WO1982002784A1

WO1982002784A1 - Data communications network

Info

Publication number: WO1982002784A1
Application number: PCT/SE1982/000017
Authority: WO
Inventors: Telefon Ab L M Ericsson; Nils Herbert Edstroem
Original assignee: Telefon Ab L M Ericsson
Priority date: 1981-01-30
Filing date: 1982-01-21
Publication date: 1982-08-19
Also published as: GB2110505B; SE8100654L; SE425282B; IT8219244A0; ES8302389A1; GB2110505A; ES509173A0; NO823168L; NL8220011A; DK433182A

Abstract

In a single-base data communications network the data base includes at least two data base units (1-3) which are geographically separated from each other but otherwise identical and connected to data terminals (6-14) by a telecommunications network (15-35). Each data base unit is connected to at least one of connecting notes (15-22) of the communications network, provided with path selectors, and includes an updating transmitter/receiver which is connected by permanent established connections (4-5) to the updating transmitter/receiver of the other data base units. The data base units include selecting means (36-38) which generate designation signals for selecting one of the base units at a time as an executive unit. The randomly generated designation signal is transmitted at least to the data base unit selected as the executive unit to start its selecting means and updating transmitter (43), and to all the path selectors of the network which control calls from the data terminals to the executive unit. The updating transmitter of the executive unit works until all data needed for updating the other data base units is transmitted.

Description

DATA COMMUNICATIONS NETWORK

TECHNICAL FIELD

The present invention relates to a data communications network including a single data base which is connected to data terminals by a telecom¬ munications network containing connecting nodes. The invention thus re¬ lates to a single-base system provided with a central data bank used by terminals spread over a wide area, the terminals fetching stored data in formation from the data bank or sending information to the data bank, in which the information is stored and thereby available for the whole sys¬ tem. In order to transfer the data between the terminals and the base and vice versa the global single-base system includes a telecommunications network known per se, the regional connecting nodes of which are provided with path selectors for selecting the most favourable transfer path with regard to the present traffic load of the network.

BACKGROUND ART

Systems with only one central data bank for all the terminals have known advantages compared to multi-base systems. For example, unnecessary sprea of data information is avoided and handling of the inforπ-ation is facil¬ itated since it can be sent and received only to and from, one position. Handling includes control and use of the information stored in the data bank. Furthermore, handling of the information includes the establishment of the connections between the data base and the terminals. When there is only one data base, each call carried out by a terminal means that there is an unambiguous command to the telecommunications network to connect this terminal to the central data base.

On the other hand a single data base system is very vulnerable. It is indeed known to increase the reliability of a stored program controlled single-processor system, for example, with a so-called parallel-synchron¬ ous working executive computer and reserve computer as described in the Swedish Patent No 369.345. The synchronous working computers'^" each include a data memory, an instruction memory and a processor. Both the computers receive data generated by the system, but the system is controlled by the executive computer only. When a fault occurs in one cf the computers the faultless computer takes over the system control on its own without down time. However, the considerable ability to master technical computer faults in a known way is worthless .for the protection of a single data base, in a nation-wide data communications system, for example, against sabotage or when this single data base falls into the hands of the enemy in time of war. .

DISCLOSURE OF THE INVENTION

A data communications network according to the invention includes at least two data base units which are in.principle identical but separated geographically from each other for reasons of security. Each data base unit constitutes a -data bank in a single-base system, which is able to service in a satisfactory manner the data terminals of the system in real time. The arrangement of said data base units does not involve any loss of the above-mentioned advantages of a single-base system shared by a large number of terminals, but results in a system tolerating a number of faults without its function being impaired.

A terminal which calls the data base by an address, common for all the data base units, does not know to which base unit it will be connected by the path selectors of the network. The terminals must neither know that there are several base units nor their geographical position. In return a designation signal is stored in the path selectors which signal selects one of the base units as the executive unit. Calling terminals will automatically be connected to this executive data base unit.

Said selection of an executive base unit by a designation signal has nothing in common with the above-mentioned parallel-synchronous working system, and the invention is not effected by the manner in which internal reliability is assured, in a data base unit. In order to achieve consid¬ erable internal reliability each data base unit may include the executive computer and the reserve computer which are working in a parallel-syn¬ chronous manner.

The base units, which are not synchronous between themselves, are ar- ranged in the data communications network so that the transfer network connects each base unit to at least one of the connecting nodes and so that permanent connections are established from each base unit to the other base units.

In order, to effect an executive-change without disturbing the present data traffic flow, selecting means included in each data base unit re- spectively, generate one at a time and at random one of said designa¬ tion signals, each associated with a data base unit. The selecting means of the previously executive data base unit, generates the signal which designates the newly selected executive data base unit. The designation signal is transmitted to all the path selectors and to the newly select- ed executive data base unit. If, for example, there is a risk of one of the data base units falling into enemy hands, it can be easily isolated from the network by preventing the selecting means generating the as¬ sociated designation signal and by breaking the connections to this data base unit.

Said permanent established connections between the data base units are used for the automatic internal updating of. the data base. The base unit selected as the executive unit, includes an updating transmitter which starts when receiving the associated designation signal and works until all the data is transmitted which is needed to update- the other data base units.

The characterizations referred to above and characterisations which in detail relate to a data communications network provided with only two data base units and a data network provided with at least three data base units will be seen from the claims.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described below with reference to attached drawings, the Fig 1 of which shows the terminals, connecting nodes, base units of the data communications network and the network paths and the Fig 2 of which shows a selecting means included in each data base unit. MODE FOR CARRYING OUT THE INVENTION

Fig 1 shows a single-base data communications network, the central data base of which consists of three data base units 1-3, which are alike in principle but geographically separated from each other. As will be de¬ scribed with reference to Fig 2, only one of the data base units is al- ways designated as the executive unit by a signal identifying this data base unit, the other base units then automatically being designated as passive units. The data base units 1-3 each include an updating transmit ter/receiver, not shown in Fig 1. Each updating transmitter is connected to both updating receivers remote from this transmitter, via permanent established connections, of which in Fig 1 the two one-way connections 4 and 5 are indicated by dashed lines. These connections^' permanently con¬ nect the transmitter of the data base unit 1 to the receivers of the dat base units 2 and 3. The excutive data base unit updates continuously in a way known per se the passive base units so that it is possible to se- Lect a previously passive data base unit as a newly executive unit. The indicated connections 4 and 5 are consequently used when the base unit 1 is in the executive mode and the base units 2 and 3 are in the passive mode.

Furthermore, Fig 1 shows data, terminal groups 6-14 which as well as the data base units 1-3 are connected to a telecommunications network in¬ cluding a number of connecting nodes 15-22 and path groups 23-35, ai— ranged for two-way traffic. The base unit 1 is connected to the connect¬ ing nodes 15 and 18, the base unit 2 to the connecting node 21, and the base unit 3 to the connecting nodes 19 and 22. It is possible to provide said permanent established connections between the updating transmitters and receivers of the data base units by means of direct links or by mean of the ordinary paths of the telecommunications network. For example, th connection 5 between the base units 1 and 3 may be permanently establish ed by. eans of path 32 between the connecting nodes 18 and 19.

The telecommunications network is controlled by a conventional signallin system which is increased by -the above-mentioned designation signals in order to designate each a data base unit as the executive unit. As soon as a previously passive base unit is designated as a newly executive base unit, .the associated designation signal is received by this base unit and by all the connecting nodes of the network, each of which includes a conventional path selector. Depending on the present traffic situation, the path selectors, communicating between each other by the signalling system, select a suitable path. For example, the path selec¬ tor of the connecting node 16 contains a path group table, according to which a data terminal belonging to group 7 or 8 is connected to the central data base by path 24 or 26 in the event of a call if the base unit 1 is executive, by paths 29 + 33 or path 30 if the base unit is executive, and by paths 26 + 32 or paths 29 + 34 or paths 30 + 35 if the base unit 3 is executive.

The path selectors immediately take into consi eration an executive change in path selection due to new calls from the terminals. An execu¬ tive change, however, does not affect the connections already establish- ed when the change occurs, the change period thus including a short pe¬ riod during which the previously executive base unit terminates initiate services and the newly executive base unit as well as the remaining pas¬ sive base unit and during which the newly executive base unit starts re¬ ceiving new calls, supplying services and updating the previously execu- tive base unit as well as the remaining passive base unit.

If at least three data. units co-operate as described above, each base unit includes a selecting means, shown in Fig 2, the main parts of which consist of a random time generator 36, a random number generator 37 and a signal converter 38 to convert a random time signal, generated by the random time generator, into the designation signal which selects the data base unit designated by the random number generator as the executiv unit. Fig 2 shows a base unit 39 provided with a signal decoder 40 which has its input connected to the signalling system 41 of the telecommunica tions network. The output of the signal decoder, which is activated when the signalling system sends the signal designating the base unit 39, and thereby selecting this base unit as the executive unit, is connected to a first input of a selecting flip-flop 42 and to start inputs of the random time generator, the random number generator^' and the updating transmitter 43 of the base unit 39. The random time generator is so dimensioned that within a fixed period of time, for example, the second

URE<< half hour, it generates a random time signal after each time it is start¬ ed. The random number generator is so dimensioned that, at arbitrary moments of time, it generates arbitrary numbers each associated with one of the remote data base units. The signal converter 38 includes a random number decoder 44, the number-receiving input of which is connected to the random number generator and the activating input of which is connect¬ ed to the random time generator. The outputs of the random number de¬ coder, each assigned to one of the numbers generated by the random number generator, are each connected to -an activating input of a designation signal generator 45, the output- of- which is connected to the signalling system 41 of the data -communications network. The designation signal generator generates signals, depending on which of its inputs is acti¬ vated, which each selects one of the data base units geographically remote from the base unit 39. Furthermore, the designation signal gener- ator 45, when activated, sends a signal pulse to stop inputs of the random time generator 36 and the random number generator 37 and to a second input of the selecting flip-flop 42, both the stable positions of which thus indicate whether the base unit 39 is in the executive or passive mode.

In Fig 2 is not shown the use of the signal decoder 40 for controlling the base unit by the signalling system 41, but a gate arrangement 46, controlled by the selecting flip-flop 41, is indicated for blocking, for example, call signals which by mistake have been sent to a passive data base unit. As mentioned above the updating transmitter 43 works until the base unit 39 has terminated all services, started at said signal pulse from the signal converter 38. In Fig 2 this is performed by a counter 47 counting the working services and an AND-gate 48, the output of which is connected to the stop inputs of the updating trans¬ mitter and the inputs of which are connected respectively to the "pas- sive"-position of the flip-flop 42 and to the counter output which is activated when the counting reaches zero. Finally Fig 2 shows a fault indicator 49 of the base unit, the output of which, as well as the out¬ put of the random time generator 36, is connected to the activating input of the random number decoder 44. When a serious total fault occurs in the executive base unit, the fault indicator generates an alarm sig¬ nal which is treated by the signal converter 38 as a random time signal transmitted from the random time generator.

Selecting means, used in a data communications network including only two data base units, do not need a random number generator and a random number decoder, as the previously executive base unit can only designate the previously passive base unit as the newly executive unit. In this case the designation signal generator is started by the random time sig^¬ nals or alarm signals generated by the random time generator or fault indicator, respectively, to generate the designation signal which desig- nates the other data base unit of the network as the executive unit.

"_TL^A

Claims

WHAT WE CLAIM IS :

1 A data communications network including a single data base which is connected to data terminals by a telecommun cations network contain¬ ing connecting nodes, characterized in

• that the data base includes at least two data base units (1-31) which are geographically separated from each other but otherwise identical, that the telecommunications network connects each data base unit to at least one of the connecting nodes (15-21), that the data communications network includes permanent established con¬ nections (4-5) from each one of the data base units to the other data base units, that the data communications network further includes identical selecting means (36-38) each included in a data base unit in order to select the data base units one at the time as the executive unit by designation sig¬ nals which are sent at least to the data base unit selected as the exec- utive unit and to each of the connecting nodes, that the connecting nodes each contain a path selector for controlling calls from a data terminal to the executive unit, and that the executive unit includes an updating transmitter (43) connected to said permanent established connections which is started upon receipt of an associated designation signal and works until all data needed to update the other data base units is transmitted.

2 A data communications network according to claim 1, characterized in that the data base includes only two data base units, that each selecting means includes a random time generator which upon receipt of the designation signal, that selects its data base unit as the executive unit starts a time count and which within a fixed period of time generates a random time signal, and that each selecting means further includes a signal converter for con-^ verting said random time signal from the associated random time genera- tor to a stop signal which deactivates the random time generator and to the designation signal which selects the remote base unit as the executive unit.

OMPI 3 A data communications network according to claim 1, characteriz¬ ed in that the data base includes at least three data base units, that each selecting means includes a random time generator ⁽36) which upon receipt of the designation signal which selects its data base unit as the executive unit starts a time count and which within a fixed pe¬ riod of time generates a random time signal, that each selecting means further includes a random number generator (37 for generating random numbers each identifying one of the remote data base units, and that each selecting means further includes a signal converter (38) con¬ nected to the random time generator and the random number generator for converting said random time signal to a stop signal which deactivates the random time generator and to the designation signal which selects the data base unit which is identified by the random number generator as the executive unit.

4 A data communications network according to claims 2 or 3, charact¬ erized in that the executive unit includes a fault indicator (49) connected to the signal converter (38) which generates an alarm signal when the executive base unit malfunctions, and that the signal converter treats the alarm signal in the same manner as said random time signal.