The Cisco 12000 OC-48c/STM-16c Rev-B Dynamic Packet Transport (DPT) Rev-B line cards allow rings of up to 128 nodes whereas the Rev-A cards have a 62 node limit. The Rev-B cards also incorporate a Stratum-3 oscillator for increased transmit frequency accuracy. The Rev-B cards are backward compatible and can interwork with Rev-A cards. They require an IOS software release level of 12.0(15)S or greater.