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CiscouBR924 Software Configuration Guide
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Chapter4 Voice over IP Configurations
Overview
•The IP address of the gateway for the destination dialed—In Cisco uBR924 IOS Rel ease 12.0(4)XI
or higher interim builds, configure these IP addresses statically via the command-line interface
(CLI) using voip dial peer group commands. When running Cisco IOS Re lease 12.0(5)T or higher
interim images on Cisco gatekeeper products, the router obtains these addresses dynamically from
the gatekeeper using the Registration, Admission, and Status (RAS) protocol .
•The telephone numbers of the attached devices—In Cisco IOS Relea se 12.0(4)XI or higher interim
builds, you configure these IP addresses statically via the CLI pots port commands. When using
Cisco Network Registrar (CNR) version 3.0 or higher with the re lay.tcl and setrouter.tcl scripts,
and Cisco gatekeeper products in your network running Cisco IOS Release 12.0(5)T or higher
images, you can obtain these addresses dynamically from CNR. The telephone numbers of attached
devices are then sent in DHCP response messages. When the Cisco uBR924 processes the DHCP
response, it automatically creates the pots dial peer for each port, creates the voip dial peer for the
RAS target, and starts the H.323v2 RAS gateway support.
Note To support voice configurations involving Cisco gatekeeper products using RAS, Cisco IOS
Release 12.0(5)T or higher images with gatekeeper support are required. The headend must have IP
multicast enabled. The cable interface must be designated as the default for RAS to discover the
gatekeeper. The gatekeeper then resolves all dialed destinations sent to the RAS protocol.
SGCP and MGCP Protocol Stack
When using a Cisco IOS Release 12. 0(5)T or higher image with voice support, the Cisco uBR92 4 router
supports the Simple Gateway Control Protocol (SGCP). When using a Cisco IOS Release 12.1(3)T or
higher image with voice support, the Cisco uBR924 router also s upports the MGCP protocol, which is
intended to eventually supersede the SGCP protocol. Both MGCP and SGCP are signaling prot ocols that
interact with a remote call agent (CA) to provide call setup and teardown for VoIP calls.
Using the call agent, SGCP and MGCP communicate with the voice gateways, dynamically resolving
and routing calls. This creates a distributed system that enhances performance, reliability, and scalability
while still appearing as a single VoIP gateway to external clients.
The remote call agent also provides the signaling and feature negotiation that would otherwise be
provided by the Cisco uBR924 router when using the H.323v2 protoc ol. Similarly, the call agent also
provides the mapping of IP addresses to telephone numbers, eliminating the dia l plan mapper and static
configurations that are required on the router when using the H.323v2 protocol.
The SGCP and MGCP protocols implement the gateway functionality using both trunk and residential
gateways. The Cisco uBR924 router functions in this mode as a residential ga teway with two endpoints.
SGCP and MGCP can preserve Signaling System 7 (SS7) style call control information as well as
additional network information such as routing information and authentication, authorization, and
accounting (AAA) security information. SGCP and MGCP allow voice calls to originate and terminate
on the Internet, as well as allowing one end to terminate on the Internet and the other to terminate on a
telephone on the PSTN.
Note The Cisco uBR924 cable access router supports both H.323 and SGCP/MGCP call control, but only one
method can be active at a time.