Cisco Voice Interworking Services (VISM) Manual de usuario descargar pdf (Pagina 11)

2-11

Cisco Multiservice Packet Network Solution Overview

OL-3025-01

Chapter 2 Solution Components

Media Gateways

Voice Bearer Traffic

The voice traffic is first formatted into an RTP packet, then encapsulated in a UDP and then an IP packet,

for transmission over Fast Ethernet to the Cisco router and thus the network. RTP is used to allow

time-stamping of the voice samples to permit dejittering of samples transmitted to the destination TDM

line. Figure 2-7 shows the voice bearer protocols in a sample configuration with AS5400s connected to

edge routers dedicated to voice traffic.

Figure 2-7 Voice Bearer Trafﬁc

Physical Layout

See Figure 2-8 for a sample physical configuration for a voice-only deployment of AS5400s as the media

gateways. The AS5400s support the TDM links to the Public Switched Telephone Network (PSTN) and

are connected to edge routers dedicated to voice traffic. The call agent for this configuration is the

iMSS-4050 running in a pure configuration.

The redundancy in the topology is achieved using dual VLANs and multiple components—AS5400s,

Catalyst switches, and Cisco routers—with multiple connections to the MPLS core. The AS5400 accepts

a dual power supply, although it is not a fully redundant system. Because a failure of the media gateway

would disable the communication, it is recommended to use a minimum of two gateways with the trunk

group split between them.

Cisco routerCisco router

Voice payload

RTP

UDP

Ethernet

Voice payload

RTP

UDP

MPLS

72458

Voice payload

RTP

UDP

Ethernet

Cisco AS5400 Cisco AS5400

Cisco Catalyst

switch

Cisco Catalyst

switch

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Cisco Voice Interworking Services (VISM) Manual de usuario Pagina 11