Manual

VIII. More About SIP

Before we get into a conversation about routers and SIP issues, it’s important to understand the basics of how SIP

works.

The great thing about SIP is that the same protocol is used between devices along the chain. In our example

shown in Figure the figure above, a SIP PBX uses the protocol to register and place and receive calls with a SIP

service provider on the Internet. In this scenario, the provider is acting like a SIP host and the PBX is acting like a

client.

Further down the chain, the PBX has a similar but inverse relation with its extensions - the PBX in this link is the host

and the extensions are the clients.

But in both links, the protocol is the same - the client is registering with the SIP host, the host is notifying the client

of incoming calls and handling outbound call routing. The way the clients and hosts are set up is identical.

If in this scenario, you replace the phone extension with an EarShot IFB system, you can see how lines can now be

shared between a PBX and your studio telephone system. The EarShot IFB acts like a SIP extension to the PBX. This

requires some PBX programming to keep straight, but offers the ultimate in flexibility and utility. Of course, since

the protocol is the same, the EarShot IFB can register with the SIP provider directly, bypassing the PBX entirely.