Information Technology Reference
In-Depth Information
G.711 requires a transmission rate of 50 packets per second (pps) with this payload size.
Note that G.711 has a codec bit rate of 64 Kbps, meaning that this (payload) bit rate that must be maintained.
The number of packets per second that must be transmitted per second to maintain a codec bit rate of 64 Kbps is given by the
following formula:
Packets per second (pps) = Codec bit rate (bps) / Voice payload size (in bits)
So, for G.711, if the codec bit rate is 64 Kbps and the voice payload size is 1280 bits (160 bytes), the number of packets per
second required is 50 pps.
G.729 uses a sample size of 10 bytes/10 ms and has a default voice payload size of 20 bytes/20 ms (default payload includes
two samples). If the payload is 30 bytes, this equates to 30 ms.
G.729 requires a transmission rate of 50 pps with this payload size.
Note that G.729 has a codec bit rate of 8 Kbps.
Media gateway Control Protocol
Media Gateway Control Protocol (MGCP) is defined in RFC 3435 (which obsoletes RFC 2705), and it specifies an application
programming interface (API) and text-based master/slave protocol used by a media gateway controller (MGC) or call agent to control
media gateways (MG). MGCP is based on two other (now obsolete) protocols: the Simple Gateway Control Protocol (SGCP) and
Internet Protocol Device Control (IPDC).
MGCP MGCs and MGs can be described as follows:
■
MGC/call agent:
This element possesses call control intelligence and controls MGs. An MGC/call agent could, for example,
be a Cisco CUCM. MGCP allows the centralization of the dial plan on the call agent.
■
MG:
This device provides translation between data packets and audio signals received over VoIP networks and other
networks, such as the public switched telephone network (PSTN). A media gateway could, for example, be an IOS router
with analog or digital voice ports.
