Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L47/00—Traffic control in data switching networks
  • H04L47/10—Flow control; Congestion control
  • H04L47/24—Traffic characterised by specific attributes, e.g. priority or QoS
  • H04L47/2441—Traffic characterised by specific attributes, e.g. priority or QoS relying on flow classification, e.g. using integrated services [IntServ]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L47/00—Traffic control in data switching networks
  • H04L47/10—Flow control; Congestion control
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L47/00—Traffic control in data switching networks
  • H04L47/10—Flow control; Congestion control
  • H04L47/215—Flow control; Congestion control using token-bucket
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L47/00—Traffic control in data switching networks
  • H04L47/10—Flow control; Congestion control
  • H04L47/32—Flow control; Congestion control by discarding or delaying data units, e.g. packets or frames

Definitions

• the field of the invention is that of communication networks, and in particular but not exclusively of networks of IP type or equivalent. More specifically, the invention relates to a method for controlling traffic of data packets entering a network, in the case where the traffic comprises a plurality of streams and / or substreams each associated with a priority level , and where each of the packets is marked with the priority level associated with the stream or substream to which this packet belongs. In other words, the invention relates to a network mechanism making it possible to optimize the flow of incoming traffic on a network.
• the invention has numerous applications, such as for example the control of multimedia streams (for example MPEG streams), alone or by aggregates, or even the control of a multiplex of streams of different natures (for example a video stream / multiplex audio with a TCP stream, on an ADSL access).
• multimedia streams for example MPEG streams
• aggregates for example a video stream / multiplex audio with a TCP stream, on an ADSL access.
• a multiplex of streams of different natures for example a video stream / multiplex audio with a TCP stream, on an ADSL access.
• TCP Transmission Control Protocol
• TCP Transmission Control Protocol
• session level control the protocol parameters make it possible to detect possible congestion, and to adapt the bit rate of the source to the constraints of the network. The objective is then to limit the speed if the network cannot handle everything, and to avoid sending packets which will be lost.
• Many studies today seek to apply equivalent mechanisms to video streams, with the real-time constraint of a dynamic adaptation of coders to the available bit rate.
• the real-time and audiovisual protocols currently do little processing, and are mainly limited to marking the transmission time and the encapsulation of packets of the application for their routing in the IP layer (for example RTP / UDP), in charge of the applications to cope with the received data.
• IP layer for example RTP / UDP
• IntServ defines means for reserving a resource with guaranteed speed between two nodes of a network
• DiffServ defines means for dynamically controlling the flow of flow aggregates as a function of the network load. Compared with end-to-end solutions (analogous to TCP) solutions located in routers have several advantages:
• Processing in routers is based on a distinction between packets arriving in routers supporting “quality of service” (QoS, “Quality of Service”) mechanisms.
• QoS quality of service
• the size of the images P is generally much smaller than that of the images I, and coding with few I images makes it possible to obtain, at equivalent bit rate, a much higher decoding quality. Under these conditions, the loss of an image is not equivalent depending on the nature of the information it contains. This structure of information must lead to considering the importance or the weight of each piece of information in its processing by the network. There are two reasons for keeping images I:
• Another way of considering this weight of information is to split an MPEG4 stream into several hierarchical levels to obtain a variable quality according to the overall content received by the user.
• a hierarchical level N must be supported on the presence of the Nl lower levels to provide additional quality.
• An elementary case is to consider a video made up of a basic stream (containing I and P images) and of an enhancement stream (containing P and B images). For this elementary case, the basic flow as a whole is considered to have higher priority than the enhancement flow.
• ADSL Asymmetry Digital Subscriber Line
• bursts are the most important information because they correspond to a change of scene or at least to a significant change in the content of the image. Very often, these images are of type I (Intra) whose loss is very critical, because it becomes impossible to reproduce the following images, even if the latter are correctly received.
• I Intra
• Traffic shaping and conditioning mechanisms are used in “quality of service” (QoS) IP networks.
• QoS quality of service
• TSPEC Traffic Specifier
• Traffic specification Traffic smoothing
• Traffic smoothing (TS) algorithms are however widely used in coding in order to control the bit rate of coders. This remains insufficient to control flows at the network level.
• TS Smoothing smoothes the bursts by “buffering” (that is to say by buffering) the packets concerned by the excess of bursts in the border equipment of the network. It can reduce congestion to acceptable levels, especially that scheduling algorithms such as CBQ (“Class Based Queuing” ie “management of queues based on service classes) ”) Or PQ (“ Priority Queuing ”that is to say“ queue management by priorities ”) are not able to do this. Used alone, these mechanisms propagate bursts in the network.
• CBQ Class Based Queuing
• PQ Priority Queuing
• traffic rule control limits the traffic rate to the configured rate. But instead of "buffering" packets like smoothing (TS), non-compliant packets are either rejected or noticed to lower their priorities. Traffic rule control (TP) therefore does not smooth traffic, but it does not introduce a "buffering" delay either.
• the network service provider (NSP) is not required to treat MPEG streams differently.
• the traffic aggregate resulting from several audio-visual streams is generally difficult to describe: - the packet arrival process is self-similar;
• the media access gateway (MAG, for “Media Access Gateway”) is for example responsible for this task.
• This MAG gateway manages traffic according to the specified SLS. This approach facilitates the negotiation of SLA / SLS for services in continuous mode (“Streaming”) and imposes on the client a very specific traffic profile.
• the WRED Weighted Random Early Drop
• This mechanism is based on an average filling rate of the transmission queue on a network link.
• this technique introduces a random nature of packet rejections, and the filling rate of the queue is not optimized. Depending on the size of the bursts and their frequency, these rejections can occur for a low filling or a very high filling of the queue. This leads on the one hand to an underuse of the queue, and on the other hand to the reservation of consequent memory size for the realization of this queue. This problem exists for any type of application, and it is even more real for audiovisual streams because of their large bursts.
• the WRED mechanism is therefore not suitable for controlling flows characterized by an average value over a fixed duration.
• the invention particularly aims to overcome these drawbacks of the prior art and offer an optimal solution in the event of network congestion.
• one of the objectives of the present invention is to provide a method and a device for traffic control making it possible to control gusts and to smooth traffic over a set of flows and / or substreams associated with levels of priorities.
• an objective of the present invention is to provide a method and a device for traffic control making it possible to protect the important information from the bursts, in order to provide a solution to the contradiction between the optimization of a stream (for example a video stream) containing bursts and smoothing the bursts for quality transport in the network.
• a stream for example a video stream
• the invention also aims to provide such a method and device which are simple to implement and inexpensive.
• Another objective of the invention is to provide such a method and device making it possible to efficiently offer traffic contracts (SLA / SLS) between network operators and service providers.
• SLA / SLS traffic contracts
• a method for controlling a traffic of data packets entering a network comprising N stream and / or substream each associated with a priority level, N> 2, each of the packets being marked with the priority level associated with the stream or substream to which said packet belongs, said method comprising an implementation step an N-level token bucket mechanism with N token buffers each containing a number of available tokens, the tokens of each of the N token buffers being used to process one of the N levels of priority, each packet being accepted or refused depending on whether or not it is possible to allocate tokens according to it tokens available at least in the token buffer used to process the priority level of said packet.
• the general principle of the invention therefore consists in using a multi-level token bucket (MLTB, for “Multi Layer Token Bucket”) to reject packets outside a required profile and characterized by the N operating levels of the bucket multi-level tokens.
• MLTB multi-level token bucket
• Each packet undergoes processing according to a marking corresponding to its priority level. Accepted packets are placed in a queue.
• the multi-level token bucket makes it possible to selectively and jointly process several levels of flow priorities. It is well suited to characterizing traffic between the size of incoming gusts and the flow of outgoing traffic. We know that in the event of network congestion, it is illusory to seek available bandwidth.
• the adjustment of the parameters of the multi-level token bucket ensures a relationship between the priority levels to balance the operating constraints between the flow rates by priority levels and the bursts acceptable by the token bucket according to the constraints of the transported applications.
• the characterization of the parameters of the N sets of parameters of the multi-level token bucket allows numerous solutions and can be adapted to almost all operating cases:
• an extreme case is the behavior with N sets of independent parameters acting like buckets with independent tokens;
• another extreme case is the possibility for the highest priority level to take all the tokens and result in a rejection of the packets from all the other levels;
• the invention therefore makes it possible to process bursts on the highest priority levels, because there is for each priority level a reserve available to prevent any sudden arrival of a set of data which must not be rejected.
• a usual token bucket has only one operating level (it has a single set of parameters) and therefore processes all packets indiscriminately. Packets are therefore dropped in the event of network congestion regardless of their priority level.
• the present invention is fully compatible with IP streams “unicast” (single recipient) and “multicast” (selectively broadcast). It will also be noted that the present invention makes it possible to transmit several groups of flows with different priorities in the same class of service.
• the invention makes it possible to provide processing adapted to one or a group of video streams (IPB or hierarchical) in accordance with a contracted traffic profile (SLS) by characteristic values of the token bucket type.
• SLS traffic profile
• the easily measurable and adaptable parameters of a multi-level token bucket (MLTB) are an effective means of proposing traffic contracts (SLA / SLS) between network operators and service providers. The presence of priority information leads to the specification of this bucket.
• the multiple versions of this bucket are a means of offering classes of services adapted to customer requirements.
• the traffic profile involves the main elements of characterization of a flow in a network: the speed and the delay.
• the invention is therefore a means of defining a contract with a negotiated compromise between the speed, the size of the bursts, and the transmission time.
• the traffic comprises N sub-flows each corresponding to one of the N hierarchical levels of a hierarchical flow or of an aggregate of hierarchical flows.
• the traffic comprises N sub-streams each corresponding to one of the N types of images of a multimedia stream or of an aggregate of multimedia streams.
• the traffic comprises N streams each corresponding to one of the stream of a multiplex of at least two streams.
• This is for example a multiplex video / audio stream with a TCP stream, on an ADSL access.
• the traffic comprises N flows and / or substreams belonging to the same class of service.
• the invention thanks to the multi-level token bucket, makes it possible to transmit several flows and / or sub-flows with different priorities in the same service class.
• service classes such as for example the "streaming" class (containing audio and video streams, the "priority TCP” class, the "Best IP network effort” class, ...) and use a bucket with multi-level token for each class.
• Each class of service can be defined by marking packets, by the source or destination IP address of the packets, by the protocol used for the packets, etc.
• the refused packets are discarded.
• the packets refused are those which do not comply with the traffic profile defined by the parameters of the N operating levels of the multi-level token bucket.
• Another option, less efficient but which nevertheless falls within the scope of the present invention, is to transmit the refused packets after having marked them again with a lower priority level.
• this option has the disadvantage of increasing the probability of packet rejection in congested network nodes.
• the network is of IP type or equivalent.
• each of the N operating levels of the token bucket mechanism is managed by a regulator bi (r b b ⁇ i;), i G ⁇ 1 to N ⁇ , with: r j the nominal flow rate of the regulator; - bn; the maximum size of the controller token buffer; bi (t) the instantaneous value of the filling of the regulator token buffer.
• the tokens of the N token buffers are shared between the N priority levels, a packet of priority level i being able to be allocated tokens of a token buffer associated with a priority level j less priority when the tokens available in the token buffer of priority level i are not sufficient.
• the allocation of tokens to a packet of priority level i is carried out according to a discontinuous mode per packet and consists in assigning: either tokens available in the token buffer memory of priority level i; - or tokens available in a token buffer of priority level j with lower priority, when the tokens available in the buffer of tokens of priority level i are not sufficient.
• a packet can use resources (tokens) only on one level of operation of the multi-level token bucket.
• the allocation of tokens to a packet of priority level i is carried out in a continuous mode per bit and consists in allocating: tokens available in the buffer of level tokens of priority i; and in addition to the tokens available in at least one buffer of tokens of priority level j with lower priority, when the tokens available in the buffer of tokens of priority level i are not sufficient.
• a packet in the continuous mode, can use the resources (tokens) of several operating levels of the multi-level token bucket at a time.
• the packets accepted by the token bucket mechanism with N operating levels are placed in a queue.
• the method further includes a step of implementing a token bucket mechanism at a single level of operation with a single token buffer, so as to take the packets contained in the queue and send them over the network by performing traffic smoothing by limiting the instantaneous speed to a value acceptable by the network .
• the single-level token bucket (TBTS, for “Token
• Bucket Traffic Shaper therefore makes it possible to limit the peak bit rates emitted by the network equipment supporting the invention. It delays gusts when they exceed the tolerated flow in the network.
• the invention also relates to a computer program comprising program code instructions for executing the steps of the method as mentioned above, when said program is executed on a computer.
• the invention also relates to a device for controlling a traffic of data packets entering a network, the traffic comprising N streams and / or substreams each associated with a priority level, N> 2, each of the packets being marked with the priority level associated with the stream or sub-stream to which said packet belongs, said device comprising means for implementing a token bucket mechanism with N operating levels with N token buffer memories each containing a number of tokens available, the tokens of each of the N token buffer memories being used to process one of the N priority levels, each of the packets being accepted or refused according to whether or not it is possible to assign tokens to it according to the tokens available at least in the token buffer memory used to process the priority level of said packet.
• said method comprises means for sharing the tokens of the N token buffer memories between the N priority levels, a packet of priority level i being able to be allocated tokens from a token buffer associated with a lower priority level j when the tokens available in the token buffer of priority level i are not sufficient.
• said sharing means comprise means for guaranteeing a quantity of tokens reserved exclusively for packets having said priority level.
• the invention also relates to network equipment comprising a control device as mentioned above, said network equipment belonging to the group comprising: network equipment located between a network of an application or service provider and a network of a provider of 'a network service, constituting said network at the input of which is carried out the control of a data packet traffic; - routers included in nodes of a network of a network service provider, constituting said network at the input of which is carried out the control of a traffic of data packets
• FIG. 1 presents an example of network architecture in which the traffic control method according to the invention can be implemented
• FIG. 2 illustrates a particular embodiment of the method according to the invention, implementing two functions, based on the use respectively of a multi-level token bucket and a single-level token bucket
• FIG. 3 illustrates a regulator managing an operating level of the multi-level token bucket illustrated in FIG. 2, as well as the use in this regulator of a parameter K j guaranteeing a minimum of resource for the priority level associated with this regulator;
• FIG. 1 presents an example of network architecture in which the traffic control method according to the invention can be implemented
• FIG. 2 illustrates a particular embodiment of the method according to the invention, implementing two functions, based on the use respectively of a multi-level token bucket and a single-level token bucket
• FIG. 3 illustrates a regulator managing an operating level of the multi-level token bucket illustrated in FIG. 2, as well as the use in this regulator of a parameter K j guaranteeing a minimum of resource for the priority level associated with this regulator
• FIG. 4 illustrates an example of allocation of tokens in the case where the operation of the multi-level token bucket is described with independent buffer memories (buffers);
• FIG. 5 illustrates an example of allocation of tokens in the case where the operation of the multi-level token bucket is described with correlated buffers.
• the invention therefore relates to a method for controlling data packet traffic entering a network.
• the traffic is of the type comprising N streams and / or substreams each associated with a priority level, with N> 2.
• Each of the packets is marked with the priority level associated with the stream or substream to which it belongs.
• the invention makes it possible to transmit, as a priority, the essential information of a video stream, or of several video streams grouped in an aggregate.
• this distinction is for example possible either by IBP type images (see definition above), or by the n layers of a hierarchical flow. If in the first case the average bit rate of the images I remains low compared to the global bit rate, in the second case the most important information and to be protected as much as possible is defined by the fraction of the global bit rate occupied by the base layer, and which can represent up to 50% of the flow. In general, the base layer is the only one to contain the reference information contained in the images I.
• all data with the same priority level is treated the same.
• all basic streams or all I frames are treated as a single higher bit rate stream than a single video.
• Internet Service provider offering a streaming video transmission service.
• the example of (simplified) architecture illustrated in Figure 1 includes:
• IP network of type "DiffServ” an IP network of type "DiffServ" 1, managed by a network operator (also called network service provider, or NSP (for "Network service
• Each network of service providers 3, 4 also comprises end equipment 8 , 9 connected to one of the routers on the IP network, called the edge router 2 , which is responsible for sending data from a server to a main route of an IP core network;
• the method according to the invention is implemented in network equipment forming a traffic conditioner for entry into the IP network 1.
• This network equipment can be located between the network of the service provider 3, 4 and the IP network 1 :
• the network equipment implementing the method according to the invention can also be any router placed at a congestion point in the network (in particular for any access to an ADSL link).
• FIG. 2 a particular embodiment of the method according to the invention. It protects important information from bursts and provides solutions to the contradiction between optimizing a video stream containing bursts and smoothing the bursts for quality transport in the network.
• the overall mechanism forms a “multi-layer decentralized traffic conditioner” called “MLDTC” (for “Multi-Layers Decentralized Traffic Conditioner”). It consists of two functions executed sequentially:
• MLTR Multi-Layers Traffic Regulator
• N operating levels
• N buffers of virtual tokens Each token buffer corresponds to a hierarchical level. Each operating level is defined by a set of parameters (see detailed discussion below).
• TBTS for “Token Bucket Traffic Shaper” because it is based on a single-level token bucket algorithm (“Token Bucket”) (referenced 31) and performs a smoothing of the traffic for a regular flow on the network by limiting the instantaneous flow to a value acceptable by the network.
• the TBTS function buffer is of reasonable capacity to guarantee a lower cost of the systems and a limited transfer time in the supply of information to the user.
• the counterpart of the finite size is the limitation of the bursts accepted at the input of the network.
• the MLTR function is adapted to the differentiated acceptance of bursts according to the priority level. It applies to IP packets (referenced 20 to 26 in Figure 2) whose DSCP (“Differentiated Services Code point”) field is marked either by the source or by a classification system.
• Each priority level i has its own parameters, for a single buffer, common to the 3 levels, but with varying levels of acceptance of data packets. This mechanism meets the expectations of a video signal, since it does not process all information uniformly. Indeed, it is recalled that an MPEG coding results in several levels of information which should be treated differently according to their importance.
• the objective is to favor the bursts of a level i compared to a level j, whose information is less important (j> i).
• the packets relating to level i then have priority to exploit the available resources.
• the same average bit rate is obtained for different burst sizes, and taking into account the interval separating them.
• Such a mechanism is well suited to bursts of video streams, which are variable, due to the great diversity of content transported (sports, news, landscapes, ).
• each operating level i of the token bucket with three operating levels 30 is managed by a regulator bj, bm ; ), i E ⁇ 1, 2, 3 ⁇ , with: - the nominal flow of this regulator;
• Compliant packets i.e. those to which it has been possible to allocate tokens by the multi-level bucket 30
• a buffer of packets to be sent 28 which forms a means of managing a queue wait. If an insufficient number of tokens is available in the multi-level bucket, the packets are then considered as non-compliant and are discarded. They are thrown in the trash referenced 27.
• Another option is to transmit these packets with a lower priority. However, re-marking packets to give them a lower priority increases the probability of packet rejection in congested nodes.
• a packet of priority level i can be allocated tokens from a token buffer associated with a priority level j of lower priority (j> i) when the tokens available in the buffer of level tokens of priority i are not sufficient.
• the solution is to limit this borrowing by a parameter K j , specific to level j, the objective of which is to protect the latter from higher priority levels by guaranteeing a quantity of resources (tokens) reserved exclusively for packets of level j. Consequently, the parameter K j guarantees a threshold for filling the token buffers below which packets of a higher priority level can no longer be used.
• the parameter K j of the level regulator j is illustrated in Figure 3.
• K j The value of K j must be chosen such that bmj> K j > MTU.
• K j is adapted to the useful size of a packet on the network (MTU (“Maximum Transfer Unit”, ie “maximum size of an elementary transfer unit”) for a network IP) corresponds to a guarantee of the nominal flow rate r j for level j but without guarantee of gusts. Token resources could be used by higher priority levels.
• MTU Maximum Transfer Unit
• FIG. 4 is a graphic representation of this token allocation algorithm in the case where the operation of the multi-level token bucket is described with independent buffers. It shows the possible use of the resources b t , b 2 and b 3 for each of the levels.
• the thick lines (referenced 41, 42 and 43) show the filling of the token buffers (that is to say the number of tokens available) for each level, and the arrows the resources (that is to say tokens) taken by incoming packets (PI, P2 or P3) according to their priority.
• B x ⁇ t + T) b x (t) + b 2 (t) + b 3 (t) + (r x + r 2 + r 3 ) l
• B 2 (t + ⁇ ) b 2 ( ⁇ + b 3 (t) + (r 2 + r 3 ) TB 3 (t + T) ⁇ b 3 (t) + r 3 .T
• FIG. 5 is a graphic representation of the token allocation algorithm in the case where the operation of the multi-level token bucket is described with correlated buffers. It shows the possible use of resources B ,, B 2 and B 3 for each of the levels. As in Figure 4, the thick lines (referenced 51, 52 and 53) show the filling of the token buffers (that is to say the number of tokens available) for each level, and the arrows the resources (i.e. tokens) taken by incoming packets (PI, P2 or P3) according to their priority.
• a packet can only use one regulator
• a packet can use several regulators at the same time.
• the taking into account of the arrival of the packet is obtained by the following algorithm:
• a packet is served by the resources of the level corresponding to the packet (level i) or of a lower priority level (level j). It should be noted that this operation is not optimal, since an incoming packet is rejected even if the sum of the available resources distributed over the 3 levels is sufficient.
• the taking into account of the arrival of the packet is obtained by the following algorithm: shipment;
• bits is more optimal than the discontinuous mode (packets). Indeed, it allows maximum use of own resources of the level before requesting resources at a lower priority level.
• the single-level token bucket 31, on which this SELV function is based is for example defined by the following parameters:
• - S the instantaneous value of filling the packet buffer 28 (S max is the maximum size of the packet buffer 28); - T, the time between the arrival of two consecutive packets;
• Compliant packets i.e. those to which it was possible to allocate tokens by the single-level bucket 31
• non-compliant packets are transmitted while non-compliant packets are delayed in the packet buffer 28 to contain them in the targeted traffic envelope.
• the size of the packet buffer 28 should be handled with care because it can induce an additional delay, which must remain reasonable.

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