decide whether or not to accept a subscription and to determine which policies are Hilt, et al. Expires January 13, 2006 [Page 15] Internet-Draft Session-Specific Policies July 2005 applicable. 6.2.2 The Use of URIs The SUBSCRIBE request URI for the 'policy' profile is a policy server URI the user agent has received through mechanisms described in Section 5. A policy server URI MAY contain a 'document' URI parameter when it is received by the UA. This parameters can be used to identify a specific document on the policy server, to which the UA should subscribe. If this parameter is present in a policy server URI, it MUST be copied into the 'document' event header parameter of the SUBSCRIBE request. The 'document' parameter MUST be removed from the policy server URI before it is used in the SUBSCRIBE request URI. 6.2.3 Subscriber Behavior The 'policy' profile SHOULD be used when subscribing to a policy server URI. The UA SHOULD establish a separate subscription to each policy server URI it has received. It may receive session-specific policies through each of these subscriptions. The subscriber SHOULD include the 'network-user' parameter in the SUBSCRIBE request. 6.2.4 Notifier Behavior A notifier (i.e. a policy server) MUST immediately respond to SUBSCRIBE requests and MUST immediately send a NOTIFY in case it accepts the subscription. If the notifier cannot respond with a session policy right away, it must send an empty policy document and later update this policy. Note that updating a policy may require the subscriber to re-negotiate session parameters and should be avoided if possible. The timely transmission of session policies is in particular important if the UA (i.e. the subscriber) is requesting policies for an offer in an INVITE response (see Section 4.2). The policy server SHOULD authenticate the user before submitting a policy that grants additional privileges to the user. 6.2.5 Example The following example contains a policy server URI and a SUBSCRIBE message. Hilt, et al. Expires January 13, 2006 [Page 16] Internet-Draft Session-Specific Policies July 2005 Policy Server URI: sip:policy@ps.example.com;document=session-id/48ei48rj474k SUBSCRIBE sip:policy@ps.example.com SIP/2.0 Via: SIP/2.0/TCP terminal.example.com;branch=z9hG4bK6d6d35b6 Event: sip-profile;profile-type="policy"; document="session-id/48ei48rj474k"; vendor="vendor.example.com";model="Z100";version="1.2.3"; network-user="alice@example.com" To: sip:policy@ps.example.com From: sip:alice@example.com;tag=1234 Call-ID: ue8K743jRhr83@terminal.example.com CSeq: 1 SUBSCRIBE Contact: Accept: message/external-body, application/session-policy+xml Content-Length: 0 7. Updating Policies A UA may receive policy updates through a policy channel. The UA SHOULD apply these policies to the current session. It MUST generate a re-INVITE or UPDATE request if the updated policies modify aspects of the session that need to be communicated to the peer UA. 8. Security Considerations In particular authentication and authorization are critical issues that need to be addressed here. [TBD.] 9. IANA Considerations [TBD.] 10. References 10.1 Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Petrie, D., "A Framework for Session Initiation Protocol User Agent Profile Delivery", draft-ietf-sipping-config-framework-06 (work in progress), February 2005. Hilt, et al. Expires January 13, 2006 [Page 17] Internet-Draft Session-Specific Policies July 2005 [3] Rosenberg, J., "The Session Initiation Protocol (SIP) UPDATE Method", RFC 3311, October 2002. [4] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. 10.2 Informative References [5] Hilt, V. and G. Camarillo, "Use Cases for Session-Specific Session Initiation Protocol (SIP) Session Policies", draft-hilt-sipping-policy-usecases-00 (work in progress), June 2005. [6] Hilt, V., Camarillo, G., and J. Rosenberg, "Session Initiation Protocol (SIP) Session Policies - Document Format and Session- Independent Delivery Mechanism", draft-ietf-sipping-session-indep-policy-03 (work in progress), June 2005. [7] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. Camarillo, "Best Current Practices for Third Party Call Control (3pcc) in the Session Initiation Protocol (SIP)", BCP 85, RFC 3725, April 2004. [8] Rosenberg, J., "Requirements for Session Policy for the Session Initiation Protocol (SIP)", draft-ietf-sipping-session-policy-req-02 (work in progress), July 2004. Authors' Addresses Volker Hilt Bell Labs/Lucent Technologies 101 Crawfords Corner Rd Holmdel, NJ 07733 USA Email: volkerh@bell-labs.com Hilt, et al. Expires January 13, 2006 [Page 18] Internet-Draft Session-Specific Policies July 2005 Gonzalo Camarillo Ericsson Hirsalantie 11 Jorvas 02420 Finland Email: Gonzalo.Camarillo@ericsson.com Jonathan Rosenberg Cisco Systems 600 Lanidex Plaza Parsippany, NJ 07054 USA Email: jdrosen@cisco.com Appendix A. Acknowledgements Many thanks to Allison Mankin for the discussions and the suggestions for this draft. A big thanks also to everyone who contributed by providing feedback on the mailing list and in IETF meetings. Hilt, et al. Expires January 13, 2006 [Page 19] Internet-Draft Session-Specific Policies July 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Hilt, et al. Expires January 13, 2006 [Page 20]