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IP-based trunks
In circuit switched networks, trunks provide the means to interconnect PBXs with each other
and to the PSTN. Connection to the public network allows PBX station users to call and be
called by terminals that are not part of the PBX private network of the PBX. An analogous
arrangement exists in packet-switched IP networks.
H.323 trunks connect H.323 systems or gateways over IP networks, similar to circuit-switched
tie trunks. Similarly, SIP trunks connect SIP systems or gateways over IP networks.
A set of Communication Manager switches can each be attached to an IP network, and voice
and fax calls can flow between them in the usual manner except that the call signaling and
audio/fax streams are carried over the IP network. The signaling is carried on a TCP connection
through the C-LAN circuit packs, and the audio and fax streams are carried between switches
through the Media Processor circuit packs.
The benefits of using IP trunks include:
Reducing long distance voice and fax expenses
Facilitating global communications
Providing a fully functional network with data and voice
Converging and optimizing networks by using the available network resources
IP trunk calls can be compressed to save network bandwidth. Repeated compression and
decompression (transcoding) results in a loss of data at each stage and degrades the final
quality of the signal. The maximum recommended number of compression cycles on a call is
three. Normal corporate voice calls or fax calls typically go through fewer than three
compression cycles.
IP (H.323 and SIP) trunks can also connect to other vendors' compliant PBXs.
SIP trunk capacities
Table 17
shows the maximum number of SIP trunks supported out of the total number of IP
trunks supported.
Table 17: SIP Trunk Capacities by Platform Configuration
Platform Configuration
S8700 Multi-Connect
S8700 IP-Connect
S8700/G700/G350/LSP
S8500
S8300/G700/G350
Maximum Number of SIP IP Trunks
of the Total IP Trunks Supported
1000 of 8000
1000 of 4000
1000 of 8000
800 of 800
100 of 450
IP-based trunks
Issue 3.4.1 June 2005
99
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