Frame Relay - for Faster and More Efficient Data Communications ...

4Fig. 2Distributed computer environment based on LocalArea Networks using internal transmissionspeeds of several Mbit/s. This places exactingdemands on the datacom network, which is requiredto provide cost-effective LAN-to-LANcommunicationsFig. 3The transfer time varies with the link transmissionspeed, which in turn is dependent on thetype of file transferred. When programs or filescontaining graphics are to be transferred, a linktransmission speed of 64 kbit/s will result in unsatisfactoryresponse timeFig. 4A client-server application makes efficient use ofthe combined processing power provided by thehost computer and the personal computer/workstation.This makes exacting demands on thenetworkType of file 64 kbit's 2 Mbit*2 text pages 1/3s 1/100 s1 page of spreadsheet 6 s 1/5 s1 drawing page 15 s 1/2 sLarge program file 1 min 2 sThe design of protocols for Local Area Networkshas been based on the demand forthese networks to be capable of handlingshort response times and transferringlarge amounts of data (file transfers, etc).This has been achieved by building LANswith internal cabling for data transmissionat high speeds. The Wide Area Networks,on the other hand, use the existing transmissioninfrastructure, which is primarilydesigned for telephone traffic.Increasingly, applications in the LAN environmentare introducing more graphics,which accentuates the need for large fileinformation transfer at high speed. An LANcan manage transmission speeds of 4,10or 16 Mbit/s, or even more. The transfertime is short even for large information volumes,and databases, program librariesand advanced I/O devices serving the entirenetwork have become a reality. In atypical LAN, data is processed on theuser's own personal computer or workstation.The user connects himself to the networkonly to print out files or to transfer filesor programs to a server or retrieve themfrom that server. Information is transferredin the form of short bursts at a relativelylow frequency.The need for communications outside thelocal environment requires adistributed infrastructure,as exemplified in Fig. 2. ButLAN-to-LAN traffic in Wide Area Networksis not altogether uncomplicated. Both technologyand economy make the transmissionspeed on the links between local environmentsa restricting factor. Fig. 3 illustratesthe differences in transfer time fordifferent file types transferred on a link at9.6 kbit/s, 64 kbit/s and 2 Mbit/s.New architecturesThe processing power offered by today'sPCs and workstations is sufficient for mostapplications. Databases, program librariesand many other applications are characterisedby the need for common resourcesfor storing information or for tellingusers where a certain type of informationcan be accessed. In LANs, thesecommon resources are available in servers.In most PC networks, however, servershave so far been used only as an extrahard disk for storage and printout of data.All processing of data has taken placein the local workstation. In order to makemore efficient use of the processing powerERICSSON REVIEW No. 1-2, 1992