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Asynchronous vs Synchronous Framing
All data links have to provide byte-level
synchronisation of the sender and receiver.
In an asynchronous system, such as is normally
used with modems, each character (or byte) sent on a data link is
prefixed with an extra start bit and has a
stop bit appended, thus:
In synchronous systems, a whole
block or frame of data is sent as
a single unit, with a synchronising preamble of a few bytes. This
has much lower overhead, and is by far the most common in
"leased-line" data links, see later.
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