Samsung Ubigate iBG3026, Configuration Manual

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CHAPTER 28. SIP Gateway Management
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© SAMSUNG Electronics Co., Ltd.
How SIP Works
On SIP network, SIP user has a unique SIP address. SIP address has the form
similar to that of an e-mail address. The typical form of SIP address is
sip:userID@hostname. userID can be a user name or E.164 address. Hostname
can be IP address or domain address.
SIP user register his SIP address and current location information to a registrar
server. Registrar server provides the information to SIP server(either a proxy
or a redirect server), and SIP server maps the SIP address of the request
received from a user agent to the current location information.
This is called as a location service.
When SIP user attempts a call, it sends a SIP request to SIP server. From
header field of SIP request includes the caller information, and To header field
includes the callee information. In SIP server, a location service necessary for
signaling routing is executed. After the request is sent to a proxy server, the
proxy server proceeds with the call using the address resulting from the
location service. Finally, SIP request is delivered to a callee, to complete a call
setup.
After a request is sent to a redirect server, the redirect server sends the location
service result to a caller using the Contact header field of a response.
The redirect server does not participate in the call anymore. Caller sends a
new SIP request to the address specified in Contact header field.
How SIP Works with a Call Manager
If Call Manager is used, a user agent sends a REGISTER request to Call
Manager. Here, the REGISTER request includes the SIP address and current
location information of a caller. All the call attempted by a user agent is made
via Call Manager. A caller sends a INVITE request to Call Manager, and Call
Manager determines a path via a location service. Call Manager delivers a
request to a callee using the determined path. A callee sends a response to Call
Manager, and the response is delivered to a caller. A caller sends ACK for the
response. A session between a caller and callee is established, and session data
is delivered to caller and callee using Real-time Transfer Protocol(RTP).