A method of sending hypertext transfer protocol (HTTP) adaptive streaming (HAS) content from a content source to a client over a transmission control protocol (TCP) connection between the content source and the client may include receiving a request for one or more first HAS data chunks from the client; sending the one or more first HAS data chunks to the client; generating idle delay values indicating an amount of delay in the TCP connection during an idle time period, the idle time period being a time period over which no HAS data chunks are being sent from the content source to the client; receiving a request for a second HAS data chunk from the client; setting the size of a starting TCP congestion window based on the idle delay values; and sending the second HAS chunk to the client using the starting TCP congestion window.