WO2004006619A1

WO2004006619A1 - Early packet discard method for asynchronous transmission packets of fixed length

Info

Publication number: WO2004006619A1
Application number: PCT/EP2002/007302
Authority: WO
Inventors: Athanase Mariggis
Original assignee: Siemens Aktiengesellschaft
Priority date: 2002-07-02
Filing date: 2002-07-02
Publication date: 2004-01-15
Also published as: AU2002328834A1

Abstract

The invention relates to an efficient handling of a buffer overflow which is achieved by means of a method for the asynchronous transmission of data in cells (2 to 6) of packets (7) of the same packet length, by means of a connection (8,9,10), whereby each cell (6) of a packet (7), arriving in a buffer (14) along the connection (8,9,10), is monitored for whether a given buffer threshold for said buffer (14) is exceeded. In the case where the buffer threshold for the buffer (14) is not exceeded, the cell (6) is forwarded, whilst in the case where the buffer threshold of said buffer (14) is exceeded, the cell (6) is discarded without forwarding and a flag (EPD) is established. The flag (EPD) remains until the last cell (2) of said packet (7) has arrived in the buffer (14) and been discarded, whereby, so long as the flag (EPD) is active the arriving cells (6,5,4,3,2) of said connection are discarded.

Description

EARLY PACKET DISCARD PROCESS FOR ASYNCHRONOUS PACKAGES OF FIXED LONG

The invention relates to methods and devices for the asynchronous transmission of data in cells of packets of the same packet length, in particular of ATM packets of a VPI / VCI connection.

For example, WO 01/93598 A2 discloses a method for the asynchronous transmission of packets in cells (in particular ATM transmission). Such procedures require

Congestion in buffers (intended for processing the congestion)

Interfaces / Switches / forks. Despite being big

Buffer cell memory overflow of a buffer occur (FIFO overflow), which means that cells have to be thrown away.

The present method relates to the transmission of packet-switched data such as can be carried out, for example, with so-called ATM (Asynchronous Transfer Mode) methods. In the case of an ATM transmission in an ATM network, data to be transmitted are contained in a multiplicity of cells, each cell containing, for example, 53 consecutive bytes, of which 48 bytes contain useful information and 5 further bytes in the header of a cell contain routing information. Each cell contains an identification that specifies which specific virtual channel. (Virtual Channel = VC) it belongs to which VC is a virtual communication link between the source (sending the data) and a destination (to which the

Data should arrive). Each VC runs through a network from an origin node (Source Node = SN) through several intermediate nodes and these connecting connections to a destination node (Destination Node DN). Data on a variety of VCs is typically transmitted on each of these connections. All cells of a particular VC contain the VC in their headers representative VC indicator (VCI). Each header also contains a virtual path indicator (VPI), which can be identical for several VCs in individual cases, but each special combination of VPI and VCI only occurs once on each interface / board. All VCs that share a path between a particular node and another node contain an indication of the particular VP to which they belong and, as a rule, their headers contain the identical VPI. For each connection, cells of different VCs are in one

Transmit order which ensures that they remain in their original order, although they do not necessarily have to be transmitted consecutively. Data arriving at an exchange (switch etc.) is stored in a buffer in front of and / or behind the switch

(usually of the FIFO type) stored until they can be retransmitted. The maximum capacity (defined in a FIFO threshold for individual VPI / VCI connections or for the entire buffer) specifies how many cells can be buffered in the buffer for later retransmission without the buffer overflowing.

An earlier solution provides that ATM cells arriving in a buffer memory are monitored when the buffer is full. As a result, many packets consisting of several ATM cells (some of which have been discarded) are sometimes forwarded incorrectly ("corrupted") (for example to a SAR module which discards the entire ATM packet). As a result, not only are the interfaces to the SAR free of faulty packets, but also (OAM-F5) cells are thrown away, which transmit information for traffic control. As a result, the system becomes unstable and difficult to control.

Another solution known to the person skilled in the art was implemented by using ASICS. Here is per connection (in ATM, for example, per VPI / VCI connection) an extra queue is set up and checked separately. However, this requires complex logic and a large amount of memory, since several thousand connections can usually be set up at the same time, so this solution is expensive.

The object of the present invention is to enable the most efficient possible processing of an overflow of a buffer in an asynchronous packet transmission connection. The object is achieved in each case by the subject matter of the independent claims.

According to the invention, a marker (flag, here EOP flag = End Of Packet Flag = flag that indicates that the end of a packet has been reached) is activated (set high) for a specific connection (in ATM: VPI / VCI connection) , if the last cell of a packet of this connection is detected (buffer arrives etc.). The last cell is identified using a PTI byte in the ATM header. A control circuit according to the invention thus recognizes (for example in the ATM-FPDEA, a following new packet (or the first cell of a new packet) by previously reading this flag for this connection. If a new packet is detected in a connection (= if EOP is set when the marking is set) = 1 a new cell arrives, which must be the first cell of a new packet), the control circuit checks whether the corresponding buffer full threshold (FIFO threshold, for example EPD threshold) has been exceeded Packet (for reasons of rationalization) are discarded (i.e. deleted without further transmission via the connection in the direction of the destination), even if the threshold has been fallen below again. If a cell of a packet is discarded, a specific marking (flag = EPD flag) set (EPD is set to high) Marking is referred to in the following EPD flag = early packet discard flag (= early utilization of a packet flag). If this EPD flag is set to "high" (ie at least one cell of a packet had to be discarded), this flag (for the connection from which a packet was discarded) remains set to "high" until the last cell of the same packet the corresponding connection (in ATM VPI / VCI connection) has arrived and has been rejected. According to the invention, the use of the marker (EPD flag) means that all cells of a packet in a connection are discarded simply and efficiently whenever a cell in this packet had to be discarded.

Further features and advantages of the invention result from the following description of an exemplary embodiment with reference to the drawing. It shows:

Figure 1 shows schematically an inventive treatment of a full buffer by discarding cells from packets.

FIG. 1 shows a source (source) 1, from which data in packets 7 containing a plurality of cells 2-6 (in ATM usually 48 useful cells) via a plurality of sections 8, 9, 10 of a connection and switching devices connecting these sections (for example ATM switch 11 , 12) are transmitted to a target (Target 13). It can be in front of and / or behind a

Switching device one or more buffers 14 (each a buffer for one connection or a buffer for several connections). Between two

Switching devices 11, 12 may run a large number of connection sections of connections (that is to say here, in addition to the connection section 9 of the connection in question, a connection section 15 and a connection section 16 each of a connection independent of this). When the last cell (cell 2 of the packet 7) arrives in a switching device 11 (or in a buffer 14 in a switching device 11) (which is identified on the basis of a PTI byte in the header), a control device 15 of the switching device or the Buffers that the last package has arrived and now a new package is coming. When a new packet arrives (i.e. a cell of another packet arrives), a flag is set (EOP flag = End of Packet Flag = end of the packet flag) (EOP is set to high or 1, for example), and it is checked whether the buffer 14 is full, that is to say whether a buffer fill threshold (FIFO threshold / EDP threshold etc.) has been exceeded. If the buffer full threshold is exceeded (i.e. the buffer is full), this buffer overflow (of the buffer or part of the buffer for this VPI-VCI-

Connection) -conditional cell and, in addition, all cells of the packet should be discarded, to which packet this discarded cell belongs (if the buffer full threshold has now been undershot (i.e. the buffer would have space for a short time) has been discarded that connection-specific (in ATM: the VPl / VCI-specific) flag (= EPD = Early Packet Discard = early discarding of packets) has been set, as long as this flag is set to high, from one

Control device 15 of the switching device or the buffer all cells of the same packet deleted this VPI / VCI connection. It is determined that the last cell of the same packet has been deleted by checking before the deletion of a cell whether the EOP flag (which indicates that the last cell of a packet has arrived and a cell of a new packet has arrived is set to high, i.e. a new packet has arrived, the cells of which are no longer to be thrown away. The method is suitable for ATM transmissions with or without an IP protocol or for other asynchronous packet cell transmissions.

Claims

claims

1. Method for the asynchronous transfer of data in cells

(2 to 6) of packets (7) of the same packet length via a connection (8,9,10), whereby in the case of a cell (6) of a packet arriving in a buffer (14) along the connection (8,9,10) (7) is checked in each case whether a predetermined buffer full threshold of the 'buffer (14) has been exceeded, whereby in the event of a drop below the

Buffer full threshold of the buffer (14) is forwarded to the cell (6), while if the buffer full threshold of the buffer (14) is exceeded, the cell (6) is discarded without forwarding and a marker (EPD) is set, the marker (EPD ) remains set until the last cell (2) of this packet (7) has arrived in the buffer (14) and has been discarded, the incoming cells (6,5,4,3, 2) this connection can be discarded.

2. The method according to claim 1, characterized in that after receipt of the last cell (2) of the packet (7) whose cells (2 to 6) are all to be discarded because one cell of the packet has a buffer overflow of the buffer (14) above the buffer full threshold has been rejected, the marking is deleted again.

3. The method of one of the preceding claims, characterized in that a marker is only set for a connection for which a cell (6) should be transmitted, which has triggered a buffer overflow above the buffer full threshold and that only lines of this connection thereupon checked whether they represent the last cell of the packet from which a cell (6) was thrown away.

4. The method according to the following claims that the packets are ATM packets and that the connection is a VPI / VCI connection.

5. The method according to one of the following claims that a forwarding is a forwarding along the connection, in particular the VPI / VCI connection.

6. The method as claimed in one of the following claims, that it is determined that the last cell is a

Packet was discarded, from which packet a cell (6) had to be discarded by checking for this connection (8) incoming cells (2 to 6) whether a cell (2) contains a marker (EOP) indicating that it is the last cell of the packet, after which cell the marker (EPD) which triggers the deletion of cells of this connection is deleted again (EPD = low).

7. The device (15) for performing the method according to one of the preceding claims.