DE2843088C2 - System for the transmission of time division multiplex signals with a line network in a ring structure - Google Patents

Description

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The main patent 28 20 428 relates to a system for the transmission of time division multiplex signals a line network in a ring structure, a head end, connection points with subscriber stations and in parallel running ring lines with opposite transmission facilities, in which the functionality of the time division multiplex system in the event of a cable break or a similar malfunction is preserved, and in the case of the two ring lines as independent, but with a uniform Time division multiplex frames for all transmitted and received messages operated transmission paths switched and the connection points with both Ring lines are connected.

In the case of double ring networks that have become known so far (see e.g. DE-AS 24 09 471, also 1978 International Zurich Seminar on Digital Communications F5, “A Proposal for the Introduction of Digital Techniques into Local Distribution «; 1974 International Zurich Seminar D2, "Reliability - a Key Element in Loop Systems" should a second ring line parallel to the ring line with the subscriber stations connected to it are laid, which is provided as a reserve. There are several places on the ring Transfer devices (switching units), in which the interconnected ends of the other ring line separated in the event of damage and connected to the ends of the other ring main. Kick a unpredictable, sudden malfunction, e.g. B. a cable break in the main line, can after Detection of the fault and its location until it is rectified - as well as in foreseeable cases - the section of the ring network located between two gateways can be switched off. the remaining parts of the network remain functional during the repair work by being switched off Part of the main ring, a diversion via the transfer devices adjacent to the damage site and the reserve line is switched.

Since cable breaks occur in most cases as a result of external influences (e.g. excavation work), we will not only the main ring line but also the reserve ring line at the same point in the network must be destroyed. Therefore, the diversion via the reserve line between the relevant gateways will not take place over the short distance in the same transmission direction as on the main line, but over the long one Line led with opposite transmission direction.

Without going into further details, it can be seen from this that in the known prior art in the headend (ring control unit) depending on the length of the diversion for appropriate time compensation between the frame beginnings on the main and secondary lines must be taken care of and the number of in A subscriber switched off in the event of damage, the greater, the fewer gateway devices are available are. Of course, there are options for detecting a fault in the line network, for locating it and to switch off the affected section remotely from the headend. In each Such a network falls in the event of an unforeseen fault in the main line for everyone connected subscriber until the forwarding is activated. The one between the In addition, participants located at the point of damage adjacent to the transfer facilities remain for the Duration of the damage, i.e. until the repair is completed and the bypass circuit is canceled, Out of service.

Although with such a structure of a double ring network with gateways at opposite Transmission directions, even if both ring lines break at the same point, do not affected power supplies remain largely functional, it is not considered satisfactory that for the participants in the known ring networks the mean time between two errors (MTBF) very strongly of an effective technique for fault detection and location as well as of the number of Transition facilities depends. Compared to other network structures in which z. B. the participants in a star shape to an exchange or to a head end and from there in multiplex technology with an exchange are connected, but result in known ring structures and less effective Techniques for fault detection and location and low number of gateways very quickly for the mean time between two errors, lower and even worse values than those compared

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other structures (see 1978 International Zurich Seminar, F5. 3, Fig. 4 and related explanations, right column on the same page). From the perspective of a participant, it must therefore be required that recognition, Changeover and repair times approach zero. In practice this means that a cable break should be for not be noticeable to the participant.

Overhead control devices, as they are in the known, designed with a main and a reserve line Double ring nets are required, are omitted in the embodiments according to main patent 28 20 428 or are remotely comparable to the connection of the subscriber stations to both loops, where It is not possible to distinguish between a main and a reserve line, since both have equal rights and carry the messages to be transmitted independently of each other at all times. This double Keeping the messages in a double ring network can certainly not be considered a disadvantage compared to such Double ring networks are considered, in which only in the event of damage, parts of the second, the reserve ring, switched on and which normally remains completely unused. (Incidentally, needs to be from time to time an unused reserve line can be checked for functionality.) These are transferred twice Messages are of course only required once for reception. But that means for him There are normally two reception options and in the event of damage (cable break) there are still two reception options one of the two is available, since the doubly transmitted messages each come from opposite sides Directions to get to each subscriber station. As long as only one place according to the Main patent 28 20 428 trained double ring network a disturbance, z. B. a broken cable - even both Ring lines - if this occurs, the minimum requirements for undisturbed operation are still maintained and damage so narrowly confined to one point that for all those connected to the ring network Subscriber stations the damage effect for receiving and sending messages without Meaning is. Of particular advantage is the fact that the main patent 28 20 428 according to Solution in the event of damage, no frame runtimes for transmission links with changed cable length compensated must be, since both ring lines are operated independently of each other not only in the event of damage and each independent ring is opened in the event of a cable break. So maturities are in this one Context meaningless. In the event of interruptions - according to the probability calculation - a maximum of half of the currently existing connections are received by one of the alternatives Reception options can be switched to the other. Since in the subscriber stations over running Both transmission paths are observed, the decision can be made for one of the two alternatives Receipt of messages can be revised at any time. An error that has occurred is corrected before the next occurrence, which should apply in practice, goes to a system structured in this way for everyone connected participants the mean time between two errors towards infinity.

The invention aims at a further development of the Subject of the main patent 28 20 428 and is characterized by facilities in the head end and in the subscriber stations for the central switching of the messages transmitted in the network. In addition are fixed for each participant both for sending and receiving messages Time slots of the time division multiplex frame for signaling and exchanging narrowband messages with assigned to the head office. The number of participants is thus limited by the number of time slots within a time division multiplex frame. The broadband channels can, on the other hand, be assigned randomly, so that a similarly good channel utilization of the transmission medium can be achieved as can result from decentralized brokerage.

Although in the event of an unexpected sudden malfunction, e.g. B. in the event of a cable break, in the network with a Plant with the structure according to the invention, the function is not impaired, is here too Detection and localization of the error is important in order to ensure that it is rectified immediately, which is normally the case restore existing operational safety. The detection of an error is based on the concept in the invention, which is also based on the main patent (application P 28 20 428) by itself, there then the connection point of the line in question, which is located behind the fault location in the transmission direction no longer receives messages. This is done by the affected connection point and also in the head end recognized.

Preferred embodiments of the invention can as well as in the main patent 28 20 428 for problem-free fault location with devices in the connection points or in the headend for transmission or receiving alarm signals when a transmission path is interrupted. Through a - appropriately preferred - alarm signal, from which the connection point can be recognized, can be in the headend It can be recognized immediately whether the fault affects one of the two transmission lines or both. 1st only one Line broken, the headend receives alarm signals from the connection point in the direction of transmission the broken line is behind the point of failure.

If both lines are broken, the alarm signals come from the connection points adjacent to the break point in the same way on the broken lines with the opposite transmission directions to the headend. The junction that does not receive any messages or synchronization information on the broken line, this is the point of failure immediately adjacent and can address this regardless of their operating status by a Communicate corresponding additional information in connection with the alarm signal to the headend. So is the error also always accurate to the area between two connection points within a very short time to locate. For this purpose, it is advantageous to have all connection points each with two time frame generators and one equip frequency-stable phase-locked loop. These facilities are used to secure the transmission a cable break or such a fault in which the transmission medium does not receive any information about the timeframe structure are received.

As in the known systems with double ring networks, there are also embodiments of the invention the possibility of connecting several participants to one connection point (concentrator). Here is the distance between the individual participants is of crucial importance. With several Subscriber connections in z. B. a building, such a measure makes sense. In sparsely populated Areas, especially in rural areas

you assign the participants their own connection points.

For the operation of communication systems, it is required for various reasons that the subscriber equipment be ^{supplied with energy from the transmission unit 7.} In optoelectronic systems with fiber optic cables for the transmission of the messages, the energy supply cannot take place via such lines. Accordingly, as in the main patent 28 20 428 in embodiments of the invention, a separate pair of lines is provided for this purpose, which - z. B. also for the energy supply of the repeater - is laid in parallel with the fiber optic cables. For the energy supply of the subscriber stations in this way, of course, an interruption in the supply cable at one point has no effect. However, in order to prevent a second or any other simultaneous and similar error, the subscriber stations can be equipped with circuits that also supply these parts of the subscriber station from a localized power supply unit that is connected to the subscriber's supply network if the network's own power supply line fails. Z. B. the voltage in the power supply line below a predetermined threshold value is automatically switched to the other location-based power supply. Such a power supply, independent of the transmission network, is required in any case where the subscribers have other terminals than a telephone, e.g. B. data transmission devices, video telephones and the like., Are operated.

Apart from the fact that in the embodiments of the invention in the event of a sudden, unexpected Disturbance, e.g. B. in the event of a line break due to mechanical action or failure of circuit components in a connection point that deals with the transmission of the messages sent and received could affect, even in the short term no interruptions occur, this is all the more true for planned Repair and expansion work to be carried out, e.g. B. when inserting new connection points for which - In contrast to the well-known double ring networks - it is not necessary to temporarily remove and remove ring sections to turn it on again. Faults of this kind are of course to be rectified immediately, if possible several points are not affected at the same time and do not constitute a malfunction.

Another major advantage of the invention is that in the embodiments in particular the unpredictability of damage that could lead to malfunctions in hard-to-reach places, e.g. B. lines laid in the ground are low. Other sensitive parts, for example the connection points, are easily accessible and easy to understand. Disturbances, which occur there are accordingly easy to fix. Since systems structured according to the invention do not fail even in the event of a malfunction of the type mentioned, no building planning measures are required to be taken (see DE-AS 24 09 471, column 10, line 7 ff.), which are intended to accelerate the detection and location of a fault and its isolation by z. B. endangered components or those where a The possibility of intervention in such cases must be centralized at one point in the network. The one The advantage of ring networks, namely their short average cable length per subscriber, would result from such Measures not only given up, but in a substantial, general assessment of ring networks detrimental disadvantage if all these components are centralized in one place to provide a separate ring section with a large spatial extension, i.e. the line network to several large loops would be deformed.

In the drawing, embodiments of the invention are shown schematically. It shows

: o F i g. 1 a double ring network with head and exchange and connection point for a subscriber station or concentrator,

F i g. 2 is a block diagram with the circuit parts of a subscriber station used for transmission security

is station,

F i g. 3 shows an illustration of the taki care in a Interruption of both rings,

4 shows a representation of the message flow in an interruption of both rings, FIG. 5 shows the flow of messages Failure of a ring,

6 shows a representation of the message flow in the case of several interruptions in both rings, 7 shows a block diagram for the energy supply to the subscriber stations.

The line-based communication network shown in FIG. 1 consists of two parallel-laid ring lines Ri and Ra with an antidirectional transmission direction. Both ring lines begin and end in a headend in which, on the one hand, controlled by a highly stable clock generator, the time frame for a time-division multiplex transmission is generated and fed into the rings Ri and Ra and, on the other hand, the switching function is carried out. At the connection points of the

Rings are the subscriber stations, which are either intended as concentrators for several connected subscribers or for individual subscribers. There messages are fed into the two rings Ri and Ra or extracted from them (see the

enlarged highlighted schematic diagram of the

Coupling point). These messages are in the form

Individual time slots lead in the same way in both rings R / and Rage.

The block diagram shown in Figure 2 shows the

Circuit components that are used for transmission security as well as for error detection and location. Every connection point is provided with a time frame generator per ring. Both timeframe generators will supplied by a phase locked loop with a clock;

the reference required for this is derived from the edge changes in the message stream of both rings. A clock indicator per ring line and connection point allows the detection of a cable break. One such disruption triggers in the assigned time frame

generator sets off an alarm, which is picked up in the headend in particular.

The time division multiplex transmission system with central switching and a ring network for the connected Subscriber stations must have at least two points at which the messages sent out can be removed from the message stream. It has been found appropriate to the received Messages at the destination or destination, namely at the relevant connection point, from the Remove message stream. With the specified direction of transmission on the lines and the double transmission of the messages sent on the two anti-parallel transmission paths

therefore two time slots are required for a connection between two participants on each line In the detailed illustration in FIG. 1 it can be seen that according to the principle of a relay station for one connected participants determined time slots from the receiving direction against those of him with his Messages to be sent out occupied the same time slots. The same functional scheme is also available at the exchange.

Establishing and clearing connections

To set up a connection, a subscriber simultaneously occupies his channels (time slots) in rings Ra and Ri via the connection point assigned to him by writing in identical signaling information.

The monitoring station in the head-end station observes both lines alternating in time frames and searches them for signaling information. After the first detection of signaling, it only tracks the call on the relevant ring line, generates a second signaling (e.g. audible tones) after a processing time and sends this to the assigned time slots of the target subscriber in both rings. The calling subscriber alternately tracks both rings - Ä / and Ra - and searches his return channel for acknowledgment information from the exchange. If acknowledgment information is recognized on one of the ring lines, the calling subscriber station only observes the channel assigned to it on this line. The connection was thus established in the signaling phase. The transition to data transmission takes place when the called subscriber starts the data transmission due to the signaling of the exchange (lift the receiver at the telephone) The control of the exchange recognizes the beginning of the data transmission and switches off its signaling and the channels assigned to the subscriber together for data exchange via the switching matrix.

The calling subscriber for his part recognizes the beginning of the data transmission by suspending the Acknowledgment signaling from the exchange.

The connection is cleared down by terminating the data transmission (hang up the receiver) by a subscriber. The data is replaced by end information. The end information is provided by the other participant acknowledged If both participants send out the end criterion, the exchange releases the channel connection in the coupling field. After a time of sending determined by a time criterion, the sending of the End information replaced by sending a free time slot and finally completely discontinued. So they are Channels free.

Disruptions

Figures 3 to 6 show that with the invention presented double ring communication network also for systems with central switching against disturbances is largely insensitive, as this is also during the connection setup and cleardown as well as in the Conversation phase can be neutralized.

a) No call or call acknowledgment

If there is no signaling after an initially correctly recognized call or a correctly recognized call acknowledgment, i.e. an empty time slot is received, see above the switching center or the participants concerned observe the alternative ring with the assigned ones Time slots. If no signaling is recognized there either (time slot is empty), the connection will be triggered:

The sending subscriber or the exchange replaces the sending of calls due to missing call acknowledgments for a limited time by sending out end information and free time slots and then provides sending quite a.

ίο The receiving subscriber or the exchange replaces the call acknowledgment signaling by sending out end information and free time slots due to a missing call and then completely stops sending.

b) Ring system with a cable break

(Both cables are interrupted at the same point)

As from the central clock generator in the headend

If a highly stable time frame is sent in both rings, the synchronism on both sides of the break point can occur can still be derived from one ring each (s.

Fig. 3).
The from sending subscriber A in both rings in

Signaling information sent to channels assigned to subscriber A reaches the exchange

because of the cable break only on one ring conductor.
The exchange calls destination subscriber B.

its channel again on rings. Subscriber B , however, can only be reached via the second ring.
The called subscriber acknowledges with replacement of the call on both rings. The flow of information therefore remains undisturbed.

c) Ring system with failure of a ring line

If only one of the two ring lines fails (Fig. 5), so the transmitted call reaches the exchange in the head-end station on the other ring.

The called subscriber acknowledges. This receipt also reaches the exchange on the intact ring.

The partial failure of a connection point is equivalent to the failure of a ring line and remains without Influence on the functionality of the network.

d) Multiple cable breaks /
Total failure of connection points

Multiple cable defects lead to the failure of participant groups. A partial maintenance of operation in the emerging network sections

this is not possible in contrast to operation with decentralized switching.

The one in F; G. 7 shown circuit for power supply the connection points enables the ineffectiveness when using the double ring principle described a cable break that usually occurs at the same time in the message and supply double ring for the supply double ring.

If there are further cable breaks in the supply double ring at the same time, potential-free sections are created there. This criterion is used to determine from the power supply unit which is usually present for each connection point (Connection points must only have one subscriber and do not have their own power supply unit) Feed in potential-free pieces. Junction points, the do not have their own power supply unit, the remaining connection points in the section provided

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For this purpose 4 sheets of drawings

Claims (6)

Patent claims: 1. System for the transmission of time division multiplex signals with a line network in a ring structure, a s Headend, connection points with subscriber stations and ring lines running in parallel with opposite ones Transmission directions, in which the functionality of the time division multiplex system at Occurrence of a cable break or a similar malfunction persists, and both Ring lines as independent, but with a uniform time-division multiplex frame for everyone transmitted and to be received messages operated transmission paths switched and the Connection points are each connected to both ring lines, according to patent 2820428, characterized by devices in the head end and in the subscriber stations for the central switching of the messages transmitted in the network. 2. Plant according to claim 1, characterized by devices in the connection points and in the Headend for sending or receiving alarm signals when the transmission path is interrupted. 3. System according to claim 1 or 2, characterized by two time frame generators and a frequency-stable phase-locked loop per connection point. 4. System according to one of claims 1 to 3, characterized in that several participants are connected to a connection point. 5. Plant according to one of claims 1 to 4, characterized by a pair of lines to at least partial power supply of connection points, the ring-shaped and parallel to the message transmission lines is relocated. 6. Plant according to claim 5, characterized by a voltage-dependent circuit for power supply from the network devices of the subscriber stations in the event of failure of the power supply line of the network.