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 ...
10er (DE, Fig. 12) should be set to 1. If thisis not done in the DTE, it will be done bythe access node of the network. If overloadoccurs, queued frames whose DE bitis set will be discarded before other, unmarkedframes. The DTE is allowed to exceedthe assigned CIR by apredeterminedvalue, the Excess Burst Size. If largeramounts of data are being transmitted, allexcess frames will be discarded, regardlessof the load situation in the network,Fig. 14.An overload situation may remain in thenetwork even after all frames with set DEbits have been discarded. In order to furtherorganise the continued discarding, itis also possible to establish an order of priorityfor the different virtual connections.This is up to the manufacturer or operatorto decide, since the Frame Relay recommendationdoes not define any priorities.Supervision of the interfaceSupervisory frames with reserved DLCIaddresses are used for two purposes: forsupervision and for exchange of informationbetween the network and the DTEs.The link status and the information indicatingactive or inactive link are transferredin these frames. Indication of the status ofpermanent virtual connections and executionof changes in the DLCIs used areother functions of these informationframes.Implementation of FrameRelay-Frame Relay can be implemented in differentways:• As part of a private packet switching networkthat also supports other types ofcommunication, such as X.25 and SNA.• As a virtual private network consisting ofan operator network section dedicated touse by a specific customer, a companyor an organisation.• As a public Frame Relay service providedby the PTT or some other operator.• As a hybrid solution: a private networkcovering the primary geographical areaof a company, and peripheral units connectedvia public Frame Relay services.Fig. 14Handling an overload situation in a Frame Relaynetwork. Each Virtual Connection through thenetwork is assigned a Committed InformationRate (OR). The CIR value is generated by thenetwork and indicates that the DTE on this connectionis capable of sending a given amount(Committed Burst Size, Be) of data during a givenperiod of time (Tc), CIR=Bc Tc. Provided thenetwork is not overloaded, the DTE is allowed tosend a somewhat larger amount of data (ExcessBurst Size, Be) on the connection. But if an overloadsituation occurs, this extra amount will becancelled and any frames above the CIR valuediscarded. If the DTE exceeds the maximum permissiblequota (Be + Be) for a given connection,the network will always discard the excess numberof framesCommitted RateMeasurement IntervalERICSSON REVIEW No. 1-2, 1992
11Frame Relay in ERIPAXEricsson's packet switching system ERIPAX iscontinuosly improved to meet the emerging demandsfor an enhanced packet switching service.Frame Relay services is currently added toERIPAX functionality.The implementation of Frame Relay in ERIPAXconforms to applicable international standards butalso includes additional services of value to theuser. To follow and influence the Frame Relaystandardisation process, Ericcson has been amember of the Frame Relay Forum since itsfounding in 1991.Frame Relay will be offered as an integrated softwarefunction in the ERIPAX node, allowing packetswitching and Frame Relay services to co-existin the node. Packet-switched services, such asX.25 and SNA/SDLC, may use Frame Relay as abearer service within the network and - withoutany additional investments - benefit by the higherspeed and capacity of the Frame Relay service.If so required, certain parts of a network can berestricted for use of one of the services only.Frame Relay services in ERIPAX will be describedby Goran Ingemarsson and Bo Karlander in an articlein the next issue of Ericsson Review.A study of the 1000 largest companies inthe USA, made by the Yankee Group andpublished in Data Communications International,January 1992, shows that 64 %of these companies were planning to installcommunications systems based onFrame Relay technology within the nexttwo to five years. Western Europe is probablysome years behind the developmentin the US, where deregulation has playedan important role and where LANs are inmore frequent use than in Europe.Advantages of Frame RelayFrame Relay is basically a simplified implementationof the X.25 protocol, aimedat facilitating a marked increase of thetransmission speed on network links andDTE lines. The advantages of the X.25 protocolremain unchanged, i.e. efficient trafficinterleaving and the possibility of establishingseveral connections over thesame physical channel. The consequencesof the removal of the error-correctingfunction and the greatly simplified flowcontrol on individual network links aremore than compensated for by the improvedtransmission quality obtained byextensive digitalisation of the public transmissionfacilities.Frame Relay is therefore a logical consequenceof the technological development— in two respects. Firstly, in terms of thenew needs emerging in the increasinglyadvanced computer environment. Secondly,in terms of faster and cheaper transmission(characterised by a lower level ofsensitivity to interference), which is the resultof improved digital technology andwhich is probably also enhanced by the ongoingderegulation of public telecom operations.Another important factor is the ease withwhich Frame Relay can be introduced intoday's data communications environment.A PC, a workstation or a server becomesa Frame Relay DTE after addingsoftware of low complexity. Frame Relay,just as X.25, is a specification of the interfacebetween the DTE and the network,and many of the functions offered today bythe X.25 networks (such as alternativerouting and charging) can be directly appliedwhen implementing Frame Relayfunctionality in an X.25 node.No network-to-network interface is specifiedin the present version of the standard,but the standardisation work is in progress.The result of this work is likely to furtherstrengthen the position of Frame Relay asan attractive public and private service.Effective LAN-to-LAN communication isthe driving force behind the introduction ofFrame Relay, but once the Frame Relaynetworks have been implemented it will bepossible to offer better solutions to otherdatacom needs too. Therefore, it is not surprisingthat Frame Relay has been widelyaccepted, both by operators and by suppliersof equipment for corporate datacomnetworks.ERICSSON REVIEW No. 1-2, 1992
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11<strong>Frame</strong> <strong>Relay</strong> in ERIPAXEricsson's packet switching system ERIPAX iscontinuosly improved to meet the emerging dem<strong>and</strong>s<strong>for</strong> an enhanced packet switching service.<strong>Frame</strong> <strong>Relay</strong> services is currently added toERIPAX functionality.The implementation of <strong>Frame</strong> <strong>Relay</strong> in ERIPAXcon<strong>for</strong>ms to applicable international st<strong>and</strong>ards butalso includes additional services of value to theuser. To follow <strong>and</strong> influence the <strong>Frame</strong> <strong>Relay</strong>st<strong>and</strong>ardisation process, Ericcson has been amember of the <strong>Frame</strong> <strong>Relay</strong> Forum since itsfounding in 1991.<strong>Frame</strong> <strong>Relay</strong> will be offered as an integrated softwarefunction in the ERIPAX node, allowing packetswitching <strong>and</strong> <strong>Frame</strong> <strong>Relay</strong> services to co-existin the node. Packet-switched services, such asX.25 <strong>and</strong> SNA/SDLC, may use <strong>Frame</strong> <strong>Relay</strong> as abearer service within the network <strong>and</strong> - withoutany additional investments - benefit by the higherspeed <strong>and</strong> capacity of the <strong>Frame</strong> <strong>Relay</strong> service.If so required, certain parts of a network can berestricted <strong>for</strong> use of one of the services only.<strong>Frame</strong> <strong>Relay</strong> services in ERIPAX will be describedby Goran Ingemarsson <strong>and</strong> Bo Karl<strong>and</strong>er in an articlein the next issue of Ericsson Review.A study of the 1000 largest companies inthe USA, made by the Yankee Group <strong>and</strong>published in <strong>Data</strong> <strong>Communications</strong> International,January 1992, shows that 64 %of these companies were planning to installcommunications systems based on<strong>Frame</strong> <strong>Relay</strong> technology within the nexttwo to five years. Western Europe is probablysome years behind the developmentin the US, where deregulation has playedan important role <strong>and</strong> where LANs are inmore frequent use than in Europe.Advantages of <strong>Frame</strong> <strong>Relay</strong><strong>Frame</strong> <strong>Relay</strong> is basically a simplified implementationof the X.25 protocol, aimedat facilitating a marked increase of thetransmission speed on network links <strong>and</strong>DTE lines. The advantages of the X.25 protocolremain unchanged, i.e. efficient trafficinterleaving <strong>and</strong> the possibility of establishingseveral connections over thesame physical channel. The consequencesof the removal of the error-correctingfunction <strong>and</strong> the greatly simplified flowcontrol on individual network links aremore than compensated <strong>for</strong> by the improvedtransmission quality obtained byextensive digitalisation of the public transmissionfacilities.<strong>Frame</strong> <strong>Relay</strong> is there<strong>for</strong>e a logical consequenceof the technological development— in two respects. Firstly, in terms of thenew needs emerging in the increasinglyadvanced computer environment. Secondly,in terms of faster <strong>and</strong> cheaper transmission(characterised by a lower level ofsensitivity to interference), which is the resultof improved digital technology <strong>and</strong>which is probably also enhanced by the ongoingderegulation of public telecom operations.Another important factor is the ease withwhich <strong>Frame</strong> <strong>Relay</strong> can be introduced intoday's data communications environment.A PC, a workstation or a server becomesa <strong>Frame</strong> <strong>Relay</strong> DTE after addingsoftware of low complexity. <strong>Frame</strong> <strong>Relay</strong>,just as X.25, is a specification of the interfacebetween the DTE <strong>and</strong> the network,<strong>and</strong> many of the functions offered today bythe X.25 networks (such as alternativerouting <strong>and</strong> charging) can be directly appliedwhen implementing <strong>Frame</strong> <strong>Relay</strong>functionality in an X.25 node.No network-to-network interface is specifiedin the present version of the st<strong>and</strong>ard,but the st<strong>and</strong>ardisation work is in progress.The result of this work is likely to furtherstrengthen the position of <strong>Frame</strong> <strong>Relay</strong> asan attractive public <strong>and</strong> private service.Effective LAN-to-LAN communication isthe driving <strong>for</strong>ce behind the introduction of<strong>Frame</strong> <strong>Relay</strong>, but once the <strong>Frame</strong> <strong>Relay</strong>networks have been implemented it will bepossible to offer better solutions to otherdatacom needs too. There<strong>for</strong>e, it is not surprisingthat <strong>Frame</strong> <strong>Relay</strong> has been widelyaccepted, both by operators <strong>and</strong> by suppliersof equipment <strong>for</strong> corporate datacomnetworks.ERICSSON REVIEW No. 1-2, 1992
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