WO1988007295A1

WO1988007295A1 - Communication network

Info

Publication number: WO1988007295A1
Application number: PCT/EP1988/000177
Authority: WO
Inventors: Jan Gaston Bauwens
Original assignee: Alcatel N.V.; Bell Telephone Manufacturing Company, Naamloze Ven
Priority date: 1987-03-18
Filing date: 1988-03-05
Publication date: 1988-09-22
Also published as: AU1263088A; AU602058B2; ES2006596A6; BE1000395A4

Abstract

A ring communication network to transmit packets of data between terminal stations (U1 to U5) connected to this network via respective nodes (N1 to N5), each of these nodes comprising a first receiver circuit (RC0) and a first transmitter circuit (TC0) connected to segments of the network by respective terminals (R0 and T0), a second receiver circuit (RC1) and a second transmitter circuit (TC1) connected to the terminal station by respective terminals (R1 and T1), and control means (SB, SEC) comprising a multiplexer/demultiplexer circuit (SB) controlled by routing information contained in the packets and adapted to cyclically read (SEC) the first (RC0) and the second (RC1) receiver circuits and to transfer the packets stored in the read receiver circuit to the transmitter circuit (TC0/TC1) which is selected by these informations. This network may also include protection means (D1, IR, CR, IT, CT) against a faulty node.

Description

INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PC

(51) International Patent Classification ⁴ (11) International Publication Number WO 88/ H04L 11/16 Al (43) International Publication Date

22 September 1988 (22.

(21) International Application Number: PCT/EP88/00177 (74) Agents: ROSENOER, Jacques et al.; Patent D ment, Bell Telephone Manufacturing Compan

(22) International Filing Date: 5 March 1988 (05.03.88) amloze Vennootschap, B-2018 Antwerp (BE).

(31) Priority Application Number: 8700281 (81) Designated States: AT (European patent), BE ( pean patent), CH (European patent), DE (Eur

(32) Priority Date: 18 March 1987 (18.03.87) patent), FR (European patent), GB (Europea tent), IT (European patent), LU (European p

(33) Priority Country : BE NL (European patent), SE (European patent),

(71) Applicant (for BE only): BELL TELEPHONE MANUPublished FACTURING COMPANY, NAAMLOZE VEN- With international search report. NOOTSCHAP [BE/BE]; Francis Wellesplein 1, B- 2018 Antwerp (BE).

(71) Applicant (for all designated States except BE US): AL¬

CATEL NV [NL/NL]; World Trade Center, Strawins- kylaan 537, NL-1077 XX Amsterdam (NL).

(72) Inventor; and

(75) Inventor/Applicant (for US only) : BAUWENS, Jan, Gaston [BE/BE]; Groenenborgerlaan 20, B-2610 Wil- rijk (BE).

(54) Title: COMMUNICATION NETWORK

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A t 1

N1

RO TO

R1 *4 T1 r

(57) Abstract U1

A ring communication network to transmit packets of data between terminal stations (Ul to U5) connected to network via respective nodes (Nl to N5), each of these nodes comprising a first receiver circuit (RCO) and a first trans ter circuit (TCO) connected to segments of the network by respective terminals (R0 and TO), a second receiver circuit (R and a second transmitter circuit (TCI) connected to the terminal station by respective terminals (Rl and Tl), and con means (SB, SEC) comprising a multiplexer/demultiplexer circuit (SB) controlled by routing information contained in packets and adapted to cyclically read (SEC) the first (RCO) and the second (RCl) receiver circuits and to transfer packets stored in the read receiver circuit to the transmitter circuit (TCO/TCl) which is selected by these informations. network may also include protection means (Dl, IR, CR, IT, CT) against a faulty node. FOR THE PURPOSES OFINFORMAπON ONLY

Codes used to identify States party to the PCT on the front pages of pamphlets publishinginternational applications under the PCT.

AT Austria FR France ML Mali

AU Australia GA Gabon MR Mauritania

BB Barbados GB United Kingdom MW Malawi

BE Belgium HU Hungary NL Netherlands

BG Bulgaria IT Italy NO Norway

BJ Benin JP Japan RO Romania

BR Brazil KP Democratic People's Republic SD Sudan

CF Central African Republic ofKorea SE Sweden

CG Congo ER Republic ofKorea SN Senegal

CH Switzerland LI Liechtenstein SU Soviet Union

CM Cameroon LK Sri Lanka TD Chad

DE Geπnany, Federal Republic of LU Luxembourg TG Togo

DK Denmark MC Monaco US United States of America

El Finland MG Madagascar

COMMUNICATION NETWORK The present invention relates to a communication network to transmit packets of data, each containing routing information, between terminal stations connected to said network via nodes, each of said nodes including at least a first receiver circuit and a first transmitter circuit to respectively receive and transmit packets from and to said network, at least a second receiver circuit and a second transmitter circuit to respectively receive and transmit packets from and to the terminal station connected to said node, and control means to route packets received by said first receiver circuit either to said first or to said second transmitter circuit in function of said routing information contained in said packets and to transfer packets received by said second receiver circuit to said first transmitter circuit.

Such a network is already known in the art. e.g. from the Belgian patent No 895.438. In this known network, the control means include a queue and temporarily store the packets of data intended for the first transmitter circuit in this queue and afterwards transfer either the thus stored packets, or those stored in the second receiver circuit to this first transmitter circuit in function of the priority allocated to either the queue or the second receiver circuit.

Hence, these known control means are relatively complex because they contain a queue and their operation makes it necessary to establish a predetermined priority between this queue and the second receiver circuit.

An object of the present invention is to provide a network of the above type, but wherein the control means do not necessitate either the use of a queue or the establishment of a processing priority.

According to the invention, this object is achieved due to the fact that said control means comprise a multiplexer/demultiplexer circuit controlled by said routing information and adapted to cyclically read out said first and said second receiver circuits and to route packets stored in the receiver circuit thus read out to the transmitter circuit selected by means of said routing information contained in these packets. Because the multiplexer/demultiplexer circuit cyclically reads out the two receiver circuits, no queue is required, thus reducing the volume of the control means. This is a serious advantage especially when these control means have to be integrated on a chip. Also no priority whatsoever has to be established a priori.

The above mentioned and other objects and features of the invention will become more apparent and the invention itself will be best understood by referring to the following description of an embodiment taken in conjunction with the accompanying drawings wherein :

Fig. 1 shows a communication network according to the invention;

Fig. 2 represents node N1 and terminal station U1 of the communication network of Fig. 1 in more detail; and

Fig. 3 also represents node N1, but provided with a node failure protection circuit.

The communication network shown in Fig. 1 is a Local Distribution Network of the type Broadband Integrated Services Data Network (ISDN) including several terminal stations U1 to U5 respectively connected to identical nodes N1 to N5 which are constituted by switching systems (SW1) described below and interconnected so as to form a ring network topology. A terminal station U1/U5 may for instance be a telephone subset, a video-phone set, a television set, a personal computer, a radio, a telecommunication exchange or another ring network. In the ring network shown, signals such as voice, computer data and video are transmitted between these terminal stations U1 to U5 under the form of data packets and in the single direction indicated by the arrow A. Each packet circulating in the ring network includes a header containing routing information indicating to the node N1/N5 to which it is supplied whether this packet has to be routed further in the ring network or is destined to the terminal station U1/U5 connected to this node N1/N5. The bitrate of transmission of the signals may be different for each ring segment, i.e. between two nodes N1-N5, of the ring network with a maximum value of, e.g. 560 Megabits/second.

Each switching system (SW1) constituting a node N1/N5 is for instance of the type disclosed in the Belgian patent No 904.100 and uses switching techniques called Fast Packet Switching (FPS) or by Asynchrone Time Division (ATD). Node N1, to which terminal station U1 is connected, is represented in more detail in Fig. 2. The node N1 or more particularly its switching system (SW1) includes control means constituted by a central Time Division Multiplex (TDM) switching bus SB whose operation is controlled by a timing circuit SEC and which is able to transmit packets of data from any of 8 receiver circuits to any of 8 transmitter circuits. However, since in the present case the packets circulate in the ring only in a single direction and that only one terminal station U1 is connected to the node N1, only 2 receiver circuits RC0 and RC1 and 2 transmitter ci rcuits TC0 and TC1 are required and represented in Fig. 2. This node N1 has a first input terminal R0 and a first output terminal T0 connecting ring segments of the network to the first receiver circuit RC0 and to the first transmitter circuit TC0 respectively. N1 also has a second input terminal R1 and a second output terminal T1 connecting the terminal station U1 to the second receiver circuit RC1 and to the second transmitter circuit TC1 respectively. Both the receiver circuits RC0 and RC1 are connected to the switching bus SB which is itself further connected to both the transmitter circuits TC0 and TC1. It is to be noted that although in the present case the switching capacity of the disclosed node is not fully exploited, i.e. that only 2 of the 8 receiver and transmitter circuits are used, its use is economic because, due to its wide use in telecommunication switching networks, it has been possible to reduce its production cost. The switching capacity of this switching system is for instance fully exploited in a broadband ISDN switching network such as the one disclosed in the Belgian patent No 903.261 to exchange packets of data between terminal stations which generally are subscriber stations.

A packet travelling on the ring network is supplied to the receiver circuit RC0 of the node N1 via its input terminal R0 and has its header analyzed by this receiver circuit RC0. Depending on the routing information contained in this header, the packet is then routed to the transmitter circuit TC0 or TC1 via the switching bus SB. In practice, if the routing information is recognized by the receiver circuit RC0 as indicating the relative address of the transmitter circuit TC1, for instance the number 1, or of the terminal station U1 connected thereto, the packet is routed to this terminal station U1 via the transmitter circuit TC1 and the output terminal T1. In the other case, i.e. when the routing information is not recognized by the receiver circuit RC0, the packet is transferred to the transmitter circuit TC0 and so further on the ring network via the output terminal T0.

Since packets may be simultaneously present in the receiver circuits RC0 and RC1 and can be destined to a same transmitter circuit, e.g. TC0, the transmitter circuits TC0 and TC1 are each provided with a buffer queue Q0 and Q1 respectively so that the peak transmission rate of these transmitter circuits TC0 and TC1 is not exceeded. The length of this buffer queue Q0/Q1 is so calculated that the risk of overflow is lower than a predefined probability for an assumed maximum traffic load at the input terminals R0 and R1. In each receiver circuit RC0 and RC1 a respective buffer B0 and Bl having the length of one packet of data is provided to ensure that an incoming packet is delayed over a maximum of one TDM switching bus SB cycle. In order to be able to transfer all incoming packets sufficiently fast, the minimum TDM speed or bitrate of the switching bus SB is at least equal to the sum of the bitrates of the data signals arriving to the different receiver circuits RC0 and RC1. In other words, the maximum TDM cycle duration of the switching bus SB is equal or less than the time needed to receive one packet at any receiver circuit RC0/RC1. It is to be noted that a node is in fact a statistical multiplexer/demultiplexer. Indeed, all the incoming packets from different receiver circuits RC0 and RC1 may be routed to one single transmitter circuit TC0/TC1 (multiplexing) or be distributed to different transmitter circuits TC0 and TC1 (demultiplexing). Each node is provided with a signal regenerator (not shown) to reshape the data signals before transmitting them to the ring network. Moreover, to prevent the ring from becoming inoperative by a failure of a node N1/N5, each node is bypassed by a protection circuit allowing the transmission of the packets of data.

When optical fibers are used as ring segments, such a bypass circuit is constituted by an optical fiber path presenting a certain attenuation for the signals flowing through it. In this way, when all the nodes N1 to N5 operate normally, the signals regenerated in each node N1/N5 are strong enough to override those passing through and attenuated by the bypass circuit. In case of failure of a node N1/N5, the signals only pass through the bypass circuit of that faulty node N1/N5 and are so supplied to the receiver circuit RC0 of the next node whose signal regenerator compensates the loss of amplitude caused by the preceding bypass attenuator circuit. It is to be noted that in this case of optical transmission, all the receiver circuits RC0 connected to the ring network are provided with an optical receiver and all the transmitter circuits TC0 connected to this ring network are provided with an optical transmitter. When electrical connections are used as ring segments, e.g. coaxial cables, each bypass circuit is constituted by a diode D1 and each node N1/N5 is provided with an additional equipment such as shown in Fig. 3 for the node N1. The bypass diode D1 is connected between terminals R'0 and T'0 of the ring segments and the node N1 is also connected to the ring network via these terminals R'0 and T'0. Terminal R'0 is connected to input terminal R0 of the switching system SW1 by a capacitor CR, whilst output terminal T0 of this switching system SW1 is connected to terminal T'0 via a capacitor CT identical to CR . R'0 is further connected to a reference voltage VR (ground) via a current sink IR sinking a constant DC current I, whilst this same reference voltage VR is connected to T'0 via a current source IT generating a same constant DC current I. The capacitors CR and CT prevent the DC current I to flow through the switching system SW1 but allow the packets of data to flow through it. When this node N1 is operative, the current source IT coupled to SW1 generates a DC current I which flows to the next node, i.e. N2 (Fig. 1), additionally to the signals already present on the ring network. This DC current I is sunk in the current sink IR of the node N2. The same is true for a DC current I generated by the current source IT of the node preceding N1, e.g. N5, and which will be sunk in the current sink IR of the node N1. As a consequence, when all the nodes N1 to N5 are active, constant DC currents I flow from current sources IT to current sinks IR and no current flows through the diodes D1 which remain thus blocked. However, when a node, e.g. N1, is inactive, faulty or when it is removed from the ring network, the DC current I generated by the current source IT of the preceding node N5 can only be sunk by the current sink IR of the node N2 normally following N1. So, the diode D1 present at the location of the node N1 becomes conductive because of this DC current I. As a result, all the packets of data circulating on the ring network between N5 and N2 are flowing through the diode D1 of the node N1 and the operation of the ring network is not affected.

The ring network may be folded so as to form a bus topology with two wires or coaxial cables, one for each transmission direction. Other network topologies such as a star or an hybrid structure are also possible. However, the above unidirectional ring network is preferred because of its point-to-point transmission between nodes which avoids reflections problems and because only one receiver circuit RC0 and one transmitter circuit TC0 are connected to this network. A ring network may also easily be extended by making an opening, generally at the location of a node N1/N5, and by inserting there a new ring segment.

While the principles of the invention have been described above in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

Claims

1. Communication network to transmit packets of data, each containing routing information, between terminal stations (U1 to U5) connected to said network via nodes (N1 to N5), each of said nodes including at least a first receiver circuit (RC0) and a first transmitter circuit (TC0) to respectively receive and transmit packets from and to said network, at. least a second receiver circuit (RC1) and a second transmitter circuit (TC1) to respectively receive and transmit packets from and to the terminal station connected to said node, and control means (SB, SEC) to route packets received by said first receiver circuit either to said first or to said second transmitter circuit in function of said routing information contained in said packets and to transfer packets received by said second receiver circuit to said first transmitter circuit, characterized in that said control means (SB, SEC) comprise a multiplexer/demultiplexer circuit (SB) controlled by said routing information and adapted to cyclically read out (SEC) said first (RC0) and said second (RC1) receiver circuits and to route packets stored in the receiver circuit thus read out to the transmitter circuit (TC0/TC1) selected by means of said routing information contained in these packets.

2. Communication network according to claim 1, characterized in that said transmitter circuits (TC0 and TC1) each includes a buffer queue (Q0 and Q1) for storing packets of data provided by said control means (SB, SEC) prior to transmitting them on said network.

3. Communication network according to claim 1, characterized in that said receiver circuits (RC0 and RC1) each includes a buffer (B0 and B1) for storing at least one of said packets of data before it will be read out by said control means (SB, SEC).

4. Communication network according to claim 1, characterized in that said nodes (N1 to N5) are connected so as to form a ring network topology with ring segments interconnecting the first transmitter circuit (TC0) of one node to the first receiver circuit (RC0) of the following node in the ring network.

5. Communication network according to claim 1, characterized in that the bitrates at which the data are received by said receiver circuits (RC0 and RC1) are different.

6. Communication network according to claim 5, characterized in that said control means (SB, SEC) transfer said data read out in a receiver circuit (RC0/RC1) to a transmitter circuit (TC0/TC1) at a bitrate which is at least equal to the sum of the bitrates at which data are received by said receiver circuits (RC0 and RC1).

7. Communication network according to claim 1, characterized in that the bitrates at which the data are transmitted by said transmitter circuits (TC0 and TC1) are different.

8. Communication network according to claim 4, characterized in that said ring segments are optical fibers, and in that each of said first receiver circuits (RC0) is provided with an optical receiver, whilst each of said first transmitter circuits (TC0) is provided with an optical transmitte..

9. Communication network according to claim 8, characterized in that it includes at least one node failure protection circuit constituted by an optical fiber circuit able to attenuate signals flowing through it and bypassing said node (N1/N5).

10. Communication network according to claim 4, characterized in that it includes protection means (D1, IR, CR, IT, CT) against node (N1/N5) failure comprising at each node location a diode (D1) which bypasses said node (N1/N5) and, associated to each node (N1/N5), a current sink (IR) coupled to the anode (R'0) of said diode, a first capacitor (CR) coupled between said anode and the receiver circuit (RC0) of said node, a current source (IT) coupled to the cathode (T'0) of said diode and a second capacitor (CT) coupled between the transmitter circuit (TC0) of said node and said cathode.

11. Communication network according to any of the claims 1 to 10, characterized in that it constitutes a broadband integrated services data network (ISDN) to transfer signals such as voice, computer data and video between said terminal stations (U1 to U5).