WO2008128958A1

WO2008128958A1 - Method and device for controlling a data rate

Info

Publication number: WO2008128958A1
Application number: PCT/EP2008/054662
Authority: WO
Inventors: Wenrong Weng
Original assignee: Siemens Aktiengesellschaft
Priority date: 2007-04-23
Filing date: 2008-04-17
Publication date: 2008-10-30
Also published as: EP2140629A1; DE102007019090B3

Abstract

The invention relates to a method and a device for controlling a data rate having a predefined transmission delay and a current transmission delay, wherein the following steps are performed: -Lowering the data rate, if the predefined transmission delay is smaller than the actual transmission delay and a differential current transmission delay exceeds the time ≥ 0, - Increasing the data rate, if the predefined transmission delay is greater than the current transmission delay and a differential current transmission delay exceeds the time ≤ 0.

Description

description

Method and device for regulating a data rate

The invention relates to a method according to the preamble of claim 1 and an apparatus for regulating a data rate of an application according to the preamble of claim 5.

In a transmission of data, a quality and a throughput of a data transmission through a bandwidth, a delay and a packet loss rate are limited. The delay can be divided into two categories, real-time and non-real-time transmission. In a classic OSI (Open Systems Interconnection) layer model, a lowest layer describes the physical layer, which normally operates in real time. Since a data transfer rate, e.g. in kbit / s, the physical layer is limited, a buffer system is introduced, which prevents an over- or underrun of the physical transmission path. Depending on the storage management policy, higher layer applications may be executed in real time or non-real time.

To avoid overrun, data is written to the transmit buffer, causing a delay in transmission. The greater the level of the buffer increases, the greater the delay. To avoid delays for real-time applications (applications), the higher layer application should deliver its data at a data rate that is below the physical layer's data rate. This requirement is particularly difficult to meet if the bandwidth of the physical layer varies. Furthermore, there are difficulties with this requirement because the application may not have information about the current available bandwidth, such as GSM or GPRS (GSM Global System for Mobile Communications, GPRS - General Packet Radio service). To avoid overrun and minimize data transfer delays, applications would have to keep their data rate below the lowest-guaranteed physical-layer data rate, leaving bandwidth unused under good transmission conditions.

Even in systems such as UMTS (UMTS - Universal Mobile Telephony System), which guarantee bandwidth for an application, a maximum available bandwidth can only be approximately exploited, for example, with a small bandwidth mismatch, an accumulated data surplus a time delay of the transmission leads.

In another system, such as TCP / IP (IP - Internet Protocol, TCP - Transmission Control Protocol), the rate control is determined based on a round trip delay and a timeout window. In the case of a congestion of the data transmission, such a system immediately reduces its transmission rate and subsequently increases the transmission rate step by step. Other such systems allow filling of the transfer buffer only if a level of the buffer falls below a predetermined limit and prevent filling of new data of an application if the buffer level exceeds a predetermined maximum threshold. This results in non-uniform data streams between the application and the buffer, since the data may either be written to the buffer or not, depending on the level of the buffer. In the event that the buffer level of the application is not directly accessible to the application, the application must, for example, use an auxiliary application to obtain information about which data rate may be transferred to the buffer or via the physical layer. This causes an additional delay, which is unacceptable for real-time applications.

Thus, the object is to provide a method and a device with which a transmission of data at different the bandwidths of a transfer layer can be controlled in a simple and efficient manner.

This object is solved by the independent claims. Further developments of the invention can be found in the dependent claims.

The invention relates to a method for regulating a data rate of an application, with a predefinable transmission delay and a current transmission delay, in which the following steps are carried out:

Decreasing the data rate if the predetermined transmission delay is less than the current transmission delay and a differential current transmission delay over time is greater than or equal to zero;

Increasing the data rate if the predetermined transmission delay is greater than the current transmission delay and the differential current transmission delay over time is less than or equal to zero;

Furthermore, the data rate can be left unchanged if none of the given queries are true.

With the aid of this method for regulating the data rate of the application, it is achieved that on the one hand the current transmission delay for transmitting a data packet is set to a small value and, on the other hand, that a fill level of a data buffer is kept low. By linking the current transmission delay with the differential transmission delay, it is achieved, in particular, that the data rate can be brought to the maximum available transmission bandwidth, ie maximum data rate, without the current transmission delay rising too much or even at all. Furthermore, the above-mentioned approach is characterized in that no information about buffer levels is needed because the procedure is controlled solely on the basis of the transmission delay.

In a preferred extension, the method for regulating is carried out at predeterminable time intervals. This ensures that the data rate can be adapted to current conditions of the physical data transmission layer.

If the predefinable time interval is selected as a function of a difference of the predefinable transmission delay from the current transmission delay and / or a value of the differential current transmission delay over time, then the predefinable time interval can be adapted individually to the current transmission delay. If, in addition, the predefinable time interval is selected to be inversely proportional to the difference and / or an amount of the value, the predefinable time interval is shortened if the difference and / or the value of the value increases or the predefinable time interval increases, if the difference and / or the Amount of the value is reduced.

If the reduction and / or increase of the data rate is carried out in each case in a step of about 5% of the available maximum data rate, it has been shown in practice that both a stable regulation of the data rate and simultaneously rapid adaptation to changes in the current data rate. hurry transmission delay is achieved.

The invention also relates to a device for regulating a data rate, wherein there is a predetermined transmission delay and a current transmission delay, the device comprising processing means and the processing means being adapted to reduce the data rate if the predetermined transmission delay is less than the current transmission delay and a differential ak - For example, if the predetermined transmission delay is greater than the current transmission delay and the differential current transmission delay over time is less than or equal to zero.

With the aid of the device, the method for regulating the data rate can be implemented and executed.

The invention will be explained in more detail with reference to drawings. Show it :

Figure 1 is a flow chart for carrying out a method for

Regulating a data rate of an application;

FIG. 2 shows a device for regulating the data rate of an application.

Elements with the same function and mode of operation are provided in FIGS. 1 and 2 with the same reference numerals.

FIG. 1 schematically shows a flow chart for carrying out a method for regulating a data rate DD of an application. The application is, for example, a voice application for the transmission of voice data packets over the Internet. The invention is generally applicable to any type of data for voice, music, image, video, text, executables, presentations and others.

The diagram starts in state STA. In the following first step Sl, a predetermined transmission delay C and a current transmission delay TD are considered. The predetermined transmission delay C is an end-to-end delay for transmitting the data packet from a transmitter to a receiver, for example C = 100 ms. The current transmission delay TD indicates how long transmitted data packets are currently being transmitted from the transmitter to the receiver. ger. The current transmission delay is, for example, 50 ms.

In addition, it is determined in step S1 how the current transmission delay TD has changed over time t, that is to say the differential current transmission delay over time t, ie d (TD) / d (t). This differential indication is represented by a reference symbol "d." It is well known to a person skilled in the art of communication technology how the mathematical equation d (TD) / d (t) can be realized, for example by means of a difference quotient. Procedure, so that will not be discussed further.

In the second step S2, it is determined whether the data rate DD should be increased, decreased or kept constant. The following rule is processed:

(a) if TD> C and d (TD): d (T)> = 0, then reduce the data rate DD;

(b) if TD <C and d (TD): d (T) <= 0, then increase the data rate DD;

(c) otherwise leave the data rate unchanged,

where "<=" means less than and "> =" means greater than or equal.

In the present example, TD = 50 ms, C = 100 ms, i. TD <C and, for example, - d (TD) / d (t) = -1.2, i. d (TD) / d (t) <0.

This example corresponds to case (b), so that the data rate is reduced. If, for example, d (TD) / d (t)> 0, then the data rate would remain the same, see case (c). The term d (TD) / d (t) indicates whether the current transmission rate increases, stays the same or decreases over time. In a third step S3 this becomes the second step

52 evaluated result and the data rate DD of the speech data in response to the result of step Sl increased, decreased or left unchanged. The change of the data rate for the speech data of the speech application may e.g. by switching over a coding mode, as with AMR NB (AMR - Adaptive Mulirate, NB - narrow band).

The change of the data rate takes place, for example, in 5% steps of a maximum data rate MDD. If the data is transmitted via a GSM channel with a maximum data rate MDD = 9.6 kbit / s, the change of the data rate DD is carried out in 5% * 9.6 kbit / s = 480bit / s steps.

In the last step with the reference character END, the method for regulating the data rate is ended.

In an alternative, after completion of the third step S3, the steps S1, S2, S3 may be repeatedly executed. In Figure 1, this is illustrated by the dashed path. This repeated execution of the steps Sl to

53 can be performed at predetermined intervals TA. The predefinable time intervals can be selected as a function of a difference U = C - TD and / or a value W = d (TD) / d (t).

If the difference is U = C - TD = 100 ms - 50 ms = 50 ms, then, for example, the predefinable time interval TA = 1 second is selected. If, on the other hand, the difference U = 10 ms, then the specifiable time interval TA = 5 seconds is selected. In this case, the predefinable time interval was selected in inverse proportion to the difference U, it being possible to perform a normalization with multiplication of a constant. In the present example, the constant was chosen to be 1/20 so that TA = 1 / 50ms * 1/20 = 1 second.

Instead of the difference U, the value W or a combination of the difference U and the value W can also be used to determine the specifiable time interval. The time intervals used in this example are merely exemplary. The method for regulating the data rate may also select other time intervals, care being taken to establish a stable control.

FIG. 2 shows a device for regulating the data rate DD. In this case, the device V comprises a processing means VM, which executes the steps S1 to S3 from FIG. In this case, the predetermined transmission delay C and the current transmission delay TD are introduced to the processing means VM. From this, the processing means VM determines the differential current transmission delay and information, according to step S2, as to whether the data rate should be increased, reduced or left unchanged. FIG. 2 depicts a new data rate X (DD) on the basis of the result of this determination. In addition, the maximum data rate MDD can be explicitly transferred to the processing means VM. This is indicated in Figure 2 with a dashed arrow.

The device for regulating the data rate is integrated, for example, in a PC, a video distribution server or a portable device, in particular a mobile telephone, and can be implemented and executed in hardware, software or a combination of hardware and software.

Should the bandwidth of the physical transmission system be subject to strong fluctuations, it can be achieved by using predeterminable levels in increasing or decreasing the data rate, a rapid approximation to the currently underlying bandwidth.

Claims

claims

Method for regulating a data rate (DD), having a predetermined transmission delay (C) and a current transmission delay (TD), characterized in that the following steps are carried out:

Decreasing the data rate (DD) if the predetermined transmission delay (C) is less than the current transmission delay (TD) (TD> C) and a differential current transmission delay (TD) greater than or equal to zero (d) over time (t) (TD) / d (t)> = 0), increasing the data rate (DD) if the predetermined transmission delay (C) is greater than the current transmission delay (TD) (TD <C) and the differential current transmission delay (TD ) are less than zero (d (TD) / d (t) <= 0) over time (t).

2. The method according to claim 1, characterized in that the method for controlling in predetermined time intervals (TA) is performed.

3. The method according to claim 2, characterized in that the predeterminable time interval (TA) as a function of a difference (U) of the predetermined transmission delay (C) from the current transmission delay (TD) and / or a value (W) of the differential current transmission delays - (TD) over time (t) (d (TD) / d (t)) is selected.

4. The method according to claim 3, characterized in that the predeterminable time interval (TA) is chosen inversely proportional to the difference (U) and / or an amount of the value (W).

5. Method according to one of the preceding claims, characterized in that the reduction and / or increase of the data rate (DD) in each case in a step of about 5% of an available maximum data rate (MDD) is performed.

6. A device (V) for regulating a data rate (DD), wherein a predetermined transmission delay (C) and a current transmission delay (TD) are present, characterized in that the device (V) comprises a processing means (VM), wherein the processing means ( VM) is designed to reduce the data rate (DD) if the predetermined transmission delay (C) is less than the current transmission delay (TD) (TD> C) and a differential current transmission delay (TD) over time (t) is greater than zero (d (TD) / d (t)> = 0) for increasing the data rate (DD) if the predetermined transmission delay (C) is greater than the current transmission delay (TD) (TD <C) and the differential current transmission delay (TD) over time (t) is less than zero (d (TD) / d (t) <= 0).