Passive measurement of available link bandwidth

1. A method of passively measuring available link bandwidth at a client device that receives media data over a network connection comprising:

receiving packets of a media stream at said client device, wherein one or more said receiving packets comprises a unique identifier indicating that one or more said receiving packets are associated with a macro burst or a micro burst, wherein said unique identifiers are indicated in timestamp fields of Transmission Control Protocol (TCP) headers, and wherein the unique identifiers are indicated in reserved 3-bit fields in the TCP headers;

sorting said receiving packets into one or more of said macro bursts or micro bursts based on said unique identifier; and

determining the link bandwidth available to said client device based at least in part on the time intervals between arrival times of the packets sorted into individual macro bursts or micro bursts,

wherein said macro bursts and said micro bursts each comprise a plurality of packets transmitted together by a sending device to regulate the sending device's transmission rate.

2. The method of claim 1 , wherein said unique identifiers are tags that were inserted into said receiving packets by said sending device.

3. The method of claim 1 , wherein said unique identifiers are burst delimiters that were transmitted by said sending device at the beginning of each said macro burst.

4. The method of claim 3 , wherein said burst delimiter is a burst header comprising a sequence number and a timestamp field.

5. The method of claim 1 , wherein said receiving packets are received at said client device over an HTTP connection.

6. The method of claim 1 , wherein said receiving packets are TCP packets.

7. The method of claim 1 , wherein each said macro burst is an HTTP partial response transmission and said unique identifiers are tags within HTTP range headers.

8. The method of claim 1 , wherein said receiving packets received as part of a media stream were transmitted as an adaptive bitrate stream.

9. The method of claim 8 , further comprising transmitting a request that subsequent portions of said adaptive bitrate stream be sent at a bitrate appropriate for said link bandwidth determined to be available to said client device.

10. The method of claim 1 , wherein said receiving packets received as part of a media stream were transmitted as a scalable media stream.

11. The method of claim 10 , further comprising transmitting a request for a data range of said scalable media stream corresponding to a version of said media stream appropriate for said link bandwidth determined to be available to said client device.

12. The method of claim 1 , wherein said client device receives said receiving packets of said media stream over a network from a content server.

13. The method of claim wherein said client device receives said receiving packets of said media stream over a network from a second client device as part of a video chat.

14. The method of claim 13 , further comprising:

transmitting feedback from said client device to said second client device, said feedback comprising information about said link bandwidth determined to be available to said client device,

wherein said feedback allows said second client device to adjust the encoding parameters of said media stream based on said link bandwidth determined to be available to said client device.

15. The method of claim 1 , wherein determining the link bandwidth available to said client device further comprises:

monitoring the arrival times of said receiving packets when said receiving packets are received;

determining if said unique identifiers have changed from one receiving packets to the next receiving packets;

determining a macro burst duration based on the time interval between the arrival times of receiving packets between which said unique identifiers changed; determining amount of data received during said burst duration;

determining said link bandwidth available to said client device during said macro burst duration based at least in part on total data received in said macro burst and said macro burst duration.

16. The method of claim 1 , further comprising determining an average link bandwidth over a moving window by averaging the link bandwidth determined to be available to said client device for each of a predetermined number of previously received said macro bursts.