Method and apparatus to estimate the sender's congestion window throughout the life of a TCP flow (socket connection)

1. A method of estimating a sender's congestion window throughout the life of a Transfer Control Protocol (TCP) flow, comprising:

observing data transmission sequence and sequence expected values from a sender;

observing receiver advertised window and ACK data and determining an estimated congestion window size based thereon;

determining an amount of data outstanding (S_OUT) to be sent from the sender;

determining maximum congestion window estimate during a monitoring period by determining if S_OUT is more than a prior determined maximum value whereby if a prior determined advertised window is less than S_OUT then S_OUT can be used as the congestion window estimate;

determining minimum congestion window estimate during a monitoring period by determining if S_OUT is lower than a prior determined minimum value whereby if a prior determined advertised window is greater than S_OUT then S_OUT can be used as the congestion window estimate: and

updating the maximum congestion window estimate or the minimum congestion window estimate to the S_OUT value, if it is determined S_OUT can be used as the congestion window estimate, wherein said determining an amount of data outstanding (S_OUT) to be sent from the sender, further comprises subtracting a last highest acknowledged sequence number from an observed highest outgoing sequence number.

2. A network test instrument for estimating a sender's congestion window, comprising:

a network interface for observing network traffic; and a processor, said processor including employing observed network traffic to determining data transmission sequence values sent from a server and determining receiver advertised window and ACK data and determining an estimated congestion window size based thereon said processor further determining:

an amount of data outstanding (S_OUT) to be sent from the sender;

a maximum congestion window estimate during a monitoring period by determining if S_OUT is more than a prior determined maximum value whereby if a prior determined advertised window is less than S_OUT then S_OUT can be used as the congestion window estimate;

a minimum congestion window estimate during a monitoring period by determining if S_OUT is lower than a prior determined minimum value whereby if a prior determined advertised window is greater than S_OUT then S_OUT can be used as the congestion window estimate; and

updating the maximum congestion window estimate or the minimum congestion window estimate to the S_OUT value, if it is determined S_OUT can be used as the congestion window estimate, wherein said determining an amount of data outstanding (S_OUT) to be sent from the sender further comprises subtracting a last highest acknowledged sequence number from an observed highest outgoing sequence number.