| Protocol Basics | |
|---|---|
| Layer: | Application |
| Transport: | TCP or UDP |
| Port(s): | 5060, 5061 |
| RFC(s): | 2543, 3261 |
SIP (Session Initiation Protocol)
SIP is by far the most popular protocol used in VoIP communication today. SIP was designed as a signaling protocol in charge of setting up and tearing down sessions between two or more devices. Additionally, SIP can be used to modify existing sessions. The protocol was designed to be independent of transport protocols. Thus, SIP can be used over both TCP and UDP. As of this writing, popular open source PBX Asterisk only supports SIP over UDP.

If you’ve ever built a site that has different kinds of users, you’ve probably run across the case where you want a limited number of users to appear in a particular list. For example, you may only want staff members to be assigned ownership of a particular object. If your site has a really huge user list, combing through the users to find staff members can get annoying fast.
A special extended edition of Tech Messages for 2010-03-05 through 2010-03-09:
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