H3C Technologies H3C MSR 50 - Manual (Page 700)

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Configuring SIP trunk
As shown in Figure 707 , on a typical telephone network, internal calls of the enterprise are made through
the internal PBX, and external calls are placed over a PSTN trunk.
Figure 707 Typical telephone network
With the development of IP technology, many enterprises deploy SIP-based IP-PBX networks as shown
in
Figure 708 . Internal calls of the enterprise are made by using the SIP protocol, and external calls are
still placed over a PSTN trunk. The problem is that the enterprises have to maintain both the SIP network
and PSTN trunk. This increases the difficulty of network management.
Figure 708 SIP+PSTN network
As more enterprise IP-PBX networks run SIP and more Internet Telephone Service Providers (ITSPs) use SIP
to provide basic voice communication structures, enterprises need a technology that uses SIP to connect
the enterprise IP-PBX network to the ITSP. This is necessary to have network that is entirely IP-based. This
technology is called SIP trunk. A typical SIP trunk network is shown in Figure 709 .
The SIP trunk function can be embedded into the voice gateway or the firewall deployed at the edge of
an enterprise private network. The device providing the SIP trunk function is called the SIP trunk device,
or the SIP trunk gateway.