Network Working Group C. Jennings Internet-Draft Cisco Systems Expires: January 12, 2006 July 11, 2005 Conventions for Voicemail URIs in SIP draft-jennings-sip-voicemail-uri-04 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 12, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract The SIP protocol is often used to initiate connections to voicemail or unified messaging systems. This specification describes a convention for forming SIP Service URIs that request particular services from unified messaging systems. Jennings Expires January 12, 2006 [Page 1] Internet-Draft SIP Voicemail URI July 2005 Table of Contents 1. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Mechanism (UAS and Proxy) . . . . . . . . . . . . . . . . . 4 3.1 Target . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2 Cause . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.3 Retrieving Messages . . . . . . . . . . . . . . . . . . . 5 4. Interaction with History . . . . . . . . . . . . . . . . . . 5 5. Limitations of Voicemail URI . . . . . . . . . . . . . . . . 5 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.1 Proxy Forwards No Answer to Voicemail . . . . . . . . . . 6 6.2 Zero Configuration UM System . . . . . . . . . . . . . . . 8 6.3 TDM Voice Mail Connected via a Gateway . . . . . . . . . . 9 6.4 Call Coverage . . . . . . . . . . . . . . . . . . . . . . 9 7. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8. PSTN Mapping . . . . . . . . . . . . . . . . . . . . . . . . 10 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 11 10. Security Considerations . . . . . . . . . . . . . . . . . . 11 10.1 Integrity Protection of Forwarding in SIP . . . . . . . 12 10.2 Privacy Related Issues on the Second Call Leg . . . . . 13 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 14 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 12.1 Normative References . . . . . . . . . . . . . . . . . . 14 12.2 Informative References . . . . . . . . . . . . . . . . . 15 Author's Address . . . . . . . . . . . . . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . 16 Jennings Expires January 12, 2006 [Page 2] Internet-Draft SIP Voicemail URI July 2005 1. Conventions 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 [1]. 2. Introduction Unified messaging systems (UM) have developed out of traditional voice mail systems. They can be used for storing and interacting with voice, video, faxes, email, and instant messaging. Users often use SIP to initiate communications with them. When a SIP call is routed to a UM, it is necessary that the UM be able to obtain several bits of information from the call so that it can deliver the desired services. The UM needs to know what mailbox should be used and possible reasons for the type of service desired from the UM. This includes knowing the type of media (voice or IM, for example). Many voice mail systems provide different greetings depending whether the call went to voicemail because the user was busy or because the user did not answer. All of this information can be delivered in existing SIP signaling from the call control that retargets the call to the UM, but there are no standardized conventions for describing how the desired mailbox and service requested are expressed. It would be possible for every vendor to make this configurable so that any site could get it to work; however, this approach is unrealistic for achieving interoperability among call control, gateways, and unified messaging systems from different vendors. This specification describes a convention for describing this mailbox and service information in the SIP URI so that vendors and operators can build interoperable systems. The work in the History Info [9] draft can be used in similar systems. It is more comprehensive and covers a much wider set of requirements. A key difference from this system is that History allows the UM to look at the history of the call and decide on the best treatment for the call. This work requires the call control system to know something about the history of the call and specifically ask the UM to invoke a particular service. If there were no need to interoperate with TDM based voicemail systems or to allow TDM systems to use VoIP unified messaging systems, this problem would be a little easier. The problem that is introduced in the VoIP to TDM case is as follows. The SIP system needs to tell a PSTN GW both the subscriber's mailbox identifier (which typically looks like a phone number) and the address of the voicemail system in the TDM network (again a phone number). One topic that causes some confusion in the requirements has to do Jennings Expires January 12, 2006 [Page 3] Internet-Draft SIP Voicemail URI July 2005 with the fact that the related PSTN mechanism can carry two addresses. These correspond to the original target of the call and the most recent target to which it has been redirected. In general, the original target is used to find the voice mail box. The target that most recently redirected is not as useful for voicemail but is very useful for billing. It is often used to bill the most recent portion of the call leg. This work addresses only the requirements for a UM system, and billing is completely out of scope. The History draft is much more extensive and covers more cases that might be useful for billing, but this work does not. The question has been asked why the To header cannot be used to specify which mailbox to use. One problem is that the call control proxies cannot modify the To header, and the UACs often set it incorrectly because they do not have information about the subscribers in the domain they are trying to call. This happens because the routing of the call often translates the URI multiple times before it results in an identifier for the desired user that is valid in the namespace that the UM system understands. Another set of requirements that this mechanism can deal with is the call coverage naming issues. When Bill calls the 800 number that sends him to the helpdesk, the proxy may first fork the call to Alice (who works at the help desk), and then if Alice does not answer in a few seconds fork the call on to Bob (who also works at the helpdesk). Both Alice and Bob would like to be informed that the call has been sent to the help desk before they answer the call. If neither answers, the call may get sent to the help desk's voice mailbox, not Bob's or Alice's. 3. Mechanism (UAS and Proxy) The mechanism works by encoding the information for the desired service in the SIP URI that is sent to the UM system. Two chunks of information are encoded, the first being the target mailbox to use and the second being the SIP error code that caused this retargeting and indicates the desired service. The target mailbox can be put in the user part of the URI and is also put in a target URI parameter, while the reason is put in the URI cause parameter. For example, if the proxy wished to use Alice's mailbox because her phone was busy, the URI sent to the UM system could be something like: sip:alice@um.example.com;target=alice;cause=486 3.1 Target The target parameter indicates the mailbox to use. In many cases the Jennings Expires January 12, 2006 [Page 4] Internet-Draft SIP Voicemail URI July 2005 user portion of the SIP URI could be set to the same value, but it does not have to be. For example in the case of a voice mail system on the PSTN, the user portion will contain the phone number of the voice mail system, while the target will contain the phone number of the subscriber's mailbox. 3.2 Cause The URI cause parameter is used to indicate the service that the UAS receiving the message should perform. It corresponds to the SIP Status-Code that results in the desired service being requested. A mapping between some common services and reason codes are: +------------------------------+-----------------+ | Service | Cause Parameter | +------------------------------+-----------------+ | Busy | 486 | | No answer | 408 | | Unconditional | 302 | | Deflect | 487 | | No Contacts/Failure of UA | 410 | +------------------------------+-----------------+ 3.3 Retrieving Messages The UM system MAY use the fact that the From header is the same as the URI target as a hint that the user wishes to retrieve messages. 4. Interaction with History The History mechanism[9] provides considerably more information that is useful for a UM system. This work does not stop a UM system from taking advantage of the History information if it is present and using that to handle the call. It is reasonable to have systems in which both the information in this specification and the History information are included and one or both are used. 5. Limitations of Voicemail URI This system requires the proxy that is requesting the service to understand what are valid targets on the UM system. For practical purposes this means that the approach is unlikely to work in many cases in which the proxy is not configured with information about the UM system or is not in the same administrative domain. This system requires the call control proxy to know what it wants the UM to do, instead of giving the UM system information about the call Jennings Expires January 12, 2006 [Page 5] Internet-Draft SIP Voicemail URI July 2005 that allows it to decide what to do. For example, if a call to the help desk got forwarded first to Alice, then to Bob, and then finally to the helpdesk UM system, the UM system might want to leave a copy of the message in the primary help desk mailbox and also leave a copy in Alice's mailbox since she was the primary person at the helpdesk. In addition the UM system might want to page Alice, Bob, and their supervisor to let them know that no one is staffing the help desk. This system does not provide enough information to the UM system about what happened to the call to meet the needs of such a scenario. This system only works when the service the call control wants applied is fairly simple. For example it does not allow the proxy to express information like "Do not offer to connect to the target's colleague because that address has already been tried". Some systems have expressed the requirement that the UAC understand when the call is re-targeted and get updated information about where it was targeted to as the call proceeds. This work does not address this requirement - History does, as does the option of just sending a 1xx class message with a Reason header[7]. The mechanism in this specification do not address any billing issues associated with forwarded calls. This is a separate problem. The limitations discussed in this section are addressed by the History[9] work. 6. Examples 6.1 Proxy Forwards No Answer to Voicemail In this example, Alice calls Bob. Bob's proxy runs a timer and determines that Bob has not answered his phone, and the proxy forwards the call to Bob's voicemail. Alice's phone is at 192.168.0.1 while Bob's phone is at 192.168.0.2. The important things to note is the URI in message F4. Jennings Expires January 12, 2006 [Page 6] Internet-Draft SIP Voicemail URI July 2005 F1: INVITE 192.168.0.1 -> proxy.example.com INVITE sip:15555551002@example.com;user=phone SIP/2.0 Via: SIP/2.0/TCP 192.168.0.1:5060;branch=z9hG4bK-74bf9 From: Alice ;tag=9fxced76sl To: sip:15555551002@example.com;user=phone Call-ID: c3x842276298220188511 CSeq: 1 INVITE Max-Forwards: 70 Contact: Content-Type: application/sdp Content-Length: *Body length goes here* * SDP goes here* F2: INVITE proxy.example.com -> 192.168.0.2 INVITE sip:line1@192.168.0.2 SIP/2.0 Via: SIP/2.0/TCP 192.168.1.4:5060;branch=z9hG4bK-ik80k7g-1 Via: SIP/2.0/TCP 192.168.0.1:5060;branch=z9hG4bK-74bf9 From: Alice ;tag=9fxced76sl To: sip:15555551002@example.com;user=phone Call-ID: c3x842276298220188511 CSeq: 1 INVITE Max-Forwards: 70 Contact: Content-Type: application/sdp Content-Length: *Body length goes here* * SDP goes here* F3: 486 192.168.0.2 -> proxy.example.com SIP/2.0 486 Busy Here Via: SIP/2.0/TCP 192.168.1.4:5060;branch=z9hG4bK-ik80k7g-1 Via: SIP/2.0/TCP 192.168.0.1:5060;branch=z9hG4bK-74bf9 From: Alice ;tag=9fxced76sl To: sip:15555551002@example.com;user=phone;tag=09xde23d80 Call-ID: c3x842276298220188511 CSeq: 1 INVITE Contact: Content-Length: 0 Jennings Expires January 12, 2006 [Page 7] Internet-Draft SIP Voicemail URI July 2005 F4: INVITE proxy.example.com -> um.example.com INVITE sip:bob@um.example.com;target=bob;cause=486 SIP/2.0 Via: SIP/2.0/TCP 192.168.1.4:5060;branch=z9hG4bK-ik80k7g-2 Via: SIP/2.0/TCP 192.168.0.1:5060;branch=z9hG4bK-74bf9 From: Alice ;tag=9fxced76sl To: sip:15555551002@example.com;user=phone Call-ID: c3x842276298220188511 CSeq: 1 INVITE Max-Forwards: 70 Contact: Content-Type: application/sdp Content-Length: *Body length goes here* * SDP goes here* 6.2 Zero Configuration UM System In this example, the UM system has no configuration information specific to any user. The proxy is configured to pass a URI that provides the prompt to play and an email address in the user portion of the URI to which the recorded message is to be sent. The call flow is the same as in the previous example, except that the URI in F4 changes to specify the user part as Bob's email address, and the netann [8] URI play parameter specifies where the greeting to play can be fetched from. F4: INVITE proxy.example.com -> um.example.com INVITE sip:bob@um.example.com;target=mailto:bob%40example.com;cause=486; play=http://www.example.com/bob/busy.way SIP/2.0 Via: SIP/2.0/TCP 192.168.1.4:5060;branch=z9hG4bK-ik80k7g-2 Via: SIP/2.0/TCP 192.168.0.1:5060;branch=z9hG4bK-74bf9 From: Alice ;tag=9fxced76sl To: sip:15555551002@example.com;user=phone Call-ID: c3x842276298220188511 CSeq: 1 INVITE Max-Forwards: 70 Contact: Content-Type: application/sdp Content-Length: *Body length goes here* * SDP goes here* Jennings Expires January 12, 2006 [Page 8] Internet-Draft SIP Voicemail URI July 2005 In addition, if the proxy wished to indicate a VXML script that the UM should execute, it could add a parameter to the URI in the above message that looked like: voicexml=http://www.example.com/bob/busy.vxml 6.3 TDM Voice Mail Connected via a Gateway In this example, the voicemail system has a TDM interconnect to a gateway to the VoIP system. Bob's mailbox is +1 555 555-1002, while the address of the voicemail system on the TDM network is +1 555 555- 2000. The call flow is the same as in the previous example except for the URI in F4. F4: INVITE proxy.example.com -> gw.example.com INVITE sip:+1-555-555-2000@um.example.com;user=phone;\ target=tel:+1-555-555-1002;cause=486 SIP/2.0 Via: SIP/2.0/TCP 192.168.1.4:5060;branch=z9hG4bK-ik80k7g-2 Via: SIP/2.0/TCP 192.168.0.1:5060;branch=z9hG4bK-74bf9 From: Alice ;tag=9fxced76sl To: sip:15555551002@example.com;user=phone Call-ID: c3x842276298220188511 CSeq: 1 INVITE Max-Forwards: 70 Contact: Content-Type: application/sdp Content-Length: *Body length goes here* * SDP goes here* 6.4 Call Coverage In this example a user on the PSTN calls a 800 number. The GW sends this to the proxy which recognizes that the helpdesk is the target. Alice and Bob are staffing the help desk and are tried sequentially but neither answers, so the call is forwarded to the helpdesk's voice mail. The key item in this flow is that the invite to Alice and Bob looks like Jennings Expires January 12, 2006 [Page 9] Internet-Draft SIP Voicemail URI July 2005 INVITE sip:bob@um.example.com;target=helpdesk;cause=302 SIP/2.0 7. Syntax This specification updates the ABNF in Section 25 of RFC 3261 [3] to add the target-param to the uri-parameter as shown below. uri-parameter = transport-param / user-param / method-param / ttl-param / maddr-param / lr-param / other-param / target-param / cause-param target-param = "target" EQUAL pvalue cause-param = "cause" EQUAL Status-Code It is worth noting that the ABNF requires some characters to be escaped if they occur in the value of the target parameters. For example, the "@" character needs to be escaped. 8. PSTN Mapping The mapping to the PSTN protocols is important both for gateways that connect the IP network to existing TDM equipment, such as PBXs and voicemail systems, and for gateways that connect the IP network to the PSTN network. Both ISDN and ISUP have signaling for this information that can be treated as roughly equivalent for the purposes here. The user portion of the URI SHOULD be used as the address of the voicemail system on the PSTN, while the target SHOULD be mapped to the original redirecting party on the PSTN side. If the gateway and Proxy are in the same Trust Domain (defined in RFC 3325 [5]), and the Spec(T) includes compliance with this specification, and the Spec(T) asserts that the Proxy will do screening (whatever that means), then the gateway MAY claim it is screened; otherwise it SHOULD NOT assert that the diversion information is screened. This draft says nothing about what to put into the redirecting numbers, as that has billing implications outside the scope of this work. The requirements here will work fine if the redirecting number is not set on the PSTN side. It is not recommended that the GW map the target information into the redirecting party information, but doing so is not in violation of this specification. Jennings Expires January 12, 2006 [Page 10] Internet-Draft SIP Voicemail URI July 2005 The following SHOULD be used as the mapping between reason parameters and ISUP/ISDN redirect reason codes: +-----------+----------------------------------------+--------------+ | ISUP or | PSTN Reason | URI Cause | | ISDN | | Parameter | +-----------+----------------------------------------+--------------+ | 0000 | Unknown | 300 | | 0001 | Call forwarding busy or called DTE | 486 | | | busy | | | 0010 | Call forwarding no reply | 408 | | 1111 | Call forwarding unconditional or | 302 | | | systematic call redirection | | | 1010 | Call deflection or call forwarding by | 487 | | | the called DTE | | | 1001 | Call forwarding DTE out of order | 410 | +-----------+----------------------------------------+--------------+ The redirection counters SHOULD be set to one unless additional information is available. 9. IANA Considerations This specification adds a new value to the IANA registration in the "SIP/SIPS URI Parameters" sub-registry at http://www.iana.org/assignments/sip-parameters as defined in [6]. Parameter Name Predefined Values Reference ____________________________________________ target No [RFCAAAA] cause Yes [RFCAAAA] [Note to IANA: Please replace AAAA with the RFC number of this specification. 10. Security Considerations This draft discusses transactions involving at least three parties, which increases the complexity of the privacy issues. The new URI parameters defined in this draft are generally sent from a Proxy or call control system to a unified messaging (UM) system or gateway to the PSTN, and then to a voicemail system. These new parameters tell the UM what service the proxy wishes to have performed. Just as any message sent from the proxy to the UM needs to be integrity protected, these messages need to be integrity protected to stop attackers from, for example, causing a voicemail Jennings Expires January 12, 2006 [Page 11] Internet-Draft SIP Voicemail URI July 2005 meant for a company's CEO to go to an attacker's mailbox. RFC 3261 provides a TLS mechanism suitable for performing this integrity protection. The signaling from the Proxy to the UM will reveal who is calling whom and possibly some information about a user's presence based on whether the call was answered or sent to voicemail. This information can be protected by encrypting the SIP traffic between the Proxy and UM. Again, RFC 3261 contains mechanisms for accomplishing this using TLS. The S/MIME based mechanisms in RFC 3261 will generally not be applicable for protecting this information because they are meant for end to end issues and this is primarily a middle to end scenario. Ongoing work on middle to end [10] may allow S/MIME based schemes to be used for protecting this information. These schemes would allow the information to be hidden and integrity protected if there was another administrative domain between the Proxy and UM. The current scheme is based on hop by hop security and requires that all hops between the Proxy and UM be trusted, which is the case in many deployment scenarios. 10.1 Integrity Protection of Forwarding in SIP The forwarding of a call in SIP brings up a very strange trust issue. Consider the normal case when A calls B and the call gets forwarded to C by a network element in B's domain, and then C answers the call. A has called B but ended up talking to C. This scenario may be hard to separate from a man in the middle attack. There are two possible solutions. One is that B sends back information to A saying don't call me, call C and signs it as B. The problem is that this solution involves revealing that B has forwarded to C, which B often may not want to do. For example, B may be a work phone that has been forwarded to a mobile or home phone. The user does not want to reveal their mobile or home phone number but, even more importantly, does not want to reveal that they are not in the office. The other possible solution is that A needs to trust B only to forward to a trusted identity. This requires a hop by hop transitive trust such that each hop will only send to a trusted next hop and each hop will only do things that the user at that hop desired. This solution is enforced in SIP using the SIPS URI and TLS based hop by hop security. It protects from an off axis attack, but if one of the hops is not trustworthy, the call may be diverted to an attacker. Any redirection of a call to an attacker's mailbox is serious. It is Jennings Expires January 12, 2006 [Page 12] Internet-Draft SIP Voicemail URI July 2005 trivial for an attacker to make its mailbox seem very much like the real mailbox and forward the messages to the real mailbox so that the fact that the messages have been intercepted or even tampered with escapes detection. 10.2 Privacy Related Issues on the Second Call Leg When A calls B and gets redirected to C, occasionally people say there is a requirement for the call leg from B to C to be anonymous. This is not the PSTN and there is no call leg from B to C; instead there is a VoIP session between A and C. If A had put a To header containing B in the initial invite message, unless something special is done about it, C will see that To header. If the person who answers phone C says "I think you dialed the wrong number, who were you trying to reach?" A will probably specify B. If A does not want C to see that the call was to B, A needs a special relationship with the forwarding Proxy to induce it not to reveal that information. The call should go through an anonymizer service that provides session or user level privacy (as described in RFC 3323 [4]) service before going to C. It is not hard to figure out how to meet this requirement, but it is unclear why anyone would want this service. The scenario in which B wants to make sure that C does not see that the call was to B is easier to deal with but a bit weird. The usual argument is Bill wants to forward his phone to Monica but does not want Monica to find out his phone number. It is hard to imagine that Monica would want to accept all Bill's calls without knowing how to call Bill to complain. The only person Monica will be able to complain to is Hillary, when she tries to call Bill. Several popular web portals will send SMS alert message about things like stock prices and weather to mobile phone users today. Some of these contain no information about the account on the web portal that initiated them, making it nearly impossible for the mobile phone owner to stop them. This anonymous message forwarding has turned out to be a really bad idea even where no malice is present. Clearly some people are fairly dubious about the need for this, but never mind: let's look at how it is solved. In the general case, the proxy needs to route the call through an Anonymization Service and everything will be cleaned up. Any Anonymization service that performs the "Privacy: Header" Service in RFC 3323 [5] MUST remove the reason and target URI parameters from the URI. RFC 3325 already makes it pretty clear you would need to clean up this sort of information. There is a specialized case of some interest in which the mechanisms Jennings Expires January 12, 2006 [Page 13] Internet-Draft SIP Voicemail URI July 2005 in this specification are being used in conjunction with RFC 3325, and the UM and the Proxy are both in the trust domain. In this limited case, the problem that B does not want to reveal their address to C can be solved by ensuring that the target parameter URI should never be in a message that is forwarded outside the trust domain. If it is passed to a PSTN device in the trust domain, the appropriate privacy flag needs to be set in the ISUP or ISDN signaling. 11. Acknowledgments Mary Barnes, Dean Willis, and Steve Levy have spent significant time with me helping me understand the requirements and pros and cons of various approaches. Lyndsay Campbell helped catch mistakes. I would like to thank them very much for this assistance, and I would also like to acknowledge Rohan Mahy's help and encouragement with respect to this subject. 12. References 12.1 Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [3] 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. [4] Peterson, J., "A Privacy Mechanism for the Session Initiation Protocol (SIP)", RFC 3323, November 2002. [5] Jennings, C., Peterson, J., and M. Watson, "Private Extensions to the Session Initiation Protocol (SIP) for Asserted Identity within Trusted Networks", RFC 3325, November 2002. [6] Camarillo, G., "The Internet Assigned Number Authority (IANA) Uniform Resource Identifier (URI) Parameter Registry for the Session Initiation Protocol (SIP)", BCP 99, RFC 3969, December 2004. [7] Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason Header Field for the Session Initiation Protocol (SIP)", RFC 3326, December 2002. Jennings Expires January 12, 2006 [Page 14] Internet-Draft SIP Voicemail URI July 2005 12.2 Informative References [8] Burger, E., "Basic Network Media Services with SIP", draft-burger-sipping-netann-11 (work in progress), February 2005. [9] Barnes, M., "An Extension to the Session Initiation Protocol for Request History Information", draft-ietf-sip-history-info-06 (work in progress), January 2005. [10] Ono, K. and S. Tachimoto, "End-to-middle security in the Session Initiation Protocol(SIP)", draft-ono-sipping-end2middle-security-04 (work in progress), February 2005. Author's Address Cullen Jennings Cisco Systems 170 West Tasman Drive Mailstop SJC-21/2 San Jose, CA 95134 USA Phone: +1 408 421-9990 Email: fluffy@cisco.com Jennings Expires January 12, 2006 [Page 15] Internet-Draft SIP Voicemail URI 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. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), 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. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Jennings Expires January 12, 2006 [Page 16]