ATM TRANSMISSION SYSTEM

Abstract: ATM (Asynchronous Transfer Mode) transmission system, comprising mutually connected transmission exchanges, transmission nodes connected via virtual transmission paths with these exchanges and access means connectable to these transmission nodes via virtual transmission channels. Data are exchanged in packet or cell form via a transmission combination comprising a virtual transmission channel and a virtual transmission path, in which a transmission node is provided connection means for exchanging data with an accompanying transmission exchange via a transmission combination comprising a pre-assigned or default-virtual transmission path. The connection means can comprise a routing table for selecting assigned virtual transmission paths via pre-adjustable routing data.

Description: ATM transmission system The invention relates to an ATM (Asynchronous Transfer Mode) transmission system, comprising mutually connected transmission exchanges, transmission nodes connected with these exchanges via virtual transmission paths and access means connectable with these nodes via virtual transmission channels for exchanging data in packet or cell form via a transmission combination comprising a virtual transmission channel and a virtual transmission path, in which each cell contains an identification of an activated transmission combination. ATM transmission systems have been developed for transporting and exchanging in a uniform way data with different characteristics and properties. Because all ATM cells are provided with an own label (header), cells of different users can be mixed on a transmission connection, so that the transmission means can be used dynamically. For that reason with ATM there is spoken about transmission connections in the form of virtual transmission paths (Virtual Path Connections) (VPCs) and virtual channels (Virtual Channel Connections). Virtual paths can be regarded as semi-permanent connection pipes, switched by the nodes. The throughput capacity of a virtual channel can be chosen according to the need. The virtual channels can be regarded as a dial connection (on demand). By choosing a transmission combination comprising a virtual path and a virtual channel (VPC/VCC) a complete meshing can be created at logical level, while this does not need to be the case on the physical level. However, this requires transmission nodes which are able to rout the cells by means of the labels in such a way that they arrive at the right access means or users. In practice VPC/VCC transmission combinations are utilised in which 8 bits are reserved for choosing a virtual transmission path (Virtual Path Identifier) (VPI) and 16 bits for selecting a virtual transmission channel (Virtual Channel Identifier) (VCI). This means that for exchanging information with more than 256 users, continually a VPI/VCI value us required for identifying a user in question or the access means in question. Particularly for large transmission systems with a large number of users, a large number of transmission nodes will be required for connecting users or their access means to the transmission exchanges. Furthermore, the transmission nodes need to be able to rout the cells sufficiently fast, to prevent undesired delays, which is especially the case for exchanging speech or other so-called real time data. In practice, it is therefore pursued to construct the transmission nodes as simple and passive as possible as regards their involvement in effectuating and exchanging information between users, exchanging system administration information and transactions for settling costs for use of the transmission system. The invention provides to this end an ATM transmission system, characterised in that a transmission node comprises connection means for exchanging data with an accompanying transmission exchange of data via a transmission combination comprising a pre-assigned virtual transmission path. The invention is based on the understanding that the switching functions of a transmission node can be highly reduced by pre-assigning of default virtual transmission paths for exchanging data between a transmission node and an accompanying transmission exchange. Especially then, when according to further embodiments of the invention the connection means are fit out for exchanging data via pre-assigned virtual transmission paths on the basis of desired transmission properties or services such as via pre-assigned virtual transmission paths of different transmission capacity. The access to one of the pre-assigned or default virtual transmission paths concerned can be guided on the basis of a subscription or on request, via suitable signalling data. By assigning to every user or the access means connected to a transmission node, a virtual transmission path for information exchange with a transmission exchange, via a VPI value, as user is uniquely addressable by means of a transmission combination consisting of the VPI value and a VCI value for the virtual transmission channel between the user's access means and the transmission node concerned. Hereby the switching function of the transmission node can be reduced to translating a VPI/VCI transmission combination on the transmission path between the access means and the transmission node in a VPI/VCI transmission combination on the connection path between a transmission node and an accompanying transmission exchange, when the assigned virtual transmission path concerned itself is divided into different virtual transmission channels and vice versa. For translating and routing cells in this way, in an even further embodiment of the invention, the connection means can comprise a routing table for selecting assigned virtual transmission paths via in advance adjustable routing data. In an preferred embodiment of the invention the connection means in a transmission node are fit out in such a way, that cells originating from a transmission exchange can be exchanged with one or more of the connected access means and that cells originating from the access means can exclusively be exchanged via one of the assigned virtual transmission paths for exchanging information and signalling data with an exchange. Herewith, a so-called copy function is provided, in which data of e.g. a service, in which video data are disseminated on demand, can be simultaneously exchanged with different users or access means. In that cells originating from different users or access means can only be exchanged via a specific, activated transmission combination, it is possible to detect and, if necessary to delete, cells that do not belong to an activated transmission combination to prevent interference with other cells and data exchange. In a further embodiment of the invention, the transmission nodes are also provided with means for monitoring the use of a transmission combination according to in advance adjustable user parameters. With such monitoring (policing) in a transmission node, overloads and thereby failures of the data exchange can be prevented in a simple way. The user parameters will in practice mostly be related to the transmission capacity that has been assigned to a user, like e.g. 64 kb/s for telephone and e.g. up to 2 MB/s for data interchange for Internet traffic and the like. For establishing connections in an ATM transmission exchange it is necessary to exchange signalling data, in which the access means can be advantageously fit out for exchanging information and signalling data via separate, pre-assigned virtual transmission paths. In an embodiment of the ATM transmission system according to the invention, the connection means of a transmission node are fit out for exchanging information and signalling data with an accompanying transmission exchange via separate, pre-assigned virtual transmission paths and in which the signalling data of the access means are joined on one or more virtual transmission paths which are specially assigned for exchanging signalling data. Also in this case it applies that the transmission nodes only need to perform passive routing and translation of VPI/VCI values for exchanging cells between users or their access means. The addressing of the cells is implicitly fixed by the pre-assigned or default VPI values. The invention also provides transmission nodes provided with connection means and/or monitoring means for application in an ATM transmission system with pre-assigned virtual transmission paths and provides an access means provided with means for disseminating with a cell of a transmission combination comprising a pre-assigned virtual transmission path and means for receiving of a cell with a transmission combination comprising a pre-assigned virtual transmission path, such as described in the above. The invention is described in more detail in the following and is illustrated with reference to the attached drawings. Herein shows: Fig. 1 schematically the exchange of data between a transmission exchange and different users of their access means via an intermediate transmission node in an ATM transmission system, which is known per se. Fig. 2 schematically the exchange of data between a transmission exchange and different users or their access means via an intermediate transmission node in an ATM transmission system according to the invention. Fig. 3 schematically the monitoring in a transmission node of the data exchange between access means and a transmission exchange in an ATM transmission system according to the invention. Fig. 1 shows schematically the make-up of an ATM (asynchronous Transfer Mode) transmission system 1 . Of these, are shown only a single transmission exchange (Switch) (SW) 2, a single transmission node connected herewith (Connection Point) (CP) 2 and some users I, J, K, L to be connected to the transmission node 3 that are provided with access means 4, as is illustrated in more detail for user K. A practical ATM transmission system 1 comprises a number of mutually connected transmission exchanges 2 with a plurality of transmission exchanges and access means 4 that are connected to it. In accordance with the ATM concept, the transmission exchanges 2 and the transmission nodes 3 are mutually connected via virtual transmission paths (Virtual Path Connections) (VPCs). In an advanced embodiment these VPCs can be further subdivided into virtual transmission channels (Virtual Channel Connections) (VCCs). A virtual transmission path and a virtual transmission channel are identified with a transmission combination consisting of an identification of the transmission path (Virtual Path Identifier) (VPI) and an identification of the virtual transmission channel (Virtual Channel Identifier) (VCI). The transmission combination concerned or VPI/VCI combination represents in fact a transmission connection via physical media like metallic cables, fibre optic cables and/or radio connections. Virtual paths can be selected on the basis of a certain transmission capacity and/or transmission quality. Between the access means 4 and the accompanying transmission node 3 virtual transmission channels (Virtual Channel Connections) (VCC) are situated, which can be selected by a user I, J, K, L according to demand of transmission capacity. The transmission channels concerned are indicated by means of a VCI value (Virtual Channel Identifier). According to the ATM concept, data are exchanged between the access means 4 and the transmission exchange 2 in the form of cells, each having an own label (header), which comprises among others a selected transmission combination, i.e. a VPI/VCI combination. The connections between a transmission exchange 2 and the access means 4 of the users, via a transmission node 3, are thus in fact so called dial connections, in which a transmission connection concerned is selected after exchanging signalling information, for which a separate transmission combination, different from the transmission combination for exchanging information, is used. Therefore, in Fig. 1 a distinction is made between exchanging information, such as voice or computer data, indicated by solid double arrows and signalling data, indicated by dashed double arrows. Via administration or control means 5 of a transmission node 3, a suitable VPI/VCI combination with the transmission exchange 2 is for instance selected on request of the access means 4 by the transmission node 3 and the transmission connection concerned is established. On the other hand, for a connection from the transmission exchange 2 to a user concerned I, J, K, L, a connection is realised by the administration and control means 5 from the transmission node 3 to the user concerned. In such an ATM transmission system, the transmission nodes 3 perform an important switching function by analysing the signalling data and the labels (headers) of the cells to be transported. The administration or control means 5 must therefore be fit out with adequate administration and control software in order to establish the desired virtual connections. As already mentioned in the preamble, especially for large systems with a large number of users, a large number of transmission nodes will be required for connecting the users or their access means with the transmission exchanges. For exchanging real-time data undesired delays in the data interchange must be prevented, which imposes requirements on the switching or routing speed of the transmission nodes 3. Fig. 2 shows an ATM transmission system 6 according to the invention, comprising a transmission exchange 2, a transmission node 7 and access means 8, with which users I, J, K, L, can exchange information through virtual transmission channels and virtual transmission paths via the transmission node 7 with a transmission exchange 2. In deviation from the known ATM system 1 shown and discussed in the above, the virtual transmission paths between the transmission exchange 2 and the transmission node 7 have been pre-assigned in the ATM transmission system 6 according to the invention. That means that the information between a user I, J, K, L, and the transmission exchange 2 cannot be handled through a random virtual transmission path, but is restricted to the pre-assigned default virtual transmission paths concerned, which can have different transmission capacities, if desired. As indicated schematically in Fig. 2, the users J and L exchange, via their accompanying access means 8, information via the virtual transmission path indicated with VPI = 0. The users I and L, though not shown in operation, will also exchange information with the transmission exchange 2 vi the virtual transmission path with VPI = 0, which has been assigned for this purpose. As regards the signalling data, these are exchanged via a virtual transmission path between the transmission node 7 and the transmission exchange with VPI = 1 . By making use of the default virtual transmission paths between the transmission node 7 and the transmission exchange 2, the administration and control means 5 in the ATM system according to the invention can be reduced to connection means 9 in the form of routing tables or other connection means controlling on the basis pre-adjusted data. That means, for the active connections that are shown with the users J and L the connection means 9 need only to perform a simple translation or mutual imaging of the VCI values concerned. The example shown in Fig. 2 is a situation, in which the cells originating from the transmission exchange 2 via the virtual transmission path with transmission combination VPI/VCI = 0/10 are exchanged with the access means 8 of the users J and L, via respective virtual transmission channels with values VCI = 9, or a transmission combination VPI/VCI = 0/9 on the transmission path between the transmission node 7 and the access means 8 of the respective users J and L. This is a so-called copy function, in which for instance video data and other data that are distributed on demand are exchanged simultaneously with different users or access means. Of course, also singular connections between a transmission exchange 2 and a user I, J, K, L are possible. Cells originating from the access means 8 can in general be exchanged only via one of the assigned virtual transmission paths for exchanging information and signalling data with an exchange 2. In the example shown in Fig. 2, the information and signalling data are exchanged with an accompanying transmission exchange 2 via separate, pre-assigned or default virtual transmission paths. The signalling data of the access means 8 are in this example joined together on a virtual transmission path, with VPI = 1 , which is not further subdivided into specific transmission channels. The signalling data of the respective users I, J, K, L are however discriminated with an accompanying VCI value. For instance, VPI/VCI = 1 /J refers to the signalling data of user J, exchanged via the virtual transmission path having VPI = 1 . Also now, it applies that the transmission node 7 only needs to perform a simple translation of the transmission combination on the path between the transmission node 7 and the access means 8 concerned to the virtual transmission path between the transmission node 7 and the transmission exchange 2 and vice versa. For the active connections shown in Fig. 2 the VPI/VCI = 0/5 should therefore be translated into VPI = 1 /J respectively L and conversely. The assignment of a default virtual transmission path can be controlled on the basis of a subscription, a desired transmission quality (Quality of Service) (QoS) and other parameter values, among which of course the transmission capacity for e.g. video or voice services. Via a control interface, e.g. of the type VB5.1 , shown in Fig. 2 schematically with the reference numeral 10, a fixed set routing of the connection means 9 can, if desired, be adjusted from network control unit of the ATM transmission system. This will in general be a static adjustment, depending on the modifications in the assignment of a virtual transmission path on modification of a subscription of a user or similar. Monitoring on the right usage of the facilities assigned to a user can, in the embodiment of the ATM transmission system according to the invention, be carried out as illustrated in Fig. 3. The access means 8 communicate in this example via three virtual transmission channels and the transmission node 7 with the transmission exchange 2. In the example shown, these are a 2 MB/s connection for exchanging computer data and the like, and a 64 kb/s connection for signalling. Al these connections are exchanged on the default virtual path between transmission exchange 2 and the transmission node having VPI = 0 and respectively virtual transmission channels between access means 8 and the transmission node 7 with the values VCI = 60, VCI = 50 and VCI = 5. By the pre-assigned VPI values, relatively simple monitoring means 1 1 , 1 2, 1 3 can be applied in the transmission node 7 to prevent improper use of the assigned virtual transmission connection. In addition, in the transmission exchange 2 a monitoring function (policing) of the use of the transmission means can also be fit, such as schematically indicated with the monitoring means 14 for information traffic, such as voice, computer data etc. and monitoring means 1 5 for signalling traffic. By the pre-assignment of VPI values, cells with other than the default VPI values can easily be recognised by the monitoring means 1 1 -15 and be removed from the data stream, because these cells are not exchanged via a transmission node 7. This gives an effective monitoring of the correct use of the transmission connections. The access means 8 (X-box) are established in such a way, by means of means 16 which are suitable for this purpose, that they place the VPI/VCI values concerned in the labels (headers) of the cells and can recover the VPI/VCI values of labels of cells received via means 17. The assigned or default VPI values can be taken up semi-permanently in the access means s8 concerned of the user I, J, K, L, which reduces the complexity of a transmission node even further.

Claims: CLAIMS 1 ATM (Asynchronous Transfer Mode) transmission system (6), comprising mutually connected transmission exchanges (2), transmission nodes (7) connected with these exchanges (2) via virtual transmission paths (VPI) and access means (8), which are connectable to these nodes (7) via virtual transmission channels (VCI) for exchanging data in packet or cell form via a transmission combination (VPI/VCI) comprising a virtual transmission channel (VCI) and a virtual transmission path (VPI), in which each cell contains an identification of an activated transmission combination (VPI/VCI), characterised in that a transmission node (7) comprises connection means (9) for exchanging data with an accompanying transmission exchange (2) via a transmission combination (VPI/VCI) comprising a pre-assigned virtual transmission path (VPI). 2. ATM transmission system (6) according to claim 1 , characterised in that the connection means (9) are fit out for exchanging data via pre-assigned virtual transmission paths (VPI) on the basis of desired transmission properties or services. 3. ATM transmission system (6) according to claim 1 , characterised in that the connection means (9) are fit out for exchanging data via pre-assigned virtual transmission paths (VPI) of different transmission capacity. 4. ATM transmission system (6) according to claim 1 , characterised in that the access means (8) and the transmission nodes (7) are fit out for exchanging information and signalling data via separate virtual transmission channels (VCI), in which the connection means (9) of a transmission node (7) are fit out for exchanging information and signalling data with an accompanying transmission exchange (2) via separate, pre-assigned virtual transmission paths (VPI) and in which the signalling data of the access means (8) are joined together on one or more virtual transmission paths (VPI), which are assigned for exchanging signalling data. 5. ATM transmission system (6) according to claim 1 , characterised in that the connection means (9) comprise a routing table for selecting assigned virtual transmission paths (VPI) via pre-adjusted routing data. 6. ATM transmission system (6) according to claim 1 , characterised in that the connection means (9) in a transmission node (7) are fit out in such a way, that cells originating from a transmission exchange (2) can be exchanged with one or more of the connected access means (8) and that cells originating from access means (8) can only be exchanged via one of the assigned virtual transmission paths (VPI) for exchanging information and signalling data with an exchange (2). 7. ATM transmission system (6) according to claim 1 , characterised in that the access means (8) are fit out for activating a transmission combination (VPI/VCI) according to demand. 8. ATM transmission system according to claim 1 , characterised in that a transmission node (7) is provided with means (1 1 , 1 2, 13) for monitoring the use of a transmission combination (VPI/VCI) according to pre-adjustable user parameters 9. Transmission node (7) for application in an ATM (Asynchronous Transfer Mode) transmission system (6) comprising mutually connected transmission exchanges (2), transmission nodes (7) connected with these exchanges (2) via virtual transmission paths (VPI) and access means (8), which are connectable to these nodes (7) via virtual transmission channels (VCI) for exchanging data in packet or cell form via a transmission combination (VPI/VCI) comprising a virtual transmission channel (VCI) and a virtual transmission path (VPI), in which each cell contains an identification of an activated transmission combination (VPI/VCI), characterised in that a transmission node (7) comprises connection means (9) for exchanging data with an accompanying transmission exchange (2) via a transmission combination (VPI/VCI) comprising a pre-assigned virtual transmission path (VPI), as defined in or more of the above claims. 10. Access means (8) for application in an ATM (Asynchronous Transfer Mode) transmission system (6), mutually connected transmission exchanges (2), transmission nodes (7) connected with these exchanges (2) via virtual transmission paths (VPI) and access means (8), which are connectable to these nodes (7) via virtual transmission channels (VCI) for exchanging data in packet or cell form via a transmission combination (VPI/VCI) comprising a virtual transmission channel (VCI) and a virtual transmission path (VPI), in which each cell contains an identification of an activated transmission combination (VPI/VCI), characterised by means (16) for disseminating with a cell a transmission combination (VPI/VCI) comprising a pre-assigned virtual transmission path (VPI) and means (17) for receiving from a cell having a transmission combination (VPI/VCI) comprising a pre-assigned virtual transmission path (VPI) according to one or more of the claims 1 to 8.

Inventors: VERVUURT FRANSISCUS ELISABETH, VERVUURT, FRANSISCUS, ELISABETH, WILLEM
Applicants: KONINKL KPN NV, VERVUURT FRANSISCUS ELISABETH, KONINKLIJKE KPN N.V., VERVUURT, FRANSISCUS, ELISABETH, WILLEM
Application year: 1999
Main classification: H04Q11
IPC codes: H04L12, H04Q11