Limiting the number of times TCP can retransmit packets in Windows

[g67575]

There's a registry command that can do this, discussed here:
https://support.microsoft.com/en-us...time-out-7ae0982a-4963-fa7e-ee79-ff6d0da73db8

The default setting for 'TcpMaxDataRetransmissions' is 5 in Windows 10.

I set mine to 1 in the registry. This is a registry key that can be added here:
Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

I've rerun a test here that checks for retransmissions and the amount of retransmissions is lower than before, with the amount varying between 0.4 and 0.6% on my FTTC line.

I found that with the default setting of 5, the amount of retransmission tended to vary anywhere between 0.5 to approximately 10%.

I can set the value to 0, which ends the test sooner during the upstream phase (so I know this command works). Wouldn't advise setting this to 0, but it does seem to lower the amount of TCP retransmissions (and probably just increases the discarded packets).

Mlab test here (there's now a London server):
https://speed.measurementlab.net/#/

Is lowering the number of retransmission attempts a bad idea?

I haven't noticed any interruptions in browsing or file downloads yet.

 

[g67575]

It's just an experiment for now, I'm curious to see what affect this will have. It also potentially highlights a flaw in the test, that it seems to allow too many retransmissions (and therefore gives results that don't seem consistent or accurate between different runs).

I think there is still a problem on my FTTC line, the more upstream I allow to be used (via QOS), the higher the packet loss. Realistically, I've no idea if this is even something BT Openreach engineers could fix (perhaps 1% or less is normal for VDSL2 lines).

In terms of there being a problem, I think my line may be good enough (in terms of packet loss) to run Stadia on some of the time, but it's hard to say at this point (as the line is often congested anyway).

 

[g67575]

Yup. UDP is pretty basic from what I've heard, designed for fast transmission of data.