Cables And Loopback Plugs For Pics; Transition Cables For The At-Ar023 Pic - Allied Telesis AT-AR020 PRI E1/T1 Hardware Reference Manual

Hardware Reference
C613-03023-00 REV N

Cables and Loopback Plugs for PICs

This section describes how to make cables for connecting PIC interfaces to
other devices, and loopback plugs for testing PIC interfaces.
The following topics are covered:
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Transition Cables for the AT-AR023 PIC

■
ISDN Interface Cables
■
BT Adaptor Cable for the AT-AR027 PIC
■
Terminal and Modem Cables
■
Ethernet Transceivers and AUI Cables
■
Loopback Plugs for Testing Interfaces
Transition Cables for the AT-AR023 PIC
The synchronous port on the AT-AR023 SYN PIC uses an AMPLIMITE 50-way
connector wired as a universal connector to support RS-232/V.28, V.35 and
X.21 interface standards in DTE and DCE modes.
A transition cable is required to convert the AMPLIMITE to the correct
physical interface for the standard required (e.g. DB15 for X.21). The transition
cable can be ordered from your distributor or reseller, or you can construct
your own cable by following the wiring diagrams in this section.
The transition cable does more than simply change the physical connector. The
switch or router hardware 'reads' the cable type from the AMPLIMITE plug
and enables or disables the internal driver electronics as required. To function
correctly, the cables must be identical to the cables described in this section.
The DCE cable type reverses the direction of the data lines as well as the clock
lines. This cable is intended to be used when the switch or router supplies the
clock for an attached device. This is commonly used when the switch or router
is connected to the synchronous port of another switch, router, or host, without
using an intermediate modem or NTU (Network Terminating Unit). Therefore,
the DCE cable must only be connected to a port which is set to generate the
clock. The Interfaces chapter of the AlliedWare
Reference for your switch or router has more information. The AMPLIMITE
connector supports both DTE and DCE modes for all three physical standards.
The switch or router interface is fully compliant with V.35 but many DCE
(DSU/CSU) devices are not. Therefore, pay particular attention to V.35
connections. Because of the low signal levels used for V.35 (500mV point-to-
point), issues such as ground loops and excess cable length become more
important than with X.21. In particular, some DCE devices connect the cable
ground to chassis or safety ground. This can create an earth loop condition
through the shield wire of the V.35 interface. The symptom of this condition is
unexpectedly high received packet errors (CRC, Abort etc.) as seen in the
output of the show syn counters command. In these cases the suggested
remedy is to break the earth loop by disconnecting (and isolating) pin A inside
the M34 connector. This action does not compromise the safety of the product
in any way.
The transition cable can be changed at any time. It is not necessary to power-
down the switch or router.
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Operating System Software
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