SIP Registration

Revision as of 04:07, 21 March 2016

SIP Registrar

A registrar is a SIP endpoint that accepts REGISTER requests and places the information it receives in those requests into a location service for the domain it handles. The location service links one or more IP addresses to the SIP URI of the registering agent. The URI uses the sip: scheme, although other protocol schemes are possible, such as tel:. More than one user agent can register at the same URI, with the result that all registered user agents receive the calls to the URI.

SIP registrars are logical elements, and are commonly co-located with SIP proxies. But it is also possible and often good for network scalability to place this location service with a redirect server.

If clients send SIP requests and responses directly to the other clients in point-to-point mode and not through a proxy, REGISTER is not required. In this case, clients are required to know the IP addresses of all the other clients they wish to communicate with.

Polling

• In Tmedia, option "Poll Remote Proxy?" is enabled by default
• Tmedia SIP polling is using SIP OPTIONS method to "poke" a SIP Network Access Point (NAP) to see if it's alive or not, that is, NAP availability
• Upon a response from the SIP NAP, Tmedia will determine whether to mark the NAP as up
• This is true, only if the option "Map any response to available status" is checked (by default), otherwise, only a 200 OK to a SIP OPTIONS will bring the NAP up
• With "Map any response to available status" checked, 200-600 answer response can return from OPTIONS request, with these response the NAP is considered up
• The first time a SIP NAP is added in configuration and configuration activated, Tmedia polls at 5s, after that and general use is polling at 60s

Registration

• Registration is when Tmedia sending SIP REGISTER to Registrar, and getting answer response which could be accepted (200 OK) or refused (anything else) that may require further action
• Even if there is no call on the system, Tmedia will send SIP REGISTER
• If it is not registered already, the Tmedia will send SIP REGISTER at 5s interval, otherwise it is at the half of the minimum registration negotiated with the remote proxy(endpoint)
• The SIP REGISTER is "valid" for 3600s

• There is no way to extend SIP registration, so Tmedia has to send a new REGISTER (to refresh a registration) after half of the minimum registration negotiated, general use will be at 1800s (3600/2)
• Sending SIP REGISTER will happen when the option "Register to Proxy?" is selected for a specific SIP NAP
• If you apply a new configuration and the option "Register to Proxy?" is present it will start sending SIP REGISTER

Nap Availability

If "Polling Remote Proxy?" and "Register to Proxy?" are both checked, only the SIP OPTIONS answers will affect the NAP availability.

Configuration

• Allocating a SIP NAP Configuration v2.9
• Allocating a SIP NAP Configuration v2.8
• Allocating a SIP NAP Configuration v2.7
• Allocating a SIP NAP Configuration v2.5

References

• Wikipedia article
• Understanding SIP Registration