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Chapter 10 Migrating to an IP Telephony Network
Reference Models for Migration Configurations
The models shown in Figure 10-5 have the following characteristics:
• Model A is the simplest; it is concerned only with PBX services and does not
address voice messaging.
• Model B includes a voice messaging system behind the PBX and assumes that
the voice mail system does not offer an open interface for connection to an IP
network. Therefore, all voice mail traffic from the IP network must travel
through the PBX.
• Model C includes a voice messaging system that can connect to an IP
network, providing a stronger feature set for IP users.
• Model D introduces unified IP messaging at the same time as IP telephony,
replacing a conventional PBX and voice mail combination.
Detailed Discussion of Model A
Figure 10-6 shows the topology for model A, which includes a PBX but no voice
messaging.
Figure 10-6 Migration Model A—PBX Only
PSTN
LAN
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IP
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