The Cisco 12000 Series 2-Port Channelized OC-3c/STM-1c (DS1/E1) Line Card provides Cisco 12000 Series Internet Routers support for DS-1/E-1 aggregation. Designed for telcos and Internet service providers (ISPs), this card supports two OC-3c/STM-1c ports, each of which can be configured with multiple channels of (n)xDS-1, DS-1, fractional DS-1, or DS-0 in a Synchronous Optical Network (SONET) environment or (n)xE-1, E-1, fractional E-1, or 64 kbps in a Synchronous Digital Hierarchy (SDH) environment. Cisco 12000 Series channelized line cards integrate the channel service unit/data service unit (CSU/DSU) function on a per-port basis. In conjunction with other Cisco 12000 Series line cards, a single router in the carrier point of presence (POP) can scale fractional DS-1 to OC-192c in a SONET environment and from fractional E-1 to STM-64c (VC-4-64c) in an SDH environment.