Media Gateway Control and
Softswitch Architecture (MGCP)
Lecture 6
Media Gateway Control Protocol
• MGCP separates the functions of call control
and media translation into two separate
devices:
• The voice gateway handles media translation.
• A call agent handles call control.
Why MGCP
• MGCP was created for a centralized architecture,
where most of the configuration and call-control
intelligence resides on a call agent, such as Cisco
Call Manager.
• The traditional role of an MGCP gateway is media
translation.
• PSTN connections, such as Foreign Exchange
Office (FXO), Foreign Exchange Station (FXS), and
PRI (ISDN) lines, typically terminate in the
gateway.
MGCP Translates
• The gateway translates between the PSTN and
the IP network. MGCP gateways are
sometimes divided into two categories:
• Residential gateways— Interfaces between
analogue (RJ11) ports and the Voice over IP
(VoIP) network
• Trunking gateways— Interfaces between PSTN
trunks such as DS0s or PRIs and the VoIP
network
MGCP Operation
• To understand MGCP, you must understand
the concepts of;
• Endpoints
• Connections
• Events
• Signals
Endpoints
• An endpoint can be either the source or the
destination for a media stream.
• Some examples are an analog or digital line, or
a virtual endpoint such as DSP resources used
by a conference bridge.
• One gateway can support multiple endpoints.
• Endpoint names have two components—a
local identifier, and a gateway identifier.
Endpoint Examples
• DS0 channel: A digital channel operating at 64
Kbps. Such a channel will typically be multiplexed
within a larger transmission facility such as a DS1
(1.544 Mbps) or E1 (2.048 Mbps).
• Analogue line: Typically, an endpoint that
interfaces to a standard telephone line and
provides service to a traditional telephone. In
most cases, the media to be received on the
analog line will be an analog voice stream.
Connections
• A connection is the relationship established
between a given endpoint and an RTP/IP
session.
• For example, a DS0 endpoint.
• If the DS0 is idle, then no connection is
associated with the endpoint and no
resources are allocated to the endpoint on the
IP side of the gateway.
Events
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MGCP is able to detect changes in the line
These are known as events
Examples of these would be;
Off-hook
Dialled digits
Ringing tone etc
Signals
• In the MGCP model, the gateways focus on
the audio signal translation function, while the
Call Agent handles the call signalling and call
processing functions.
• As a consequence, the Call Agent implements
the "signalling" layers of the H.323 standard,
and presents itself as an "H.323 Gatekeeper"
or as one or more "H.323 Endpoints" to the
H.323 systems
MGCP on a Cisco Gateway Router
Configure MGCP
• To configure an MGCP gateway, you simply
identify the Cisco Unified Communications
Manager server associated with the gateway
and identify the gateway to the call agent.
• The MGCP gateway handles the translation
between voice signals and the packet network
and interacts with the Cisco Unified
Communications Manager server.
• The server performs signal and call processing.
Commands
#Router(config)# mgcp
• Enables the MGCP protocol.
#Router(config)# mgcp call-agent 10.0.0.21
mgcp 0.1
• Specifies the primary Cisco Unified
Communications Manager server's IP address
or domain name, and the port gateway service
type and version number
Commands ctd..
#Router(config)# mgcp dtmf-relay voip codec
all mode cisco
• Selects the codec type and the dual tone
multifrequency (DTMF) relay services.
#Router(config)# ccm-manager mgcp
• Enables the MGCP gateway to support
Cisco Unified Communications Manager.
Summary
• MGCP (defined under RFC 2705 ) is a
master/slave protocol that allows a call control
device (such as Cisco CallManager) to take
control of a specific port on a gateway.
• This has the advantage of centralized gateway
administration and provides for largely
scalable IP Telephony solutions.
• MGCP was also known as H248 protocol.