Speaking of Standards

Have you ever wished you could see examples of exactly how the call flows are supposed to go between endpoints in a SIP communication session? Down to the individual SIP packets sent back and forth?

Well, now you can courtesy of the newly-issued RFC 5359, SIP Service Examples. The RFC goes through a whole series of call flows in a level of detail all the way down to the packet level. Here’s the abstract:

This document gives examples of Session Initiation Protocol (SIP)
services. This covers most features offered in so-called IP Centrex
offerings from local exchange carriers and PBX (Private Branch
Exchange) features. Most of the services shown in this document are
implemented in the SIP user agents, although some require the
assistance of a SIP proxy. Some require some extensions to SIP
including the REFER, SUBSCRIBE, and NOTIFY methods and the Replaces
and Join header fields. These features are not intended to be an
exhaustive set, but rather show implementations of common features
likely to be implemented on SIP IP telephones in a business
environment.

And here is the list from the table of contents of the specific examples:

   2. Service Examples ................................................6
      2.1. Call Hold ..................................................6
      2.2. Consultation Hold .........................................19
      2.3. Music on Hold .............................................38
      2.4. Transfer - Unattended .....................................50
      2.5. Transfer - Attended .......................................58
      2.6. Transfer - Instant Messaging ..............................71
      2.7. Call Forwarding Unconditional .............................77
      2.8. Call Forwarding - Busy ....................................84
      2.9. Call Forwarding - No Answer ...............................92
      2.10. 3-Way Conference - Third Party Is Added .................101
      2.11. 3-Way Conference - Third Party Joins ....................107
      2.12. Find-Me .................................................113
      2.13. Call Management (Incoming Call Screening) ...............125
      2.14. Call Management (Outgoing Call Screening) ...............132
      2.15. Call Park ...............................................135
      2.16. Call Pickup .............................................147
      2.17. Automatic Redial ........................................154
      2.18. Click to Dial ...........................................163

Obviously there are many more call flows out there, but these are a sample that can give you a real sense of how the SIP communication is supposed to go. Great to see this out there for all the people new to SIP.

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