Contents Telektronikk - Telenor

90
CE
CE
Figure 3
IRIM with cluster links
29-m
29-m 30-n
29-m
DTRF
DTRF
30-n
30-n
29-m 30-n
of introducing an IRSU is a considerable
saving on cables if the alternative is to
connect each of the remote subscribers to
the exchange itself. If the alternative is to
put a new exchange on the remote site,
the solution of an IRSU is much cheaper
and will save administration and maintenance
costs since the administration of
the IRSU is done from the host exchange.
Only HW maintenance is necessary
on the site of the IRSU.
An IRSU is connected to the exchange
through an IRIM pair. Up to eight IRSUs
may be connected in a series and is then
called a multidrop (MD). One IRSU connected
to an IRIM pair is called a singledrop
(SD). An SD or an MD is connected
to one IRIM pair.
An MD is used primarily for low traffic
subscribers, typically a fully equipped
MD can carry up to 0.083 Erlang per
equivalent line. An analogue line and a
digital line are one and two equivalent
lines respectively. It may also be used for
high traffic subscribers, but underequipping
is then necessary.
It is important to note that an IRSU does
not have a processor PBA that takes care
of the call handling which is handled in
the exchange in the same way as for
directly connected subscribers.
3.1 Multidrop description
An MD consists of two half-systems,
called the upper and lower side. A maximum
of 8 IRSUs can be connected to the
same MD system with a maximum of
1024 equivalent lines. A maximum of 4
subscriber groups of 128 equivalent lines
may be assigned to each IRIM in the
IRIM pair.
- The IRIM/S is equipped with a DTRH
trunk PBA which terminates one PCM
link (single trunk system).
M-IRSU
Multidrop links
IRSU
- The IRIM/T is equipped with a DTRF
trunk PBA which terminates two PCM
links (double trunk system).
On the IRSU side the DTRH will usually
be connected to an IRIM/S, while the
DTRF will be connected to an IRIM/T.
An IRIM has only one processor. A maximum
of 4 MD links can be assigned to
one MD configuration (2 x IRIM/T).
The upper and lower side is cross-connected
by cross-over links in the IRSUs
as well as in the IRIM modules except
for one trunk PBA configurations (such
as mini IRSU and self restrained configurations).
This assures that from each subscriber
all trunks can be reached.
Available standard types of PBAs are
used for connecting the subscribers. Between
indicated maximum limits, any 16
analogue subscribers can be replaced by
8 ISDN subscribers.
3.2 IRSU variants
Each variant consist of one subrack containing
one (JR01), two (JR02) or three
shelves (JR03). A common rack (JR00)
has space for six shelves grouped three
and three.
The JR04 rack (mini IRSU) will occupy
one shelf in the JR00 rack.
The transmission equipment for one
IRSU is provided by a separate subrack
(JR06). The shelf variants have the following
subscriber capacities:
- JR01:
256 ASL + 0 BA to 32 ASL + 112 BA
- JR02:
512 ASL + 0 BA to 32 ASL + 240 BA
- JR03:
976 ASL + 24 BA to 64 ASL + 480 BA
- JR04:
96 ASL + 0 BA to 0 ASL + 48 BA.
JR05 is an outdoor cabinet which has
space for a JR01 rack, transmission
equipment, termination for optical fibre
cables, power supply and batteries.
3.3 Dimensioning of trunks in a
multidrop
Dimensioning of trunks is done based on
a GOS requirement of 0.5 % for the circuit
switched (CS) traffic between the
IRSU and the group switch in the exchange.
The GOS requirement is for the
‘worst case’ subscriber. In the special
configurations described later, the difference
of GOS for subscribers can be substantial.
The capacities given later are valid for
configurations with one packet switched
(PS) channel per MD link. It is possible
to allocate one PS channel on one MD
link and none on another, but the traffic
capacities for such configurations are not
described. The allocation of a PS channel
replaces a CS channel and vice versa.
Thus, as the number of allocated PS
channels increases, the CS traffic capacity
is reduced.
The two main dimensioning parts of the
system is the MD links which each has
30 channels and the cluster side links
(see Figure 3) of the IRIM which has 29
channels each for circuit and PS traffic.
The number of CS channels is shown in
Figure 3. In this figure, m and n is the
number of PS channels on the cluster
links and MD links, respectively. For a
DTRH configuration in the IRIM, n = 1
will imply m = 1. For a DTRF configuration
in the IRIM, n = 1 will imply m = 2.
The IRSU has the same schematic structure
as the IRIM. Instead of the Control
Elements (CE, i.e. the processor) there
are clock and alarm PBAs. Each subscriber
PBA is connected to one direct
and one cross-over link between the
clock and alarm PBA and the
DTRF/DTRH.
To fully understand the traffic capacities
in the following sections, it is important
to note that the traffic from a subscriber
group on the upper side has to go through
the upper processor (control element) in
the IRIM and similarly for the lower side
subscribers.
The normal channel allocation algorithm
is first to try the direct route, i.e. from a
subscriber on the upper to the upper control
element in the IRIM through the
direct cluster link. Only if this direct
route is blocked, the cross-over cluster
link in the IRIM will be tried. The same