Specifications

Administrator’s Guide for SIP-T2xP IP Phones
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and other control information are carried in tagged data items that are stored in the
options field of the DHCP message. The data items themselves are also called options.
DHCP can be initiated by simply connecting the IP phone with the network. IP phones
broadcast DISCOVER messages to request the network information carried in DHCP
options, and the DHCP server responds with specific values in corresponding options.
The following table lists common DHCP options supported by IP phones.
Parameter
DHCP Option
Description
Subnet Mask
1
Specify the client’s subnet mask.
Time Offset
2
Specify the offset of the client's subnet in
seconds from Coordinated Universal Time
(UTC).
Router
3
Specify a list of IP addresses for routers on the
client’s subnet.
Time Server
4
Specify a list of time servers available to the
client.
Domain Name
Server
6
Specify a list of domain name servers
available to the client.
Log Server
7
Specify a list of MIT-LCS UDP servers available
to the client.
Host Name
12
Specify the name of the client.
Domain Server
15
Specify the domain name that client should
use when resolving hostnames via DNS.
Broadcast
Address
28
Specify the broadcast address in use on the
client's subnet.
Network Time
Protocol Servers
42
Specify a list of NTP servers available to the
client by IP address.
Vendor-Specific
Information
43
Identify the vendor-specific information.
Vendor Class
Identifier
60
Identify the vendor type.
TFTP Server
Name
66
Identify a TFTP server when the 'sname' field in
the DHCP header has been used for DHCP
options.
Boot file Name
67
Identify a boot file when the 'file' field in the
DHCP header has been used for DHCP
options.