GB2154397A - Data communication system incorporating network management information arrangements - Google Patents

Abstract

The data communication system involves the incorporation of a network management information arrangement into on existing Kilostream service to allow for the operation of a network management system. The network management arrangement is incorporated into existing Kilostream service by dividing the data stream into equal length frames D and multiplexing into each frame a control channel comprising unique header H and control information C. The multiplexing is achieved by controlling the Kilostream clock in the transmitter so that it is stopped during each header/control clock period. <IMAGE>

Description

SPECIFICATION The present invention is directed to a data com munication system incorporating network manage ment information arrangements and relates to a method of modifying data communication systems using predetermined data rate communication paths to accommodate network information control chan nels.

Typically data communication networks are em ploying the British Telecom Digital Kilostream Services for the provision of communications circuits to provide a networkforconnecting remote information gathering points to a central data handling system.

It is an object ofthe present invention to incorporate network management information into a kilostream service.

According to the invention there is provided a data communication system comprising a data transmitter and a data receiver interconnected by a digital communication path operated art a predetermined data rate, characterised in that means are provided for incorporating a control channel for information comprising a unique header and a control signal portion, and the data transmitter includes means for dividing the data to be transmitted into equal length frames and means for multiplexing the control channel information into each frame.

An embodiment of the present invention will now be described with reference to the accompanying drawings wherein: Figure 1 shows the topology of a district network, Figure 2 shows an analog district line, Figure 3 shows a kilostream district line, Figure 4 shows a circuit for central and remote online monitoring, Figure 5 shows a data frame for central and remote online monitoring, Figure 6 shows the transmission of signals RTS and CTS to ensure data channel synchronisation, Figure 7 shows a transmitterforframed data and associated clock signals, Figure 8 shows a clock stopping method of clock control, Figure 9 shows a receiverforframed data and associated clock signals.

Referring to Figure 1, the topology ofthe district networks are of a star nature.

All communications circuits emanate from a central site, the Processing Centre PC and terminate at remote sites, the District Offices. The combined digitallanalog network management system NMS allow the circuits to be provided as either Kilostream or analog circuits.

In orderto provide central to remote site NMS control functions it is necessaryforthe network management system NMS to set-up a control channel for communications. In the case of analog circuits sufficient circuit bandwidth is available to permit a secondary channel to be provided outside ofthe main channel bandwidth. Main and NMS Control Channels can thus co-exist and simultaneously occupy the communica tions circuitwithout interference with each other.

The current analog circuit is shown in Figure 2 and provides two network management control lines, NMC1 and MNC2. Line NMC1 is connected to and controls a data diagonstic module DDM and line NMC2 is connected to and controls line diagnostic module LDM. The data diagnostic module DDM receives information from a front end processor NPS usingCClTTV24signallingtechniques.Theline diagnostic module LDM is linked to the data diagnos- tic module DDM by way of a modem MODEM and communicates using VF signalling to a data com munication unit DCU over a British Telecom line BTL which carries main and network management system channel data simultaneously. The data communications unit DCU communicates using CCITTV24 signalling techniques to a terminal control unit DRS.

In the case of Kilostream digital circuits the bandwith of the communication's channel is fixed by the transmit and receive data clocks provided by the circuit interface ofthe network terminating unit NTU.

Hence, for network management system control of kilostream, the control channel must be obtained by multiplexing onto the main channel in a time related manner using the data clocks.

The Kilostream circuit is shown in Figure 3 and has no VF side and no secondary communication channel.

Therefore, network management communication with the remote site must be achieved by using a proportion ofthe main channel on a time multiplex basis.

Referring to Figure 3, the kilostream diagnostic module KDM receives a network management control signal NMC. The module receives information from the front end processor NPS using CClTTV24 signall- ing techniques and passes the information by way of a first network terminating unit NTU1 to a second networkterminating unit NTU2 at a remote site over a British Telecom Kilostream Services Line KL. The networkterminating unit NTU2 transmits the information to a kilostream communications unit KCU at the remote site using CCITT V24 signalling techniques, which in turn passes the information to the terminal control unitDRS.

Referring to Figure 4, continuous communication is used between the control and remote site network monitoring units. The control channel communication is achieved by muliplexing the control channel CC with the main channel MC data from the front end processor NPS on a continuous basis, so that kilostream data passes between the network termination units NTU. Under alarm/fault conditions immediate indication is given by the system as to whether the fault is located centrally or, at the remote site.

Operator diagnostic routines are is continuously monitored and availablefor display to the network monitoring system operator.

From the above it can be seen that the multiplexing technique required to implement derivation of the network monitoring system ofthe control channel must provide a means of controlling both main and channel data. The function is achieved by the use of a sequencer and the kilostream circuit clocks.

The sequencer, fortransmission of data over kilostream, will pass N clock pulses to the main channel and N clock pulses to the network monitoring system control in a period of N + M clock pulses from the kilostream link. The structure ofthe data transmitted during the M pulses allocated to the network monitoring system will always contain a unique header and control information. Thus, for every N bits of main channel data a regular and unique header together with control information is transmitted.

Atthe receiving end of the circuit the N + M bits are received on a regular basis where Mare uniquely identifiable, and will be detected in orderto synchronise a receive sequence. The receive sequence will strip off the M bits destined forthe network monitoring system and pass the N bits to the remote data terminal equipment DTE. The data rate between the data terminal equipmentDTE is NR/N+M bits/sec where R is the kilostream bit rate.

N and M will typically be ofthe oder of 1000 and 30 respectively, giving an effective clock (data rate) slowing as seen by the data terminal equipments to the 3%. The technique is transparent to protocol since It is related to framing main channel data into discrete N bit blocks without regard forthe block contents.

Data Framing Referring to Figure 5 the data is divided into equal length frames D, and a header H and control information Care inserted in between each frame. The header is a fixed length code, which is required to maintain synchronisation with the receiver.

Data Channel Synchronisation To prevent the loss of any data while the network monitoring system is out of synchronisation, the kilostream diagnostic module has control of the V24 circuits. The kiiostream diagnostic module KDM will only issue the clear to send signal CTS to the front end process NPS after it has received the signal CTS from the kilostream communications unit KCU and the signal CTSfromthelocal networktermination unit NTU as shown in Figure 6.

Transmit Communications Figure 7 shows a transmitterforframed data, and associated clock signals. The transmitter multiplexes the data from the data terminal equipment DTE with the control information, then outputs the framed data to the network termination unit NTU. The circuit timing within the transmitter is controlled by a sequence generator, which itself is clocked by the transmit clockTxC from the network terminating unit NTU. This sequence generator produces three clock cycles, TxC1, TxHC and STROBE. The STROBE signal loads the header and the encoded control information into a shift register. This is then serially unloaded by the transmit header clock RxHC. The transmit clock to the data terminal equipment DTE, TxC1 then clocks out one frame of data.Signal TxD represents the transmit data sent from the data terminal equipment DTE, and signal TxD1 represent the transmit data sentto the networkterminating unit NTU. This sequence will be continually repeated to produce a continuous stream offrames.

Clock Stopping To provide a clock which will demultiplexthe data and the header/control block, the clock cycles must only be present during the period that data is on the channel. This means that the clock wil I 'stop' during the header/conarol block and continue for the data block. The delay between the data clocks will only be about 32 clock cycles which isfartoo small to cause a timeout, and because it is a synchronous system, the network will be seen to operate as normal. Figure 8 shows this method, and depicts the transmit clockTxC from the network terminating unit NTU, and the transit clockTxC1 to the data terminal equipment DTE stopped during the header and control clock periods H and C.

Receive Communications Referring to Figure 9, a receiver is shown for framed data, and associated clock signals. The received data RxD from the network terminating unit NTU is continually clocked through the receiver by the receive clock RxC from the network terminating unit NTU. For valied control data to be received, two headers must first be recognised by the comparators, spaced exactly one frame apart. This separation determines the size of the buffer. When this event happens a sequence generator is triggered, which will produce two clocks cycles, STROBE and RxC1.After'H' clock cycles from the detection of a valid frame, the control information is present in the shift register.At this time the STROBE signal is generated, which latches the control information into another register.

Then 'C' cycles later, the data content of the frame is available at the output ofthe receiver. The receive clock RxC1 to the data terminal equipment DTE is generated which will clockthisdata intothe data terminal equipment DTE. Signal RxD1 represents the receive data sent to the data terminal equipment DTE.

Tlmis sequence will be repeated everytimetwo heacers are recognised.

Network lLWonitoring System Diagnostic Loop Control Of he switch states employed on kilostream circuits the application of STAY BY front end processor S/BY FEP, PROTOCOL MONITOR, DATA TESTER and EQUIPMENT LOOP are identical to that used on anall23 circuits. The LINE LOOP is synonymous to that Go analog circuits, it being a loop applied at the V24 interEace cable ofthe Kilostream networkterminating unit NTU. Network monitoring system control of netviorkterminating loops and remote V24 loops on Kilostream circuits are achieved as follows.

Table 1: NMS OPERATOR REQUESTED MNS SYSTEM ACTIONS TO FUNCTION APPLY REQUESTED CONDITION 1. LOCAL NTU LOOP Request remote NMS unit to drop request to send signal RTS Drop central RTS Raise Local Analog Loopback CCITT circuit 141, LALB (141) Pause 1250mSecs Raise central RTS Check receive data from NTU Signal RxD = Transmit data from DTE, Signal TxD and Test indicator CCITT circuit 142, T1 (142) is ON If not, then "LOOP FAiLED" and return to normal.

2. REMOVE LOCAL NTU LOOP Drop LALB (141) Pause 1250mSecs Check communication with remote NMS unit is re established and signal T1 is OFF.

If not, then "LOOP REMOVAL FAILED" Request remote NMS unit to return signal RTS to the DTE 3. REMOTE NTU LOOP As at 1, except Remote Digital Loopback CCITT Circuit 140, RDLB (140) in place of LALB 4. REMOVE REMOTE NTU LOOP As at 2, except RDLB (140) in place of LALB 5. REMOTE NMS UNIT V24 LOOP Using control channel communications, request remote site NMS unit to perform V24 loopback.

6. REMOVE REMOTE MNS UNIT Reverse of 5.

V24 LOOP Network monitoring system detection of alarm conditions related to NTU's on kilostream circuits are achieved as follows: Table 2: NTU ALARM CONDITION DETECTED ON THE MNS BY NTU CIRCUIT FAILURE Signal RxD = Signal UNCNR (ie. NTU line fault or (Uncontrolled Not Ready, power failure at remote all binary 'O's being site) received from line) NB: 1. This would also arise if the data terminal ready signal DTR was dropped, (Terminal control at district only was powered down), however, remote NMS unit will maintain the signal DTR to the NTU whilst monitoring the signal DTR from the DTE to prevent this.

2. Signal UNCNR would also be received at remote site if the signal DTR at central site went down. Thus to enable data tester and switch states to be used whilst the mainframe is down the central site NMS unit also maintains the signal DTR to the NTU whilst monitoring the signal DTR from the mainframe.

2. CENTRAL NTU IN LOOPBACK. Signal RxD = Signal TxD and signal TI (142) is ON 3. REMOTE NTU IN LOCAL Signal RxD = Signal CNR LOOP (Controlled binary '1's and '0's being received from line) 4. REMOTE NTU IN REMOTE Signal RxD clamped to LOOP binary '1'

Claims (7)

1. A data communication system comprising a data transmitter and a data receiver interconnected bya digital communication path operated ata predetermined data rate, characterised in that means are provided for incorporating a control channel for information comprising a unique header and a control signal portion, and the data transmitter includes means for dividing the data to be transmitted into equal length frames and means for multiplex ing the control channel information into each frame.

2. A data communications system as claimed in claim 1 wherein a sequence generator is used at the transmittertogetherwith header, control and data clocks, and arranged to pass N clock pulses to a main channel and M clock pulses to the control channel to multiplex the control channel with the main channel.

3. A data communication system as claimed in claim 2 wherein the sequence generator produces a first signal, a second signal and a third signal, the first signal controls the loading ofthe unique header portion and encoded control signal portion into a shift register, and is subsequently unloaded underthe control ofthe second signal and multiplexed with a frame of data which is latched out of a latch circuit underthe control of the third signal .

4. A data communication system as claimed in claim 3 wherein the third signal is arranged to stop during the period that the header and control clocks operate, and start during the period that the data clock operates.

5. A data communication system as claimed in claim 1 or 4 wherein the receiver is provided with a buffer register into which received data is loaded under control of a receive clock signal, and two comparator circuits are provided, each being connected to the buffer register at a different shift register bit position to determine the length of one frame, so that each comparator circuit recognises a header, and together cause a sequence generatorto betriggered.

6. A data communication system as claimed in claims 4 and 5 wherein the sequence generator produces a first signal and a second signal, the first signal controls the latching of control information from the buffer register into a further register, and the second signal is used to control the data into data terminal equipment.

7. Adata communications system substantially as herein before described with reference to the accompanying drawings.