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401

402

403

404

405

406

407

408

409

410

Network features 409

Table 91

IP Phone network configuration parameters (cont’d.)

Parameters requested by IP Phone

(Option Code 55)

DHCP server

response: Option

Code

IP Line site-specific or vendor-specific encapsulated or

site options.

43, "128" (page 409)

, 131, 144, 157, 188,

191, 205, 219, "223"

(page 409) , 224, 227,

230, 232, 235, 238,

241, 244, 247, 249,

251, and 254

RFC 3942 states that DHCP site-specific options 128 to 223 are hereby

reclassified as publicly defined options. The IP Phone supports 9 vender

specific options in this range and continues to do so for backward compatibility.

However, as suggested in RFC 3942, the use of these options is discouraged to

avoid potential future collisions.

The first eight parameters in Table 91 "IP Phone network configuration

parameters" (page 408) are standard DHCP options and have pre-defined

option codes. The last parameter is for Call Server or TPS information,

which do not have a standard DHCP option. The server administrator must

define a vendor-encapsulated or site-specific option or both to transport

this information to the IP Phone.

This non-standard information includes the unique string identifying the IP

Phone and the Connect Server parameters for the primary and secondary

servers. The IP Phone must receive the Connect Server parameters to

connect to the IP Telephony node.

The administrator must use one of the site-specific or vendor-encapsulated

option codes to implement the Call Server or TPS information. This

user-defined option can then be sent as-is, or encapsulated in a Vendor

Encapsulated option with Option Code 43. The method used depends on

the DHCP server’s capabilities and what options are already in use by

other vendors.

The IP Phone rejects any DHCPOFFER and DHCPACK messages that

do not contain the following options:

• a router option — IP Phone requires a default gateway (router)

• a subnet mask option

• a vendor-specific option or a site-specific option

The vendor-specific option code is 43. A Windows NT DHCP Server

(up to SR4) supports only 16 octets of data for the vendor-specific

option, which is insufficient to support the minimum length of the IP

Nortel Communication Server 1000

IP Phones Fundamentals

NN43001-368 05.02 26 May 2009