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
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