Internet Engineering Task Force                                   SIP WG
Internet Draft                                          Oran/Schulzrinne
draft-oran-sip-visited-00.txt                           Cisco/Columbia U.
August 6, 2000
Expires: December 2000

             SIP extension for tracking locations attempted


   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-

   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

   To view the list Internet-Draft Shadow Directories, see


   Proxying hides the destinations tried by the proxy. Since this
   information is sometimes useful to the requestor, this draft proposes
   a new optional SIP request header called Contacts-Tried listing the
   locations tried unsuccessfully during a search.

1 Introduction

   It may be useful for the initiator of a request to track which
   locations have been tried while forking calls, particularly if
   recursive indirection is involved. For example, this allows a caller
   to avoid manually calling a person that has already been tried as
   part of proxy forking.

2 Syntax

Oran/Schulzrinne                                              [Page 1]

Internet Draft                    SIP                     August 6, 2000

        Contacts-Tried  =  "Contacts-Tried" ":" # ( name-addr | addr-spec
                           *(";" ct-params )
        ct-params       =  "reason" = quoted-string
                       |   "status" = Status-Code

   The "reason" parameter contains the reason phrase from the response,
   while the "status" parameter identifies the numeric status code. The
   "reason" parameter MAY be present if and only if the "status"
   parameter is present.

   The order of elements has no significance. Each proxy adds to the
   list in responses returned from downstream servers.


     Contacts-Tried: "A. G. Bell" <>
       ;reason="Busy" ;status=600,
       "T. Bell" <>
       ;reason="I don't talk to telemarketers" ;status=603

3 Security Considerations

   Users may expect proxying and forwarding information to remain
   private.  Thus, proxies MUST NOT reveal this information by default
   and MUST only reveal this information only if the party designated in
   the To header field has agreed to have this information revealed.

4 Authors' Addresses

   David R. Oran
   Cisco Systems
   7 Ladyslipper Lane
   Acton, MA 01720

   Henning Schulzrinne
   Dept. of Computer Science
   Columbia University
   1214 Amsterdam Avenue
   New York, NY 10027

Oran/Schulzrinne                                              [Page 2]