Specifications

FOM-E3, FOM-T3 Ver. 1.0 Overview 1-1
Chapter 1
Introduction
1.1 Overview
FOM-E3 and FOM-T3 are fiber optic modems for transmission of E3
(34.368 Mbps) or T3 (44.736 Mbps) over multimode- or single-mode fiber optic
media.
The units are transparent to framing, and can transmit data using any framing
pattern with HDB3 or B3ZS coded signals.
The electrical signal is converted into an optical signal using an infrared light
emitting diode or laser diode transmitter. At the opposite end of the fiber, the
optical signal is converted back into an electrical signal and amplified to the
required level. FOM-E3 and FOM-T3 utilize a Phase Locked Loop (PLL) circuit to
recover data and clocking from the signal and provide electrical interface of two
BNC connectors with 75Ω impedance.
Diagnostic and alarm features include LED status indicators, V.54 loopbacks
activated from the front panel, and an alarm relay port for reporting the system
status.
When the FOM-E3 or FOM-T3 detects electrical interface levels below G.703
electrical levels, the modem transmits an "all 1s" signal (AIS) to the optical
interface. When an "all 1s" (AIS) signal is detected at the optical or electrical
interface, the modem converts this signal transparently and alerts the user via
front panel LEDs and the supervisory port.
The electrical interface meets requirements of ITU G.703, G.921 and G.935
standards for E3 and T3.
Versions
Electrical Interface
The units are available in the following electrical interface versions:
• FOM-E3: E3 electrical interface fully compatible with the applicable ITU-T
standards. HDB3 line coding is used.
• FOM-T3: T3 electrical interface, fully compatible with requirements of ITU-T
G.703 and G.824 standards. B3ZS line coding is used.