lan cable and wifi discrepancy

[#1]

So, Im wondering - Ive been running some speed tests since recently getting fibre.   I've just noticed that running on the lan cable I get around 27/28mbps but the wifi returns 19/20mbps.   I'm sat next to the router so there is no real distance issues.  Is this generally correct?  Should it be that different?

[#2]

Hi there,

Speed tests over WiFi are always slower than via ethernet just due to differences in how the two technologies work.

I'd try following the checks here which should hopefully let you get a little more from WiFi

https://goo.gl/OwfjxM

[#3]

Thanks. But that's a 25% speed loss.
Any one else get this from the home hub?

[#4]

Thanks. But that's a 25% speed loss.
Any one else get this from the home hub?
Maybe it's my laptop. Who knows....

[#5]

As adamwalker says, its a consequence of the fact that WiFi is half duplex ( the laptop can either receive or send but not both at once) while a wired connection is full duplex (the laptop can send and receive at the same time).

A TCP/IP data stream consists of packets of data coming to your laptop from the server, and packets going back from your laptop to the server to acknowledge receipt (acks).

On a wired connection the laptop can send the acks while continuing to receive more data packets. On a WiFi connection the laptop has got to tell the router to stop sending data packets, send its acks, then tell the router to restart the data stream.  The gaps that are needed to do this result in the loss of speed you are seeing.

Exactly how big a loss will depend on multiple factors including the relative size of the data packets, the size of the ack packet, the efficiency of the turnaround on the WiFi link and the number of packets that the laptop can receive without an ack being sent back to the server.

However that said a quick test here shows the same speed on Wired (Gigabit), 2.4 and 5Ghz wireless connections to the BT Hub. All three are saturating the broadband link.