Telos Zephyr Xstream User Manual page 171

required V.35 or X.21 standard and in the case of Switched‐56 provides dialing capability. (Some
have keypads and LCD displays for this function; others rely upon external computer control.)
The designation DSU is most often used when terminating Switched‐56 lines. Modular DSU's are
also used within a Multiplexer to break out the various paths. Originally, the CSU and DSU were
separate pieces of equipment. Today however, the equipment sold for use on DDS lines is
nearly always an integrated piece of gear variously referred to as a CSU, DSU, CSU/DSU, or a
DSU/CSU.
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DEEP TECH NOTE!
In the old days a CSU (Channel Service Unit) was used to terminate the digital circuit (to use
the generic term, it was the NCTE or Network Channel Terminating Equipment).
One or more DSUs (often in the form of plug in cards) were used to provide the interface to
the terminal equipment. These days the 2 devices are nearly always combined and are
variously referred to as CSUs, DSUs, CSU/DSUs, and DSU/CSUs! We prefer CSU/DSU and
will use that term.
Note that the Telos web site (www.telos‐systems.com) includes a glossary if you need help with
any of the other terms.
Cables
The Zephyr Xstream connects to digital transmission channels via the ports from the V.35/X.21
interface module.
The cables available from Telos, connect to standard terminal adapters or CSUs, which, in turn,
connect to the digital network channels. The design of the port electronics permits interface
with either V.35 or X.21 equipment – the connector style and pin‐out is the only difference.
X.21
Use Telos Part
# 2091-00024
You can tell whether you have V.35 or X.21 by looking at the connectors. These are the "footprints"
of the two types to help you select the proper Telos cable to interface to your datacom gear.
Each V.35/X.21 connection conveys both send and receive digital signals.
The V.35 or X.21 cable from Telos includes two V.35 or X.21 plugs. This two‐port cable may be
used for single‐port applications by simply letting the unused plug (usually port 1) go
unconnected.
USER'S MANUAL
V.35
Use Telos Part
# 2091-00023
Section 9: The V.35/X.21 Interface Option 159