Round-trip estimation

Abstract

A networking arrangement is comprises a first network device for transmitting a data stream to a second network device over a network, the method comprises: transmitting a series of first packets to the second network device, each of the first packets having an transmission time and comprising a unique identification value, receiving, from the second network device, a second packet, the second packet indicating receipt of a least one of the first packets by the second network device, determining a standard round-trip time and determining a current round-trip time in dependence on a transmission time of an oldest first packet for which no indication of receipt has been received, and a receipt time of a most recently received second packet, determining an unused network bandwidth between the first network device and the second network device in dependence on the current round-trip time and standard round-trip time.

Claims

1. A method performed by a first network device, the first network device being configured to transmit a data stream to a second network device over a network at a bit rate, the method comprising: transmitting a series of first packets to the second network device over the network, each of the first packets having an associated transmission time and comprising a unique identification value, wherein the series of first packets comprises a first Real-time Transport Control Protocol, RTCP, packet and one or more Real-time Transport Protocol, RTP, packets, and wherein the unique identification value of each of the one or more RTP packets is a sequence number, receiving, from the second network device, a second packet, the second packet indicating receipt of at least one of the first RTCP packet of the series of first packets by the second network device, the second packet having a receipt time T.sub.4 at the first network device, wherein the second packet is a second RTCP packet further comprising a highest sequence number of an RTP packet of the series of first packets received at the second network device, determining a standard round-trip time in dependence on at least: a transmission time T.sub.1 of the first RTCP packet of the series of first packets, and a receipt time T.sub.2 of the first RTCP packet of the series of first packets at the second network device, the transmission time T.sub.3 of the second RTCP packet from the second network device, and the receipt time T.sub.4 of the second RTCP packet, and calculated as T.sub.4−(T.sub.3−T.sub.2)−T.sub.1, identify that for a first packet having a transmission time T.sub.1a>T.sub.1 no indication of receipt has been received at T4 in the second RTCP packet, during a period after the receipt time T4 of the second RTCP packet until before receipt of a next second RTCP packet: determining a current round-trip time in dependence on: a transmission time T.sub.1a of an oldest RTP packet of the series of first packets for which no indication of receipt has been received at the first network device, where T.sub.1<T.sub.1a<T.sub.4, and the receipt time T.sub.4 of the second RTCP packet, and wherein the current round-trip time is calculated as T.sub.4−T.sub.1a, determining whether an unused network bandwidth between the first network device and the second network device exists in dependence on the current round-trip time and standard round-trip time, wherein no unused network bandwidth exists when the standard round-trip time exceeds a first threshold and/or the current round-trip time exceeds a second threshold, and updating the bit rate for the transmitted data stream in dependence on the existence of the unused network bandwidth.

2. The method of claim 1, wherein the second threshold is greater than the first threshold.

3. The method of claim 1, wherein updating the bit rate for the transmitted data stream in dependence on the existence of the unused network bandwidth comprises: decreasing the bit rate for the data stream when the unused network bandwidth does not exist.

4. The method of claim 1, wherein updating the bit rate for the transmitted data stream in dependence on the existence of the unused network bandwidth comprises: increasing the bit rate for the data stream when the unused network bandwidth exists.

5. The method of claim 1, wherein updating the bit rate for the transmitted data stream in dependence on the existence of the unused network bandwidth comprises: decreasing the bit rate of the data stream when the standard round-trip time and/or the current round-trip time is increased.

6. The method of claim 1, wherein the data stream comprises at least one of a video stream and audio stream.

7. The method of claim 6, wherein updating the bit rate for the transmitted data stream comprises updating at least one of a target bit rate, average bit rate, resolution, colour depth, frame rate, sampling frequency, bit depth, and channel count.

8. The method of claim 1, further comprising: determining a used network bandwidth between the first network device and the second network device based on a total size of data packets transmitted between the first network device and the second network device per second; determining a network throughput value in dependence on the used network bandwidth, the network throughput value being an amount of data the first network device is able to deliver to the second network device per second; determining a total size of data packets buffered in the network based on a total size of data packets transmitted by the first network device and on a total size of data packets delivered to the second network device; determining a reserved bandwidth required to deliver data packets buffered in the network to the second network device within a time interval reasonable to empty buffers in the network; determining a remaining bandwidth for the data stream based on the network throughput value and the reserved bandwidth, and possibly based on a bandwidth used by an additional data stream; and updating the bit rate for the data stream in dependence of the determined remaining bandwidth for the data stream.

9. A first network device configured to transmit a data stream to a second network device over a network at a bit rate, the first network device further comprising a processor and a memory and being configured to: transmit a series of first packets to the second network device over the network, each of the first packets having an associated transmission time and comprising a unique identification value, wherein the series of first packets comprises a first Real-time Transport Control Protocol, RTCP, packet and one or more Real-time Transport Protocol, RTP, packets, and wherein the unique identification value of each of the one or more RTP packets is a sequence number, receive, from the second network device, a second packet, the second packet indicating receipt of a last one of the first RTCP packet of the series of first packets by the second network device, the second packet having a receipt time T.sub.4 at the first network device, wherein the second packet is a second RTCP packet further comprising a highest sequence number of an RTP packet of the series of first packets received at the second network device, determine a standard round-trip time in dependence on at least: a transmission time T.sub.1 of the first RTCP packet of the series of first packets, and a receipt time T.sub.2 of the first RTCP packet of the series of first packets at the second network device, the transmission time T.sub.3 of the second RTCP packet from the second network device, and the receipt time T.sub.4 of the second RTCP packet, and calculated as T.sub.4−(T.sub.3−T.sub.2)−T.sub.1, identify that for a first packet having a transmission time T.sub.1a>T.sub.1 no indication of receipt has been received at T.sub.4 in the second RTCP packet, during a period after the receipt time T.sub.4 of the second RTCP packet until before receipt of a next second RTCP packet: determine a current round-trip time in dependence on: a transmission time T.sub.1a of an oldest RTP packet of the series of first packets for which no indication of receipt has been received at the first network device, where T.sub.1<T.sub.1a<T.sub.4, and the receipt time T.sub.4 of the second RTCP, and wherein the current round-trip time is calculated as T.sub.4−T.sub.1a, determine whether an unused network bandwidth between the first network device and the second network device exists in dependence on the standard round-trip time and current round-trip time, wherein no unused network bandwidth exists when the standard round-trip time exceeds a first threshold and/or the current round-trip time exceeds a second threshold, and update the bit rate for the transmitted data stream in dependence on the existence of the unused network bandwidth.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the will become apparent from the following detailed description of an example, with reference to the accompanying drawings, in which:

(2) FIG. 1 is sequence diagram showing a standard round-trip determination according to RTCP,

(3) FIG. 2 is a network system according to an aspect of the description,

(4) FIG. 3 is a flowchart for a technique for determining an increased network latency and responding to the increased network latency accordingly according to an aspect of the description,

(5) FIG. 4 is a sequence diagram for packets used for an CRTT according to an aspect of the description,

(6) FIG. 5 provides a table with packet transmission and acknowledgement data,

(7) FIG. 6 is a flowchart of a technique for determining a bit rate of a transmitted media stream according to an aspect of the description,

(8) FIG. 7 is a diagram showing a set of round-trip time thresholds and corresponding bandwidth availability, and

(9) FIG. 8 is a flowchart of a method of selecting a suitable bit rate to reduce buffering of media stream packets on the network.

DESCRIPTION

(10) The present description relates to apparatuses and techniques for usage optimisation of available network bandwidth between two network connected devices. Throughout the description, the same reference numerals are used to identify corresponding elements.

(11) FIG. 2 is a diagram of a networked system 100 comprising first network device 20 connected to second network device 30 by network 10. In one embodiment, the network 10 is an ethernet network using Internet Protocol (IP) for the network layer, User Datagram Protocol (UDP) as the transport layer, and Real-time Transport Protocol (RTP) at the application layer. However, other protocol stacks can be envisaged where the same or substantially equivalent techniques may be applied. In FIG. 2, first network device 20 is configured to transmit a data stream 25 to the second network device 30 by network 10.

(12) In one embodiment, the data stream 25 is a media stream comprising a video stream and/or an audio stream. The media stream comprises a continuous video or audio content that is converted by first network device 20 from a first media format into the media stream. This conversion is known as media encoding and may be performed by a device or computer program known as a codec. The conversion process carried out by the codec may be performed using a number of configuration options that affect the resulting media stream. These options include the bit rate used to encode the media. Bit rate options may include employment of a target bit rate, an average bit rate. Other codec options may include the choice of video resolution, video colour depth, video frame rate, audio sampling frequency, audio bit depth, audio channel count, the choice of encoding algorithm, etc. In one embodiment, the configuration used to encode the media may be changed at any time during the streaming, so as to allow dynamic changes to the properties of the streaming media. This provides the significant advantage of allowing the streaming media to be adapted to the network environment it is being transmitted over. Although the present disclosure will now focus on adaptations of the bit rate configurations of the streamed media in response to the network environment, it is understood that any of the codec configurations options may be adjusted in response to a changing network environment to enable better usage of the available network bandwidth.

(13) After being encoded and transmitted across network 10, the data stream 25 is then received by the second network device 30 and decoded and played to a user at the second network device 30 or at a device connected to second network device 30. Alternatively, the media stream received by second network device 30 may be stored by second network device 30 or by a device connected to second network device 30.

(14) FIG. 3 shows an embodiment of the disclosure for rapidly determining an increased network latency and responding to the increased network latency accordingly. FIG. 3 will be described below with reference to FIG. 4 showing a sequence diagram for packets used for an CRTT according to an aspect of the description.

(15) In step 310, a series of first packets 40 are transmitted by the first network device 20 to the second network device 30 over the network 10. The first packets 40 may comprise the data forming the streaming media. In one embodiment, the first packets 40 comprise RTP packets and at least one RTCP packet. Each of the first packets 40 comprise a unique identification value 60 capable of uniquely identifying the first packet 40. The unique identification value 60 is shown as the ‘RTP packet sequence number’ in the embodiment shown in FIG. 5.

(16) In one embodiment, first network device 20 records the unique identification value 60 and time of transmission T.sub.1 of each of the first packets 40.

(17) In step 320, second network device 30 transmits a second packet 50 to the first network device 20. The second packet 50 may be a Real-time Transport Control Protocol (RTCP) packet. In one embodiment, the second packet 50 comprises an indication of receipt of a first packet 40 by the second network device 30. This may comprise the unique identification value 60 of the corresponding first packet 40. The second packet 50 may further comprise a time of receipt T.sub.2 of the first packet 40 at the second network device 30. The second packet 50 may further comprise a time of transmission T.sub.3 of the second packet 50 from the second network device 30. In an alternative embodiment, instead of time of receipt T.sub.2 and time of transmission T.sub.3, the second packet 50 comprises a ‘processing time’ which records the time between time of receipt T.sub.2 and time of transmission T.sub.3. i.e. (T.sub.3−T.sub.2). In one embodiment, first network device 20 records the time of receipt T.sub.4 of each of the second packets 50.

(18) In step 330, the first network device 20 determines a standard round-trip time (RTT) using at least one first packet 40 and: the time of transmission T.sub.1 of the first packet 40 the time of receipt T.sub.4 of a second packet 50 which contained an indication of receipt corresponding to the first packet 40, and the time of receipt T.sub.2 of the first packet 40 at second network device 30 subtracted from the time of transmission T.sub.3 of the second packet 50 from the second network device 30, i.e. (T.sub.3−T.sub.2).

(19) The RTT may then be calculated as T.sub.4−(T.sub.3−T.sub.2)−T.sub.1. In an example shown in the sequence diagram of FIG. 4 and the packet table of FIG. 5, a first packet 40 was transmitted at time 15.608353 seconds (T.sub.1) according to a clock on the first network device 20. Then a second packet 50 was transmitted from the second network device 30 and received at time 16.43566 seconds (T.sub.4) according to a clock on the first network device 20. The second packet 50 comprises the processing time (T.sub.3−T.sub.2), also known as the Delay Since Last Sender Report Packet (DLSR). The DLSR in this example is 0.826 seconds. The round-trip time is then determined by subtracting the delay between the second network device 30 receiving the first packet 40 and transmitting the second packet 50, is 0.001307 seconds, or 1.307 milliseconds≈1.31 milliseconds as stated in FIG. 5.

(20) In step 340, an alternative method is also used to estimate the round-trip time. In step 340 a current round-trip time is determined in dependence on a transmission time (T.sub.1) of a first packet 40 for which no indication of receipt has been received, and in dependence on a receipt time (T.sub.4a) of the most recently received second packet 50. The steps of this alternative method are shown in FIG. 6.

(21) In step 610 of FIG. 6, the first network device 20 identifies a first packet 40 having a transmission time (T.sub.1a), for which no indication of receipt has yet been received from second network device 30.

(22) In step 620, the first network device 20 identifies a time of receipt (T.sub.4a) of the most recently received second packet 50 (regardless of its contents).

(23) In step 630, the first network device 20 determines the current round-trip time (CRTT) to be a time difference between the transmission time (T.sub.1a) of the oldest first packet 40 for which no indication of receipt has been received, and the time of receipt (T.sub.4a) of the most recently received second packet 50. In an example, also shown in FIG. 6, where a first packet 40 was transmitted at time 16.136001 seconds (T.sub.1a) and a second packet 50 was received at time 16.43566 seconds (T.sub.4a) according to a clock on the first network device 20, the round-trip time, is 0.299659 seconds, or 300 milliseconds.

(24) Instead of relying upon just the RTT calculated using the most recently received second packet 50 (e.g. RTCP reports) or waiting for the next RTT to be calculated when next second packet 50 arrives, the above techniques compare the transmission time of the oldest unacknowledged data packet (i.e. an ordinary RTP packet, not an RTCP report) and the receipt time of the latest received RTCP report to provide another useful determination of the latency of the network 10. This does not require using a stale RTT calculated using an older first packet 40 and corresponding second packet 50 and can be calculated using data packets transmitted more recently than those used for the RTT.

(25) In at least one situation, detecting whether an unused network bandwidth exists can be especially advantageous. For example, in situations involving low latency, live streaming video, such as live sport, where huge pre-buffers are undesirable for the latency they introduce, it is critical that the networked system 100 is able to respond as quickly as possible to changes in the availability of unused network bandwidth 90.

(26) As shown in FIG. 7, optionally, the step of determining an existence (i.e. availability) of unused network bandwidth 90 comprises determining that the standard RTT exceeds a first threshold 710 and/or that the CRTT exceeds a second threshold 720. Where the first threshold 710 and/or second threshold 720 are exceeded, it is determined that no unused network bandwidth 90 exists or is available. Optionally, the second threshold 720 is greater than the first threshold 710. In one embodiment, a suitable first threshold 710 value is 200 milliseconds. In one embodiment, a suitable second threshold 720 value is 300 milliseconds. Suitable threshold values can be selected in dependence on system design and testing.

(27) Returning to FIG. 3, in step 350, first network device 20 determines the existence or non-existence of unused network bandwidth 90 between the first network device (20) and the second network device (30) in dependence on both the CRTT and the standard RTT. Where the first threshold 710 and/or second threshold 720 are exceeded, it is determined that no unused network bandwidth 90 exists or is available. Where neither the first threshold 710 nor the second threshold 720 are exceeded, it is determined that there may be unused network bandwidth 90.

(28) In step 360, first network device 20 may be configured to alter the codec configuration to update the bit rate for the transmitted data stream 25 in dependence on the determined unused network bandwidth 90.

(29) Optionally, the step of updating the bit rate for the transmitted data stream 25 in view of the determined availability of unused network bandwidth 90 comprises decreasing the bit rate for the data stream 25 when the unused network bandwidth 90 is not available. That the unused network bandwidth 90 is not available could also be stated as the unused network bandwidth 90 is insufficient for the transmission of the data stream at a certain bit rate and thus that the bit rate for the data stream has to be decreased in order to enable the transmission. In other words, an available network bandwidth for transmission of the data stream at the certain bit rate is insufficient, and therefore, the bit rate has to be decreased in order to enable the transmission of the data stream. That unused network bandwidth 90 is available (or ‘exists’) means that the amount of available unused network bandwidth is sufficient for transmitting the data stream at a higher bit rate and therefore the bit rate of the data stream is increased. In one embodiment, the bit rate for the transmitted data stream 25 is decreased when the standard round-trip time and/or the current round-trip time is increased. For example, this may be the case when the standard round-trip time and/or the current round-trip time is increased even if unused network bandwidth 90 is still available. The reason for decreasing the bit rate is to avoid or reduce delays and congestions over the network.

(30) In one embodiment, the bit rate for only the video stream and not for the audio stream is adjusted in response to changes in network latency. This has the advantage that a recipient may not detect a reduced bit rate of the video stream while he/she may be more sensitive to a reduced bit rate in the audio stream, causing a deteriorated experience of the streamed media.

(31) In an embodiment shown in FIG. 8, a method is provided for selecting a suitable bit rate for encoding of the data stream 25 that will allow the system 100 to reduce a buffering of the first packets 40 on network 10.

(32) In step 810 of FIG. 8, a used network bandwidth 95 between the first network device 20 and the second network device 30 is determined. The used network bandwidth 95 may be determined based on a total size of data packets transmitted between the first network device 20 and the second network device 30 per second. Alternatively, the use of other methods of determining a used network bandwidth 95 over a network 10 known in the art may be envisaged.

(33) In step 820, a network throughput value 96 is determined in dependence on the used network bandwidth 95. The network throughput value 96 corresponds to an amount of data that the first network device 20 is able to deliver to the second network device 30 per second. This value may be known in advance, e.g. as part of a theoretical network bandwidth, or it may be periodically determined. The use of methods for determining a network throughput value 96 of a network 10 known in the art may be envisaged.

(34) In step 830, a total size of the first packets 40 buffered in the network 10 is determined based on a total size of data packets transmitted by the first network device 20 and on a total size of data packets delivered to the second network device 30. The total size of the first packets 40 may be determined as a function of the total number of the first packets 40, the average size of the first packets 40, and/or the amount of data transmitted using the first packets 40.

(35) In step 840, an amount of reserved bandwidth 97 is determined that will enable the delivery of the first packets 40 buffered in the network 10 to the second network device 30 within a time interval reasonable to empty buffers in the network 10.

(36) In step 850, an amount of remaining bandwidth 98 is determined for the data stream 25 based on at least the network throughput value 96 and the reserved bandwidth 97. In one embodiment, the remaining bandwidth 98 is determined for the data stream 25 based on the network throughput value 96, the reserved bandwidth 97, and the bandwidth used by an additional data stream 26.

(37) In step 860, the bit rate for the data stream 25 is updated in dependence of the determined remaining bandwidth 98 for the data stream 25.

(38) In one embodiment, the CRTT determined in steps 610-630 can be used independently of RTT to determine unused network bandwidth 90 and to determine suitable media streaming bit rates over network 10. In this embodiment, the CRTT may be used alone or in combination with other methods of determining unused network bandwidth 90 known in the art.