The 1OC-12/STM-4 SRP line card equips the Cisco 12000 series Internet Router 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.