User's Manual

Network features 439

Case 1

Case 1 is a typical situation where an IP Phone 2004 requests services

from a DHCP server. See Figure 77 "IP acquisition phase: Case 1" (page

439).

Figure 77

IP acquisition phase: Case 1

Step Action

1 The IP Phone initiates the sequence by broadcasting a

DHCPDISCOVER message.

2 A DHCP server on the network sees the broadcast, reads the

message, and records the MAC address of the client.

3 The DHCP server checks its own IP address pool(s) for an

available IP address and broadcasts a DHCPOFFER message

if one is available. Usually the server ARPs or PINGs the IP

address to make sure it is not being used.

4 The IP Phone sees the broadcast and after matching its MAC

address with the offer, reads the rest of the message to find out

what else is being offered.

5 If the offer is acceptable, the IP Phone sends out a

DHCPREQUEST message with the DHCP server’s IP address

in the Server IP address field.

6 The DCHP server matches the IP address in the Server IP

address field against its own to find out to whom the packet

belongs.

7 If the IPs match and there is no problem supplying the requested

information, the DHCP server assigns the IP address to the

client by sending a DHCPACK.

Nortel Communication Server 1000

IP Phones Fundamentals

NN43001-368 05.06 30 April 2010