The 1OC-12/STM-4 SRP line card equips the Cisco series 12000 Gigabit Switch Router (GSR) with a total of two OC-12c fiber-optic SC duplex ports. The line card provides two duplex SC connections for either the single-mode or multimode version. The synchronous payload envelope (SPE) is concatenated, which increases efficiency by eliminating the need to partition the bandwidth. The 1OC-12/STM-4 SRP line card is slot independent. The 1OC-12/STM-4 SRP line card allows networks to accommodate large-scale network topology, leverage fiber-optic capacity at OC-12 line rates, control the rate at which new packets are inserted on the media, allow data fair-shared access to the OC-12 rings, implement protection mechanisms, including wrap or unwrap, in the event of fiber or node failure, and support both single-mode and multimode fiber transmissions.