SE511957C2 - Broadcasting over ATM - Google Patents

Abstract

The present invention relates to a method and apparatus for the broadcasting/multicasting of ATM cells from an ATM node towards physical interfaces (PI 1-PI m), taking into account the priority class or traffic class to which the cell belongs by arranging a buffer (TCB 1-TCB n) for each priority class in each interface, and sorting the cells into said buffers. An address field is added to the cell having a bitmap (PI A) to define the physical interfaces to receive the cell. The address field is also arranged to comprise an indication (TCB A) of the priority class to which the cell belongs.

Description

1.5 20 25 30 511957 2 Thus the data in the cells is multiplexed over ATM connections with very high capacity up to switch matrices with switch elements which when activated are to direct the cells to the respective intended output channel and then on to the correct destination. A conventional switch therefore handles one-to-one communication by switching a cell from one input to only one output of a plurality of possible outputs. Therefore, it is a problem to provide multicasting / broadcasting because there is no possibility for one-to-several communication, ie from a sender node to a plurality of receiver nodes by transmitting the same cell from a certain input channel on the switch via a plurality of output channels. .

In order to still be able to achieve multicasting / broadcasting, the cells can be duplicated in as many copies as. corresponds to the number of physical interfaces to which they are to be transmitted. This information can be retrieved via the header information in a routing table.

By stopping the incoming stream of cells and duplicating them one at a time, they can be forwarded to the desired physical interface. The disadvantage is that this operation takes time as you have to store the cells to be copied in a buffer and send them out to the different interfaces, which introduces CDV (Cell Delay Variation) and CTD (Cell Transfer Delay). This is unsustainable in certain types of traffic that require a steady bit rate.

The UTOPIA specification (Universal Test and Operations PHY Interface for ATM) from ATM Forum shows a solution in this way where you also. must introduce additional address ~ signals and. thus extra address pins to handle multiple physical interfaces.

This solution can cause a blockage in the switch as the traffic in the ATM network is congested and at certain unfavorable times can cause filled buffers. In addition, UTOPIA means that you can address a maximum of 31 physical interfaces when using a 5-bit field for addressing.

EP 0 448 046 discloses a system for broadcasting over ATM where a label is added to the header of the ATM cell arriving at the switch, whereupon the cell is copied to the switch elements leading to the outputs of the switch to which the cell is destined, all following the information in the label. Switch elements then simultaneously transmit the cell on desired output channels and in this way realize a broadcasting. The length of the label is here in proportion to the number of switch elements connected to the respective input channel. The document shows nothing about how different types of traffic, such as CBR (Continuous Bit Rate), VBR (Variable Bit Rate), ABR (Available Bit Rate) or UBR (Unspecified Bit Rate) are handled.

DESCRIPTION OF THE INVENTION Broadcast / Multicast functionality is fairly easy to implement in most ATM switch architectures as all that is needed is to have an option to copy an incoming cell with a particular VPI / VCI to more than one outbound link a new VPI / VCI and most architectures use some form of internal bus or shared memory. However, problems can arise as a consequence of the implementation of so-called point-to-multipoint connections. When broadcasting to a large number of physical interfaces, each cell must be copied up to an equal number of copies. Each cell copy takes up one cell period.

The incoming cell current must therefore be stopped and stored in buffers, which can create problems with congestion as the traffic, for example, comes in extremely heavy traffic. The waiting time will then be long and in the case of CBR traffic needed when transmitting, for example, video data, this waiting time may become unsustainable. A priority function would also be desirable that can work in broadcasting in order to be able to differentiate the types of traffic and provide them with the necessary service.

The invention shows a device and a method for solving the problem of the time delay in broadcasting and for being able to. provide the service sonx needs different types of traffic, by identifying which type of traffic the cell belongs to and adding to it a prefix or a “label” that shows which physical interfaces should be addressed by the cell in question and also what priority the cell should have. These measures achieve the object of the invention, namely to arrange in a safe and fast manner the possibility for cells with different transfer requirements to be broadcast from an ATM layer to an arbitrary number of physical interfaces.

According to the invention, the addressing to the various physical interfaces takes place over the data pins defined by SINGLE-PHY-UTOPIA and no additional address pins are needed by adding a minimal prefix to the SINGLE-PHY-UTOPIA standardized cell format. The prefix should serve as an address and is hereinafter referred to as the "address field". The address field that is suitably added to the cell's header can address both several physical interfaces as well as different buffers within each physical interface where the buffers can be used to sort different types of traffic, e.g. high or low priority.The address field is added to the cell and used in the direction of the physical interfaces as indicating the destination of the cell sent from an ATM node j. the ATM layer.This direction is hereinafter referred to as the Egress direction.In the opposite direction ie from the physical interfaces to the ATM node, the address field is used as an identification of which physical interface sent the cell.

This direction is called the Ingress direction. An ATM node is usually equivalent to an ATM switch.

The address field is of such a nature that each physical interface corresponds to a specially reserved bit that tells whether the interface in question. should receive this cell, just so-called "bit mapping". thus the field identifies through a bit mapping pattern the physical interfaces to be addressed. A great advantage is then given that you can send the same cell to several physical interfaces during only one cell interval and then avoid the problem of need to stop the incoming cell current in the switch to copy the cells because all cells are sent to all physical interfaces and these receive or reject depending on the bitmap pattern.

The address field can also be considered to contain an identification of which traffic class, for example CBR, VBR, ABR or UBR to which the cell belongs and in each physical interface a buffer can therefore be implemented for each traffic class.

There are several benefits to the above idea. No additional pins are needed compared to "point-to-point" connections as well as no extra links are needed to handle different traffic classes. Furthermore, the invention means that it is possible to broadcast cells to an unlimited number of physical interfaces and the length of the address field is not dependent on the number of switch elements inside the switch. If the physical interfaces are provided with capacity for address recognition, less decoding logic is needed in them. DESCRIPTION OF THE DRAWINGS Embodiments of the invention will be described below in connection with the accompanying drawings, in which: Figure 1 shows a block diagram with an ATM node connected to a plurality of physical interfaces by means of a bus where each interface comprises a plurality of buffers, Figure 2 shows a schematic view of broadcasting over ATM and in particular the principal function of the bit mapping technique, Figure 3 shows an address field according to a preferred embodiment and in addition the same address field added to a standard ATM cell and Figure 4 shows another embodiment of the invention. illustrated by a block diagram with an ATM node connected to a plurality of physical interfaces by means of a bus where each interface comprises only one buffer.

PREFERRED EMBODIMENT Fig. 1 'shows' a. ATM switch connected to a plurality of physical interfaces FYG 1 - FYG m. When broadcasting, the incoming cell 1 to the switch must be transmitted from it further via a bus 5 to all the different physical interfaces FYG 1 - FYG m and during multicasting the cell is sent out to a number of selected interfaces in the so-called Egress direction. According to the invention, all cells are sent just as usual (without being copied) through the switch and then pass, according to the preferred embodiment, an identification module 2 which reads which cells are to be broadcast to which physical interfaces via information in each cell's header. The information is retrieved in routing tables by reading the header's VPI / VCI value and from which physical interface the cell originates.

It is also conceivable in another embodiment to let the cell pass the identification module before the switch. The identification module 2 then adds an address field to the cell header based on said information in the routing table. Fig. 3 shows an ATM cell with header and payload as usual. The extra address field can be seen as an extension of the cell header.

The address field is added to the header in the identification module 2 and is used to "bitmapping" the physical interfaces FYG 1 - FYG m that are to receive the cell in question. Therefore, only one bit per physical interface is needed to indicate whether this particular interface should receive the cell or not.

Figure 2 shows an example of this bit mapping where we have an ATM switch that will broadcast a cell 4 to two of four connected interfaces. The bit mapping pattern 3 'shows that the leftmost and rightmost interfaces should receive the cell 4.

The cell is thus sent to all interfaces, but those that have a zero in the bit mapping pattern (in this example) reject the cell.

Figure 1 also shows that each physical interface, according to the idea of the invention, can use different buffers TKB 1 - TKB n for each traffic class, so-called Traffic Class buffers (TKB). By having one buffer per traffic class, some cells can be prioritized over others. For example, CBR cells with high demands on passability and continuity can be offered the service they must have, while other types of more low-priority traffic, such as ABR or UBR, can expect a longer waiting time in their respective buffers. These buffers can also be implemented as only one large buffer per interface where each traffic class of cells is instead sorted into different address areas in the same buffer (TKB) which is illustrated in Figure 4 where each physical interface has only one buffer .

The different TKBs can be addressed using binary numbers. If there are n different traffic classes, it is sufficient to add logy bits in the address field to identify which TKB cell to load in because each cell can be assumed in the same buffer in all the physical interfaces it is destined for. For example, it does not appear that the same cell is placed in the "CBR buffer" in one interface and in the "ABR buffer" in another interface.

Just as with the identification of to which physical interfaces FYG 1 - FYG m the cell is destined, the identification of which traffic class the cell belongs to also takes place in the identification module 2.

The information about this is also retrieved via the cell's header to the routing tables.

The extra address field which to the identification module 2 thus contains both information about the added header in which physical interfaces are to receive the cell and also to which traffic class the cell belongs and thus which buffer in each interface is destined. In this embodiment, the different traffic classes and thus the different TKBs represent different traffic types (CBR, VBR ....). However, the invention should not be seen as a limitation to sorting the cells according to traffic classes, but can of course also be arranged to sort the cells according to other criteria and grounds. To get a more general term for "traffic classes", it is appropriate to use the word "priority classes".

Fig. 3 further shows what an address field according to a preferred embodiment of the invention can look like. The address field is divided into two parts here. One (FYG A) addresses the different physical interfaces (FYG 1 - FYG m) while the other (TKB A) addresses the different TKBs For the bit mapping of the (TKB 1 - TKB n). physical interfaces are thus needed m bits in the address field and to indicate to which TKB cell to go, as previously mentioned the log bits are needed. The address field, which is preferably added to the cell's header, thus only needs to consist of m + log bits.

In another embodiment, the address field may consist of only FYG A if only one traffic class exists and therefore only one buffer per physical interface is necessary. In yet another embodiment, the address field may consist of only TKB A if there are several traffic classes but only one interface. Then, however, it is no longer a question of broadcasting. The mutual placement of the two address field parts, FYG A and TKB A, has no significance for the functionality of the invention.

In the Ingress direction, i.e. from the physical interfaces to the ATM node, the address field part FYG A is used to identify from which physical interface FYG 1 - FYG m the cell originates.

In another embodiment, one would use the same idea without introducing extra bytes into the ATM cell by using that HEC field in, however, the address field would be 8 or 16 bits. already defined the header of the ATM cell as the address field. This entails a restriction of the HEC field can be used provided that it is regenerated in the physical interface after the cell is transmitted from the switch. It is often common that the interfaces that pack ATM cells in, for example, SDH frames often generate HEC, i.e. HEC which is used on the connection but not internally in the ATM switch. Instead, parity control is often used internally.

When sending a cell to a physical interface whose buffer / buffers are full, a type of backpressure mechanism is needed that sends back an indication that the same cell must be returned so that the buffer will hopefully not be full and then be able to receive the cell.

It then follows logically that the invention with addressing 'via a bit field added to the header according to the invention gains its greatest advantages when the buffers are so large that they never have to use their backpressure mechanism. Otherwise, a certain amount of time is needed by the person who earns it, as you do not have to copy cells in the switch to return cells.

In both Ingress and Egress directions, of course, a bus is needed between the interfaces and the switch. The invention does not require whether the arbitration is implemented with daisy-chaining, token rings or other protocols.

Claims (6)

”511 957 PATENT REQUIREMENTS Method for broadcasting / multicasting ATM cells (1) from an ATM node to a plurality of physical interfaces (FYG1 - FYGm), characterized in that the cells are bit mapped at the ATM node to the physical interfaces to which they are destination and that information (TKB A) is added to the cells about which priority class they belong to, by adding to the header in each ATM cell an address field containing the bitmap pattern (FYG A) and the priority class information (TKB A) and -that each cell is forwarded from The ATM node to buffers (TKB1 - TKBn) located in the physical interfaces and representing the priority class specified in the address field and -that each physical interface (FYG1 - FYGm) either receives or rejects the cell (1) depending on the information in the address field. Method for broadcasting / multicasting ATM cells (1) according to claim 1, characterized in that the division into priority classes is based on which traffic class (CBR, VBR, ABR or UBR) the cell belongs to and that each physical interface (FYG1 - FYGm) sorts the cells according to this criterion into dedicated traffic class buffers (TKB1 - TKBn). Device for broadcasting / multicasting ATM cells (1) comprising at least one ATM node connected to a plurality of physical interfaces (FYG1 - FYGm), characterized by 511 957. identification module (2) is arranged to i. Egress direction of the cell stream add an address field to the cell where the physical interfaces (FYG1 - FYGm) to which the cell is destined to be bit mapped, -that the physical interfaces (FYG1 - FYGm) are arranged to or reject the cells transmitted from the ATM node, -that the address field is also arranged to indicate which priority class the cell belongs to. Device for broadcasting / multicasting ATM cells (1) according to claim 3, characterized in that each physical interface (FYG1 - FYGm) comprises a buffer (TKBI - TKBn) for each conceivable priority class and where each interface is arranged to according to the information in the address bar, sort the cells in the dedicated buffer. Device for broadcasting / multiCasting of ATM cells (1) according to claim 3, characterized in that each physical interface (FYG1 - FYGm) comprises a buffer and that each buffer has an address area set aside for each conceivable priority class and where each interface is arranged to sort the cells in the intended address area according to the information in the address field. Device for broadcasting / multicasting ATM cells (1) comprising at least one ATM node connected to a plurality of physical interfaces (FYG1 - FYGm), characterized in that the physical interfaces are addressed by an address field added to the cell, where said address field consists of two parts, one of which (FYG A) for identifying in the Egress direction by bit mapping which physical interface the cell is destined for and in the Ingress direction defining from which physical interface the cell originates, and -the other (TKB A) to define in Egress' direction which priority class the cell belongs to.