Data Communications Networking Devices - 4th Ed.pdf

1.14 THE PHYSICAL LAYER _______________________________________________________ 105ApplicationsSince its initial development in 1989 HSSI has been incorporated into a largenumber of products designed to support high speed serial communications. Inaddition,its relatively simple interface has resulted in its use at data rates thatwould normally require the use of a V.35 or RS-499 interface. For example,manyrouters,multiplexers,inverse multiplexers and Channel Service Units operating at1.544 Mbps can now be obtained with HSSI as well as products designed tooperate at T3 44.736 Mbps) and SONET Synchronous Transmission ServiceLevel 1 STS-1) 51.84 Mbps).High Performance Parallel InterfaceThe High Performance Parallel Interface HIPPI) represents an ANSI switchednetwork standard which was originally developed to support direct communicationsbetween mainframes,supercomputers and directly attached storage devices.A series of ANSI standards currently de®ne the physical layer operation of HIPPIas well as data framing,disk and tape connections and link encapsulation. Table1.27 lists ANSI HIPPI related standards and their areas of standardization.Table 1.27 ANSI HIPPI-related standardsANSI standardArea coveredX3.183-1991Physical layerX3.222-1993Switch controlX3.218-1993Link encapsulationX3.210-1992Framing protocolANSI/ISO 9318-3Disk connectionsANSI/ISO 9318-4Tape connectionTransmission distanceAlthough its name implies the use of a parallel interface,a number of extensions toHIPPI resulted in its ability to support a 300 meter serial interface over multimodecopper as well as parallel transmission via a 50-pair shielded twisted-pair wiringgroup for relatively short distances. In its basic mode of operation a HIPPI basednetwork consists of two computers connected via a pair of 50-pair copper cables toHIPPI channels on each device. Each 50-pair cable supports transmission in onedirection,resulting in the pair of 50-pair cables providing a full-duplextransmission facility. That transmission facility can extend up to 25 meters andoperate at either 800 Mbps or 1.6 Gbps,the latter accomplished by doubling thedata path.Through the use of one or more HIPPI switches you can develop an extendedHIPPI network. That network can use copper cable between switches whichpermits cabling runs up to 200 meters in length,or a ®ber extender can be used tosupport extending the distance between switches up to 10 km. The ®ber extender