SIP presence is a tricky subject, mainly because there are some different ways to achieve the same thing. VoIP users are interested to know if “something” has happened in their network. They don’t care how this is technically done, or how many RFCs describe a simple scenario. The truth is that there are indeed many RFCs that handle various aspects:

• the message-summary event allows the user to learn about new voice mail messages
• the dialog event advertises when users are initiating, accepting or terminating voice conversations
• presence events let users know when the status of a resource has changed

Over 130 years ago, Graham Bell managed to get ahead his competitor Elisha Gray with just a few hours and fill in the paperwork required to patent the telephone. Even then, speed was essential in creating a technical advantage over the competition.