COSA and SRP are synchronous serial boards for ISA bus which have two channels. Each channel can be set up to one of the X.21, V.24, V.35 and V.36 hardware interfaces. The Linux kernel driver and user-space tools serve for setting up and using the COSA and SRP boards under Linux. It allows you to use it with the following link-level protocols: Cisco HDLC , synchronous PPP, or as the frame-based character device.