Telos Zephyr User Manual page 100

First, A Glossary
Some terms you will need to navigate this section:
V.35. A standard for interconnecting synchronous digital data paths. Like RS- 232, it
defines signals and (not officially) connectors and pin- outs so that equipment from
various manufacturers may talk with each other. The usual connector is a big boxy AMP
type which was chosen by AT&T decades ago. Most terminal equipment sold for the US
market supports the V.35 standard.
X.21. A more modern standard, also for interconnecting synchronous digital data
paths. This standard specifies the much more reasonable DB- 15 connector.
Fortunately, it is possible to design a receiver which accepts both V.35 and X.21 signals.
This we have done with the Zephyr, allowing connection to both types just by changing
the interconnect cables. The X.21 standard is frequently seen in Europe.
Throughout this manual, we use the universal designation
" V.35/X21"
CSU.
interface between the Zephyr and digital channel is usually called. It converts the
signals from the telephone line to the required V.35 or X.21 standard and provides
dialing capability. (Some have keypads and LCD displays for this function; others rely
upon external computer control.) The designation CSU is most often used when
terminating Switched- 56 lines. Modular CSUs are also used within a Channel Bank to
break out the various paths. Originally the CSU and DSU were separate pieces of
equipment. Now they are nearly always one piece of gear variously referred to as a CSU,
DSU, CSU/DSU, or a DSU/CSU.
TA. Terminal Adapter. Performs same function as CSU. This terminology is most
commonly used with equipment applied to ISDN lines.
Throughout this manual, we use the universal designation "TA/CSU" to refer
generally to an external ISDN or Switched- 56 interface device.
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Section 6
DEEP TECH NOTE!
The standard uses electrically balanced transmission for both
clock and data (but not for the special auxiliary signals, which
are identical to RS-232). The transmit voltage level is ± 5.5V,
but receivers must handle wider swings.
CURIOSITY NOTE!
You might wonder why the much more common RS-232 is not
used. Answer: V.35 is synchronous, meaning that the bit clock
is transmitted between the two ends. Self-clocking standards,
like RS-232, require overhead start and stop bits, slowing and
chopping the bit flow. And, just as with audio, balanced
transmission is more reliable in a noisy environment, or in one
which has ground potentials at differing levels.
to refer to the Zephyr's digital I/O port protocol.
Channel Service Unit. DSU. Data Service Unit. This is what the
NON-ISDN NETWORKS