SIP Callflow Examples

	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 implementers, designers, and protocol researchers alike and will
   help further the goal of a standard implementation of RFC 3261 [1].
   These flows represent carefully checked and working group reviewed
   scenarios of the most basic examples as a companion to the
   specifications.

1.3.  SIP Protocol Assumptions

   This document does not prescribe the flows precisely as they are
   shown, but rather the flows illustrate the principles for best
   practice.  They are best practices usages (orderings, syntax,
   selection of features for the purpose, handling of error) of SIP
   methods, headers and parameters.  IMPORTANT: The exact flows here
   must not be copied as is by an implementer due to specific incorrect
   characteristics that were introduced into the document for
   convenience and are listed below.  To sum up, the basic flows
   represent well-reviewed examples of SIP usage, which are best common
   practice according to IETF consensus.

   For simplicity in reading and editing the document, there are a
   number of differences between some of the examples and actual SIP
   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    Alice          
 This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
    192.0.2.101
   User Agent    Bob            
 This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
       192.0.2.201
   User Agent                   
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      192.0.2.100
   Proxy Server                 ss1.atlanta.example.com     192.0.2.111
   Proxy/Registrar              ss2.biloxi.example.com      192.0.2.222
   Proxy Server                 ss3.chicago.example.com     192.0.2.233
   ALG                          alg1.atlanta.example.com    192.0.2.128

2.  SIP Registration

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


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