Switching to VoIP

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

Network Environment

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• DHCP server

• Firewall, NAT device, or Internet gateway router

• Default router

None of these need to be located on the same Ethernet segment as the IP phones

(except the DHCP server), though disaster planning and bandwidth preservation

often dictate that they be. (More on disaster planning is found in Chapter 13.) For

example, if you’re using a softPBX call path for all calls originating from a segment

with 1,000 IP phones, it’s probably a good idea to locate that softPBX on the same

segment as the phones. This is because an IP-over-T1 link, for example, wouldn’t

have enough bandwidth to carry the media channels of even 50 G.729A/RTP calls.

Such a link would be required if the softPBX were located on a remote LAN segment.

The TFTP, DNS, and DHCP servers are used to provide network configuration infor-

mation and firmware updates to IP phones. Like a desktop PC, an IP phone needs an

IP address, a subnet mask, a DNS address, and a default router address (if it will be

used with a WAN or the Internet). These configurations can be centrally managed

using a DHCP server and then automatically assigned to each phone during the

DHCP host registration process. Some VoIP-specific configurations, such as SIP

proxy addresses or H.323 gatekeeper addresses, can also be set ...