SIP Registration

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SIP Registrar

A SIP registrar’s role is to accept REGISTER requests with an Address Of Record (URI) and write the associated contact bindings to a location service. The location service is a logical entity and is simply a database that contains a list of AOR to contact address bindings. Very often a registrar functions as a location service. It is also very common for a registrar/location service to be co-located with the proxy server for the same domain. The example below shows a typical registration transaction.

SIP Registration Process.jpg

Tmedia does not provide registrar functionality, therefore, a SIP client cannot register to a Tmedia. If a SIP clients communicate to another SIP clients (B2BUA) in point-to-point fashion and not through a SIP proxy, REGISTER is usually not required. In that case, the SIP clients are required to know the IP addresses or DNS of all the other clients they wish to communicate with.

Registration

The Tmedia supports to register a SIP NAP to a SIP proxy. Registration, can be used, for example, to authenticate the Tmedia Gateway IP address to a SIP provider proxy or SBC and allow the SIP traffic from the Tmedia to that SIP provider.

  • Registration is when Tmedia sends a SIP REGISTER to a Registrar, and gets a response which could be accepted (200 OK) or refused (4xx reason code). Upon refusal, the registration is not stopped and is retried after 5 seconds.
  • If Authentication is required, the Registrar returns a 401 Unauthorized response with a WWW-Authenticate header
  • The WWW-Authenticate header contains nonce to encrypt user’s communications password, user then sends a second REGISTER containing an Authorization header with the user's encrypted password
  • 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 5 seconds interval, otherwise it is at the half of the minimum registration negotiated with the remote proxy (endpoint)
  • The SIP REGISTER is "valid" for 3600 seconds
  • Tmedia will send a new REGISTER (to refresh a registration) after half of the minimum registration negotiated, general use will be at 1800 seconds (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


Register with negotiation (contact expire)

SIP Register negotiated expire time example 1.png


Register with negotiation (contact expire not provided, default Expires header)

SIP Register negotiated expire time example 2.png


Register Authentication

SIP Register 401 authentication example.png


Register with no answer from registrar

The message flow below shows the retransmission of SIP REGISTER over UDP. The request is retransmitted for 32 seconds before the request transaction timeout, then a new SIP REGISTER is sent after 5 seconds. Over TCP, if the SIP registrar does not listen on the TCP port, a new TCP connection is retried every 5 seconds. If the TCP connection is established but no SIP responses returned by the Registrar, the transaction timeout after 32s and then a new SIP REGISTER is sent after 5 seconds. SIP Register no answers.png

Network Access Point (NAP) Availability

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


Configuration

References

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