Data compression reduces the size of data frames to be transmitted over a network link, thus reducing the time required to transmit the frames across the network. Data compression works by providing a coding scheme at each end of a transmission link that allows characters to be removed from the frames of data at the sending side of the link and then replaced correctly at the receiving side. Because the condensed frames take up less bandwidth, more frames can be transmitted per unit of time. Data compression schemes used in internetworking devices are referred to as loss less compression algorithms. These schemes reproduce the original bit streams exactly, with no degradation or loss, a feature required by routers and other devices to transport data across the network. The two most commonly used compression algorithms on internetworking devices are the Stacker compression and the Predictor data compression algorithms.The CSA provides high-performance, hardware-based, data compression capabilities. The CSA faceplate has no media interfaces. The CSA offloads all compression- and decompression-related packet handling from host processors by compressing and decompressing packets passing through interfaces on serial port adapters. The CSA supports simultaneous Stacker data compression algorithms, with independent full-duplex compression and decompression capabilities. The CSA supports only PPP and Frame Relay encapsulation.This compression module uses 256 VCs Stac algorithm. Based on the Lempel-Ziv compression algorithm, stacker compression was developed by STAC Electronics. The Stacker algorithm uses an encoded dictionary that replaces a continuous stream of characters with codes. The symbols represented by the codes are stored in memory in a dictionary-style list. Because the relationship between a code and the original symbol varies as the data varies, this approach is more responsive to variations in the data. This flexibility is particularly important for local-area network (LAN) data, because many different applications can be transmitting over the wide-area network (WAN) at any one time. In addition, as the data varies, the dictionary changes to accommodate and adapt to the varying needs of the traffic.