AVT MAGIC ISDN, Hardware Description

Page: 24 / 66

PA G E 2 4
S Y S T E M D E S C R I P T I O N
mission of one audio signal. These include the assignment of the individual
encoded audio signals within the transmission data stream. The extension
possibilities are not available for dialled connections in the ISDN.
For more comprehensive advice on the connection of MAGIC Extension units
please refer to the MAGIC BASIC Hardware Description.
REMARK At any given time in the 1x X.21 mode, all audio inputs must
receive the same type of audio signals, i.e. either analogue or
digital. If one input is switched from analogue to digital or vice-
versa, all other inputs are also switched.
2.4 Interface Unit
In addition to the network interfaces, the Interface Unit provides a wide range
of data interfaces for the transmission of user data in addition to the encoded
audio data. A further audio codec has been integrated to operate an indepen-
dant command channel. This audio codec supports the audio encoding stan-
dards G.711 (3.1-kHz bandwidth), G.728 (3.1-kHz bandwidth at 16-kbit/s) and
G.722 (7-kHz bandwidth).
For ISDN transmission, an up to six-fold inband signalling (J.52) has been im-
plemented. This signalling enables, on the one hand, byte-synchronisation
which is lost at an X.21 interface, and on the other hand, a synchronisation
between the individual data channels, which is required because of the dif-
ferent transmit times in ISDN.
For X.21 transmission, J.52 inband signalling is used to guarantee frame syn-
chronisation and to report the assignment of the individual timeslots of the
frame to the remote end. If the J.52 signalling is switched off, a maximum of
one encoded audio signal can be transmitted. In this case, the framing of the
data signal is guaranteed by the ISO/MPEG framing.
A multiplex frame of the X.21 signal at 1920-kbit/s consists of 30 timeslots with
8 bits each. The frame length is 125
µ
s (the frame frequency is 8 kHz). The
structure is shown in the following figure:
FIGURE 2.5 MULTIPLEX FRAME OF THE X.21-SIGNALS (I.E. 1920-KBIT/S)
Timeslot 1 contains the J.52 inband signalling (1.6-kbit/s). The remaining
62.4-kbit/s can be filled with a single Low Speed Data channel or a single
Command channel as per G.711, G.728 or G.722.
1 2 3 4 5 1 2 3 4 5 27 28 29 30
Timeslot
Frame 125
µ
s
Bit2 Bit3 Bit4 Bit5 Bit6 Bit7 Bit8 Bit1
Frame 2
Frame 3
Frame 78
Frame 79
Frame 80
Frame 1
Frame 16
J
.
5
2
LS
D
and C
M
D
LSD: Low Speed Data channel (e.g. for remote control)
CMD: Command channel G.728, G.711 or G.722