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Cisco uBR924 Software Configuration Guide
OL-0337-05 (8/2002)
Chapter 4 Voice over IP Configurations
Overview
Figure 4-1 Simplified VoIP Network
The CMTS at the headend routes IP telephony calls from the point of origination to the destination,
transmitting them along with other traffic (both voice and data). To route voice calls across the local IP
network to a destination on the Internet or the public switched telephone network (PSTN), the
Cisco uBR924 router and CMTS deploy IP telephony as a local-loop bypass service. One of the
following routing methods is then used, depending on the protocol being used:
• If using H.323v2, the Cisco uBR924 acts as the H.323v2 gateway that forwards the voice packets to
the CMTS, which then sends them to a telephony gatekeeper. The gatekeeper transmits the packets
to their ultimate destination.
• If using SGCP or MGCP, the Cisco uBR924 router acts as the residential gateway that forwards the
voice packets to the CMTS, which then connects to the external call agent (SGCP or MGCP) or
media gateway controller (MGCP). The call agent or controller determines how to transmit the call
across the network to the trunking gateway that will be its ultimate destination.
The gateway at the destination typically interconnects the IP network to the public switched telephone
network (PSTN) so that calls can be made to any phone, not just those that are part of the IP telephony
network.
Voice calls are digitized, encoded, compressed, and packetized in an originating gateway; and then,
decompressed, decoded, and reassembled in the destination gateway. A server maintains subscriber
profiles and policy information. See the Cisco service provider voice documentation set if you have
Cisco gatekeeper, gateway, or other applicable products.
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Gatekeeper or
calling agents
Service
provider
backbone
HFC
cable plant
HFC
cable plant
Cisco uBR924
Cisco uBR924
CMTS rack
equipment
CMTS rack
equipment
Gateway/PSTN
Calling party
Residence or SOHO
subscriber site 1
Residence or SOHO
subscriber site 2
Called party
Policy
server