AU641828B2 - A method of transmitting data on a telecommunications network - Google Patents

Description

648 2Regulation 32

AUSTRALIA

Patents Act 1952 COMPLETE SPECIFICATION FOR A STANDARD PATENT

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Name of Applicant: AUSTRAL T OM MUNICATI--N-S- -6.Ria ofA9UWSTRALL+ -eloun-Jfl Actual Inventors: Gary FOSTER and Paul Anthony KIRTON Address for Service: DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne 3000, Victoria, AUSTRALIA Invention Title: A Method of Tra nsmitting Data on a Telecommunications Netwf~ork Details of Associated Provisional Application No: PK3567/90 The following statement is a full description of this invention, including the best method of performing it known to us: 1- -2- A METHOD OF TRANSMITTING DATA ON A TELECOMMUNICATIONS

NETWORK

a o*o d ""The present invention relates to a method of transmitting data on a 15 telecommunications network. More specifically, the method relates to transmitting 0o data from a plurality of sources to a single destination on the network.

The Broadband Integrated Services Digital Network (B-ISDN) has been developed to transmit a wide variety of information at different baud rates. The 20 network is to operate in an asynchronous manner and is to be capable of transmitting high speed data such as HDTV as well as voice signals. Data to be transmitted on the S• network is divided up into short fixed length packets called cells which include a S• header comprising transmission information and a payload portion which includes at •least part of the data to be transmitted. Links between switching nodes or stations are a. o 25 used to transmit a large number of cells belonging to different messages and bound for different destinations. To enable correct switching to be made at the nodes, the cells are allocated a respective virtual channel across links, the channel being stipulated by a virtual channel identifier (VCI) which is placed in the header of each cell. Switching of a cell at a node to an appropriate output link is determined on the basis of the VCI of the cell and the link on which the cell has arrived at the node.

The above features of the B-!SDN have been determined by the international telecommunication standards body CCITT.

911127,dbwspc.037,tlcecom. 1,2 -3- A number of protocols have been developed for transmission of messages on the network and most have concentrated on establishing and maintaining a connection between a single source terminal and a single destination terminal. Some proposals have also been made with respect to providing broadcasts services where a source terminal is able to simultaneously transmit information to a number of destinations but a protocol has not yet been proposed which would enable a number of source terminals to simultaneously trapsmit information to a single destination on the B-ISDN. The ability to establish an effective multiple source to single destination connection would, of course, be particularly advantageous in situations where a number of terminals are required to report to a central or main terminal. For example, the connection would enable efficient reporting of faults or alarms by terminals to a central database and, would improve communication from automatic teller machines to respective central banking databases 15 In accordance with the present invention there is provided a method of 00 transmitting data on a telecommunications network, comprising: forming cells for transmission, said cells including data to be transmitted and a header which has a virtual channel identifier (VCI) for identifying a virtual transmifsion channel for the respective cell, 20 storing transmission information for at least one switch node in said network to form a virtual connection at said node between a plurality of incoming virtual 00*0* "channels and an outgoing virtual channel, said transmission information allocating cells with VCIs of a predetermined group received by said node to said outgoing virtual channel, and 25 transmitting said cells on the network and substituting at said switch node the VCI of cells having VCIs of said predetermined group with a VCI corresponding to said outgoing channel.

Preferably said transmission information allocates cells received by said node to said outgoing channel on the basis of each cell's VCI and the link on which the cell is received.

911127,dbwspc.037,tcecom. 1,3 -4- Preferably said at least one switch node is a fast packet switch.

Preferably said network is a B-ISDN.

According to a particular embodiment of said method, cells having a predetermined VCI are transmitted across said network to a destination switch node using said predetermined VCI on all transmission links.

Preferred embodiments of the present invention will hereinafter be described, by way of example only, with reference to the accompanying drawings wherein: Figure 1 is a diagram of the format of a cell used in a B-ISDN; Figure 2 is a diagram of a network virtual connection between a source and destination; Figure 3 is a diagram illustrating point to point virtual connections across a 15 B-ISDN; Figure 4 is a diagram illustrating a multiple source to single destination connection across the B-ISDN; Figure 5 is a diagram of a switch node forming a multiple source single destination connection; 20 Figure 6 is a diagram of signal information transfer using a multiple source to a single destination connection; and Figure 7 is a diagram illustrating comparative aspects of multiple source and single destination virtual connections compared to point to point virtual connections.

25 A cell 2 having a format for the asynchronous transfer mode designated for the B-ISDN includes, as shown in Figure 1, a header 4 of five octets and a payload 6 of 48 octets. The header 4 is placed at the beginning of the cell 2 so it is received first by circuitry of the network when transmitted in a direction indicated by the arrow 8.

The header includes a virtual channel identifier (VCI) 10. The payload 6 includes at least part of the data to be transmitted in a message and which has been allocated to the cell 2.

911127,dbwspc.037,tIc~xm. 1,4 A point to point connection between a source terminal 12 and a destination terminal 14 on the B-ISDN is illustrated in Figure 2. The terminals 12 and 14 are connected by three links 16, 18 and 20, and two switch nodes 22 and 24, a first link 16 connecting the source 12 and first node 22, the second link 18 connecting the two nodes 22 and 24 and the third link 20 connecting the second node 24 and the destination 14. The links 16, 18 and 20 preferably comprise optical fibres but may be implemented using electrical telecommunications links. The switch nodes 22 and 24 are fast packet switches which can be implemented using a number of different hardware structures. Four switch structures which could be employed to implement the nodes 22 and 24 are discussed in a paper by Andrew R Jacob entitled "A Survey of Fast Packet Switches", Computer Communications Review, Vol 20 No 1 January 1990. The terminals 12 and 14 may comprise a telephone, a computer, a facsimile machine, a television or any other telecommunications device which is able to transmit and receive data to and from the B-ISDN. The connection between the source 12 and 15 the destination 14 is established during a call setup procedure during which three virtual channels 26, 28 and 30 are defined across the links 16, 18, and respectively, to transmit information from a source to the destination. Three additional virtual channels can also be established during the call setup procedure to enable the e•oc e transmission of information from the destination 14 to the source 12. All of the cells o 20 which are used to transmit a message or data from the source 12 to the destination 14 are allocated to the same virtual channel over each link 16, 18 and 20. The channel allocated to a cell 2 over a link is determined by the VCI inserted in the cell's header 4. The nodes 22 and 24 include routing information 32 and 34 which is stored therein cm. dii'rig the call setup procedure. The routing information 32 and 34 enables received 25 cells to be correctly directed to the appropriate output links with the correct VCI inserted therein so the cells can be transmitted to the desired destination 14. For example, if the first and second channels 26 and 28 are allocated the VCIs 5 and respectively, and the links 16 and 18 re designated links a and b, respectively, then the first node 22 ensures any cell received on link a with a VCI of 5 is outputted on link b with a new VCI 10. Similarly, if the third link 20 to the destination 14 is designated output link c of the second switch node 24, the node 24 includes information 34 which ensures cells received on input link b with a VCI 10 are sent 911127,dbwspc.037,teleom.l,5 -6to output link c for transmission to the destination 14. A virtual channel is defined as a logical association between the end points of a link that enables the unidirectional transfer of cells over that link. The connection between the source 12 and the destination 14 illustrated in Figure 2 is a virtual connection which is defined as being one or more concatenations of virtual channels to provide the transfer of cells between a point and one or more other points in the network. A virtual connection, like a virtual channel, is a unidirectional device.

To transmit data from a number of sources 40 to a single destination 42 over the B-ISDN 44 using presently available protocols requires separate virtual connections 46 to be established between each of the sources 40 and the destination 42, as shown in Figure 3. A method according to a preferred embodiment of the O ~.present invention, however, enables a single virtual connection 50 to be made on the B-ISDN 44 between the sources 40 to the destination 42, as shown in Figure 4. This s 15 provides a number of advantages, as described in detail hereinafter, including significant savings with respect to the number of virtual channels which need to be established and monitored to enable multiple source to single destination data transfer, particularly when the number of sources 40 becomes relatively large. The connection 50 may be termed a Multiple Source to Single Destination Virtual Connection

(MSSD-VC).

*U a *men*: Configuring the MSSD-VC 50 according to the method involves adjusting the *:set# S• routing information 32 and 34 stored in the nodes 22 and 24 of the B-ISDN so as to provide allocation of a liumber of incoming virtual channels to a single outgoing 0oo e 25 channel. For example, a node 22, as shown in Figure 5, has three virtual channels 52, 54 and 56 transmitting information which is to go to a single destination and are allocated the VCIs 4, 23 and 18, respectively. The first two channels 52 and 54 are received by the node 22 on a link a 58 and the third virtual channel 56 is received on a link b 60. Instead of allocating the three channels 52, 54 and 56 to respective outgoing channels, they are all allocated to a single outgoing virtual channel 62 on an outgoing link c 64. The channel 62 has the VCI 52. This is achieved by configuring the routing information 32 stored in the node 22 during call setup to ensure cells 911127,dbwspe.037,tclexom. 1,6 -7received on link a having VCIs 4 and 23 are outputted on link c with a VCI 52 and cells received on link b with a VCI of 18 are also outputted to link c with a VCI of 52. A further virtual channel 66 is shown on the incoming link b 60 and is allocated the VCI 11. A standard point to point virtual connection is used to connect the channel 66 to a channel 68 having the VCI 7 on an outgoing link d 70. The connection of the channels 52, 54 and 56 to the single outgoing channel 62 constitutes an MSSD-VC.

One application for MSSD-VCs is the fast implementation of network signalling. Destination routing is a technique currently used by networks, such as the Common Channel Signalling System No. 7 (CCS#7), to transfer signalling information between network nodes. The technique involves assigning each node in the network a unique address. To send a message to a particular node, the destination node's address is placed in a header of the message, which is then sent into the network. On 15 receiving the message, intermediate nodes read the address in the message header and determine where the message is to be sent via a pre-established dedicated routing table. The routing procedure at transit nodes to transfer the signalling information is relat .ely slow in current signalling networks primarily because the procedure is generally implemented in software. In a B-ISDN the delays can be significantly 20 reduced by implementing the routing procedure primarily in hardware and employing MSSD-VCs instead of a separate distinct routing procedure which is peculiar to signalling information transferred between nodes.

For a network 72 illustrated in Figure 6, all of the nodes 74, 76, 78, 80, 82 and 25 84 are allocated a unique VCI and the routing information in the nodes is established so any cell received with the unique VCI is routed towards the respective destination node. If node 84 is allocated the unique VCI x, this VCI is used to identify all the channels 86, 88, 90, 92 and 94 which extend from the other nodes and lead to the destination node 84. For example, cells having the VCI x and which are received on the link of channel 88 or channel 86 are sent by node 78 to the link of channel with a VCI x. The connection of channels 86 and 88 to channel 90 is an MSSD-VC.

This technique of routing signalling information not only results in reduced 911127,dbwspc.037, telcom. 1,7 -8information transfer delays by using existing switching circuity it can also lead to a significant improvement in the information carrying capacity of a B-ISDN.

The number of virtual channels employed in some links of a B-ISDN network can be significantly reduced by using MSSD-VCs. This is clearly illustrated in Figure 7, where two networks 100 and 110 having similar physical characteristics are shown with three source nodes 112, 114 and 116 connected to a destination node 118 via four other nodes 120. The network 110 employs standard point to point virtual connections and hence three separate virtual connections 1.22, 124 and 126 are required to connect the source nodes 112, 114 and 116 to the destination node 118.

The last two links 128 and 130 to the destination node 118 must support three virtual channels and another link 132 supports two virtual channels. The other network 100, however, employs a single MSSD-VC 134 and all of the links only need to support a single virtual channel to connect the source nodes 112, 114 and 116 to the 15 destination node 118. A reduction in channels employed gives rise to reduced network management and control costs.

The use of MSSD-VCs also provides connection establishment benefits as new sources can be simply connected to an existing MSSD-VC as required. For some 20 sources this may simply involve connection onto an existing branch of an MSSD-VC.

A full end to end cross network setup procedure, between source and destination, is Sa not required. Improved reconfiguration methods also pertain to the use of a MSSD-VCs. Reconfiguring the network in the event of a link failure may be •achieved with less delay by virtue of the reduced number of virtual channels on some

*O•

25 links.

An MSSD-VC in effect performs a multiplexing function by multiplexing the information from a plurality of sources into a single information stream for delivery to the destination. For some applications, this may be a particularly desirable way of receiving the information and remove the requirement for some destination equipment to internally multiplex information streams.

911127,dbwspc.037,tclecom.1,8 -9- For instances where it is desirable to be able to determine the source of a cell which has been received via an MSSD-VC, a source address may be included in part of the payload 6.

The use of MSSD-VCs is particularly advantageous on a network in instances where traffic levels are relatively low, the number of sources is relatively large and the information transferred is predominantly one way. Recording faults and alarms from a number of sources to a central terminal and transferring data from a number of automatic teller machines to a central banking database can be performed far more efficiently with the use of an MSSD-VC.

0*.

4l .4 911127,dbwspe.037lecom..1,9

Claims (7)

1. A method of transmitting data on a telecommunications network, comprising: forming cells for transmission, said cells including data to be transmitted and a header which has a virtual channel identifier (VCI) for identifying a virtual transmission channel for the respective cell, storing transmission information for at least one switch node in said network to form a virtual connection at said node between a plurality of incoming virtual channels and an outgoing virtual channel, said transmission information allocating cells with VCIs of a predetermined group received by said node to said outgoing virtual channel, and transmitting said cells on the network and substituting at said switch node the S. VCI of cells having VCIs of said predetermined group with a VCI corresponding to said outgoing channel. S*

2. A method as claimed in claim 1, wherein said transmission information allocates cells received by said node to said outgoing channel on the basis of each cell's VCI and the link on which the cell is received. 20 3. A method as claimed in claim 2, wherein said outgoing channel is allocated an outgoing link and a VCI, said cells having said VCIs of said predetermined group being routed onto said outgoing link.

4. A method as claimed in any one the preceding claims, wherein said 25 transmission information is established during a procedure for setting up a call between a plurality of source terminals and a destination terminal. A method as claimed in any one of the preceding claims, wherein said node is a fast packet switch.

6. A method as claimed in any one of the preceding claims, said network is a B-ISDN. 911 127,dbwspe.037,lecoo.1,1O 11

7. A method of transmitting data on a telecommunications network substantially as hereinbefore described with reference to the accompanying drawings.

8. 14 steps, fe7atureS, C011OpOs1itios and compounds-refe-e-t-@-r4ndieated- DATED this 27th day of November 1991 By its Patent Attorneys 15 DAVIES COLLISON CAVE 4 ONA 04 000 *9. *0 a s 0 9 00 9 C>- 911 127,dbwspc.037,tecacom.1,1 1

12- ABSTRACT A method of transmitting data on a telecommunications network (44), comprising forming cells for transmission, the cells including data to be- 5 transmitted and a header which has a virtual channel identifier (VCI) (10) for identifying a virtual transmission channel (52) for the respective cell storing transmission information (32) for at least one switch node (22) in said network (44) to form a virtual connection (50) at the node (22) between a plurality of incoming virtual channels (52,54,56) and an outgoing virtual channel said transmission information (32) allocating cells with VCIs of a predetermined group received by said node (22) to said outgoing channel and transmitting said cells on the network (44) and substituting at said switch node (22) the VCI of cells having VCIs of said predetermined group with a VCI corresponding to said outgoing channel (32). 911 127,dbwsp.037,tlcoom.1,12