remote axe 10 subscriber switch in a container an optical fibre line ...

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188Fig. 9Synchronization of the transmultiplexerMO_•—,____Master oscillatorIncoming timingOutgoing timingTDM signalsFDM signalsFig. 10Synchronization of the transmultiplexer whenworking towards a synchronous digital networkSynchronization pathclocks. This means that problems areavoided that would otherwise arise, forexample because of the different frequencyaccuracy requirements that applyfor FDM and TDM signals respectively.This method also eliminates therisk of slip, and data signals can thereforebe transmitted over the speechchannels without excessive error rates.The timing signal for the outgoing PCMflow is generated by a built-in oscillatorin the PCM part concerned, fig.9. Thecarriers in the FDM part are derived froman external basic frequency. 12 or124kHz, which in accordance with normalFDM practice is available in the centralfrequency generating equipment ofthe terminal.The transmultiplexer can work towardsa synchronous digital network. In thiscase the recovered timing signal fromthe incoming PCM streams controls theinternal clocks so that the outgoing signalshave the same bit rate, fig. 10. Thecontrol signal is obtained by making asimple loop connection via two externalcables on the front of the equipment.SignallingSignalling information on carrier circuitsis usually transmitted by means ofchannel-associated outband signallingat 3825 Hz. In digital circuits one or moresignalling channels in the common signallingtimeslot, T16, of the PCM systemare used foreach speech channel. In thetransmultiplexer the signalling informationin the outband signal is converted,for each channel, to the correspondinginformation in timeslot 16 and vice versa.This method makes the transmultiplexerwholly transparent to differentsignalling diagrams as long as only onebit in T16 is used foreach speech channelOn the FDM side the equipment caneasily be matched to outband signallingwith either high or low level. Only lowlevel is suitable for continuous signallingdiagrams. The equipment can alsobe adapted to either of the two possiblesignalling diagrams where "tone" correspondsto "1" or "0".Signalling system R2, in its original ormodified form, is widely used for internationaland national traffic The systemis designed to transmit the line signallingin the signalling channel, whereasthe register signalling is carried out bymeans of MFC in the speech channel.The equipment meets the relevantCCITT recommendations for signallingsystem R2. For example, it is equippedwith pilot receivers for interruption control.In the analog version of system R2 a linkisestablished foreach channel betweenbit a and the signalling frequency,whereas bit b in the FDM-PCM directionis used to transmit alarm informationfrom the pilot receiver.In FDM systems there are only two signallingconditions in each direction perspeech channel, and the analog versionof system R2 therefore contains certaintiming conditions which supplementthe two signalling conditions. In the digitalversion of system R2. however, twobits (a and b) per speech channel areused to transmit the corresponding information,which amounts to four signallingconditions. This means that simplerterminal circuits can be used in theswitching equipment.Using the digital version of R2 meansthat extensive recoding of the signallinginformation has to be carried out in thetransmultiplexer However, this recodingcan be arranged for all 60 channelsby adding just two control units containingmicroprocessors The generalnature of processor control means thatadaptation can also be made to othersignal conversion requirements.The transmultiplexer is transparent tochannel-associated inband signalling. Avariant of the transmultiplexer withoutsignalling equipment is available fornetworks with inband signallingCommon channel signalling with a capacityof 64 kbit/s is normally not possibleon circuits containing transmultiplexers,since the transmission capacityof a transmultiplexer channel is limitedto what the band 300-3400 Hz permits.This applies for all transmultiplexers, regardlessof design approach However,common channel signalling at a reducedrate can be used on a speechchannel via modems.
189The transmultiplexer with no signallingequipment offers economical advantagesin networks where common channelsignalling is used and the signallingis transmitted via a separate circuitReliabilityTransmission equipments require ahigh degree of reliability. Breakdowns inthe long-distance network, with the consequentloss of traffic, can be very expensive.Poor reliability in the otherparts of the network can lead to unacceptablyhigh maintenance costs.Ericsson has developed several generationsof FDM and PCM systems. One ofthe objectives in this development workhas been to obtain high reliability. Thisaim has been met by adhering to strictdesign rules and by careful choice ofcomponents. At the same time the numberof components has been kept low.The power dissipation has also beenkept low, and since this gives a low operatingtemperature it is another factorcontributing to high reliability The reliabilityof the transmultiplexer is expectedto be very high since most componentsare well-proven types that havebeen used in the individual FDM andPCM systems.The structure of a system has an effecton its function. For example, it determinesthe consequences of differentfaults. The structure of Ericssons transmultiplexersis such that very few itemsare common to many channels. Theprobability that a fault will affect severalchannels is low, and the probability of atotal breakdown is extremely low. Sincethe transmultiplexer is thus built up ofsystem components with very high reliabilityand has been given the most adequatestructure, the prerequisites havebeen created for very good operationalreliability of the equipment. This is confirmedby the calculations of the MTBF(Mean Time Between Failures) that havebeen carried outFlexibilityMany administrations use the supergroupas the smallest extension unit,which gives many advantages as regardshandling and administration.However, the group may be a more suitablebasic unit in certain network configurationsand for special temporary requirementsIn Ericsson's transmultiplexerthe groups are therefore accessibleboth towards the TDM and the FDMside. A program channel, high-speeddata modem, through-connectionequipment etc. can be connected towardsthe FDM side.The equipment can be made transparentto a channel having a transmissionspeed of 64 kbit/s. This means thatcommon channel signalling can be usedover a transmultiplexer circuit. For example,remote subscriber stages forAXE 10 can be connected over a carriercircuit via transmultiplexers supplementedby external modems, fig. 11.This can solve certain network problems,for example in large-mesh ruralnetworks. The transmission capacity requiredfor the remote subscriber stage isoften no more than 30 channels, andthus the loss of the 12 channels that areneeded for the 64 kbit/s transmission isquite acceptable. The necessary synchronizationinformation is transmittedvia the data modem.Individual speech channels are also accessibleand can be used, for example,for connecting data modems in eitherdirection.Fig. 11Transmission of a synchronous 64kbit/s channelover a carrier system via transmultiplexersT16BG64 kbit/s interlaceBasic group interface
Page 1: ERICSSONREVIEW41982REMOTE AXE 10 SU
Page 4 and 5: ;2Remote AXE 10 Subscriber Switchin
Page 6 and 7: Fig. 3The container is brought out
Page 8 and 9: An Optical Fibre Line Systemfor 34
Page 10 and 11: Fig. 3Repeater spacings and hardwar
Page 12 and 13: 182The primary alarms are those rec
Page 14 and 15: 184Technical dataDigital interface
Page 16 and 17: Fig. 2, leftThe transmultiplexer as
Page 20 and 21: Fig. 13The M5/BYB bay equipped with
Page 22 and 23: Fig. 17ZAJ 5x24/2x60, transmultiple
Page 24 and 25: ERITEX10 for Teletex and WordProces
Page 26 and 27: Fig. 5The central processing unit i
Page 28 and 29: 198Fig. 8The floppy disc unit with
Page 30: 200- finding space for a document o
Page 33 and 34: Local Area Radio System-LARSHans Li
Page 35 and 36: Fig. 5One of the thick film hybrids
Page 37 and 38: 207Technical data for LARSSelective
Page 39 and 40: 209BERTH EKLUNDHDAVID RAPPDepartmen
Page 41 and 42: 211over, the type of traffic handle
Page 43 and 44: 213Models of CPA comparison between
Page 45 and 46: ETable 2The table shows the differe
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