Synchronous Serial Interface and PRIs

UNIX systems provide excellent support for high-performance T1/E1 and some T3/E3 interface cards, as well as for some High-Speed Serial Interface (HSSI) adapters (up to 52 Mbps) and PRIs. Several vendors provide dedicated drivers and management software for open-source Unices. The NICs integrate nicely into a Cisco WAN network and provide varying telecommunication characteristics:

• Clear-channel/channelized/fractional operation

• Multiple ports

• Physical interfaces: V.35, V.36, X.21, RS-232

• With or without integrated CSU/DSU

• RAS option: with or without integrated digital modems (DSPs)

• PRI signaling

• Internal/external clocking

Almost all synchronous serial NICs support the following Layer 2 encapsulation formats:

• LAPB (X.25 Layer2)

• Frame Relay

• Cisco HDLC

• Synchronous PPP

Frame Relay services are deployed by carriers up to T3 bandwidth in the United States and up to E1 bandwidth in Europe and most other countries in 56/64-kbps or sometimes even smaller increments (subrates/derived channels). Configuration of X.25 or Frame Relay is similar to Cisco configurations with regard to virtual/subinterface concepts and topology (point to point, point to multipoint, and so on).