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Fig. 12
The principle for common transmission equipment
and Individual equipment tor each type ot
communication with the CCITT signalling system
No. 7
References
1. Meland, F. and Rishoj, E.: Crossbar
Exchanges in Arhus become SPC
Exchanges. Ericsson Rev. 54
(1977):2, pp. 86-89.
2. Hinwood, J. D. and Clark, D. W.:
Field Trial of CCITT Signalling
System using AKE13. Ericsson Rev.
49 (1972):4, pp. 124-138.
3. CCITT Orange Book, Vol. Vl.2.
4. Morlinger, R. and Viktorsson, O.:
ARE 11 -System Description. Ericsson
Rev. 54 (1977):2, pp. 67-76.
5. Hemre, A. and Hagard, G.: The
Software and Its Handling in ARE
System. Ericsson Rev. 54 (1977):2,
pp. 77-85.
6. Andersson, B. et al.: ARE Systems
in Modern Networks. Ericsson Rev.
54(1977):2, pp. 54-66.
very suitable for adaption to CCS signalling
and for STP functions.
With direct signalling between two exchanges
the analogue version of system
No. 6 gives a signalling time that is of the
same order of magnitude as MFC and
d.c. code signalling. In the case of transit
traffic the link-by-link principle is
used for CCS, whereas the faster endto-end
signalling is used for MFC and
d.c. code signalling. Thus in this case
the signalling time is longer for the CCS
analogue version than the other two
methods. This becomes more apparent
when the connection is made via two
transit points with signalling via STP.
However, it is possible to start the setting
up process earlier, whereby the wait
for the ringing signal —the post dialling
delay — is reduced to a satisfactory level.
The field trial has not, however, provided
sufficient basic data for reliable
cost calculations, and thus it has not
been possible to make economic comparisons
between a CCS and a MFC
network.
Plans for the future
Signalling system No. 6 is now being introduced
on many international telephone
circuits. The interest in CCS has
grown also in other parts of the telecommunications
field, which has meant
that the fundamentals of the system are
having to be reconsidered.
Thus it can no longer be assumed that
CCS must only be suitable for international
circuits, where the cost of the
signalling equipment is not decisive.
Now it must also be suitable for the national
network, where the cost aspect is
of greater importance.
Since PCM is now beginning to be an
economic form of transmission even for
long distances, it is possible to use a 64
kbit/s digital channel for CCS. This
means that the signalling rate can be increased,
and furthermore the analogue
modem will not be required.
Finally the introduction of the digital
group selector is now imminent. As was
made clear in a previous article in Ericsson
Review 6 this can be done with
advantage even in an existing ARE
network. This development will lead to a
changed network structure and also the
introduction of concentrators around
the new exchanges. Moreover measures
will then be taken to prepare for an integration
of different forms of communication,
such as telephony, telex,
data, gentex, and also network management,
maintenance etc.
Consequently CCITT is now in the process
of preparing a new CCITT system,
No. 7. It will contain a message transfer
part that is common for all forms of
communication, and which will constitute
the actual common signalling
channel. Individual parts, fig. 12, foreach
communication form will then be connected
to the ends of the common message
transfer part.
The specifications for this signalling
system are expected to be completed
around 1980. The main features are
already known, however, and thus it is
possible to plan how the system should
be used in principle. It is even considered
that it will be possible to use the
transmission principles of system No. 7
between concentrators and the parent
exchange.