If no apps or games were running in the background, the window increased to 650KB. When apps like Netflix were running in the background, the TCP Receive Window was set to 128KB. Snellman investigated, and found that when a game was running in the background, the console was setting the TCP Receive Window size to smaller than it typically would be – 7KB, at least 100-times smaller than expected. However, the reported download speeds on PS4 were below the theoretical Mathis limit.
Packet loss causes a theoretical limit on the bitrate of a connection, calculated using an equation referred to as the Mathis Equation. This is known as packet loss.Īs there is a maximum size for the amount of data that can be sent over TCP before waiting for an acknowledgement – the TCP Receive Window – the amount of time you have to wait for an acknowledgement can impair throughput. Until the sender receives confirmation, the next packet will not be sent.Īfter enough time has passed without an acknowledgement, it is assumed the data was lost in transit, and it is retransmitted. TCP ensures transferred data ends up where it must go, using a system of sending packets of data and waiting for them to be acknowledged by the recipient device. This is due to the way Transmission Control Protocol (TCP) works. Slow downloads on the PS4 can also be attributed to high latency, which can drastically reduce download speeds.Ĭalled the Bandwidth Delay Product, high ping to a server essentially affects download speeds from that server. Snellman said this may be a reason why users report faster download speeds after a firmware update, as the firmware installation requires a system reboot – closing all apps. To close an app, you hold the PS4 button on the controller and select “Close applications”. “This is not how other apps work – they remain in the background indefinitely until you explicitly close them.” “For games, the interaction model is that opening a new game closes the previously-running one,” said Snellman.
Snellman said Sony was “throttling downloads” when apps were running on his console in the background, and that the throttling was excessive. Swiss systems programmer Juho Snellman recently discovered why his PlayStation 4 downloads from the PlayStation Network were slow, publishing his findings.
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