AVT Titan, Руководство оператора

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1 – 1 4 040 7448 329657 (04.97) PC-SW 4.5
C H A P T E R 1 : S Y S T E M D E S C R I P T I O N
Timeslot 0 contains alternately the frame alignment signal and the service di-
gits. The frame alignment signal is for synchronisation, the service digits
transmit alarms to the remote end. Timeslot 16 is for the transmission of dial-
ling information and cannot be used for the transport of data.
Two different frame formats have been defined for the 2-Mbit/s data stream:
– the double-frame format
– the CRC4-frame format
The double-frame format corresponds exactly with FIGURE 1.3, in the CRC4
frame format, a so-called check bit is transmitted as the first bit of the frame
alignment word. In order to make optimum use of the capabilities of the con-
nected terminals, the ITU-T Recommendation H.242 has been fully integrated
in addition to H.221. For unidirectional connections, the ITU-T Recommenda-
tion H.331 is used. This information is transmitted in timeslot 1. The inband si-
gnalling as per H.221/H.242 or H.331 is repeated every 80 frames (10 ms). In
the first 16 frames, the eighth bit is used for inband signalling (
= 1.6 kbit/s).
The remaining seven bits in timeslot 1 of each frame, as well as the eighth bits
of frames 17 to 80 can be used for other signals (see FIGURE 1.4).
FIGURE 1.4 POSITION OF INBAND SIGNALLING WITHIN THE 2-MBIT/S DATA STREAM
1.3.2 Frame structure of the T1 1.544-Mbit/s signal
The frame structure is as defined in ITU-T G.704.
Note: In T1 Restricted mode (56 kbit/s), the a/b bits (see Rec. G.704) are set
to 0/0 in unused channels and to 1/1 in used channels. The data in unused
channels is 0111111.
1.3.3 Frame structure of the data stream as per X.21 and RS449
The frame structure for 1
×
X.21 and for RS449 is similar to that of E1. The
number of available timeslots, however, depends on the data rate of the trans-
mission path. A network clock of 256 kHz, for example, can be used to trans-
mit 256 kbit/s which corresponds to four timeslots at 64 kbit/s. FIGURE 1.5
shows the multiplex frame for a network clock of 384 kHz (
=
6 timeslots at
64 kbit/s).
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H-bit: Bit i of the inband signalling
?-bit: Data e.g. audio or LSD
(TCOG K K VQ (TCOG L L VQ
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