WO2007148027A2

WO2007148027A2 - System and method for managing access to a time division multiple access network

Info

Publication number: WO2007148027A2
Application number: PCT/FR2007/051497
Authority: WO
Inventors: Joël PENHOAT; Thomas Richon; Brice Cassagnabere
Original assignee: France Telecom
Priority date: 2006-06-23
Filing date: 2007-06-21
Publication date: 2007-12-27
Also published as: WO2007148027A3

Abstract

Method of managing access to a time division multiple access network that is distributed over time segments of predetermined duration (PTDMA), for at least one station (STi, STj, STk) having at least one data stream to be sent or received through said network, in which a stream to be sent/received during the next time period of duration PTDMA, is allocated a network access authorization duration, dependent on an access authorization mean duration (txop_m(i,n)) and a mean number of lost packets (lost_m(i,n)), said mean duration and said mean number relating to a time period of duration PMI comprising at least one past time period of duration PTDMA.

Description

System and method for managing access to a time division multiple access network

The invention relates to a method and a telecommunication system in a network including at least one station having at least one data stream to be transmitted or received, the network being a time division multiple access network. More specifically, the method and the system according to the invention concern the temporal regulation of access to a Time Division Multiplex Access (TDMA) network.

In time-division multiple access networks, for example in the case of a radio network meeting the IEEE 802.11 (Institute of Electrical and Electronics Engineers) standard, a network access authorization period is allocated to different streams to be transmitted so as to regulate, for each period during which time-division multiple access is provided, access to the network for the different transmitters of these streams.

With the advent of high-speed access networks (for example broadband ADSL techniques) and the deployment of high-speed Internet access, audio or video streams can now be transmitted in real time using Real Time Transport Protocol (RTP) and Real Time Control Protocol (RTCP) over 802.11 type radio networks, offering guarantees of quality of service and transmission delay.

As a result, the same shared radio transmitter in an 802.1 1 network is likely to handle RTP streams of very different natures, both by their bit rate and by the length of the packets. A process of regulating network access times is therefore necessary to avoid a reduction in the quality of transmission due to collisions occurring between the different streams.

The 802.11 standard defines a regulation mechanism by assigning an access authorization duration to each stream to be transmitted. However, this access authorization duration is fixed for each stream to be transmitted. However, the flow rate of a stream or the length of the packets of a stream can vary greatly over time. The access authorization times may therefore be inappropriate for the actual instantaneous need of each stream transmitter, which has the consequence of increasing the risk of collision between the different streams.

Thus, the state of the art does not propose a time-controlled mechanism for access to a time-division multiple access network, which to reduce collisions between streams when the flow rate or the packet length of the streams to be sent varies. The present invention does not have these disadvantages.

According to a first aspect, the invention relates to a method of managing access to a time division multiple access network over time segments of predetermined duration, for at least one station having at least one data stream to be transmitted or to receive through said network, the method comprising

a step of obtaining, for each stream included in at least part of the streams to be transmitted or received during a next time segment, values representing a bit rate, a packet length and a number of lost packets, said values being relative to a time interval prior to said next time segment,

a determination step, for each stream included in said part, of a period of access authorization to said network allocated to the stream under consideration for the transmission or reception of said stream in question during said next time segment, said duration of access authorization being determined according to said values obtained.

The method according to the invention makes it possible to take into account various parameters representing the state of the network, parameters such as the bit rate of the streams to be transmitted, the packet length of the streams to be transmitted and the number of packets lost. Since the number of lost packets is representative of the overhead of the network, the method allows a regulation of the access to the network and therefore of the load of the network, by assigning access authorization durations taking into account this overload information. In addition, the method preferably uses information in the form of average values, and is thus able to take into account the variations of these parameters over a relatively long period of time.

According to a particular embodiment, the method comprises a step of determining, for each stream included in said part, a first duration corresponding to a time necessary to transmit or receive a stream having a rate and a packet length corresponding to the values packet rate and packet length obtained for the stream in question, the access authorization time determined for said stream considered being a function of the first determined duration for said stream considered. The method makes it possible to simply obtain a first estimate of the access authorization time to be attributed to a stream. According to a particular embodiment, the method comprises a step of determining, for each stream included in said part, a second duration corresponding to the time required for a transmission or reception of a number of packets corresponding to the number value. lost packets obtained for the stream in question, the access authorization duration determined for said stream considered being a function of said second determined duration for said stream in question. The method corrects the first estimate of the access authorization time to be allocated to a stream based on the packet loss of that stream. As a result, the assigned duration of authorization is adapted to the real needs of the station having to transmit or receive this flow and the packet losses suffered by the station.

According to a particular embodiment, the method comprises a step of determining a third duration corresponding to the difference between a duration of said next time segment and a sum of said first and second durations determined for the flows of said part, the duration of determined access authorization for a stream depending on said third duration. In this way, the entire duration of the available time segment is distributed among the different flows authorized to access the network.

In addition, the duration of authorization can be calculated simply from the different durations calculated, so as to take into account both the packet loss, the characteristics of the stream to be transmitted and the total duration of access. Indeed, when said difference is negative, the access authorization duration determined for a flow of said portion is equal to the sum of:

said first determined duration for the flow in question,

said second duration determined for the flux in question, an amount equal to said third duration divided by the number of flows of said part.

According to a particular embodiment, the part of the stream considered corresponds to the streams to be sent whose priority level is greater than a predetermined threshold value. It is thus possible to favor higher priority flows than others when allocating access authorization time.

According to a particular embodiment, when said difference is negative and when the priority level of a stream is less than a predetermined threshold value, a zero access authorization duration is attributed to the stream in question. Thus access to the network is temporarily prohibited to less priority streams or deemed not priority, so as to free access time for higher priority flows. According to a particular embodiment, when said difference is positive and when the priority level of a stream is less than a predetermined threshold value, the access authorization time allocated to the stream considered is equal to said difference divided by the number of streams having a priority level lower than said threshold value. This allows a fair distribution of the total access authorization time between non-priority flows.

According to a particular embodiment, the step of obtaining said values is repeated for successive time intervals, the duration of the next time interval being increased at the end of the current time interval if, for at least one flow of said part, a value of average number of lost packets different from zero was obtained during said current time interval. In this way, the period during which the average values are determined has a variable duration. It is thus possible to adjust the duration of this period as a function of the packet losses observed. It is for example possible to take into account significant variations of these parameters by averaging over a longer period. The access authorization duration is better adapted to the actual need of the flow.

According to a particular embodiment, the maximum number of streams, to which a non-zero access authorization duration is allocated for said next time segment, is adjusted at the end of said current time interval, this maximum number being decreased if for at least one stream of said part, a value of average number of lost packets different from zero was obtained during said current time interval. In this way, it is possible to improve the quality of service for the streams sent, by limiting the number of flows actually issued, and thus by allowing to assign longer access authorization durations to the selected streams.

Correlatively, the invention also relates to a program comprising program code instructions recorded on a data processor readable by a data processor, for implementing the steps of a method according to the invention when said program is executed by said processor.

Another aspect of the invention is a system for managing access to a time division multiple access network over time segments of predetermined duration, for at least one station having at least one flow of time. data to be transmitted or received through said network, said system comprising means for obtaining, for each stream included in at least part of the streams to be transmitted or received during a next time segment, values representative of a bit rate, a packet length and a number of packets lost, said values being relative to a time interval prior to said next time segment,

means for determining, for each stream included in said part, an access authorization duration to said network intended to be allocated to the stream under consideration for the transmission or reception of said stream in question during said next time segment, said access authorization duration being determined according to said values obtained.

In a particular embodiment, the telecommunication system according to the invention comprises a data processor adapted to read an information medium on which is recorded a program executable by said processor, said program comprising program code instructions for the program. implementing the steps of a method according to the invention.

Other objects, features and advantages of the invention will become apparent from the description which follows, given solely by way of nonlimiting example, and with reference to the appended drawings in which: FIG. 1 schematically represents a configuration of FIG. a network to which the invention applies;

FIG. 2 is a timing diagram representing different time periods considered in the management of access to a radio network meeting the 802.11 standard; FIG. 3 is a time diagram representing, by way of example, different access authorization durations to a radio network complying with the 802.11 standard;

FIGS. 4a and 4b are timing diagrams each illustrating a particular mode of calculating access authorization durations during the method according to the invention;

FIG. 5 is a flowchart of the method according to the invention;

FIG. 6 illustrates the dependencies between the variables used in an implementation of the method according to the invention.

Figure 1 schematically illustrates the configuration in a radio network meeting the IEEE 802.1 1 standard.

Each station ST ₁ , ST _j , ST _k having a stream to send or receive dialogue with an AP base station of the network, also called access point ("Access Point") in the 802.11 e standard. This transmitter or access point is responsible for managing and regulating access to the radio network, that is to say managing the temporal scheduling of the streams to be transmitted by the various stations associated with it. For this purpose, the transmitter communicates with the different stations ST ,, ST _j , ST _k .

This dialogue comprises three phases:

during a first phase, the transmitter obtains a description of each RTP stream for which a station has sent a transmission request request: source address, destination address, source port, destination port, average length of an IP packet; a stream, rate measured over one second, number of lost RTP packets;

during a second phase, the access point determines, for each stream to be transmitted, a time slot (called TXOP, "transmission opportunity" in the 802.11 e standard) during which the transmission of this stream will be carried out; this time interval is defined by means, on the one hand, of an access authorization period during which the station concerned will be able to access the network, and, on the other hand, of a date from which this access authorization time will start running;

in a third phase, the authorization period allocated to a stream is transmitted to the station concerned;

When a station has been served, that is to say it has accessed the network, it must wait for a delay P _S ι (called "Scheduled Service Interval" or SI in 802.11 e) before being able to again access the network. This delay is common to all stations. For an access point, the value of the period P _S ι used is the minimum of the "Service_lnterval" values claimed by the audio or video applications generating the streams to be transmitted. In the determination of the value of the period P _S ι, the greatest constraint is due to audio streams that require a time interval of between 200 and 300 milliseconds to obtain a quality of service equivalent to that existing on a PSTN type network. (switched telephone network). In the case of a radio network meeting the 802.1 1 standard, a period of time Psi is divided into two parts (see Figure 2):

a first time period or time segment P _TDMA (time- _division multiple access period) during which deterministic access to the network is possible for transmission of RTP streams by the aforementioned time slot allocation mechanism TXOP to each authorized flow; a second period of time P _CSMA during which a random access to the network is possible for the transmission of flows other than the RTP streams.

The period P _TDMA is divided into time intervals, each interval being reserved for the transmission of one of the streams for which a transmission request has been made to the shared transmitter. Thus, according to the example of FIG. 3, the stations ST ₁ , ST _j , ST _k in turn take over the network, respectively during the time intervals TXOP (i, n), TXOP (J, n), TXOP ( k, n) for the first period Psi. For the next period Psi, the time slots TXOP (i, n + 1), TXOP (J, n + 1), TXOP (k, n + 1) are assigned respectively to these three stations for access to the network. The time slot allocation process is thus repeated at each period P _S ι for all the streams to be transmitted.

The IEEE 802.11e standard presents the specifications of a Quality of Service (QoS) mechanism. This mechanism allocates, deterministically, a duration of access authorization to the RTP streams to be transmitted. The 802.11 e standard specifies that, for each new stream to be transmitted, the TXOP time slot allocated to this stream is calculated based on the number of packets that have accumulated, in the transmission buffer of the station concerned by the transmission. of this stream, during the first period P _S ι, following the registration of the station with the base station. However, if the quantity of packets accumulated in the transmission buffer varies over time, in particular from one period Psi to another, the TXOP allocated according to the 802.11e standard does not follow these variations, since this standard assumes that this quantity does not vary. does not vary and remains the same as the quantity determined at the beginning of the program.

The invention differs from the solution recommended by the 802.11 e standard in that the algorithm for determining access authorization times adapts to the state of the network. More precisely, the invention makes it possible to take into account the variations over time of the characteristics of the flows, in particular as regards the flow rate, the packet length of the streams and the number of packets lost, and to adapt over time the values of the access authorization times assigned based on the values taken by these parameters during a time interval prior to accessing the network. In this way we take into account both the current need of the stations having access to the network (via the flow rate and the packet length of the streams considered) and the state of saturation of the network (via the number of packets lost for the networks). considered flows). The approach is global, since it is the values taken by these various parameters for the flows to be managed which are taken into account for the determination of the duration of access authorization for one of these flows. The method according to the invention is now described in more detail with regard to FIG. 5. This method is implemented by an access management system comprising notably the base station AP. The access management system includes a communication interface for communicating with the station or stations for which access to the network is to be managed.

The following notations are used in the rest of this document: Psi service period (in seconds) as defined in 802.11e (Scheduled Service Interval, or SI), including the PTDMA period and P _CSMA ! P _MI period of time (in seconds) multiple of Psi with P _MI = MI ^* P _S ι θ

Ml is a strictly positive integer;

Psc period of time (in seconds) multiple of Psi with Psc = SC ^* Psι where SC is a strictly positive integer;

N (i) number of packets of the stream i arriving in the transmit buffer of the station during the duration Psi

D (i) rate (in bytes per second) nominal filling of the transmission buffer associated with the stream i calculated during a reference period of duration Psi; this period is usually the first period Psi, following the registration of the station near the base station; this rate corresponds to the rate of the application generating the packets to be transmitted and filling the transmission buffer

M (i) nominal or average length (in bytes) of an IP packet during a reference period of duration Psi; this period is usually the first period P _S ι, following the registration of the station with the base station

Phy minimum physical rate (in bytes per second) of the radio network; this bit rate is the rate at which a transmission buffer associated with the stream i empties when the transmitting station of this stream is authorized to transmit;

Q (i) number of packets of stream i accumulating in the transmission buffer during a period P _S i rate (i, n) rate (in bytes per second) of stream i during the ^nth period Psi length (i , n) packet length (in number of bytes) of stream i during the ^nth period P _S ι txop (i, n) access authorization time (in seconds) required to send the N (i) packets of the stream i which have accumulated in the transmission buffer during the ^nth period P _S ι; lost (i, n) number of lost packets (not transmitted and / or not received) for stream i during the ^nth period P _S ι state (i, n) value indicating whether stream i is present or not during n ^6th period

Psi, preferably coded as a binary value; rate_m (i, n) average rate (in bytes per second) of the stream i over Ml periods P _S ι, calculated at the end of the ^nth period Psi length_m (i, n) average packet length (in number of bytes ) of the stream i over Ml periods P _S ι, calculated at the end of the ^nth period P _S ι txop_m (i, n) average access authorization time (in seconds) of the stream i over Ml periods P _S ι , calculated at the end of the ^nth period P _S ι lost_m (i, n) average number of packets lost for the stream i over Ml periods P _S ι, calculated at the end of the ^nth period Psi txop_a (i, n ) access authorization time (in seconds) actually allocated to stream i for transmission during the nth ^Psy period

During a period of time P _S ι the number of packets of the stream i accumulating in the transmission buffer is equal to:

N (i) = P _s , ^* (D (i) / M (i)) (1)

The access authorization time txop (i, n) corresponds to the time required to send these N (i) packets with a physical rate Phy. However, after the transmission of each packet, an acknowledgment is exchanged between the transmitting station and the access point.

The transmission of this acknowledgment, as well as the waiting times between the transmission of the packet and the transmission of this acknowledgment or between the transmission of this acknowledgment and the transmission of the next packet, require an additional time interval δt of known value. As a result, the necessary access authorization time txop (i, n) can be calculated as follows:

txop (i, n) = N (i) ^* ((M (i) / Phy) + δt) (2)

Between the time interval txop (i, n) and the following time interval txop (i, n + 1) (see Figure 3), the transmission buffer of stream i fills with packets. The number Q (i) of accumulated packets in the buffer can be calculated as follows:

Q (i) = (D (i) / M (i)) ^* (P ₃ , - txop (i, n)) (3)

Equation (3), however, is only valid if we assume that the rate D (i) and the length of a packet M (i) are invariable. However, if the rate of the application generating the packets to be transmitted increases, the access authorization time txop (i, n + 1) will not be sufficient to send all the packets accumulated during the ^nth period Psi. On the other hand, if the rate of the application decreases, the access authorization duration txop (i, n + 1) will be too long to send all the packets accumulated during the ^nth period P _S |. As a result, a fraction of the access authorization time txop (i, n + 1) will not be used.

The method according to the invention makes it possible to adapt the allocated authorization duration as a function of the state of the network, as a function of the variations of the flow rate of the different flows and as a function of the variations in the length of the packets of these flows.

The steps of the method according to the invention are described in more detail with reference to FIG. 5. The execution of this method assumes the use of 3 different clocks, the first of period Psi, the second of period P _MI and the third of period P _S c-

Thus, step 510 is executed cyclically, with a period equal to Psi. Given the manner in which this period is determined, the period P _S ι is likely to vary in time as a function of the periods requested by the stations. having streams to send.

Steps 520 to 560 are also executed cyclically, with a period equal to P _M ι with P _M ι = MI ^* P _S ι where M1 is a strictly positive integer.

Step 570 is executed cyclically, with a period equal to Psc with Psc = SC ^* P _S ι where SC is a strictly positive integer.

In step 510, the values of the variables rate (i, n), length (i, n), txop (i, n) and lost (i, n) relative to the ^nth period P _S ⁱ are stored in memory in a matrix M (n) for all the N flows i present, the line i of the matrix corresponding to the stream i: rate (l, n) length (l, n) txop (l, n) lost (l, n) rate (2, n) length (2, n) txop (2, n) lost (2, n)

M (n) = rate (N, n) length (N, n) txop (N, n) lost (N, n)

The values of the variables rate (i, n), length (i, n) and lost (i, n) are obtained from the parameters obtained by the access point during the first phase of the dialogue with the base station. The value of lost (i, n) is in particular calculated by the base station AP from the RTP sequence numbers sent during this first phase, by the difference between the sequence number of the last packet received and the sequence number of the previous packet received.

The value of txop (i, n) is calculated using equations (1) and (2) in which we replace M (i) (static parameter by length (i, n) and D (i) by rate (i, n), that is to say :.

txop (in) = Psi ^* (rate (i, n) / length (i, n)) ^* ((length (i, n) / Phy) + δt) (5)

In step 520, the values of the variables rate_m (i, n), length_m (i, n), txop_m (i, n) and lost_m (i, n) are calculated from the values of the matrix M (n) relating to the last Ml periods P _S ι- The values of the variables rate_m (i, n), length_m (i, n), txop_m (i, n) and lost_m (i, n) are stored in memory in a matrix M_m (n ). rate _ m (l, n) length _ m (l, n) txop _ m (l, n) lost _m (l, n) rate _ m (2, n) length _m (2, n) txop _ m ( 2, n) lost _m (2, n)

M _ m (n) - rate _ m (N, n) length _ m (N, n) txop_m (N, n) lost _m (N, n)

The value of the variable rate_m (i, n) is obtained by averaging the Ml values rate (i, n), rate (i, n-1), ... rate (i, n-MI + 1) relative at the last Ml periods P _S |. Similarly, the value of the variable length_m (i, n) is obtained by averaging the Ml values length (i, n), length (i, n-1), ... length (i, n-MI + 1).

The value of the variable lost_m (i, n) is obtained by averaging the Ml values taken by the variable lost (i, n), lost (i, n-1), ... lost (i, n-MI +1).

The value of txop_m (i, n) corresponds to the duration necessary to transmit with a physical rate Phy a stream having a bit rate equal to rate_m (i, n) and a packet length equal to length_m (i, n). The value of txop_m (i, n) corresponds to the duration necessary to transmit, with a physical rate Phy, an average number N_m (i, n) of packets equal to

N_m (i, n) = P _S ι ^* rate_m (i, n) / length_m (i, n) (6)

The number N_m (i, n) corresponds in fact to an estimate of the average number of packets arriving in the transmission buffer for the stream during the preceding period P _MI . The value of txop_m (i, n) is thus calculated using the following relation, modeled on the preceding relation (5):

txop_m (i, n) = P _S ι ^* (rate_m (i, n) / length_m (i, n)) ^* ((length_m (i, n) / Phy) + δt) (7)

The value of txop_m (i, n) can also be calculated by averaging the relative values Ml txop (i, n), txop (i, n-1), ... txop (i, n-MI + 1). at the last Ml periods P _S ι-

In step 530, the presence state of each of the streams i recorded in the matrix M_m (n) is determined. In case of absence of a stream i (which means that the emission of this stream is completed or is momentarily interrupted), the line i corresponds to the stream i is removed from the matrix M_m (n).

In step 540, the value of the variable NF _max corresponding to the maximum number of flows that will obtain an access authorization duration different from zero for the next period of duration P _TDMA is determined. This determination is made according to the MAX_FLUX number corresponding to the maximum number of streams that can be issued during a period of duration P _TDMA - This MAX_FLUX number is determined assuming that all these streams are given a minimum value TXOP_MIN of access authorization time. The TXOP_MIN value is the time required to send a single 1500-byte packet with an 11 Mbps radio rate (TXOP_MIN is 1 millisecond). To determine the value of MAX_FLUX, it is also necessary to take into account the duration δt1 necessary for the access point PA to send the station the value of the access authorization duration allocated, as well as an additional time interval δt2. existing between the transmit time slot allocated to a station and the transmit time slot allocated to the next station. So we have the following relation: P _TDMA = MAX_FLUX ^* (TXOP_MIN + δt1 + δt2) (8)

The value of MAX_FLUX can thus be determined according to P _TDMA st of the value TXOP_MIN.

The value of the maximum NF _max number of flows is readjusted taking into account the lost packets for the priority streams, the aim being to limit the number of packets lost for the highest priority streams in order to preserve the resources of the network. The access point has information on the priority level of each stream to be sent. In the context of the invention, a stream is said to have priority if its priority level is greater than a predetermined threshold value. The value of NF _max is between a minimum value, preferably equal to MAX_FLUX / 2 and a maximum value equal to MAX_FLUX.

The initial value of NF _max is chosen equal to MAX_FLUX / 2. The value of NF _max is then adjusted at each execution of step 540, that is to say at each period P _M ι. The procedure for adjusting the value NF _max is as follows. If for at least priority stream i the variable lost_m (i, n) has a value other than zero, the value of NF _max is decreased by one unit, provided that the new value of NF _max remains always within an interval [ MAX_FLUX / 2, MAX_FLUX] and the current number of streams to be sent is less than or equal to the new value of NF _max . If these two conditions are not fulfilled, the value of NF _max remains unchanged. If the value of the variable lost_m (i, n) is equal to zero for all priority streams, the maximum number of RTP streams is increased by one, provided that the value of NF _max is always within an interval [ MAX_FLUX / 2, MAX_FLUX].

After obtaining the _maximum number NF at step 540, if the current number of streams to be transmitted is greater than NF _max , only NF _max streams are selected for transmission, preferably among the streams having the highest priority levels. high. The unselected flows will be processed and transmitted during the next periods P _M ι, when the emission of the highest priority streams will make this transmission possible. If the current number of streams to be sent is less than or equal to NF _max , all the streams to be sent are selected.

In step 550, the value of the access authorization time txop_a (i, n + 1) allocated to this stream i for the next period Psi is determined for each stream selected in step 540. This access authorization duration txop_a (i, n + 1) is determined as a function of the average value txop_m (i, n) obtained in step 520 for this stream during the last Ml periods P _S ι- The mode determining the value txop_a (i, n) takes in account the state of the network, as it is known through in particular the lost_m (i, n) values obtained at step 520 for the priority streams.

If the stream i considered is not a priority stream, the allocated access authorization time is equal to the average value txop_m (i, n). If the stream i considered has priority, and the variable lost_m (i, n) has a value other than zero, the access authorization duration value assigned txop_a (i, n + 1) is the average value txop_m ( i, n) corrected by adding the time needed to transmit lost_m (i, n) lost packets. The estimation of the time necessary to transmit the lost packets is done for example by using average values of packet length length_m (i, n) and rate rate m (i, n). In other words: txop_a (i, n + 1) = txop_m (i, n) + (lost_m (i, n) ^* length_m (i, n) / rate_m (i, n)) (8) When a access authorization duration has been assigned to all priority flows, it is verified that the sum of the txop_a (i, n + 1) values assigned to the priority flows is less than or equal to the period P _TDMA - In other words , we calculate the sum:

^S TX0PM = Σ ^tX ° P - ^a ( ^{H + V} > i), priority flow then the difference:

A - P - Ç

^ ¹ TDMA ^ιJ 'TXOPM

If Δ <0 (as illustrated in FIG. 4a), the different access authorization duration values of the priority streams are corrected by subtracting from each the

quantity - where N _P is the number of priority flows, the different duration values

access authorization of non-priority flows being set to zero. In other words, for a priority stream:

Δ txop_a (i, n + 1) = txop_m (i, n) + (lost_m (i, n)) ^{* -} length (i, n) / rate_m (i, n)

N _P and for a non-priority flow: txop_a (i, n + 1) = 0,

Δ, being the absolute value of the difference Δ.

If Δ> 0 (as illustrated in FIG. 4b), the different access authorization duration values of the priority streams are unchanged and the non-priority streams share the remaining time interval Δ. In other words, for a priority stream: txop_a (i, n + 1) = txop_m (i, n) + (lost_m (i, n) ^* length_m (i, n) / rate_m (i, n)) and for a non-priority flow: Δ txop_a (i, n + 1) =

N NP where N _NP is the number of non-priority flows.

In all cases, it is ensured that the value txop_a (i, n + 1) allocated to a stream is at least equal to the minimum value TXOP_MIN as defined above.

At step 560 the values of the periods P _M ι and P _S c are re-evaluated. The initial value of the period P _M ι is chosen equal to P _S ι, that is to say that the matrix M_m of the average values is calculated at each period Psi. The value of P _MI varies between its minimum value equal to P _S ι and a maximum value, chosen for example equal to 4 ^* Psi- The maximum value of P _M ι is preferably a multiple of P _S ι, the multiplicative factor being a power of 2.

If, for at least one priority stream, the value of the variable lost_m (i, n) determined in step 520 is other than zero, the value of P _MI is increased, for example multiplied by two, provided that this new value remains less than or equal to the maximum value chosen for P _M ι- When the value of the variable lost_m (i, n) is equal to zero for all priority streams, the value P _M ι is decreased, for example divided by two, provided however that this new value remains greater than or equal to the minimum value chosen for P _M |.

The new value of P _MI determines the new periodicity with which steps 520 to 560 will execute.

Thus, when there is loss of packets for at least one priority stream, the duration of the period on which the calculation of the average values is carried out is lengthened progressively until reaching a predetermined maximum value. In other words, the method makes it possible to assign an access authorization duration which takes into account the fluctuations in the rate and the packet length over several periods P _S ι-

The value of P _S c varies between its minimum value equal to P _S ι and a maximum value, chosen for example equal to 2 ^* P _S |. The maximum value of Psc is preferably an integer multiple of P _S ι, the multiplicative factor being a power of 2. The initial value of Psc is chosen equal to its maximum value.

If, for at least one priority stream, the value of the variable lost_m (i, n) determined in step 520 is other than zero, the value of P _S c is decreased, for example divided by two, provided, however, that this new value remains less than or equal to the minimum value chosen for P _S c- When the value of the variable lost_m (i, n) is equal to zero for all the priority streams, the value of P _S c is increased, for example chosen equal to its maximum value.

The new value of the duration Psc determines the new periodicity with which step 570 will execute. The current period of duration P _S c therefore ends earlier than expected when, due to the readjustment of the value of P _S c , the value of the duration Psc is decreased. Conversely, the current period of duration Psc ends later than expected when, due to the readjustment of the value of P _S c, the value of the duration Psc is increased.

In step 570, the value of the state variable (i, n) is re-evaluated for all streams i of the matrix M_m (n). The value of the state variable (i, n) indicating whether the transmission of the stream i is complete or not, the rows of the matrix M_m (n) corresponding to a stream whose transmission is completed are deleted. As a result, when the next steps 520 to 560 are executed, the values of the relative variables lost_m (i, n) and txop_m (i, n) will no longer be taken into account for this stream.

Thus, when there is loss of packets for at least one priority stream, the duration of the period P _S c on which the state of presence of the streams is determined, is shortened progressively until reaching a predetermined minimum value. This improves the accuracy of taking into account the flows present.

The described control method therefore comprises four interdependent mechanisms of regulation:

the regulation R1 of the access authorization duration values by calculation of average values txop_m (i, n) and lost_m (i, n);

the regulation R2 of the period P _M ι as a function of the values lost_m (i, n);

the regulation R3 of the period P _S c as a function of the values lost_m (i, n);

the regulation R4 of the maximum number NF _max of stream RTP as a function of the values lost_m (i, n). Figure 6 illustrates the interdependence between these mechanisms and between the different variables, each of the variables being represented by a rectangle in solid lines bearing the name of this variable, each of the mechanisms being identified by a dashed rectangle surrounding the rectangles representing the variables determined during the execution of this mechanism. A dotted line arrow of a rectangle A representing one of the periods P _M ι, Psc to one of the rectangles representing one of the regulation mechanisms, indicates that the regulation mechanism is carried out with a periodicity equal to the value of the variable A. Thus the regulation mechanisms R1, R2, R3, R4 are executed with the period P _MI . A solid line arrow, from a rectangle representing a variable A to a rectangle representing a variable B, indicates that the determination of the value of the variable B is performed according to the value of the variable A. Thus,

the value of the variable rate_m (i, n) is determined from rate values (i, n); the value of the variable length_m (i, n) is determined from values of length (i, n);

the value of the variable lost_m (i, n) is determined from values of lost (i.n);

the value of the variable txop_m (i, n) is determined from values of rate_m (i, n) and length_m (i, n);

the value of the variable S _TXOPM is determined from values of txop_m (i, n);

the value of the variable txop_a (i, n + 1) is a function of the value of txop_m (i, n), STXOPM, NF _MA χ and state (in); the value of the variable P _MI is a function of values of lost_m (i, n);

the value of the variable P _S c depends on values of lost_m (i, n).

According to a preferred implementation, the various steps of the regulation method are implemented by means of a data processor of the base station PA and of computer program instructions executable by said data processor, which processor uses programs or subroutines designed to perform the different steps of this process.

Accordingly, the invention also relates to a computer program on an information medium, this program being capable of being implemented in a computer or by a data processor, this program comprising instructions adapted to the implementation of a method as described above.

This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other form desirable shape. The invention also relates to a data carrier readable by a computer or data processor, and comprising instructions of a computer program as mentioned above.

The information carrier may be any entity or device capable of storing the program. For example, the medium may comprise storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a magnetic recording medium, for example a floppy disk or a disk. hard.

On the other hand, the information medium may be a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention can be downloaded in particular on an Internet type network.

Alternatively, the information carrier may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question.

The method according to the invention makes it possible to assign an access authorization duration to a RTP stream as a function of the IP rate and the length of the IP packets generated by the audio or video application, of the state of charge of the network. network 802.1 1. The method also makes it possible to prioritize certain RTP streams, considered as priority. This results in several levels of quality of service, the quality of service being a function of the priority level of the stream.

The method does not preclude using a channel random access mode for streams other than RTP streams. Its implementation is therefore compatible with the mode of random access to the transmission channel.

Claims

A method of managing access to a time division multiple access network over time segments of predetermined duration (P _TDMA ), for at least one station (ST ₁ , ST _j , ST _k ) having at least one data stream to be transmitted or received through said network, the method comprising,

a step of obtaining, for each stream included in at least part of the streams to be transmitted or received during a next time segment, values representative of a rate (rate_m (i, n)), of a length a packet (length_m (i, n)) and a number of lost packets (lost_m (i, n)), said values being relative to a time interval prior to said next time segment,

a step of determining, for each stream included in said part, a duration (txop_a (i, n + 1)) of access authorization to said network allocated to the stream considered for transmission or reception said flow considered during said next time segment, said access authorization time being determined according to said values obtained.

2. Method according to claim 1 characterized in that it comprises a step of determining, for each flow included in said part, a first duration (txop_m (i, n)) corresponding to a time necessary to transmit or receive a stream having a rate and a packet length corresponding to the packet rate and packet length values obtained for the stream in question, the access authorization duration determined for said stream considered being a function of the first determined duration for said stream in question.

3. Method according to claim 2 characterized in that it comprises a step of determining, for each stream included in said part, a second duration corresponding to the time required for a transmission or reception of a number of packets corresponding to the value of the number of lost packets obtained for the stream in question, the access authorization duration determined for the said stream being a function of the said second determined duration for the said stream.

4. Method according to one of claims 2 or 3 characterized in that it comprises a step of determining a third duration corresponding to the difference (Δ) between a duration of said next time segment (P _TDMA ) and a sum ( S _TX O _PM ) of said first and second durations determined for the streams of said part, the access authorization duration determined for a stream being function of said third duration.

5. Method according to claim 4, characterized in that, when said difference is negative, the access authorization duration determined for a stream of said part is equal to the sum of: said first duration determined for the stream in question,

said second duration determined for the flow in question,

an amount equal to said third duration divided by the number of flows of said part.

6. Method according to any one of claims 1 to 5, characterized in that said portion corresponds to the streams to be transmitted or received whose priority level is greater than a predetermined threshold value.

7. Method according to any one of claims 4 to 6 characterized in that, when said difference is negative and when the priority level of a stream is less than a predetermined threshold value, a period of access authorization none is attributed to the flow in question.

8. Method according to any one of claims 4 to 7 characterized in that, when said difference is positive and when the priority level of a stream is less than a predetermined threshold value, the access authorization period. assigned to the flow considered is equal to said difference divided by the number of flows having a priority level lower than said threshold value.

9. Method according to any one of the preceding claims, characterized in that the step of obtaining said values is repeated for successive time intervals, the duration of the next time interval being increased at the end of the interval of time. current time if, for at least one stream of said part, a value of average number of lost packets different from zero was obtained during said current time interval.

10. The method as claimed in claim 9, characterized in that the maximum number of flows, to which a non-zero access authorization duration is allocated for said next time segment, is adjusted at the end of said current time interval, this number maximum being decreased if, for at least one stream of said part, a value of average number of lost packets different from zero was obtained during said current time interval.

1. Program comprising program code instructions, for carrying out the steps of a method according to any of claims 1 to 10 when said program is executed by said processor.

12. System (AP) for managing access to a time division multiple access network over time segments of predetermined duration (P _TDMA ). for at least one station (ST ₁ , ST _j , ST _k ) having at least one data stream to be transmitted or received through said network, said system comprising - means for obtaining, for each stream included in at least a part flows to be transmitted or received during a next time segment, values representing a bit rate (rate_m (i, n)), a packet length (length_m (i, n)) and a number of lost packets (lost_m (i, n)), said values being relative to a time interval prior to said next time segment, - means for determining, for each flow included in said part, a duration (txop_a (i, n + 1 )) access authorization to said network intended to be allocated to the stream in question for the transmission or reception of said stream considered during said next time segment, said access authorization time being determined according to said values obtained.

13. System according to claim 12, comprising

a communication interface for communicating with said at least one station,

a data processor adapted to read an information medium on which is recorded a program executable by said processor, said program comprising program code instructions for implementing the steps of a method according to any one of claims 1 to 10.