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8/6/2019 Switch Signaling
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SWITCHING
& SIGNALLING
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INTRODUCTING TO SWITCHING contd«
4 .THE FIRST ELECTRONIC EXCHANGE WAS
SPACE DIVISION SWITCHING WHICH USED ONE
PHYSICAL PATH FOR ONE CALL.
5. T/A DEVELOPED TIME DIVISION SWITCHING
WHICH ENABLED SHARING A SINGLE PATH BY
SEVERAL CALLS
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INTRODUCTING TO SWITCHING contd«
SOME IMPORTANT TERMS .
BUSY HOUR :The hour in which max traffic occurs.BUSY HOUR TRAFFIC : It is the average value of maximum
traffic in the busy hour
HOLDING TIMEHOLDING TIME : The duration during which equipments are heldwhen a call is made called holding time
GRADE OF SERVICE : Allowable lost calls is called Grade Of Service If one call is lost per 500 calls then GOS=1/500 =0.002
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INTRODUCTING TO SWITCHING contd«
SOME IMPORTANT TERMS .
TRAFFIC INTENSITY :Average number of calls simultaneously
in progress. The unit of tfc intensity is Erlang . If S is the sum
of holding time during the period T then tfc intensity is S/T
PROBLEM : Calling rate per line per day of an exchange of
5000 lines is 6.0 & busy hour tfc is 12 % , holding time per call
is 2.5 minutes. Find busy hour tfc in Erlang
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SOME ELECTRONIC EXCHANGES
E10B was the first digital electronic exchange . But it hadcertain drawbacks
yThe ISDN and CCS7 signaling was not supported.
yThe traffic handling capacity and BHCA capacity was low.
In our country where small capacity exchanges wererequired, CDOT switch (CDOT 128P, 256P, SBM, MBMetc) was installed. It is indigenous technology.
Now 256P independent exchanges have been convertedinto AN-RAX (Access Network Ruaral Automatic
Exchange) and they are parented to nearby CDOT
SBM/MBM or NT exchange. With this development now allremote ANRAXs can be maintained from the SBM/MBM.BSNL has 44% CDOT switches.
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SOME ELECTRONIC EXCHANGES Contd«
� Beside CDOT switch the following switchingsystems (NT) were inducted in BSNL network.
� 1. EWSD Supplied by M/s Siemens, Germany
�2. OCB-283 Supplied by M/s Alcatel, France
� 3. 5ESS Supplied by M/s Lucent, USA
� 4. AXE-10 Supplied by M/s Ericsson
� Some new Salient features of those NT switches
are:� They support ISDN, C#7, V5.2, centrex facility.
� The traffic handling capacity and BHCA capacityare sufficient.
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Facilities provided by Electronic Exchanges.
Facilities offered by electronicexchanges can be categorized in threearts.
� (I) Facilities to the Subscribers.
� (ii) Facilities to the Administration.
� (iii) Facilities to the MaintenancePersonnel.
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Facilities to the Subscribers.
� Some Important Facilities to the Subscribers.
� MFC Push-button Dialing :All subscribers in an electronic
exchange can use push-button telephones, which use DualTone Multi- frequency
� Priority Subscriber Lines: These subscribers are
attended by the central processor, even during heavycongestion
� Outgoing Call Restriction :This can be easily achieved by
using certain service codes.
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Facilities to the Subscribers.
Contd«
� Abbreviated Dialing:This shortens the process of dialing all the digits.
� Call Forwarding : The subscriber having the call forwarding
facility can keep his telephone in the transfer condition in case he wishes his
incoming calls to be transferred to another telephone number during his
absence.
� Conference Calls: Subscribers can set up connections to more
than one subscriber and conduct telephone conferences under the provision of
this facility.
� Call Waiting :The µCall Waiting¶ service notifies the
already busy subscriber of a third party calling him. He isfed with a special tone during his conversation.
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Facilities to the Administration
� Some Important Facilities to the Administration
� 1.Reduced Switch Room Accommodation: Reduction in
switch room accommodation to about 1/6th to 1/4th ascompared to Cross-bar system is possible.
� 2.Faster installation and Easy Extension: The reduced
volume of equipment, printed cards and automatic testing of exchange
equipment result in faster installation (about six months for a 10,000
line exchange) Due to modular structure, the expansion isalso easier
and quicker.
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Facilities to the Administration Contd«
� 3.Economic Consideration :The switchingspeed being much faster as compared toCross-bar system, the use of principle of fullavailability of trunk circuits and other
equipment makes the system economicallysuperior to electromechanical systems.
4. Automatic test of Subscriber line :Routinetesting of subscriber lines for Insulation,capacitance, foreign potential, etc., are
automatically carried out during night. Theresults of the testing can be obtained in theprintout form, the next day.
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Facilities to the Maintenance
personnel Contd«
� Blocking: In case of congestion or breakdown of aspecific route, facility of blocking such routes is available
� Overloading Security : Overloading of central
processor in an electronic exchange can lead to disastrousresults. To prevent this, central processor occupancy ismeasured automatically periodically, when it exceeds aspecified percentage, audio-visual alarms are activated, inaddition to printing out the message. Maintenancepersonnel have the following options.
� (i) Block some of the facilities temporarily, or
� (II) Reduce the load by blocking some of the congested routes.
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Constraints of Electronic ExchangesContd«
5)Static Electricity & Electromagneticinterference.
� Due to the presence of static electricity on thebody of persons handling the equipment, the
stored data may get vitiated. Handling of PCB¶ stherefore, should be done with utmost care
� 6)PCB Repair The repair of PCB¶ s is extremelycomplicated
7) Faster Obsolescence : The equipment becomesobsolete before it can possibly complete one third of its life
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DIGITAL SWITCHING,CONCEPT OF TIME & SPACE SWITCHING
� A Digital switching system, is one in which
signals are switched in digital form. Thesesignals may represent speech or data. Thedigital signals of several speech samples aretime multiplexed on a common media beforebeing switched through the system.
� To connect any two subscribers, it is necessary to
interconnect the time-slots of the two speech
samples which may be on same or different PCM
highways.� The digitalised speech samples are switched in two
modes, viz., Time Switching and Space Switching.
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TIME & SPACE SWITCHING
� SPACE SWITCHING : HERE TIME SLOT OF I/C & O/G PCM
HIGHWAYS ARE INTERCONNECTED. SO THERE IS NO DELAY IN
SWITCHING
� TIME SWITCHING : HERE TIME SLOT IS CHANGED. So there is
delay.
The prime purpose of an exchange is switching i.e.to provide path for transmission of speech between(1) SUBSCRIBERS IN THE SAME EXCHANGE ( LOCAL
SWITCHING )
(2) SUBSCRIBER OF ONE EXCHANGE TO OTHER EXCHANGE (TRUNK CALL)
(3) BETWEEN TWO TRUNK EXCHANGE CALLED TANDEMEXCHANGE.
THE OTHER FUNCTIONS OF AN EXCHANGE ARE
SIGNALLING , CHARGING & BILING.
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Digital Space Switching contd..
� Illustration
Consider the transfer of a samplearriving in TS7 of I/C HWY X1 to O/G
HWY Y3. Since this is a space switch,the sample will be transferred withoutany time delay, via the appropriate
cross point. In other words, theobjective is to connect TS7 of HWY X1and TS7 of HWY Y3.
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Practical Space Switch
In a practical switch, the digital bits are
transmitted in parallel rather than serially,
through the switching matrix
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Practical Space SwitchContd«
In a serial 32 time-slot PCM multiplex,
all the bits of the various time-slots follow oneanother. This single wire stream of bits, when
fed to Serial to Parallel Converter is
converted into 8-wire parallel output.
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Practical Space SwitchContd«
For example, all 8 bits corresponding to TS3
serial input are available simultaneously on eightoutput wires (one bit on each output wire), during
just one bit period
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Practical Space SwitchContd«
This parallel output on the eight wires is fed to the
switching matrix. It can be seen that during one full time-slot
period, only one bit is carried on the each output line, whereas 8
bits are carried on the input line during this period. Therefore,
bit rate on individual output wires, is reduced to 1/8th of input
bit rate=2048/8=256Kb/s
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Practical Space SwitchContd«
Due to reduced bit rate in
parallel mode, the cross point is required to
be operated only for 1/8th of the timerequired for serial working. It can, thus, be
shared by eight times more channels, i.e.,
32 x 8 = 256 channels, in the same frame.
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Practical Space Switchcontd«
Since The eight bits of one TS are carried on eight
wires, each cross point have eight switches to
interconnect eight input wires to eight output wires .
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Practical Space Switchcontd«
For example, to connect 40 PCM I/C highways, a
matrix of 40x 40 = 1600 cross points each having a
single switch, is required in serial mode working.Whereas in parallel mode working, a matrix of (40/8
x 40/8) = 25 cross point is sufficient.
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Practical Space Switchcontd«
As eight switches are required at each cross point 25
x 8 = 200 switches only are required. Thus, there is areduction of the matrix by 1/8th in parallel mode
working, hence reduction in size and cost of the
switching matrix.
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Digital Time Switch
� PrincipleA Digital Time Switch consists of two
memories, viz., a speech or buffer memory to
store the samples till destination time-slotsarrive, and a control or connection or address
memory to control the writing and reading of
the samples in the buffer memory and
directing them on to the appropriate time-slots.
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Digital Time Switch
� The writing/reading operation in the speechmemory is controlled by the Control Memory.It has same number of memory locations asfor speech memory, i.e., 32 locations for 32channel PCM system. Each location containsthe address of one of the speech memorylocations where the channel sample is eitherwritten or read during a time-slot. These
addresses are written in the control memoryof the CC of the exchange, depending uponthe connection objective.
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Digital Time Switch
� Time switch can operate in two modes, viz.,� I. Output associated control
In this mode of working, 32 samples of I/C PCM arewritten cyclically in the speech memory locationsin the order of time-slots of I/C PCM, i.e., TS1 is
written in location 1, TS2 is written in location 2,and so on
The contents of speech memory are read on output PCM
in the order specified by control memory. Each location
of control memory is rigidly associated with the
corresponding time-slot of the O/G PCM and containsthe address of the TS of incoming PCM to be connected
to.
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TIME SWITCHING (Output associated control )
I/C PCM TS4
00
01
O6 TS04
31
TIME
SLOT
COUNTER
00
02
03
04
31
OG PCM TS6
CONTROL/
CONNECTION/ ADDRESS
MEMORY
BUFFER/SPEECH MEMORY
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Digital Time Switch
� II. Input associated control� Here, the samples of I/C PCM are written in acontrolled way, i.e., in the order specified bycontrol memory, and read sequentially.
� Each location of control memory is rigidly associated with the
corresponding TS of I/C PCM and contains the address of TS
of O/G PCM to be connected to.
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TIME SWITCHING (Input associated control )
I/C PCM TS4
00
01
O4 06
31
TIME
SLOT
COUNTER
00
02
03
06
31
OG PCM TS6
CONTROL/
CONNECTION/ ADDRESS
MEMORY
BUFFER/SPEECH MEMORY
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T-S-T SWITCHINGSPACE SWITCH
HWY0 ,TS4 I/T-0 TS 10TS 11 O/T-0 TS4
I/C TIME
SWITCH O/G TIMESWITCH
I/C PCM HIGH WAYSO/G PCM H/WAYS
HWY 1
HWY 2
I/T-3 TS 11HWY3,TS6TS 10
O/T-3TS6
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BLOCK DIAGRAM OF SPC (STORED PROGRAM
CONTROL) EXCHANGE
LINES & TRUNKSTERMINAL EQUIPMENT
SWITCHING NETWORK
DISTRIBUTORSIGNALLING
TERMINALSCANNER MARKER
CENTRAL CONTROL
(CC)& MEMORIESomc
bus
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BLOCKS OF ELECTRONIC EXCHG
� 1. Terminal Equipment: Subscribers & Trunk ccts are terminated here.
� 2.Switching Network : It may be time or spaceswitching.
� 3.Switching processors :Consists of processors& memories
� 4. Switching Peripherals::: (scanner,distributer
& marker ) interface between control system ,trml equipment
& switching n/work
� 5. OMC.
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BLOCKS OF ELECTRONIC EXCHG
contd«� Scanner :To detect & inform CC of all events
� Marker : It sets up & release path through
switching network under control of CC.
� Distributor :It is the buffer between high speedCC & slow speed signalling terminal ccts. It
operates on trunks & svc circuits under CC.
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BLOCKS OF ELECTRONIC EXCHG
contd«
Function of subscriber line interface :
B:BATTERY FEED. O:OVERLOAD
PROTECTIONR:RINGING,S:SUPERVISION OF LOOP
STATUS
C:CODEC (A/D, D/A CONVERTER)
H:HYBRID , T :TESTING.
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RSU (Remote Switching Unit )
� Standalone RSU : All exchanges have thisfacility while in case of main link with the
exchange is down subscribers of RSU can
call among themselves. In 5ESS & CDOT
Exchanges in standalone condition
metering is done while in case of OCB-283
and EWSD metering is not possible.
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Signaling in Telecom Network
�� The term ³signaling´ consists of a wordThe term ³signaling´ consists of a word
signal, which means ³indication´ about somesignal, which means ³indication´ about someinformation.information.
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Signaling in Telecom Network
�� The procedure for transfer of theThe procedure for transfer of thesignal between two nodes/points insignal between two nodes/points in
telecom network is known as signalingtelecom network is known as signaling..
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Signaling in Telecom Network
contd«� 1)Subscriber Signaling: Signaling systems used
between the exchange and subscriber equipment
2) Trunk Signaling :Trunk signaling are signals used
between public exchanges. They are used to connect
exchanges.
exchg1 exchg2
Subscriber
Signaling
Subscriber
Signaling
Trunk
signaling
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Signaling in Telecom Network
contd«.
� Subscriber Line signalling1) Calling Subscriber Line Signaling:
In automatic exchanges the power is fed over the
subs loop by the centralized battery at the exchange.
Normally, it is 48 V. The power is fed irrespective of
the state of the subscriber, viz., idle, busy or talking.
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Signaling in Telecom Network
contd«.
� Subscriber Line signalling
2) Call report
� When the subscriber is idle, the lineimpedance is high. The line impedance falls,
as soon as, the subscriber lifts the hand-set,
resulting in increase of line current. This isdetected as a new call signal.
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Signaling in Telecom Network contd..
� Call connection
1) A request for originating a call is initiated whenthe calling subscriber lifts the handset.(off hook)
2) The exchange (after verification of subs status &
connecting an appropriate equipment to receivethe address information ) sends dial-tone signal tothe calling subscriber to start dialing.
3) When the calling subscriber dials the number,
the called number is transmitted to the exchange,
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Signaling in Telecom Network contd..
4)The address receiver is disconnected after thereceipt of complete address. The exchangesends any one of the following signals.
If the called number is free, the exchange sendsringing current to him (This is typically 25or 50Hz with suitable interruptions.) &Ring-back tone to the calling subscriber otherwisebusy tone or announcement if the called subscriber
is busy.
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Signaling in Telecom Network contd..
5) When the called subscriber, lifts the hand-set onreceipt of ring, the line impedance goes low. This isdetected by the exchange which cuts off the ringingcurrent and ring-back tone and establishes a connectionbetween the calling and called subscribers.
6) In case trunk call the originating exchange seizes an idletrunk ckt which is connected to a digit register at theterminating exchange.
7) The originating exchange begins to send digits & abovesteps are followed as before.
Ring back, tone and ringing current are alwaystransmitted from the called subscriber local exchange
and busy tone and recorded announcements, if any,by the equipment as close to the calling subscriber aspossible to avoid unnecessary busying of equipmentand trunks.
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Signaling in Telecom Network
contd«.
� 3)Address Signal : (Means Dialing) : It is two types.A) Decadic Dialling & B)Multi frequency Push-button Dialling
� The address digits may be transmitted as a sequence of interruption of the DC loop by a rotary dial or a decadicpush-button key pad.
� The number of interruption (breaks) indicate the digit,exept 0, for which there are 10 interruptions. The rate of such interruptions is 11 per second and the make/break ration is 1:2. There has to be a inter-digital pause of a fewhundred milliseconds to enable the exchange to distinguish
between consecutive digits. This method is, therefore,relatively slow.
Signaling in Telecom Network contd
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Signaling in Telecom Network contd«
� B)Multi frequency Push-button Dialling
� It uses two sets of four voice frequencies. Pressing a button (key),generates a signal comprising of two frequencies. one from each group.Hence, it is also called Dual-Tone Multi-frequency (DTMF) dialling.By this method, the dialling time is reduced and almost 10 digits can betransmitted per second.
Key pad : (1209+697 FOR 1 ,1336+697 FOR 2 LIKE THIS)
1209HZ 1336HZ 1477HZ
697HZ 1 2 3
770HZ 4 5 6
852HZ 7 8 8
941 HZ * 0 #
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Signaling in Telecom Network
contd«.5) Release signal
When the calling subscriber releases i.e., goes onhook, the line impedance goes high. The exchangerecognizing this signal, releases all equipmentinvolved in the call. This signal is normally of morethan 500 milliseconds duration.
6) Permanent Line (PG) SignalPermanent line or permanent glow (PG) signal is sent to the calling
subscriber if he fails to release the call even after the called subscriberhas gone on-hook and the call is released after a time delay. The PGsignal may also be sent, in case the subscriber takes too long to dial. It isnormally busy tone.
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Signaling in Telecom Network
contd«.
Inter exchange signaling or trunk signaling:The Exchanges are to provide certain signaling facilities::
1) The originating exchange should be able to call the
required exchange.
2) Return of supervisory signal to the originatingexchange when called subscriber answers & calledsubscriber clears
3) Maintaining engaged condition of the o/g exchange tillthe calling party clears.
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Signaling in Telecom Network
contd«.Inter exchange signaling or trunk signaling: It is two types:
1)Line signaling (Supervision Signaling )
2) Register signaling ( Address signaling)
Line signaling (Supervision Signaling ):Is used to control andmonitor the status of the transmission circuits. It isconcerned with conveying information on the state of the
line or channel, such as on-hook, off-hook i.e. seizure signaland idle state signal.
ThisThis signalssignals dodo notnot containcontain anyany specificspecificsubscribersubscriber informationinformation suchsuch asas thethe directorydirectory numbernumber..
RegisterRegister SignalingSignaling (( isis alsoalso calledcalled AddressAddress SignalingSignaling ))
ItIt isis usedused toto transfertransfer thethe specificspecific subscribersubscriber informationinformationnecessarynecessary toto connectconnect thethe callingcalling partyparty toto thethe calledcalled partyparty.. ThisThis signalingsignalingisis relatedrelated toto aa certaincertain callcall.. ExamplesExamples of of registerregister signalingsignaling informationinformationareare thethe calledcalled party'sparty's directorydirectory numbernumber andand thethe callingcalling party'sparty's categorycategory..
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Signaling in Telecom Network
contd«.DIFFERENTDIFFERENT TYPESTYPES OFOF LINELINE SIGNALLINGSIGNALLING
1)1) RINGRING DOWNDOWN SIGNALLINGSIGNALLING ::InIn thisthis methodmethod 1717 HzHz ringingringing currentcurrent isis sentsent onon thethe
junction junction byby thethe O/GO/G exchangeexchange..22)) DCDC SIGNALLINGSIGNALLING ::
TheThe simplestsimplest cheapest,cheapest, andand mostmost reliablereliable systemsystem
of of signalingsignaling onon trunks,trunks, waswas DCDC signaling,signaling, alsoalso knownknownasas metallicmetallic looploop signaling,signaling, exactlyexactly thethe samesame asas usedusedbetweenbetween thethe subscribersubscriber andand exchange,exchange, ii..ee..,,
LINELINE LOOPLOOP ISIS MADEMADE OR OR BROKENBROKENCORRESPONDINGCORRESPONDING CKTCKT SEIZER SEIZER OR OR RELEASERELEASE
(( OFF/ONOFF/ON--HOOKHOOK SIGNALSIGNAL OFOF THETHE SUBSCRIBER SUBSCRIBER..))
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Signaling in Telecom Network
contd«.EE & & MM SignalsSignalsEE && MM leadlead signalingsignaling maymay bebe usedused forfor signalingsignaling onon perper--trunk trunk basisbasis..
AnAn additionaladditional pairpair of of circuit,circuit, reservedreserved forfor signalingsignaling isis employedemployed.. OneOnewirewire isis dedicateddedicated toto thethe forwardforward signalssignals ((M((M--WireWire forfor transmittransmit oror mouth)mouth)whichwhich correspondscorresponds toto receivereceive oror R R--leadlead of of thethe destinationdestination exchange,exchange, andandthethe otherother wirewire dedicateddedicated toto thethe backwardbackward signalssignals (E(E--wirewire forfor receivereceive ororear)ear) whichwhich correspondscorresponds transmittransmit oror sendsend wirewire oror SS--LeadLead of of thethe
destinationdestination exchangeexchange..
HEREHERE SIGNALSIGNAL ININ ONEONE PAIR PAIR && SPEECHSPEECH ONON OTHER OTHER PAIR PAIR..
SPEECHSPEECH
MM (MOUTH)(MOUTH) EE (EAR)(EAR)
EE (EAR)(EAR) MM (MOUTH)(MOUTH)
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Signaling in Telecom Network
contd«.REGISTER REGISTER SIGNALLINGSIGNALLING ::
TRUNK TRUNK REGISTER REGISTER ISIS ANAN ADDRESSADDRESS DIGITDIGIT RECEIVER RECEIVER ..
THISTHIS SIGNALSIGNAL ISIS USEDUSED FOR FOR TRANSMITTINGTRANSMITTING ADDRESSADDRESSINFORMATIONINFORMATION..
REGISTER REGISTER SIGNALSSIGNALS AREARE INTERCHANGEDINTERCHANGED BETWEENBETWEENREGISTERSREGISTERS DURINGDURING AA PHASEPHASE BETWEENBETWEEN RECEIPTRECEIPT OFOF TRUNK TRUNK SEIZURESEIZURE SIGNALSIGNAL && THETHE EXCHANGEEXCHANGE SWITCHINGSWITCHING TOTO THETHESPEECHSPEECH PHASEPHASE..
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Signaling in Telecom Network
contd«.
Compelled Signalling :The term Compelled Signalling refers to the
case where receipt of each signal needs to be
explicitly acknowledged before the next signalis able to be sent. R2 register signalling is
Example of compelled signalling.
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Signaling in Telecom Network
contd«.R R22 SignallingSignallingCCITTCCITT standardizedstandardized thethe R R22 signalingsignaling systemsystem toto bebe
usedused onon nationalnational andand internationalinternational routesroutes.. However,However,thethe IndianIndian environmentenvironment requiresrequires lesserlesser numbernumber of of signalssignals andand hence,hence, aa slightlyslightly modifiedmodified versionversion isis beingbeingusedused..
ThereThere isis aa provisionprovision forfor havinghaving 1515 combinationscombinations usingusing twotwo outout of of sixsixfrequenciesfrequencies vizviz..,, 13801380,, 15001500,, 16201620,, 17401740,, 18601860 andand 19801980 Hz,Hz, forfor forwardforwardsignalssignals andand anotheranother 1515 combinationcombination usingusing twotwo outout of of sixsix frequenciesfrequencies vizviz..,,11401140,,10201020,, 900900,, 780780,, 660660 andand 540540 Hz,Hz, forfor backwardbackward signalssignals.. InIn India,India, thethehigherhigher frequencyfrequency inin thethe forwardforward groupgroup ii..ee..,, 19801980 Hz,Hz, andand thethe lowerlowerfrequencyfrequency inin thethe backwardbackward group,group, ii..ee..,, 540540 hz,hz, areare notnot usedused.. ThisThis isis whywhyitit isis calledcalled modmod R R22 signallingsignalling..
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Signaling in Telecom Network
contd«.
� Digital signaling: This class of signaling isnormally used in digital media
of transmission of telecom network.
It is of two types.� 1. Channel Associated signaling (CAS)
� 2. Common Channel Signaling (CCS)
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Signaling in Telecom Network
contd«.
� Channel Associated Signaling:� A signaling system is called CAS when the location of
the signaling information is related directly to the user
voice/data or . In the 30 channel PCM link (also called
2Mb link), a frame consists of 32 timeslots. Of the 32
timeslots, 30 channels are used to transport user voice/
data, one channel (timeslot 0) is used for timing, status
and synchronization. One channel (timeslot 16) is used
to carry signaling information
Every timeslot consists of 8 bits.
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Signaling in Telecom Network
contd«.
� FRAME 1:(2nd Frame Of a Multi Frame)
TS-0 TS-1 to
TS -15
TS-16 TS-17 to
TS-31
ALARM SPEECH SIGNAL OF
TS-1 & TS-17
4b+4b
SPEECH
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Signaling in Telecom Network
contd«.
� FRAME 2:(3rd Frame Of a Multi Frame)
TS-0 TS-1
to
TS -15
TS-16 TS-17
to
TS-31
FAW SPEECH SIGNAL OFTS-2 & TS-18
4b+4b
SPEECH
i i i
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Signaling in Telecom Network
contd«.
± FRAME 15:(16th i.e. Last Frame Of aMulti Frame)
TS-0 TS-1
to
TS -15
TS-16 TS-17
to
TS-31
ALARM SPEECH SIGNAL OFTS-15 & TS-31
4b+4b
SPEECH
Si li i T l N k
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Signaling in Telecom Network
contd«.
� POINTS TO BE NOTED:
� One Multi Frame consists of 16 Frames
� One Frame consists of 32 Time Slots.� Every Time slot consists of 8 bits.
� For signaling only 4 bits are required.
So in TS16 signal of 2 T/slots are sent
Si li i T l N k
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Signaling in Telecom Network
contd«.
� POINTS TO BE NOTED:� Duration of one frame = 125 micro sec
� Duration of Multiframe (16 frame)=2milisec
( 125*16=2000 microsec=2 msec).
� FAW : Frame alignment word. Faw & Alarm
appear one after another .
� MFAW : Multiframe AW. Comes after 16 frame.
Si li i T l N t k
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Signaling in Telecom Network
contd«.
� POINTS TO BE NOTED:� Duration of a T/SLOT= 125/32=3.9 micro
sec(as frame duration=125mico sec)
� Duration of One bit ::One time slot=8 bit &duration of one time slot is 3.9 micro sec
As Duration of 8 bits= 3.9 micro sec
So Duration of 1 bit =3.9/8=o.488 micro sec =488 nano sec
Si li i T l N t k
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Signaling in Telecom Network
contd«.
� CCS (Common Channel Signalling )#7� A signaling system is called a Common channel
signaling system when a channel is common for
sending all the signaling information of a nos. of users on sharing basis. In this case also TS16 is
normally used as common channel i.e. signaling
link. All the 8 bits of time slot 16 are used for
signaling / control information.
Signalling network
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Signalling network � It is made of :
� 1. SP( signalling point) :Signal source(orig exchg) &signal sink (destn exchg). All SPs are identified by means of a code. Theoretically there can 16384 codes within anetwork .These are collocated with exchg.
� 2.STP(signalling transfer point): Switch signaling
messages received to another STP or to a SP on the basis of the destination address.
� At the originating SP ( exchg A ) STP will create SU(signalling unit) I.e. frame. & will be sent through link. Thisframe will be decoded at the destination STP & sent to SP (
exchg B)� 3. SIGNALLING LINK:A time slot of a pcm is used as
signalling link. There may be more than one links betweentwo SPs which provide redundancy. All the links betweentwo SPs form a Signaling Link Set.
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Difference between cas & ccs#7
� Cas
1.low bit rate(2kbps)
2.not internationallystandardized
3.shared signalling
4.uses 4 bits so 2^4=16
types of signalling possible
5.less reliable/less fast
� Ccs#7
1.high bit rate (64kbps)
2.internationally
standaerdized
3. Dedicated signalling
4. Uses 8 bits so 2^8= 256
types of signalling possible.
5. Highly reliable/faster.
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DIFFERENT LAYERS OF
(STP) CCS#7IT HAS MAINLY TWO LAYERS :
1.UP USER PART ( LEVEL 4)
2.MTP MEESAGE TRANSFER PARTAGAIN MTP HAS THREE PARTS:
MTPL3 (LEVEL 3)
MTPL2 (LEVEL 2)
MTPL1 (LEVEL 1)
(FUNCTIONS ARE DESCRIBED IN NEXTSLIDE)
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DIFFERENT LAYERS & ITS FUNCTIONS.IN BRIEF FUNCTIONS OF 4 LAYERS :
User information MTP L3, where RL is
attachedMTP L2, where SU is formed
MTP L1 , converts the frame into bitstream. According to physical
connectivity it is sent over the media.
SIGNALLING UNIT (SU)
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SIGNALLING UNIT (SU)
� SU is formed at MTPL2 with the msgs of UP & MTPL3. SUsare three types :
a) M SU (msg signl unit) It contains actual signaling information.That is msgs of level 4 & level3.
b) LSSU (link status signal units). Facilitates informationexchanges between adjacent SPs about the operational status of the links connecting them. The link status may be normal,out of service etc
c) FISU ( fill-in signal units ). It has two functions :
1)It is for ack of MSU.Rx end will send FISU to Tx end.2) When no MSU or LSSU are passing ,FISUs keep a link active so
that all signaling points utilizing that link know that the link isoperational.
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