AT&T MERLIN LEGEND Installation & Maintenance Manual page 80

System Description
Mu-Law 255
Mu-Law 255 is a commanding scheme that uses a compression
ratio compatible with modern channel bank equipment. The
scale is divided into 16 intervals, with each interval having 16
levels. Therefore, the scale has 256 discrete values. But since
Mu-Law 255 has a negative and a positive zero, it really has only
255 discrete values. This commanding scheme is used in the
United States and Japan.
Digital Switching
The TDM bus allows many users to communicate over a
common electrical connection because it is physically distributed
across the backplane of the CU and connects all line/trunk and
station modules.
The TDM bus has specific time slots for various functions. For
example, during a conversation between station A and station B,
a time slot is resewed for station A to transmit on and for station
B to receive on. An analog station can transmit on time slot 150
and receive on time slot 160. Because the TDM bus cycles 8000
times per second, the conversation is continuous.
The TDM bus carries tones and control signals to stations via
time slots 0 to 39. Unlike other bus configurations, the stations on
the TDM bus receive all transmissions. If a station is not
assigned to any of the time slots, the station ignores the data.
The digital switch element (DSE) is a digital switch for voice and
data. It also performs the operations for commanding schemes
such as Mu-Law and A-Law. Each module has a DSE to interface
codecs or digital transceivers to the TDM bus. The actual digital
switching occurs when the DSE is programmed by the system
I/O bus to transmit data on or receive data from the TDM bus in
specific time slots. For example, the digital station can send data
on time slot 200 and receive data on time slot 220.
Signal Processing 1-49