Multiplex communications – Data flow congestion prevention or control
Reexamination Certificate
1999-09-08
2004-01-20
Vanderpuye, Kenneth (Department: 2661)
Multiplex communications
Data flow congestion prevention or control
C370S235000, C370S252000
Reexamination Certificate
active
06680907
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a shaping method to convert an incoming data flow with an incoming data packet rate into an outgoing data flow with an outgoing data packet rate, to a shaper realizing such a shaping method and a communication network including such a shaper.
As described in the ATM Forum, Technical committee “Traffic Management Specification” Version 4.0 ATM Forum/95-0013R10, February 1996, at section 5.5
Traffic Shaping,
page 41, traffic shaping is a mechanism that alters the traffic characteristics of a stream of cells on a connection to achieve better network efficiency whilst meeting the Quality Of Service objectives, or to ensure conformance at a subsequent interface. Traffic shaping maintains cell sequence integrity on a connection. Examples of traffic shaping are e.g., mean cell rate reduction, burst length limiting, reduction of Cell Delay Variation by suitable spacing cells in time and cell scheduling policy.
Shaping methods have also been proposed to reduce the burstiness of video traffic. Indeed, a shaping method realized by a shaper being included in a communication network is already known in the art, e.g., from the article “Adaptive traffic smoothing for live VBR MPEG video service” written by Jin-soo Kim and Jae-kyoon Kim and published in
Computer Communications
21 (1998) pages 644-653 by Elsevier Science B. V.
Therein, an on-line source traffic smoothing method is proposed that can be effectively used in live video applications such as visual lectures or television news. Through experimental results, it is shown that the proposed scheme, which is designed in such a dynamic way as to smooth maximally the transmission rate, is effective in reducing the peak rate, temporal variations, and effective bandwidth of a given video stream. According to the system model that is described in section 2 of this article, the method converts an incoming data flow with an incoming data packet rate into an outgoing data flow with an outgoing data packet rate. Indeed, the system model includes a buffer, called in the article the sender buffer, wherein the received data packets of the incoming data flow transmitted by the source are buffered. The buffered data packets are leaked with a transmission rate, called hereafter outgoing data packet rate, whereby an outgoing data flow is provided.
In section 3 of the above article it is mentioned that the video smoothing method of the above mentioned article depends on the past information of the outgoing data packet rate as well as the buffer occupancy of the buffer. Furthermore, the system model, called hereafter shaper, includes a Lth order linear predictor in order to efficiently estimate a future incoming data packet rate by using a linear combination of the previous values of the incoming data packet rate.
In this way, the shaping method of the prior art document includes among others the steps of:
determining a value of a future incoming data packet rate of the incoming data packet rate; and
determining a value of a buffer occupancy related to the number of data packets of the incoming data flow which are received and are buffered by the buffer; and the step of
determining a value of an outgoing data packet rate in function of among others a value of the future incoming data packet rate and a value of the buffer occupancy.
As it is described in the article, the video smoothing method supports Variable bit Rate VBR MPEG video services.
However, a quality of service category that provides a service with a predetermined minimum guaranteed bandwidth according to a predetermined minimum data packet rate of an incoming data flow and which allows use of excess bandwidth, being limited according to a predetermined peak data packet rate, over this predetermined minimum guaranteed bandwidth, is not supported by the prior art method. Such a service category is e.g., the Guaranteed Frame Rate GFR service category. This service category provides a service with a minimum guaranteed bandwidth while allowing the users to transmit at a higher rate than this guaranteed bandwidth. The data packets that are part of the minimum guaranteed bandwidth will be delivered to the destination while the data packets which are not part of this guaranteed bandwidth will be delivered to the destination on a best-effort basis depending on the amount of the unreserved bandwidth inside the network. A traffic contract for such a GFR service includes the definition of a Minimum Cell Rate MCR and a Peak Cell Rate for each data flow. Such a minimum cell rate MCR, called hereafter minimum data packet rate, is expressed in cells per second. The minimum guaranteed bandwidth according to this minimum data packet rate is the minimum bandwidth that is guaranteed at any time for each established data flow following the contract and is determined during connection set-up of the data flow. Such a peak cell rate, called hereafter peak data packet rate, is the maximum transmission rate that is allowed according to the contract.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a shaping method and a shaper realizing such a shaping method in a communication network that does not reduce the burstiness of the incoming data packet rate of the incoming data flow while supporting a quality of service category which provides a service with a predetermined minimum guaranteed bandwidth according to a predetermined minimum data packet rate of an incoming data flow and which allows use of excess bandwidth, being limited according to a predetermined peak data packet rate, over this predetermined minimum guaranteed bandwidth.
Indeed, due to the fact that the shaping method further includes determining the value of the outgoing data packet rate also in function of a predetermined peak data packet rate and a predetermined minimum data packet rate. In this way, the minimum data packet rate according to the contract of the incoming data flow is taken into account in order to determine a value for the outgoing data packet rate whereby the shaping method is enabled to guarantee a minimum guaranteed bandwidth according for the data flow. Moreover, the shaper is enabled to allow the use of excess bandwidth over the minimum guaranteed bandwidth if this bandwidth is available in the network and to limit the use of excess bandwidth, however, according to the predetermined peak data packet rate.
It has to be remarked that the minimum data packet rate is, as already mentioned above, a data packet rate that is guaranteed to the incoming data flow. This does not mean that the minimum value of incoming data packet rates of the incoming data flow is equal to this minimum data packet rate. Indeed, the incoming data packet rate might be smaller than this minimum data packet rate but the minimum data packet rate is always guaranteed to this incoming data flow.
A possible implementation of the step of determining a value of a future incoming data packet rate is to determine a value of an average incoming data packet rate of the incoming data packet rate.
A simple solution in order to reduce the burstiness of the incoming data packet rate is to use the above mentioned value of an average incoming data packet rate in order to determine a value for the outgoing data packet rate. Although this solution would limit the burstiness of the incoming data packet rate, it would result in a large and uncontrolled occupancy of the buffer included in the shaper. Therefore two thresholds are predetermined on the occupancy of the buffer: a predetermined minimum buffer occupancy and a predetermined maximum buffer occupancy.
As long as the value of the buffer occupancy is smaller than the predetermined minimum buffer occupancy or substantially equal to the predetermined minimum buffer occupancy, the shaper is allowed to leak the buffer with an outgoing data packet rate which is at least equal to the guaranteed minimum data packet rate. However, in the event when a bigger incoming data packet rate is expected, i.e., a bigger value of the future incoming data pa
Alcatel
Nguyen Brian
Vanderpuye Kenneth
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