CODEWITHSUNDEEP
timersipregistrationmulticast
sudeep
sudeep

Reputation: 81

registration process in sip protocol

I am new to sip protocol,i went through the basics and have these following doubts
1)In registering process when i captured using wireshark,i figured out that from and to headers are same when i read rfc 3261,it says that "to" header indicates whose registration is to be done and from" indicates person responsible for registration.The to and from fields are same unless it is a third party registration.it is not clear to me,how can it both be same and what is a third party registration.

2)Does sip have any keep alive mechanism,in zoiper we have the option of giving expiry time (3600 default),but for registration it is 70,for subscribe it is 60 and for invite it is 3600. how these values are automatically selected?

3)The user agent finds registrars using configuration.dns look up and multi-casting.In what case multi casting is preferred,pls explain the method also what i did was ,installed an asterisk server ,zoiper applicationregister msg capture is attached,created a zoiper account,captured using wireshark in loop back mode.attaching screenshots of captures.Thanks in Advance

Upvotes: 2

Views: 1141

Answers (1)

Istvan
Istvan

Reputation: 1665

Regarding to and from fields in REGISTER:

The "from" field here is just a logical field which should not be checked. If differs from the "to" field that means that "from" registers in name of "to". But I can't think of any scenario when this should be checked (maybe it can be used for something -app specific- in some complicated scenario). You should just follow the usual authentication process (digest auth or other) and skip this field.

Regarding point 2 (expiry time):

Your mentioned settings in Zoiper are just arbitrary.

  • Low values (below 200) can be used if client or server doesn't support NAT keep alive (via NOTIFY or simple \r\n\r\n messages). In this case the REGISTER message will keep alive the UDP binding in NAT routers.
  • Higher values can save some server side processing work and CPU resources

I usually recommend a 600 sec expire timer and 40 sec NAT keep-alive messages. For INVITE the expire field actually means maximum ring time and it is rarely used.

Regarding point 3 (finding registrars):

The SIP server (registrar server) is usually entered manually in client configuration or set by auto-provisioning. If the server is on the same LAN, then you might be also to detect it also by multicast but this is rarely used.

Here is a good tutorial.

Upvotes: 2

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