Note: Descriptions are shown in the official language in which they were submitted.
- CA 02216~30 1997-09-26
70910P3073
PROCESS FOR OPERATING AN EXCHANGE AND SC~ RT~ DIGITAL
SWITCH SYSTEM FOR CARRYING OUT THE PROCESS
The invention relates to processes according to
precharacterizing clause of Claim 1; in particular, it
relates to an exchange consisting of a switch and a
host and also to a process for operating said exchange.
An exchange has to perform various tasks. These
include call setup and call routing, which are also
referred to as call management; furthermore, the so-
called call services, which include call charging among
other things. For this purpose, a data record in which
the start and end times of the call, date information,
the telephone numbers involved and the costs of the
call are entered and are permanently stored is created,
for example, for each newly setup call, that is to say
when a connected subscriber himself calls or is called.
Finally, it is also necessary to mention the operator
services, which account for the more organizational
part of the system, ~or example setup and clearance of
customers, configuration of circuits or the charge
services based on the call service data.
Until a few years ago, the telecommunication
switches were provided with "intelligence" so that the
total handling of a call could be performed in the
switch itself. Progr~mming was carried out essentially
in a so-called assembler with non-standardized
operating systems which had to be specially developed
for each switch. A great deal of time was required for
the development and modifications were very expensive.
Outgoing services over and above the elementary call
management could of course scarcely be implemented, if
at all.
An important improvement arises from the use of
a standardized operating system, such as, for example,
interactive UNIX of a higher programming language, such
CA 02216~30 1997-09-26
70910P3073 2
= as, for example, "C", and of a standardized, very
rugged database system, such as, for example,
"Informix". These software modules are available for
all hardware platforms from the simplest PC to so-
called mainframes, so that the software adaptatlon to
hosts o~ different efficiencies can be carried out in a
simple manner.
Since, however, the tasks to be performed by the
host are very varied and furthermore must be executed
for the most part in real time, creation of the
software can be extremely complex. Moreover, where the
sizes o~ the switch differ, the host has to meet very
different performance requirements. In particular,
hard disk accesses during the database operations
impose a very considerable burden on the host.
Furthermore, in general different operating systems and
database programs are required for different
performance ratings, with the result that software
creation and adaptatlon to different numbers of
subscribers continues to be very expenslve. Several
hosts which execute the various tasks essentially
parallel are therefore frequently networked with one
another and moreover the operations executed in real
tlme are reduced to a minlmum.
The problem of hard disk access for extractlon
of the data from the typically indexed databases
r~mAin~. Therefore a flrst object of the invention is
to provide a simpllfied and/or faster access to the
data, and this is achieved by the characterlzlng
features of Clalm 1.
Relevant advantageous embodlments are described
ln Claims 2 to 4.
As mentioned above, conventional exchanges
comprise one or more hosts. In addition there are the
actual swltch matrix and one or more telephone servers.
Because of the virtual absence of modularity, thls
architecture can be expanded only at great financial
CA 022l6~30 l997-09-26
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cost and with a great deal of work. Modular
architectures typically have small "sub-exchanges",
formed by elementary telephone switches which are
connected, by way of a bus or by way of a ring
structure, to each other and to the hosts and the
telephone servers. Thls architecture is modular and
therefore can also be more easily expanded or adapted
to varylng requirements. The primary problem lies on
the one hand ln the lack of reliability in bus-based
systems and generally the capacity limit, which is
quickly rea,ched when the system is expanded, in respect
of the transmission medium, whether it is a bus or a
ring.
Therefore the second object of the invention is
to provide an architecture for an exchange, which
permits virtually any expandability with an inexpensive
modular structure, with enhanced reliability of the
overall system.
This is achieved by the features of Claim 5.
The use of the elementary telephone switches
(ETS) affords the possibility of building very small
installations up to installations of almost unlimited
size, with a suitable high speed communication network.
The advantage of a solution according to Claim
6, in which the communication network is formed by at
least one ATM-switch lies in the enormously high
processible data rate (about 150 Mbps) at each port of
the ATM-switch, whereby it is possible to achieve an
enormous gain in speed in terms of the throughput of
data through the entire installation, and the
installation can be expanded virtually without limit.
The problem when using an ATM-switch in
exchanges is that the PCM (pulse code modulated) data
rates are not sufficiently high with small elementary
telephone switches (ETS) and therefore, without further
measures, it is only meaningful for large elementary
telephone swltches (ETS) to be connected together by
CA 022l6~30 l997-09-26
70910P3073 4
way of an ATM-switch. This results in a rather
confused design configuration in which expansion is
possible only ln very large steps in terms of capacity,
which lS contrary to the desired modular structure.
Data concentrators (which are known to be used for
reducing channels in data transmission) in conjunction
with ATM-switches were not used hitherto, probably for
reasons of the level o~ complexity which is difficult
to control
As mentioned above, these disadvantages are
ellminated ,by the features of Claim 6 In accordance
with the lnventlon, a plurality of elementary telephone
switches (ETS: small, simple, modular) are not directly
connected to ATM-ports but by way of concentrators; in
this way the ATM-switch is no longer used as a switch
in the true sense but is only used as a link between a
plurality of partial switches formed by elementary
telephone switches (ETS) and down-circuit
concentrators In this way an ATM-switch, as a
connecting element, can advantageously display its
enormously high data rate
By using an ATM-switch as a link and not as a
switch, it is possible to achieve a substantially
higher data transmisslon rate than hitherto, Gbytes per
second being thought to be achievable This combines
the two above-mentioned aspects of the invention, in
that not only is an expandable circuit obtained but
also the deslred faster operation is permitted To
this extent, the embodlment protected in Claim 6 is an
independent invention, even separately from the other
features of Claim 5, although the modular structure
according to Claim 5 is thus also obtained in a
particularly advantageous manner. In any case,
however, it is also possible to offer fundamentally
novel transmission services which were possible with
the conventional circuits only to a very limited
extent, without involving a change in the architecture.
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70910P3073 5
A further advantageous embodiment of the system
according to the invention is described in Claim 7.
Further details of the inventlon are evident
from the following description of embodiments shown
schematically in the drawing.
Fig. 1 shows an exemplary arrangement for illustrating
the process according to the invention;
Fig. 2 shows the procedure for call handling by the
host;
Fig. 3 and 4 show the access to a first type of data;
Fig. 5 and 6 show the access to a second type of data;
Fig. 7 is a block diagram of a conventional exchange
having a bus structure;
Fig. 8 is a block dlagram of a conventional exchange
having a ring structure;
Fiq. 9 is a block diagram of a scaleable digital switch
system (SDSS) according to the invention;
Fig 10 is a block diagram of an expanded SDSS;
Fig. 11 shows a first example of the structure of an
elementary telephone switch (ETS); and
Fig 12shows an alternative structure of an ETS
In Fig. 1, a switch (1) is connected to other
exchanges of a telecommunication network via groups of
incoming lines (2) and outgoing lines (3).
Furthermore, subscribers (8) are connected via lines
(7) A host (4) having at least one mass storage unit
(6) controls the switch (1) via a data link (5).
The switch (1) - controlled by the host (4)
executes the actual switching of the incoming and
outgoing calls. For example, a commercial unit "Excel
Switch PCX512" may be used as switch (1), its internal
structure and the internal function being known per se
and therefore not being discussed in detail here.
On the basis of a program contained in a memory
segment of the host or of an external program, the host
(4) performs - under program control - essentially the
CA 022l6~30 l997-09-26
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above-mentioned tasks of call management, call services
and operator services.
Call management relates malnly to call setup and
call routing. A trunk group for the outgoing half of
the call and, within the trunk group, a channel are
selected in accordance with various routing tables.
The call services include call setup and call
routing, which - as explained above - are re~erred to
as call management, as well as the so-called call
services which include mainly call charging. For this
purpose, fo~ example, a data record in which the start
and end times of the call, date information, the
telephone numbers involved and the costs of the call
are entered and are permanently stored is created for
each newly set up call, that is to say when a connected
subscriber himself calls or is called The data
required for calculating the costs are taken from a
customer database as data record "ANI" which identifies
the customer and also contains a reference "DNIS" in
time-specific and weekday-specific rate tables.
The operator services include, inter alia,
customer management, which supports the setting up and
clearance of customers, switch management for
configuration of the switch, call monitor for real-time
representation of the internal state of the switch and
a billing servlce The call data records stored in the
billing period are evaluated for each customer, the
call charges incurred are summed and finally a
statement is prepared.
Fiq. 2 shows, in simplified form, the procedure
for handling a call by the host. In Fig. 2, the
handling of a call is shown schematically in the form
of a block diagram;
2a denotes entry of customer data;
2b denotes entry of the area code, exchange of data;
and
2c denotes further handling of the calls.
CA 022l6~30 l997-09-26
, 70910P3073 7
The data assigned to the customers are taken from the
ANI database (20), the subscriber number typically
serving as a key. This necessltates several hard disk
accesses, each of which requires several milliseconds
in a typical PC system. The database itself may
comprise, for example, 150000 entries.
Furthermore, the routing information required
for controlling the switch (1) (cf. Fig. 1) and billing
the calls must be taken from a further database, the
NPANXX database (21). Several hard disk accesses are
once again, required for this purpose. The NPANXX
database typically comprises 60000 entries.
Since at least 3 or 4 hard disk accesses, each
with an access time of about 10 milliseconds, are
usually requlred per database access, PCs as hosts
reach their per~ormance limit already at a low level of
traffic; disk caching reduces the access time for the
individual data record to mllliseconds, but this does
not solve the problem.
A remedy for the time-consuming hard disk access
is the holding o~ the two databases in the memory of
the host. Access to a data record ln the memory is
thus faster by a factor of about 1000 to 10000 than
access to a ~ata record on the hard disk.
As a result of this improvement in the access
time, in particular even higher-value service features,
such as the servlces call-back and ready-rlng explalned
below, are permltted wlth a single host instead of a
network of hosts connected to one another. In the case
of the call-back service, a subscriber calls the
swltchboard, l.e. practlcally, the swltch (1) with a
specified number, allows ringing to take place and
hangs up the receiver again; the exchange determines
who has called and calls the relevant subscriber back
and gives him a dial tone. The subscriber dials the
number o~ hls desired call partner and the switchboard
routes the call.
CA 02216~30 1997-09-26
70910P3073 8
The service ready-ring, that is to say periodic
polling of a subscriber line in order to determine
whether the subscriber has lifted the receiver in order
then to send him a dial tone, also requires
particularly frequent accesses to the database.
In the so-called booting process, a first
storage area for the NPANXX data records used in the
swltchboard and a second storage area for the customer-
speclfic ANI data records are set up in the memory of
the host. At the beginning of operation, these two
storage areas are still unfilled but have already been
created in a size sufficient to be able to hold the
total database in each case.
Alternatively or in a further embodiment of the
invention - particularly if the databases are so large
that they cannot be completely held in the memory - the
memory areas may be created in such a way that they can
hold only the most frequently used data records, it
being possible to use a special LRU algorithm to create
space in the event of overfilling or for selecting
external memories
When, after the beginning of operation, the
calls arrive from the various subscrlbers, the
informatlon relevant to the users and the lnformation
on the selected numbers are searched for in the
corresponding databases on the disk, read out and
stored in the pre-reserved memory areas The strategy
for access to the data involves first searching for the
data in the memory and reloading the required data from
the disk only if said data are not yet present in the
memory. In this way, the disk accesses are minimized
because, after a certain time, most data are already in
the memory and can be read out from there. New data
records must be reloaded from the disk only when new
users call or new destinations are called.
Access to the NPANXX data is described more
exactly below, with reference to Fig. 3 and 4.
CA 02216~30 1997-09-26
70910P3073 9
The database NPANXX contains location
information, coordinate information and distance
information of a telephone call. For this purpose, the
possible destinations of a call are NPANXX-encoded in a
6-digit number. Out of the 1 million possible data
records, however, only about 61000 are in fact
occupied. It would therefore not be reasonable to
reserve 1 million data records; instead, it is
sufficient in the booting process to reserve space for
the 61000 possible data records (30) in the memory. At
the same time, a field (31) for 1 million pointers is
set up, said polnters being capable of pointing to the
data records A further pointer freeptr (32) points in
each case to the first free pre-reserved data record
(33) in the memory.
If an NPANXX data record havinq a certain NPANXX
number is now requested (41), in a first step (42) a
search is carried out in the pointer field
VNHPTR[NPANXX] under the index NPANXX to determine
whether there is already an entry there which points to
a data record in the memory. If so, the data record
can be read out from the memory under the pointer
address (43) The access to the data record in this
case is permitted by only two memory accesses without a
single access to the hard disk. This process is then
complete (4a)
If no entry exists in the pointer field VNHPTR
under the index NPANXX, the relevant data record must
be read out from the hard disk (44) and is entered in a
free memory area reserved for data records in the
memory (45) The address of this newly entered data
record is en~ered in the index field VNHPTR under the
index NPANXX (46), with the result that the next access
to the relevant data record can likewise take place in
the memory. This process is then complete (4b).
This type of memory organization may be denoted
by hashing, this hashing function, which generates from
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70910P3073 10
the automatic number ldentification an index under
which the data record can be ~ound in a manner known
per se, being the identificatlon function. The key
value itself gives the index under which a pointer to
the data record can be found.
This access process is not possible for the user
data from the ANI database since the automatic number
identification ANI is formed by a 10-digit number. The
access to the ANI data is therefore described more
exactly below with reference to Fig. 5 and 6.
Here, according to the invention, the hash value
is formed by the last four digits of the automatic
number identification (= ANI number). Accordingly, a
pointer field hptr (51) havlng 9999 elements is set up,
and each element may polnt to one of the pre-reserved
ANI data records (50). A further pointer afreeptr (52)
points to the first free pre-reserved ANI data record
(53) in the memory.
As a result of the stated method of formation of
the hash value, multiple assignments of one and the
same hash value by several automatic number
identifications ANI do of course occur
According to the invention, the resulting
conflicts are solved by virtue of the fact that every
data record in the memory is extended by a
concatenation field (54) which - unless empty - points
to further data records which have the same hash value
but di~ferent automatic number identifications
If any ANI data record having a certain ANI
number is now requested, the hash value hval is first
formed (60) and a test is carried out to determine
whether an entry exists under the index hval in the
pointer field hptr (61)
If the entry is bLank, the data record must in
any case be read from the hard disk (62) and is entered
in the first free reserved storage area (63).
~ CA 02216~30 1997-09-26
70910P3073 11
If the pointer fiela for the relevant index was
free (64), the address of the newly stored data record
can be entered directly in the pointer field hptr under
the index hval (65); otherwise, the chain of all data
records concatenated with the entry hptr[hval] as the
root must be rolled up (66) so that the address of the
newly stored data record can be finally entered in the
link field of the last data record of the chain, which
in fact must be empty (67).
If testing of the pointer field hptr [hval] (61)
reveals tha~ an address entry already existed, this is
temporarily stored. This address entry addresses a
data record whose ANI field is tested for conEormity in
the next step. If the ANI entry of the data record
agrees with the required ~NI number, the correct data
record is ~ound and can be read out (72) I:~ not, a
data record havlng the correct hash value but a false
ANI number has been found
If the link fleld of this data record is blank
(70), the required data record must be read from the
hard disk, which process has already been described
(62-67).
If the link field of the data record
investigated is not blank, the new data record
addressed by the link field is investigated (71), which
process has also already been described (69-72).
6a, 6b and 6c represent the termination of the
particular process.
Figure 7 is a view showing the principle of an
exchange with elementary telephone switches (ETS): a
plurality of ETS (11, 12 ...) which each represent
small, relatively independent exchanges and which have
PCM multiplex lines (for example T1 trunks) (2)
connected to their inputs are connected by way o~ a
central bus (3). Also connected to the bus (3) are a
plurality of telephone servers (21, 22, ...) for
carrying out the switching activity which goes beyond
CA 02216~30 1997-09-26
70910P3073 12
an ETS, and a host (4). The host (4) not only permits
operation and maintenance of the installation but also
billing of the telephone calls An exchange having the
architecture shown in Figure 7 is modular in the sense
that the elementary telephone swltches (ETS) and the
telephone servers represent individual modules, and
therefore it can only be easily expanded. It does
however suffer from two major disadvantages: the
central data exchange element of the installation is
formed by the bus (30). If the bus should fail due to
a fault, the entire installation becomes inoperative.
I~ the installation is to be expanded by ha~ing
additional ETS and telephone server modules added
thereto, finally the bus will represent a hard limit in
terms of expansion, both mechanically (because of the
restricted number of plug-in locations), and
electrically (because of the restricted driver outputs)
and also from the point of view of data transmLssion
speed.
The indicated disadvantages are alleviated by an
architecture as shown in Figure 8. Here, the
elementary telephone switches (ETS) (31, 32, ...), the
telephone servers (41, 42, ...) and the host (40) are
connected together by way of a data ring (300). As the
ring is preferably in the form of a double ring,
corresponding to the prior art, failure of a ring
sector does not immediateIy result in total failure of
the entire installation. In this case also however
expandability is limited by the ring, by virtue of the
limited throughput of data.
Figure 9 shows a block diagram of a scaleable
digital switch system (SDSS) according to the
invention. The SDSS is formed from a quantity (50) of
elementary telephone switches (ETS) (100, 101, . . . ), a
host (60) and a quantity (70) of communication systems
(80) which comprise concentrators (140, 141) and at
least one ATM-switch (160)
CA 022l6~30 l997-09-26
70910P3073 13
Each o~ the elementary telephone switches (ETS)
(100, 101, ...) is connected to a respective group
(110, 111 . .) of PCM MPX lines (120, 121, ...).
Typically each elementary telephone switch (ETS) is
connected to 20 T1-MPX lines corresponding to a
capacity in each case o~ 20 x 24 = 480 PCM connections
The multlplex connections (130, 131, ...) of optionally
five such elementary telephone swltches (ETS) ln each
case are connected to a respective concentrator (140,
141) which is connected by its multiplex connection
(150, 151) ~o a data connection of an ATM-switch (160).
Connected to further connections of the ATM-switch are
one or more hosts (60) and a plurality of telephone
servers (70, 71, . ).
Each of the elementary telephone switches (ETS)
can however support a limited number of ports and has
an ATM interface which can be integrated with other ETS
by using the concentrator and the ATM-switch. The
concentrator (140, 141) is responsible for
demultiplexing the incoming bandwidth from each ETS
into the ATM-switch. The ATM-switch routes all the
incoming data streams into outgoing streams. The total
numbers of ports to be provided can be determined by
the matrix size of the ATM-switch, which can be easily
upgraded without any hardware changes in the rest of
the system.
Provided in the basic extension stage shown in
Figure 9 are 2 concentrators (140, 141) with a total of
10 elementary telephone switches (ETS) and a 2x2 ATM-
switch, which gives a switching capacity of 4800 ports.Division of the switching assembly into elementary
telephone switches (ETS) on the one hand and the high-
speed communication system with concentrator and ATM-
switch on the other hand makes it possible for the ETS
to be kept relatively small and thus flexible, while
nonetheless affording the ATM the required high data
rate (about 150 Mbit/s) at the data connections In
CA 02216~30 1997-09-26
, 70910P3073 14
this respect the ATM-switch itself is not used as a
swltch in the true sense but as a llnk for high-speed
connection of the data streams which are produced in
the ETS and which are assembled in the concentrators.
The partlcularly hlgh level o~ flexibility and
scalability of the architecture shown in Figure 9, for
very different requirements, ls described below Fig.
10 shows the expansion of the architecture described in
Fig. 9 to switch twice the number of connectlons:
Connected to a 4x4 ATM-switch (200) are a total
of ~our concentrators (201 .204) each wlth five
elementary telephone switches (ETS) 210, 211, .. 229)
The further modules connected to the ATM-switch, such
as host and telephone servers (cf. Fig 1) have been
omitted from this figure ~or the purposes of
simplification thereof. The scalability of the
architecture is clearly evident. Similar ETS, only
doubled in terms of their number, are connected to an
ATM switch of double the capacity, by way of also twice
as many similar concentrators, and afford an exchange
with a capacity which is doubled overall ~in this case
for a total of 9600 ports).
The scalability o~ the arrangement is made
further clear by the fact that, to achieve a still
substantially higher number of ports, a plurality of
ATM-switches can be connected to form an ATM-network ln
a manner known per se It is thought that ln that way
installations with up to 1 million ports are possible
The elementary telephone switch (ETS) is a non-
blocking switch with only a small to minimum capacity,which can handle approximately 480 ports (20 T1 lines).
The basic approach in the design of the ETS is open
modular architecture, such that the users can easily
change the configuration by installing more m~dules in
the switch. As a result, the switch can be upgraded to
include telephone services other than only the basic
CA 02216~30 1997-09-26
70910P3073 15
services, for example by adding ISDN interfaces or data
communication services etc.
Figures 11 and 12 show the internal
configuration of an ETS. Flgure 11 shows an embodiment
given by way of example with VME-bus modules, while
Fig 12 shows a PC-based design with corresponding
plug-in boards.
The elementary telephone switch (ETS) in Figure
11 comprises ~i~e module types each module being
preferably formed by one or more printed circuit
boards), na~ely a main control module (MCM) (301), a
switching matrix module (SMM) (302), a T1 interface
module (TIM) (303), a digital signal processor
interface module (DIM) (304) and an ATM concentrator
interface module (ACIM) (305). In the ETS every unit
except the main control module (MCM) is connected to
two standard interface units: the standard VME-bus
(307) and the telephony path unit (308). The standard
VME-bus permits the use of so-called shelf technology,
gives a certain flexibility to the system design,
reduces the costs and increases the reliability since
additional modules can easily be added to the basic
system. The ETS exchanges information to control its
modules and the telephone path unit (308) via the VME-
bus. Data exchange itself occurs by means of a memorymat I/O (input/output) with dual port RAM, that is to
say by means of shared memory. In comparison with
alternative methods such as, for example, an HDLC
connection (a high-level data link control or an ISO-
standardlzed blt-oriented data transmission protocol),
this procedure affords substantial advantages in terms
of speed.
The telephony path unit (308) consists of
conventional PCM multiplex lines and is used for
switching voice and data with a digitized PCM format.
The maximum bandwidth of the telephony path is
CA 022l6~30 l997-09-26
70910P3073 16
determined by the maximum number o~ non-blocking ports
of an ETS
The maln control module (MCM) (301) of the ETS
must be able to control the ETS and maintain its
operation, such as routing, controlling the telephony
path and generating statistics. Therefore the MCM has
a powerful micro-controller, for example based on an
MC68302 whlch lS specially designed for communication
applications; MC68302-based VME boards are available
off the shelf. To simplify control and data management
in the ETS; the MCM can be equipped with a data
interface (for example an SCSI interface) for the
connection of mass storage devices such as, for
example, a hard disk.
The SMM (302) provides a system-wide
interconnection of digital telecommunication data (i e.
both volce and data) over the PCM multlplex llnes)
(308). If the maxlmum switching slze of one S~ lS 512
x 512, an ETS can handle up to 512 non-blocking ports.
That means that an ETS is able to support the
connection of up to 512 trunk lines at the same time.
The main component of the SMM is a switching matrix
device such as, for example, Mitel MT8980
The T1 interface module (TIM) (303) interfaces
T1 trunk digital data to the telecommunication
processing system's digital data streams. For thls
purpose, one or more standardized T1 PCM multiplex
lines (309) with the data rate of, for example, 1.55
Mbps can be connected to the module (303). For
example, there are four T1 lines per circuit board,
while the functions of signalling, monitoring and
supervlsion of the connected PCM lines are also carried
out ln the T1 lnterface module (TIM), in addltion to
signal interfacing. Each elementary telephone swltch
(ETS) is provided with a number of T1 interface modules
(TIM) (303), which corresponds to the number of T1
lines (309) to be supplied If an ETS is to be able to
- CA 02216~30 1997-09-26
70910P3073 17
switch telephone lines with particular properties, in
order to offer for example ISDN services, the T1
interface modules (TIM) of the ETS have to have only
the corresponding features.
The DSP interface module (DIM) (304) preferably
includes one or more digital slgnal processors DSP;
here on the one hand multi-frequency tones are produced
and detected for dealing with certain classes of calls;
on the other hand, many different announcements can be
stored in a read only memory (ROM) and fed into the
system by way of the DSP. Finally, produced in the DIM
are all tone signals which are used within the system,
(continuous tone, cadence tone and shot tone), whose
parameters are also read out of a read only memory and
evaluated by the DSP
Finally the ETS also has an ATM-concentrator
interface module (ACIM) (305); it serves to pass on the
data in the individual ETS, in order then to have the
higher switchlng tasks performed by the ATM-switch
which is used as a link. For this purpose the ACIM has
a PCM-data connecting line (310) for connection to a
concentrator.
Figure 12 shows an alternative configuration of
an elementary telephone switch (ETS) as a PC-based
system. The main control module (MCM) (351) is, for
example, formed by a main board of a PC, provided with
a 486 or Pentium processor, to which the other modules
of the ETS are connected by one of the available PC
buses (356), such as ISA or EISA. Some commercial T1
interface boards (353) which can interface to a PC
system with ISA or EISA and MVIP bus already include a
switching matrix device (354). The use of this type of
board makes the SMM unnecessary. The DSP interface
module (DIM) (355) is formed by a DSP insert board
which ls available for PC applications. In thls design
of the ETS there is also an ATM concentrator interface
module (ACIM) (357). The ETS can be connected to a
CA 02216530 1997-09-26
70910P3073 18
concentrator by way of a PCM data connection (360)
extending from the ACIM. Transportatlon of the PCM
data between the individual modules of the ETS is
effected by way of PCM multiplex lines (358) which are
preferably formed by a MVIP bus.
