Telos Zephyr Xstream User Manual page 175

In the direction CSU/DSU ‐> Zephyr Xstream, only CD (Carrier Detect))is implemented. This
signal is used to tell the Zephyr Xstream which port/channel has been connected and activated.
It is used for internal selection of the network clock source. When the TEL menu selection
Interface is set to "V.35" the TEL status screen will indicate "Inactive" or "Active" depending on
whether the CD signal is present for that channel. NOTE that at any given time only one of the
V.35 signals is providing clock which is used for both ports. Therefore both V.35 sources must
be at the same clock frequency (which is generally the case since Telco's use highly accurate
clock sources for all of their gear).
Configuring CSU/DSUs
There will generally be at least two main configuration menus. One for interface to the DTE
(Data Terminal Equipment) and one for the interface to the "loop" or "line". Your CSU/DSU
manual (or manufacturer) should have information on the correct settings for the various
options.
DTE Options:
Set to "Synchronous" and set the bit rate to match the Zephyr Xstream's and line's bit rate
(usually 56kbps). If necessary, you may disable any handshaking signals by setting them to
"forced" or "ignored" since handshaking is not required with synchronous data. "Anti
streaming" or "scrambling" options should be disabled.
Loop or Line Options:
Set to the speed of your line (usually either 56 or 64kbps). The Xstream's CODEC menu option
Bit Rate must be set to the same rate as the line. Your Telco or CSU/DSU manual should be able
to give you the correct setting for any other options.
Clock Options:
It is essential that the clock option be set to "network" or "from loop". The Xstream will clock its
synchronous data to the clock from the CSU/DSU. In order to prevent buffer overflow or
underflow, the far end unit must share the same clock. The only way to ensure this, is for each
CSU/DSU to derive its clock from the network (i.e. from the line itself). The CSU/DSU must not
derive clock from the V.35 port.
t
DEEP TECH NOTE!
In cases where "dry line" modems are used one end can use a local clock (master) and the
other end (slave) can derive timing from the far end by using loop timing.
If a dual port scenario is to be used with these
would need to be slaved using the clock connections on the V.35 ports of these two units. It
can be done, but you will need to fabricate a special cable to do so.
USER'S MANUAL
modems, the second modem at the master end
Section 9: The V.35/X.21 Interface Option 163