Specifications

lxvi
Cisco 1751 Router Software Configuration Guide
OL-1070-01
Syntax Description
Default
1
Command Mode
Voice-port configuration.
Usage Guidelines
Use the type command to specify the E&M interface for a particular voice port. With 1, the tie-line
equipment generates the E-signal to the PBX by grounding the E-lead. The tie-line equipment detects
the M-signal by detecting current flow to ground. If you select 1, a common ground must exist between
the line equipment and the PBX.
With 2, the interface requires no common ground between the equipment, thereby avoiding ground loop
noise problems. The tie-line equipment generates the E-signal to the PBX by connecting it to SG. The
M-signal is detected by the PBX connecting it to SB. Although Type 2 interfaces do not require a
common ground, they do have the tendency to inject noise into the audio paths because they are
asymmetrical with respect to the current flow between devices.
With 3, the interface operates the same as type 1 interfaces with respect to the E-signal. However, the
M-signal is detected by the PBX connecting it to SB on assertion and alternately connecting it to SG
during inactivity. If you select 3, a common ground must be shared between equipment.
With 5, the type 5 line equipment generates the E-signal to the PBX by grounding the E-lead. The PBX
detects M-signal by grounding the M-lead. A type 5 interface is quasi-symmetrical in that, while the
line is up, current flow is more or less equal between the PBX and the line equipment, but noise
injection is a problem.
1 For the following lead configuration:
E—Output, relay to ground.
M—Input, referenced to ground.
2 For the following lead configuration:
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.
3 For the following lead configuration:
E—Output, relay to ground.
M—Input, referenced to ground.
SB—Connected to –48V.
SG—Connected to ground.
5 For the following lead configuration:
E—Output, relay to ground.
M—Input, referenced to –48V.