CA1135820A - Digital telephone exchange for areas of low subscriber's density - Google Patents
Digital telephone exchange for areas of low subscriber's densityInfo
- Publication number
- CA1135820A CA1135820A CA000345143A CA345143A CA1135820A CA 1135820 A CA1135820 A CA 1135820A CA 000345143 A CA000345143 A CA 000345143A CA 345143 A CA345143 A CA 345143A CA 1135820 A CA1135820 A CA 1135820A
- Authority
- CA
- Canada
- Prior art keywords
- control units
- units
- control
- unit
- subscriber
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/04—Selecting arrangements for multiplex systems for time-division multiplexing
- H04Q11/0407—Selecting arrangements for multiplex systems for time-division multiplexing using a stored programme control
Abstract
ABSTRACT
In a digital telephone exchange for areas of low subscriber density, a connection network of subscriber cir-cuits able to supply signalling and speech in PCM code, signal generators for generating synchronism and timing sig-nals, and a control system to control the development of the connections. The control system consists of a plurality of control units, each adapted to carry out one or more tele-phone functions concerning the control of the connection among subscribers; to control a limited position of the traffic generated by the subscribers connected with the ex-change; to examine and satisfy in allotted time-phase the interconnect requests received from other units or subscri-bers; and to communicate with other units by utilizing as connection path the connection network.
In a digital telephone exchange for areas of low subscriber density, a connection network of subscriber cir-cuits able to supply signalling and speech in PCM code, signal generators for generating synchronism and timing sig-nals, and a control system to control the development of the connections. The control system consists of a plurality of control units, each adapted to carry out one or more tele-phone functions concerning the control of the connection among subscribers; to control a limited position of the traffic generated by the subscribers connected with the ex-change; to examine and satisfy in allotted time-phase the interconnect requests received from other units or subscri-bers; and to communicate with other units by utilizing as connection path the connection network.
Description
~3~
The present invention relates to equipment for the control of telephone traffic and more particularly it relates to a digital telephone exchange for areas of low subscriber density.
Telephone exchanges intended for low subscriber den-sity areas have to meet specific requirements which are diffe-rent from those intended for high subscriber density areas.
More particularly, the capacity required is less even if the area to which the connected subscribers belong is wide, but a high degree of equipment reliability is essential to ensure a high qaulity of service. In fact, such exchanges are not assisted by skilled personnel, and therefore means must be provided to deal with failures in the best possible way.
In such cases a temporary downgrading of service, that is a reduction in the number of contemporaneous calls, i5 admissible, but the possibility of a complete interruption must be avoided. In addition, as thP exchanges are generally placed in remote areas, the intervention of skilled personnel for repair in the event of failure takes a lot of -time and is 20 very expensive. -The present trend is towards making the need for such intervantion less probable and delaying it in time, that is towards improving the exchange reliability.
The time that may elapse between one intervention and the next has been taken merely as one of the parameters which can define the reliability of a system, representing the interval between two consecutive conditions of serious equip-ment failure.
In the case of a digital exchange, the part requir-ing higher reliability is of course the one controlling thetime development of the subscriber's interconnections.
In fact, if a failure occurs in this section, very serious consequences may result in the traffic control, which -1- ~
35~
may cause a complete traffic interruption. An attempt has been made to prevent the occurren~e of such a failure, basically resorting to a solution requiring the duplication of control units.
Thus the intervention time could be increased, but a greater circuit complexit~ would be inevitable, and increased complexity would not help the system reliability. The greatest difficulty is met in making two control units cooperate without interfering.
These drawbacks can be avoided by means of operating procedures which make the two control units work one at the -~
time (cold stand-by~ or at the same time (hot stand-by). In `~
the first case, some problems for the spare unit initialization arise when the outstanding work is to be taken up~ ;
This operation must be effected so that no connection is cut-off. Another problem is in providing a unit of h.igher hierarchy than the control units which reali~es that one of two control units is not regula~ly working and makes an interven-tion in due time to start the spare oneO
In the case of a hot stand-by both the units operate at the same time under the control of one of -them.
In this case there is no initialization problem, as all the subscriber's interconnections are supervised at the sc~me time by both the control units, but the decision as to which of them is operating regularly is more difficulto :
Hence it is clear that for both solutions the prob-lem of a single control unit has been transferred to another single unit, which can be called a supervisor, which is equally subject to failures and e~uall~ important in control~ing the traffic. A failure in the super~isor presents the same ser.ious disadvantages as in the control unit.
Such disadvantages are overcome by a digital exchange in accordance with the present invention. By utilizing a ~.
, ~L~35~
_, control unit consisting of a plurality of individual units, each of them being devoted to a portion of the traffic, the system allows lon~er times be~ween the interventions before the service i5 degraded to an unacceptable level. It makes use of simple circuits equivalent to one another thus obtaining a considerable economic advantage in respect of the need for spare parts and allowing quick interventions of the maintenance personnel.
In addition it presents a great versatility in respect of the possibility of increasing the number o-f subscribers to be serviced, as it does not require modifications of the control programs of the control unit, but only the addition of individ- ;
ual circuits equivalent to the existing ones.
Finally, in the present digital exchange the same connection network is utilized both for the subscriber-to~
control unit communication and for control unit-to~control unit ;
communication, by exploiting a number of time channels in the ~ -frame PCM (Pulse Code Modulation).
According to the present invention an automatic digital -;
telephone exchange serving a group of associated subscriber stations divided into se~eral subgroups includes- a set oE
substantially identical control units assigned to each subgroup of subscriber stations and programmed to carry out different but mutually complementary operations in the establishment and termination of a telephone connecti~n involving at least one station of the respective subgroupi a common PCM coupling -network for each set accessible to each of said control units thereof, to the subscriber stations of the respective subgroup, and to terminal means common to said groupi and an access unit for each set responsive to signals from said control units thereof for satisfying requests fox connection to said coupling network/ said control units communicating with on~ another via said coupling network under the command of said access unit~
_ ~ _ These and other characteristics of the present inven-tion will become clearer from the following description of a p.referred embodiment thereof, given by way of example and not :
in a limiting sense, taken in connect.ion with the accompanying drawings, in which:
Figure 1 is a block diagram of a digital exchange according to the present invention;
Figure 2 is a detailed block diagram of blocks de-noted by OCl, -- OCn in Figure 1.
In Figure 1 references 1,2 --- 16 denote the groups `
of lines coming from the subscriber's sets, connected with the same number of subscriber's circuits CUl, CU2 --- CU16, in which the speech signals and the signalling are coded in PCM
at 64 kbit/s.
At the subscriber's circuit outputs, wires 21 and 22 respectively assigned to signalling of associated type and :~
speech signals are ioined in wire:23, passing to a PCM group at 2 Mbit/s (2.16.64 kbit/s). : ~;
On wires a and b there are present synchronism sig-nals at 125 ~s and timing signals at 2M~Iz, which are necessaryfor the corract operation of the subscriber's circuits. It will be explained subsequently how these signals are obtained. ~.
The connection between subscribers belonging to the : same exchange or with subscribers belonging to other exchanges occurs through a ncrmal connection network between lines PCM, ~ ~
denoted by RC in Figure 1. --.
This can advantageously be an overall accessilibity single stage of the time type. To simplify the desaription ; ~:
re~erence will be made hereinafter to an exchange for an area with low subscriber density where the subscribers to be ser-viced are a few hundred in number.
In this case, the connection network RC is not expen- -sive, owing to the limited capacity required. In addition to PCM lines coming from subscriber's circuits, the connection network provides access for control units OCl~ OC2 --- OCn by means of a PCM line 24, still at 2 Mbit/s; the structure of these units will be described in more detail hereinafter. There are still lines operating at 64 Kbit/s, joined into a group denoted by 25 in Figure 1. These lines arri~e from a conven-tional addressing unit for the c~nnection network, denoted by AM and structurally similar to the control units.
The number of lines forming the group 25 is e~ual to ~:
the number of control units required to allow interconnection of each unit with any unit or su~scriber through subscriber's circuits.
To the.connection network a conventional line termi-nal TL is connected, this being able to extract timing and syn-chronism signals from PCM bidireational connection 28 operating at 2 Mbit/s and coming fxom the highex hiexarchy switching centre. This PCM connection through TL arrives at the connec~
tion network RC. The time information obtained by TL is trans- : :
ferred by means of wire 29 to a time-base BT, which through :
suitable dividing operations and processing of the pulse format supplies timing and synchronism signals on wires 30 and 31.
If TL does not supply the time information on wire 29, a local oscillator OS intervenes and independently generates ~ ::
timing and synchronism signals on wires 32 and 33. of course these signals are not synchronized with those of the higher :~
hierarchy centre, but are sufficient for the normal control of :
local traffic. A normal switch SW can independently recogni~e the absence of the signals supplied by BT and then draw said signals from OS in order to transfer -them to wires a and b connected with the other blocks of the exchange.
Figure 2 shows one of the control units, in a more detailed block diagram, generically denoted by OCn. Reference CPU denotes a central processing unit, advantageously of the -5- ~.
~ ~3~2~
type contained in a single integrated circuit in order to re-duce as far as possible the encumbrance and the cost of each unit. Such processing units are nowadays readily available and are well known to the skilled in the art.
Reerence MP denotes a typical memory unit designed to store both the control programs of the control unit and data concerning the various phases of the telephone connection. For a reasonable number of subscribers served at the same time by each unit, for instance from 4 to 8, this memory unit must have a storage capacity of about 2 to 3 K-bytes. This value may be found in the memory units contained in the same chip where the CPU is located. References MI and MU denote two re~d and write memory units, able to store a predetermined number of PCM frames belonging to one or more channe~s at 64 Kbit/s.
These frames are relevant to data arriving from other control units or from subscriber's circuits, as to what concerns memory unit MI devoted to store incoming data extracted from channels at 64 Kbit/s, or arriving from the same CPU, as to what concerns memory unit MU devoted to store the data to be 20 transferred towards the outside inserting them into PCM frames ~
at 64 bit/s. ~-Reference LS denotes a specialized logic circuik for the specific functions carried out by the type o~ control unit -where it is placed. For instance LS can be a logic circuit able to recognize the digits dialed in multi-frequency code on ;~
a keyboard telephone set.
Memory units MI and MU, as well as the specialized logic circuit LS, are connected with the CPU through a bus 35, while MP connection can be integrated with the CPU and MP on the same chip. The inputs of MI and LS and the output of MU
are inserted as channels at 64 Kbit/s onto a single line PCM at
The present invention relates to equipment for the control of telephone traffic and more particularly it relates to a digital telephone exchange for areas of low subscriber density.
Telephone exchanges intended for low subscriber den-sity areas have to meet specific requirements which are diffe-rent from those intended for high subscriber density areas.
More particularly, the capacity required is less even if the area to which the connected subscribers belong is wide, but a high degree of equipment reliability is essential to ensure a high qaulity of service. In fact, such exchanges are not assisted by skilled personnel, and therefore means must be provided to deal with failures in the best possible way.
In such cases a temporary downgrading of service, that is a reduction in the number of contemporaneous calls, i5 admissible, but the possibility of a complete interruption must be avoided. In addition, as thP exchanges are generally placed in remote areas, the intervention of skilled personnel for repair in the event of failure takes a lot of -time and is 20 very expensive. -The present trend is towards making the need for such intervantion less probable and delaying it in time, that is towards improving the exchange reliability.
The time that may elapse between one intervention and the next has been taken merely as one of the parameters which can define the reliability of a system, representing the interval between two consecutive conditions of serious equip-ment failure.
In the case of a digital exchange, the part requir-ing higher reliability is of course the one controlling thetime development of the subscriber's interconnections.
In fact, if a failure occurs in this section, very serious consequences may result in the traffic control, which -1- ~
35~
may cause a complete traffic interruption. An attempt has been made to prevent the occurren~e of such a failure, basically resorting to a solution requiring the duplication of control units.
Thus the intervention time could be increased, but a greater circuit complexit~ would be inevitable, and increased complexity would not help the system reliability. The greatest difficulty is met in making two control units cooperate without interfering.
These drawbacks can be avoided by means of operating procedures which make the two control units work one at the -~
time (cold stand-by~ or at the same time (hot stand-by). In `~
the first case, some problems for the spare unit initialization arise when the outstanding work is to be taken up~ ;
This operation must be effected so that no connection is cut-off. Another problem is in providing a unit of h.igher hierarchy than the control units which reali~es that one of two control units is not regula~ly working and makes an interven-tion in due time to start the spare oneO
In the case of a hot stand-by both the units operate at the same time under the control of one of -them.
In this case there is no initialization problem, as all the subscriber's interconnections are supervised at the sc~me time by both the control units, but the decision as to which of them is operating regularly is more difficulto :
Hence it is clear that for both solutions the prob-lem of a single control unit has been transferred to another single unit, which can be called a supervisor, which is equally subject to failures and e~uall~ important in control~ing the traffic. A failure in the super~isor presents the same ser.ious disadvantages as in the control unit.
Such disadvantages are overcome by a digital exchange in accordance with the present invention. By utilizing a ~.
, ~L~35~
_, control unit consisting of a plurality of individual units, each of them being devoted to a portion of the traffic, the system allows lon~er times be~ween the interventions before the service i5 degraded to an unacceptable level. It makes use of simple circuits equivalent to one another thus obtaining a considerable economic advantage in respect of the need for spare parts and allowing quick interventions of the maintenance personnel.
In addition it presents a great versatility in respect of the possibility of increasing the number o-f subscribers to be serviced, as it does not require modifications of the control programs of the control unit, but only the addition of individ- ;
ual circuits equivalent to the existing ones.
Finally, in the present digital exchange the same connection network is utilized both for the subscriber-to~
control unit communication and for control unit-to~control unit ;
communication, by exploiting a number of time channels in the ~ -frame PCM (Pulse Code Modulation).
According to the present invention an automatic digital -;
telephone exchange serving a group of associated subscriber stations divided into se~eral subgroups includes- a set oE
substantially identical control units assigned to each subgroup of subscriber stations and programmed to carry out different but mutually complementary operations in the establishment and termination of a telephone connecti~n involving at least one station of the respective subgroupi a common PCM coupling -network for each set accessible to each of said control units thereof, to the subscriber stations of the respective subgroup, and to terminal means common to said groupi and an access unit for each set responsive to signals from said control units thereof for satisfying requests fox connection to said coupling network/ said control units communicating with on~ another via said coupling network under the command of said access unit~
_ ~ _ These and other characteristics of the present inven-tion will become clearer from the following description of a p.referred embodiment thereof, given by way of example and not :
in a limiting sense, taken in connect.ion with the accompanying drawings, in which:
Figure 1 is a block diagram of a digital exchange according to the present invention;
Figure 2 is a detailed block diagram of blocks de-noted by OCl, -- OCn in Figure 1.
In Figure 1 references 1,2 --- 16 denote the groups `
of lines coming from the subscriber's sets, connected with the same number of subscriber's circuits CUl, CU2 --- CU16, in which the speech signals and the signalling are coded in PCM
at 64 kbit/s.
At the subscriber's circuit outputs, wires 21 and 22 respectively assigned to signalling of associated type and :~
speech signals are ioined in wire:23, passing to a PCM group at 2 Mbit/s (2.16.64 kbit/s). : ~;
On wires a and b there are present synchronism sig-nals at 125 ~s and timing signals at 2M~Iz, which are necessaryfor the corract operation of the subscriber's circuits. It will be explained subsequently how these signals are obtained. ~.
The connection between subscribers belonging to the : same exchange or with subscribers belonging to other exchanges occurs through a ncrmal connection network between lines PCM, ~ ~
denoted by RC in Figure 1. --.
This can advantageously be an overall accessilibity single stage of the time type. To simplify the desaription ; ~:
re~erence will be made hereinafter to an exchange for an area with low subscriber density where the subscribers to be ser-viced are a few hundred in number.
In this case, the connection network RC is not expen- -sive, owing to the limited capacity required. In addition to PCM lines coming from subscriber's circuits, the connection network provides access for control units OCl~ OC2 --- OCn by means of a PCM line 24, still at 2 Mbit/s; the structure of these units will be described in more detail hereinafter. There are still lines operating at 64 Kbit/s, joined into a group denoted by 25 in Figure 1. These lines arri~e from a conven-tional addressing unit for the c~nnection network, denoted by AM and structurally similar to the control units.
The number of lines forming the group 25 is e~ual to ~:
the number of control units required to allow interconnection of each unit with any unit or su~scriber through subscriber's circuits.
To the.connection network a conventional line termi-nal TL is connected, this being able to extract timing and syn-chronism signals from PCM bidireational connection 28 operating at 2 Mbit/s and coming fxom the highex hiexarchy switching centre. This PCM connection through TL arrives at the connec~
tion network RC. The time information obtained by TL is trans- : :
ferred by means of wire 29 to a time-base BT, which through :
suitable dividing operations and processing of the pulse format supplies timing and synchronism signals on wires 30 and 31.
If TL does not supply the time information on wire 29, a local oscillator OS intervenes and independently generates ~ ::
timing and synchronism signals on wires 32 and 33. of course these signals are not synchronized with those of the higher :~
hierarchy centre, but are sufficient for the normal control of :
local traffic. A normal switch SW can independently recogni~e the absence of the signals supplied by BT and then draw said signals from OS in order to transfer -them to wires a and b connected with the other blocks of the exchange.
Figure 2 shows one of the control units, in a more detailed block diagram, generically denoted by OCn. Reference CPU denotes a central processing unit, advantageously of the -5- ~.
~ ~3~2~
type contained in a single integrated circuit in order to re-duce as far as possible the encumbrance and the cost of each unit. Such processing units are nowadays readily available and are well known to the skilled in the art.
Reerence MP denotes a typical memory unit designed to store both the control programs of the control unit and data concerning the various phases of the telephone connection. For a reasonable number of subscribers served at the same time by each unit, for instance from 4 to 8, this memory unit must have a storage capacity of about 2 to 3 K-bytes. This value may be found in the memory units contained in the same chip where the CPU is located. References MI and MU denote two re~d and write memory units, able to store a predetermined number of PCM frames belonging to one or more channe~s at 64 Kbit/s.
These frames are relevant to data arriving from other control units or from subscriber's circuits, as to what concerns memory unit MI devoted to store incoming data extracted from channels at 64 Kbit/s, or arriving from the same CPU, as to what concerns memory unit MU devoted to store the data to be 20 transferred towards the outside inserting them into PCM frames ~
at 64 bit/s. ~-Reference LS denotes a specialized logic circuik for the specific functions carried out by the type o~ control unit -where it is placed. For instance LS can be a logic circuit able to recognize the digits dialed in multi-frequency code on ;~
a keyboard telephone set.
Memory units MI and MU, as well as the specialized logic circuit LS, are connected with the CPU through a bus 35, while MP connection can be integrated with the CPU and MP on the same chip. The inputs of MI and LS and the output of MU
are inserted as channels at 64 Kbit/s onto a single line PCM at
2 Mbit/s, denoted in the drawing by 24. It corresponds to the PCM line denoted by the same number in Figure 1. Also in l3~
Figure 2, reference DT denotes a typical time base which recei- :
~es on wires a and b synchronism and timing signals and proces-ses them so as to obtain the suitable signals for memory units MI and MU. These signals are sent to MI and MU by means of wire 34.
The timing signal present on wire b also accesses CPU, without preprocessing effected by DT.
The individual units differ from one another solely in the program stored in the memory unit MP and in -the -type of specialized logic LS. This latter in some control units can also be absent. The number of units, even in the program, de-pends of course on the traffic ~ontrolled by the exchange and on the specific function of the unit. Now the functions to be carried out by the control units within a telephone connection will be examined.
The most important functions are the following~
a) det~ction of the seizure request sent by the calling sub-scriber;
b) making of the connection (storage of the dialing);
c) search for the path to be followed to reach the called sub- ;
scriber;
d~ check of the path chosen for the conversation;
e) call charge;
f) interchange of informa-tion, both permanent and temporary :
information on the subscriber and on the connection;
g) control of the exchange and information interchange with the higher hierarchy centre;
h) emission of instructions for timing signals of the conne~-tion network that are necessary to effect the connection. :~
30These functiQns can be grouped into homogeneous groups and allotted to the control units as follows:
- functions a) and b) to the first type of unit OCl;
- functions d) and e~ to the second type of unit OC2;
.
functions c) and f) to the third type of unit OC3;
- function g) to the fourth type of unit OC4;
- function h) to -the fifth type of.unit AM.
Now the way in which the various units connected with ~:
the connection network utili2e that same network to COmmuniGate with one another will be examined.
Each unit communicates with the others by means of message characterized by a flag of "message start" followed by a variable number of words, containing the information to be transmitted.
The commands and the infoxmation transferred from and to the subscriber, on the other hand, are contained in a single word representing the subscriber's state.
As already seen, units and subscribers access the connection network RC by means of channels at 64 Kbit/s inser-ted into groups at 2 Mbit/s. More particularly each subscriber is alloted a channel at 64 Kbit/s for speeGh and one at an equal rate for signalling.
On the signalling channel, one for subscriber, the ~ollowing information is sent on the transmission side~
- current in one of the wires of the telephone line;
- current on the other wire;
- subscriber's circuit in service;
- cut off subscriber's circuit.
The following information is sent on the reception side:
- line scanning command;
- command to put in service the subscriber's circuit; .
- command to send the call current;
- charge command;
- command to cut-off the subscriber's circuit.
Each subscriber is therefore able to signal, through the connection network, its state to any unit connected with ~ 3..3P~
the network by means of a switching operation effect by the interested unit and to receive the commands in an analogous way.
To each unit a plurality of channels at 64 Kbit/s are allotted. These channels can be utilized according to the time phase of the connection to send the request for connec-tions with other units and the commands towards the subscribers, to effect the check of the subscriber's state and the informa-tion interchange with other units.
The first type o~ unit OCl, on the basis o~ the func tions carried out, is allotted:
~ a communication channel with block AM to control the switch-ing operations;
- a channel to scan the state of each subscriber's circuit and to control its activation;
- a channel to communicate in time sharing and on demand with other units; ~ `
- a channel to request the conn~ction with other units;
- a channel to communicate with the subscriber's circuit in the phase of setting up of the connection.
The second type of unit OC2 i5 allotted: ~;
- a channel to communicate with A~ for switching control;
- a channel to effect the request for connection with other :~
units;
- a channel to communicate in time-sharing and on demand with ~ ~`
the other units; ~;
- a channel on which the communication with the subscriber's circuit is effected in the conversation phase of the con-nection.
The third type of device OC3 is allotted:
- a channel to communicate with AM for switching control;
- a channel to communicate in time-sharing ancl on demand with other units;
_g_ ~3~
- a channel to effect the connection request with other units.
The fourth type of device OC4 is allotted:
- a channel to communicate in time-sharing and on demand with other units;
- a signalling channel towards the centre of higher hierarchy;
- a channel to send the connection requast with other units. ~;;
Finally the fiEth type of unit AM, is allotted a channel for each unit to effect the switching operations.
As shown, each unit is allotted a channel to eEfect the connection re~uest with other units (communication channel with AM).
This channel is scanned, in different -time phases, by the units which can be con~ected with it.
For instance, OCl is seen by OC2 in a first time phase and by OC3 in a second time phas~ and in following phases by the other units which can communicate with it.
The request for connectionis effecte~by a characteris- ;
tic word for each lmit that remains to the moment in which it is serviced~
Now will be examined the way in which a unit is con-nected with another, for instance OCl with OC2 in the first phase of the connection. The interested unit, by utilizing the channel allotted to the request for connection with other units ef~ects the request. The other unit, during the time period it has been allotted, examines the contents of the request and, by utilizing the channel for the communication with AM, con- ~;
nects itself with the requesting party. At this point the mes-sage communication between the connected units is initiated.
Beginning from a message of "completed connection". In this way OCl can delete the request and initiate the actual ~ommunl-cation.
At the end of the information interchange the unit that has effected the request stops the communication by a
Figure 2, reference DT denotes a typical time base which recei- :
~es on wires a and b synchronism and timing signals and proces-ses them so as to obtain the suitable signals for memory units MI and MU. These signals are sent to MI and MU by means of wire 34.
The timing signal present on wire b also accesses CPU, without preprocessing effected by DT.
The individual units differ from one another solely in the program stored in the memory unit MP and in -the -type of specialized logic LS. This latter in some control units can also be absent. The number of units, even in the program, de-pends of course on the traffic ~ontrolled by the exchange and on the specific function of the unit. Now the functions to be carried out by the control units within a telephone connection will be examined.
The most important functions are the following~
a) det~ction of the seizure request sent by the calling sub-scriber;
b) making of the connection (storage of the dialing);
c) search for the path to be followed to reach the called sub- ;
scriber;
d~ check of the path chosen for the conversation;
e) call charge;
f) interchange of informa-tion, both permanent and temporary :
information on the subscriber and on the connection;
g) control of the exchange and information interchange with the higher hierarchy centre;
h) emission of instructions for timing signals of the conne~-tion network that are necessary to effect the connection. :~
30These functiQns can be grouped into homogeneous groups and allotted to the control units as follows:
- functions a) and b) to the first type of unit OCl;
- functions d) and e~ to the second type of unit OC2;
.
functions c) and f) to the third type of unit OC3;
- function g) to the fourth type of unit OC4;
- function h) to -the fifth type of.unit AM.
Now the way in which the various units connected with ~:
the connection network utili2e that same network to COmmuniGate with one another will be examined.
Each unit communicates with the others by means of message characterized by a flag of "message start" followed by a variable number of words, containing the information to be transmitted.
The commands and the infoxmation transferred from and to the subscriber, on the other hand, are contained in a single word representing the subscriber's state.
As already seen, units and subscribers access the connection network RC by means of channels at 64 Kbit/s inser-ted into groups at 2 Mbit/s. More particularly each subscriber is alloted a channel at 64 Kbit/s for speeGh and one at an equal rate for signalling.
On the signalling channel, one for subscriber, the ~ollowing information is sent on the transmission side~
- current in one of the wires of the telephone line;
- current on the other wire;
- subscriber's circuit in service;
- cut off subscriber's circuit.
The following information is sent on the reception side:
- line scanning command;
- command to put in service the subscriber's circuit; .
- command to send the call current;
- charge command;
- command to cut-off the subscriber's circuit.
Each subscriber is therefore able to signal, through the connection network, its state to any unit connected with ~ 3..3P~
the network by means of a switching operation effect by the interested unit and to receive the commands in an analogous way.
To each unit a plurality of channels at 64 Kbit/s are allotted. These channels can be utilized according to the time phase of the connection to send the request for connec-tions with other units and the commands towards the subscribers, to effect the check of the subscriber's state and the informa-tion interchange with other units.
The first type o~ unit OCl, on the basis o~ the func tions carried out, is allotted:
~ a communication channel with block AM to control the switch-ing operations;
- a channel to scan the state of each subscriber's circuit and to control its activation;
- a channel to communicate in time sharing and on demand with other units; ~ `
- a channel to request the conn~ction with other units;
- a channel to communicate with the subscriber's circuit in the phase of setting up of the connection.
The second type of unit OC2 i5 allotted: ~;
- a channel to communicate with A~ for switching control;
- a channel to effect the request for connection with other :~
units;
- a channel to communicate in time-sharing and on demand with ~ ~`
the other units; ~;
- a channel on which the communication with the subscriber's circuit is effected in the conversation phase of the con-nection.
The third type of device OC3 is allotted:
- a channel to communicate with AM for switching control;
- a channel to communicate in time-sharing ancl on demand with other units;
_g_ ~3~
- a channel to effect the connection request with other units.
The fourth type of device OC4 is allotted:
- a channel to communicate in time-sharing and on demand with other units;
- a signalling channel towards the centre of higher hierarchy;
- a channel to send the connection requast with other units. ~;;
Finally the fiEth type of unit AM, is allotted a channel for each unit to effect the switching operations.
As shown, each unit is allotted a channel to eEfect the connection re~uest with other units (communication channel with AM).
This channel is scanned, in different -time phases, by the units which can be con~ected with it.
For instance, OCl is seen by OC2 in a first time phase and by OC3 in a second time phas~ and in following phases by the other units which can communicate with it.
The request for connectionis effecte~by a characteris- ;
tic word for each lmit that remains to the moment in which it is serviced~
Now will be examined the way in which a unit is con-nected with another, for instance OCl with OC2 in the first phase of the connection. The interested unit, by utilizing the channel allotted to the request for connection with other units ef~ects the request. The other unit, during the time period it has been allotted, examines the contents of the request and, by utilizing the channel for the communication with AM, con- ~;
nects itself with the requesting party. At this point the mes-sage communication between the connected units is initiated.
Beginning from a message of "completed connection". In this way OCl can delete the request and initiate the actual ~ommunl-cation.
At the end of the information interchange the unit that has effected the request stops the communication by a
3~
message of "stop" which the request unit interprets as connec-tion release.
Now OCl can effect other requests and OC2 can examine the request channels of other units.
The time interval~ elapsing between two subsequent examinatiorsof the same request channel, is determined bv the time necessary to satisfy a request while the time interval elapsing between two examinations of the same request channel made by a unit is a function of the numher of units present.
Now the operation of the various sections of the ex-change will be examined in the case of a typical telephone call.
OCl examines the "seizure request" made by the sub-scribers (function a), cyclically connecting itself with them through the connecting path which AM supplies upon the request made by the unit itsel. When it detects one, it stops, re-maining connected with the calling subscriber during the time necessary to satisfy the request.
The dial tone and the power supply are sent immediate-ly~ The time necessary to satisfy the request must be equal to the time taken by the other units to examine the states of all the subscribers, so as to prevent another unit of the same type from stopping on the same subscriber. Now the calling party can dial the required telephone number, which is recognized by the same unit (function b) as a result o the dialing and is transEerred to unit OC3 which looks for the path to ollow to reach the called subscriber ~function c), to supply possible information necessary ta the connection (function f) and to inform OCl of the result of the path search.
I that denotes that the called subscriber is connec-ted with the same exchange, OCl connects itself with OC2 andtransers all the instructions concerning the connection that OC2 is going to control during the whole conversation phase.
The tLme intervals will be taken into account for charging za~
purposes (Eunction e), the release operation will be recognized, etc. If the result of the searah denotes that the called sub~
scriber does not belong to the sam exchange, OCl re~uires the intervention of OC4, which controls the connection with the higher hierarchy centre according to the standardized procedure (function g).
The messages exchanged among the control units are formed by a word of "start of message" one of "identification of the unit" sending the message, following by a varying number of words containing the information object of the communication, Finally there is a word o "end of message" with functions of check of the correatness of the message itself.
Modifications and variations can be given to the ways of embodiment already described without departing from the ;
scope of the invention.
message of "stop" which the request unit interprets as connec-tion release.
Now OCl can effect other requests and OC2 can examine the request channels of other units.
The time interval~ elapsing between two subsequent examinatiorsof the same request channel, is determined bv the time necessary to satisfy a request while the time interval elapsing between two examinations of the same request channel made by a unit is a function of the numher of units present.
Now the operation of the various sections of the ex-change will be examined in the case of a typical telephone call.
OCl examines the "seizure request" made by the sub-scribers (function a), cyclically connecting itself with them through the connecting path which AM supplies upon the request made by the unit itsel. When it detects one, it stops, re-maining connected with the calling subscriber during the time necessary to satisfy the request.
The dial tone and the power supply are sent immediate-ly~ The time necessary to satisfy the request must be equal to the time taken by the other units to examine the states of all the subscribers, so as to prevent another unit of the same type from stopping on the same subscriber. Now the calling party can dial the required telephone number, which is recognized by the same unit (function b) as a result o the dialing and is transEerred to unit OC3 which looks for the path to ollow to reach the called subscriber ~function c), to supply possible information necessary ta the connection (function f) and to inform OCl of the result of the path search.
I that denotes that the called subscriber is connec-ted with the same exchange, OCl connects itself with OC2 andtransers all the instructions concerning the connection that OC2 is going to control during the whole conversation phase.
The tLme intervals will be taken into account for charging za~
purposes (Eunction e), the release operation will be recognized, etc. If the result of the searah denotes that the called sub~
scriber does not belong to the sam exchange, OCl re~uires the intervention of OC4, which controls the connection with the higher hierarchy centre according to the standardized procedure (function g).
The messages exchanged among the control units are formed by a word of "start of message" one of "identification of the unit" sending the message, following by a varying number of words containing the information object of the communication, Finally there is a word o "end of message" with functions of check of the correatness of the message itself.
Modifications and variations can be given to the ways of embodiment already described without departing from the ;
scope of the invention.
Claims (5)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In an automatic digital telephone exchange serving a group of associated subscriber stations divided into several subgroups, in combination:
a set of substantially identical control units assigned to each subgroup of subscriber stations and programmed to carry out different but mutually complementary operations in the establishment and termination of a telephone connection involving at least one station of the respective subgroup;
a common PCM coupling network for each set accessible to each of said control units thereof, to the subscriber stations of the respective subgroup, and to terminal means common to said group; and an access unit for each set responsive to signals from said control units thereof for satisfying requests for connection to said coupling network, said control units communicating with one another via said coupling network under the command of said access unit.
a set of substantially identical control units assigned to each subgroup of subscriber stations and programmed to carry out different but mutually complementary operations in the establishment and termination of a telephone connection involving at least one station of the respective subgroup;
a common PCM coupling network for each set accessible to each of said control units thereof, to the subscriber stations of the respective subgroup, and to terminal means common to said group; and an access unit for each set responsive to signals from said control units thereof for satisfying requests for connection to said coupling network, said control units communicating with one another via said coupling network under the command of said access unit.
2. The combination defined in claim 1 wherein each of said control units comprises a central processor provided with a program memory, storage means for incoming and outgoing messages, and timing means for operating said program memory and said storage means under the command of a synchronizing unit common to all said control units.
3. The combination defined in claim 2 wherein each of said control units further includes a logic network connected to said central processor and said storage means thereof, said logic network being responsive to special codes individual to the respective control unit.
4. The combination defined in claim 1, 2 or 3 wherein said access unit has a structure substantially identical with that of any of said control units.
5. The combination defined in claim 1, 2 or 3 wherein at least some of said control units have identical counterparts included in said set in a standby mode.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT67544/79A IT1118433B (en) | 1979-03-15 | 1979-03-15 | NUMERICAL TELEPHONE SELF-SWITCH FOR LOW DENSITY AREAS |
| IT67544-A/79 | 1979-03-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1135820A true CA1135820A (en) | 1982-11-16 |
Family
ID=11303309
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000345143A Expired CA1135820A (en) | 1979-03-15 | 1980-02-06 | Digital telephone exchange for areas of low subscriber's density |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4356563A (en) |
| EP (1) | EP0016426B1 (en) |
| JP (1) | JPS55124387A (en) |
| CA (1) | CA1135820A (en) |
| DE (1) | DE3068846D1 (en) |
| IT (1) | IT1118433B (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2503513A1 (en) * | 1981-04-03 | 1982-10-08 | Cit Alcatel | TEMPORAL SELF-TIMER WITH DISTRIBUTED CONTROL |
| FR2513471A1 (en) * | 1981-09-18 | 1983-03-25 | Cit Alcatel | SIGNAL DISTRIBUTION DEVICE FOR TEMPORAL SELF-TIMER |
| FR2513470B1 (en) * | 1981-09-18 | 1986-02-21 | Cit Alcatel | GROUP OF TERMINAL UNITS FOR DIGITAL AUTOMATIC SWITCHES |
| US4456991A (en) * | 1981-09-18 | 1984-06-26 | International Telephone And Telegraph Corporation | Telephone line circuit and system |
| US4504942A (en) * | 1982-04-22 | 1985-03-12 | International Telephone And Telegraph Corporation | Line switch having distributed processing |
| US4527266A (en) * | 1982-04-22 | 1985-07-02 | International Telephone And Telegraph Corporation | Interface circuit for use in a distributed processing switch unit |
| DE3377565D1 (en) * | 1982-12-22 | 1988-09-01 | Siemens Ag | Communications installation, in particular a private branch exchange with subscriber and trunk groups and interface modules |
| GB2143403B (en) * | 1983-07-15 | 1986-10-29 | Standard Telephones Cables Ltd | Telecommunication exchange |
| USRE34896E (en) * | 1985-12-04 | 1995-04-04 | International Business Machines Corporation | Multiplex interface for a communication controller |
| EP0232437B1 (en) * | 1985-12-04 | 1990-06-13 | International Business Machines Corporation | Multiplex interface for a communication controller |
| ES2091832T3 (en) * | 1991-05-08 | 1996-11-16 | Siemens Ag | CONTROL PROVISION FOR A BROADBAND SWITCHING SYSTEM. |
| US5610912A (en) * | 1994-08-01 | 1997-03-11 | British Telecommunications Public Limited Company | Switching in a telecommunications service node |
| JPH09233181A (en) * | 1996-02-21 | 1997-09-05 | Fujitsu Ltd | Configuration system for v5 interface |
| US6038228A (en) * | 1997-04-15 | 2000-03-14 | Alcatel Usa Sourcing, L.P. | Processing call information within a telecommunications network |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1300421A (en) * | 1969-04-14 | 1972-12-20 | Marconi Co Ltd | Improvements in or relating to data transmission arrangements |
| US3974343A (en) * | 1975-01-10 | 1976-08-10 | North Electric Company | Small modular communications switching system with distributed programmable control |
| DE2621603C3 (en) * | 1976-05-14 | 1978-11-16 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Method and circuit arrangement for the independent transmission of PCM message words and signaling words between a subscriber station and an exchange |
| US4074072A (en) * | 1976-05-24 | 1978-02-14 | Bell Telephone Laboratories, Incorporated | Multiprocessor control of a partitioned switching network by control communication through the network |
| US4256926A (en) * | 1976-10-21 | 1981-03-17 | Wescom Switching, Inc. | Microprocessor control complex for a telecommunication switching system |
| US4201891A (en) * | 1978-03-17 | 1980-05-06 | International Telephone And Telegraph Corporation | Expandable digital switching network |
| GB1583633A (en) * | 1977-03-02 | 1981-01-28 | Int Standard Electric Corp | Distributed control for switching system |
| AT380980B (en) * | 1978-03-17 | 1986-08-11 | Int Standard Electric Corp | TELECOMMUNICATION SYSTEM |
-
1979
- 1979-03-15 IT IT67544/79A patent/IT1118433B/en active
-
1980
- 1980-02-06 CA CA000345143A patent/CA1135820A/en not_active Expired
- 1980-03-12 JP JP3043180A patent/JPS55124387A/en active Pending
- 1980-03-14 DE DE8080101327T patent/DE3068846D1/en not_active Expired
- 1980-03-14 EP EP80101327A patent/EP0016426B1/en not_active Expired
-
1981
- 1981-06-18 US US06/275,020 patent/US4356563A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| IT1118433B (en) | 1986-03-03 |
| EP0016426A1 (en) | 1980-10-01 |
| EP0016426B1 (en) | 1984-08-08 |
| IT7967544A0 (en) | 1979-03-15 |
| DE3068846D1 (en) | 1984-09-13 |
| JPS55124387A (en) | 1980-09-25 |
| US4356563A (en) | 1982-10-26 |
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| MKEX | Expiry |