The Site Specific Option Number (SSON) is used by IP phones to request information from a DHCP server that is specific to the phones and not to other IP devices being supported by the DHCP server. The number must match a similarly-numbered 'option' set on the DHCP server that defines the various settings required by the phone.

The default SSON used by Avaya 1600 Series and 9600 Series phones is 242. For phones being supported by IP Office DHCP, the SSON used by the phone must match one of the site specific option numbers set in the IP Office configuration