Ref: 13680012
Title: Remote Bridge/Brouter Loopback Test with a Breakout Box
Date: 5/4/90

Copyright 3Com Corporation, 1991.  All rights reserved.

A loopback test can detect problems with the system, modem cables, modems,
or phone lines when a link does not come up or if you want to check the
bridge with no lines connected.

All SIO cards and ITC/M cards are set up to provide both transmit and
receive clocks.  When physical loopback is detected, a bridge will
display "Path # Loopback" on the screen.  If there is a problem, then
"Path # Down" will be displayed on the screen.

Note:  The current IB software (2.0 and 2.1) does not detect loopback,
but the new release (3.0) will.  Use version 11000 software for loopback
testing.

Following are breakout boxes that work with various communication
interfaces.

V.35:    NAVTEL BREAKOUT BOX
         BLACKBOX SAM V.35
         with a straight cable
         SDA(P) - RDA(R)
         SDB(S) - RDB(T)
         RTS(C) - CTS(D) - DCD(F)

         with a null modem cable (CBL-V35ME-25)
         SDA(P) - RDA(R)
         SDB(S) - RDB(T)
         CTS(D) - DCD(F)

RS-232:  DATATRAN DATA TRACKER
         with a straight cable
         with a null modem cable (CBL-SME-25)
         BA(2) - BB(3)
         CF(8) - CD(20)

RS-422:  BLACKBOX SAM 449
         with a straight cable
         with a null modem cable (CBL-449ME-25)
         SDA(4)  - RDA(6)
         SDB(22) - RDB(24)

RS-449T: BLACKBOX SAM 449
         with a straight cable
         SDA(4)  - RDA(6)
         RTA(8)  - TTA(17)
         RTB(26) - TTB(35)

         with a null modem cable (CBL-449ME-25)
         SDA(4)  - RDA(6)
         RTA(8)  - TTA(17)
         SDB(22) - RDB(24)
         RTB(26) - TTB(35)
