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1、6 ATM Network Handling,EN/LZT 123 6795 R2A,Copyright Ericsson AB,2003,-197,Frame Synchronization,Before a node can start search for synchronization it must be ableto know what is the beginning and end of the ATM cells thatarrives to the node.This is done in when Cell Delineation isperformed.Network
2、Synchronization is responsible for the distribution ofclocks,and allows the clocks to operate at the same frequency indifferent nodes.Node Synchronization functionality is the basis for the numberingof frames between the RNC and RBS nodes,and for frame timing.The correct operation of Node Synchroniz
3、ation functionality isdependent on the proper operation of Network Synchronization.Frame Synchronization functionality is responsible for thenumbering of user frames,and for the transmission and receptionof frames to and from the RNC node at the correct times,tocompensate for transfer and processing
4、 delay in the RNC-RBSpath.The correct operation of the Frame Synchronizationfunctionality on Intra-RNS case is dependent on the properoperation of the Node Synchronization functionality.CELL DELINEATIONCell delineation and scrambling objectivesCell delineation is the process,which allows identificat
5、ion of thecell boundaries.The ATM cell header contains a HEC field,which is used toachieve cell delineation.The ATM signal is required to be self-supporting in the sense that it has to be transparently transported onevery network interface without any constraints from thetransmission systems used.Sc
6、rambling will be used to improve thesecurity and robustness of the HEC cell delineation mechanism asdescribed below.In addition it helps randomizing the data in theinformation field for possible improvement of the transmissionperformance.Any scrambler specification must not alter the ATMheader struc
7、ture,-198,Copyright Ericsson AB,2003,EN/LZT 123 6795 R2A,SYNCH,PRESYNC,CPP SurveyCell delineation algorithmCell delineation is performed by using the correlation between theheader bits to be protected(32 bits)and the relevant control bits(8bits)introduced in the header by the HEC using a shortened c
8、ycliccode with generating polynomial x8+x2+x+1.The figure belowshows the state diagram of the HEC cell delineation method.NOTE For a cell-based Physical Layer,during descrambleracquisition and verification states,only the last six bits of the HECfield are to be used for cell delineation checking,and
9、 all eightthereafter.For an SDH-based interface,all 8 bits of the HEC areused for acquiring cell delineation.Correct HECHUNT,Incorrect HEC,Cell-by-Cell,DELTA,ALPHA,consecutiveincorrect HEC,consecutivecorrect HECCell-by-CellFigure 6-42 Cell delineation state diagramThe details of the state diagram ar
10、e described below:1.In the HUNT state,the delineation process is performed bychecking bit by bit for the correct HEC(i.e.syndrome equalszero)for the assumed header field.For the cell-based PhysicalLayer,prior to descrambler synchronization,only the last sixbits of the HEC are to be used for cell del
11、ineation checking.Forthe SDH-based interface,all 8 bits are used for acquiring celldelineation.Once such an agreement is found,it is assumedthat one header has been found,and the process enters thePRESYNC state.When octet boundaries are available withinthe receiving Physical Layer prior to cell deli
12、neation as with theSDH-based interface,the cell delineation process may beperformed octet-by-octet.,EN/LZT 123 6795 R2A,Copyright Ericsson AB,2003,-199,6 ATM Network Handling2.In the PRESYNC state,the delineation process is performed bychecking cell by cell for the correct HEC.For the cell-basedPhys
13、ical Layer,prior to descrambler synchronization,only thelast six bits of the HEC field are to be used for cell delineationchecking.The process repeats until the correct HEC has beenconfirmed DELTA times consecutively,at which point theprocess moves to the SYNC state.If an incorrect HEC is found,the
14、process returns to the HUNT state.The total number ofconsecutive correct HECs required to move from the HUNTstate to the SYNC state is therefore DELTA+1.3.In the SYNC state the cell delineation will be assumed to belost if an incorrect HEC is obtained ALPHA timesconsecutively.4.For SDH-based Physica
15、l Layer,cells with correct HECs(or cellheaders with single bit errors which are corrected)that areprocessed while in the SYNC state shall be passed to the ATMlayer.For cell-based Physical Layer,cells with correct HECs(or cell headers with single bit errors which are corrected)thatare processed while
16、 in the SYNC state shall be passed to theATM layer provided the descrambler is in steady state.Idlecells and Physical Layer OAM cells are not passed to the ATMlayer.The parameters ALPHA and DELTA are to be chosen to make thecell delineation process as robust and secure as possibleIdle cellsIdle cell
17、s cause no action at a receiving node except for celldelineation including HEC verification.They are inserted anddiscarded for cell rate decoupling.Idle cells are identified by thestandardized pattern for the cell header shown in the table below.,-200,Copyright Ericsson AB,2003,EN/LZT 123 6795 R2A,C
18、PP SurveyTable 6-1 Header pattern for idle cell identification(before scrambling)NETWORK SYNCHRONIZATIONThe Network Synchronization function in CPP supports the MasterSlave configuration of the Synchronization Network.In the master-slave configuration,the master clock is normallyprovided by a primar
19、y reference clock(PRC)to which all nodesare slaved.The synchronization reference is transmitted via thetransport network or via the dedicated synchronization network.Cascading of CPP nodes in terms of Network Synchronization ispossible.Transport signals provided by a CPP node are usable forNetwork S
20、ynchronization by other nodes.The network synchronization reference can be provided by anytype of SDH/PDH traffic carrying signals that are connected to theCPP Exchange Terminals(ET)presupposed that the signalcharacteristics fulfils the requirements for synchronization.Alsodedicated synchronization
21、references,e.g.2 MHz or 2Mb/s can beconnected to the node.If external synchronization references are lost or disconnected thesystem clock can also be temporarily provided by an internal clockin the hold over mode,EN/LZT 123 6795 R2A,Copyright Ericsson AB,2003,-201,CPP,CPP,6 ATM Network HandlingCPPCP
22、PCPP,PRC,CPPFigure 6-43 The Network Synchronization Reference originates from theprimary reference clock and is transported via the transport network.Synchronization Inputs in CPP NodeTraffic carrying synchronization signalsThe network synchronization references can be provided by trafficcarrying fr
23、amed line signals that are connected to the ETs in thenode.Any type of traffic carrying line signals that are terminated in CPPshall be possible to be used as synchronization references.,CPP Survey,-202,Copyright Ericsson AB,2003,EN/LZT 123 6795 R2A,NetworkSynchronization,System Clock and Radio BB C
24、lockStatus Interface for clocks A/B,TU Dedicated synchronizationinput port A/B:1,5/2/10 MHz,E,E,I,E,EI,IE,I,System clock/local clockselection status(provided by the,Logical interfaces,Physical interfacesPhysical line terminationinput ports onET-xx,Physical line terminationoutput ports on ET-xx19,44M
25、Hz system clock(after the redundancy terminationon device boards),30,72MHz Radio BB clock A/B(for generation of application clockson TU A/B)2 MHz synchronization reference output(extracted from the 155 Mb/s linetermination input ports on ET-M4x boards),ManagementInterface,GPS interface A/B on TU,(on
26、ly HW),E,system clock redundancy terminationon each device board)E=Node external interfaceI=Node internal interfaceFigure 6-44 Interfaces to the Network Synchronization functionThe generic CPP internal interfaces are not shown.Dedicated synchronization signalsThe dedicated synchronization signals ca
27、n be connected to thenode via ET-xx or via TU.The following types of signals can beconnected:,1.544 MHz,2.048MHz and 10MHz,one common input on TU1.5/2 Mb/s framed signals(any type used in the node),input on,ET-M1/MC1The framed line signals may be traffic carrying,containingordinary data,or dedicated
28、 synchronization signals,containingsome framed pattern,which means,all ONEs.Synchronization reference selectionSynchronization references are connected via the physical linetermination or dedicated synchronization reference inputs.The CPP internal synchronization reference is extracted from therecei
29、ved signal and transferred to the clock function.The operator can choose between two different types ofsynchronization references:,6 ATM Network Handling,EN/LZT 123 6795 R2A,Copyright Ericsson AB,2003,-203,Traffic carrying line signals.The synchronization references are extracted at the physicalline
30、 terminations from the framed line signals.Dedicated synchronization signals.,These signals are non-traffic carrying framed or non-framedsignals,(2 Mb/s or 2 MHz)Reference redundancy and reference selectionThe network synchronization function coordinates the referenceselection within the node.Coordi
31、nation includes for example thereference preselection,control of reference switching,faultlocalization and fault management.Co-operation is needed between the network synchronizationfunction and other CPP system functions,(for example withphysical path termination function).The system supports the s
32、ynchronization reference redundancy asfollows.,It is possible to preselect at a maximum of eight referencesto be used as synchronization references in the node.The active reference is chosen according to signalavailability,synchronization status of the signal and thepreference order.Each preselected
33、 synchronization reference is given apriority by the operator.There are eight priority levels,i.e.as many as is the maximum number of the references thatcan be preselected.A dedicated priority level shall be given to each preselectedreference.The system will not accept the same priority level for tw
34、oor more references.The default value for synchronization usage for all ports(that are possible to be selected as a reference)is“do notuse as synchronization reference”before the possiblepriority is set.Operator has to select and to give the priorityfor the ports that are wanted to be subject to the
35、 referenceselection process.,CPP Survey,-204,Copyright Ericsson AB,2003,EN/LZT 123 6795 R2A,The system will automatically select the most preferredavailable reference,i.e.the reference with highest availablepriority.The main principle is that the same reference will be,provided for both TUs and for
36、both the system and the radioBB clock.Revertive reference switchingOnly revertive reference switching is supported.Revertive switching means that if a failed reference restores and ithas higher priority than what the current reference in use has,thereference with the higher priority shall be taken a
37、utomatically inuse.An originally failed reference must be fault free for the“wait torestore time”before it can be regarded to be usable forsynchronization again.The status of the restored reference(subjectto the selection process)shall be changed from“failed”to“ok”.The revertive switching does not a
38、pply to references which hasbeen detected to be failed due to“loss of tracking”(LTR)failure ifthere are other non failed references available.The reason is that the possible restoration from this failure can notbe detected reliably by the CPP node.Operator interaction is needed(to clear the LTR stat
39、us for areference)and to take these references again in normal use for thereference selection process.A reference with failure status“faileddue to loss of tracking fault”may only be tried to be taken into useagain autonomously by the synchronization function if there areonly LTR failed references av
40、ailable.Application Specific AdaptationsThe Network Synchronization function in CPP is responsible togenerate both the System Clock(the transport clock)and the radioBB reference clock.The radio BB clock is used/needed in RBS and RNC applicationsfor the application specific functions on the TUB and f
41、orgeneration of the radio frequency clocks in RBS.,EN/LZT 123 6795 R2A,Copyright Ericsson AB,2003,-205,6 ATM Network HandlingIn a non radio application only the system clock is used.(Theradio BB clock may though be generated all the time since thecommon oscillator is used as the hold over clock and
42、radio BBclock is used for the traceability supervision.)The System Clock is used by the CPP for the transport functions inthe node.System Clock GenerationThe system clock shall be phase locked to the selectedsynchronization reference.The system clock shall follow the phaseof the selected active refe
43、rence in conditions when the reference isfault free.By a fault free synchronization reference is meant that for examplethe jitter/wander characteristics of the reference shall be in thelimits of the specifications and there shall not be signal interruptsor phase discontinuity.The system clock filter
44、s out jitter and wander from thesynchronization reference according to specifications for thesystem clock(transport clock).If synchronization reference is changed/lost the phasesynchronization of system clock to the original reference is lost andsynchronization to the new reference is performed.The
45、clock characteristics are specified later in this document.,-206,Copyright Ericsson AB,2003,EN/LZT 123 6795 R2A,LOCKE DMODE,No reference,selected,2c)1),Locked tothe referenceLOSS OFTRACK INGMODE,2a),CPP SurveySystem clock modes to be shown for the operatorWarm restartAccuracy not defined,1),HOLD OVE
46、RMODE2)hold overtime expiredFREE RUNNINGMODE,1)START UP,Hold over accuracyaccording to G.813 opt.1Accuracy is betterthan 4.6 ppm,3),Reference is not traceable,3),MODEAccuracy not definedFault(including faults in the Radio BB clock)1)A traceable referenceis available2a)No reference available2b)this m
47、ode only Radio BB clock is in Sync1/2/32c)No reference available andRadio BB clock is inLocked Mode,Re-t race1)2b),Figure 6-45 System Clock working modes on TUThe System clock can work in the next physical(modes 1-6)andlogical(1-8)working modes.The modes 1-8 are indicated for theoperator via the Syn
48、chronization MO.The modes 1-6 are indicatedfor the system clock users via the SCSPI interface.1.Start-up(Warm up,including the oscillator warm-up time)2.Locked mode(normal working mode,locked to the reference)3.Hold over mode(no reference available)4.Free running mode(no reference available)5.Failur
49、e mode(when a HW fault is detected/suspected)6.Loss of tracking mode(when the clock can not trace thereference)7.Unknown(the system clock quality is not known)8.Not applicable(TU board is not present),restart,via start/restart.2)No reference available,EN/LZT 123 6795 R2A,Copyright Ericsson AB,2003,-
50、207,6 ATM Network HandlingStart-up mode includes the oscillator warm-up time,that is neededin case when no reference is available before the clock can switchto the free running mode.If a reference exists immediately afterwarm restart the clock can switch immediately to the locked modewhen the SW is
