SE515054C2 - Improvements to or related to multicasting - Google Patents

Abstract

The present invention relates to multicasting in an ATM based public data network. Multicasting can be defined as the ability to send a single message to multiple recipients at different locations. A method of multicasting, of the present invention, operates in a packet switched data transmission system typically an ATM broadband data service system. A data packet, intended for transmission to a plurality of addresses, is copied at each node of the system to which one, or more, subscribers, to which said data packet is addressed, are connected. A copy of said data packet is transmitted to each addressed subscriber and to adjacent nodes to which addressed subscribers are connected. This procedure is continued until all addressed subscribers have received a copy of the data packet.

Description

25 30 35 551.5 0554 2 multi-address broadcast / broadcast. Broadband Data Services (BDS) must also support multi-address transmission if the service is to be attractive to users. Group addresses are used to support multi-address transmission applications in these networks.

Typically, BDS is implemented at different ATM exchanges.

The "connectionless" server functions (CLSs) can be installed in, or in connection with, the ATM selectors.

CLSs cannot be connected in all selector nodes. The CLSs can form worm networks, ring networks, star networks or tree networks. The CLSs control the functions of the individual networks and mediate data packets within networks and between networks.

Typical of ATM is that an information packet, or cell, comprises five bytes of startup data and 48 bytes of user data. The startup data includes data that identifies the cell, a logical address that identifies routing, forward error correction bits, plus bits for priority management and network administration functions.

Forward error correction is only used in startup data.

All cells in a virtual connection follow the same path through the network, which is determined during a call connection. There are no fixed time slots so that each user can access the transmission medium whenever a free cell is available. ATM is able to work with bit rates of 155.52 and 622.08 Mbit / s.

Where a BDS, which works with a data packet transmission technology such as ATM, includes a plurality of switching nodes, the transmission of a plurality of identical data packets from node A, via nodes B, C, D and E to subscribers served from node E, is a considerable waste. with traffic capacity. The same information is sent between the same nodes many times. The present invention is intended to reduce this redundant transmission. The present invention uses in its implementation "agents" which are object-oriented programmed units which include both data and operation code, and which have the ability to "negotiate" with other agents or units, e.g. subscribers.

According to general practice in the field of telecommunications, there is an extensive use of abbreviations in this specification. To support the reader, the detailed description starts with a list of abbreviations used in the specification.

The present invention can, of course, be used to advantage in any telecommunication network with packet switching using worm, ring or tree network architecture in which the transmission paths are interconnected by switching nodes, some of which are CLS nodes, i.e. switching nodes having a CLS function.

However, the invention has in reality been implemented using an experimental BDS system developed by the patent applicant. For the sake of completeness, a brief description of the experimental BDS system is included in the present specification.

According to a first object of the present invention, there is provided a method of multi-addressing in a packet data transmission system having a plurality of switching nodes, each serving a large number of subscribers, characterized in that a data packet intended for transmission to a large number of addresses is copied at each node. , to which one or more subscribers, to which said data packets are addressed, are connected, and a copy of said data packets is sent to each addressed subscriber and to the next node to which addressed 10 15 20 25 30 35 515 054 ßf subscribers are connected, until all addressed subscribers received a copy of said data packet.

Preferably, a CLS node sends one and only one copy of said data packet to each CLS node: - to which it is directly connected; and - to which addressed subscribers are connected.

Alternatively, a CLS node sends one and only one copy of said data packet to each CSL node: - to which it is directly connected; and - to which either: - addressed subscribers; or - a CLS node connected to addressed subscribers; are connected.

Each multi-address data packet can include a group address.

A multi-address data packet transmitted from a first CLS node and intended for a large number of subscribers is transmitted from said first CLS node in a data packet which encapsulates the group address.

Preferably, data packets are transmitted along trees in tree form; the packets are copied only where the branches of the tree divide, and in that the structure of said tree is determined so as to minimize system utilization, but with the limitation that the transmission delay to each group address is kept within a predetermined limit.

Said roads can form a Steiner tree.

According to a second object of the present invention, there is provided a transmission system for data packets with a large number of switching nodes, each serving a large number of subscribers, characterized in that each node includes a copying device for duplicating data packets, intended for transmission to a large number of addresses. and a transmission device arranged to send copies of multi-addressed data packets to each addressed subscriber and to the next node to which addressed subscribers are connected.

Preferably, said transmission device is adapted to send one and only one copy of said data packet to each CLS node: - to which its CLS node is directly connected; and - to which addressed subscribers are connected.

Alternatively, said transmission device is adapted to send one and only one copy of said data packet to each CLS node: - to which its CLS node is directly connected; and to which either: - addressed subscribers; or - a CLS node connected to addressed subscribers; is connected.

Each multi-address data packet can include a group address.

Said data transmission system for packet transmission may include at least one ATM-based general data network.

Preferably, at least one CLS node, in said packet switching data transmission system, includes group addressing means which for each group address has a database of all individual addresses comprising the group address, said group addressing tool being adapted to direct a multiple addressing to a group address and to completely divide a group address.

Alternatively, one and only one CLS node in said data packet transmission system includes a group addressing tool which for each group address has a database of all individual addresses included in a group address, said group addressing tool being arranged to direct multiple addressing to a group address and capable of completely splitting a group address.

Alternatively, one and only one CLS node, in said data packet transmission system, includes a first group addressing aid, said first group addressing means being arranged to control a 5.15 054? multiple addressing to a group address, and partially dividing a group address, in that each of a plurality of CLS nodes has a second group addressing means arranged to complete division of a group address which has been partially divided by said first group addressing means, in that only one first group addressing aid is allowed per group address, and in that more than one second group addressing aid is allowed per group address.

Embodiments of the invention will now be described by way of example, with reference to the accompanying figures in which: Figure 1 illustrates the composition of an ATM address.

Figure 2 illustrates a centralized group address agent structure.

Figure 3 illustrates a road tree based on a route selection destination / destination.

Figure 4 illustrates the protocol architecture for a connectionless service utilizing CL servers.

Figure 5 illustrates cell data processing in a CL server.

A glossary of abbreviations used in this specification is shown below: AAL3 - ATM adaptive layer, type 3 AAL4 - ATM adaptive layer, type 4 AAL5 - ATM adaptive layer, type 5 AC - access code ATM - asynchronous transmission mode B-ISDN - broadband integrated services digital network 10 15 20 25 30 35 515 054 2 BDS - broadband data service BOM - start of message CBDS - connectionless broadband data service CC - country code CL - connectionless CLNAP - connectionless network access protocol CLNAP-PDU - more commonly a data unit in CLNAP protocol (group addressed data packet, more generally a CLNAP protocol data unit) CLNIP - connectionless network interface protocol CLSIP - connectionless server (connectionless server) CLSF - connectionless service function (connectionless) service function) cnf - extension for confirm. messages (extension for confirm messages) COM - continuation of message CPE - equipment at customer (customer premises equipment) DG - designated gateway (designated gateway) EOM - end of message FTP - filtering transfer protocol (file transfer protocol) GA - group address (GA) - group address agent (group address agent) GAP - group addressed data packet IP - internet protocol (internet protocol) LAN - local area network LEC - local exchange code ME - structure description unit (mapping entity) 10 15 20 25 30 35 s1ssøs4 q NDC - national destination code NGAA - nested group address agent NNI - network node interface OSPF - open shortest path first (open shortest path first) PDU - packet data unit PVC - permanent virtual circuit QoS - quality of service RD - path routing domain req - extension for request message SMS - switched multi-megabit data service SN - subscriber number SSM - single segment message SVC - virtual line for signaling virtual circuit UNI - user network interface VCI - virtual line identifier VP - virtual path (virtual path) VPI - virtual path identifier A multi-address information transmission enables a subscriber to send to a packet data system data packets which are transmitted by the system to several recipients. The present invention utilizes group addressing to achieve multiple addressing, and is described with respect to an ATM-based general data service. It will be apparent to those skilled in the art how to adapt 654m I / O to the present invention with other packet-switched data transmission systems.

The system is required to deliver one and only one copy of a group addressed data packet (GAP) over each of the connectionless access interfaces associated with the individual addressees represented by the group address. Each recipient of a GAP can use the destination group address, which is carried by that GAP, to multi-address the GAP addressees (except its own).

Non-members of a group identified by a group address (GA) can send GAPs to that group. The service provider is responsible for assigning group addresses and for ensuring that each GA uniquely identifies only one set of individual addressees. Within the network, the group-addressed data packets are structured in AAL5 feeds.

The address structure used in the BDS in the present embodiment of the invention has the form: The address type C or E is a hexadecimal number that identifies the address as an individual address, or a group address. For example, C 4687O75565H represents a BDS individual address, and E 4687075565H a BDS group address. The composition of ATM addresses is shown in Figure 1. The ATM address is first divided into address type and E.l64 number. The E.l64 number can then be divided into: - country code, CC, (1 to 3 digits); - national destination code, NDC; SN - routing domain, RD (1 to 2 digits); (3 to 4 digits); - subscriber number, (8 digits) - area 10 15 20 25 30 35 5 1. 5 * Û 5-4 Ü - local exchange code, LEC (3 digits); and - access code, AC (5 digits) as shown in Figure 1.

A Group Address Agent (GAA) acts as the centralized administrator of a group address. The GAA interacts with a subscriber to handle requests for the creation, modification or deletion of group addresses, and provides "membership" information in an address. Group addresses can be stored in the BDS in three ways: - centralized storage; - copied storage; and - encapsulated centralized storage.

In the centralized method of storing group addresses, one of the "connectionless" service nodes administers the assignment, removal and modification of group addresses, and the inclusion, addition and removal of individual addresses to the group, based on the user's instructions. From a numerical point of view, GAA assigns a group a globally unique group address that belongs to GAA's area. The GAA performs a complete address division function. This approach has the following advantages and disadvantages: The advantages of a centralized approach are: - it creates a clarity of an address group within a BDS system; - simpler administration and maintenance; - no need to introduce special measures to ensure consistency; and - it is easy to switch to a methodology with encapsulated group addressing. The disadvantages of a centralized approach are: - the delay time during transmission increases; - the load on an individual address agent increases; - the load on the network increases; and - lack of point insensitivity (which can be improved by redundant agent implementation).

In the copied, ie distributed, database method, the division of the group addresses requires that each network has its own database which must hold all the information regarding all the group addresses defined in all networks, regardless of their location. This method provides minimal delay in transmission because each copy is routed directly to its destination after division of the group address in the source network. It is insensitive because, if errors occur in the network, the remaining networks can split the group-addressed packets.

In addition, fewer packages are generated. On the other hand, this method increases the network load because the entire multiple addressing takes place in the source network. Maintaining consistency on "up to date" information is also difficult. For these reasons, this method does not form part of the current description.

Encapsulated group addressing is used in conjunction with a centralized database structure. A group address agent handles each individual group address, as previously described for the centralized method. Encapsulated group addressing can be used to avoid sending repetitive information to individual members of a group that is reached over the same network and uses an NGAA.

Since only one GAA is allowed per group address, an NGAA can be dedicated to serve each separate network that assembles BDS. It can be more than one NGAA per 10 15 20 25 30 35 5 15/3 group address. Any network that has one or more members in GA can have NGAA functionality. Thus, in the encapsulated group addressing method, GAA performs a partial address division function. Encapsulated group addressing is an efficient technology for transporting group-addressed data packets. This results in lower network load because only one copy of the data needs to be sent to each of the incoming networks.

However, it also causes increased transmission delay because the packets need to be routed to the central multi-address network. Another problem with this method is a lack of insensitivity; single point errors can make it impossible to transfer or manage group address packets.

The central database method is favored when the number of subscribers is rather small. However, as the number of subscribers increases, the centralized method is upgraded to an encapsulated group addressing system.

It is assumed that the ATM address in GAA is well known by all subscribers to BDS. A user can thus establish a control channel to the GAA to send a request for registration / deregistration of individual addresses and receive a response to the corresponding group addresses. The channel used to send multi-address packets (data channel) to the GAA may or may not be the same as the control channel. However, there may be some advantages to separating the control channel from the data channel, as QoS and bandwidth requirements may be different for the different channels. Preferably, the control channel can be released after a predetermined period of inactivity has ended.

The protocol for registering a group address takes place in the manner outlined below. 10 15 20 25 30 35 s1s 054 fff All individual addresses belonging to the same group are registered to a central GAA unit. A designated subscriber is an end user who is authorized to create a new group address. A designated subscriber is not authorized to create a new group address that excludes himself.

The following messages can be exchanged between a specified subscriber and the GAA device: Registersubs_reg (IndATMaddr1: IndATMaddr2: ..... IndATMaddr3, transaction_ID) Registersubs_pnf (GroupATMaddress, transaction_ID, failure / success).

Non-group members can send packages to a group.

Confirmation messages are only distributed to the designated subscriber. (Optionally, the confirmation message can be sent to all members of a group from a security point of view). Transaction_ID in the confirmation message should be the same as in the registration message. This ID is used for local purposes (eg the validity of the confirmations). A given group address can only have one GAA.

The designated subscriber may, through interaction with the GAA, remove or add a new group member to an existing group of which he is a member. The designated subscriber can also ask the GAA to split a group address. This feature can be used in a useful way to check the current status of membership.

Among other things, to prevent non-group members from becoming group members without notifying other 10 15 20 25 30 35 s1seos4 [Y group members, only a designated subscriber is allowed to initiate the following command operation: Deletesubs_req (GroupATMaddress, IndATMaddr1: IndATMaddr2: ...... ..IndATMaddr3, transaction_ID) Deletesubs_çnf (GroupATMaddress, transaction_ID, failure / success) Addsubs_req (Group Aïnaddress, IndATMaddrl; IndATMaddr2: ........ IndATMaddr3, transaction_ID) Addsubs_cnf (GroupATMaddoup_grance_dress_olveq_dqq, transaction_IDve , transaction_ID) Resolvegroup_onf (IndATMaddr1: IndATMaddr2: ...... IndATMaddr3; transaction_ID) A group address that has no members is automatically deleted by GAA.

Multi-address packets are sent out according to the following protocol: - source S sends a packet with destination address GA to the nearest connectionless node e.g. N; - N identifies GA as a group address and encapsulates the original package in a new cover with source address (S, GA); - N forwards the packet to the central GAA unit; 10 15 20 25 30 35 515 os4i / é - GAA receives the packet and divides the GA using the centrally managed address table; GAA sends out as many packets as are needed for transfer to team members within the group; and - to transmit the unicast packets, the GA unit calculates the shortest path to all members of the group.

It should be noted that encapsulation means that the user data unit, when addressed to a remote node, is encapsulated as the payload of a new data unit whose start packet contains the appropriate addressing information it needs to reach its destination. The overlay of all the shortest paths calculated by the GAA forms a multi-address tree.

The detailed functions of this protocol can be more easily understood if one considers an example illustrated in Figure 2. The DG identifies members designated 1 to 9 in Figure 2. cLsa contains GAA for GA.

The operation of the centralized system protocol is as follows: - user S, connected to CLSa, generates a cLNAP PDU with DA = GA (GA1>); - this PDU is controlled to CLSc which contains the GAA for GA; - CLSc divides GA into individual addresses for all members (ie 1 to 9): 10 15 20 25 30 35 515 054 f? - CLSc delivers the GAP directly to its own members (5,6,7) and sends to each of the external members a CLNIP PDU bearing the member's individual destination address; - no packet is sent back to the sender.

Multiple addressing, ie. group-addressed packets are transmitted encapsulated in the data field of a CLNAP PDU. The GAA can transmit the individual packets either through point-to-point connections, or point-to-point connections, where GAA is the root of the tree and individual members are the leaves of the tree.

The multi-address packets are copied from the GAA to all other receivers, including network nodes, ie ATM nodes as well as connectionless servers. The multi-address packets are transmitted via paths that form a tree structure. The tree has its root at the GAA and the branches terminate at subscribers who are members of the group. The packages are copied when, and only when, branches on the tree split in two. Postponing the copying of the packets in this way preserves bandwidth in the network. If a single link leads to a multiple group of members, only a single copy of the package passes the link; if required, it will be copied later.

Since the multi-address path is calculated as a tree at GAA, the path that a multi-address packet takes depends on both the location of the GAA in relation to the source and its multi-address destination. This function is called "source / destination routing" and should be set in contrast to OSPF (Open Shortest Path First) routing, in which the path is based solely on destination. In fact, the route taken between the packet source and each particular destination group member is the least expensive route available 10 15 20 25 30 35 515 054/8. ", in contrast to the OSPF, a road similar to a minimal" spanning tree "is calculated. This type of road is usually called a Steiner tree.

A typical path, corresponding to the centralized group address agent structure illustrated in Figure 2, is shown in Figure 3. The GAA, located in the CSLc, is the root of the propagation path. The branches terminate at group members 1 to 9. It should be noted that the packages are copied when, and only when, two branches of the road go in different directions.

This results in a significant reduction in copying, which means that there will be a significant reduction in data processing and bandwidth consumption.

Road calculations can be modified to take into account the QoS required by specific applications or team members, e.g. delay, throughput, reliability, cost, operator, etc.

The present invention has in fact been realized on a prototype BDS based on the direct "connectionless" broadband data service model (CBDS) of the ITU / ETSI (1364) standard. This prototype will now be briefly described as an aid to understanding how the present invention may be implemented. A connectionless service function (CLSF) is installed in B-ISDN. The CLSF terminates the CL protocols and directs the CL packets to its destinations, according to control information in CL PDUs. The ATM connections between the user and the CLSF, as well as the connection between the CLSFs, can be either PVC or SVC. The CL servers can be installed at various ATM switches, as well as at ATM cross-connect nodes.

The connectionless user sends data to a CL server whose address and identity it knows, e.g. the nearest, to which it either signals or has 10 l5 20 25 30 35 515 los4i f? a semi-permanent connection already established. The CL server then forwards the data to the target subscriber, possibly via a path that includes other CL servers. The CL servers can be connected via a virtual superimposed network consisting of several VPs with pre-allocated bandwidth resources. The choice of PVC or SVC depends on the characteristics of the user traffic and the QoS requirements.

The use of CL servers in the ATM network will lead to a reduction in the number of required VPs (compared to fully worm-shaped VP networks) and consequently to a concentration of connectionless traffic on fewer VPs. By statistical multiplexing of several sources on the same VP, burst transmission can be reduced, although the losses due to buffering spills can increase. In addition, the number of connections required by each endpoint, for connection, is reduced to only one.

Figure 4 illustrates the protocol architecture of the CL server at the user interface (UNI) as well as between the network nodes (NNI).

The CLSF terminates the B-ISDN CLNAP which includes functions for the structural description of connectionless protocols to the connection-oriented ATM service using AAL3 / 4 devices. The CLNAP includes functions such as routing, addressing, multi-address transmission, QoS selection, carrier selection, etc. The route selection is based on E.l64 address information contained in the CLNAP PDU start block.

CLNIP supports the CL service between CL servers within a network operator area as well as between operator areas CLNIP handles the transport of both encapsulated and non-encapsulated data devices. Mutual influence functions between CLNAP and CLNIP are provided by an ME in CL servers. The CLNAP layer includes, inter alia, functions for selecting and addressing variable length CBDS packets transmitted between a source and one or more targets, without the establishment of any ATM connection by the user. It also supports multi-protocol encapsulation and QoS parameters: transit delay, cost, and probability of remaining errors. To achieve higher traffic concentration at CLSs, VPs between CLs can be configured so that they do not have full connectivity for worm networks. Alternatively, the CL servers can be connected to each other arbitrarily, or by means of other topological systems such as hierarchical trees, buses or rings.

The service provided by BDS is quite similar to that of the IEEE MAC service: - BDS_UNIDATA.request (Source E.l64, Destination E.l64, User Data, QoS) - BDS_UNIDATA.indication (Source E.164, Destination E.164 , User Data, QOS) This service has been implemented on a prototype BDS system consisting of a Fore System's ATM switch and 4 Sun / SPARC workstations. Each workstation is equipped with a Fore System's ATM data interface and a fiber connection to the exchange. A workstation can be configured either as a terminal, or as a server. Implementation of BDS-related routines can be performed on Fore System's host interface version 2.1.1., In a way that maximizes the use of existing Fore System's code for segmentation, reassembly, data structures, etc.

The terminal code mainly consists of an output routine and an input routine that constructs and analyzes BDS 10 15 20 25 30 35 515 054 31 PDU start blocks, respectively. On the output side, the routine calls up Fore System's AAL5 protocol. Since this protocol requires a VPI / VCI pair to transmit to, a table lookup must be designed that provides such a pair corresponding to a given E.164 destination address. On the input side, the AAL5 unit delivers a buffer along with a BDS PDU start block that is analyzed by the input routine and then forwarded to a suitable higher level unit. Currently, two "upper layer" protocols have been taken into account: - IP for transparent use of current Internet applications such as FTP, virtual terminal (TELNET) etc; and - a "Raw socket" interface that gives end users direct access to the BDS service described above.

Because the server operates on a "per cell" basis, the server code must be placed at the lowest possible level above Fore System's data interface. Once a cell boot block has been retrieved from the ATM cell input FIFO queue, the server code checks if VPl is one specified as part of the BDS network (VPI = "CLS"), as shown in Figure 5. If so, perform a table search for To find the appropriate outgoing VPI / VCI pair, for efficiency reasons, the table mapping is maintained per session (using timeouts), rather than per packet, as it can be assumed that an application unit will generally generate more than one packet in its interaction with application units on other systems.If a cell is part of a COM, this entails entry in a table.

More complicated procedures are required if a cell is a BOM or EOM, see Figure 5.

Claims (22)

10 15 20 25 30 35 40 515 054 '21 i PATENTKRAV A method of multi-addressing in a packet-switched data transmission system, having a plurality of switching nodes, each serving a plurality of subscribers, characterized in that a data packet, intended for transmission to a plurality of addresses, is copied at each node to which one or more subscribers, to which said data packets are addressed, are connected, and that a copy of said data packets is sent to each addressed subscriber and to the next node to which addressed subscribers are connected, until all addressed subscribers have received a copy of said data packets, wherein said packet switching data transmission system includes at least one ATM-based public data network, and in that one and only one CLS node in said packet switching data transmission system includes group addressing device which for each group address has a database of all individual addresses covered by a group address, where said group addressing device is arranged to control a fle address to a group address and to be able to completely divide a group address. Method according to claim 1, characterized in that a CLS node sends one and only one copy of said data packets to each CLS node: - to which it is directly connected; and - to which addressed subscribers are connected. Method according to claim 1, characterized in that a CLS node sends one and only one copy of said data packets to each CLS node: - to which it is directly connected; and - to which either: - addressed subscribers; or - a CLS node connected to addressed subscribers 10 15 20 25 30 35 40 51.5 054 23 is connected. Method according to one of the preceding claims, characterized in that each multi-addressed data packet includes a group address. Method according to any one of the preceding claims, characterized in that at least one CLS node in said data transmission system for packet switching includes group addressing device which for each group address has a database with all individual addresses covered by a group address, and in that this said group addressing device is arranged to direct a multiple addressing to a group address and to completely divide a group address. Method according to claim 4, characterized in that one and only one CLS node in said data transmission system for packet transmission includes a first group addressing device, wherein said first group addressing device is arranged to direct a multiple addressing to a group address, and to partially divide a group address; in that each of a plurality of CLS nodes has a second group addressing device arranged to complete the division of a group address which is partially divided by said first group addressing device; that only a first group addressing device is allowed per group address, and that more than one second group addressing device is allowed per group address. Method according to any one of claims 5 or 6, characterized in that a multi-address data packet originating from a subscriber connected to a first CLS node is sent to said CLS node, in a data packet encapsulating said group address. Method according to any one of claims 5-7, characterized in that a multi-address data packet is sent from a first CLS node and destined to a plurality of subscribers is sent from said first CLS node in a data packet encapsulating the group address. Method according to any one of claims 6-8, characterized in that said group addressing device, said first group addressing device, and said second group addressing device are agents, and in that said group addressing device and said first group addressing device are arranged to interact with a subscriber to handle requests for creation, modification or deletion of group addresses. 10 15 20 25 30 35 40 51 5 025.4 211 Method according to any one of the preceding claims, characterized in that data packets are transmitted along trees in tree form where packets are only copied where the branches of the tree divide, and in that the structure of said tree is determined so as to minimize system utilization, taking into account the restriction that the transmission delay for each group address is kept within a predetermined limit. Method according to claim 10, characterized in that said path forms a Steiner tree. A plurality of switching nodes, each serving a multi-packet data transmission system having a number of subscribers, characterized in that each node includes a copying device for duplicating data packets, intended to be sent to a plurality of addresses, and a transmitting device arranged to send copies of multi-addressed data packets to each addressed subscriber and to the next node to which addressed subscribers are connected, including at least one ATM-based public data network, and in that one and only one CLS node in said packet switching data transmission system includes device for group addressing, which for each group address has a database with all individual addresses comprising a group address, and in that said group address device is arranged to direct a multi-address transmission to a group address and to completely divide a group address. Data transmission system for packet transmission according to claim 12, characterized in that said transmission device is arranged to send one and only one copy of said data packets to each CLS node: - to which its CLS node is directly connected; and - to which addressed subscribers are connected. Data transmission system for packet transmission according to claim 12, characterized in that said transmission device is arranged to send one and only one copy of said data packets to each CLS node: - to which its CLS node is directly connected; and 105 20 25 30 35 40 sm 054 íS '- to which either: - addressed subscribers; or - a CLS node connected to addressed subscribers; is connected. Any one of claims 12-14, characterized in that each multi-data transmission system for packet transmission according to address data packets includes a group address. Any of claims 12-15, characterized in that at least the data transmission system for packet transmission according to a CLS node, in said data transmission system for packet transmission, includes a group addressing device, which for each group address has a database with all individual addresses comprising a group address , and in that said group address device is arranged to direct a multi-address transmission to a group address and to completely divide a group address. Packet switching data transmission system according to claim 12, characterized in that one and only one CLS node in said packet switching data transmission system includes a first group addressing device, said first group addressing device being arranged to direct a multi-address breathing to a group address, and to partially divide a group address; in that each of a plurality of CLS nodes has a second group addressing device arranged to complete division of a group address which has been partially divided by said first group addressing device; that only one first group addressing device is allowed per group address, and that more than one second group addressing device is allowed per group address. Packet switching data transmission system according to any one of claims 16 or 17, characterized in that a multi-address data packet emanating from a subscriber connected to a first CLS node is sent to said CLS node in a data packet encapsulating said group address. Any of claims 16-18, A packet switching data transmission system according to the characterization of a multi-address data packet transmitted from a first CLS node and destined for 515 054m SLL; to a plurality of subscribers is sent from said first CLS node in a data packet which encapsulates the group address. Data transmission system for packet transmission according to any one of claims 16-19, characterized in that said group addressing device, said first group addressing device, and said second group addressing device are agents, and in that said group addressing device and said first group addressing device are arranged to interact with a subscriber to handle requests for creation, modification or deletion of group addresses. Data transmission system for packet transmission according to any one of claims 12-20, characterized in that the data packets are transmitted via paths in tree form, where packets are only copied where the branches of the tree divide, and in that the structure of said tree is so determined that system utilization is minimized. that the transmission delay to each group address is kept within a predetermined limit. Data transmission system for packet transmission according to claim 21, characterized in that said paths form a Steiner tree.