Specifications

Introduction
MP2100M-LS-2 Modules - Installation and Operation Manual 1-11
1.2 System Planning Considerations
This section explains the multiplexing formats used by the different LS-2
models, and provides information regarding the number of channels versus
channel data, and information on LS-2 time slot routing.
Byte Interleaved
Multiplexing
Formats
The LS-2 modules perform byte-interleaved time division multiplexing (TDM).
In byte-interleaved TDM, the information received from each module is inserted
in an eight-bit envelope. The envelopes received from the various channels are
then sequentially transmitted via the main link. The byte interleaving technique
for the particular case of all channels operating at the same rate is illustrated in
figure 1-6.
Byte 1 CH 1 Byte 1 CH 2
. . . . . .
Byte 1 CH N Byte 2 CH 1
. . . . . .
Byte 2 CH 2
. . . . . .
Byte 2 CH N Byte 3 CH 1
. . . . .
8-Bit
Envelope
Byte
Multiplexer
CH 1
CH 2
.
.
.
.
.
.
CH N
Byte-Interleaved Multiplexed
Data Stream
Figure 1-6. Typical Byte Interleaved TDM
The sub-multiplexing techniques specified by ITU-T Rec. X.50, ITU-T Rec.
X.58 and AT&T Pub. 54075 define the organization of data in the multiplexed
frame, and thus determine the number of channels (and their data rates) that can
be carried in the allocated main link bandwidth, which is always 64 kbps.
ITU-T Rec. X.50 Multiplexing Format
The ITU-T Rec. X.50, Division 3 format is based on the envelope structure
shown in figure 1-7. The envelope consists of one frame synchronization bit,
designated F bit, 6 user data bits, and one S (status) bit. Therefore the
multiplexing overhead is 25%, and the maximum user payload carried by a time
slot multiplexed in accordance with ITU-T Rec. X.50, Division 3, i.e., the sum
of the data rates of all the user's channels connected to a /X.50 module, is
48 kbps.
To understand this limitation, it is necessary to understand the structure of a
ITU-T Rec. X.50 submultiplexed signal. ITU-T Rec. X.50 divides the available
transmission bandwidth, 64 kbps, into equivalent channels, in accordance with
a structure that was originally designed for a maximum user channel data rate
of 9.6 kbps (it can however be extended to 19.2 kbps as explained below).