Avaya 1110 Fundamentals page 386

Features
encoded in a Site Specific option. Avaya has provided a list of five possible Site Specific option
codes to implement the Voice Gateway Media Card information. Only one of the five codes
must be configured to carry the information, but the choice is available to offset the possibility
that the option code chosen has been used for other purposes.
IP acquisition sequence
This section focuses on the mechanics and sequence of the DHCP message exchange as the
IP Phone uses DHCP for IP acquisition. Although the IP Phone requests many network
configuration parameters as well as an IP address, the following cases focus on the concept
of "how" instead of "what" information is acquired. Also, the IP Phone is used as the sample
client but the situations apply to other DHCP clients as well.
Case 1
Case 1 is a typical situation where an 2004 IP Phone requests services from a DHCP server.
See Figure 69: IP acquisition phase: Case 1
Figure 69: IP acquisition phase: Case 1
1. The IP Phone initiates the sequence by broadcasting a DHCPDISCOVER
2. A DHCP server on the network sees the broadcast, reads the message, and records
3. The DHCP server checks its own IP address pool(s) for an available IP address and
4. The IP Phone sees the broadcast and after matching its MAC address with the offer,
5. If the offer is acceptable, the IP Phone sends out a DHCPREQUEST message with
6. The DCHP server matches the IP address in the Server IP address field against its
386 IP Deskphones Fundamentals
message.
the MAC address of the client.
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.
reads the rest of the message to find out what else is being offered.
the DHCP server's IP address in the Server IP address field.
own to find out to whom the packet belongs.
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on page 386.
February 2013