3Com 5500-EI PWR Reference Manual page 708

By default, a DHCP server global address pool does not assign Option 184 and the corresponding
sub-options to the client.
Related commands: dhcp server voice-config.
Examples
# Enter system view
<Sysname> system-view
System View: return to User View with Ctrl+Z.
# Enable the DHCP server to support Option 184 in global address pool 123. The NCP IP address is
1.1.1.1 and the IP address of the alternate server is 2.2.2.2. The voice VLAN is enabled, with the ID
being 3. The fail-over IP address is 3.3.3.3 and the dialer string is 99*.
[Sysname] dhcp select global all
[Sysname] dhcp server ip-pool 123
[Sysname-dhcp-pool-123] voice-config ncp-ip 1.1.1.1
[Sysname-dhcp-pool-123] voice-config as-ip 2.2.2.2
[Sysname-dhcp-pool-123] voice-config voice-vlan 3 enable
[Sysname-dhcp-pool-123] voice-config fail-over 3.3.3.3 99*
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