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

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40Fig. 9Combination of layering and partitioning; exampleLRDXCLocal networkRegional networkDigital cross connectFig. 10PDH-based Transport Network Layered Model(CEPT hierarchy)local level, NET 2 at the district, NET 3 atthe regional and NET 4 at the national level.Signal transport in real networks leads toa combination of layering and partitioning,Fig. 9. A 2 Mbit/s signal passes throughdigital cross connects (DXC) located in alocal network, is transmitted via a 140Mbit/s line between the cross connectsand via an STM-1 system between the localnetworks, and then passes againthrough DXCs in a local region. Three ofthe DXCs use the 2 Mbit/s and one of themthe 140 Mbit/s switching level. The exam-pie shows that all Reference Points andTransport Processing Functions involvedin the transport of information can be identifiedas belonging to a certain layer of thetransport network and a certain level of abstraction.In CCITT draft Recommendation G.snal,the transport network is divided into threelayers, which in turn can be divided intosublayers. The layers are as follows:-The Circuit Layer network is concernedwith the transfer of information betweenusers, in direct support of telecommunicationservices. This circuit definition isspecifically used to describe network architectureand differs from CCITT circuitdefinitions used for other purposes-The Path Layer network supports theCircuit Layer network and may consist ofvarious sublayers- The Transmission Media Layer networksupports the Path Layer network andconsists of a function for transfer of informationbetween two nodes and afunction concerned with the physical media.The concepts introduced above are applicableto transport networks based on PDHand SDH.Plesiochronous Digital Hierarchy(PDH)In this article, the following PDH characteristicsignal types are considered:DSn Binary digital signals with datarates and framing according to theorder n in Rec. G.702. (Signalsgenerated and processed in terminalequipment)Dn Digital signals with data rates andpulse masks according to Rec.G.703. (Signals transmitted viastandardised interfaces).ERICSSON REVIEW No. 1-2, 1992
41Fig. 11Functional Model of PDH multiplexerFramed 2 Mbit/s signalHDB-3 coded 2 Mbit's signalClient-to-server AdaptationTrail TerminationIn PDH, the following transport networklayers are defined:- The Path Layer network consists of sublayersfor various data rates (e.g. DSn =2, 8, 34 and 140 Mbit/s sublayers)- The Transmission Media Layer networkconsists of a Signal Layer (e.g. Dn = 2,8, 34, and 140 Mbit/s) and a media-dependentPhysical Media Layer (for thetransmission of non-standardised 2, 8,34, 140 and 565 Mbit/s line signals).The use of the Functional Model will be illustratedby a number of examples basedon the Transport Network Layered modelfor PDH, Fig. 10. The lines between theblocks represent different alternatives fortransporting information. The Physical MediaLayer belonging to the transport networkrepresents the physical media appearingin the transmission network.Plesiochronous digital networks containthe following Transport Processing Functions:PPA Plesiochronous Path Adaptationfor the client-server relationshipsDSn-1/DSn required for multiplexing/demultiplexingand framingPPTSLASLTPPIPlesiochronous Trail Terminationsfor the DSn Trails required for overheadinsertion and extractionSignal Layer Adaptation for theclient-server relationships DSn-1/Dn required for line coding/decodingSignal Layer Trail Terminations forthe Dn Trails required for line codecheckingPlesiochronous Physical Interfacesrequired for the adaptation ofsignals to cables, and vice versa.Fig. 11 shows in detail the unidirectionalsignal transport of 30x64 kbit/s circuitsbetween a multiplexer and a demultiplexer.The lower part of the figure shows thephysical representation in the transmissionnetwork; the upper part the functionalrepresentation in various layers of thetransport network. The send terminal containsthe multiplexing function, generatesthe 2 Mbit/s framed signal, and containsfunctions for signal conversion to HDB-3coding and for connection of the interfacecable. The receive terminal contains thecorresponding functions. The TransportFunctions appear in various transportERICSSON REVIEW No. 1-2, 1992
Page 1: ERICSSONREVIEW1-21992Frame Relay -
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Page 6 and 7: 4Fig. 2Distributed computer environ
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Page 16 and 17: Box 1Code39, the first alphanumeric
Page 18 and 19: 16Fig. 6Cable attenuation test at E
Page 20 and 21: 18Fig. 9Installing the Dehlfi syste
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Page 24 and 25: 221 Use the user's model2 Introduce
Page 26 and 27: 24Fig. 5Advanced Human Factors desi
Page 28 and 29: Fig. 7User interface for PBX attend
Page 30 and 31: Cell-voltage EqualisersSeries BMP 1
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Page 36 and 37: In Search of Managed ObjectsWalter
Page 38 and 39: Fig. 4The telecommunication network
Page 40 and 41: Fig. 6Functional Model illustrating
Page 44 and 45: 42Table 2Relationship between Funct
Page 46 and 47: 44No1PPI2PPI3SLTTransport Function(
Page 48 and 49: 46Table 4SDH functions, Resources a
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Page 52 and 53: 50Fig. 21Information Model of PDH d
Page 54 and 55: Fig. 25Information Model of SDH mul
Page 56 and 57: 54Table 5Cross-connect functions, R
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