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Versions: 00 01 02 RFC 3665

   SIPPING Working Group                                    A. Johnston
   Internet Draft                                              WorldCom
   Document:                                                 S. Donovan
    draft-ietf-sipping-basic-call-flows-01.txt                R. Sparks
   Expires: April 2003                                    C. Cunningham
                                                            dynamicsoft
                                                             K. Summers
                                                                  Sonus
                                                           October 2002


           Session Initiation Protocol Basic Call Flow Examples


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 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.


Abstract

   This informational document gives examples of Session Initiation
   Protocol (SIP) call flows.  Elements in these call flows include SIP
   User Agents and Clients, SIP Proxy and Redirect Servers.  Scenarios
   include SIP Registration and SIP session establishment.  Call flow
   diagrams and message details are shown.


Conventions used in this document

   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].



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Table of Contents

   1. Overview.......................................................2
      1.1 General Assumptions........................................3
      1.2 Legend for Message Flows...................................3
      1.3 SIP Protocol Assumptions...................................3
   2. SIP Registration...............................................5
      2.1 Successful New Registration................................5
      2.2 Update of Contact List.....................................7
      2.3 Request for Current Contact List...........................9
      2.4 Cancellation of Registration..............................11
      2.5 Unsuccessful Registration.................................13
   3. SIP Session Establishment.....................................15
      3.1 Successful Session Establishment..........................15
      3.2 Session Establishment Through Two Proxies.................18
      3.3 Session with Multiple Proxy Authentication................28
      3.4 Successful Session with Proxy Failure.....................38
      3.5 Session Through a SIP ALG.................................47
      3.6 Session via Redirect and Proxy Servers with SDP in ACK....55
      3.7 Session with re-INVITE (IP Address Change)................62
      3.8 Unsuccessful No Answer....................................68
      3.9 Unsuccessful Busy.........................................76
      3.10 Unsuccessful No Response from User Agent.................81
      3.11 Unsuccessful Temporarily Unavailable.....................86
   Security Considerations..........................................91
   References.......................................................91
   Acknowledgments..................................................92
   Author's Addresses...............................................92

1.   Overview

   The call flows shown in this document were developed in the design of
   a SIP IP communications network.  They represent an example
   minimum set of functionality.

   It is the hope of the authors that this document will be useful for
   SIP implementors, designers, and protocol researchers alike and will
   help further the goal of a standard implementation of RFC 3261[2].
   These flows represent carefully checked and working group reviewed
   scenarios of the most basic examples as a companion to the
   specifications.

   These call flows are based on the current version 2.0 of SIP in
   RFC 3261[2] with SDP usage described in RFC 3264[3]. Other RFCs also
   comprise the SIP standard but are not used in this set of basic call
   flows.

   Call flow examples of SIP interworking with the PSTN through gateways
   are contained in a companion document, RFC xxxx[4].


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1.1     General Assumptions

   A number of architecture, network, and protocol assumptions underlie
   the call flows in this document. Note that these assumptions are not
   requirements.  They are outlined in this section so that they may be
   taken into consideration and to aid in the understanding of the call
   flow examples.

   The authentication of SIP User Agents in these example call flows is
   performed using HTTP Digest as defined in [2] and [5].

   Some Proxy Servers in these call flows insert Record-Route headers
   into requests to ensure that they are in the signaling path for
   future message exchanges.

   These flows show TCP, TLS, and UDP for transport.  Other transport
   schemes could also be used.  If UDP is used, care must be taken to
   avoid packet fragmentation and congestion.

1.2     Legend for Message Flows

   Dashed lines (---) represent signaling messages that are mandatory to
   the call scenario. These messages can be SIP or PSTN
   signaling.  The arrow indicates the direction of message flow.

   Double dashed lines (===) represent media paths between network
   elements.

   Messages with parentheses around their name represent optional
   messages.

   Messages are identified in the Figures as F1, F2, etc.  This
   references the message details in the list that follows the Figure.
   Comments in the message details are shown in the following form:

    /* Comments. */

1.3     SIP Protocol Assumptions

   This document is informational only and is NOT NORMATIVE in any
   sense, in that it does not prescribe the flows that are shown, indeed
   they MUST NOT be copied due to the reasons described in the next
   paragraph.  On the other hand, the basic call flows represent well-
   reviewed examples of SIP usage that are best common practice
   according to community consensus.

   For simplicity in reading and editing the document, there are a
   number of differences between some of the examples and actual SIP


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   messages.  For example, the HTTP Digest responses are not actual MD5
   encodings.  Call-IDs are often repeated, and CSeq counts often begin
   at 1.  Header fields are usually shown in the same order.  Usually
   only the minimum required header field set is shown, others that
   would normally be present such as Accept, Supported, Allow, etc are
   not shown.

   Actors:

   Element       Display Name   URI                  IP Address
   -------       ------------   ---                  ----------

   User Agent    BigGuy         UserA@atlanta.com    192.0.2.101
   User Agent    LittleGuy      UserB@biloxi.com     192.0.2.201
   User Agent                   UserB@chicago.com    192.0.2.100
   Proxy Server                 ss1.atlanta.com      192.0.2.111
   Proxy/Registrar              ss2.biloxi.com       192.0.2.222
   Proxy Server                 ss3.chicago.com      192.0.2.233
   ALG                          alg1.atlanta.com     192.0.2.128
































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2.   SIP Registration

   Registration binds a particular device Contact URI with a SIP user
   Address of Record (AOR).

2.1     Successful New Registration

    User B                        SIP Server
     |                               |
     |          REGISTER F1          |
     |------------------------------>|
     |      401 Unauthorized F2      |
     |<------------------------------|
     |          REGISTER F3          |
     |------------------------------>|
     |            200 OK F4          |
     |<------------------------------|
     |                               |

   User B sends a SIP REGISTER request to the SIP server.  The request
   includes the user's contact list.  This flow shows the use of HTTP
   Digest for authentication using TLS transport.  TLS transport is used
   due to the lack of integrity protection in HTTP Digest and the danger
   of registration hijacking without it, as described in RFC 3261 [2].
   The SIP server provides a challenge to User B.  User B enters her/his
   valid user ID and password.  User B's SIP client encrypts the user
   information according to the challenge issued by the SIP server and
   sends the response to the SIP server.  The SIP server validates the
   user's credentials.  It registers the user in its contact database
   and returns a response (200 OK) to User B's SIP client.  The response
   includes the user's current contact list in Contact headers.  The
   format of the authentication shown is HTTP digest.  It is assumed
   that User B has not previously registered with this Server.


   Message Details


   F1 REGISTER B -> SIP Server

   REGISTER sip:ss2.biloxi.com SIP/2.0
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7
   Max-Forwards: 70
   From: LittleGuy <sip:UserB@biloxi.com>;tag=a73kszlfl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 1 REGISTER
   Contact: <sip:UserB@client.biloxi.com>


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   Content-Length: 0


   F2 401 Unauthorized SIP Server -> User B

   SIP/2.0 401 Unauthorized
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7
    ;received=192.0.2.201
   From: LittleGuy <sip:UserB@biloxi.com>;tag=a73kszlfl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=1410948204
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 1 REGISTER
   WWW-Authenticate: Digest realm="atlanta.com", qop="auth",
    nonce="ea9c8e88df84f1cec4341ae6cbe5a359",
    opaque="", stale=FALSE, algorithm=MD5
   Content-Length: 0


   F3 REGISTER B -> SIP Server

   REGISTER sip:ss2.biloxi.com SIP/2.0
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7
   Max-Forwards: 70
   From: LittleGuy <sip:UserB@biloxi.com>;tag=ja743ks76zlflH
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 2 REGISTER
   Contact: <sip:UserB@client.biloxi.com>
   Authorization: Digest username="UserB", realm="atlanta.com"
    nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="",
    uri="sip:ss2.biloxi.com", response="dfe56131d1958046689d83306477ecc"
   Content-Length: 0


   F4 200 OK SIP Server -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7
    ;received=192.0.2.201
   From: LittleGuy <sip:UserB@biloxi.com>;tag=ja743ks76zlflH
   To: LittleGuy <sip:UserB@biloxi.com>;tag=37GkEhwl6
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 2 REGISTER
   Contact: <sip:UserB@client.biloxi.com>;expires=3600
   Content-Length: 0






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2.2     Update of Contact List


   User B                        SIP Server
     |                               |
     |          REGISTER F1          |
     |------------------------------>|
     |            200 OK F2          |
     |<------------------------------|
     |                               |


   User B wishes to update the list of addresses where the SIP server
   will redirect or forward INVITE requests.

   User B sends a SIP REGISTER request to the SIP server.  User B's
   request includes an updated contact list.  Since the user already has
   authenticated with the server, the user supplies authentication
   credentials with the request and is not challenged by the server.
   The SIP server validates the user's credentials.  It registers the
   user in its contact database, updates the user's contact list, and
   returns a response (200 OK) to User B's SIP client.  The response
   includes the user's current contact list in Contact headers.

   Message Details


   F1 REGISTER B -> SIP Server

   REGISTER sip:ss2.biloxi.com SIP/2.0
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7
   Max-Forwards: 70
   From: LittleGuy <sip:UserB@biloxi.com>;tag=a73kszlfl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 1 REGISTER
   Contact: mailto:UserB@biloxi.com
   Authorization: Digest username="UserB", realm="atlanta.com",
    qop="auth", nonce="1cec4341ae6cbe5a359ea9c8e88df84f", opaque="",
    uri="sip:ss2.biloxi.com",
   response="71ba27c64bd01de719686aa4590d5824"
   Content-Length: 0


   F2 200 OK SIP Server -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7


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    ;received=192.0.2.201
   From: LittleGuy <sip:UserB@biloxi.com>;tag=a73kszlfl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=34095828jh
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 1 REGISTER
   Contact: <sip:UserB@client.biloxi.com>;expires=3600
   Contact: <mailto:UserB@biloxi.com>;expires=4294967295
   Content-Length: 0











































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2.3     Request for Current Contact List


   User B                        SIP Server
     |                               |
     |          REGISTER F1          |
     |------------------------------>|
     |            200 OK F2          |
     |<------------------------------|
     |                               |

   User B sends a register request to the Proxy Server containing no
   Contact headers, indicating the user wishes to query the server for
   the user's current contact list.  Since the user already has
   authenticated with the server, the user supplies authentication
   credentials with the request and is not challenged by the server. The
   SIP server validates the user's credentials.  The server returns a
   response (200 OK) which includes the user's current registration list
   in Contact headers.


   Message Details

   F1 REGISTER B -> SIP Server

   REGISTER sip:ss2.biloxi.com SIP/2.0
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7
   Max-Forwards: 70
   From: LittleGuy <sip:UserB@biloxi.com>;tag=a73kszlfl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 1 REGISTER
   Authorization: Digest username="UserB", realm="atlanta.com",
    nonce="df84f1cec4341ae6cbe5ap359a9c8e88", opaque="",
    uri="sip:ss2.biloxi.com",
   response="aa7ab4678258377c6f7d4be6087e2f60"
   Content-Length: 0


   F2 200 OK SIP Server -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7
    ;received=192.0.2.201
   From: LittleGuy <sip:UserB@biloxi.com>;tag=a73kszlfl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=jqoiweu75
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 1 REGISTER


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   Contact: <sip:UserB@client.biloxi.com>;expires=3600
   Contact: <mailto:UserB@biloxi.com>;expires=4294967295
   Content-Length: 0
















































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2.4     Cancellation of Registration

   User B                         SIP Server
     |                               |
     |          REGISTER F1          |
     |------------------------------>|
     |            200 OK F2          |
     |<------------------------------|
     |                               |

   User B wishes to cancel their registration with the SIP
   server. User B sends a SIP REGISTER request to the
   SIP server.  The request has an expiration period of 0 and applies to
   all existing contact locations.  Since the user already has
   authenticated with the server, the user supplies authentication
   credentials with the request and is not challenged by the server.
   The SIP server validates the user's credentials.  It clears the
   user's contact list, and returns a response (200 OK) to User B's SIP
   client.

   Message Details


   F1 REGISTER B -> SIP Server

   REGISTER sip:ss2.biloxi.com SIP/2.0
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7
   Max-Forwards: 70
   From: LittleGuy <sip:UserB@biloxi.com>;tag=a73kszlfl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 1 REGISTER
   Expires: 0
   Contact: *
   Authorization: Digest username="UserB", realm="atlanta.com",
    nonce="88df84f1cac4341aea9c8ee6cbe5a359", opaque="",
    uri="sip:ss2.biloxi.com",
   response="ff0437c51696f9a76244f0cf1dbabbea"
   Content-Length: 0


   F2 200 OK SIP Server -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7
    ;received=192.0.2.201
   From: LittleGuy <sip:UserB@biloxi.com>;tag=a73kszlfl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=1418nmdsrf


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   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 1 REGISTER
   Content-Length: 0
















































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2.5     Unsuccessful Registration

   User B                        SIP Server
     |                               |
     |          REGISTER F1          |
     |------------------------------>|
     |      401 Unauthorized F2      |
     |<------------------------------|
     |          REGISTER F3          |
     |------------------------------>|
     |      401 Unauthorized F4      |
     |<------------------------------|
     |                               |



   User B sends a SIP REGISTER request to the SIP Server.  The SIP
   server provides a challenge to User B.  User B enters her/his user ID
   and password.  User B's SIP client encrypts the user information
   according to the challenge issued by the SIP server and sends the
   response to the SIP server.  The SIP server attempts to validate the
   user's credentials, but they are not valid (the user's password does
   not match the password established for the user's account).  The
   server returns a response (401 Unauthorized) to User B's SIP client.



   Message Details


   F1 REGISTER B -> SIP Server

   REGISTER sip:ss2.biloxi.com SIP/2.0
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7
   Max-Forwards: 70
   From: LittleGuy <sip:UserB@biloxi.com>;tag=a73kszlfl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 1 REGISTER
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F2 Unauthorized SIP Server -> User B

   SIP/2.0 401 Unauthorized
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7
    ;received=192.0.2.201


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   From: LittleGuy <sip:UserB@biloxi.com>;tag=a73kszlfl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=1410948204
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 1 REGISTER
   WWW-Authenticate: Digest realm="atlanta.com", qop="auth",
    nonce="f1cec4341ae6ca9c8e88df84be55a359",
    opaque="", stale=FALSE, algorithm=MD5
   Content-Length: 0


   F3 REGISTER B -> SIP Server

   REGISTER sip:ss2.biloxi.com SIP/2.0
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7
   Max-Forwards: 70
   From: LittleGuy <sip:UserB@biloxi.com>;tag=JueHGuidj28dfga
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 2 REGISTER
   Contact: <sip:UserB@client.biloxi.com>
   Authorization: Digest username="UserB", realm="atlanta.com",
    nonce="f1cec4341ae6ca9c8e88df84be55a359", opaque="",
    uri="sip:ss2.biloxi.com",
   response="61f8470ceb87d7ebf508220214ed438b"
   Content-Length: 0


   /*  The response above encodes the incorrect password */

   F4 401 Unauthorized SIP Server -> User B

   SIP/2.0 401 Unauthorized
   Via: SIP/2.0/TLS client.biloxi.com:5061;branch=z9hG4bKnashds7
    ;received=192.0.2.201
   From: LittleGuy <sip:UserB@biloxi.com>;tag=JueHGuidj28dfga
   To: LittleGuy <sip:UserB@biloxi.com>;tag=1410948204
   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.com
   CSeq: 2 REGISTER
   WWW-Authenticate: Digest realm="atlanta.com", qop="auth",
    nonce="84f1c1ae6cbe5ua9c8e88dfa3ecm3459",
    opaque="", stale=FALSE, algorithm=MD5
   Content-Length: 0









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3.    SIP Session Establishment

   This section details session establishment between two SIP User
   Agents (UAs): User A and User B.  User A (LittleGuy
   sip:UserA@atlanta.com) and User B (BigGuy sip:UserB@biloxi.com) are
   assumed to be SIP phones or SIP-enabled devices.  The successful
   calls show the initial signaling, the exchange of media information
   in the form of SDP payloads, the establishment of the media session,
   then finally the termination of the call.

   HTTP Digest authentication is used by Proxy Servers to authenticate
   the caller User A. It is assumed that User B has registered with
   Proxy Server Proxy 2 as per Section 2 to be able to receive the calls
   via the Proxy.

3.1     Successful Session Establishment

   User A                  User B
     |                        |
     |       INVITE F1        |
     |----------------------->|
     |    180 Ringing F2      |
     |<-----------------------|
     |                        |
     |       200 OK F3        |
     |<-----------------------|
     |         ACK F4         |
     |----------------------->|
     |   Both Way RTP Media   |
     |<======================>|
     |                        |
     |         BYE F5         |
     |<-----------------------|
     |       200 OK F6        |
     |----------------------->|
     |                        |

   In this scenario, User A completes a call to User B directly.


   Message Details


   F1 INVITE User A -> User B

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70


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   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F2 180 Ringing User B -> User A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=8321234356
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com;transport=tcp>
   Content-Length: 0


   F3 200 OK User B -> User A

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=8321234356
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 141

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0


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                     SIP Basic Call Flow Examples         October 2002


   a=rtpmap:0 PCMU/8000


   F4 ACK User A -> User B

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bd5
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=8321234356
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   /* RTP streams are established between A and B */

   /* User B Hangs Up with User A. Note that the CSeq is NOT 2, since
      User A and User B maintain their own independent CSeq counts.
      (The INVITE was request 1 generated by User A, and the BYE is
      request 1 generated by User B) */

   F5 BYE User B -> User A

   BYE sip:UserA@client.atlanta.com SIP/2.0
   Via: SIP/2.0/TCP client.biloxi.com:5060;branch=z9hG4bKnashds7
   Max-Forwards: 70
   From: LittleGuy <sip:UserB@biloxi.com>;tag=8321234356
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0


   F6 200 OK User A -> User B

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP client.biloxi.com:5060;branch=z9hG4bKnashds7
    ;received=192.0.2.201
   From: LittleGuy <sip:UserB@biloxi.com>;tag=8321234356
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0







Johnston et al           Expires - April 2002                [Page 17]

                     SIP Basic Call Flow Examples         October 2002



3.2     Session Establishment Through Two Proxies

   User A          Proxy 1          Proxy 2          User B
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|                |                |
     |     407 F2     |                |                |
     |<---------------|                |                |
     |     ACK F3     |                |                |
     |--------------->|                |                |
     |   INVITE F4    |                |                |
     |--------------->|   INVITE F5    |                |
     |     100  F6    |--------------->|   INVITE F7    |
     |<---------------|     100  F8    |--------------->|
     |                |<---------------|                |
     |                |                |     180 F9     |
     |                |    180 F10     |<---------------|
     |     180 F11    |<---------------|                |
     |<---------------|                |     200 F12    |
     |                |    200 F13     |<---------------|
     |     200 F14    |<---------------|                |
     |<---------------|                |                |
     |     ACK F15    |                |                |
     |--------------->|    ACK F16     |                |
     |                |--------------->|     ACK F17    |
     |                |                |--------------->|
     |                Both Way RTP Media                |
     |<================================================>|
     |                |                |     BYE F18    |
     |                |    BYE F19     |<---------------|
     |     BYE F20    |<---------------|                |
     |<---------------|                |                |
     |     200 F21    |                |                |
     |--------------->|     200 F22    |                |
     |                |--------------->|     200 F23    |
     |                |                |--------------->|
     |                |                |                |

   In this scenario, User A completes a call to User B using two proxies
   Proxy 1 and Proxy 2.  The initial INVITE (F1) contains a pre-loaded
   Route header with the address of Proxy 1 (Proxy 1 is configured as a
   default outbound proxy for User A).  The request does not contain the
   Authorization credentials Proxy 1 requires, so a 407 Proxy
   Authorization response is sent containing the challenge information.
   A new INVITE (F4) is then sent containing the correct credentials and
   the call proceeds.  The call terminates when User B disconnects by
   initiating a BYE message.



Johnston et al           Expires - April 2002                [Page 18]

                     SIP Basic Call Flow Examples         October 2002


   Proxy 1 inserts a Record-Route header into the INVITE message to
   ensure that it is present in all subsequent message exchanges.  Proxy
   2 also inserts itself into the Record-Route header.  The ACK (F15)
   and BYE (F18) both have a Route header.


   Message Details


   F1 INVITE A -> Proxy 1

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74b43
   Max-Forwards: 70
   Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* Proxy 1 challenges User A for authentication */

   F2 407 Proxy Authorization Required Proxy 1 -> User A

   SIP/2.0 407 Proxy Authorization Required
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74b43
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=3flal12sf
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 INVITE
   Proxy-Authenticate: Digest realm="atlanta.com", qop="auth",
    nonce="f84f1cec41e6cbe5aea9c8e88d359",
    opaque="", stale=FALSE, algorithm=MD5
   Content-Length: 0




Johnston et al           Expires - April 2002                [Page 19]

                     SIP Basic Call Flow Examples         October 2002


   F3 ACK A -> Proxy 1

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74b43
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=3flal12sf
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   /* User A responds be re-sending the INVITE with authentication
      credentials in it. */

   F4 INVITE A -> Proxy 1

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserA@client.atlanta.com;transport=tcp>
   Proxy-Authorization: Digest username="UserA", realm="atlanta.com",
    nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="",
    uri="sip:UserB@biloxi.com", response="42ce3cef44b22f50c6a6071bc8"
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* Proxy 1 accepts the credentials and forwards the INVITE to Proxy
   2.  Proxy 1 is assumed to have been authenticated by Proxy 2 using
   IPSec.  Client for A prepares to receive data on port 49172 from the
   network. */

   F5 INVITE Proxy 1 -> Proxy 2

   INVITE sip:UserB@biloxi.com SIP/2.0


Johnston et al           Expires - April 2002                [Page 20]

                     SIP Basic Call Flow Examples         October 2002


   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserA@client.atlanta.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F6 100 Trying Proxy 1 -> User A

   SIP/2.0 100 Trying
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 2 INVITE
   Content-Length: 0


   F7 INVITE Proxy 2 -> B

   INVITE sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/TCP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 68
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserA@client.atlanta.com;transport=tcp>


Johnston et al           Expires - April 2002                [Page 21]

                     SIP Basic Call Flow Examples         October 2002


   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F8 100 Trying Proxy 2 -> Proxy 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 2 INVITE
   Content-Length: 0


   F9 180 Ringing B -> Proxy 2

   SIP/2.0 180 Ringing
   Via: SIP/2.0/TCP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 3848276298220188511@atlanta.com
   Contact: <sip:UserB@client.biloxi.com;transport=tcp>
   CSeq: 2 INVITE
   Content-Length: 0


   F10 180 Ringing Proxy 2 -> Proxy 1

   SIP/2.0 180 Ringing
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111


Johnston et al           Expires - April 2002                [Page 22]

                     SIP Basic Call Flow Examples         October 2002


   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 3848276298220188511@atlanta.com
   Contact: <sip:UserB@client.biloxi.com;transport=tcp>
   CSeq: 2 INVITE
   Content-Length: 0


   F11 180 Ringing Proxy 1 -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 3848276298220188511@atlanta.com
   Contact: <sip:UserB@client.biloxi.com;transport=tcp>
   CSeq: 2 INVITE
   Content-Length: 0


   F12 200 OK B -> Proxy 2

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserB@client.biloxi.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 141

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0


Johnston et al           Expires - April 2002                [Page 23]

                     SIP Basic Call Flow Examples         October 2002


   a=rtpmap:0 PCMU/8000


   F13 200 OK Proxy 2 -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserB@client.biloxi.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 141

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F14 200 OK Proxy 1 -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserB@client.biloxi.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 141

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


Johnston et al           Expires - April 2002                [Page 24]

                     SIP Basic Call Flow Examples         October 2002




   F15 ACK A -> Proxy 1

   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74b76
   Max-Forwards: 70
   Route: <sip:ss1.atlanta.com;lr>, <sip:ss2.biloxi.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 2 ACK
   Content-Length: 0


   F16 ACK Proxy 1 -> Proxy 2

   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74b76
    ;received=192.0.2.101
   Max-Forwards: 69
   Route: <sip:ss2.biloxi.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 2 ACK
   Content-Length: 0


   F17 ACK Proxy 2 -> B

   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/TCP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74b76
    ;received=192.0.2.101
   Max-Forwards: 68
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 2 ACK
   Content-Length: 0


   /* RTP streams are established between A and B */

   /* User B Hangs Up with User A. */


Johnston et al           Expires - April 2002                [Page 25]

                     SIP Basic Call Flow Examples         October 2002



   /* Again, note that the CSeq is NOT 3.  User A and User B maintain
      their own separate CSeq counts */

   F18 BYE User B -> Proxy 2

   BYE sip:UserA@client.atlanta.com SIP/2.0
   Via: SIP/2.0/TCP client.biloxi.com:5060;branch=z9hG4bKnashds7
   Max-Forwards: 70
   Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0


   F19 BYE Proxy 2 -> Proxy 1

   BYE sip:UserA@client.atlanta.com SIP/2.0
   Via: SIP/2.0/TCP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Via: SIP/2.0/TCP client.biloxi.com:5060;branch=z9hG4bKnashds7
    ;received=192.0.2.201
   Max-Forwards: 69
   Route: <sip:ss1.atlanta.com;lr>
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0


   F20 BYE Proxy 1 -> User A

   BYE sip:UserA@client.atlanta.com SIP/2.0
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/TCP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   Via: SIP/2.0/TCP client.biloxi.com:5060;branch=z9hG4bKnashds7
    ;received=192.0.2.201
   Max-Forwards: 68
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0


   F21 200 OK User A -> Proxy 1


Johnston et al           Expires - April 2002                [Page 26]

                     SIP Basic Call Flow Examples         October 2002



   SIP/2.0 200 OK
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   Via: SIP/2.0/TCP client.biloxi.com:5060;branch=z9hG4bKnashds7
    ;received=192.0.2.201
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0


   F22 200 OK Proxy 1 -> Proxy 2

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   Via: SIP/2.0/TCP client.biloxi.com:5060;branch=z9hG4bKnashds7
    ;received=192.0.2.101
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0


   F23 200 OK Proxy 2 -> User B

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP client.biloxi.com:5060;branch=z9hG4bKnashds7
    ;received=192.0.2.201
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0












Johnston et al           Expires - April 2002                [Page 27]

                     SIP Basic Call Flow Examples         October 2002



3.3     Session with Multiple Proxy Authentication

     User A       Proxy 1     Proxy 2       User B
       |            |           |             |
       |  INVITE F1 |           |             |
       |----------->|           |             |
       |  407 Proxy Authorization Required F2 |
       |<-----------|           |             |
       |   ACK F3   |           |             |
       |----------->|           |             |
       |  INVITE F4 |           |             |
       |----------->|           |             |
       |   100 F5   |           |             |
       |<-----------| INVITE F6 |             |
       |            |---------->|             |
       |            |  407 Proxy Authorization Required F7
       |            |<----------|             |
       |            |   ACK F8  |             |
       |            |---------->|             |
       |  407 Proxy Authorization Required F9 |
       |<-----------|           |             |
       |   ACK F10  |           |             |
       |----------->|           |             |
       |  INVITE F11|           |             |
       |----------->|           |             |
       |   100 F12  |           |             |
       |<-----------| INVITE F13|             |
       |            |---------->|             |
       |            |  100 F14  |             |
       |            |<----------|  INVITE F15 |
       |            |           |------------>|
       |            |           | 200 OK F16  |
       |            | 200 OK F17|<------------|
       | 200 OK F18 |<----------|             |
       |<-----------|           |             |
       |   ACK F19  |           |             |
       |----------->|  ACK F20  |             |
       |            |---------->|   ACK F21   |
       |            |           |------------>|
       |           RTP Media Path             |
       |<====================================>|

   In this scenario, User A completes a call to User B using two proxies
   Proxy 1 and Proxy 2.  User A has valid credentials in both domains.
   Since the initial INVITE (F1) does not contain the
   Authorization credentials Proxy 1 requires, so a 407 Proxy
   Authorization response is sent containing the challenge information.
   A new INVITE (F4) is then sent containing the correct credentials and


Johnston et al           Expires - April 2002                [Page 28]

                     SIP Basic Call Flow Examples         October 2002


   the call proceeds after Proxy 2 challenges and receives valid
   credentials.  The call terminates when User B disconnects by
   initiating a BYE message.

   Proxy 1 inserts a Record-Route header into the INVITE message to
   ensure that it is present in all subsequent message exchanges.  Proxy
   2 also inserts itself into the Record-Route header.



   Message Details


   F1 INVITE A -> Proxy 1

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b03
   Max-Forwards: 70
   Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* Proxy 1 challenges User A for authentication */

   F2 407 Proxy Authorization Required Proxy 1 -> User A

   SIP/2.0 407 Proxy Authorization Required
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b03
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=876321
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Proxy-Authenticate: Digest realm="atlanta.com", qop="auth",
    nonce="wf84f1cczx41ae6cbeaea9ce88d359",


Johnston et al           Expires - April 2002                [Page 29]

                     SIP Basic Call Flow Examples         October 2002


    opaque="", stale=FALSE, algorithm=MD5
   Content-Length: 0


   F3 ACK A -> Proxy 1

   ACK sip:UserB@biloxi.com SIP/2.0
   Max-Forwards: 70
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b03
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=876321
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   /* User A responds be re-sending the INVITE with authentication
      credentials in it.  The same Call-ID is used, so the CSeq is
      increased. */

   F4 INVITE A -> Proxy 1

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b21
   Max-Forwards: 70
   Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Proxy-Authorization: Digest username="UserA", realm="atlanta.com",
    nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="",
    uri="sip:UserB@biloxi.com", response="42ce3cef44b22f50c6a6071bc8"
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* Proxy 1 accepts the credentials and forwards the INVITE to Proxy
   2.  Proxy 1 is assumed to have been authenticated by Proxy 2 using
   IPSec.  Client for A prepares to receive data on port 49172 from the


Johnston et al           Expires - April 2002                [Page 30]

                     SIP Basic Call Flow Examples         October 2002


   network. */

   F5 100 Trying Proxy 1 -> User A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b21
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 INVITE
   Content-Length: 0


   F6 INVITE Proxy 1 -> Proxy 2

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK230f2.1
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b21
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* Proxy 2 challenges User A for authentication */

   F7 407 Proxy Authorization Required Proxy 2 -> Proxy 1

   SIP/2.0 407 Proxy Authorization Required
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK230f2.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b21
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl


Johnston et al           Expires - April 2002                [Page 31]

                     SIP Basic Call Flow Examples         October 2002


   To: LittleGuy <sip:UserB@biloxi.com>;tag=838209
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 INVITE
   Proxy-Authenticate: Digest realm="biloxi.com", qop="auth",
    nonce="c1e22c41ae6cbe5ae983a9c8e88d359",
    opaque="", stale=FALSE, algorithm=MD5
   Content-Length: 0


   F8 ACK Proxy 1 -> Proxy 2

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b21
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=838209
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 ACK
   Content-Length: 0


   /* Proxy 1 forwards the challenge to User A for authentication from
   Proxy 2 */

   F9 407 Proxy Authorization Required Proxy 1 -> User A

   SIP/2.0 407 Proxy Authorization Required
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b21
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=838209
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 INVITE
   Proxy-Authenticate: Digest realm="biloxi.com", qop="auth",
    nonce="c1e22c41ae6cbe5ae983a9c8e88d359",
    opaque="", stale=FALSE, algorithm=MD5
   Content-Length: 0


   F10 ACK User A -> Proxy 1

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b21
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=838209
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 ACK
   Content-Length: 0


Johnston et al           Expires - April 2002                [Page 32]

                     SIP Basic Call Flow Examples         October 2002




   /* User A responds be re-sending the INVITE with authentication
   credentials for Proxy 1 AND Proxy 2.  */

   F11 INVITE A -> Proxy 1

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 3 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Proxy-Authorization: Digest username="UserA", realm="atlanta.com",
    nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="",
    uri="sip:UserB@biloxi.com", response="42ce3cef44b22f50c6a6071bc8"
   Proxy-Authorization: Digest username="UserA", realm="biloxi.com",
    nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="",
    uri="sip:UserB@biloxi.com", response="f44ab22f150c6a56071bce8"
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* Proxy 1 finds its credentials and authorizes User A, forwarding
   the INVITE to Proxy.  */


   F12 100 Trying Proxy 1 -> User A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 3 INVITE
   Content-Length: 0




Johnston et al           Expires - April 2002                [Page 33]

                     SIP Basic Call Flow Examples         October 2002


   F13 INVITE Proxy 1 -> Proxy 2

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK230f2.1
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 3 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Proxy-Authorization: Digest username="UserA", realm="biloxi.com",
    nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="",
    uri="sip:UserB@biloxi.com", response="f44ab22f150c6a56071bce8"
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* Proxy 2 finds its credentials and authorizes User A, forwarding
   the INVITE to User B.  */

   F14 100 Trying Proxy 2 -> Proxy 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK230f2.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 3 INVITE
   Content-Length: 0


   F15 INVITE Proxy 2 -> User B

   INVITE sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK31972.1


Johnston et al           Expires - April 2002                [Page 34]

                     SIP Basic Call Flow Examples         October 2002


   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK230f2.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 68
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 3 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* User B answers the call immediately */

   F16 200 OK User B -> Proxy 2

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK31972.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK230f2.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=9103874
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 3 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Type: application/sdp
   Content-Length: 141

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0


Johnston et al           Expires - April 2002                [Page 35]

                     SIP Basic Call Flow Examples         October 2002


   a=rtpmap:0 PCMU/8000


   F17 200 OK Proxy 2 -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK230f2.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=9103874
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 3 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Type: application/sdp
   Content-Length: 141

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F18 200 OK Proxy 1 -> User A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=9103874
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 3 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Type: application/sdp
   Content-Length: 141

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


Johnston et al           Expires - April 2002                [Page 36]

                     SIP Basic Call Flow Examples         October 2002




   F19 ACK User A -> Proxy 1

   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b44
   Max-Forwards: 70
   Route: <sip:ss1.atlanta.com;lr>, <sip:ss2.biloxi.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=9103874
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 3 ACK
   Content-Length: 0


   F20 ACK Proxy 1 -> Proxy 2

   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK230f2.1
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b44
    ;received=192.0.2.101
   Max-Forwards: 69
   Route: <sip:ss2.biloxi.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=9103874
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 3 ACK
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F21 ACK Proxy 2 -> User A

   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK31972.1
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK230f2.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b44
    ;received=192.0.2.101
   Max-Forwards: 68
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=9103874
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 3 ACK
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0





Johnston et al           Expires - April 2002                [Page 37]

                     SIP Basic Call Flow Examples         October 2002


3.4     Successful Session with Proxy Failure

   User A          Proxy 1          Proxy 2          User B
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|                |                |
     |   INVITE F2    |                |                |
     |--------------->|                |                |
     |   INVITE F3    |                |                |
     |--------------->|                |                |
     |   INVITE F4    |                |                |
     |--------------->|                |                |
     |   INVITE F5    |                |                |
     |--------------->|                |                |
     |   INVITE F6    |                |                |
     |--------------->|                |                |
     |   INVITE F7    |                |                |
     |--------------->|                |                |
     |     INVITE F8                   |                |
     |-------------------------------->|                |
     |            407 F9               |                |
     |<--------------------------------|                |
     |             ACK F10             |                |
     |-------------------------------->|                |
     |           INVITE F11            |                |
     |-------------------------------->|   INVITE F12   |
     |             100  F13            |--------------->|
     |<--------------------------------|                |
     |                                 |     180 F14    |
     |             180 F15             |<---------------|
     |<--------------------------------|                |
     |                                 |     200 F16    |
     |             200 F17             |<---------------|
     |<--------------------------------|                |
     |             ACK F18             |                |
     |-------------------------------->|     ACK F19    |
     |                                 |--------------->|
     |                Both Way RTP Media                |
     |<================================================>|
     |                                 |     BYE F20    |
     |             BYE F21             |<---------------|
     |<--------------------------------|                |
     |             200 F22             |                |
     |-------------------------------->|     200 F23    |
     |                                 |--------------->|
     |                                 |                |





Johnston et al           Expires - April 2002                [Page 38]

                     SIP Basic Call Flow Examples         October 2002


   In this scenario, User A completes a call to User B via a Proxy
   Server. User A is configured for a primary SIP Proxy Server Proxy 1
   and a secondary SIP Proxy Server Proxy 2 (Or is able to use DNS SRV
   records to locate Proxy 1 and Proxy 2).  User A has valid credentials
   for both domains.  Proxy 1 is out of service and does not respond to
   INVITEs (it is reachable, but unresponsive).  User A then completes
   the call to User B using Proxy 2.


   Message Details


   F1 INVITE A -> Proxy 1

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK465b6d
   Max-Forwards: 70
   Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F2 INVITE A -> Proxy 1

   Same as Message F1


   F3 INVITE A -> Proxy 1

   Same as Message F1


   F4 INVITE A -> Proxy 1

   Same as Message F1



Johnston et al           Expires - April 2002                [Page 39]

                     SIP Basic Call Flow Examples         October 2002



   F5 INVITE A -> Proxy 1

   Same as Message F1


   F6 INVITE A -> Proxy 1

   Same as Message F1


   F7 INVITE A -> Proxy 1

   Same as Message F1


   /* User A gives up on the unresponsive proxy */


   F8 INVITE A -> Proxy 2

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b8a
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* Proxy 2 challenges User A for authentication */

   F9 407 Proxy Authorization Required Proxy 2 -> User A

   SIP/2.0 407 Proxy Authorization Required
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b8a
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl


Johnston et al           Expires - April 2002                [Page 40]

                     SIP Basic Call Flow Examples         October 2002


   To: LittleGuy <sip:UserB@biloxi.com>;tag=2421452
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 1 INVITE
   Proxy-Authenticate: Digest realm="biloxi.com", qop="auth",
    nonce="1ae6cbe5ea9c8e8df84fqnlec434a359",
    opaque="", stale=FALSE, algorithm=MD5
   Content-Length: 0


   F10 ACK A -> Proxy 2

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b8a
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=2421452
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   /* User A responds be re-sending the INVITE with authentication
   credentials in it.  */

   F11 INVITE A -> Proxy 2

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Proxy-Authorization: Digest username="UserA", realm="biloxi.com",
    nonce="1ae6cbe5ea9c8e8df84fqnlec434a359", opaque="",
    uri="sip:UserB@biloxi.com",
    response="8a880c919d1a52f20a1593e228adf599"
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000



Johnston et al           Expires - April 2002                [Page 41]

                     SIP Basic Call Flow Examples         October 2002



   /* Proxy 2 accepts the credentials and forwards the INVITE to User B.
   Client for A prepares to receive data on port 49172 from the network.
   */

   F12 INVITE Proxy 2 -> B

   INVITE sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss2.biloxi.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F13 100 Trying Proxy 2 -> User A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 2 INVITE
   Content-Length: 0


   F14 180 Ringing B -> Proxy 2

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101


Johnston et al           Expires - April 2002                [Page 42]

                     SIP Basic Call Flow Examples         October 2002


   Record-Route: <sip:ss2.biloxi.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F15 180 Ringing Proxy 2 -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F16 200 OK B -> Proxy 2

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Type: application/sdp
   Content-Length: 141

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F17 200 OK Proxy 2 -> A


Johnston et al           Expires - April 2002                [Page 43]

                     SIP Basic Call Flow Examples         October 2002



   SIP/2.0 200 OK
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Type: application/sdp
   Content-Length: 141

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F18 ACK A -> Proxy 2

   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b8g
   Max-Forwards: 70
   Route: <sip:ss2.biloxi.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 2 ACK
   Content-Length: 0


   F19 ACK Proxy 2 -> B

   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b8g
    ;received=192.0.2.101
   Max-Forwards: 69
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 2 ACK
   Content-Length: 0




Johnston et al           Expires - April 2002                [Page 44]

                     SIP Basic Call Flow Examples         October 2002


   /* RTP streams are established between A and B */

   /* User B Hangs Up with User A. */

   F20 BYE User B -> Proxy 2

   BYE sip:UserA@client.atlanta.com SIP/2.0
   Via: SIP/2.0/UDP client.biloxi.com:5060;branch=z9hG4bKnashds7
   Max-Forwards: 70
   Route: <sip:ss2.biloxi.com;lr>
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0


   F21 BYE Proxy 2 -> User A

   BYE sip:UserA@client.atlanta.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Via: SIP/2.0/UDP client.biloxi.com:5060;branch=z9hG4bKnashds7
    ;received=192.0.2.201
   Max-Forwards: 69
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0


   F22 200 OK User A -> Proxy 2

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP client.biloxi.com:5060;branch=z9hG4bKnashds7
    ;received=192.0.2.201
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0


   F23 200 OK Proxy 2 -> User B

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP client.biloxi.com:5060;branch=z9hG4bKnashds7


Johnston et al           Expires - April 2002                [Page 45]

                     SIP Basic Call Flow Examples         October 2002


    ;received=192.0.2.201
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0













































Johnston et al           Expires - April 2002                [Page 46]

                     SIP Basic Call Flow Examples         October 2002




3.5     Session Through a SIP ALG

   User A            ALG           Proxy 2          User B
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|   INVITE F2    |                |
     |     100 F3     |--------------->|   INVITE F4    |
     |<---------------|     100 F5     |--------------->|
     |                |<---------------|      180 F6    |
     |                |     180 F7     |<---------------|
     |     180 F8     |<---------------|                |
     |<---------------|                |      200 F9    |
     |                |    200 F10     |<---------------|
     |     200 F11    |<---------------|                |
     |<---------------|                                 |
     |     ACK F12    |                                 |
     |--------------->|             ACK F13             |
     |                |-------------------------------->|
     |    RTP Media   |        Both Way RTP Media       |
     |<==============>|<===============================>|
     |     BYE F14    |                                 |
     |--------------->|             BYE F15             |
     |                |-------------------------------->|
     |                |             200 F16             |
     |     200 F17    |<--------------------------------|
     |<---------------|                                 |
     |                |                                 |

   User A completes a call to User B through a ALG (Application Layer
   Gateway) and a SIP Proxy.  The routing through the ALG is
   accomplished using a pre-loaded Route header in the INVITE F1. Note
   that the media stream setup is not end-to-end - the ALG terminates
   both media streams and bridges them.  This is done by the ALG
   modifying the SDP in the INVITE (F1) and 200 OK (F10) messages, and
   possibly any 18x or ACK messages containing SDP.

   In addition to firewall traversal, this Back-to-Back User Agent
   (B2BUA) could be used as part of an anonymizer
   service (in which all identifying information on User A would be
   removed), or to perform codec media conversion, such as mu-law to A-
   law conversion of PCM on an international call.

   Also note that Proxy 2 does not Record-Route in this call flow.

   Message Details




Johnston et al           Expires - April 2002                [Page 47]

                     SIP Basic Call Flow Examples         October 2002


   F1 INVITE A -> SIP ALG

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Route: <sip:alg1.atlanta.com;lr>
   Proxy-Authorization: Digest username="UserA", realm="biloxi.com",
    nonce="85b4f1cen4341ae6cbe5a3a9c8e88df9", opaque="",
    uri="sip:UserB@biloxi.com",
    response="b3f392f9218a328b9294076d708e6815"
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* Client for A prepares to receive data on port 49172 from the
   network. */

   F2 INVITE SIP ALG -> Proxy 2

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP alg1.atlanta.com:5060;branch=z9hG4bK739578.1
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:alg1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Proxy-Authorization: Digest username="UserA", realm="biloxi.com",
    nonce="85b4f1cen4341ae6cbe5a3a9c8e88df9", opaque="",
    uri="sip:UserB@biloxi.com",
    response="b3f392f9218a328b9294076d708e6815"
   Content-Type: application/sdp
   Content-Length: 142


Johnston et al           Expires - April 2002                [Page 48]

                     SIP Basic Call Flow Examples         October 2002



   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.128
   t=0 0
   m=audio 2000 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 100 Trying SIP ALG -> A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   /* SIP ALG prepares to proxy data from port 192.0.2.128/2000 to
   192.0.2.101/49172.   Proxy 2 uses a Location Service function to
   determine where B is located. Based upon location analysis the call
   is forwarded to User B */

   F4 INVITE Proxy 2 -> B

   INVITE sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP alg1.atlanta.com:5060;branch=z9hG4bK739578.1
    ;received=192.0.2.128
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 68
   Record-Route: <sip:alg1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 142

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.128


Johnston et al           Expires - April 2002                [Page 49]

                     SIP Basic Call Flow Examples         October 2002


   t=0 0
   m=audio 2000 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F5 100 Trying Proxy 2 -> SIP ALG

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP alg1.atlanta.com:5060;branch=z9hG4bK739578.1
    ;received=192.0.2.128
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F6 180 Ringing B -> Proxy 2

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP alg1.atlanta.com:5060;branch=z9hG4bK739578.1
    ;received=192.0.2.128
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:alg1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F7 180 Ringing Proxy 2 -> SIP ALG

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP alg1.atlanta.com:5060;branch=z9hG4bK739578.1
    ;received=192.0.2.128
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:alg1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE


Johnston et al           Expires - April 2002                [Page 50]

                     SIP Basic Call Flow Examples         October 2002


   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F8 180 Ringing SIP ALG -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:alg1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F9 200 OK B -> Proxy 2

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP alg1.atlanta.com:5060;branch=z9hG4bK739578.1
    ;received=192.0.2.128
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:alg1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Type: application/sdp
   Content-Length: 141

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F10 200 OK Proxy 2 -> SIP ALG

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP alg1.atlanta.com:5060;branch=z9hG4bK739578.1


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                     SIP Basic Call Flow Examples         October 2002


    ;received=192.0.2.128
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:alg1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Type: application/sdp
   Content-Length: 141

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F11 200 OK SIP ALG -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:alg1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Type: application/sdp
   Content-Length: 141

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.128
   t=0 0
   m=audio 1734 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* The ALG prepares to proxy packets from 192.0.2.128/
      1734 to 192.0.2.201/3456 */

   F12 ACK A -> SIP ALG



Johnston et al           Expires - April 2002                [Page 52]

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   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bhh
   Max-Forwards: 70
   Route: <sip:alg1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   F13 ACK SIP ALG -> B

   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP alg1.atlanta.com:5060;branch=z9hG4bK739578.1
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bhh
    ;received=192.0.2.101
   Max-Forwards: 69
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   /* RTP streams are established between A and the ALG and
   between the ALG and B*/

   /* User A Hangs Up with User B. */

   F14 BYE A -> SIP ALG

   BYE sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74be5
   Max-Forwards: 70
   Route: <sip:alg1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 BYE
   Content-Length: 0


   F15 BYE SIP ALG -> B

   BYE sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP alg1.atlanta.com:5060;branch=z9hG4bK739578.1
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74be5
    ;received=192.0.2.101


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   Max-Forwards: 69
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 BYE
   Content-Length: 0



   F16 200 OK B -> SIP ALG

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP alg1.atlanta.com:5060;branch=z9hG4bK739578.1
    ;received=192.0.2.128
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74be5
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 BYE
   Content-Length: 0


   F17 200 OK SIP ALG -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74be5
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 BYE
   Content-Length: 0


















Johnston et al           Expires - April 2002                [Page 54]

                     SIP Basic Call Flow Examples         October 2002



3.6     Session via Redirect and Proxy Servers with SDP in ACK

   User A       Redirect Server     Proxy 3           User B
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|                |                |
     |     302 F2     |                |                |
     |<---------------|                |                |
     |     ACK F3     |                |                |
     |--------------->|                |                |
     |     INVITE F4                   |                |
     |-------------------------------->|    INVITE F5   |
     |             100  F6             |--------------->|
     |<--------------------------------|      180 F7    |
     |             180 F8              |<---------------|
     |<--------------------------------|                |
     |                                 |     200 F9     |
     |             200 F10             |<---------------|
     |<--------------------------------|                |
     |             ACK F11             |                |
     |-------------------------------->|     ACK F12    |
     |                                 |--------------->|
     |                Both Way RTP Media                |
     |<================================================>|
     |                                 |     BYE F13    |
     |             BYE F14             |<---------------|
     |<--------------------------------|                |
     |             200 F15             |                |
     |-------------------------------->|     200 F16    |
     |                                 |--------------->|
     |                                 |                |

   In this scenario, User A places a call to User B using first a
   Redirect server then a Proxy Server.  The INVITE message is first
   sent to the Redirect Server.  The Server returns a 302 Moved
   Temporarily response (F2) containing a Contact header with User B's
   current SIP address.  User A then generates a new INVITE and sends to
   User B via the Proxy Server and the call proceeds normally.  In this
   example, no SDP is present in the INVITE, so the SDP is carried in
   the ACK message.

   The call is terminated when User B sends a BYE message.


   Message Details


   F1 INVITE A -> Redirect Server


Johnston et al           Expires - April 2002                [Page 55]

                     SIP Basic Call Flow Examples         October 2002



   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bKbf9f44
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Length: 0


   F2 302 Moved Temporarily Redirect Proxy -> A

   SIP/2.0 302 Moved Temporarily
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bKbf9f44
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=53fHlqlQ2
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@chicago.com;transport=tcp>
   Content-Length: 0


   F3 ACK A -> Redirect Server

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bKbf9f44
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=53fHlqlQ2
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   F4 INVITE A -> Proxy 3

   INVITE sip:UserB@chicago.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserA@client.atlanta.com;transport=tcp>
   Content-Length: 0



Johnston et al           Expires - April 2002                [Page 56]

                     SIP Basic Call Flow Examples         October 2002



   F5 INVITE Proxy 3 -> B

   INVITE sip:UserB@client.chicago.com SIP/2.0
   Via: SIP/2.0/TCP ss3.chicago.com:5060;branch=z9hG4bK721e418c4.1
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss3.chicago.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserA@client.atlanta.com;transport=tcp>
   Content-Length: 0


   F6 100 Trying Proxy 3 -> A

   SIP/2.0 100 Trying
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 INVITE
   Content-Length: 0


   F7 180 Ringing B -> Proxy 3

   SIP/2.0 180 Ringing
   Via: SIP/2.0/TCP ss3.chicago.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.233
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss3.chicago.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserB@client.chicago.com;transport=tcp>
   Content-Length: 0


   F8 180 Ringing Proxy 3 -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9


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    ;received=192.0.2.101
   Record-Route: <sip:ss3.chicago.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserB@client.chicago.com;transport=tcp>
   Content-Length: 0


   F9 200 OK B -> Proxy 3

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP ss3.chicago.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.233
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss3.chicago.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserB@client.chicago.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 142

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.chicago.com
   s=-
   c=IN IP4 192.0.2.100
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F10 200 OK Proxy -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss3.chicago.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 INVITE
   Contact: <sip:UserB@client.chicago.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 142



Johnston et al           Expires - April 2002                [Page 58]

                     SIP Basic Call Flow Examples         October 2002


   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.chicago.com
   s=-
   c=IN IP4 192.0.2.100
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* ACK contains SDP of A since none present in INVITE */

   F11 ACK A -> Proxy 3

   ACK sip:UserB@client.chicago.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bq9
   Max-Forwards: 70
   Route: <sip:ss3.chicago.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 ACK
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F12 ACK Proxy 3 -> B

   ACK sip:UserB@client.chicago.com SIP/2.0
   Via: SIP/2.0/TCP ss3.chicago.com:5060;branch=z9hG4bK721e418c4.1
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bq9
    ;received=192.0.2.101
   Max-Forwards: 69
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 ACK
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com


Johnston et al           Expires - April 2002                [Page 59]

                     SIP Basic Call Flow Examples         October 2002


   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000

   /* RTP streams are established between A and B*/

   /* User B Hangs Up with User A. */

   F13 BYE B -> Proxy 3

   BYE sip:UserA@client.atlanta.com SIP/2.0
   Via: SIP/2.0/TCP client.chicago.com:5060;branch=z9hG4bKfgaw2
   Max-Forwards: 70
   Route: <sip:ss3.chicago.com;lr>
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0


   F14 BYE Proxy 3 -> A

   BYE sip:UserA@client.atlanta.com SIP/2.0
   Via: SIP/2.0/TCP ss3.chicago.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.100
   Via: SIP/2.0/TCP client.chicago.com:5060;branch=z9hG4bKfgaw2
   Max-Forwards: 69
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0


   F15 200 OK A -> Proxy 3

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP ss3.chicago.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.233
   Via: SIP/2.0/TCP client.chicago.com:5060;branch=z9hG4bKfgaw2
    ;received=192.0.2.100
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0


Johnston et al           Expires - April 2002                [Page 60]

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   F16 200 OK Proxy 3 -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/TCP client.chicago.com:5060;branch=z9hG4bKfgaw2
    ;received=192.0.2.100
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 BYE
   Content-Length: 0







































Johnston et al           Expires - April 2002                [Page 61]

                     SIP Basic Call Flow Examples         October 2002



3.7      Session with re-INVITE (IP Address Change)


        User A               Proxy 2              User B
           |   F1 INVITE        |                    |
           |------------------->|      F2 INVITE     |
           |   F3 100 Trying    |------------------->|
           |<-------------------|   F4 180 Ringing   |
           |   F5 180 Ringing   |<-------------------|
           |<-------------------|                    |
           |                    |    F6 200 OK       |
           |    F7 200 OK       |<-------------------|
           |<-------------------|                    |
           |                 F8  ACK                 |
           |---------------------------------------->|
           |      Both Way RTP Media Established     |
           |<=======================================>|
           |                                         |
           |            B changes IP address         |
           |                                         |
           |                 F9 INVITE               |
           |<----------------------------------------|
           |                F10 200 OK               |
           |---------------------------------------->|
           |                 F11  ACK                |
           |<----------------------------------------|
           |         New RTP Media Stream            |
           |<=======================================>|
           |                 F12 BYE                 |
           |---------------------------------------->|
           |               F25 200 OK                |
           |<----------------------------------------|
           |                                         |


   This example shows a session in which the media is changes midway
   through the session.  When User BÆs IP address changes during the
   session, User B sends a re-INVITE containing a new Contact and SDP
   (version number incremented) information to A.  In this flow, the
   proxy does not Record-Route so is not in the SIP messaging path after
   the initial exchange.


   Message Details

   F1 INVITE A -> Proxy 2

   INVITE sip:UserB@biloxi.com SIP/2.0


Johnston et al           Expires - April 2002                [Page 62]

                     SIP Basic Call Flow Examples         October 2002


   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F2 INVITE Proxy 2 -> B

   INVITE sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 100 Trying Proxy 2 -> A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl


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   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F4 180 Ringing B -> Proxy 2

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F5 180 Ringing Proxy 2 -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F6 200 OK B -> Proxy 2

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Type: application/sdp
   Content-Length: 141



Johnston et al           Expires - April 2002                [Page 64]

                     SIP Basic Call Flow Examples         October 2002


   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F7 200 OK Proxy 2 -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Type: application/sdp
   Content-Length: 141

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.biloxi.com
   s=-
   c=IN IP4 192.0.2.201
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F8 ACK A -> B

   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74b7b
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   /* RTP streams are established between A and B */

   /* B changes IP address and re-INVITEs A with new Contact and SDP */

   F9 INVITE B -> A



Johnston et al           Expires - April 2002                [Page 65]

                     SIP Basic Call Flow Examples         October 2002


   INVITE sip:UserA@client.atlanta.com SIP/2.0
   Via: SIP/2.0/UDP client.chicago.com:5060;branch=z9hG4bKlkld5l
   Max-Forwards: 70
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 14 INVITE
   Contact: <sip:UserB@client.chicago.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserB 2890844527 2890844528 IN IP4 client.chicago.com
   s=-
   c=IN IP4 192.0.2.100
   t=0 0
   m=audio 47172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F10 200 OK A ->B

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP client.chicago.com:5060;branch=z9hG4bKlkld5l
    ;received=192.0.2.100
   Max-Forwards: 70
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 14 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 1000 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F11 ACK B -> A

   ACK sip:UserA@client.atlanta.com SIP/2.0
   Via: SIP/2.0/UDP client.chicago.com:5060;branch=z9hG4bKlkldcc
   Max-Forwards: 70
   From: LittleGuy <sip:UserB@biloxi.com>;tag=314159


Johnston et al           Expires - April 2002                [Page 66]

                     SIP Basic Call Flow Examples         October 2002


   To: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 14 ACK
   Content-Length: 0


   /* New RTP stream established between A and B */

   /* A hangs up with B */

   F12 BYE A -> B

   BYE sip:UserB@client.chicago.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bo4
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 BYE
   Content-Length: 0


   F13 200 OK B -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bo4
    ;received=192.0.2.101
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 2 BYE
   Content-Length: 0


















Johnston et al           Expires - April 2002                [Page 67]

                     SIP Basic Call Flow Examples         October 2002


3.8     Unsuccessful No Answer

   User A          Proxy 1          Proxy 2          User B
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|   INVITE F2    |                |
     |     100  F3    |--------------->|   INVITE F4    |
     |<---------------|     100  F5    |--------------->|
     |                |<---------------|                |
     |                |                |      180 F6    |
     |                |     180 F7     |<---------------|
     |     180 F8     |<---------------|                |
     |<---------------|                |                |
     |                |                |                |
     |   CANCEL F9    |                |                |
     |--------------->|                |                |
     |     200 F10    |                |                |
     |<---------------|   CANCEL F11   |                |
     |                |--------------->|                |
     |                |     200 F12    |                |
     |                |<---------------|                |
     |                |                |   CANCEL F13   |
     |                |                |--------------->|
     |                |                |     200 F14    |
     |                |                |<---------------|
     |                |                |     487 F15    |
     |                |                |<---------------|
     |                |                |     ACK F16    |
     |                |     487 F17    |--------------->|
     |                |<---------------|                |
     |                |     ACK F18    |                |
     |     487 F19    |--------------->|                |
     |<---------------|                |                |
     |     ACK F20    |                |                |
     |--------------->|                |                |
     |                |                |                |

   In this scenario, User A gives up on the call before User B answers
   (sends a 200 OK response).  User A sends a CANCEL (F9) since no final
   response had been received from User B.  If a 200 OK to the INVITE
   had crossed with the CANCEL, User A would have sent an ACK then a BYE
   to User B in order to properly terminate the call.

   Note that the CANCEL message is acknowledged with a 200 OK on a hop
   by hop basis, rather than end to end.






Johnston et al           Expires - April 2002                [Page 68]

                     SIP Basic Call Flow Examples         October 2002



   Message Details


   F1 INVITE A -> Proxy 1

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Proxy-Authorization: Digest username="UserA", realm="atlanta.com",
    nonce="ze7k1ee88df84f1cec431ae6cbe5a359", opaque="",
    uri="sip:UserB@biloxi.com",
    response="b00b416324679d7e243f55708d44be7b"
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /*Client for A prepares to receive data on port 49172 from the
   network.*/

   F2 INVITE Proxy 1 -> Proxy 2

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143


Johnston et al           Expires - April 2002                [Page 69]

                     SIP Basic Call Flow Examples         October 2002



   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 100 Trying Proxy 1 -> A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F4 INVITE Proxy 2 -> B

   INVITE sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss2.client.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   Max-Forwards: 68
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000




Johnston et al           Expires - April 2002                [Page 70]

                     SIP Basic Call Flow Examples         October 2002


   F5 100 Trying Proxy 2 -> Proxy 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F6 180 Ringing B -> Proxy 2

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss2.client.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F7 180 Ringing Proxy 2 -> Proxy 1

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F8 180 Ringing Proxy 1 -> A


Johnston et al           Expires - April 2002                [Page 71]

                     SIP Basic Call Flow Examples         October 2002



   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F9 CANCEL A -> Proxy 1

   CANCEL sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F10 200 OK Proxy 1 -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F11 CANCEL Proxy 1 -> Proxy 2

   CANCEL sip:UserA@atlanta.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 CANCEL
   Content-Length: 0




Johnston et al           Expires - April 2002                [Page 72]

                     SIP Basic Call Flow Examples         October 2002


   F12 200 OK Proxy 2 -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F13 CANCEL Proxy 2 -> B

   CANCEL sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F14 200 OK B -> Proxy 2

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F15 487 Request Terminated B -> Proxy 2

   SIP/2.0 487 Request Terminated
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE


Johnston et al           Expires - April 2002                [Page 73]

                     SIP Basic Call Flow Examples         October 2002


   Content-Length: 0


   F16 ACK Proxy 2 -> B

   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   F17 487 Request Terminated Proxy 2 -> Proxy 1

   SIP/2.0 487 Request Terminated
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F18 ACK Proxy 1 -> Proxy 2

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   F19 487 Request Terminated Proxy 1 -> A

   SIP/2.0 487 Request Terminated
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com


Johnston et al           Expires - April 2002                [Page 74]

                     SIP Basic Call Flow Examples         October 2002


   CSeq: 1 INVITE


   F20 ACK A -> Proxy 1

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0






































Johnston et al           Expires - April 2002                [Page 75]

                     SIP Basic Call Flow Examples         October 2002


3.9     Unsuccessful Busy

   User A          Proxy 1          Proxy 2          User B
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|   INVITE F2    |                |
     |     100  F3    |--------------->|   INVITE F4    |
     |<---------------|     100  F5    |--------------->|
     |                |<---------------|                |
     |                |                |      486 F6    |
     |                |                |<---------------|
     |                |                |     ACK F7     |
     |                |      486 F8    |--------------->|
     |                |<---------------|                |
     |                |      ACK F9    |                |
     |     486 F10    |--------------->|                |
     |<---------------|                |                |
     |     ACK F11    |                |                |
     |--------------->|                |                |
     |                |                |                |


   In this scenario, User B is busy and sends a 486 Busy Here response
   to User A's INVITE.  Note that the non-2xx response is acknowledged
   on a hop-by-hop basis instead of end-to-end.  Also note that many SIP
   UAs will not return a 486 response, as they have multiple line and
   other features.


   Message Details


   F1 INVITE User A -> Proxy 1

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com;transport=tcp>
   Proxy-Authorization: Digest username="UserA", realm="atlanta.com",
    nonce="dc3a5ab2530aa93112cf5904ba7d88fa", opaque="",
    uri="sip:UserB@biloxi.com",
    response="702138b27d869ac8741e10ec643d55be"
   Content-Type: application/sdp
   Content-Length: 143


Johnston et al           Expires - April 2002                [Page 76]

                     SIP Basic Call Flow Examples         October 2002



   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /*Client for A prepares to receive data on port 49172 from the
   network.*/

   F2 INVITE Proxy 1 -> Proxy 2

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 100 Trying Proxy 1 -> User A

   SIP/2.0 100 Trying
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0



Johnston et al           Expires - April 2002                [Page 77]

                     SIP Basic Call Flow Examples         October 2002



   F4 INVITE Proxy 2 -> User B

   INVITE sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/TCP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 68
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F5 100 Trying Proxy 2 -> Proxy 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F6 486 Busy Here User B -> Proxy 2

   SIP/2.0  486 Busy Here
   Via: SIP/2.0/TCP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111


Johnston et al           Expires - April 2002                [Page 78]

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   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F7 ACK Proxy 2 -> User B

   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/TCP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   F8 486 Busy Here Proxy 2 -> Proxy 1

   SIP/2.0  486 Busy Here
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F9 ACK Proxy 1 -> Proxy 2

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/TCP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   F10 486 Busy Here Proxy 1 -> User A



Johnston et al           Expires - April 2002                [Page 79]

                     SIP Basic Call Flow Examples         October 2002


   SIP/2.0  486 Busy Here
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F11 ACK User A -> Proxy 1

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0































Johnston et al           Expires - April 2002                [Page 80]

                     SIP Basic Call Flow Examples         October 2002


3.10      Unsuccessful No Response from User Agent

   User A          Proxy 1          Proxy 2          User B
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|   INVITE F2    |                |
     |     100  F3    |--------------->|   INVITE F4    |
     |<---------------|     100  F5    |--------------->|
     |                |<---------------|   INVITE F6    |
     |                |                |--------------->|
     |                |                |   INVITE F7    |
     |                |                |--------------->|
     |                |                |   INVITE F8    |
     |                |                |--------------->|
     |                |                |   INVITE F9    |
     |                |                |--------------->|
     |                |                |   INVITE F10   |
     |                |                |--------------->|
     |                |                |   INVITE F11   |
     |                |     480 F12    |--------------->|
     |                |<---------------|                |
     |                |     ACK F13    |                |
     |     480 F14    |--------------->|                |
     |<---------------|                |                |
     |     ACK F15    |                |                |
     |--------------->|                |                |
     |                |                |                |

   In this example, there is no response from User B to User A's INVITE
   messages being re-transmitted by Proxy 2.  After the sixth re-
   transmission, Proxy 2 gives up and sends a 480 No Response to User A.


   Message Details


   F1 INVITE User A -> Proxy 1

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Proxy-Authorization: Digest username="UserA", realm="atlanta.com",
    nonce="cf5904ba7d8dc3a5ab2530aa931128fa", opaque="",


Johnston et al           Expires - April 2002                [Page 81]

                     SIP Basic Call Flow Examples         October 2002


    uri="sip:UserB@biloxi.com",
    response="7afc04be7961f053c24f80e7dbaf888f"
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /*Client for A prepares to receive data on port 49172 from the
   network.*/

   F2 INVITE Proxy 1 -> Proxy 2

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 100 Trying Proxy 1 -> User A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>


Johnston et al           Expires - April 2002                [Page 82]

                     SIP Basic Call Flow Examples         October 2002


   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F4 INVITE Proxy 2 -> User B

   INVITE sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 68
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F5 100 Trying Proxy 2 -> Proxy 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F6 INVITE Proxy 2 -> User B

   Resend of Message F4


Johnston et al           Expires - April 2002                [Page 83]

                     SIP Basic Call Flow Examples         October 2002




   F7 INVITE Proxy 2 -> User B

   Resend of Message F4


   F8 INVITE Proxy 2 -> User B

   Resend of Message F4


   F9 INVITE Proxy 2 -> User B

   Resend of Message F4


   F10 INVITE Proxy 2 -> User B

   Resend of Message F4


   F11 INVITE Proxy 2 -> User B

   Resend of Message F4


   /* Proxy 2 gives up */

   F12 480 No Response Proxy 2 -> Proxy 1

   SIP/2.0 480 No Response
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F13 ACK Proxy 1 -> Proxy 2

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl


Johnston et al           Expires - April 2002                [Page 84]

                     SIP Basic Call Flow Examples         October 2002


   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   F14 480 No Response Proxy 1 -> User A

   SIP/2.0 480 No Response
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F15 ACK User A -> Proxy 1

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0























Johnston et al           Expires - April 2002                [Page 85]

                     SIP Basic Call Flow Examples         October 2002


3.11      Unsuccessful Temporarily Unavailable

   User A          Proxy 1          Proxy 2          User B
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|   INVITE F2    |                |
     |     100  F3    |--------------->|   INVITE F4    |
     |<---------------|     100  F5    |--------------->|
     |                |<---------------|      180 F6    |
     |                |     180 F7     |<---------------|
     |     180 F8     |<---------------|                |
     |<---------------|                |     480 F9     |
     |                |                |<---------------|
     |                |                |     ACK F10    |
     |                |     480 F11    |--------------->|
     |                |<---------------|                |
     |                |     ACK F12    |                |
     |     480 F13    |--------------->|                |
     |<---------------|                |                |
     |     ACK F14    |                |                |
     |--------------->|                |                |
     |                |                |                |


   In this scenario, User B initially sends a 180 Ringing response to
   User A, indicating that alerting is taking place.  However, then a
   480 Unavailable is then sent to User A.  This response is
   acknowledged then proxied back to User A.


   Message Details


   F1 INVITE A -> Proxy 1

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Proxy-Authorization: Digest username="UserA", realm="atlanta.com",
    nonce="aa9311cf5904ba7d8dc3a5ab253028fa", opaque="",
    uri="sip:UserB@biloxi.com",
    response="59a46a91bf1646562a4d486c84b399db"
   Content-Type: application/sdp


Johnston et al           Expires - April 2002                [Page 86]

                     SIP Basic Call Flow Examples         October 2002


   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /*Client for A prepares to receive data on port 49172 from the
   network.*/

   F2 INVITE Proxy 1 -> Proxy 2

   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 100 Trying Proxy 1 -> A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


Johnston et al           Expires - April 2002                [Page 87]

                     SIP Basic Call Flow Examples         October 2002




   F4 INVITE Proxy 2 -> B

   INVITE sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Max-Forwards: 68
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@client.atlanta.com>
   Content-Type: application/sdp
   Content-Length: 143

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.atlanta.com
   s=-
   c=IN IP4 192.0.2.101
   t=0 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F5 100 Trying Proxy 2 -> Proxy 1

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F6 180 Ringing B -> Proxy 2

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1


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                     SIP Basic Call Flow Examples         October 2002


    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F7 180 Ringing Proxy 2 -> Proxy 1

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F8 180 Ringing Proxy 1 -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss2.biloxi.com;lr>, <sip:ss1.atlanta.com;lr>
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com>
   Content-Length: 0


   F9 480 Temporarily Unavailable B -> Proxy 2

   SIP/2.0 480 Temporarily Unavailable
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
    ;received=192.0.2.222
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111


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                     SIP Basic Call Flow Examples         October 2002


   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F10 ACK Proxy 2 -> B

   ACK sip:UserB@client.biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss2.biloxi.com:5060;branch=z9hG4bK721e418c4.1
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   F11 480 Temporarily Unavailable Proxy 2 -> Proxy 1

   SIP/2.0 480 Temporarily Unavailable
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F12 ACK Proxy 1 -> Proxy 2

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP ss1.atlanta.com:5060;branch=z9hG4bK2d4790.1
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0


   F13 480 Temporarily Unavailable Proxy 1 -> A



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                     SIP Basic Call Flow Examples         October 2002


   SIP/2.0 480 Temporarily Unavailable
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 INVITE
   Content-Length: 0


   F14 ACK A -> Proxy 1

   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/UDP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0

Security Considerations

   Since this document contains examples of SIP session establishment,
   the security considerations in RFC 3261 [2] apply.  RFC 3261
   describes the basic threats including registration hijacking, server
   impersonation, message body tampering, session modifying or teardown,
   and denial of service and amplification attacks.  The use of HTTP
   Digest as shown in this document provides one-way authentication and
   protection against replay attacks.  TLS transport is used in
   registration scenarios due to the lack of integrity protection in
   HTTP Digest and the danger of registration hijacking without it, as
   described in RFC 3261 [2].  A full discussion of the weaknesses of
   HTTP Digest is provided in RFC 3261 [2].  The use of TLS and the
   Secure SIP (sips) URI scheme provides a better level of security
   including two-way authentication.  IPsec can also improve security.
   S/MIME can provide end-to-end confidentiality and integrity
   protection of message bodies, as described in RFC 3261.

References


   1  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997

  2 Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
      Peterson, J., Sparks, R., Handley, M., and Schooler, E., "SIP:
      Session Initiation Protocol", RFC 3261, June 2002.



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                     SIP Basic Call Flow Examples         October 2002




  3 Rosenberg, J. and Schulzrinne, H., "An Offer/Answer Model with
      SDP", Internet Engineering Task Force, RFC 3264, April 2002.

  4 Johnston, A., Donovan, S., Sparks, R., Cunningham, C., Summers, K.,
      "Session Initiation Protocol PSTN Call Flows", RFC xxxx, August
      2002.

  5 Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach,
      P., Luotonen, A. and Stewart, L., "HTTP authentication: Basic and
      Digest Access Authentication", RFC 2617, June 1999.





Acknowledgments

   This document is has been a group effort by the SIP and SIPPING WGs.
   The authors wish to thank everyone who has read, reviewed, commented,
   or made suggestions to improve this document.

   Thanks to Rohan Mahy, Adam Roach, Gonzalo Camarillo, Cullen Jennings,
   and Tom Taylor for their detailed comments during the final review.
   Thanks to Dean Willis for his early contributions to the development
   of this document.

   The authors wish to thank Neil Deason for his additions to the
   Torture Test messages and Kundan Singh for performing parser
   validation of messages.

   The authors wish to thank the following individuals for their
   participation in the review of this call flows document: Aseem
   Agarwal, Rafi Assadi, Ben Campbell, Sunitha Kumar, Jon Peterson, Marc
   Petit-Huguenin, Vidhi Rastogi, and Bodgey Yin Shaohua.

   The authors also wish to thank the following individuals for their
   assistance: Jean-Francois Mule, Hemant Agrawal, Henry Sinnreich,
   David Devanatham, Joe Pizzimenti, Matt Cannon, John Hearty, the whole
   MCI WorldCom IPOP Design team, Scott Orton, Greg Osterhout, Pat
   Sollee, Doug Weisenberg, Danny Mistry, Steve McKinnon, and Denise
   Ingram, Denise Caballero, Tom Redman, Ilya Slain, Pat Sollee, John
   Truetken, and others from MCI WorldCom, 3Com, Cisco, Lucent and
   Nortel.

Author's Addresses




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                     SIP Basic Call Flow Examples         October 2002


   All listed authors actively contributed large amounts of text to this
   document.

      Alan Johnston
      WorldCom
      100 South 4th Street
      St. Louis, MO 63102
      USA

      EMail:  alan.johnston@wcom.com


      Steve Donovan
      dynamicsoft, Inc.
      5100 Tennyson Parkway
      Suite 1200
      Plano, Texas 75024
      USA

      EMail:  sdonovan@dynamicsoft.com


      Robert Sparks
      dynamicsoft, Inc.
      5100 Tennyson Parkway
      Suite 1200
      Plano, Texas 75024
      USA

      EMail:  rsparks@dynamicsoft.com

      Chris Cunningham
      dynamicsoft, Inc.
      5100 Tennyson Parkway
      Suite 1200
      Plano, Texas 75024
      USA

      EMail: ccunningham@dynamicsoft.com


      Kevin Summers
      Sonus
      1701 North Collins Blvd, Suite 3000
      Richardson, TX 75080
      USA

      Email: kevin.summers@sonusnet.com



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                     SIP Basic Call Flow Examples         October 2002



   Copyright Notice

   "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 is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS 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.


Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.
















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