Because RFL™ and Hubbell® have a policy of continuous product improvement, we reserve the right to change designs and specifications without notice.
2.2.1 MULTIPLEXER FUNCTIONALITY
The multiplexer serves as an interface between T1 “high-speed” circuits and multiple voice and data
“low-speed” circuits. Channel modules convert voice and data signals into single or multiple 64,000-
bits/second (64-kbps) digital signals. These 64-kbps signals or “time slots” are then combined by time
division multiplexing (TDM) into a T1 signal. The multiplexed voice and data circuit becomes
payloads within the T1 circuit.
A single T1 circuit provides 24 full-duplex, 64-kbps time slots for an aggregate payload capacity of
1.536 Mbps in each direction. The time slots are numbered 1 through 24. Because the signal format
includes an 8-kbps overhead channel for frame synchronization, error detection, and other functions,
the actual T1 interface rate is 1.544 Mbps. See Section 10 for more information on T1 framing.
2.2.2 T1 TIME SLOT USAGE
The specification for the T1 system calls for 24 full-duplex 64 Kbps time slots, numbered 1 to 24,
providing a payload rate of 1,536,000 bps, or 1.536 Mbps
Some applications, such as voice communications, require additional data such as ring, on-hook, or
off-hook state to be associated with the payload. This additional information is referred to as signaling.
In T1 systems this data is passed between nodes using RBS (Robbed Bit Signaling), within the payload
time slot. Channel modules that require signaling, insert the data into the payload when configured to
do so.
Although 4 of the 8-kbps of the T1 overhead channel is used for network management communication,
the M-DACS, using a single timeslot, can be equipped with an optional Network Communications
Module (NCM) for faster network communications.
Note from the above discussion that a T1 network can have between 23 and 24 time slots available for
user payload depending on the system configuration.
M-DACS-T1 RFL Electronics Inc.
October 16, 2012 2-2 (973) 334-3100
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