Frame Relay - for Faster and More Efficient Data Communications ...
Frame Relay - for Faster and More Efficient Data Communications ... 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
Fig. 5The X.25 protocol places the users' data In packets,which are sent one after the other on theline. In this way, maximum use Is made of the capacityof the connection. Each connection is virtual,which means that several sessions can usethe same physical line simultaneouslyPacket, virtual channel 1Packet, virtual channel 2Fig. 6X.25 switching permits maximum utilisation ofthe capacity of the connection, all of which isavailable for use by the party who needs it forthe momentBandwidthprovided by the server, a new type of applicationhas emerged in which the serverand the workstation share the processingwork. This new way of designing applicationsis called the client-server model,Fig. 4.In the future, the client-server concept maypermit use of the network as an externaldata bus between workstation and server,a configuration which will place very highdemands on fast and safe informationtransfer in the network.The client-server model does not requirethat the user knows where the requestedinformation is stored. It may be in a serverin his own LAN or in another LAN thatforms part of the network. The location ofdata is transparent to the user: he addressesthe service he wants to use, leaving itto the network to keep track of where it isexecuted. These conditions set the requirementsfor LAN-to-LAN traffic thatcharacterise future development of longdistancenetworks.Improved transport networksThe ongoing modernisation of public telecomnetworks replaces analog transmissionto a great extent with more robust digitaltechnology, including extensive useof fibre optic cables that are immune to interference.The result is significantly decreasederror rate and a dramatic reductionin the leasing cost of digitalconnections for transmission speeds of 64kbit/s and upwards.Planning for highertransmission speedThe Local Area Networks have the capacityrequired to meet the need for highspeedconnections with very short delay,which is the result of increased workstationprocessing power and larger informationvolume in each transfer. The digitalisationof public networks makes it possibleto meet this need in Wide Area Networkstoo. However, a traffic pattern characterisedby short information bursts and hightransmission speed means poor utilisationof point-to point connections between twoLocal Area Networks. Communication protocolswhich permit interleaving of trafficfrom a large number of users over a singlecommunication line, are a prerequisitefor cost-effective handling in Wide AreaNetworks.X.25So far, X.25, or packet switching, has beenthe leading established communicationsprotocol capable of interleaving data frommany users over a single line. Packetswitching is used both for public servicesand in private networks in order to ensuresatisfactory economic utilisation of networktrunks, Fig. 5.X.25 is an effective method for meetingintermittent data communication needs,and today's X.25 networks have worldwidecoverage. X.25 does not stipulate pre-allocationof a specific portion of the bit flowto a specific connection between two users.As opposed to time division multiplexing,this means that the whole bit flow isavailable to the user who has data to sendat the moment, Fig. 6. This also means thatseveral so-called "virtual connections" areset up in parallel over the same physicallink. Each of these connections is allocateda logical channel: a unique identity indicatedin the data packet header.Two types of connection are defined inX.25: Permanent Virtual ConnectionsERICSSON REVIEW No. 1-2, 1992
- Page 1: ERICSSONREVIEW1-21992Frame Relay -
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Fig. 5The X.25 protocol places the users' data In packets,which are sent one after the other on theline. In this way, maximum use Is made of the capacityof the connection. Each connection is virtual,which means that several sessions can usethe same physical line simultaneouslyPacket, virtual channel 1Packet, virtual channel 2Fig. 6X.25 switching permits maximum utilisation ofthe capacity of the connection, all of which isavailable <strong>for</strong> use by the party who needs it <strong>for</strong>the momentB<strong>and</strong>widthprovided by the server, a new type of applicationhas emerged in which the server<strong>and</strong> the workstation share the processingwork. This new way of designing applicationsis called the client-server model,Fig. 4.In the future, the client-server concept maypermit use of the network as an externaldata bus between workstation <strong>and</strong> server,a configuration which will place very highdem<strong>and</strong>s on fast <strong>and</strong> safe in<strong>for</strong>mationtransfer in the network.The client-server model does not requirethat the user knows where the requestedin<strong>for</strong>mation is stored. It may be in a serverin his own LAN or in another LAN that<strong>for</strong>ms part of the network. The location ofdata is transparent to the user: he addressesthe service he wants to use, leaving itto the network to keep track of where it isexecuted. These conditions set the requirements<strong>for</strong> LAN-to-LAN traffic thatcharacterise future development of longdistancenetworks.Improved transport networksThe ongoing modernisation of public telecomnetworks replaces analog transmissionto a great extent with more robust digitaltechnology, including extensive useof fibre optic cables that are immune to interference.The result is significantly decreasederror rate <strong>and</strong> a dramatic reductionin the leasing cost of digitalconnections <strong>for</strong> transmission speeds of 64kbit/s <strong>and</strong> upwards.Planning <strong>for</strong> highertransmission speedThe Local Area Networks have the capacityrequired to meet the need <strong>for</strong> highspeedconnections with very short delay,which is the result of increased workstationprocessing power <strong>and</strong> larger in<strong>for</strong>mationvolume in each transfer. The digitalisationof public networks makes it possibleto meet this need in Wide Area Networkstoo. However, a traffic pattern characterisedby short in<strong>for</strong>mation bursts <strong>and</strong> hightransmission speed means poor utilisationof point-to point connections between twoLocal Area Networks. Communication protocolswhich permit interleaving of trafficfrom a large number of users over a singlecommunication line, are a prerequisite<strong>for</strong> cost-effective h<strong>and</strong>ling in Wide AreaNetworks.X.25So far, X.25, or packet switching, has beenthe leading established communicationsprotocol capable of interleaving data frommany users over a single line. Packetswitching is used both <strong>for</strong> public services<strong>and</strong> in private networks in order to ensuresatisfactory economic utilisation of networktrunks, Fig. 5.X.25 is an effective method <strong>for</strong> meetingintermittent data communication needs,<strong>and</strong> today's X.25 networks have worldwidecoverage. X.25 does not stipulate pre-allocationof a specific portion of the bit flowto a specific connection between two users.As opposed to time division multiplexing,this means that the whole bit flow isavailable to the user who has data to sendat the moment, Fig. 6. This also means thatseveral so-called "virtual connections" areset up in parallel over the same physicallink. Each of these connections is allocateda logical channel: a unique identity indicatedin the data packet header.Two types of connection are defined inX.25: Permanent Virtual ConnectionsERICSSON REVIEW No. 1-2, 1992
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