diavox courier 700, digital system telephone for md 110 data

Fact Panel no. 2
CCITT Recommendations
A number of recommendations have been prepared
within CCITT in order to standardize interface
etc. for data communication. The CCITT
recommendations that are most important to
AXB 30 are listed here:
85
X.1 specifies the speed categories for subscriber
terminals. AXB 30 provides for all asynchronous
terminal speeds and all synchronous
speeds up to and including 9600 bit/s.
X.2 concerns subscriber facilities. AXB 30 follows
the recommendations for all facilities in
circuit switched networks with a few exceptions.
X.20 bis, X.21 and X.21 bis constitute recommendations
for interfaces between terminals
and networks, for asynchronous terminals
with V interface (X.20 bis), for synchronous
terminals with X interface (X.21) and for synchronous
terminals with V interface (X.21 bis).
X.51 gives the frame structure on international
multiplex circuits and is applied in AXB 30 between
data network exchanges, and between a
data network exchange and concentrators and
multiplexors respectively.
X.54 gives supplementary information to X.51.
The recommendation defines 56 different channel
distribution alternatives for the speed categories
of the subscriber channels concerned.
X.71 defines the channel associated traffic signalling
between exchanges.
X.96 defines approximately 20 call progress
signals. In AXB 30 these are transmitted to the
DSE subscriber in the form of a two-digit code
and contain information of the type: Called
subscriber is engaged, please wait; Called subscriber
is out of operation; Congestion in the
network; etc.
X.121 gives the new international number plan
for data networks.
DCC is remotely controlled by the data
network exchange, DSE, over two control
channels which are included in the
two first multiplex circuits towards DSE.
The control channels normally work in
the load sharing mode, but if a fault
occurs one control channel can handle
all the control information.
Up to 500 subscribers can be connected
to DCC, either direct or via RMX. The
number of multiplex circuits to DSE is
dependent on the traffic volume and
varies from two to a maximum of ten.
DCC carries out the following traffic
functions:
- identifying calls from connected subscribers
and calling the data exchange,
DSE, over the control channel
- on order from the data exchange,
DSE, connecting a subscriber line to
a specified channel in a multiplex circuit
to DSE
- disconnecting the data circuits on
command from DSE.
DCC also contains built-in functions for
supervising that the equipment works
satisfactorily. If a fault occurs the alarm
information is transmitted to DSE via
one of control channels.
The alarms are coordinated by DSE,
which can, for example, order DCC to
carry out tests for fault localization.
In order to obtain good operational reliability
the logic units and control
channels of the data concentrator are
duplicated. The subscriber connections
are grouped in modules of 50 subscribers,
with one subscriber module per
multiplex channel. The operation and
maintenance module is not duplicated.
Data network exchange, DSE
The data exchange constitutes the central
part of the data network. It controls
and supervises the setting up and disconnection
of data circuits between
subscribers in the network and towards
subscribers in other data networks.
DSE has a maximum connection capacity
of 508 multiplex circuits of 64 kbit/s
each for the connection of DCCs and
DfvlXs/RMXs in the network and circuits
to other networks. The call capacity of
DSE is 70-100 calls per second.
The subscriber channels are always
connected through DCC and DMX/
RMX. The switching network is designed
so that it is free from congestion.
Fig. 4
Block diagram of the data concentrator, DCC
• Data bus
Bus for control channel signalling
Control bus
——— Multiplex circuit, 64 kbit/s