User's Manual

Network features 441

Finally, when a client is finished with a particular IP address, it sends a

DHCPRELEASE message to the server which reclaims the IP address. If

the client requires the same IP address again, it can initiate the process as

follows:

The IP Phone broadcasts a DHCPREQUEST to a particular DHCP

server by including the server’s IP address in the Server IP Address

field of the message. Since it knows the IP address it wants, it

requests it in the DHCP message.

2. The DHCP server sends a DHCPACK message if all the parameters

requested are met.

Case 3 is similar to Case 1, except the first two messages have been

eliminated. This reduces the amount of traffic produced on the network.

See Figure 79 "IP acquisition sequence: Case 3" (page 441).

Figure 79

IP acquisition sequence: Case 3

Multiple DHCPOFFERS

In some networks, if more than one DHCP server is present, a client

can receive multiple DHCPOFFER messages. Under these situations,

the IP acquisition sequence depends on the client. The client can wait

for multiple offers, or accept with the first offer it receives. If it accepts

multiple offers, it compares them before choosing one with the most

fitting configuration parameters. When a decision is made, the message

exchange is the same as if there is only one DHCP server and proceeds

as in the previous cases. The servers that were not chosen to provide the

service do not participate in the exchange.

Nortel Communication Server 1000

IP Phones Fundamentals

NN43001-368 05.06 30 April 2010