SIP network overview

xiaoxiao2021-03-06  22

NOIILE

A pure SIP network consists of several parts:

SIP User Agent: SIP User Agent, is a terminal device, in a call application, is equivalent to an IP phone.

SIP Proxy Server: SIP proxy server, which proxy user agent processes all network services.

SIP Redirect Server: Responsible for providing Location Service, Location Services

SIP Registra: All User Agents belonging to this domain must be registered at Registrar to bind your own actual contact address.

The SIP number consists of two parts, username and host. Where Host can be an IP address and a domain name. such as:

Sip: carol@astro.com

SIP: carol@192.168.1.22

The front NAME is specified by the user, which can be any character or number. But it must be unique in the network. Proxy can find an IP address that can be connected according to the user name in Registrar.

The general SIP network operation mechanism is as follows:

1. After the UA is launched, the registration message is not intermittently transmitted to its own proxy, and then forward to the registration server registrar, or the UA can also send the registration message to Registrar.

2. When the UA needs to call other UA, enter its SIP address, if it belongs to the same SIP network, you can enter only the USERNAME section on the GUI, send to Proxy.

3. Proxy is requested to request the called party's IP address to the Redirect Server.

4. After proxy gets the called party's IP address, turn the call to the called party.

This is a rough process for a call established.

But if there are multiple SIP networks, how do they communicate with each other?

The network is as follows: There are two SIP networks: 1) astro_gz.com 2) astro_bj.com

SIP UA from domain Astro_GZ to call the SIP UA of Astro_bj. How is the network addressing?

In fact, the SIP network system is the same as the Email system. To make a cross-network call, you can't just rely on UserName, but a complete SIP URI address. The domain name of the rear is specified which SIP network belongs to this user. Each domain needs to have a complete SIP network. Registered users of each domain can only send registration information and other SIP messages (except for point-to-point communication). The SIP server can only find registration support belonging to this domain. If you need to find SIP UA of other domains, you need to transfer the SIP Message to the SIP server of the domain belonging to the target UA, which is used to find the final address of the target UA.

For example: carol@astro_gz.com To invite Bob@astro_bj.com, it passes this INVITE to SIPPROXY.ASTRO_GZ.COM, and proxy learned from the called SIP address that the user does not belong to this domain, it is addressed by DNS. , Pass this message to SipProxy.astro_bj.com. Ultimate users found by Proxy of astro_bj.com.

Because no matter where a SIP UA is logged in, it is configured to be fixed. The user's proxy of Astro_BJ can only be sipproxy.astro_bj.com, and may not choose sipproxy.astro_gz.com. Its registration information can only be sent to the registration server of the domain.

It can be seen from the above, the working principle of the SIP network is consistent with the working principle of the Email system. A domain is responsible for all users in their domain, and communication between cross-domains needs to be addressed by DNS domain name to obtain UA's Proxy, and then find the target UA. It can be seen that the SIP number is not only composed of username, and the domain name behind is also indispensable. Of course, in some applications, the domain name part of the SIP URI is not involved in some applications, and the domain name portion of the SIP URI is often replaced by the IP address of Proxy, or the direct point of communication, directly by the IP address of the target UA. Of course, it can't achieve interconnection.

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