Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1997-12-16
2001-01-16
Pham, Chi H. (Department: 2731)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S231000
Reexamination Certificate
active
06175568
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods and apparatus for adjusting policing rates in Available Bit Rate dynamic policing.
BACKGROUND OF THE INVENTION
Policing is a key function normally performed at the edge of a public network where bad traffic should never be allowed to cause the violation of quality of service guarantees on good traffic. Policing of available bit rate (ABR) end systems is more challenging than for constant bit rate (CBR) or even variable bit rate (VBR). This is mainly because the allowed cell rate (ACR) for an ABR source can change with every resource management (RM) cell that returns to it and thus the ABR policer cannot simply assume static policing parameters. This is why ABR policing is usually described as dynamic. In particular, when the generic cell rate algorithm (GCRA) is used for ABR, it is called dynamic GCRA or DGCRA.
An ideal ABR DGCRA is too costly to implement, since it requires storing a potentially very large number of policing rate updates and their associated application times per ABR connection. Hence, several approximate DGCRAs have been proposed where only two delayed rate updates need to be stored per connection.
In general, a public network cannot and should not blindly trust its users. Through policing, the network ensures that bad traffic (i.e. the traffic emitted onto the network in violation of the traffic contracts between the network and the involved users) does not result in violating the network's quality of service guarantees to users submitting good traffic. Furthermore, a user who persists in violating his contract with the network may be declared as non-compliant.
Conventional generic cell rate algorithms (GCRAs) are bufferless leaky bucket algorithms which are widely accepted and used for CBR, VBR and unspecified bit rate (UBR) policing. During connection setup, the GCRA policer is provided with the connection's traffic descriptor. For CBR, that includes peak cell rate (PCR) and cell delayed variation tolerance (CDVT). For BVR, it includes PCR, sustainable cell rate (SCR), Maximum Burst Size (MBS) and CDVT. For UBR, it includes PCR and CDVT. Non-conforming cells may be CLPl-tagged (cell loss priority 1) (in the case of VBR and UBR) or discarded (in the case of CBR, VBR and UBR).
The GCRA policer simply ensures that the source rate is within the contracted traffic descriptor. ABR policing is much more challenging because of two main reasons, namely the dynamic nature of the allowed cell rate (ACR of the ABR source) which can change with every returning backward resource management (BRM) cell, and the many rules that the ABR end system is required to follow. The dynamic nature of the allowed cell rate provides a reason for why the GCRA is called dynamic, when used for ABR policing.
The main objective behind ABR policing is to identify and possibly take actions against ABR traffic/users which do not follow the reference behaviour specified by the ATM forum, so that they may not impact good traffic.
Generally, good ABR users are ones which follow the ATM Forum (ATMF) specifications and thus generate forward resource management (FRM) cells including both in-rate and out of rate cells, as specified, insert the correct values in the current cell rate (CCR) and minimum cell rate (MCR) fields of FRM cells, schedule FRM cells, BRM cells and data cells as specified, obey network feedback carried by returning BRM cells by adjusting the ACR accordingly, reduce the ACR when BRM cells do not return as required, or when used after a long period of idleness, and turn around FRM cells received after changing DIR bits.
An ideal ABR policer should monitor the RM cell flow, particularly BRM cells and emulate the expected ABR end system behaviour to determine if the end system is doing what it is supposed to do. Furthermore, the feedback delay from and to the end system must be taken into account. The ideal ABR policer, however, is too complex to build because it requires emulation of the already complex ABR source behaviour with all the processing and parameter storage required and requires storing a potentially large number of ER updates and their associated application times for each ABR connection.
The application time for a given ER is the time at which that ER becomes a policing rate and this depends on the feedback delay to the source. When the policer sees a BRM cell heading to the source with a certain ER value, it cannot simply and immediately adjust its policing rate to that ER. It must allow enough time before allowing the recently observed ER. The time which must be allowed is the time needed for the BRM cell to reach the source, the source to adjust its ACR accordingly, and the new rate to be felt at the policer.
Therefore, depending mainly on the distance between the source and the policer, a potentially large number of outstanding ER updates may have to be stored. For example, if the source is 100 kilometres away from the policer and the rate fluctuates, say between 500 Mbps and 600 Mbps on a given connection then using NRM equals 32, more than 368 ER updates and their associated application times have to be stored, which is too costly to implement. (NRM is the number of cells that the source end system is required to send between each successive RM cell.)
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, there is provided a method of adjusting policing cell rates at a switch interface, for cells received from a source in an allowed cell rate system, the method including the steps of:
a) storing a current policing rate (PACR) in a current policing rate buffer;
b) storing a plurality of policing rates and policing rate application times in respective policing rate and policing rate application time buffers; and
c) in response to the departure of a backward resource management cell to the source at time tb(j), setting the contents of the policing rate buffers and the policing rate application time buffers according to the relative magnitudes of the current policing rate and the contents of the policing rate buffers.
Preferably, the method includes the steps of, storing a current policing rate (PACR) in a current policing rate buffer, storing a first policing rate (DER
first
) and a first policing rate application time (t
first
) in a first policing rate buffer and a first policing rate time buffer respectively and storing a last policing rate (DER
last
) and a last policing rate application time (t
last
) in a last policing rate buffer and a last policing rate time buffer respectively.
Preferably, the method includes the steps of receiving a backward resource management cell and on receiving such cell, determining whether or not a current cell rate is greater than or equal to the first policing rate and if so copying the first policing rate into the current policing rate buffer, copying the last policing rate application time into the first policing rate application time buffer, copying the last policing rate into the first policing rate buffer and setting the contents of the last policing rate buffer and the last policing rate application time buffer to zero.
Preferably, the method includes the steps of determining whether or not the first policing rate application time is earlier than the last policing rate application time and if so copying the first policing rate into the current policing rate buffer, copying the last policing rate application time into the first policing rate application time buffer, copying the last policing rate into the first policing rate buffer and setting the contents of the last policing rate buffer and the last policing rate application time buffer to zero.
Preferably, the method includes the steps of receiving a cell from the source at a time ta(k) and determining whether or not the current policing rate should be updated.
Preferably, the method includes the steps of determining whether the current policing rate is equal to the first policing rate and whether the first policing rate application time is equal to the last policing rate application t
Nortel Networks Limited
Pham Brenda H.
Pham Chi H.
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