GB2113953A - Local loop communication network for routing date and telephone speech signals in digital form - Google Patents

Abstract

A local area network, e.g. serving several floors in a building, is formed from sections of transmission line (Li) coupled together via repeaters (R1, Rn), the loop being closed by a common circuit (UCB), which inter alia, provides synchronisation. Each repeater can also give access to the loop to a station or port (see below). The signals are routed in a time frame the first part of which is used in a packet switching mode and the second part of which is used in a circuit switching mode. To increase the telephone traffic capacity, telephone ports (P1, P2, P3, P4) are provided at various points of the loop to purge it of the 8-bit bytes used in the second segment of the time frame. A port does this by removing bytes circulating upstream of that port, and inserting bytes for circulators towards a downstream port or station into the loop. A time switch (CT) interconnects the loop sector and the outside world, public exchange or PBX, under control of a common control circuit (UCT). <IMAGE>

Description

SPECIFICATION Local loop communication network for routing data and telephone speech signals in digital form This invention relates to a local loop communication network conveying both data and telephone speech signals in digital form, the network having a loop formed by transmission line sections connected in series via repeaters, each of which permits the access of a station to the loop. The network also has a loop control unit which closes the loop, introduces a periodic synchronization signal and completes by a delay the transmission time in the loop to define a time frame. The frame contains a first segment of k eight-bit bytes to transmit data in the "packet" mode, the other bytes forming a second segment used to transmit telephony.

In a local network conveying both digital speech signals and data there is usually disproportion between the bit rates needed for the flow of these two types of information. On the coding standard used on public networks, a telephone call needs a permanent bit rate of 1 28 kbit/s, which is high with respect to the bit rates needed for data transmission. Bit rate limits on transmission circuitry thus require them to be split up so that they can provide the necessary bit rate for speech signals, which means that in a local loop network, the subscribers must spread over several separate loops. However, this leads to complex interconnection problems for data signals whose total rate does not usually justify such splitting.

An object of the invention is to overcome this problem in a local loop network.

According to the invention, there is provided a local loop communication network conveying both data and telephone speech signals in digital form, which network includes a loop formed of transmission line sections connected in series via repeaters, each permitting the access of a station to the loop, and a loop control unit used to closed the loop; to introduce a periodic synchronisation signal and to complete by a delay the transmission time in the loop in order to form a time frame, wherein the frame contains a first segment of k bytes to transmit data in "packet" mode, the other bytes forming a second segment used to transmit the telephone communication signals, wherein the network includes at least two telephone ports each connected at a different point in the loop by a repeater to extract the used bytes of the second segment flowing on the sector of the loop on the upstream side of the port and to insert the used bytes of the second segment flowing on the sector of the loop on the downstream side of that port, the port being transparent for the other bytes, wherein the network has a time switch connected to each of the ports and to the outside by digital multiplex links in the two transmissidn directions and permitting the interconnectidn of the various sectors of the loop to each other and to the outside by said links, and wherein there is a telephone control unit which, for each telephone call, marks the time switch and the ports concerned and assigns a free time slot of the second segment of the frame to each station having to enter into communication.

An , at embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a block diagram of the network embodying the invention; Figure 2 shows the organisation of the time frame used; Figure 3 shows an example of real topology of the loop; Figure 4 is a diagram of a repeater showing the way in which a port or station gains access to the loop; Figure 5 is an example of a telephone port; and Figure 6 is a time switch for a network embodying the invention.

Figure 1 shows the general lay-out of a local loop network embodying the invention. This network includes transmission line sections such as I connected in series via the repeaters RI to Rn. A loop control unit UCB which closes the loop L generates a periodic sync signal Sy, and introduces a delay to make the loop transmission time equal to the time separating two successive sync signals to create a time frame. Each repeater can provide access to the loop for a station SI to Sm. Each station permits the connection of a number of subscribers connected to it, and can receive the sync signal Sy and locate a time slot IT of the time frame by the difference between the instant of its passage and that of the sync signal.

A number, four in this case, of telephone ports P1 to P4, connected to the loop through repeaters, are provided, which may be combined with the stations Si. The functions of these ports, which divide the loop L into sectors, is to extract the bytes relating to telephone calls in progress flowing in the upstream sector of the loop (ahead of the port concerned) and to insert the corresponding bytes flowing in the downstream sector. The ports P 1 to P4 are all connected to a time switch CT through 2 Mbit/s digital multiplex links, LN1 to LN4. The time switch CT is also connected to the outside through digital links LNE to a conventional private or public branch exchange.

A telepone control unit UCT controls all of the telephone calls in the loop L a-nd with the outside. It marks the time switch, telephone ports and stations, and is connected to the loop through a repeater and sends its orders as described below.

The operation of the system will be described with reference also to figure 2 which shows the organisation of the time frame. This frame has the conventional width of one hundred twenty-five microseconds and is composed of a number (one hundred twenty-eight in this case) of time slots IT, each containing eight bits (thus a byte) transmitted serially. The first byte is transmitted by the loop control unit UCB and constitutes the synchronisation signal Sy. The foilowing k bytes are processed in the "packet" mode and constitute a first segment of the frame. A station Si can transmit a packet if it finds a free indication in the form of a "free" flag in the first byte J. It identifies the addressed station by the following byte Ad. A station Si can also receive a packet if it recognises a "busy" flag in the first byte J and its own address in the following byte Ad.The k bytes in the "packet" mode are transmitted with transparency in the loop L by the stations and ports not concerned with packet transmission.

The remaining bytes are processed in the "circuit" mode and constitute a second segment of the frame. The allotment of one byte per frame is equivalent to a bit rate of 64 Kbit/s, that is to say the bit rate necessary for a telephone call in one direction. A two-way telephone call can be established by the use of the same byte alternately by two stations.

The length kofthe "packet" segment can be modified as a function of the respective amounts of telephone and data traffic.

The ports Pj (j in this case having a value of 1 to 4) purge the loop L of its telephone traffic at several point, to permit the transmission of several two-way telephone calls over a single byte of the second segment of the frame. Thus, due to the extraction of the used bytes of the "circuits" segment flowing in the sector on the upstream side of the port and the insertion by the ports of the used bytes flowing in the downstream sector, a byte transmitted by a station will only congest the loop until the next telephone port. Similarly, a byte addressed to a station will congest the loop only from the last upstream telephone port. As already mentioned, the sync byte and the "packet" segment flow through the ports without modification unless the packet is addressed to the port in question.

The time switch CT interconnects the various sectors of the loop and connects these sectors to the outside, via a public or private automatic branch exchange (not shown) connected to the time switch through the links LNE.

Since the same byte of the original frame can be used several times on the loop for different communications in different sectors of the loop, the number of bytes of the "circuit" segment of the frame can therefore be reduced, compared with a conventional solution, for a given traffic and congestion rate, and the "packet" segment can thus be lengthened. This permits the data traffic in "packet" mode to be increased.

The digital links LN1 to LN4 and LNE include, as usual, a device for resetting to local time on arrival. If we let the value of k be equal to 34, three digital links designated A, B and C, each conveying thirty-one channels, are sufficient for one port. Table I below gives a particularly simple rule of correspondence between the bytes carried by the second segment of the frame and the channels of the three digital links of each port in the two transmission directions. For bytes having a number less than k + 1, the port should be transparent for the loop except when it is concerned by a packet transmission.

We see that a call involving a station of the sector between ports Pj and Pj + 1 and using the channel m of link B to the port Pj in the incoming direction, uses the channel m of link B starting from port Pj + 1 in the return direction. Thus the time switch CT can consider the pairformed by a line going to a port and the line of the same number coming from the following port as a normal two-way link in which the channels having the same number carrying signals associated with both direction of the same call. The time switch CT, then of conventional design and marking of the switch, can be done in a single operation. This is true for any fixed relationship other than that indicated in Table I.

TABLE I

No. of Link A No. of Link B No. of Link C Loop No. of Loop No. of Loop No. of Byte Channel Byte Channel Byte Channel 35 1 66 1 97 1 36 2 67 2 98 2 37 3 68 3 99 3 38 4 69 4 100 4 39 5 70 5 101 5 40 6 71 6 102 6 41 7 72 7 103 7 42 8 73 8 104 8 43 9 74 9 105 9 44 10 75 10 106 10 45 11 1 76 11 107 11 46 12 77 12 108 12 47 13 78 13 109 13 48 14 79 14 110 14 49 15 80 15 -111 15 50 16 81 16 112 16 51 17 82 17 113 17 52 18 83 18 114 18 53 19 84 19 115 19 54 20 85 20 116 20 55 21 86 21 117 21 56 22 87 22 118 22 57 23 88 23 119 23 58 24 89 24 120 24 59 25 90 25 121 25 60 26 91 26 122 26 61 27 92 27 123 27 62 28 93 28 124 28 63 29 94 29 125 29 64 30 95 30 126 30 65 31 96 31 127 31 Thus the loss of a digital line from a port to the time switch renders unusable the corresponding spaces of the frame for stations in the sector upstream from that port, which reduces the volume of traffic acceptable by these stations. Furthermore, the loss of a ditigal line from the time switch to a port renders unusable the corresponding spaces of the frame for stations in the downstream sector with the same consequences for the volume of traffic acceptable by this sector.

If, for equipment reasons, we pair digital lines of the two directions, it is advantageous to associate at the time switch' the two lines of the same number and of opposite direction serving the same sector; the loss of an equipment then has the same impact as the loss of one of the lines. On the other hand, if, for practical reasons, we associate two lines of opposite direction connected to the same port, then the loss of an equipment spreads the disturbance to the sectors both downstream and upstream of that port.

As an installation example, figure 3 shows a possible real topology for the loop L. In practice, it is possible to use optical fibre cables as transmission lines, and then have an optical distributing frame R from which various loop sectors depart, each serving for example a floor or main part of a building. It is then easy and advantageous to arrange all of the ports around this frame R. All of the digital links with the switch are then grouped together geographically.

Figure 4 shows the design of any repeater, which has two shift registers Rel and Re2 in series in the loop L. A clock circuit H extracts, at input E of the repeater, the bit frequency of the signal in the loop. We can assume, for example, that the data are transmitted serially in the loop according to a code such as the so-cailed "Manchester" code which permits easy extraction of the bit rate. This circuit H furnishes a signal hb at that frequency to the shift registers Re 1 and Re2 to permit the data flowing in the loop to pass through them. The circuit H also furnishes a clock signal hw, synchronised with the time slots IT of the frame, to the station Si or to the port Pj associated with the repeater, so that the latter can extract the bytes or insert them with the correct phase.Shift register Re 1 has a parallel output connected to the station Si or to the associated port Pj for the extraction of bytes in the loop, whereas the station or port inserts the bytes via a parallel input to register Re2. The station or port thus has a time slot IT to decide te change the received byte up to the instant at which it is correctly registered in register Re2. If no write order is given, the byte passes through the station or port in transparency.

In the case of transmission by optical fibres, it is clear that an optoelectronic receiver will be required at the input E as well as a light transmitter at the output S.

Up to this point, we have discussed the simplest case of operation. However, there is another arrangement in which a certain "mutual aid" between contiguous sectors of the loop can be used to reduce the effect of the loss of a digital line or an equipment (two associated lines). To this end, any port Pj receives an instruction not to insert in the downstream sector certain channels of its active lines from the time switch. The bytes of the corresponding time slots of the frame are then sent in transparency by the port and everything takes place as if a new sector had been created, for these time slots, between the ports Pj - 1 and Pj + 1. Depending upon the operating mode chosen, these time slots can be used for communications for the stations of one of the former sectors or for all of the stations of the new sector.

Note that, in this variant, the bytes for the two directions of transmission of the same call are no longer carried systematicaliy by the channels of the same number of two lines of the same number serving adjacent ports. Thus, the time switch cannot be marked in a single operation. Hence it is no longer useful to pair at the switch the two lines of the same number going to the port Pj and coming from the port Pj + 1. On the contrary, it is better to pair, in the same equipment, the two lines of the same number associated with the same port since it is useful to extract a byte of the frame only if we can re-use its location in the downstream sector.Further it is detrimental to insert a byte in a time interval or space which has not first been emptied of its contents. in case of fault, the failure of a pair of lines between the port Pj and the time switch causes that port to be transparent to all the spaces in the frame corresponding to the lost channels and the sharing (defined by the selected mode of operation) of these spaces to serve the rest of the stations in the two sectors concerned. The reduction in traffic capacity can thus be apportioned as desired between the two sectors.

In the context of this second embodiment, we shall now describe in a more detailed manner the designs of a port and time switch, with reference to figures 5 and 6.

Correspondences such as shown in Table I could be set up by a completely-wired method in the port, but the circuit of figure 5 uses a conventional time switch, in which the interconnections between the input and output channels are modifiable. In figure 5, we seethe shift registers Rel and Re2 of the repeater, but the clock circuit H has been omitted. The parallel output of the register Re 1 is connected to a receive speech memory MPRj of the associated port Pj. This memory MPRj is ordered on write (input W) by the clock signal how to store the bytes of all the time slots IT of the second segment of the frame ("circuit" segment). The bytes which are to be extracted by the port are read in the memory MPRj upon the order (input R) of a receive time address memory MATRi in which are marked, by a marking logic circuit LMPj, the spaces in the memory MPRj to be read. The memory MATRj is itself read synchronously with the time slots of the second segment of the frame under the control of the signal hw.

The bytes read in the speech memory MPRj are sent to a parallel-to-serial converter/demultiplexer DMXj which, under the control of signal hw, distributes serially the bytes, read parallel-wise from the memory MPRj, to the corresponding channels of the digital multiplex lines A'j, B'j and C'j from the port Pj to the time switch CT. Similarly, on transmission, the bytes to be inserted are received on the channels of the multiplex lines Aj, Bj and Cj from the time switch CT. These bytes are transmitted in parallel form to a transmit speech memory MPEj through a serial-to-parallel converter/multiplexer MXj controlled by the clock signal hw.As for reception, the transmit speech memory MPEj is associated with a transmit time address memory MATEj read synchronously with the time slots of the second segment of the frame (signal hw at the read input R) to order the reading of the transmit speech memory MPEj at the spaces marked by the marking logic circuit LMPj. The speech memory MPEj is connected to the parallel input of the shift register Re2 through a transfer gate circuit 1 0 which enables bytes to be transferred to register Re2-only for time slots in which the bytes on the loop are not to be transmitted necessarily in transparency (bytes of the "packet" segment and bytes of the second segment to be transmitted in transparency because of the mutual aid operating mode selected).The locations of the bytes to be transmitted transparently are stored in a transmit enable memory MAEj which controls the gate circuit 10.

Lastly, the marking logic circuit LMPj has access to the "packet" channel of the loop through a link PC of a conventional design, whose details are therefore not shown, which permits the extraction by means of register Re 1 of packets addressed to the port and the insertion of packets by register Re2 when the channel is free. The marking logic circuit LMPj is thus connected to the telephone control unit UCT (Figure 1) from which it receives the marking orders.

Local time resetting circuits RH are provided at the input of the digital lines Aj, Bj and Cj.

The operation of the system can be inferred from the above description. The bytes to be extracted are read in the speech memory MPRj at the locations marked in the address memory MATRj and sent to the time switch CT over the corresponding channel of the digital li ne A'j, B'j or C'j according to the rule of correspondence adopted. Bytes to be inserted are likewise stored in the speech memory MPEj which is read at locations marked in the address memory MATEj, the authorisation to insert being furnished by the transmit enable memory MAEj. This later unit is marked ohly in the case of a system reconfiguration.

One advantage of using such a time-switching arrangement for the ports is first of all that it is closely related to the one used for the stations, which should be able to associate with the demand the time slots operated in "circuit" mode of the frame and the channels serving the active subscribers which are connected to it.

Another advantage is the possibility of masking a line failure by modifying the correspondence table when the current value' of the parameter k makes it impossible for all the channels serving a port to be used simultaneously.

Figure 6 shows the time switch CT for the second embodiment. It includes a speech memory MP in which the bytes of all of the channels of all of the incoming lines A'1 to C'4,from the ports, and A'e to C'e, from the outside, are entered synchronously at the rate of the local clock H' after passing through a serial-to-parallel converter/multiplexer device MX. This speech memory MP is read (input R) at the locations marked in a time address memory MAT read under the control of the local clock H'. Marking in the memory MAT is performed by a marking logic circuit LM which receives order directly from the telephone control unit UCT. The bytes read in the speech memory MP are sent over-the corresponding channels of lines Al to C4 and Ae to Ce of the links to the ports and to the outside via a parallel-to-serial converter multiplexer DMX.Local time resetting circuits are provided at the input of the digital lines in the time switch CT.

Such a switch can be built around a 512-word speech memory, and could then serve, for example, three ports by three lines each and seven lines to the outside. Higher traffic levels would require more complex structures, for example of the TST type, without having basically to modify the operation of the system.

Table II below gives three examples to illustrate the operation of the switch in figure 6 and its marking. Case 1 is that of a local call between two stations placed on sectors s1, between ports P 1 and P2, and s3 between ports P3 and P4. Case 2 is that of a local call between two stations in the same sectors of the loop. Case 3 is that of a call between a station ofsectorsl and the outside.

TABLE II

Sector Sector Frame Space of of Outside Station 1 Station 2 1 2 Channel Marking 1 Marking 2 1 sl s3 92 107 - C' 1,27 B B'2,27 C3, C 4,11 1,27 2,27 3,11 2 sl s1 92 92 - B'2,27 B1,27 - 3 sl - 92 - Ae13 A e13 B1,27 2,27 Ae13 In case 1, two markings are needed to associate in both directions of transmission the time slots 92 and 107 of the frame, respectively assigned to the connection in the two sectors in question. In case 2, a single marking is sufficient to return to the chosen frame location through the time switch. Lastly, in case 3, two markings are again necessary, one for each direction of transmission.

The identity of the time slots assigned to a communication is transmitted to the stations and ports concerned by the telephone control unit UCT by means of the "packets" channel of the frame.

Claims (8)

1. A local loop communication network conveying both data and telephone speech signals in digital form, which network includes a loop formed of transmission line sections connected in series via repeaters, each permitting the access of a station to the loop, and loop control unit used to close the loop, to introduce a periodic synchronisation signal and to complete by a delay the transmission time in the loop in order to form a time frame, wherein the frame contains a first segment of k bytes to transmit data in "packet" mode, the other bytes forming a second segment used to transmit the telephone communication signals, wherein the network includes at least two telephone ports (p1 to P4), each connected at a different point in the loop (L) by a repeater (RI to Rn) to extract the used bytes of the second segment flowing on the sector of the loop on the upstream side of the port and to insert the used bytes of the second segment flowing on the sector of the loop on the downstream side of that port, the port being transparent for the other bytes, wherein the network has a time switch (CT), connected to each of the ports and to the outside by digital multiplex links (LN1 to LN4;; LNE1 in the two transmission directions and permitting the interconnection of the various sectors of the loop to each other and to the outside by said links, and wherein there is a telephone control unit (UCT) which, for each telephone call, marks the time switch (CT) -and the ports concerned (P 1 to P4) and assigns a free time slot (IT) of the second segment of the frame to each station (SI to Sm) having to enter into communication.

2. A network according to claim 1, wherein the telephone control unit (UCT) is connected to a repeater (Ri) of the loop (L) and sends the marking orders for the ports (Pj) and the stations (Si) through the "packet" mode channel consisting of the first segment of the frame.

3. A network according to claim 1 or 2, wherein each said repeater has two shift registers (Re1, Re2) in series in the loop (L) and a clock circuit (H) to extract from the signal at the input the bit frequency and to furnish a clock signal (hb) at this frequency, which controls the shift of the registers, wherein the clock circuit also extracts a clock signal (how) synchronised with the time slots of the frame, for the station (Si) or the port (Pj) associated with the repeater, wherein the first register (Rel ) has a parallel output by which the port or the station can read the contents of the first register and the second register has a parallel input by which the port or the station can enter, at a desired time slot, a byte in this second register in place of the byte already present there, and wherein the repeater transmits in transparency the bytes for which the port of the associated station does not enter a new byte in the second shift register.

4. A network according to claim 1,2 or 3, wherein some of the telephone ports do not extract all of the used bytes flowing in the upstream sector of the loop, but allow some of them to pass transparently so as to create extended loop sectors for the corresponding time slots.

5. A network according to claim 1,2, 3 or 4, wherein each said telephone port includes: (a) a receive speech memory (MPRj) connected to the first shift register (Rel) of the associated repeater and ordered synchronously on write to store the bytes of all the time slots (IT) of the second segment of the frame; (b) a receive time address memory (MATRj) read synchronously with the time slots of the second segment of the frame to order the reading of the receive speech memory (MPRj) at the marked locations;; (c) a parallel-to-serial converter/demultiplexer (MDXj) to distribute the bytes read in the receive speech memory (MPRj) to the corresponding channels of the digital multiplex lines (A'j, B'j, C'j) going from the port (Pj) to the time switch (CT) (d) a transmit speech memory (MPEj) connected to the second shift register (Re2) of the associated repeater, by a transfer gate circuit (10), and controlled on write synchronously with the time slots of the second segment of the frame to store the bytes to be inserted in the loop (L); (e) a serial-to-parallel converter/multiplexer (MXj) to bring together the bytes from the various channels of the digital multiplex lines (Aj, Bj, Cj) from the time switch (CT) and to send them to the transmit speech memory (MPEj) at the corresponding time slots of the second frame segment;; (f) a transmit time address memory (MATEj) read synchronously with the time slots of the second segment of the frame to order the reading of the transmit speech memory (MPEj) at the marked locations; (g) a transmit enable memory (MAEj) which stores the time slots of the first and second segments of the frame in which the bytes of the loop should be transmitted transparently by the associated repeater, the output of this memory controlling the transfer gate circuit (10); and (h) a marking logic circuit (LMPj) having access through the repeater to the "packet" channel of the loop and, under the control of the telephone control unit (UCT), marking the time address memories (MATRj, MATEj) required to establish telephone calls passing through the port (Pj).

6. A network according to claim 1, 2, 3, 4 or 5 wherein the time switch (CT) includes: (a) a speech memory (MP) in which the speech bytes are stored cyclincally; (b) a serial-to-parallel converter/multiplexer (MX) to bring together the bytes from the various channels of the digital multiplex lines (A'j, B'j, C'j; A'e, B'e, C'e) coming from the ports (Pj) and from the outside and to send them to the speech memory (MP) at the corresponding time slots of the local frame determined by the clock signals (H') of the time switch (CT); (c) a time address memory (MAT) read synchronously with the time slots of the said local frame to control the reading of the speech memory (MP) at the marked locations; (d) a parallel-to-serial converter/demultiplexer (DMX) to distribute the bytes read in the speech memory (MP) to the corresponding channels of the digital multiplex lines (Aj, Bj, Cj;Ae, Be, Ce) going from the time switch (CT) to the ports (Pj) and to the outside; and (e) a marking logic unit (LM) connected to the telephone control unit (UCT) to mark the time address memory (MAT).

7. A local loop communication network, substantially as described with reference to the accompanying drawings.

New claims or ammendments to claims filed on 7 February 1983.

Superseded claims.

New or amended claims

8. A local loop communication network conveying both data and-telephone speech signals in digital form, which network includes a loop formed of transmission line sections connected in series via repeaters, each permitting the access of a station to the loop, and a loop control unit used to close the loop, to introduce a periodic synchronisation signal and to complete by a delay the transmission time in the loop in order to form a time frame, wherein each said frame includes a said synchronisation signal, a segment of k bytes to transmit data in "packet" mode, and a further segment the bytes of which are used to transmit telephone communication signals, wherein the network includes at least two telephone ports, each connected into the loop at a different point therein by a said repeater, wherein each said port is arranged to extract the used bytes of the further segment flowing in the sector of the loop on the upstream side of the port and to insert the used bytes of the further segment flowing in the sector of the loop on the downstream side of that port, the port being transparent for the other bytes, so that the same bytes of the further segment can be used in different parts of the loop for different calls, wherein the network has a time switch connected to each of the ports and to the outside by digital multiplex links for the two transmission directions, thus permitting the interconnection of the various sectors of the loop to each other and to the outside by said links, wherein there is a telephone control unit which, for each telephone call, marks the time switch and the ports concerned and assigns a free time slot of the second segment of the frame to each station having to enter into communication, and wherein the telephone control unit is connected to a repeater of the loop and sends the marking orders for the telephone ports and the stations through the segment of the frame which provides the "packet" mode channel.