AU670662B2 - A telecommunications system and a method of transmitting data in a telecommunications system - Google Patents

Description

Rcgulhtio 32

AUSTRALIA

Patents Act 1952 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

Name of Applicant: TELSTRA CORPORATION LIMITED Actual Inventor: Addres for Service: David Harry Macfarlane Giddy DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000.

"A Telecommunications System and a Method of Transmitting Data in a Telecommunications System" Invention Title: Details of Associated Provisional Application: No: PL7482/93 The following statement is a full description of this invention, including the best method of performing it known to me/us: -1- 94OM4,p.\op.cmtcU1"si.se,1 -2- A TELECOMMUNICATIONS SYSTEM AND A METHOD OF TRANSMITING DATA IN A TELECOMMUNICATIONS SYSTEM The present invention relates to a telecommunications system and a method of transmitting data in a telecommunications system.

In digital telecommunic fions systems such as asynchronous transfer mode (ATM) networks, information is segmented into short fixed length packets called cells which include a header containing information as to the destination of the cell on the network.

As the cells are carried through the network they are switched at switching nodes or exchanges, according to the information contained in their header. All forms of digital telecommunications data may be transmitted in this way such as digitised voice data, facsimile data and computer communications data as part of, for example, a metropolitan area network (MAN), or wide area network (WAN). In implementing telecommunications such as computer communications or constant bit rate video it is generally desirable that a guaranteed bandwidth of telecommunication service be available on demand to enable prompt communication between computer or video installations. Analogue telecommunication systems achieve this end by the provision of leased line services, 20 where a user is provided with exclusive use of a telecommunications line between remote sites, having a specified bandwidth of transmission. An equivalent result may be achieved on a digital telecommunications network, such as a broadband integrated service digital network (B-ISDN), by the use of virtual channels, (VCs) and virtual paths (VPs).

25 In accordance with the present invention there is provided a method of transmitting data by way of a telecommunications network from a first user network termination coupled to an originating exchange of said network to a second user network termination coupled to a terminating exchange of said network, comprising establishing a first user-network virtual path between the first user network termination and the originating exchange, establishing a network-network virtual path from the originating exchange to the terminating exchange, establishing a second user-network virtual path between the terminating exchange and the second user network termination, transmitting 94n4,v*\mjp tcchtW.a V -3data in digital cells from the first user network termination to the second user network termination by transmitting the cells to the originating exchange by way of virtual channels of the first user-network virtual path, transmitting the cells to the terminating exchange by way of virtual channels of the network-network virtual path, and transmitting the cells to the second user network termination by way of virtual channels of said second user-network virtual path corresponding to the virtual channels on which the cells arrive at the terminating exchange.

Preferably virtual channel switching is performed at the originating and terminating exchanges on the virtual channels of the network-network virtual path.

Preferably virtual path switching is performed on the network-network virtual path at an exchange through which the network-network virtual path, in use, passes between the originating and terminating exchanges.

The invention also provides a method of transmitting data by way of a telecommunications network from at least one first user network termination coupled to ee.o o .oan originating exchange of said network to at least one second user network termination coupled to a terminating exchange of said network, comprising arranging data at the at .".least one first user network termination into cells having a path identifier field for 20 transmission of a path identifier and a channel identifier field for transmission of a channel identifier, establishing first virtual paths from the at least one first user network termination to the originating exchange, the first virtual paths being characterised by respective first path identifiers and by restricted ranges of channel identifiers, establishing a network virtual path from said originating exchange to said terminating exchange, 25 establishing second virtual paths from the terminating exchange to the at least one second user network termination, transmitting said cells from the at least one first user network termination to the originating exchange by way of said first virtual paths, translating the path identifiers of cells from different said first virtual paths to the path identifier of said network virtual path and translating the channel identifiers to mutually exclusive channel identifiers of said network virtual path, transmitting the cells to the terminating exchange by way of said network virtual path, translating the path identifiers of the received cells for transmission on said second virtual paths and reverting the channel identifiers, and 940224,p.pa\jcznitctaliO5jpc -4transmitting the cells to the at least one second user network termination by way of said second virtual paths.

The invention also provides a method of transmitting data in a telecommunications network comprising arranging the data into cells including a header field having a path identifier and a channel identifier, transmitting the cells to an originating exchange whereat a plurality of said cells having different path identifiers are modified by substituting a single path identifier indicative of the destination of the cells on the network, and modifying the channel identifiers thereof so as to be mutually exclusive, and transmitting the cells to a terminating exchange on the basis of the single path identifier.

Where the cells pass through one or more network exchanges between the originating exchange and the terminating exchange said single path identifier may be translated and altered at each exchange through which the cells pass.

Preferably each cell received at the terminating exchange having said single path identifier is translated by substituting the single path identifier or altered single path S*t. identifier with a path identifier indicative of a destination user network termination and substituting the translated channel identifier with the original channel identifier as 20 received at the originating exchange.

The invention further provides a telecommunications system for transmitting •.digital telecommunications data between user nodes by way of a telecommunications network, the digital data being transmitted in the form of cells or packets each having a 25 header field including a fixed length path identifier and a fixed length channel identifier, the telecommunications system comprising an originating network node and a terminating network node interconnected to form said telecommunications network, at least one user node coupled to said originating network node, and a network management means for controlling telecommunications on said telecommunications network, wherein the originating network node comprises a translation means to translate and modify the channel identifier and the path identifier of a cell received from said user node on the basis of stored translation data from said network management means and switching 9N0224,p:\opajcm,4abO5.zpc,4 means to direct the received cell to a network destination on the basis of the modified path identifier, wherein first and second cells in use received at said originating network node from said at least one user node destined for said terminating network node and having first and second path identifiers are each modified by said translating means so as to have a third path identifier and mutually exclusive channel identifiers.

Preferably the terminating network node also comprises translation means which modifies the path identifier of received cells originating from said originating exchange on the basis of the channel identifiers thereof.

Preferably the translation means of the terminating network node acts such that the channel identifier of a said received cell is modified so as to be the same as the channel identifier when received at the originating exchange.

In a complex network the originating and terminating nodes may not be directly connected and at least one network node may be interposed between them in the network.

In this instance the third path identifier may be translated and modified at said at least one interposed network node.

The present invention further provides a method of transmitting data by way of a telecommunications network from first user network terminations coupled to an originating exchange of said network to second user network terminations coupled to a terminating exchange of said network, comprising establishing a first user-network virtual path from each of said first user network terminations to said originating exchange, establishing a network-network virtual path from said originating exchange to said terminating exchange, establishing a second user-network virtual path from said terminating exchange to each of said second user network terminations, and transmitting data in digital cells from said first user network terminations by way of restricted range of virtual channels of the first user-network virtual paths as virtual channels of said network-network virtual path, and transmitting respective said cells to said second user network terminations by way of said second user-network virtual paths according to virtual channel identifiers of the cells received at the terminating exchange.

940o4,pMpic ztcat -6- The invention is described in greater detail hereinafter, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 illustrates the hierarchical relationship between virtual channels, virtual paths, and the telecommunications transmission path; Figure 2 is a simplified block diagram illustrating the structure of a digital cell; Figure 3 is a schematic diagram illustrating virtual path switching at a network node; Figure 4 is a schematic diagram illustrating both virtual path and virtual channel switching at a network node; Figure 5a) is a schematic diagram illustrating a transmission path between two user network terminations; Figure 5b) is a schematic diagram illustrating a conventional user-user virtual path; Figure 5c) is a schematic diagram illustrating a segmented user-user virtual path, embodying the invention as applied to the network configuration illustrated in Figure Figure 6 is a schematic diagram illustrating a segmented user-user virtual path; Figures 7a), 7b) and 7c) are block diagrams illustrating methodologies in e establishing virtual path connections in a telecommunications network; Figure 8 is a diagram illustrating transmission of information using a known 20 method; and Figure 9 is another diagram illustrating information transmission using the known method.

In a digital telecommunications network, such as a broad band integrated services 25 digital network (B-ISDN), digital information to be transmitted by way of the network is first segmented into a series of packets or cells. Each cell comprises a data field containing a segment of the digital data to be transmitted, and a header field which contains signalling information as to the destination of the cell on the network. The network itself consists of a plurality of interconnected packet switching exchanges (PSX), each of which may be coupled to a plurality of user-network terminations. A number of methodologies for transmitting cells from one user-network termination to another are presently known, and one is described, by way of background, in relation to Figures 8 94o224,ppmjcrtjslzO5.mp -7and 9.

Figure 8 shows a route 120 between data terminal equipment (DTE) 124 comprising a first user network termination and DTE 126 of a second user network termination. The route 120 includes two units 128 and 130 of terminal interface equipment, three ATM packet switching exchanges (PSX) 132, 134 and 136 between the interface units 128 and 130 and telecommunications links 138 between the terminals 124 and 126, the interface units 128 and 130 and the exchanges 132, 134 and 136. The terminal 124 is connected directly to the first interface unit 128 and packet switching exchange 132. The PSXs 132 and 136 would normally have a plurality of attached interface units 130 and be connected to a plurality of user network terminations. The PSX's 132 and 136 effectively act as gateways to the switching exchanges and the plurality of telecommunications links associated therewith, which together form a telecommunications network. The route 120 is established during a call establishment process in which signalling information is stored in the form of translation tables 140, 142 and 144, as illustrated in Figure 8, which map virtual channel index (VCI) numbers of incoming cells to VCI's of outgoing cells. The call establishment process, on an ATM network, may take place by way of CCITT Common Channel Signalling system No. 7 (CCS7) protocol, in which CCS7 signalling data is transferred between exchanges by way 20 of communications paths which may be considered as distinct from the communications paths used for transferring message data cells. Once the translation tables 140, 142 and 144 are established in the switching exchanges 132, 134 and 136 a call has been established and data cells may be transmitted from the first terminal 124 to the second terminal 126 with the switching being carried out at the exchanges 132, 134 and 136 as described below with reference to Figure 9.

Once the translation labels 140, 142, 144 have been established at the switching exchanges 132, 134, 136 a virtual channel connection (VCC) is said to exist between the first terminal 124 and the second terminal 126, the virtual channel connection being a concatenation of virtual channel links between the ATM network entities. A virtual channel (VC) is a generic term used to describe a unidirectional communication capability for the transport of ATM cells. A VCI identifies a particular VC link, and a specific %024~kkUtr 5xm7h value of VCI is assigned each time a VC is switched in the network. A VC link is a unidirectional capability for the transport of ATM cells between two consecutive ATM entities where the VCI value is translated. A VC link is originated or terminated by the assignment or removal of the VCI value. Routing functions of virtual channels are done at a VC switch/cross-connect (a function of a PSX). This routing involves translation of the VCI values of the oncoming VC links into the VCI values of the outgoing VC links. A virtual channel connection may be provided for the purpose of information transfer between two or more network users (a user-user VCC, as illustrated in Figure 8) or for user-network or network-network information transfer. Each VCC provides a predetermined bandwidth and quality of service (QOS) which is established at the time the VCC is set up and enforced by the network management controller.

Figure 9 illustrates a packet switching exchange 146 having two output ports 148 and 150, an input port 152 and a translation table 154 stored therein. Three packets of data 156, 158 and 160 are shown as being input consecutively to the port 152, each packet 156, 158 and 160 including a header 162 followed by information 164 of a particular call. The packets 158, 156 and 160, illustrated in Figure 9, include information 164 relating to three different calls. The headers 162 of each packet 156, 158 and 160 comprise a VCI which is processed by the switching exchange 146 in order to determine 20 from which output port 148 or 150 a respective packet is to be output. The VCI's of the headers 162 also enable the switching exchange 146 to determine that VCI is to be placed in the headers 162 of the packets 156, 158 and 160 when they are output from the exchange 146 so that succeeding exchanges are able to appropriately direct the packets 156, 158 and 160. The switching process is based on the information contained in the 25 translation table 154 and, as shown in Figure 9, the first packet 156 is to be placed on the second output port 150 and its header 162 is to include the VCI 388. Similarly packet 158 is to be placed on the first output port 148 and its header is to include the VCI 141 and the third packet 160 is to be placed on the second output 150 and its header 162 is to include the VCI 625.

It can now be seen how information is transmitted, according to the above method, between the first terminal 124 and the second terminal 126, illustrated in Figure 940224,p\opcAicmt.eh,1z5.Vc,8 -9- 8. Information to be transmitted from the first terminal !24 to the first exchange 132 is initially arranged into consecutive packets of data 166 so that each has a header 162 which includes the VCI 3. With the translation tables 140, 142 and 144 established, as illustrated in Figure 8, the packets 146 are received by the first exchange 132 and the VCI 3 stored therein indicates to the first exchange 132 that the packets 166 are to be output to the second exchange 134 with headers 162 including the VCI 7, which indicates to the second exchange 134 that the packets 166 are to be output to the third exchange 136. The packets 166 are similarly processed by the second and third exchanges 134 and 136 so that they are transmitted to the destination terminal 126.

There are a number of telecommunications applications in which it is advantageous for two or more user network terminations to have available a path of communication through the telecommunications network which requires a minimum of call setup and in which a predetermined bandwidth and quality of service (QOS) is guaranteed by the network controller. For example, a company may have two or more offices at remote locations, each having a computer installation comprising a local area network (LAN). In order to couple the LAN's into a single wide area network (WAN) it is necessary for a telecommunication path to be continuously available between the remote office sites, at least during business hours, for the computer network 20 communications. If other forms of communication between the remote offices is also frequent then it may be advantageous to also have easily available channels of communication for facsimile and voice data, for example. On an analog telecommunications network a leased line may be provided for continuous telecommunications between two or more such remote sites, however the nature of packet 25 switching exchanges and the available bandwidth of digital transmission mediums such as optical fibres makes a leased line type solution inefficient and uneconomical in the general case.

The concepts of virtual channels (VCs) and virtual paths (VPs) has been internationally endorsed by the CCITT for ATM based broadband ISDN (refer CCITT recommendation 1.311, the contents of which are included herein by reference). A virtual path (VP) is a generic term for a bundle of virtual channel links, all the VC links in the 94O4,pvcmWc3AdbOipc bundle having the same end points. Figure 1 illustrates diagrammatically the hierarchical relationship between a plurality of virtual paths 4, each comprising a number of virtual channels 6, carried on a single transmission path 2. Each ATM cell transmitted on the transmission path 2 contains a label in its header to explicitly identify the VC to which the cell belongs. This label consists of two parts: a virtual path identifier (VPI) which indicates the VP 4 to which the cell belongs, and a virtual channel identifier (VCI) which indicates the VC 6 within the VP 4 to which the cell belongs. Therefore, a VPI identifies a group of VC links, at a given reference point, that share the same virtLue path connection 0 PC). A specific value of VPI is assigned each time a VP is switched in the network. A VP link is a unidirectional capability for the transport of ATM cells between two consecutive ATM entities where the VPI value is translated. A VP link is originated or terminated by assignment or removal of the VPI value. VP links are concatenated to form a VPC, which extends between two VPC end points or, in the case of point to multi point arrangements, more than two VPC end points. A VPC end point is the point where the VCI's are originated, translated or terminated. Routing functions for VPs are performed at a VP switch/cross-connect (a function of a PSX). This routing involves translation of the VPI values of the incoming VP links into the VPI values of the outgoing VP links. In a manner similar to virtual channel connections, virtual path connections may be provided for the purpose of user-user, user-network and network- S: 20 network information transfer.

In the case of the two remote office sites described above, a virtual path connection may be established between the remote sites to provide a semi- permanent path of telecommunications therebetween. The bandwidth and quality of service of the 25 virtual path connection is negotiated at the time of establishment of the VPC and, once established remains fixed and is administered by the network management controller.

Each VC within the VPC may be utilised by the user without restriction, other than that the aggregate traffic parameters of VCs within the VPC must not exceed the predetermined allocated traffic parameters for the VPC.

Figure 2 illustrates the structure of an ATM cell 10, comprising a data segment 12 and a header segment 14. As mentioned, the header segment 14 itself includes the 940224,p:\pckzca41Oit jIc.1O 11 signalling information for the cell, comprising the VPI 16 and VCI 18. According to the CCITT recommendations for virtual paths and virtual channels the VPI field 16 is twelve bits in length for network-network VPCs and eight bits in length for user-network VPCs, whilst the VCI field 18 is sixteen bits in length for both cases. These restrictions allow the telecommunications network to carry up to 4,096 VPs which may each have up to 65,536 VCs per physical bearer.

Figure 3 is a diagrammatic illustration of a VP switch/cross connect which is implemented in a PSX of an ATM based B-ISDN network. A VP switch/cross connect 22 is shown having incoming virtual paths designated by VPI 1, VPI 2 and VPI 3. The virtual paths output from the VP switch 22 comprises VPI 4, VPI 5 and VFI 6. The action of the VP switch/cross connect 22 is such that cells incoming on one of the input virtual paths, VPI 1, VPI 2, VPI 3 are directed to one of the output virtual paths VPI 4, VPI 5, VPI 6 in accordance with information contained in a VP translation table 19. In this instance, cells carried in on virtual path VPI 1 are output on virtual path VPI 6, cells on VPI 2 are output on VPI 4 and cells on VPI 3 are output on VPI 5. Further, virtual paths VPI 1 and VPI 6 constitute a virtual path connection (VPC) designated by reference numeral 24, whilst VPI 2, VPI 4 constitute VPC 26 and VPI 3, VPI 5 constitute VPC 28.

As illustrated in Figure 3, the virtual channels carried by each VPC are not altered by the VP switch/cross connect 22. For example, the VCs carried by VPI 1 comprise VCI 21 and VCI 22, and these VCs are designated by the same VCI numbers in VPI 6 at the output of the VP switch/cross connect 22.

0**o In Figure 4 there is illustrated a switching exchange 30 which comprises a VP 25 switch/cross connect 22 together with a VC switch/cross connect 32. The VC switch 32 operates upon virtual channels, and therefore requires that the VPC carrying the VCs to be switched must be terminated before VC switching. A virtual path designated VPI 1 is shown carrying virtual channels 34, 36 designated by VCI 21 and VCI 22. The S" switching exchange 30 is provided with both a VPI translation table and a VCI translation table to enable switching of both virtual paths and virtual channels. The VP switch/cross connect 22 operates in a manner similar to that described in relation to Figure 3, where VPI's are translated whilst VCI's remain unchanged. The VC switch/cross connect 32, 940224,p:\opjcmt&b.teJO.p11 -12on the other hand, translates VCI values. For example, virtual channels 34 and 36 are input to the switching exchange 30 as VCI 21 and VCI 22 of VPI 1. The virtual channels are passed to the VC switch/cross connect 32 whereupon the VCI values are translated to VCI 23 and VCI 24 respectively, according to information held in the VCI translation table. The translated virtual channels are passed back to the VP switch/cross connect 22 whereupon the VPI values are translated such that VCI 23 is assigned VPI 3 and VCI 24 is assigned VPI 2. An example of the translation table is shown at 31.

A user to user VPC, as discussed above, does not prevent the user from selecting any number of VCI values to partition their traffic within the VPC. Thus the network must assume that all 65536 VCI values are unavailable for use on that VPC, since the VPC must be carried through the network as a single entity. The result is that every user to user VPC removes VPI values from internal network trunks that could be used by the network for traffic management and protection switching. Figures 5c) and 6 illustrate a 15 system (termed segmented user-user VPs) in which user-user VPCs may be implemented with increased network efficiency. In establishing the VPC the range of VCI values made available to a user is restricted on a negotiation basis with the network management controlle. This allows the VPC to be treated as individual VCCs at the originating exchange and carried to the destination exchange in VPCs shared with unrelated VCCs.

At the destination exchange, the VCCs are reassembled into a VPC to the destination user. A. ')ng as the VCI values remain the same within the originating and terminating VPC, t~-c the user will see no difference.

In Figure 5a) there is shown a network telecommunications path 40 between an originating user network termination 42 and a destination user network termination 54.

The originating terminal 42 is cc ,pled to an originating exchange 46 by way of a telecommunications path 44, whilst destination terminal 54 is coupled to a terminating exchange 50 by way of a telecommunications path 52. The originating and termina:ing exchanges 46, 50 are interconnected by way of the telecommunications network 48 which may comprise a plurality of intermediate switching exchanges. Figure 5b) is a diagrammatic illustration of a convention user-user virtual path connection between originating terminal 42 and destination terminal 54. Upon establishing the VPC 56, a 94O24,p\opcjcmtczO5.xpe,12 13 VPI value in the range 0 to 4,095 is assigned at the originating terminal 42, in this instance VPI 200. The VPI of the VPC 56 may be translated at the originating exchange 46, the terminating exchange 50, and at any intermediate switching exchanges in the network 48, in this instance resulting in a VPI 300 at the destination terminal 54. The originating terminal 42 is then free to utilise any of the virtual channels VCI 0 to VCI 65535 of the virtual path 56, so long as the aggregate of the traffic parameters of the constituent VCCs do not exceed the specified traffic parameters for the virtual path 56.

Only VP switching (ie translation of VPI values) takes place in transmitting cells over convention user-user virtual path 56, and thus the VCI values of virtual channels 58 at the originating terminal correspond to the VCI values of the virtual channels 60 at the destination terminal.

In contrast, Figure 5c) illustrates the abovementioned alternative implementation of a user-user VPC, which may be referred to as a segmented user-user virtual path. A 15 segmented user-user virtual path 59 is shown for the transmissioL, path between S. originating terminal 42 and destination terminal 54 of the transmission path 40 illustrated in Figure 5a). A user-network virtual path 62 is established from the originating terminal 42 to the originating exchange 46, comprising virtual channels 58 which are restricted to limited VCI values, in this instance VCI 1 to VCI 1000. At the originating exchange 46 the VPC 62 (VPI 200) is terminated, and both VP and VC switching takes place, whereby the virtual channels 64 arriving at the originating exchange 46 by way of the usernetwork VPC 62 are translated for transmission on a network-network VPC 66. The network-network VPC 66 extends from the originating exchange 46 to the terminating exchange 50, along which VP switching may take place at any interposed intermediate switching exchanges in the network 48. A user-network VPC 70 is established from the terminating exchange 50 to the destination terminal 54, and VP and VC switching of VCs 68 transmitted on VPC 66 is carried out, resulting in VCI values which correspond with the VCI values of the VCs 58 at the originating terminal 42.

Figure 6 shows a more complex arrangement of segmented user-user virtual paths An originating exchange 78 is shown coupled to a terminating exchange 82 by way of a network-network VPC 80. A user-network VPC 74 is shown carrying virtual 902244opakjcrmtc~aUO5.pc,13 14 channels 71 of VCI 21 to VCI 30 from a first user to the originating exchange 78 and a user-network VPC 76 is shown carrying virtual channels 72 of VCI 25 to VCI 39 from a second user to the originating exchange 78. The VPCs 74, 76 are terminated at the originating exchange, and VC switching translates VCs 71 from VCI 21-30 to VCI 41- 50 and VCs 72 from VCI 25-39 to VCI 51-64. The VCI values of the VCs 71 and 72 are translated so that no overlap in VCI values exists to enable the VCs 71 and 72 of VPCs 74 and 76 to be combined into a single VPC 80 from the originating exchange 78 to the terminating exchange 82. At the terminating exchange 82 the VCI values of the incoming network-network VPC 80 are translated back to VCI values corresponding to those of VCs 71 and 72, and assigned to user-network VPCs 84 and 86 for transmission to respective destination terminals. The virtual channels 75, 73 thus comprise VCI values which correspond respectively to VCs 71, 72.

Figures 7a), 7b) and 7c) are block diagrams of a digital telecommunications 15 network 92 in which two packet switching exchanges 98 and 106 are shown coupled to a network management centre 100. Terminal equipment 94 is connected to PSX 98 by way of a digital interface 96. These figures illustrate two means of signalling communication within the network 92, namely management plane (M-plane) communication between the network management centre 100 and the PSX's 98, 106, and control plane (C-plane) communication which may take place between the PSX's 98, 106 and the terminal equipment 94. Figures 7a), 7b) and 7c) each illustrate a different method of establishing a VPC on the network 92. In the network illustrated in Figure 7a), M-plane communication is utilised, instigated by the network management centre with reference to a resource reservation data base 102, to establish a semi-permanent VPC. This form of VPC establishment can be used to create a semi permanent networknetwork VPC, such as VPC 80, shown in Figure 6, the operation of which is dependent "upon more that one user. Figure 7b) illustrates on demand VPC establishment whereby a VPC establishment request is issued from the terminal equipment 94 to the PSX 98, which request is then routed by the management plane communication to the network management centre 100. Establishment of the VPC is then carried out by the network management centre with reference to the resource reservation data base 102 in the same manner as the network described in relation to Figure 7a). Another method of VPC 940224,p:\opcrjcmtdztsO5 c,14 establishment in illustrated in Figure 7c), wherein a VPC establishment request issued from the equipment 94 via the C-plane is distributed by the C-plane communication network and processed at the individual PSXs 98, 106 with reference to the resource reservation database 102.

The VP plays a dual role in a B-ISDN network, as a type of user connection and at the same time a tool for traffic management within the network. As a user connection type, it should be controllable via C-plane signalling procedures (Figures 7b) and 7c)), while as a traffic management tool, it must be under control of the network management systems (Figures 7a) and 7b)).

To establish a VPC, several function are performed. They include:route calculation; 15 capacity allocation; and -updating connection state information at PSX's.

In setting up semi-permanent VPCs, these functions are implemented in the Mplane, either at a centralised or distributed network management centre 100. The creation of a VPC using C-plane procedures also requires these functions. The way these functions are duplicated for C-plane procedures can affect the speed of VPC establishment. Two scenarios are examined below.

The C-plane can forward VPC establishment request to the M-plane (see Figure 25 Therefore, the C-plane is nothing more than a means of conveying the requests.

The M-plane performs the route calculating, capacity allocation and connection state information updating. There is little, if any, time reduction in establishing a VPC this way when compared to VPC establishment by the M-plane alone. Thus, the only benefit is the use of a common protocol to establish VCCs and VPCs.

Alternatively, the route calculation, capacity allocation and connection state information updating functions may be duplicated at the PSX's for C-plane procedures.

pc3lcmstcizbO5jp,15 -16- In this way, the processing speed is increased (due to the removal of the delay associated with a query to the M-plane) and the delay for VPC establishment is reduced.

In a small B-ISDN, the resource reservation database 102 is likely to be located centrally at a VP Management Centre. As the B-ISDN grows in size and traffic carrying capacity, the network may be divided into regions, each with a regional VP Management Centre. In this case, the resource reservation database will be distributed. There is a trade-off between access speed to resource reservation database information and the added complexity of maintaining a distributed database in real time.

In summary, a user-user virtual path is a VP which extends from a user's network termination through to another user's network termination. The VCs within it are carried transparently across the network and the user is free to allocate the virtual channels within the VP in m'ny way they wish. The parameters of the user-user VP are agreed 15 between the user and the network management when the path is established and the network will monitor the traffic on the path as a whole to ensure compliance with those parameters. The allocation of resources such as bandwidth and virtual channel identifiers within the user-user VP is under the total control of the user.

Segmented user-user Virtual Paths, described in detail hereinbefore, differ from conventional user-user Virtual Paths in a number of ways: 1) They are not carried through the network as single Virtual Paths, and require switching or cross-connecting of the Virtual Channels at the *o network bound-ries; and 2) The range of VCI's available to the user is limited by negotiation at establishment time.

By way of contrast, a group of semi-permanent virtual channels may be established to perform a similar function to Segmented User-user Virtual Paths. A semipermanent virtual channel is a virtual channel established by the network management system which extends from one user's network termination to another user's network termination. The important difference between a semi-permanent Virtual Channel and 940224,popaicmcIsfOsjj6 17a Segmented User-user Virtual Path is that the former are resourced on an individual basis whereas the latter are resourced as a group. In the former case, any modification to the resources allocated to a particular virtual channel must be made with reference to the network, whereas the latter allows modification to the virtual channels within the Virtual Path independently of the network. Furthermore, a Virtual Channel connection will result in the Virtual Channel Identifiers at each end of the connection being independently assigned. In both a User-user Virtual Path and a Segmented User-user Virtual Path, the Virtual Channel Identifier values will be the same at each end of the connections within the VP.

The foregoing detailed description has been forward merely by way of explanation only, and is not intended to be limiting to the invention, which is defined in the claims appended hereto.

*e* 940224,p.v\pn\wIatzSjpcqj17

Claims (5)

1. A method of transmitting data by way of a telecommunications network from a first user network termination coupled to an originating exchange of said network to a second user network termination coupled to a terminating exchange of said network, comprising establishing a first user-network virtual path between the first user network termination and the originating exchange, establishing a network-network virtual path from the originating exchange to the terminating exchange, establishing a secnd user- network virtual path between the terminating exchange and the second user network termination, transmitting data in digital cells from the first user network termination to the second user network termination by transmitting the cells to the originating exchange by way of virtual channels of the first user-network virtual path, transmitting the cells to the terminating exchange by way of virtual channels of the network-network virtual path, and transmitting the cells to the second user network termination by way of virtual channels of said second user-network virtual path corresponding to the virtual channels on which the cells arrive at the terminating exchange.

2. A method as claimed in claim 1, wherein the virtual channels from said first user- network virtual path are combined with virtual channels from other sources on the network to form said network-network virtual path.

3. A method as claimed in claim 1 or 2, wherein the virtual channel identifiers of the cells transmited from said first user-network virtual path are translated at the originating exchange to an exclusive subset of the channel identifiers of the network- 25 network virtual path.

4. A method as claimed in claim 1 including the step of establishing with a network controller a minimum quality of service for data to be transmitted by way of the virtual channels of the first user-network virtual path, and allocating an equivalent minimum quality of service for data transmission by way of the virtual channels of said network- network virtual path. 94024 )-.opycntcJhtesh,18

19- A method as claimed in any one of claims 1 to 4, including the step of establishing an agreed number and range of virtual channel identifiers for the virtual channels of said first user-network virtual path by negotiation with a network controller. 6. A method as claimed in any preceding claim, wherein the virtual channel identifiers of the cells transmitted from the first user network termination to the second user network termination are translated at both said originating exchange and said terminating exchange. 7. A method as claimed in claim 6 wherein the virtual channel identifiers associated with said second user-network virtual path are the same as the channel identifiers associated with said first user-network virtual path. 8. A method of transmitting data by way of a telecommunications network from at 15 least one first user network termination coupled to an originating exchange of said network to at least one second user network termination coupled to a terminating i ""exchange of said network, comprising arranging data at the at least one first user network termination into cells having a path identifier field for transmission of a path identifier and a channel identifier field for transmission of a channel identifier, establishing first virtual paths from the at least one first user network termination to the originating exchange, the first virtual paths being characterised by respective first path identifiers and by restricted ranges of channel identifiers, establishing a network virtual path from said originating exchange to said terminating exchange, establishing second virtual paths from the terminating exchange to the at least one second user network termination, transmitting a 0 said cells from the at least one first user network termination to the originating exchange by way of said first virtual paths, translating the path identifiers of cells from different said first virtual paths to the path identifier of said network virtual path and translating the channel identifiers to mutually exclusive channel identifiers of said network virtual path, transmitting the cells to the terminating exchange by way of said network virtual path, translating the path identifiers of the received cells for transmission on said second virtual paths and reverting the channel identifiers, and transmitting the cells to the at least one second user network termination by way of said second virtual paths. 94a24,pIcajcsftWO5.spe.9 20 9. A method of transmitting data in a telecommunications network comlprising arranging the data into cells including a header field having a path identifier and a channel identifier, transmitting the cells to an originating exchange whereat a plurality of said cells having different path identifiers are modified by substituting a single path identifier indicative of the destination of the cells on the network, and modifying the channel identifiers thereof so as to be mutually exclusive, and transmitting the cells to a terminating exchange on the basis of the single path identifier. A method as claimed in claim 9, wherein said single path identifier is translated at each intermediate exchange in the transmission path between the originating exchange and the terminating exchange. 11. A method as claimed in claim 9 or 10, wherein each cell received at the terminating exchange having said single path identifier is translated by substituting the 15 single path identifier or altered single path identifier with a path identifier indicative of a destination user network termination and substituting the translated channel identifier with the original channel identifier as received at the originating exchange. 12. A telecommunications system for transmitting digital telecommunications data between user nodes by way of a telecommunications network, the digital data being transmitted in the form of cells or packets each having a header field including a fixed length path identifier and a fixed length channel identifier, the telecommunications system comprising an originating network node and a terminating network node interconnected to form said telecommunications network, at least one user node coupled to said originating network node, and a network management means for controlling telecommunications on said telecommunications network, wherein the originating network node comprises a translation means to translate and modify the channel identifier and the path identifier of a cell received from said user node on the basis of stored translation data from said network management means and switching means to direct the received cell to a network destination on the basis of the modified path identifier, wherein first and second cells in use received at said originating network node from said at least one user node destined for said terminating network node and having first and second path 940224,p:opcjcmtcttU5UMWc20 -21- identifiers are each modified by said translating means so as to have a third path identifier and mutually exclusive channel identifiers. 13. A telecommunications system according to claim 12, wherein the terminating network node also comprises translation means which modifies the path identifier of received cells originating from said originating exchange on the basis of the channel identifiers thereof. 14. A telecommunications system according to claim 13, wherein the translation means of the terminating network node acts such that the channel identifier of a said received cell is modified so as to be the same as the channel identifier when received at the originating exchange. A method of transmitting data by way of a telecommunications network from first 15 user network terminations coupled to an originating exchange of said network to second *user network terminations coupled to a terminating exchange of said network, comprising establishing a first user-network virtual path from each of said first user network terminations to said originating exchange, establishing a network-network virtual path from said originating exchange to said terminating exchange, establishing a second user- network virtual path from said terminating exchange to each of said second user network terminations, and transmitting data in digital cells from said first user network terminations by way of restricted range of virtual channels of the first user-network virtual paths as virtual channels of said network-network virtual path, and transmitting respective said cells to said second user network terminations by way of said second user-network virtual paths according to virtual channel identifiers of the cells received at the terminating exchange. 16. A method of transmitting data in a telecommunications network substantially as hereinbefore described with reference to the accompanying drawings. 940224,p\opccitlszO5.pc,21 22 17. A telecommunications system substantially as hereinbefore described with reference to the accompanying drawings. DATED this 24th day of February 1994. TELSTRA CORPORATION LIMITED By DAVIES COLLISON CAVE Patent Attorneys for the Applicant 94M24,p:\opccr,ceotxOp,22 ABSTRACT A method of transmitting data by way of a telecommunications network from a first user network termination coupled to an originating exchange of said network to a second user network termination coupled to a terminating exchange of said network, comprising establishing a first user-network virtual path between the first user network termination and the originating exchange, establishing a network-network virtual path from the originating exchange to the terminating exchange, establishing a second user-network virtual path between the terminating exchange and the second user network termination, transmitting data in digital cells from the first user network termination to the second user network termination by transmitting the cells to the originating exchange by way of virtual channels of the first user-network virtual path, transmitting the cells to the terminating exchange by way of virtual channels of the network-network virtual path, and transmitting the cells to the second user network termination by way of virtual channels of said second user-network virtual path corresponding to the virtual channels on which the cells arrive at the terminating exchange. e So. •04 o 940o24,p.Wapac bntstrhO5.spc,23