3
Troubleshooting The Protocol Layer
Four protocols are supported:
•
E & M
•
DID
•
Ground Start
•
Loop Start
Ground and loop start are subscriber-end only (DXP Plus end) not office-end (network end).
Before starting protocol layer troubleshooting, make sure you have completed all physical layer
troubleshooting to ensure that no alarms are occurring and that the DXPT1 board has no red LEDs lit
except for the large status LED.
Troubleshooting the protocol layer consists of checking the A and B transmit and receive signalling bits.
Depending on the protocol that is active and on which function is occurring, A and B signalling bits can
be a digital one (“1") or a zero (”0"). In some cases, the level (“0" or ”1") doesn’t matter and could be
either one (X). These levels are designated by a “0,” “1,” or “X” in the following tables.
When the function involves a user dialing a number with a rotary dial, the signalling bit designated by
“DP” in the following tables, represents the dial pulse (make= 1 ; break = 0). For a ground start protocol,
the signalling bit representing a dial pulse will be a digital one (“1") when a tone dial is used in place of a
rotary dial.
NOTE: In the table below, an X is a don’t care. Signalling can be a 1 or 0. DP is a dial pulse (make = 1,
break = 0).
3.1
Defining The Signalling Bits For The E & M Protocol
FUNCTION
TRANSMIT
RECEIVE
EIA/TIA 464-A
STANDARD
^
A
B
A
B
^
OUTGOING CALL
Idle
DXP off-hook
Wink
Wink
Dial pulsing
Wait for ANS
Far end ANSW
INCOMING CALL
Idle
CO goes off-hook
DXP sends wink
DXP after wink
Far end DP
Far end wait FR ANS
DXP answers call
0
1
1
1
DP
1
1
0
0
1
0
0
0
1
0
1
1
1
DP
1
1
0
0
1
0
0
0
1
0
0
1
0
0
0
1
0
1
1
1
DP
1
1
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Wink on
Wink off
Make=1, Brk=0
IMI89–207
Troubleshooting The DXPT1 Installation
10 – Troubleshooting The DXPT1 Installation
