[dispatch] Call Control UUI Problem Statement
Alan Johnston <alan@sipstation.com> Fri, 22 May 2009 17:19 UTC
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Date: Fri, 22 May 2009 12:20:50 -0500
From: Alan Johnston <alan@sipstation.com>
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Cc: Joanne McMillen <joanne@avaya.com>
Subject: [dispatch] Call Control UUI Problem Statement
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Several approaches to transporting the ITU-T Q.931 User to User Information Element (UU IE) data in SIP have been proposed. As networks move to SIP it is important that applications requiring this data can continue to function in SIP networks as well as the ability to interwork with this ISDN service for end-to-end transparency. While the information is carried in ISUP, the contents can be in a number of protocols that are not ISUP, and as such it is architecturally unreasonable to interwork these protocols at the SIP / ISUP gateway. This work area involves defining a new SIP mechanism to transport this information. Since the INFO method, RFC2976, was developed for ISUP interworking of user-to-user information, it might seem to be the logical choice here. For non-call control user-to-user information, INFO can be utilized for end to end transport. However, for transport of call control user-to-user information, INFO can not be used. Since the contents carry information that can impact call handling at the UAC, the information must be conveyed with the INVITE transaction. As the call flows in the previous section show, the information is related to an attempt to establish a session and must be passed with the session setup request (INVITE), responses to that INVITE, or session termination requests. As a result, it is not possible to use INFO in these cases. Also, the use of message body is another obvious mechanism, but this is not suitable for a number of reasons including difficulty with multipart MIME INVITEs and 200 OKs, and in escaping UUI information into redirects and REFERs. The I-D draft-johnston-sipping-cc-uui will be used as the basis for this work. This draft was first submitted 3 years ago and has had plenty of discussion in the old SIPPING Working Group. The requirements in this document completed a WGLC in SIPPING in December 2008 with strong support from the group. This draft proposes a new SIP header field User-to-User and parameters for transporting this information. This extension will also be used for native SIP endpoints implementing similar services and interworking with ISDN services. Example use cases include an exchange between two user agents, retargeting by a proxy, and redirection. An example application is an Automatic Call Distributor (ACD) in a contact center. The coordinators for this work will be Alan Johnston <alan@sipstation.com> and Keith Drage <drage@alcatel-lucent.com> Thanks, Alan
- [dispatch] Call Control UUI Problem Statement Alan Johnston
- Re: [dispatch] Call Control UUI Problem Statement Dean Willis
- Re: [dispatch] Call Control UUI Problem Statement Alan Johnston
- Re: [dispatch] Call Control UUI Problem Statement Dean Willis
- Re: [dispatch] Call Control UUI Problem Statement Alan Johnston
- Re: [dispatch] Call Control UUI Problem Statement Mary Barnes