WO2001024461A1

WO2001024461A1 - Bundle shaping or policing

Info

Publication number: WO2001024461A1
Application number: PCT/US1999/022643
Authority: WO
Inventors: Trevor Jones
Original assignee: Ahead Communications Systems, Inc
Priority date: 1998-05-11
Filing date: 1999-09-29
Publication date: 2001-04-05

Abstract

In an ATM-type switch, cells are processed independently on the basis of VCI values, in a conventional manner. In addition, a bundle of cells having a common VPI value is processed together to adjust aggregate cell rate for multiple VCI values simultaneously. The processing includes shaping and/or policing.

Description

BUNDLE SHAPING OR POLICING

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to telecommunications . More particularly, the present invention relates to traffic shaping or policing in a data network, particularly an ATM (or similar) network in which virtual path and virtual channel identifiers are employed to control routing of cells .

2. State of the Art

In an ATM network, an ATM cell is routed on the basis of VPI and VCI values contained in the cell. On a particular virtual path (VP) , defined by the VPI value of cells on a particular physical link, there may be a number of virtual connections (VCs) , each identified by a particular VCI value. As is well known, the VPI and VCI values are neither globally unique nor fixed; the values may change from node to node across a network (and it may even be possible for independent connections on different ports of a single switch to share VCIs and VPIs, although this may cause some implementation difficulties) .

In an ATM switch, traffic on each virtual connection is monitored individually, and cell counts and routing performed individually for each VC (different VCs on a common VP may, for example be routed within the switch to separate output ports) . Incoming traffic is normally "policed" to ensure that the incoming data rate does not exceed the maximum rate allowed for that connection, and the outgoing cells may be "shaped" to attempt to ensure that the outgoing cells are more evenly spread (for example to alleviate any bunching that may have occurred in the switch) , to reduce the risk of cells being discarded by a subsequent policing mechanism.

In certain network configurations, an ATM switch may receive cells on multiple VCs all having a common VPI and received from a single user. Conversely, multiple VCs may be destined for transmission along a single VP over a common physical link. As mentioned above, each VC would conventionally be treated independently; this is required as cell counts and routing must be handled independently for each VC.

SUMMARY OF THE INVENTION

According to the invention, enhanced functionality is obtained in an ATM switch by performing functions such as policing or shaping on an aggregate basis for a particular VC. For example, such an arrangement may allow a subscriber and telecommunications supplier to negotiate an aggregate bandwidth for a particular VP, the subscriber being free to distribute the agreed bandwidth at will among individual VCs on the VP. While policing and shaping are conducted on an aggregate basis, other functions continue to be performed independently for each VC,

Thus, according to a first aspect of the invention, a method of processing cells in an ATM-type switch is provided. The method generally comprises receiving a plurality of cells, at least two cells having different VCI values and a common VPI value from an input port of the switch, processing cells on the basis of the VCI value of each cell whereby at least one function (preferably including cell counting or routing) can be performed independently for each VC, and policing the cells on the basis of the VPI value whereby control of the aggregate cell rate can be effected.

In a corresponding manner, in the case of outgoing VCs on a common output port having a common VP, these may be processed subsequently on the basis of the VPs alone (in a so-called "cross-connect" or VP switch) , and according to the invention, traffic is shaped for such processing, whilst each VC is handled individually. This arrangement enables subsequent nodes in the network to be provided with a more uniform supply of cells on a particular VP. Thus, according to a complementary second aspect of the invention, a method of processing cells is provided in an ATM- type switch, each cell containing a VCI value and a VPI value. The method generally comprises processing the cells on the basis of the VCI value of each cell whereby at least one function (preferably including cell counting or routing) can be performed independently for each VC, outputting processed cells from an output port of the switch, wherein cells for output from the output port include at least two cells having mutually different VCI values and a common VPI value, and shaping the outgoing cell traffic on the basis of the VPI value whereby control of the aggregate cell rate for said VPI value can be effected.

Both aspects of the invention may be combined in a single switch. Of course, in both aspects, other cells may be processed differently within the switch; a typical switch may handle a large number of simultaneous connections, including multiple VPs each having multiple VCs, and the VP based ("bundle") policing or shaping of each inventive aspect may be applied only to selected VPs on selected input ports. It will be appreciated that it is possible for different VCs originating from a common VP from a single port and policed as a bundle to be routed to different output ports. Similarly, multiple VCs output via a common VP on an output port may have been processed differently within the switch and may have originated from different input ports .

Preferably, the policing or shaping comprises processing all the cells having a common VPI value with common "leaky bucket" processor means. Shaping may include delaying cells to maintain a desired traffic shape.

The invention extends to corresponding apparatus .

Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures . BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a simplified schematic overview of an ATM switch incorporating a policing mechanism according to the invention;

Figure 2 is a schematic diagram of an ATM cell; and

Figure 3 is a simplified schematic overview of an ATM switch incorporating a shaper according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Figure 1, the operation of a simplified ATM switch incorporating a policing mechanism according to the invention will be explained. Features of the switch not described in detail may be implemented in a conventional manner, or may employ advantageous developments described in the

Appendices of U.S. Serial No. (Docket GDC-134) filed on even date herewith, and hereby incorporated by reference herein in its entirety.

By way of background, as is well known, and as schematically illustrated in Fig. 2, ATM cells comprise a five byte header incorporating a VPI and VCI values, other flags (not shown) and a checksum, and a forty-eight byte data payload. Further details of the format of an ATM cell (which changes depending on the location of the cell in a network) may be found in ATM standards documentation, for example the ATM Forum UNI 3.0 specification or in any of a number of reference books, an example of which is Broadband Communications by Balaji Kumar, published by McGraw-Hill, 1994, the disclosures of which are incorporated herein by reference in their entireties .

In the following description, only a few ATM cells will be schematically exemplified to simplify explanation of the principles involved. It will, of course, be appreciated that, in practice, a switch may handle many millions of cells a second, but the principles now described apply.

Referring back to Fig. 1, incoming ATM data cells 100 received at a single port of an ATM switch are supplied to Leaky Bucket Policers 10 on the basis of the VPI and VCI values contained in the cells. In the example shown, cells 100a... lOOd all have a common VPI, here "X" (this represents a numerical value), but have varying VCIs. Here two cells, 100a and lOOd also have a common VCI, here "A". The switch is configured to police all these cells on a per VP basis, and hence all cells are supplied to a single policing mechanism 10a. Other than the fact that the policing mechanism operates on all cells having a particular VPI irrespective of their VCI the operation of the policing mechanism may be entirely conventional and will not be described further. An example of a leaky bucket policing mechanism may be found in co-owned application GB 2 287 854 the complete disclosure of which is hereby incorporated herein by reference. Although cells lOOe and lOOf share a VPI value, here "Y" , they are not configured to be policed on a per VP basis, and are passed to separate policers 10b and 10c on the basis of their VCI values .

After policing, the cells are counted by means of cell counters 12 , with individual counts being recorded for each VPI,VCI combination. The cells are then fed via a common channel 13 (which may include other processing steps, not shown) to an input INI of a switch fabric 16, which is arranged to receive routing information from a routing table 14 for each VPI,VCI combination. In the embodiment shown, the switch fabric performs the dual functions of: (1) routing cells received from its various inputs IN1,IN2 (and others, not shown) to its outputs OUT1...0UT4 (and others, not shown) on the basis of the information stored in the routing table 14, and (2) translating VPI and VCI values as necessary, also on the basis of the information stored in the routing table 14.

For ease of understanding, the switch has been shown operating without policing resulting in discarding of cells so all input cells have emerged from the cell outputs. In operation, of course, not all cells may be passed by the leaky bucket policers 10, or some cells may have Cell Loss Priority bits set by the policers and be discarded by the switch.

As will be appreciated, an analogous arrangement may be employed to perform traffic shaping. In this case, however, cells emerging from an output of the switch are shaped by passing to leaky bucket policers on the basis of VPI and VCI values. For example, in the embodiment of Fig. 1, assuming the cells emerging from output 0UT2 having VPI,VCI values of X',C and Y',P' in fact had a common VPI value, Z. The switch may further include a shaper arranged to delay cells when the aggregate rate exceeded a predetermined value .

Referring to Fig. 3, a leaky bucket shaper will be described. To assist in understanding the invention, the implementation of a leaky bucket shaper will be further explained in terms of a pseudo-code implementation, where -> indicates storing a value in a variable store.

Store: [Predetermined] Increment value, I [Predetermined] Overflow value, Max [Current] Bucket level , L [Current] Last cell time, T

When Cell arrives at new time, T ' : L + I - (T ' -T) -> L T ' -> T IF (L > Max) THEN delay cell , preferably by time _ (L - Max) IF (L < 0) THEN 0 -> L

Referring to Fig. 3, cells 100a... lOOf are all output from a single common port of a switch fabric, not shown in the figure. For ease of explanation, the output cells exemplified are the same as the input cells exemplified in Fig. 1. In practice, of course, in a single switch fabric the cells output from the switch fabric may have different VCI and VPI values to those input, and may not be routed to a common output port .

In the example shown, all cells having a VPI value of "X" are routed to a common Leaky Bucket Shaper 20a, which performs shaping according to the above algorithm for all cells having that VPI value, regardless of the VCI values. Some cells may be delayed, as indicated in the above algorithm, if the total cell rate on that VPI is above a desired value. Cells having a VPI value of "Y" are intended to be shaped in the conventional manner, based on the VCI value. Thus, cells having a VCI value of "P" are passed to Leaky Bucket Shaper 20b and cells having a VCI value of "Q" are passed to Leaky Bucket Shaper 20c. The outputs of all the shapers 20a, 20b, 20c are passed via a common channel 33 to physical output port 35 for output via a conventional medium, for example over a SONET optical interface. Additional processing may be performed along output channel 33 if required. The shaping function described above may be applied to some or all of the outputs of the switch fabric 16 described with reference to Fig. 1.

It will be appreciated that both the shaping and policing functions are based on the same principle and can be implemented together or independently in an ATM switch as required, and may coexist with conventional VC based shaping and policing.

There has been described and illustrated herein preferred embodiments of methods and apparatus for bundle shaping and policing in data networks . While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow. Thus, while the invention was described in the context of an ATM switch, it will be appreciated that the invention may be applied to derivatives or variants of the defined standard ATM format. Specifically, the invention may be applied to any data packet routing system in which routing is carried out on the basis of virtual channel identifiers (whether termed VCIs or otherwise) and in which a certain range of values of virtual channel identifiers are reserved and a range of other values are available for use by a user. Thus, references to ATM-type cells and ATM-type switches in this specification are intended to encompass such variants. In the case of an application other than standard ATM cells or switches, the terms VCI and VPI are to be construed as applying to corresponding routing identifiers. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its spirit and scope as claimed.

Claims

Claims :

1. A method of processing cells in an ATM-type switch, the method comprising: a) receiving a plurality of cells, at least two cells having different VCI values and a common VPI value, from an input port of the switch; b) processing cells on the basis of the VCI value of each cell whereby at least one function can be performed independently for each VC; and c) policing the cells on the basis of the VPI value whereby control of the aggregate cell rate can be effected.

2. A method according to claim 1, wherein: said processing comprises directing cells having different VCI values to different output ports within the ATM switch as specified in routing information after policing on the basis of the VPI value.

3. A method according to claim 1, wherein: said at least one function includes routing.

4. A method according to claim 1, wherein: said at least one function includes cell counting.

5. A method according to claim 1, wherein: other cells having a VPI value other than said common VPI value are policed or shaped on the basis of cell VCI values, whereby individual VC rate control can be effected.

6. A method of processing cells, each containing a VCI value and a VPI value, in an ATM-type switch, the method comprising: a) processing the cells on the basis of the VCI value of each cell whereby at least one function can be performed independently for each VC; b) outputting processed cells from an output port of the switch, wherein cells for output from said output port include at least two cells having mutually different VCI values and a common VPI value; and c) shaping the outgoing cell traffic on the basis of the VPI value whereby control of the aggregate cell rate for said VPI value is effected.

7. A method according to claim 6, wherein: said processing comprises receiving cells having a common VPI value and output from said output port at different input ports within the switch.

8. A method according to claim 6, wherein: said at least one function includes routing.

9. A method according to claim 6, wherein: said at least one function includes cell counting.

10. A method according to claim 6, wherein: other cells having a VPI value other than said common VPI value are policed or shaped on the basis of cell VCI values, whereby individual VC rate control is effected.

11. An ATM-type switch having a plurality of input ports and a plurality of output ports for switching ATM-type cells each having associated VPI and VCI values and further comprising: a) means for processing cells on the basis of the VCI value of each cell whereby at least one function can be performed independently for each VC; and b) means for policing the cells received on a defined input port on the basis of the VPI value whereby control of the aggregate cell rate of cells having a defined common VPI value is effected.

12. An ATM-type switch having a plurality of input ports and a plurality of output ports for switching ATM-type cells each having associated VPI and VCI values and further comprising: a) means for processing cells on the basis of the VCI value of each cell whereby at least one function can be performed independently for each VC; b) means for shaping the outgoing cell traffic from a defined output port on the basis of the VPI value whereby control of the aggregate cell rate for cells having a defined common VPI value is effected.