KR19990087607A - Method of transmitting ATM cell over ATM network - Google Patents

Abstract

The present invention relates to a method of transmitting an ATM cell over an ATM network between an asynchronous transfer mode (ATM) input interface and an ATM output interface, wherein the ATM network comprises a series of interconnected switches 110-118 and a gateway 131. 133, and may provide a conventional connection-oriented service or a connectionless service, and when a connectionless service is requested, at the input interface, a source and a destination address are inserted into the header, and the fields of the header are connected to the connectionless service. Set to a value indicating whether additional processing is requested, and at each node between the input interface and the output interface, when a connectionless service is requested, each ATM cell is assigned a source address and a destination address and / or a path. Route assignment according to a route assignment table set by an assignment protocol or network management. All.

Description

Transmission method of ATM cells via ATM network

The present invention relates to a method of transmitting an ATM cell over an ATM network between an asynchronous transfer mode (ATM) input interface and an ATM output interface.

In a conventional ATM network, when a cell arrives at an ATM input interface, an initial value is inserted into the virtual path identifier (VPI) and virtual channel identifier (VCI) fields of the header. The VPI field provides rough path allocation for ATM cells, and the VCI field provides fine path allocation. At each switching node between the ATM input interface and the ATM output interface, the VPI and / or VCI fields are read and the output port is selected based on the value of one or both of these fields using the route assignment table included with that node. do. The values of one or both of these fields are updated before sending the cell to the selected output port.

At each switching node, the update values of the route assignment table and the VPI and / or VCI fields are set in part by network management and signaling while the call is being set up. As a result, conventional ATM networks provide connection-oriented services. In connection-oriented services, the call is established by signaling when initiating the call and cleared at the end of the call. Alternatively, the route assignment table and update values may be set to provide a permanent connection.

If it is desirable to transfer data over a switched ATM network, for example from a computer with an ATM card, it is necessary to establish a call before the data can be transferred. If the data is transmitted somewhat continuously during the call period, the connection oriented service provided by the conventional ATM network is sufficient. However, it is sometimes desirable to transmit data intermittently, i.e., transmitting one cell burst at a time, and stopping for a long time before transmitting the next cell burst. However, in this case, there is a cost loss due to setting and clearing each call burst. Thus, conventional switched ATM networks are not suitable for intermittent data transmission.

It has been proposed to add a server to provide connectionless services as an overlay to an ATM network to provide connectionless services over an ATM network. However, this approach is disadvantageous in that there is a call establishment step between the input interface and the server.

According to one aspect of the invention, at a source node, each having a network address, over an ATM network comprising a network consisting of interconnected nodes, at least some of which are in a disconnected manner between the ATM input interface and the ATM output interface. A method for transmitting an ATM cell including a header and a user part to a destination node, the method comprising:

In an ATM input interface, setting one field of a header of an ATM cell to a value indicating connectionless transmission, inserting a source address, which is a network address of a source node, and a destination address, which is a network address of a destination node, into the header;

At each switching node between the ATM input interface and the ATM output interface, the fields of the header are read, the destination address of the header is read, the output port is selected at least according to the destination address, and the cell is sent to the selected output port. A method is provided, comprising setting up a cell to be transmitted in an access manner.

The present invention provides the advantage that the routing table does not need to be set up by signaling for the transfer of ATM cells between a particular access node and a particular destination node. As a result, there is no cost for setting up a call for each call burst when the cell is sent in burst form.

According to another aspect of the present invention, a source node and a destination node each having a network address through an ATM network including a network consisting of interconnected nodes, at least some of which are switching nodes, either in a connectionless or connection-oriented manner. A method of operating an ATM network to transmit a cell comprising a header and a user portion,

When transmitting ATM cells over a network in a connectionless manner between an ATM input interface and an ATM output interface,

In an ATM input interface, setting one field of a header of an ATM cell to a value indicating connectionless transmission, inserting a source address, which is a network address of a source node, and a destination address, which is a network address of a destination node, into the header;

At each switching node between the ATM input interface and the ATM output interface, the fields of the header are read, the destination address of the header is read, the output port is selected at least according to the destination address, and the cell is sent to the selected output port. Setting the cell to be transmitted in a connected manner;

In the case of transmitting ATM cells over a network in a connection-oriented manner between an ATM input interface and an ATM output interface,

Setting the virtual path identifier (VPI) and virtual channel identifier (VCI) fields in the header at the ATM input interface; and

At each switching node between the ATM input interface and the ATM output interface, read the VPI and / or VCI fields in the header, select the output port according to the VPI and / or VCI values, update the VPI and / or VCI fields, and And transmitting the cell to the selected output port.

According to another aspect of the present invention, there is provided a multicast service over an ATM network comprising a network consisting of interconnected nodes, at least some of which are switching nodes, between an ATM input interface and an ATM output interface in a disconnected manner. A method of transmitting an ATM cell from one source node to at least one destination node,

In the ATM input interface, setting one field of the header to a value indicating connectionless transmission, inserting a field into the header, a source address which is a network address of a small node and a destination address which is a network address of a destination node, and

At each switching node between the ATM input interface and the ATM output interface, read the fields of the header, read the destination address of the header, select at least one output port according to at least the destination address, and at least one selected output port. And transmitting the cell to the cell and setting the cell to be transmitted in a disconnected manner.

The present invention will now be described in more detail with reference to the accompanying drawings.

1 is a block diagram of a conventional asynchronous transmission mode (ATM) network,

2 is a diagram showing the structure of a basic ATM cell;

3 shows header fields used in a basic ATM cell during transmission between a user and an ATM network interface;

4 shows the fields used in the header of a basic ATM cell during transmission between nodes in an ATM network;

5 is a block diagram of an ATM network implementing the present invention;

6 is a flow chart of the operations performed on an ATM cell at the input interface to the network of FIG. 5;

7 is a flow chart showing operations performed on an ATM cell at the switching node of the network of FIG. 5;

8 is a flow chart of a series of operations used to form an ATM cell at an Internet Protocol (IP) gateway for the network of FIG.

FIG. 9 is a diagram illustrating a header field used for an ATM cell of the network of FIG. 5 when providing a connectionless service.

Referring now to FIG. 1, a block diagram of a conventional ATM network is shown. The ATM network includes a network consisting of switching nodes partially interconnected in the form of ATM switches 10-18. In the network of FIG. 1, the switches 10, 11, 12, 13, 15, 16, 17 and 18 also function as access switches. Each access switch is connected to a series of access lines that directly connect the switch to other networks or customer equipment. 1 shows a switch 17 connected to a computer 22 by one access line and to a multiplexer 24 by another access line. The computer 22 has an ATM card that allows data to be sent and received in the form of an ATM cell. The multiplexer 24 can receive video, data and audio signals and convert them into ATM cells in a multiplexed manner. Similarly, ATM cells can be received from the switch 17 and converted into video, data and audio signals. Typically, multiplexer 24 is located on the user equipment side of an ATM network.

As is well known in the art, when transferring an ATM cell between an ATM input interface and an ATM output interface, an initial value is inserted into the virtual path identifier (VPI) and virtual channel identifier (VCI) fields of the header. The ATM input or output interface may be located outside of the access node or ATM network, such as computer 22 or multiplexer 24. Next, at each switching node, the values of the VPI and / or VCI fields are read and one or both of these values are used with the routing table to select the output port. Before the ATM cell leaves the switch, the values of one or both of the VPI and VCI fields are updated according to the data contained in the route assignment table. The VPI field provides rough path assignment, while the VCI field provides fine path assignment. While not all of the calls are established, mainly the virtual path routing table is set up by network management and the virtual channel routing table is set up by signaling.

Now describe the structure of the basic ATM cell and header fields.

Referring to FIG. 2, the basic ATM cell includes a 5-octet header 40 and a 48-octet user payload unit 42. The cell header 40 is used to route cells between switches in the network, and the user payload 42 contains the user's data, which is transmitted transparently through the network and transmitted unchanged until the end. .

3 and 4, the fields of the header of a basic conventional ATM cell are shown. FIG. 3 shows the fields used to transmit ATM cells over a user-network interface, and FIG. 4 shows the fields used to transmit cells over a network node interface within an ATM network. In both cases these fields are identical except for one case described below. The keys of these fields are listed in Table 1 below.

GFC Generic flow control VPI Virtual path identifier VCI Virtual channel identifier PT Payload form CLP Cell loss priority HEC Head error correction

The generic flow control (GFC) field is present only at the user network interface. This field is for mediating use among a plurality of terminals sharing the same access switch.

The Virtual Path Identifier (VPI) field provides an approximate path assignment for an ATM cell. The VPI value changes each time the cell is switched in a switch that provides virtual path switching. In the user network interface, the VPI field is only 8 bits. This is increased to 12 bits between network nodes when no generic flow control bits are needed when the cell is transmitted over the network.

The Virtual Channel Identifier (VCI) field provides fine path allocation for ATM cells. The VCI value in the header changes each time the cell is switched by a switch that provides virtual channel routing. The VCI field is 16 bits long.

The Payload Type (PT) field is used to indicate the general type of cell data. Typically using this field is to identify the last cell of the operation, management and maintenance cell, excess state and resource management or multi-cell message. This field is 3 bits long.

In ATM networks, there is always the risk of cell loss. The Cell Loss Priority (CLP) field is 1 bit long. When this bit is set, it is to inform the network that this cell is not very important and should be discarded for another cell when a loss occurs.

The Head Error Check (HEC) field provides a sum check on the cell header. This can be used to detect bit errors in cell headers and sometimes correct these errors. This field is 8 bits long.

Conventional switched ATM networks, such as the network shown in FIG. 1, are not suitable for transmitting data transmitted intermittently or in burst form. If a conventional switched ATM network is used to transfer this type of data, the route assignment table is established while the call is established before the transfer of data is requested, and the connection is maintained as long as the transfer of data is requested. This is wasteful because of the inconvenience of maintaining a connection during a pause during data transfer. The form of service provided by conventional ATM networks is generally unsuitable for transmitting data in burst form. Burst-type data transfers are generally better suited to what are known as connectionless services. In a connectionless service, no call setup procedure is required, and the route assignment table is set by the route assignment protocol or network management process, and not while the call is set up.

In some protocols that provide connectionless services, such as, for example, Internet Protocol (IP), the header includes a field indicating the type of service requested. It is contemplated that each of the possible service types may have a value corresponding to this field. Examples of service types include low latency, requests for switches to reserve buffer space for return calls, and multicasting in which one call is routed to one or more destinations. There is no corresponding field in the header of an ATM cell. The type of service is established while the call is being established or by network management. As a result, when an ATM network receives data from another network through which a data is transmitted according to a connectionless service through an appropriate gateway, it is impossible to provide a requested form of service in another network based on one per cell.

5, an ATM network is shown that implements the present invention. As will be apparent from the following description, an ATM network may transmit ATM cells in a connection-oriented or connectionless manner. It may also provide various types of services and additional processing, such as the services described above.

The general arrangement of the network shown in FIG. 5 is similar to that shown in FIG. 1. Thus, the network shown in FIG. 5 includes a network composed of switching nodes partially interconnected in the form of ATM switches 110-118. The switches 110, 111, 113, 115, 117 and 118 are access switches capable of receiving data directly from other networks or from user equipment on input / output line 120. In the figure, the switch 117 is generally shown as connected to a computer 122 similar to the computer 22 of FIG. 1 and generally to a multiplexer 124 similar to the multiplexer 24 of FIG. 1.

The switch 116 is connected to the IP gateway 131 by an input / output line, and the switch 112 is connected to the IP gateway 133 by a line 132. The IP gateways 131 and 133 respectively receive data from the IP network of the input / output line 134 and transmit this network data.

In operation, when one of the IP gateways 131 or 133 functions as an input access node for data received from the IP network, it splits the IP packet into ATM cells. When one of these gateways functions as an output access node, it reconfigures the ATM cell into IP packets.

When the network shown in FIG. 5 is used to transfer ATM cells in a connection-oriented manner between an ATM input interface and an ATM output interface, the ATM cells are transmitted over the network in the conventional manner described with reference to FIG. The fields are as shown in FIG. However, additional processing is provided over conventional ATM networks to establish whether the transmission is done in a connection-oriented manner or not. When the network shown in Fig. 5 is used to transfer ATM cells between an ATM input interface and an ATM output interface, the fields of the transmission mode and header are different from those of the transmission mode and header fields used in conventional ATM networks. This difference is then described.

Referring to FIG. 9, a header used for an ATM cell of the network of FIG. 5 providing a connectionless service is shown. The keys of these fields are listed in Table 2 below.

SA Source address OF Option field DA Destination address PT Payload form CLP Cell loss priority HEC Head error checking

The source address (SA) field indicates the network address of the source node. The source node will be located at the input interface to the ATM network shown in FIG. For example, the source node may be a switch 113, a computer 122, a multiplexer 124, or an IP gateway 131.

The option field OF may be set to a value indicating that a specific service is requested or additional processing is requested. Examples of services that can be supported include requests for switches, low latency, or multicasting to free up buffer space for return calls. In addition, a unique value may be assigned to an option field as a condition for executing additional processing. Examples of additional processing include intelligent network operations, network management operations or path assignment operations.

When a cell that requires additional processing is received at the switch, the cell is sent to the upper layer of the switch and the payload section is checked to determine what additional processing is required. For example, when intelligent network operation is requested, the switch can access a remote database to determine a new destination address from the cell's destination address. Next, the destination address is appropriately changed.

As another example, several bits of the payload portion of the cell may indicate that a network management operation is requested. When this cell is sent to the upper layer of the switch, the switch performs the requested operation.

The destination address (DA) field is used to indicate the network address of the destination node. The destination address can normally be located at the output interface. When providing a multicast service, the destination address is a network address for the multicasting service.

The source address, destination address, and option field alignment and structure are network domain properties, where the domain is a collection of nodes that share the same format for these fields.

The present invention is not limited to ATM networks using the conventional cell header and payload structure and size shown in FIGS. 3 and 4. As in the current example, 28 bits are allocated to the SA, DA, and OF fields when both of these conventional cell header and payload structures are used. The reason is that this is the number of bits used by the conventional GFC, VPI and VCI fields. The bits assigned to the SA, DA, and OF fields can then be arbitrarily selected, but must be unique within a particular domain.

In this example, the SA and DA fields are each 12 bits long, and the OF field is 4 bits long. As a result, the network domain shown in FIG. 5 can support 4096 source addresses, 4096 destination addresses, and 16 options.

Source and destination addresses outside the network may additionally be specified in the payload portion of the first cell of each transmission.

The Payload Type (PT) field is the same as the field used in the header of a conventional ATM cell except that a designated value, " 111 " is used in this example to indicate that the service is disconnected.

The CLP and HEC fields are the same as the fields of the header of the conventional ATM cell.

When a user of the network shown in Fig. 5 wants to transmit an ATM cell over a network using a connectionless service, one of the access switches for which the connectionless service is requested, for example, a switch 117, is displayed and a destination address. To provide. If a specific service or additional processing is requested, this is also indicated. The access switch then performs the operation shown in FIG. 6 for each ATM cell it receives from the user. Hereinafter, these operations will be described. Alternatively, if the input interface is at a node outside the network, the operations are performed at that node.

In step 200, the PT field is set to the value "111" to indicate a disconnected service. Next, in step 201, the destination address is inserted, and in step 202, the source address is inserted. Finally, in step 203, if a particular type of service or additional processing is requested, the PT field is set to an appropriate value.

7 shows the operations performed at each switch between an input interface and an output interface for each ATM cell. This operation will be described later.

In step 220, the cell enters the switch. Next, in step 221, the switch reads the PT field to determine if a disconnected service is requested. If a connectionless service is not requested, it executes the operations performed by the conventional ATM switch. Thus, in step 222, the VPI and / or VCI fields are read. Some ATM switches are just virtual path switches, some are just virtual channel switches, and some are virtual path and virtual channel switches. Thus, the fields read and used will depend on the switch type. Next, in step 223, a route assignment table is used with the values of the VPI and / or VCI fields to select the output port. Next, in step 224, the VPI and / or VCI fields are updated according to the data in the route assignment table. Finally, at step 225, the cell leaves the switch to the selected output port.

If it is found in step 221 that a connectionless service is requested, the following operations are executed.

In step 230, the source and destination addresses (SA and DA fields) of the header are read. In step 231, the OF field is read to determine the type of service. In step 232, actions that may be specified in the option field, such as, for example, freeing buffer space or executing additional processing, are performed.

Next, in step 233, the output port is selected using the destination address value or the source and destination address values and the path assignment table. Thus, the path that a non-connected ATM cell follows when transmitted over the network may depend on the destination address as well as the source address.

Finally, at step 225 the cell leaves the switch.

Referring to FIG. 8, a series of operations performed on IP packets received at one of the IP gateways 131, 133 to form an ATM cell is shown.

First, in step 250, an ATM cell is formed by separating the IP packets. As a result of separating the IP packet, the source and destination address, the type of service requested and the request for additional processing are read.

Thus, at step 251, the PT field is set to indicate that a connectionless service is requested. Next, in steps 252 and 253, the destination address and the source address are inserted into the header. Finally, at step 254, if appropriate, an option field is set to indicate that the requested service type or additional processing is requested.

The network shown in FIG. 5 may be a public wide area network (WAN) or a dedicated network, for example a local area network (LAN).

The network addresses of the source and destination nodes are set by network management. These addresses are permanent in that they are set for an indefinite period of time. The path assignment table used at the switching node for cells transmitted according to the connectionless service is set by network management and not by signaling. As a result, even in the first case where a source node transmits an ATM cell over a network to a particular destination node, the cell is transmitted without performing a signaling operation.

Claims (7)

Including a header and a user portion from a source node having a network address to a destination node, respectively, over an ATM network comprising a network consisting of interconnected nodes, at least some of which are switching nodes between the ATM input interface and the ATM output interface in a disconnected manner. In a method of transmitting an ATM cell, In an ATM input interface, setting one field of a header of an ATM cell to a value indicating connectionless transmission, inserting a source address, which is a network address of a source node, and a destination address, which is a network address of a destination node, into the header; At each switching node between the ATM input interface and the ATM output interface, the fields of the header are read, the destination address of the header is read, the output port is selected at least according to the destination address, and the cell is sent to the selected output port. Setting the cell to be transmitted in an access manner. The method of claim 1, Reading a source address at each switching node between an ATM input input interface and an ATM output interface, At each switching node between the ATM input interface and the ATM output interface, in the step of selecting an output port, selecting an output port according to a destination address and a source address; At each switching node between the ATM input interface and the ATM output interface, in the step of transmitting a cell to a selected output port, further comprising transmitting a cell. The method according to claim 1 or 2, At the ATM input interface, inserting an indication into the header requesting a particular type of service; At each switching node between the ATM input interface and the ATM output interface, adding a step of inspecting the header for an indication that a particular type of service is requested and executing at least one operation to provide the requested type of service as appropriate. It characterized in that it comprises an enemy. The method according to any one of claims 1 to 3, At the ATM input interface, inserting into the header an indication that additional processing is requested at at least one node between the ATM input interface and the ATM output interface, At each switching node between the ATM input interface and the ATM output interface, examining the header for an indication that additional processing is requested; And if appropriate, executing the requested additional processing at at least one node between the ATM input interface and the ATM output interface. The method according to any one of claims 1 to 4, If a data cell or packet is received at an ATM input interface according to a protocol other than ATM, At the ATM input interface, separating the received data cells or packets into ATM cells, and And at the ATM output interface, reconfiguring the ATM cell into data cells or packets according to the protocol in which the data cells or packets are received at the access node. A cell including a header and a user portion between a source node and a destination node having a network address, respectively, through an ATM network including a network composed of interconnected nodes, at least some of which are switching nodes, either in a connectionless or connection-oriented manner. In a method of operating an ATM network to transmit, When transmitting ATM cells over a network in a connectionless manner between an ATM input interface and an ATM output interface, In an ATM input interface, setting one field of a header of an ATM cell to a value indicating connectionless transmission, inserting a source address, which is a network address of a source node, and a destination address, which is a network address of a destination node, into the header; At each switching node between the ATM input interface and the ATM output interface, the fields of the header are read, the destination address of the header is read, the output port is selected at least according to the destination address, and the cell is sent to the selected output port. Setting the cell to be transmitted in a connected manner; When transmitting ATM cells over a network in a connection-oriented manner between an ATM input interface and an ATM output interface, Setting the virtual path identifier (VPI) and virtual channel identifier (VCI) fields in the header at the ATM input interface; and At each switching node between the ATM input interface and the ATM output interface, read the VPI and / or VCI fields in the header, select the output port according to the VPI and / or VCI values, update the VPI and / or VCI fields, and And transmitting the cell to the selected output port. At least one destination node at one source node to provide multicast service over an ATM network comprising a network consisting of interconnected nodes, at least some of which are switching nodes between the ATM input interface and the ATM output interface in a disconnected manner. In a method for transmitting an ATM cell by In the ATM input interface, setting one field of the header to a value indicating connectionless transmission, inserting a field into the header, a source address which is a network address of a small node and a destination address which is a network address of a destination node, and At each switching node between the ATM input interface and the ATM output interface, read the fields of the header, read the destination address of the header, select at least one output port according to at least the destination address, and at least one selected output port. Transmitting the cell to the cell and setting the cell to be transmitted in a disconnected manner.