KR20050023429A - Adaptive dropping of prioritized transmission packets - Google Patents

Abstract

The series of information portions is provided to the transmitter, and the information portions have a threshold time that needs to be available to the receiver. The transmitter estimates whether the information portion can be transmitted by the transmitter at a time that will be available to the receiver before the threshold time. The transmitter then only transmits the information to the receiver if it is assumed that the portion of information will be transmitted at a time that will be available to the receiver before the threshold time.

Description

Adaptive dropping of prioritized outgoing packets {ADAPTIVE DROPPING OF PRIORITIZED TRANSMISSION PACKETS}

FIELD OF THE INVENTION The present invention relates to the field of transmission of media packets over a variable delay network, such as the Internet, or a packet loss network, such as a wireless LAN (near field network), for real time presentation.

For real-time multimedia representations, such as MPEG encoded broadcasts or live performances, each video and audio frame portion (frame or field) has a representation time for which the representation of the frame portion needs to begin to provide continuous audio and video. . In order to provide a frame part on time, each frame part has a decoding time in which all packets of the frame part must be available for transmission to the decoder for decoding of the frame part.

Networks such as the Internet or wireless LANs tend to have variable bandwidth resulting in variable delays. If the bandwidth is too suppressed, the packet will not reach in time, and the frame cannot be decoded and provided in time. In general, for video, the last frame is simply dropped and the previous frame is repeated, resulting in a loss in the human perceived representational quality.

For wireless LANs, delays and transmission failures are common and bandwidths change. First, the received signal power, and thus channel throughput, decreases as the distance between the sender and receiver increases. Secondly, a collision between two transmitters in the same wireless LAN network occurs and is handled by a random delay before retransmission. Third, packet errors arise not only from random interference but also from interference from other devices emitting signals in the same frequency band. The occurrence of packet errors is especially observed in 802.11b networks, which use the 2.4 GHz ISM band, where many other devices operate, such as microwave ovens, 2.4 GHz cordless phones, and other 802.11 b networks. For wireless LANs, not only are there packet delays due to variable bandwidth, but often retransmission limits prevent packets from being transmitted.

The media access (MAC) layer of the 802.11b receiver does not make any error correction. If the packet fails to error check the receiver MAC layer, the receiver does not transmit an acknowledgment and the MAC layer of the 802.11b transmitter retransmits the packet. The transmitter continues to retransmit the packet until an acknowledgment is received or until a predetermined retransmission limit is reached.

In order to reduce the need for retransmission, it has been proposed to add error correction for media transmission over wireless LAN. One proposed error correction technique involves separating audio / video information into two layers and transmitting these layers as different streams. One stream will contain more important information and the other will contain less important information. More error protection is provided for more important streams, and less error protection is provided for less important streams (this is called unequal error protection). Overhead increases, but audio / video quality increases even more, so for a given audio / video quality, the overhead actually decreases.

Another suggestion is to send all higher priority packets and drop all lower priority packets when throughput is inappropriate.

Those skilled in the art will pay attention to WO 01/65848 and WO 01/71981, which are all incorporated herein. This document describes a configuration for separating video streams into high and low priority streams and reducing errors in the high priority streams as compared to the low priority streams.

1 shows a method of the present invention.

2 shows a relevant part of an exemplary transmitter of the invention.

3 illustrates a relevant portion of an exemplary receiver of the present invention.

4 illustrates some components of an exemplary system of the present invention.

5 illustrates a network stack of an exemplary sender of the present invention.

6 illustrates the structure of an exemplary receiver of the present invention.

7 illustrates an exemplary algorithm of the present invention for adaptively dropping prioritized packets.

8 shows a variant of the determination module of the algorithm of FIG.

In the present invention, a series of information portions are provided to the transmitter, the information portions having critical times that need to be available to the receiver. The transmitter estimates whether the information portion can be transmitted by the transmitter at a time that will be available to the receiver before the threshold time. The transmitter then only transmits the information to the receiver when it is estimated that the portion of information will be transmitted at a time that will be available to the receiver before the threshold time.

When the transmitter determines that bandwidth and delay requirements do not allow all information to be available to the receiver, the transmitter drops packets that would not be useful.

For example, in a video-layering solution, if a transmitter determines that less important video information is not useful (due to delay conditions and other requirements), the transmitter never transmits. Even if all high priority packets cannot be sent in time, even high priority packets will be dropped.

In the present invention, the transmitter must recognize the delay requirement of the video stream to predict whether the packet transmission meets the delay requirement. The delay requirement can be standardized or the receiver needs to send an indication of the delay requirement to the transmitter.

There are two competing purposes. First, successful reception of all base layer packets needs to be maximized. Secondly, discarding enhancement layer packets needs to be minimized. Proper balance between these purposes increases throughput without substantially increasing overhead in transmission. The present invention balances these two purposes so that the perceived representation quality is increased with respect to quality when attempting to transmit all packets.

Further aspects and advantages of the invention will be readily apparent to those skilled in the art from the following detailed description with reference to the following figures.

1 illustrates an exemplary method of the present invention. In step 101, a series of pieces of information is provided to a transmitter. The information portion has a threshold time when it needs to be available to the receiver. Each frame portion may have a presentation time and a decoding time for which decoding needs to begin to ensure that the decoding frame portion will be available at the presentation time, wherein the decoding time and the presentation time are proportional to the play time of the representation.

The information part may be a packet of a media frame part (frame or field of a frame) for the multimedia representation. Such representation includes a plurality of frame portions, each frame portion comprising a plurality of packets of media data.

Providing the information portion may include separating the media information into high priority and low priority portions. The high priority portion may be the so-called base layer needed to decode the information portion, and the low priority portion may be the so-called enhancement layer used to improve the decoded information portion.

For example, the information portion for the media frame may include multiple high priority packets of the base layer, and multiple low priority packets of the enhancement layer. All high priority packets of the frame portion must be available to the receiver to begin decoding the frame portion. If all high priority packets are available, then all of the low priority packets available can also be used by the decoder to improve the frame portion. Packets with different priorities may be provided consecutively interleaved for a frame. Alternatively, all higher priority packets may be provided before providing any lower priority packets of the frame. This simplifies the decision as to which packet to send if the bandwidth is inadequate for transmitting all packets in the frame.

In step 102, the transmitter estimates whether the information can be transmitted at a time that will be available to the receiver before the threshold time.

The estimation may include determining a target time, estimating a transmission time, and comparing the target time with a sum of the current time and the estimated transmission time. The target time is related to when the information portion needs to be available to the receiver to decode the information portion (decoding time). The estimated transmission time is the time required to transmit the information portion to the receiver and make the information portion available to the receiver for decoding the information portion.

The target time depends on the start-up buffering provided by the receiver. Receiver buffering is generally limited by startup limitations, not storage costs. Viewers of the expression are often antagonized by startup times exceeding a few seconds. Increasing receiver buffering reduces the effect of short-term constraints on the throughput of the wireless channel. Receiver buffering is standardized so that the transmitter is aware of the buffer limit. Alternatively, the receiver may transmit an indication of the buffering limit (eg, start time, program play time, buffer size) to the transmitter. For example, the viewer may enter a startup time preference according to his dislike to slow the startup compared to the viewer's dislike for poor expression, and the receiver transmits the startup preference to the transmitter.

The target time may be based on the time when the information portion is provided. For a media frame, it may be assumed that the packets of the frame are provided as needed for decoding, so that the target time is based on the time at which the packet was provided. Alternatively, the decoding time can be read from the packet of the media frame and used as the target time. Since all high priority packets must be at the decoder to begin decoding the frame, the target time can be the same for all high priority packets of the frame. Also, in general, all lower priority packets should be available at decoding time to improve the frame. Thus, the target time can be derived from the time at which the first portion of the frame is provided, and the same target time can be used for all packets of the frame.

The estimation may be based on the priority of the information portion, so that the higher priority information portion is more likely to be transmitted than the lower priority information portion. For example, the target time or estimated transmission time for the information portion may be adjusted (by adding a factor or multiplying a factor) according to the priority of the information portion. For example, the target time may be calculated for the media frame by adding the time that the first packet of the media frame reaches the buffering time of the receiver. Different target times may be calculated for high priority frames and low priority frames by multiplying the lower delay tolerance and buffering time for higher priority packets for higher priority packets.

The information portion may be a packet of a video representation encoded based on a Group Of Picture (GOP) such as MPEG. In such encoding, the decoded I-frame, and the P-frame decoded based on the decoding of the previous I-frame, and the B decoded based on the previous and subsequent I or P-frames, regardless of the decoding of any other frame. There are different types of video frames (frames or frame fields) that include frames. In general, there are two B-frames in each P-frame. Thus, an I-frame is the most important frame because the decoding of all other frames in the GOP depends on decoding the I-frames of the GOP. P-frames are also important because the decoding of up to four B-frames depends on the decoding of each P-frame.

For GOP encoded video frames, the estimation may depend on the type of video frame, in a manner similar to that described above for packets with different priorities (base layer to enhancement layer packets).

The estimated transmission time may be fixed and may be based on the maximum packet size and the retransmission limit. Alternatively, the estimated transmission time may be estimated dynamically based on, for example, the retransmission count when the previous packet was transmitted. For example, the average transmission time of a previous predetermined number of packets may be used, or the average may be a time weighted average in which more weight is assigned to more recently transmitted packets.

For packets of variable size, the estimated transmission time of the packet may depend on the packet size. Larger packets take longer to transmit and tend to have many errors that require a lot of retransmission. The adjustment to the packet size may be predetermined or may be based on the average or time weighted average of a predetermined number of previous packets in the same size range.

In step 103, the packet is transmitted according to the estimate. That is, packets that are transmitted at the time that will be available at the threshold time and can be processed by the receiver are transmitted, and packets that are transmitted until the threshold time and cannot be processed by the receiver are dropped.

For media frames with packets with different priorities, all higher priority packets of the frame may be transmitted before transmitting any lower priority packets. Alternatively, packets with different priorities may be interleaved and transmitted when received. The advantage of sending higher priority packets earlier is that, when the bandwidth is reduced, higher priority packets are likely to reach the receiver automatically than lower priority packets.

In general, in video encoding, all packets of a frame portion must be available for decoding the frame portion. In this case, for example, if one packet of the frame portion is dropped because the retransmission limit is consumed, all remaining packets of the frame portion may be dropped because they cannot be used by the receiver.

On the other hand, when video information is separated into a base layer and an enhancement layer, only all base layer packets are needed to decode the frame part. If the enhancement layer packet is dropped, any remaining base layer packet should still be transmitted.

The estimate may comprise a plurality of estimates during transmission of the packet of the media frame portion whether or not all packets of the media frame portion may be transmitted by the transmitter at a time that will be available by the receiver before the threshold time; The transmission depends on a number of estimates for all packets in the frame portion. Thus, when it is assumed that some packets for the frame portion are not likely to be transmitted in time, the remaining packets for the frame portion are not transmitted.

When the information portion for the frame includes an information portion with a different priority, the estimate may be sent by the transmitter at a time when all packets of the media frame portion with priority will be available to the receiver before the threshold time. Whether it is possible to include multiple estimates during the transmission of packets of the media frame portion, and the transmission of packets with the same or lower priority depends on the multiple estimates for all packets of the frame portion having the priority. . Thus, when it is assumed that some packets for the frame portion having the priority will not be transmitted in time to decode the frame, the remaining packets of the frame portion for the same or lower priority are not transmitted.

2 shows a relevant part of an example of the transmitter of the invention. Source 110 provides a series of pieces of information that need to be available to the receiver at a threshold time. The source may include an input 111 from an antenna or cable connection for receiving satellite or terrestrial broadcast signals. In addition to or in the alternative to input 111, source 110 may include source unit 112, which may include, for example, a hard drive, a media player such as a DVD player, Or an electronic storage unit; Alternatively, the source unit may comprise a camera for capturing live performance.

The controller 113 controls the transmitter operation, including transmitting the information portion to the receiver. The controller estimates whether the information portion can be transmitted by the transmitter at a time that will be available to the receiver before the threshold time.

The transmitting unit 114 transmits the information portion to the receiver (shown in FIG. 3 below) according to the estimation. The controller sends a control signal to the transmitting unit to transmit the information portion. That is, the information portion is only transmitted by the transmitter unit if the information portion is likely to be available to the receiver before the threshold time.

The information portion may comprise a high priority, and the low priority information portion or source 110 may include a separator 115 for separating the provided information into a high priority information portion and a low priority information portion. It may include.

Buffer 116 is provided to store the information portion and allows processing of the information portion by the controller. For example, separator 115 may packetize the information into a low priority packet and a line of interleaved high-priority packets that are stored in a buffer, and then the controller may then place any low priority packets. The buffer is controlled to send all high priority packets to the transmitter before sending it to the transmitter.

Receiver unit 117 receives control information from a receiver (shown in the lower part of FIG. 3). Such information may include a request to receive the information portion and information indicating the startup time (buffer limit) of the receiver of FIG. 3.

3 shows a relevant part of an exemplary receiver of the present invention. The receiver unit 131 receives the information portion. The controller 132 controls the buffer 133 to buffer the information portion and transmit the information portion to the decoder 134 at a threshold time. The buffer 133 stores the information portion for a length of time until the start-up delay time, and then passes the information portion to the decoder 134. For example, when the information portion includes encoded video information, at decoder time the decoder receives the information portion for the frame portion, and at presentation time the decoder provides the decoded frame portion to the video display 135. During the representation, the video frame is normally displayed at a constant predetermined frame rate, but the decoding time may vary depending on the frame type, frame size and frame complexity.

User input 136 may be used to initiate the receipt of the information portion and may be used to select a startup delay. The controller 132 controls the transmitting unit 137 to send a request to the transmitter of FIG. 2 to receive the information portion and the startup delay of the receiver.

The following description describes an exemplary system of the present invention. Layered multimedia streaming systems are implemented using a client-server model. The encoded bit stream has several layers, including a base layer necessary to decode the video stream, and an enhancement layer used to improve decoding. An application running on the client initiates a streaming session by sending a request to the server to begin transmission. The protocol used to exchange management information may be a Real Time Streaming Protocol (RTSP). The server responds by sending a data stream to the client. The protocol used for the data stream is RTP (Real Time Protocol). The RTSP stream depends on TCP (Transmission Control Protocol) as the transport protocol while the RTP stream uses UDP (User Data Protocol). IP (Internet Protocol) is a protocol used at the network layer, and the link layer uses IEEE 802.11 wireless technology.

In FIG. 4, the broadcast information stream is received at 150 and separated by a separator 151 into a base layer stream 152 and an enhancement layer stream 153. The streaming server 154 passes the primary and enhancement layer streams to the MAC (media access) layer 155, which passes through the wireless transmitter 156. The primary and enhancement streams are delivered to the wireless receiver 158 via the wireless medium 157. The primary and enhancement streams are then delivered to a client application 159, the client application 159 providing the stream to the decoder 160, and the decoder 160 merging the streams, Decode the stream to provide a decoded multimedia representation.

5 illustrates a portion of a sender network stack. At application layer 170, video streaming server 171 provides a layered multimedia stream. The main task of the streaming server is to build RTP packets and to manage streaming sessions (including packet scheduling). The server bases its operation on the hint information available in the video file. The server reads the implicit information and generates two streams of RTP packets. One stream contains base layer packets and the other stream contains enhancement layer packets. Each packet includes an RTP payload field, and the RTP payload field value of the base layer packet is different from the RTP payload field value of the enhancement layer packet. Thus, the base layer packet can be distinguished from the enhancement layer packet based on different values for the RTP payload field.

The server also adds an RTP timestamp to each packet. The value of the RTP timestamp is the same for all packets in the frame and represents the time at which the packet is generated.

The streaming server delivers the stream to the operating system kernel 173 using a UDP socket. At a particular moment, the server sends all packets corresponding to the same video frame to the operating system kernel. First, the server sends all base layer (high priority) packets for the frame, and then the server sends all enhancement layer (low priority) packets for the frame. Thus, the stream is sent out in alternating cycles of base and enhancement layer packets. The operating system kernel passes the stream to the 802.11 device driver 174. Operating system kernel 173 and 802.11 device driver 174 are part of the operating system layer. The 802.11 device driver passes the stream to a wireless transmission device 175 that includes an 802.11 MAC layer 176 and an 802.11 physical layer 177 for radio frequency (RF) wireless transmission.

Since the system server (as described above) sends alternating cycles of base and enhancement layer packets, and the base and enhancement layer packets have different values in the RTP payload field, the start of the frame is easily detected. An alternative way of detecting frame boundaries is to use an RTP timestamp because it has the same value for all packets in the frame and has a different value than packets in adjacent frames.

Transmitting the base layer packets first is a good way to prioritize transmissions for loss of enhancement layer packets. After all of the base layer packets have been successfully transmitted, it is possible to determine whether to drop the enhancement layer packet according to the delay limit and system conditions.

6 shows the structure of an exemplary receiver of the present invention. The packet is received by the 802.11 network device 190 over the wireless link at 191. Packets are passed from the 802.11 network device 190 through the 802.11 device driver 192 and the operating system kernel 193. The 802.11 device driver 192 and operating system kernel 193 are part of the operating system layer 197 of the receiver. The packet then passes from the operating system kernel 193 to the client buffer 194 of the client application layer 195. RTP timestamps are used to identify which packets belong to a particular frame. At the decoding time for the frame, all packets for the frame are passed to the decoder 196.

7 illustrates an exemplary algorithm of the present invention for adaptively dropping prioritized packets. The horizontal dashed line separates the steps performed in different parts of the server. In step 210, the streaming video server generates base layer and enhancement layer packets, and in step 211, the server timestamps all packets for the frame with timestamp time, and operates all packets for the frame. Send to the system kernel. The server sends all base layer packets for the frame before sending any enhancement layer packets for the frame. In step 212, the packet for the frame is stored in the socket buffering of the operating system kernel. In step 213, the 802.11 device driver reads the packet type.

The detection module 214 detects the packet type and whether the packet is the start of a new video frame. In the detection module, at step 215, the driver determines if the packet is a base layer packet. If the packet is a base layer packet, then at step 216, the driver determines if the driver is already in a base layer cycle state. If the driver is not in the base layer cycle state, this is the first packet of the frame, and in step 217, the driver enters the base layer cycle state. Further, in detection module 214, if it is determined in step 215 that the packet is not a base layer packet, then the packet is an enhancement layer packet, and in step 218, the driver is in an enhancement layer state.

In the target time module 220 for estimating the target time, at the start of the transmission of a new frame, the driver estimates the target time, which is the last time any packet in the frame should reach the receiver. In the target time module, in step 221, a target time for the base layer packet and a different target time for the enhancement layer packet are calculated. The target time for the base layer packet is the sum of the RTP timestamp time of the first packet of the frame and the buffering time of the receiver multiplied by the delay tolerance for the base layer packet. The target time for the enhancement layer packet is the sum of the RTP timestamp time of the first packet of the frame and the buffering time of the receiver multiplied by the delay tolerance for the enhancement layer packet.

The delay tolerance for base layer packets should be much larger than the delay tolerance for enhancement layer packets. The value of this delay tolerance may be constant or may be tuned according to a particular application, a particular network, and network conditions.

The buffering time of the receiver is essentially a startup delay for the stream at the receiver. This may be a predetermined fixed amount. Alternatively, the buffering time may be a variable amount that must be received from the receiver. The transmission of the buffering time can be made using RTSP (Real Time Streaming Protocol), which is also the protocol used by the receiver to initiate a streaming session.

In this embodiment, the same base layer target time is used for all base layer packets, and the same enhancement layer target time is used by all enhancement layer packets.

This delay tolerance adjustment can be used to balance two contention purposes in the transmission of media packets to maximize perceived quality. The first purpose is to maximize the successful reception of all base layer packets. The second purpose is to minimize discarding of enhancement layer packets.

The calculation of the target time for the base and enhancement layer packets is based on the RTP timestamp time of the first packet of the frame. Another alternative is to use the frame rate to estimate the decoding time. However, the RTP timestamp time and frame rate are inaccurate indicators of decoding time (true target time). However, the decoding time can be derived from the RTP time, which can then be used for the calculation of the target time for the frame.

In the determining module 230, which determines whether to transmit the packet, the driver estimates the transmission duration of each packet and whether to transmit the packet according to the target time for the type of packet determined in the target time module in step 221. Determine. In the determining module, if the packet is a base layer packet, then at step 231, the transmission time of the base layer packet is estimated.

The average transmission time of a packet can be derived based on network conditions and the size of the packet. The time weighted average may be used for network conditions. Alternatively, actual network conditions can be ignored and worst case conditions can be used. In this case, the transmission time is fixed and does not need to be calculated. The worst case transmission time may be based on the maximum retransmission limit and the maximum packet size for the type of packet. The retransmission limit may be higher for base layer packets than for enhancement layer packets. In 802.11 wireless transmissions, the typical maximum packet size for video packets is 1500 bytes.

At step 232, the driver determines if the sum of the current time and the transmission time exceeds the target time for the base layer packet. If the target time in step 232 is exceeded, then in step 233, the base layer packet is dropped. Since the target time is the same for all base layer packets of the same frame, this means that all subsequent base layer packets are also dropped. Also, the target time for all subsequent enhancement layer packets of the frame will be the same and lower, so that all subsequent enhancement layer packets of the same frame will also be dropped.

If not at step 232, if the target time is not exceeded, then at step 234 the base layer packet is transmitted to the 802.11 device.

In the determining module, if the packet is an enhancement layer packet, then at step 235, the transmission time of the enhancement layer packet is estimated. The above discussion of the estimation of the transmission time for the base layer packet is also generally applicable to the estimation of the transmission time of the enhancement layer packet.

At step 236, the driver determines if the sum of the current time and the transmission time exceeds the target time for the enhancement layer packet. If the target time in step 236 is exceeded, the enhancement layer packet is dropped in step 233. Since the target time is the same for all enhancement layer packets of the same frame, this means that all subsequent enhancement layer packets are also dropped.

Otherwise in step 236, if the target time has not been exceeded, then in step 234, an enhancement layer packet is sent to the 802.11 device.

In step 240, the 802.11 device stores the packet to be delivered in the MAC buffer and then transmits this packet. If no ACK is received, the packet is retransmitted until an ACK is received or the retransmission limit is consumed.

8 illustrates a variation of the determination module 230 of the algorithm of FIG. 7. In the algorithm of FIG. 8, the determination of whether to send or drop a frame depends on the frame type. In the modified decision module 250, if the packet is a base layer packet, then in step 251, the frame type is determined. If the frame type is an I-frame, the tolerance at step 252 is set to the I-frame tolerance value for the base layer packet for the I-frame. Otherwise, if the frame type is a P-frame, then in step 253 the tolerance is set to the P-frame tolerance value for the base layer packet for the P-frame. Otherwise, if the frame type is a B-frame, the tolerance in step 254 is set to the B-frame tolerance value for the base layer packet for the B-frame. The tolerance value for an I frame must be greater than the tolerance value for a P-frame or a B-frame. Tolerance values for B-frames should be zero, for example.

In step 255, the driver determines whether the sum of the current time and the transmission time exceeds the sum of the tolerance and the target time for the base layer packet. If the sum of the target time and the tolerance in step 255 is exceeded, then in step 233 the base layer packet is dropped. Otherwise in step 255, if the sum of the target time and the tolerance is not exceeded, then in step 234, the base layer packet is transmitted to the 802.11 device.

In modified decision module 250, if the packet is an enhancement layer packet, then frame type is determined in step 261. If the frame type is an I-frame, then at step 262, the tolerance is set to the I-frame tolerance for the enhancement layer packet for the I-frame. Otherwise, if the frame type is a P-frame, the tolerance at step 263 is set to the P-frame tolerance value for the enhancement layer packet for the P-frame. Otherwise, if the frame type is a B-frame, the tolerance at step 264 is set to the B-frame tolerance value for the enhancement layer packet for the B-frame. Again, the tolerance value for an I frame must be greater than the tolerance value for a P-frame or a B-frame. Tolerance values for B-frames should be zero, for example.

In step 265, the driver determines whether the sum of the current time and the transmission time exceeds the sum of the tolerance and the target time for the enhancement layer packet. If the sum of the target time and the tolerance in step 255 is exceeded, then in step 233 the enhancement layer packet is dropped. Otherwise in step 255, if the sum of the target time and the tolerance is not exceeded, then in step 234, the enhancement layer packet is transmitted to the 802.11 device.

The present invention has been described above in connection with specific exemplary embodiments. Those skilled in the art will know herein how to modify such exemplary embodiments within the scope of the invention. The invention is limited only by the following claims.

As described above, the present invention is used in the field of transmission of media packets through a variable delay network such as the Internet or a packet loss network such as a wireless LAN (near field network) for real time representation.

Claims (35)

Providing a series of information portions to the transmitter, the information portions having a threshold time that needs to be made available to the receiver; Estimating whether the portion of information can be transmitted by the transmitter in time to be available to the receiver before the threshold time; Transmitting the portion of information to the receiver according to the estimation. Including, method. The method of claim 1, wherein the information portion is a packet of a media frame portion for a multimedia presentation, the representation comprising a plurality of frame portions, each frame portion comprising a plurality of high priority packets and a plurality of low numbers. Including packets of priority. 3. The method of claim 2, wherein each of the plurality of frame portions has a decoding time, and all high priority packets of the frame portion prior to the decoding time are received in time for presentation at a predetermined presentation time of the frame portion. It needs to be available to the receiver to decode a portion, wherein the decoding time and representation time are proportional to the play time of the representation. 4. The method of claim 3, wherein the lower priority packet is used to improve the frame portion during decoding when some but not all of the lower priority packets are available to the receiver at a threshold time. The method of claim 1, wherein providing the information portion comprises separating the information into information portions having different priorities. 2. The method of claim 1, wherein providing the information portion comprises: providing a media frame portion, improving each frame portion, the high priority information portion needed to decode the frame portion, and the frame portion. Separating only the low priority information parts used. 2. The method of claim 1 wherein the information portion comprises high priority and low priority packets of a media frame portion, and all high priority packets for one frame portion are any low priority for the frame portion. The method is provided before the packet of rank is provided. 2. The method of claim 1, wherein the estimating comprises: determining a target time when one portion of information needs to be available to the receiver, determining an estimated transmission time for transmitting the portion of information, and Making the portion of information available to the receiver; The estimating step includes determining whether the target time exceeds the sum of the estimated transmission time and the current time of the transmission; The portion of information is transmitted according to the determination. The method of claim 1, wherein the estimation depends on a buffering limit of the receiver. 10. The method of claim 9, wherein the receiver sends an indication of the buffering limit to the transmitter. The method of claim 1, wherein the estimating step depends on the priority of the portion of information to be transmitted. 10. The apparatus of claim 8, wherein the information portion comprises a high priority packet and a low priority packet, wherein the target time is greater in advance for the high priority packet than for the low priority packet. Depending on the determined delay tolerance, the high priority packet can be better received by the receiver than the low priority packet. 2. The method of claim 1, wherein the information portion is a packet of a media frame portion and the estimating step depends on the type of media frame of the packet. The method of claim 8, The information portion is the portion of the video representation encoded based on a group of pictures of different types of video frames, wherein the video frame is an I-frame that is decoded regardless of the decoding of any other frame, and a previous I or P-frame. A P-frame decoded based on a decoding of and a B-frame decoded based on a previous and subsequent I or P-frame, The target time depends on the type of video frame. 2. The method of claim 1, wherein the information portion is a packet of a media frame portion and the estimating step depends on the decoding time of the media frame portion of the information portion to be transmitted. 9. The apparatus of claim 8, wherein the information portion is a packet of a media frame portion of the representation, and each of the plurality of media frame portions is decoded in time for the packet of the frame portion to represent at a predetermined presentation time of the frame portion. With a decoding time that must be available at the decoder of the receiver, the target time of one information part depends on the decoding time of the frame part of the information part, and the decoding time and the presentation time of the frame part are dependent on the play time of the representation. Proportional. The method of claim 1, wherein the estimating step depends on the maximum size for the information portion. The information transmission method of claim 1, wherein the transmitting step retransmits the information portion until an acknowledgment from the receiver is reached that a predetermined limit on the number of retransmissions has been reached or that the portion has been successfully received without any unrecoverable error. And the estimating step depends on the retransmission limit. The method of claim 1, wherein the estimating step depends on the actual transmission time of the previously transmitted portion of information. 2. The method of claim 1, wherein the information portion is a high priority and low priority packet of a media frame portion, and transmitting all high priority packets for one frame portion is a low priority for the frame portion. A method that starts before the start of a packet transmission. The method of claim 1, wherein transmitting the portion of information depends on whether a previous portion of information has been successfully transmitted. 2. The method of claim 1, wherein the information portion has a different priority and the step of transmitting the information portion depends on whether a previous information portion having the same or higher priority is successfully transmitted. 2. The method of claim 1, wherein the information portion is a high priority and low priority packet of a media frame portion, and wherein the transmitting of the high priority packet comprises: a previous high priority packet for the same frame portion; And whether the low priority packet was transmitted depends on whether a previous high priority and a previous low priority packet were transmitted for the same frame portion. . The method of claim 1, wherein the method further comprises receiving a request from the receiver to initiate transmitting the portion of information to the receiver. 3. The transmission of a packet of a media frame portion as recited in claim 2 wherein the estimating step comprises: whether all packets of the media frame portion can be transmitted by the transmitter in time to be available to the receiver before the threshold time. Includes a plurality of estimates, and the transmitting step depends on the plurality of estimates for all packets of the frame portion, so that when it is estimated that some packets for the frame portion will not be transmitted in time, The remaining packets for the method will not be transmitted. 3. The method of claim 2, wherein the information portion for the frame includes an information portion having a different priority, and wherein the estimating step is such that all packets of the media frame portion of priority are made available to the receiver before the threshold time. And a plurality of estimates during the transmission of packets of the media frame portion as to whether they can be transmitted by the transmitter, wherein the transmission of packets of the same or lower priority is multiple for all packets of the frame portion of the priority. Depending on the estimation of the method, when it is estimated that some packets for the frame portion of the priority will not be transmitted in time, the remaining packets for the frame portion for the same or lower priority are not transmitted. . Separating the media stream for the presentation into a plurality of media streams having different priorities for transmission over a network having variable conditions, wherein the media stream has a predetermined schedule; Determining whether to transmit a portion of a plurality of media streams in accordance with the priority and network conditions such that the perceived quality of performance increases in proportion to an attempt to transmit all the plurality of media streams; Transmitting portions of the plurality of media streams in accordance with the determination. Including, method. 28. The method of claim 27, wherein the network is a wireless network, packets are transmitted sequentially, and each packet is transmitted and retransmitted until an acknowledgment is received or a retransmission limit is reached. A transmitter for transmitting a portion of information to a receiver, Means for providing a set of pieces of information that need to be available to the receiver at a threshold time; Means for estimating whether the portion of information can be transmitted by the transmitter in time to be available to the receiver before the threshold time; A transmitting device for transmitting the information portion to the receiver according to the estimation And a transmitter for transmitting the portion of information to the receiver. The method of claim 29, The transmitter further comprises means for receiving an indication of a buffering size from the receiver, And the estimating means is adapted to transmit a portion of information to the receiver, which depends on the indication of the buffering size at the receiver. The method of claim 29, The transmitter further comprises means for determining a decoding time of the information portion, And said estimating means is dependent on the decoding time of said information portion. The method of claim 29, Means for providing the information portion comprises means for separating the information into information portions having different priorities, The estimating means for transmitting the information part to the receiver, which depends on the priority of the information part. Means for requesting the transmitter to transmit the portion of information that should be available to the receiver at a threshold time; Means for buffering a portion of the information that arrives before the threshold time; Means for transmitting an indication of the buffering size to the transmitter. Included, receiver. The method of claim 33, The information portion is a packet for an encoded media frame, each of the plurality of media frames comprising a plurality of packets, The receiver further comprising a buffer for storing the packet, and means for decoding the packet at a threshold time, All packets for a frame contain the same time stamp, All packets for a frame are identified based on the same timestamp and passed together to the decoder. The method of claim 33, The information portion is a packet for an encoded media frame, each of the plurality of media frames comprising a plurality of packets; The receiver further comprising a buffer for storing the packet, and means for decoding the packet at the threshold time, The packet comprises a high priority packet and a low priority packet, Every packet contains an indication of the priority of the packet, A high priority packet for a frame is received before a low priority packet for the frame is received, All packets for a frame are identified by a change in the indication of packet priority and forwarded together to the decoder.