System information

420 Features

the information is specific to a Nortel product, it is vendor-specific. Once

encapsulated, the information appears as one or more sub-options inside

option 43, which the IP Phone decodes.

Site Specific option

Another way to transport the Voice Gateway Media Card information is

through Site Specific options. These are unused DHCP options that have

not been predefined to carry standard information. Unlike the Vendor

Specific options, the information transported is "site" specific and option

codes 128 to 254 are used for encoding.

For Nortel IP Phones, the Voice Gateway Media Card information involves

the location of the Voice Gateway Media Card in the network. This varies

for different sites and can be implemented in a Site Specific option. If the

Vendor Encapsulation option is used, the information is first encoded in a

Site Specific option. Nortel 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 IP Phone 2004 requests services

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

421).

Nortel Communication Server 1000

IP Phones Fundamentals

NN43001-368 05.02 26 May 2009