TRANSMISSION ERRORS
Errors are introduced in the data bits during their transmission
across a sub network. These errors can be categorised into :
·
Content
errors
·
Flow
integrity errors
Content errors are the errors in the content or a message, e.g. a
"1" may be received as "0". This type of errors gets
introduced due to impairment of the electrical signal in the transmission
media.
Flow integrity errors refer to missing blocks of data. For
example, a data block may be lost in the sub-network due to its having been
delivered to a wrong destination.
In voice communication, the listener can tolerate a good deal of
signal corruption during transmission. But data is very sensitive to errors.
Measures are, therefore, built into a data communication system to counteract
the effect of errors. These measures include:
·
Introduction
of additional check bits in the data bits to detect and correct content errors.
·
Establishing
procedures of data exchange which enable recovery of corrupted/lost messages.
BIT ERROR RATE (BER)
In analog transmission, signal quality is specified in terms of
Signal to Noise ratio (S/N) which is usually expressed in decibels. In digital
transmission, the quality of received digital signal is expressed in terms of
Bit Error Rate (BER) which is number of errors in a fixed number of transmitted
bits. A typical error rate on a high quality leased telephone line is as low as
1 error in 106 bits or simply 1 x 10-6.
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