switch signaling

8/6/2019 Switch Signaling

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SWITCHING

& SIGNALLING



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




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




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



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.



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.



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.



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.



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.



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.



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.



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.



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



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.



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.



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.



Practical Space Switch

In a practical switch, the digital bits are

transmitted in parallel rather than serially,

through the switching matrix



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.




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




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




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.



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 .




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.




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.



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.



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.



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.



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



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.



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



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



BLOCK DIAGRAM OF SPC (STORED PROGRAM

CONTROL) EXCHANGE

LINES & TRUNKSTERMINAL EQUIPMENT

SWITCHING NETWORK

DISTRIBUTORSIGNALLING

TERMINALSCANNER MARKER

CENTRAL CONTROL

(CC)& MEMORIESomc

bus



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.




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.




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.



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.



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.




�� 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..




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




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.




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.



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,




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.




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.




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



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 #




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.




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.




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..




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..))




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)




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..




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.




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..




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)




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.




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




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




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




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




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




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




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



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.



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.



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)



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)



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.

switch signaling

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