DE3413144A1 - Digital local communications system with the logical structure of a loop - Google Patents

Abstract

For a digital local communications system in the form of a bus with the logical structure of a loop in which the stations connected to terminal devices are in each case connected to a transmitting line and to a receiving line running in parallel with the former, with data flow directed in the same or in the opposite direction, and transmit their data as data packets provided with a priority flag, the stations feeding their data packets into the transmitting line only, and in which the data packets are transmitted at one point in the network from the transmitting line to the receiving line, it is proposed to allocate a request flag to each data packet in addition to the priority flag. The stations can feed their data packets into the transmitting line even if data packets with a lower priority than the priority of the data packet to be transmitted arrive on the transmitting line. In equal-priority incoming data packets, the request bit of the external data packet is set to "1" by the station wishing to transmit. If heavy data traffic occurs on the receiving line, the transmission protocol causes the data packets to pass through, extensively arranged according to priority, high-priority data packets can be transmitted immediately and access is provided to the data medium in the appropriate order with maximum utilisation of the transmission medium.

Description

13description

Digital local communication system with the logical structure a loop The invention relates to a digital local communication system according to the preamble of claim 1.

Various data transmission networks have become known which the data exchange between computers, between computers and terminals, between Computers and sensors or actuators for process control tasks or between computers and devices for communication tasks, especially in in the local area or in office automation. Compared to the conventional This is the solution in centralized private branch exchanges or local exchanges Data transmission networks a greater flexibility and allow a faster integration of various services and applications in the local area.

According to the tasks and applications mentioned, two Types of data transmission networks differ, on the one hand those of transmission serve large amounts of data in a short time with a bursty character, and those, the more the Kolrlrllutliiaiion uau the data traffic with smaller amounts of data and serve a slower transfer rate. To the first type are the networks that allow computers to be connected to computers. These networks include arrangements with bus or loop structure with transfer rates around 10 Mbit / s. As typical Representatives are Ethernet, Net-One, Hyper-Channel or Express-Net. the Messages are transmitted using data packets.

A communication system of the type mentioned in the opening paragraph is known, for example from the essay by M. Ajmone Marsan and G. Albertengo: "MAP: An Insertion Protocol for an Unidirectional Bus Local Network ", Instituto di Elettronica e Telecommunicazioni, Politecnico di Torino - Italy, April 1981.

In this article a digital local communication system is described with send and receive lines laid in parallel, where the flow of messages is on of the receiving line is opposite to that of the transmitting line and each of Message packet sent to any station with a priority indicator is provided. There are only two priority classes intended. A station may, regardless of the priority of its message packet to be sent only send when no more message packets arrive on the transmission line, otherwise, it must stop transmitting immediately. Furthermore, she is allowed to just send a message packet and then continue with the transmission of yours next message packet, even if this has the highest request priority has to wait until the from the message packets on the receive line the individual stations composed of a packet train with its own message packet is over. This not only delays your own urgent messages, but the message system is also made by waiting for the end of a Parcel train with the breaks between the parcel trains not optimal exploited.

Furthermore, if the message traffic is low, the transmission time is several Message packets from a station because of the set waiting times between two message packets to be sent consecutively in many cases too high (e.g. long signal running sides with large network expansion and / or high bit rate) The invention is based on the task of improving the state of the art. In particular, should for a communication system of the type mentioned at the outset, a method for multiple access on the transmission medium, with which largely collisions during Start of transmission of a station with high priority message packets to be transmitted can be avoided and in the case of message packets with more than two priority classes can be transmitted in such a way that message packets with the highest priority the fastest access to the Transmission medium and, if There are no message packets of higher priority, several packets without waiting times can be transmitted one after the other.

The object is achieved by the invention referred to in claim 1. It is now possible to send the message packets with a minimal waiting time when the load is low transferred to. The individual stations can send their message packages with a maximum Send rate. When the load is high, there is orderly access to the communication system instead, where the transmission capacity between stations with packets is the same Priority is distributed fairly and message packets are sorted according to their priority are transmitted in close succession on the receive line.

The embodiment of the invention according to claim 2 allows the stations a quick evaluation of the message packets with little storage space requirement for the components required for this. Claims 4 to 12 give an advantageous one Embodiment for the flow control, which the transmission of a message packet adapts certain priority to the volume of messages on the transmission medium. As a result of the measure according to claim 9, message packets located on the transmission line are received same or higher priority than one pending transmission from a station Message packets take precedence.

Unnecessarily long waiting times for a station willing to transmit are avoided the measures according to claims 10 and 11 avoided.

The invention will now be explained with reference to exemplary embodiments shown in the drawings explained in more detail. They show in detail: FIG. 1 communication system with message flow directed in opposite directions on transmit and receive line FIG. 2 Koalmunica tion system with message flow directed in the same direction to broadcast and receiving line FIG. 3 Structure of a message packet FIG. 4 State flow diagram a station FIG. 5 Block diagram of a station.

In FIG. 1 is an oppositely directed communication system and in FIG. 2 with message flow directed in the same direction on transmission line SL and Receiving line EL shown. The individual stations labeled 1, 2, 3, ..., N are connected to the communication line in such a way that both the Send line SL and the receive line EL looped through the stations are. In this way, each station has an incoming and an outgoing transmission line as well as an incoming and outgoing receiving line. The station's outgoing transmission line N is connected to the receive line and that is in FIG. i the outgoing transmission line with the input for the incoming receiving line of station N and in FIG. 2 the outgoing transmission line of station N with the input for the incoming receiving line connected to station 1.

The signal propagation is always unidirectional on both lines namely on the transmission line in the direction of the transition point to the receiving line and on the Receiving line directed away from the transfer point.

The stations transmit their messages in packet form.

In FIG. Such a message packet is shown schematically in FIG. An unmistakable bit sequence, usually comprising 8 bits, the accumulation field ANF, Often referred to as a "flag", this is followed by an access control field Z-STF, a packet control field P-STF, which identifies the type of data, a field for the destination address, a field for the source address, a field marked with "identifier" for unique Identification of the data packet, the actual data field that the message is for the target station contains a field with the checksum to control the correct Data transmission and an END field which identifies the end of the packet, for example can contain the same bit sequence as the start field ANF.

According to the invention, the access control field Z-STF contains a priority of the message packet characterizing first subfield and a second subfield for the requirement identifier. To indicate the priority, up to are sufficient to 8 priority levels 3 bit and for the request identifier i bit, the stations are constructed in such a way and connected to the transmission line that they are in on the Transmission line can read and change individual bits of incoming message packets and that instead of letting the incoming message packets pass, they suppress them and be able to send your own message packages for this, even in the middle of a passing one Package. An alternative scheme is to only use entire data packets in this way to under- Press, i.e. only when sending your own packet to begin at the end of a passing data packet regardless of the priority.

The message packets transmitted on the receive line are read by all stations, but not changed by any station, and go first at the end of the receiving line, i.e. in FIG. 1 at the unconnected output of the Station 1 and in FIG. 2 lost at the output of station N that is not connected. In addition, incoming and forwarded message packets from each station regenerated. Communication networks of this type are e.g.

described in DE-OS 33'40 992 and DE-OS 33 40 993.

For, messaging is a random access protocol for Bus systems are provided in which packets with the highest priority are as dense as possible Sequence can be sent by one or more stations, initially without restrictions. As soon as the sending stations collisions between the on the transmission line coming and the message packets to be sent by them the same Determine priority1 they go to one classified according to this priority class Access mode, in which, as soon as they have a permission to send, they are identified Receive signal, send only one message packet of this priority class at a time and send the next message packet only after all other stations also had the opportunity to send a packet of this priority class.

In order to realize this regulated state, are for each station five states are provided for each priority class, which are initially based on FIG. 4 explained in more detail the. The priority of a packet on the Transmission line with p and the one pending transmission in a station (waiting) message packet denoted by q. In total, let (P + 1) -priority classes be provided, where for p or q applies: 0 Z p 'P and p = q = 0 the highest priority class should be.

In the first state Iq there is no waiting message packet in the station with priority q. All message packets arriving on the transmission line are only transmitted regenerated to the outgoing transmission line, provided that the Station is not in a state with respect to another priority class, which provides something else. When a message packet to be sent arrives the station leaves from a terminal with priority q connected to the station to the state Wq (arrow 10). The message packet to be sent is from a first Memory is copied to a sending memory, this process being repeated that many times can be, up to the receiving line of the correct passage of the sent Message packet can be detected.

In the Wq state, the station checks whether the transmission line is free or the message packets arriving on the transmission line for their priority p. If p = 0 is the highest and p = P is the lowest priority level, it leaves message packets happen for which p 3 q applies. So it leaves message packets with higher or the same priority as the one to be sent. In incoming on the transmission line Message packets with the same priority as the one to be sent, i.e. p = q, it sets the request bit to IV "1" in its request field. Detect animals they send a message packet of lower priority on the transmission line, i.e. with p > q, or if the transmission line is free, the station goes into state Aq (arrow 11) over, if they are not in the State Aq '. The minor wait t: eziL of a high priority package In some applications, q may require an alternative rule in which the Station goes into state Aq even if it is already in relation to a lower priority class q 'is in state Aq', i.e. a packet lower Priority sends.

In some applications it can be useful to set up the station in this way to set up that it is only at the end of a message packet passing on the transmission line goes into state Aq.

In state Aq, the possibly detected message packet has priority p> q suppressed by the station to the end or, if necessary, sending your own Package with priority q '> q is canceled and the station immediately begins with the Sending your message packet with the priority value assigned to the message packet q in the priority field and a request bit set to "O" in the request field. However, while the message packet of priority q is being sent, it meets the incoming transmission line a message packet with priority p # q breaks she immediately stops sending, lets the strange message packet pass and goes for a new attempt to return to state Wq (arrow 12). Each time you send one It checks that its message packets with priority q have passed through properly of your sent message package on the receiving line. If it does not run properly on the receiving line because it is, for example is incorrect or incomplete, it immediately stops sending and goes for a new attempt to return to state Wq (arrow 12).

After the station in state Aq or Bq has made the proper run of her message packet on the receive line, she removes it sent message packet from the series pending in the station to be sent Message packets.

If the station has completely sent a packet with priority q, it remains they are in state Aq, WCIlil eill another packet of priority q and no packet one higher priority is pending and if it was last properly on the receive line's own packet of priority q received the request bit was set to "O".

At the end of the send, there is no further packet with priority q or A higher priority packet to be sent, the station goes to state Bq via (arrow 14), in which they have the correct passage on the receiving line of the packet that it has just finished sending and that it was due to the Network runtime may not have been fully received.

Is the request bit of its own properly on the receive line received packet has been set to U t by another station, the station leaves from the state Aq at the end of transmission and from the state Bq at the end of reception to the State Sq over (arrow 17 or arrow 15).

In state Bq, this becomes the priority packet that was sent last q not or not completely received on the receive line, the station leaves back to state Wq (arrow 16).

In ZJust; alld Sq the station monitors the priority and the request bit of the message packets passing through on the receiving line. Is their priority p> q, a message packet with priority p = q hits with something still on "O" Request bit or the receive line remains empty for a specified time, so the station goes into the state if it still has more q-packets to send Wq (arrow 18) back. However, if one of these cases occurs, they are at the station If there are no more q packets ahead, it goes back to state Iq (arrow 19).

I FG. Figure 5 is a simplified block diagram of a station for implementation of the described transmission protocol. There are only those for understanding here the elements required for the invention are shown.

The subsequent incoming from the incoming transmission line SL.

Direction packets arrive at a non-sending or willing to send Station via a first switch S1 to a second switch S2, which is from a comparison logic VGL-L can be controlled. The comparison logic VGL-L is with a first input connected to the transmission line in front of the switch S1 and with her second input to a module called processor, the news packages receives from other terminals E or passes them on to them. The connecting line of the two switches S1 and S2, each with the first contact of the switch connected is also to the output a delay buffer VZ-P connected, whose input is connected to the second contact of the switch S1 is. The output of the processor connected to the comparison logic VGL-L is also connected to the input of a transmit memory SP1 whose output is connected to the second Contact of switch S2 is connected.

The receiving line looped through the station is connected to the Input of a receiving memory EP connected1 whose output is connected to the processor is.

If the station is not transmitting or willing to transmit, there are none Packets to be sent to, the switches S1 and S2 are in the position shown. Otherwise the comparison logic VGL-L compares the priority of the message packet to be sent with the priority of the incoming message packets, which by a few bit times in Delay buffer VZ-P can be delayed in order to initiate a reaction if necessary.

If a packet with p = q arriving on the transmission line is received from the Compare logic VGL-L recognized, the processor causes the input of a "1" from the delay buffer VZ-P in the request field of the message packet passing by, where q is the highest priority of the packets of the station wishing to send.

If a p-packet with p> q is received by the comparison logic on the transmission line recognized, it throws switch S2 and the station sends its q-packet from the Transmit memory SP on the outgoing transmission line. The others on the transmission line incoming bits of the p-packet and possibly subsequent packets of lower priority run into the delay gerungsbuffer VZ-P You walk from there to open contact of the switched switch S2 and are lost.

The switch S2 is reset to the starting position by the comparison logic, if message packets of equal or higher priority are on the transmission line are determined by the comparison logic or if there are no "own" message packets there are more to be sent in the transmission memory SP or more waiting for the priority classes Packets the request bits correctly received on the receive line own packages are set to II "1".

The switch S1 is switched back if it has already been reset Switch S2 no priority comparison with incoming packets is required and the comparison logic for a message packet that has arrived on the transmission line a sufficiently large transmission gap was discovered so that a collision between this last message packet expired from the delay buffer VZ-P and one via the possibly directly via the connection line between switches S1 and S2. running package is avoided.

The receive buffer E-P is used to store your own sent message packets Check for completeness and possibly set request bit, the priority to be able to determine the message packets passed through on the receiving line or to recognize certain message packets for the station and via the processor forward to the desired device. Message packets on the receive line are thus from the stations forwarded unchanged because the Station for which a message packet is intended - in the direction of message propagation seen on the receiving line - behind the station sending the message packet can lie.

The procedures in the stations that correspond to the protocol explained above are controlled by the processor, which for this purpose uses the comparison logic and the in FIG. 5 is in the data exchange with regard to the control data in the buffers shown. The control lines required for this are shown in FIG. 5 to improve the Clarity not shown. However, their connections arise from the schedule given above.

The states Iq to Sq described above apply to each priority level. They are stored separately in the processor of the stations for each priority level and processed in such a way that the message packets pending in the processor for transmission The highest priority must also be transferred to the transmit memory and sent first.

Claims (13)

Claims Digital local communication system in bus form with the logical structure of a loop, in which the with terminals in connection standing stations each to a transmitting and a receiving line parallel to it are connected to the same or opposing flow of messages and their messages as priority-flagged message packets transmitted, the stations monitor the transmission line and their message packets feed into the transmission line and in which the message packets in one place of the network are transmitted from the transmission line to the receiving line and the Stations that read the message packets assigned to them from the receiving line, without taking them from the receiving line, characterized in that each message packet Additionally a requirement identifier is assigned that the Stations feed their message packets into the transmission line even if Message packets with a lower priority than the priority of the message packet to be transmitted arrive on the transmission line, these incoming message packets being lower Priority during the sending of the other packet that in from Message packets sent from the source stations have the request identifier set to logical "O" is set and that in incoming message packets on the transmission line with the same priority as that to be transmitted by the forwarding station Message packet the request identifier from the forwarding station logical '' 1'l is set. 2. System according to claim i, characterized in that in each message packet after the packet start identifier an access control field follows with a priority field and a requirement field. 3. System according to claim 2, characterized in that the requirement field comprises one bit and each source station sends its message packets to logic llOfl with the set request bit. 4. System according to claim 3, characterized in that each station depending on the message flow on the sending line and the receiving line and the states following the priority q of the message packets to be sent out by it can take: a first state (Iq) in which no packets the priority q to be sent, a second state (Wq), in which they at least a message packet with priority q has to be sent and the priority of the Send line checked any incoming message packets, a third state (Aq), in which it feeds a packet of priority q to be sent into the transmission line and checks on the receiving line whether the message packet sent by it is correct runs through there and what binary value the request bit has, a fourth State (Bq) in which it checks on the receive line whether what it has sent Message packet passes through correctly and which binary value its request bit has, and if the message packet has passed through correctly, the message packet removed from the series of message packets to be sent by it and a fifth State (Sq) in which the request bit for message packets on the receive line same 'priority q as that of a message packet sent by it, its The request bit had the value "1" when it was received correctly on the receiving line, controlled. 5. System according to claim 4, characterized in that the stations for each priority class (q) assume the states and pass through, where states higher priority classes are processed preferentially and at any time a station is in the second state at most with regard to one priority class (q) (Aq) can be located. 6. System according to claim 5, characterized in that a station transition from the first state (Iq) to the second state (Wq) if it is from a Terminal has received a message packet of priority q to be seddes that it has received from the second state (Wq) changes to the third state (Aq) if it i. regarding none other priority class ql is in state Aq 'and + the probe line 1.2- a message packet of lower priority is available on the transmission line p (p> q) discovered as that of the message packet to be sent by it (p = q = 0 = highest priority level) that they go from the third state (Aq) to the fourth State (Bq) passes over when it receives the priority message packets to be sent q has sent that it changes from the fourth state (Bq) to a fifth state (Sq), if you have the The request bit is set to logic "1" and recognizes that it is from the fifth state (Sq) returns to the first state (Iq) if there are no more packets of the priori ity q has to send and 1. in a message packet passing through on the receiving line of priority q the request bit has not been changed or 2. a lower packet Priority has passed or 3. the receiving line for a specified time remained empty. 7. System according to claim 6, characterized in that the station also then from the second state (Wq) to the third state (Aq) passes, if they are in the third state with respect to a lower priority q '(i.e. q'> q) (Aq ') and then simultaneously from the third state (Aq') to the second State (Wq ') goes back. i.e. the station cancels the sending of its own packet in favor of it another own packet with a higher priority. 8. System according to claim 6, characterized in that the station only then changes from the second state (Wq) to the third state (Aq) when the The transmission line is free or when the parcel just passing by ends and the possibly the following packet has a lower priority. 9. System according to one of claims 6 to 8, characterized in that that a station goes back from the third state (Aq) to the second state (Wq), if from the transmission line a message packet of the same or higher priority p arrives (p c q) or the transmitted packet of priority q does not arrive or is incomplete is received on the receive line. 10. System according to claim 9, characterized in that a station as long as and only as long as it remains in the third state (Aq) until 1. it receives a message packet with priority q has sent completely (end of send) and 1.1 no further packets of priority q are waiting to be sent or 1.2 packets of a higher priority are waiting to be sent Pending sending or 1.3 one of the priority packets sent q correctly received with the request bit set to "1" on the receive line or 2. (aborted transmission) 2.1 a packet of the same or higher value on the transmission line Priority p (p 3 q) arrives or 2.2 the packet of priority q sent by it was not received or received improperly on the receive line. 11. System according to claim 10, characterized in that a station from the fourth state (Bq) t. reverts to the second state (Wq) if that The last packet of priority q 1.1 sent by it was not or not completely or 1.2 properly with the request bit set to "0" on the receive line has been received and further packets with priority q are waiting to be sent, or 2. returns to the first state (Iq) if 2.1 the packet it last sent of priority q properly with the request bit set to 11011 on the receive line has been received and 2.2 no further packets of priority q to be sent queue. 12. System according to claim 11, characterized in that a station from the fifth state (Sq) to the second state (Wq) if 1. in a message packet of priority q passing through on the receiving line the request bit has not been changed or 2. Passed a lower priority packet or 3. the receiving line has remained empty for a specified time and it has to send further message packets with priority q 13. System according to claim 4, characterized in that the states of each station for each priority class are storable.