Information Technology Reference
In-Depth Information
Figure 14-7 shows a company that has separate voice and data networks. Phones connect
to local PBXs, and the PBXs are connected using TDM trunks. Off-net calls are routed to
the PSTN. The data network uses LAN switches connected to WAN routers. The WAN
for data u s e s Frame Relay. S eparate operat ion s and management s ystem s are required for
these networks. Each system has its corresponding monthly WAN charges and personnel,
resulting in additional costs. With separate voice and data networks,
Atlanta
MPLS
San Diego
Houston
PSTN
Figure 14-7
Separate Voice and Data Networks
Data is primary traffic on many voice service provider networks.
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Companies want to reduce WAN costs.
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PSTN architecture is not flexible enough to accommodate data.
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PSTN cannot integrate voice, data, and video.
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With IP telephony, you can reduce the number of systems, circuits, and support person-
nel. Figure 14-8 shows a converged IP telephony network that employs Ethernet-based
phones with server-based call processing and integrated service gateway routers. Surviv-
able Remote Site Telephony (SRST) is used for failover or backup call processing if WAN
failure occurs. On-net calls travel through the Frame Relay net work, and off-net calls are
for warded to the P STN. The P STN link is als o u s ed if voice overflow or conge st ion occ ur s
on the WAN network. Calls are then routed to the PSTN.
IPT Components
The Cisco IPT architecture divides voice system architectures into four major VoIP com-
ponents, as shown in Figure 14-9:
Key
To p i c
Client endpoints
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Call processing
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Service applications
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Vo i c e - e n a b l e d i n f r a s t r u c t u r e
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