A Line Card is a device interfacing between access lines with switches, routers or other network devices and access devices. There are digital and analog line cards at various speeds, which may connect to electric cables or optical fibers. The basic functions of the digital Line Cards for data networks are packet forwarding, ping response, and packet fragmentation. The line card takes care of:

• queueing, such as First In, First out (FIFO) and Modified Deficit Round Robin (MDRR)
• congestion control - Weighted Random Early Detection (WRED)
• other features such as Access Lists (ACLs), Committed Access Rate (CAR) and statistics of data flow

Each digital data packet Line Card can be divided into three major sections:

• Physical Layer Interface Module - This is the hardware module that terminates the physical connection (media dependent; therefore, Asynchronous Transfer Mode (ATM), Packet-over-SONET (POS), and Ethernet)
• Switching Engine - This forwarding engine prepares packets for transmission across the switching fabric to the destination LC. It handles packet lookups, rewrites, buffering, and congestion control.
• Fabric Interface - The Fabric Interface ASIC (FIA) prepares the packets for transmission across the switching fabric to the destination LC. It takes care of fabric grant requests, fabric queuing, per-slot multicast replication, and so on.

Line Card