| Description | Specifies the E&M Lead Signaling type.
LEGEND: V = -48V
/\/\/ = detector/resister
X = normally open relay contact
+ = normally closed relay contact
G = ground
SB = Signal Battery
SG = Signal Ground
typeI -
Leads: E (output, relay to ground)
M (input, referenced to ground)
The tie line equipment (switch/router/etc) generates the
E-signal to the PBX type grounding the E-lead.
The tie line equipment detects the M-signal by detecting
current flow to ground. A common ground must exist
between the line equipment and the PBX.
PBX | TIE LINE
|
E: V--/\/\/---|-----X----G
|
M: V----X-----|---/\/\/--G
typeII -
Leads: E (output, relay to SG)
M (input, referenced to ground)
SB (feed for M, connected to -48V)
SG (return for E, galvanically isolated from ground)
This interface requires no common ground between the
equipment, thus avoiding ground loop noise problems.
E-signal is generated toward the PBX by connecting it
to SG. M-signal is indicated by the PBX connecting
it to SB. While this interface does NOT require a
common ground, it does have the tendency to inject
noise into the audio paths since it is asymmetrical
with respect to current flow between devices.
PBX | TIE LINE
|
E: V--/\/\/---|-----X----
| |
SG: G----------|----------
|
M: ----X-----|---/\/\/--G
| |
SB: ----------|----------V
typeIII -
Leads: E (output, relay to ground)
M (input, referenced to ground)
SB (connected to -48V)
SG (connected to ground)
This interface operates similar to type I with respect
to the E-signal. The M-signal, however, is indicated by
the PBX connecting it to SB on assertion, and alternately
connecting it to SG during inactivity. Unfortunately, a
common ground must be shared between the equipment.
PBX | TIE LINE
|
E: V--/\/\/---|-----X----G
|
SG: ----------|----------G
+ |
M: ----------|---/\/\/--G
X |
SB: ----------|----------V
typeIV -
Leads: E (output, relay to SG)
M (input, referenced to -48V)
SB (feed for M, connected to ground)
SG (return for E, galvanically isolated from ground)
This interface is fully symmetrical; it does not require
a common ground, does not inject noise into audio paths,
and can be connected back to back by swapping E/SG for
M/SB. E-signal is indicated to the PBX by connecting it
to SG. M-signal is provided by the PBX connecting it to
SB.
PBX | TIE LINE
|
E: V--/\/\/---|-----X----
| |
SG: G----------|----------
|
M: ----------|---/\/\/--V
X |
SB: ----------|----------G
typeV -
Leads: E (output, relay to ground)
M (input, referenced to -48V)
Type V line equipment indicates E-signal to the PBX by
grounding the E-lead. The PBX indicates M-signal by
grounding the M-lead. This interface does require a
common ground, but does allow back to back connections
by swapping E for M. This interface is quasi-symmetric
in that while the line is up, current flow is more or
less equal between the PBX and line equipment. But noise
injection is still a problem.
PBX | TIE LINE
|
E: V--/\/\/---|-----X----G
|
M: G-----X----|---/\/\/--V
| |