SIP FAQ : SIP Basics :
What is not described in the SIP spec?
- the color of the phones that use SIP;
- what operating system is used to implement a SIP phone;
- what language is used to display error messages;
- what sound, if any, is used to indicate ringback or ringing;
- whether a registrar, proxy or redirect server are implemented in one process, on one machine or distributed across a network;
- which media types or codecs the SIP implementation supports;
- which type of network SIP is used in;
- what type of security measures are required to be used;
- the GUI for SIP calls;
- how to build a network of proxy servers;
- whether a phone can make calls while it's in a call;
- qualifications for human beings to make use of SIP softphones;
- how generous an implementation should be in dealing with requests and responses that have mistakes and how much error detail information it should provide;
- how many simultaneous calls the device can be in.
- what parser generator tool, if any, should be used by implementations
- what threading model to use
What is RFC2543bis?