R2511-HP MSR Router Series Voice Configuration Guide(V5)

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Configuring H.323

H.323 is an application-layer control protocol for establishing and terminating multimedia sessions with

one or more participants. H.323 can dynamically adjust and modify session attributes, such as required

session bandwidth, media type (voice and video), encoding/decoding format of media, and support for

broadcast.

H.323 uses the Client/Server model to establish calls through communication between the gateway and

gatekeeper.

H.323, a packet-based multimedia communications system, is an ITU-T standard that specifies the

components, protocols, and procedures that provide multimedia communication services over an IP

network that does not provide guaranteed quality of service (QoS). As one of the standards for VoIP,

H.323 has long been used by traditional carriers and network device manufacturers in their VoIP

solutions.

As shown in Figure 65, the

H.323 stack is implemented at the application layer. The H.323 standard

includes these protocols:

• H.225.0, including Q.931 and registration, administration and status (RAS) protocol, and H.245

for signaling control

• G.711, G.729, G.723.1, and G.723.A for audio codec

• H.261 and H.263 for video codec

• T.120 series (including T.123, T.124, T.125, T.126, T.127, and T.324) for multimedia data transmission.

The real-time transport protocol (RTP) provides end-to-end real-time audio and video delivery services. Its

functionality is enhanced through its control protocol, the real-time transport control protocol (RTCP). The

primary function of RTCP is to provide feedback on the quality of data distribution, which allows the

application system to accommodate to different network conditions and helps with fault location and

diagnosis as well. These two protocols work together to ensure real-time voice transmission.

Figure 65 illu

strates the H.323 stack:

Figure 65 H.323 stack

ITU-T RAS is implemented in compliance with the H.323v2 protocol for communication between

gateway and gatekeeper. RAS adopts the communication model where a gateway sends requests and

the gatekeeper responds with confirms or rejects listed in the following table.

T.126 T.127

T.324

G.711

G.729

G.723.1

G.723.A

H.261

H.263

RTP RTCP

H.245

H.225.0

RAS

T.124 T.125

T.123

TCP UDP

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