2 – Functional Description ACS-160 Series & STL-160 Series T1 Multiplexer Installation & Operation
Version 2.11, August 2011
Harris Corporation
2-23
Intraplex Products
2.2 System Functionality
2.2.1
T1 Digital Transmission
A single T1 circuit provides twenty-four full-duplex, 64 kbps time slots to carry payload data, for an
aggregate payload capacity of 1.536 Mbps in each direction (24 x 64 = 1536). An 8 kbps overhead
channel brings the actual T1 interface rate to 1.544 Mbps (Section 2.2.1.1).
Intraplex ACS-160 Series multiplexers provide an interface between T1 circuits and one or more
payload channels, which originate and terminate at plug-in channel modules. Channel modules
convert voice, program audio, and data signals into a single or multiple 64 kbps digital signals. These
64 kbps signals are then combined by time division multiplexing into a 1.544 Mbps T1 signal.
The T1 circuit is inherently duplex; that is, there are twenty-four time slots in each direction of the
circuit (Figure 2-15). Thus, while a two-way voice or data channel may occupy Time Slot 6 in both
directions, a one-way audio signal using Time Slots 7 and 8 in one direction would allow those two
time slots to still be available to carry a different one-way signal in the other direction.
1
2
3
23
24
24
23
3
2
1
64
kbps
64
kbps
64
kbps
64
kbps
64
kbps
64
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64
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64
kbps
64
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64
kbps
Overhead
8 kbps
Overhead
8 kbps
Figure 2-15. Train Representation of T1 Circuit Duplex Nature
2.2.1.1 T1 Frame Formats
The T1 signal contains 8,000 frames per second. Each frame consists of one 8-bit byte from each of
the 24 time slots, plus one overhead bit, used to provide frame synchronization, error detection, and
other functions. Frames are arranged into larger groupings in one of these two formats:
●
Superframe (SF), which groups 12 frames together (Figure 2-16)
●
Extended superframe (ESF), which groups 24 frames together (Figure 2-17)
Whether a particular T1 line operates with SF or ESF framing depends on the T1 service provider. The
ESF format provides better error detection than SF, and you should use it whenever possible;
however, some older networks and channel service units (CSUs) do not support the ESF format. ACS-
160 Series multiplexers can be set to operate using either SF or ESF frame format.
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