H3C Technologies H3C MSR 5600 - Manual (Page 106)

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Configuring SIP trunk
This chapter describes how to configure SIP trunk.
Background
As shown in Figure 38 , in a typical telephone network, a PBX forwards internal calls among enterprise
phones and forwards outbound calls over a PSTN trunk.
Figure 38 Typical telephone network
With the development of IP technology, many enterprises deploy SIP-based IP-PBX networks as shown
in Figure 39 . All internal calls are placed using SIP, 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, which
increases the difficulty of network management.
Figure 39 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 urgently need a technology that can connect
the enterprise IP-PBX network to the ITSP over SIP. This technology is called SIP trunk. A typical network
diagram of SIP trunk is shown in Figure 40 .
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.