Specifications

Chapter 4 4-Wire E&M/TO Configuration

4-3

ABII

Radio or Microwave

Carrier

Network

4 Wire E&M

Tandem Mode

Radio or Microwave Transceiver

4 Wire E&M

Tandem Mode

PBX

ABII

Figure 5-2. Tandem Mode E&M Access to Leased Lines or Carriers

E&M SIGNALING CONVENTIONS

According E&M signaling conventions, Switching Equipment always originates signaling on the M-lead

(the “mouth” sending toward the transmission line). The E-lead of the switching equipment interface

incorporates a signaling current detector (the “ear” listening to the line). The multiplexed or carrier

Channel Equipment always originates signaling on the E-lead coming from the transmission line. The

signaling current detector is found on the M-lead going toward the transmission line.

The 4-wire E&M/TO voice card can be optioned to operate either as Channel Equipment or Switching

Equipment. Since the Access Bank I typically operates as a voice and data multiplexer, the card is usually

configured as Channel Equipment. However, the card can also be configured as Switching Equipment.

This is referred to as Tandem operation because the card operates in “tandem” (i.e. back-to-back) with

another transmission device.

The following table lists the generic functions performed by the Detector/Detector Return and

Driver/Driver Return when the 4-wire E&M card is configured to operate as Channel Equipment or

Switching Equipment.

Table 5-1. Detector-Driver Functions

Channel Equipment Detector is on M-lead function

Driver is on E-lead function