Voice Over IP Operations
Configuring the Cisco uBR900 Series Cable Access Routers 11
Figure 4 Simplified VoIP Over Cable Network
Your company can then deploy IP telephony as a local-loop bypass service where voice packets are
transferred from the CMTS to:
•A telephony gatekeeper when using H.323; the Cisco uBR924 acts as an H.323 gateway.
•A call agent when using SGCP.
The gatekeeper or call agents manage voice calls. The gateway interconnects the IP network to the
public switched telephone network (PSTN).
Voice calls are digitized, encoded, compressed, and packetized in the originating gateway, then
decompressed, decoded, and reassembled in the destination gateway. A server maintains subscriber
profiles and policy information.
You can place and receive calls without using the local exchange carrier. Two simultaneous voice
and fax calls are supported to and from each subscriber site. Multiple telephones and fax devices can
be connected to each of the two VoIP telephone lines at a subscriber site, providing the 5 REN limit
is adhered to for each telephone line.
Note the following requirements and characteristics of VoIP applications using the Cisco uBR924
cable access router:
•The telephones at each subscriber site must support touch-tone dialing; rotary dialing is not
supported.
•Special telephone features such as call waiting, call forwarding, and conferencing are not
supported.
•A two-line telephone can be connected to the V1+V2 port on the Cisco uBR924.
•Fax devices—standard Group III and computer-based Group III machines up to 14,400
baud—are supported in Cisco IOS images that support VoIP.
18194
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