Multiplex communications – Data flow congestion prevention or control
Reexamination Certificate
2000-02-07
2003-07-22
Patel, Ajit (Department: 2664)
Multiplex communications
Data flow congestion prevention or control
C370S236100
Reexamination Certificate
active
06597659
ABSTRACT:
FIELD OF INVENTION
Method of controlling the conformity of the transmission rate of data cells transmitted by a source terminal in communication with a destination termninal and a user-network interface unit provided for implementing the said method.
BACKGROUND ART
The present invention concerns a method of controlling the conformity of a flow of cells transmitted by a source application of a high-speed network, for example a network using the so-called ATM (Asynchronous Transfer Mode) transfer mode. More precisely, the invention is applied to sources whose transfer mode is an available resource sharing mode, also referred to in the art as ABR (Available Bits Rate) mode.
For whatever useful purpose it may serve, it is to be stated that the ATM transfer mode consists of conveying, in a data network, packets of information of fixed size referred to as cells. A source terminal thus sends data cells in the network, which conveys them to a destination terminal in accordance with a preestablished communication protocol. These cells are thus directed and oriented through a preestablished channel between the two terminals. This channel, which is also referred to as a connection, is notably characterised by its transmission rate, which must be sufficient to convey all the information transmitted by the source. To do this, at each element through which the said channel passes, a transmission rate is reserved for this channel.
The major advantage of high-speed networks based on the asynchronous transfer mode, in addition to the access to transmission and switching capacities which can support high transmission rates, is to be able to integrate, on the same transmission medium, applications whose requirements in terms of quality of service and resources are different. These ATM networks also allow the use of applications which transmit cells with rates which are variable over time, such as applications of the video type or Internet type, which gives rise to a variation over time of the consumption of the network resources used by these applications. In order to integrate all these applications, the ATM technique must satisfy the following three criteria: i) offer the necessary transmission rate to any application connected, ii) guarantee the quality of service level required by any application connected, iii) optimise the use of the resources available in the network.
The first two points make it possible to establish the requirements of a given application, which, after having been negotiated and accepted by the network during the call procedure, constitute what is referred to as the traffic contract between the user, who is the user of the envisaged application, and the network. This contract, which is defined by the two interfaces referred to in the art as UNI (User Network Interface), between the network and each of the two applications, defines the traffic characteristics of the source application and the quality of service QoS required for its correct operation. This contract guarantees to the source application the quality of service QoS demanded if the latter complies with the traffic characteristics which it negotiated at the time of the call.
The present application applies mainly to the so-called available resource sharing transfer mode or ABR (Available Bit Rate) mode. This ATM transfer mode is generally intended for applications capable of adapting their cell transmission rates during connection. Amongst these applications, there will for example be data transfer applications: interconnection or emulation of local networks of the so-called LAN (Local Area Network) type, or access to remote data.
This transfer mode, whose control mechanisms are implemented at the ATM layer of the network, was notably developed for the purpose of more effectively using the available passband in an ATM network while guaranteeing a transmission rate and a quality of service QoS level sufficient for the correct operation of the applications connected.
This ABR mode is first of all a communication protocol which, for a connection established between a source terminal and a destination terminal, makes it possible to share with other connections the resources available in each of the elements of the network through which the said connection passes. These available resources correspond to the sum of the transmission rates which is not used by any of the connections on the element under consideration. To effect this sharing, the transmission rate of each of the sources which are also operating in this ABR mode is regulated as a function on the one hand of the quantity of resources available in each network element and on the other hand the sharing which is performed thereof between the connections also operating according to the ABR mode. The ABR mode therefore involves a mechanism of controlling the transmission rate only of the sources which are operating in ABR mode according to the transmission rate allocated by the network elements for each connection operating in this mode. This control mechanism makes it possible to dynamically adjust the transmission rate of the sources according to the resources available in the network.
This mechanism is as follows. Each source periodically transmits a forward resource management cell, also referred to in the art as FW-RM or “Forward-Resource Management”, and is returned by the destination application in the form of a backward resource management cell, also referred to as BW-RM or “Backward-RM”. Each network element through which one or other cell passes has the possibility of explicitly indicating its congestion state to it by loading an appropriate word into one of the fields. This state is in the form of a rate hereinafter denoted ER, or Explicit Rate. After this forward and backward transmission, the B-RM cell carries congestion directives which enable the source to adapt the value of its rate, for example between a minimum value MCR and a maximum value PCR (respectively Minimum Cell Rate and Peak Cell Rate) negotiated in the traffic contract.
Thus the actual transmission rate of each source is controlled in order to make sure that they do not exceed the rate reserved for it in the network. This is because, if a malevolent source transmits at a rate greater than that allocated to it or authorised, it may saturate the capacity of the network elements. It thus jeopardizes the transfer of information and therefore the quality of service of all the other connections passing through the same network elements.
This control is referred to as a conformity control and is implemented at the interface between the network and a source, either at the UNI (User-Network Interface) by means of a so-called UPC (Usage Parameter Control) operator, or at the NNI (Network-Network Interface) by means of a so-called NPC (Network Parameter Control) operator. It is implemented by means of a conformity control algorithm which is generally referred to as a GCRA or Generic Cell Rate Algorithm. Applied to the ABR transfer mode for which, as has just been seen, the rate reserved changes all along the connection as a function of the resources available in the network elements, it is referred to as a DGCRA, or Dynamic Generic Cell Rate Algorithm.
In
FIG. 1
, a first terminal
10
can be seen, referred to as the source terminal, connected to a network
20
. A second terminal
30
, referred to as the destination terminal, is also connected to the network
20
. In the remainder of this description, it will be assumed that the terminals
10
and
30
are in communication with each other. In addition, they are both of the type operating in ABR mode with resource sharing. A virtual channel is therefore established between them to allow the transmission of data cells sent by the source terminal
10
. User-network interface units
21
(referred to as UNI in the art) are provided between the network
20
and the terminals
10
,
30
. It is in these units
21
that the functions of the UPC operators are implemented, as well as the DGCRA algorithm which is now described in relation to FIG.
1
.
Klay Francis
Rabadan Christophe
France Telecom (SA)
Lowe Hauptman & Gilman & Berner LLP
Patel Ajit
Shah Chirag
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