Contents Telektronikk - Telenor

Capacity of an Alcatel 1000 S12 exchange emphasised
on the ISDN remote subscriber unit
BY JOHN YTTERHAUG, GUNNAR NOSSUM AND ROLV-ERIK SPILLING
1 General
This article describes the dimensioning
of the main equipment of an Alcatel 1000
S12 exchange and the corresponding traffic
restrictions where this is appropriate.
It is divided into two main parts: The
first part describes the Alcatel 1000 S12
exchange, and the second part describes
the remote concentrator called ISDN
Remote Subscriber Unit (IRSU). The
IRSU is developed and maintained in
Norway. The Alcatel 1000 S12 is a common
Alcatel product with main development
in Belgium. Each country may have
different requirements for the equipment,
reliability and grade of service. This article
is based on the dimensioning rules for
the Norwegian market.
Most of the Alcatel 1000 S12 exchanges
in Norway have old software. The existing
hardware in an exchange can with
some adaptations be used with the new
software package including ISDN, Business
Communication, etc. Full functionality
is therefore possible for all exchanges.
All types of modules needed for
this can be introduced, either in existing
racks or by introduction of new rack
types. The description here only concerns
the latest versions of the modules and
rack types.
2 Dimensioning of
common exchange
equipment
This part describes the main equipment
in an Alcatel 1000 S12 exchange and the
capacities and dimensioning of the equipment
where appropriate.
2.1 Digital Switching Network
(DSN)
An exchange is built up around a Digital
Switching Network (DSN). The DSN
transports circuit switched, packet
switched and signalling traffic. All the
modules in the system are connected to
the DSN as shown in Figure 1. The modules
are connected via Terminal Sub
Units (TSU). Two access switches are
equipped per TSU, and they connect the
modules to the switching planes in the
DSN.
The following modules in Figure 1 are
not described later in the text:
TTM: Trunk Testing Module
CTM: Clock and Tone Module.
The number of switching planes is 3 or 4
depending on the traffic. All switching
planes are identically equipped. The capacity, however, will be reduced to the
number of switching units in each plane half.
is determined by the number of TSUs.
No hard restrictions exist on the penetra-
2.2 Terminal Sub Units (TSU)
tion figures for subscriber facilities.
Extending the requirements for capacity
A TSU consists of one group of terminal and availability is always possible by
modules. One TSU is connected to one proper dimensioning of the required
Access Switch (AS) pair. Figure 2 shows
how two TSUs are connected to two
Access Switches. The figure only
shows the processors (TCE is
Terminal Control Element) of the
resources. It is possible for all subscribterminal
modules.
Each AS is connected to all four
ASM
T
C
E
switching planes in the DSN.
The number of TSUs is calculated
based on the total traffic demand
ISM
T
C
E
and the total amount of terminal
equipment.
The maximum allowed mean traffic
per TSU (determined by the
GOS requirement for end-to-end
IRIM
CCM
T
C
E
T
C
E
Digital
Switching
Network
DSN
blocking probability in the
switching network) for 4 planes is HCCM
T
C
152 Erlang. This ensures that the
signalling messages between the
modules have a high probability
to succeed. If a free path is not
found, several reattempts are
done, the number of reattempts
SCM
E
T
C
E
S
A
C
E
depending on the importance of
the message.
The number of subscriber modules
and other traffic dependent
Figure 1
modules per TSU is calculated
Access Switch
based on the TSU traffic constraints
given above.
(AS)
2.3 Subscriber modules
Two types of subscriber modules
exist, one for analogue and one
for digital (ISDN) subscribers.
The maximum traffic per subscriber
module is 35.2 Erlang.
The subscriber module is connected
to the DSN via two separate
PCM systems. With a GOS
of 0.2 % the traffic capacity is
17.6 Erlang per connection. If the
required traffic per line gives a
higher total traffic per module
than 35.2 Erlang, the subscriber
modules will be underequipped.
Modules for analogue and digital
subscribers may be combined in
the same TSU. 2 modules with
the same type of subscribers work
as cross-over pairs, which means
that if one module fails another
will take over the function. The
T
S
U
T
S
U
Figure 2
TCE
1
TCE
8
•
TCE
1
TCE
8
•
•
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
•
8
9
10
11
12
13
14
15
8
9
10
11
12
13
14
15
8
9
10
11
12
13
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15
8
9
10
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13
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15
T
C
E
T
C
E
T
C
E
T
C
E
T
C
E
T
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E
T
C
E
TTM
DTM
IPTM
APM
MPM
CTM
DIAM
DSN
87