Send Window Panel

The Send Window Panel is located on the top right/left corners of the Graphical User Interface and visualizes the send window used by the left and right TCP to regulate their data send rates. Since the send window limits how much data TCP can send at any one time, it acts as a "speedometer" indicating how fast TCP is sending data.

The Send Window Panel has the following appearance.

Send Window Panel Screenshot

The peach shaded portion of the vertical strip indicates how much of the send window is being used to send data. The higher the shaded portion, the faster the data is being sent; when the strip is completely shaded, the TCP is sending data at maximum speed.

The "UNA" and "END" tags indicate the sequence numbers at the start and end of the send window respectively. The "NXT" tag in the window indicates the position of the next byte to be sent in the send window and as such always lies on the top of the peached shaded portion. If a flow control algorithm that uses a congestion window (cwnd) is loaded, NXT (almost) always lies equal to or below the "cwnd" tag. Otherwise, the "NXT" tag is always at the position of the END tag as TCP is sending data at maximum speed without a congestion window to limit it.

The labels at the bottom of the window provide information on different parts of the send window. For example, the "Sent" label denotes the number of bytes that has being sent (i.e. the peach portion) in the TCP send window.

For more information on the tags and labels present in the Send Window Panel, please refer to Section 4.3.2 for Appendix 3 in the thesis.