CHAPTER 4Timing and Synchronization

Prepared by : Mr. Muhammad AhsanLecturer Computer Science, Preston University Peshawar Pakistan.

TIMING & SYNC IN DIGITAL NETWORKS It is important to detect signals

accurately at the receiver side in terms of digital signals 0/1

Digital signals transmits in the form of pulses or clocks

The ideal system is that in which the receiver section knows exact the time the signal brought in its self at the receiver interface

CONTINUES . . . This synchronization between between

transmitter and receiver is achieved because each machine knows about each others “clock”

Clock : at which frequency on a specific time sending machine sends its traffic to receiver

The receiver can determine this time because of pulses arrived at receiver end.

TIMING ERROR EFFECTS An Error can be passed to the customer

end without having clock mechanism This error create problem and can be

passed among different nodes The error generated depend on

thetraffic being transmitted

DIFFERENT TYPES OF ERROR

Type of TrafficDigital DataEncrtpted DataFaxVideoVoiceVoice band Data

Result of ErrorReduce throughputResend KeyMissing linesPicture freezeAudible clickCarrier drop

THE CLOCKING SIGNAL It carries information about time The signal is represented by a crossing

mark To define clocking signals we use term

unit interval UI(corresponds to 1 cycle of clocking signal)

1 UI = 2 radian

METHODS OF CLOCK EXCHANGE For achieving synchronization between

the machines we use different (5) methods of clock exchange.

1) Free Running 2)Line-Timed 3)Loop-Timed 4)External 5)Through Timed

1) FREE RUNNING Each machine generates own timing(oscilator) Called free running/free running configuration No external clocking source is used Adv: no need to connect wid external timing source Dis/advn: DS3 incoming signals md outgoing buffuring

2) LINE TIMED Derives clocking on line from incoming signals Generator module fed these signals into local time nd provide

timing to outgoing signals Advn: simple Dis/advn: when several machines are connected where linearly to

each other

3)LOOP TIMED Also called gateway or Master/Slave mode Used where different timing generators are deployed/

where machins must intract with eachother Here the frequency sent from the running machine used to

derive clock at slave unit

LOOP CONTN…. The slave unit may loop the clock back

across the line or may employ an externel clock

4) EXTERNEL Machine times their transmitted signals from

internel oscillator that is locked with an externel Here synchronixation also known as plesiochronoius

5) THROUGH TIMED Last method of timing distribution Uses ring topology here

Building Integrated Timing Supply