Bit error rate (BER) is the underlying QoS parameter for data circuits. BER is not subjective; it is readily measurable. Data users are very demanding of network operators regarding BER. If a network did not ever carry data, BER requirements could be much less stringent. CCITT/ITU-T recommends a BER of 1 x 10-6 for at least 80% of a month.1 Let us assume that these data will be transported on the digital network, typical of a PSTN. Let us further assume that conventional analog moderns are not used,
and the data are exchanged bit for bit with "channels" on the digital network. Thus, the BER of the data reflects the BER of the underlying digital channel which is acting as its transport. BERs encountered on digital networks in the industrialized/postindustrialized nations are far improved, some attaining an end-to-end BER of 5 x 10-10. Thus, the data being transported can expect a similar BER.
The genesis of frame relay, discussed in Chapter 10, is based on the premise that these excellent BERs can be expected.
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