Expansion cards allow the connection of additional station and trunk modules, as well as NAM voice mails to a Norstar Modular system.The 6-port fiber expansion card allows up to six modules to be added to the system via a fiber DS-30 connection cable (included with the purchase of an expansion module).The 6-port fiber combination clocking/expansion card serves the dual purpose of allowing up to six modules to be added to the system as well as providing the clocking necessary to run a digital T-1 or PRI circuit.For purposes of T-1 or PRI clocking only (no expansion requirements), a Services Card would be recommended. Services Cards have no expansion jacks.The 2-port fiber expansion card allows up to two modules to be added to the system via a fiber DS-30 connection cable (included with the purchase of an expansion module).Refurbished 6-port and 2-port copper expansion cards are available for the M8x24 systems as well (discontinued).