VDSL2 bands - Higher bands / frequencies cause TCP packet retransmission

g67575

g67575

g67575

Soldato
Joined
30 Jun 2019
Posts
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I've been experimenting with disabling different VDSL2 frequency bands , such as D1, D2 and D3 (tested via an ethernet LAN cable). What I've found is, completely disabling the D2 and D3 bands reduces TCP packet retransmission to 0%, as shown below:

D1.jpg

However, with the default D1, D2 and D3 bands enabled, I get around 2% retransmission:

D1-D2-D3.jpg

There is also some packet retransmission with the D1 and D2 bands enabled:

D1-D2.jpg

these results were tested with the SNR margin set to 2dB on my VDSL modem / router (to increase downstream sync speed).

Also, this was the website I ran the tests on:
https://speed.measurementlab.net/#/

So, I suppose what I wonder is, how much does packet retransmission (or loss) matter for every day use, and for specific uses like voice calls and online game streaming?
 
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bremen1874 said:
So slightly higher latency and half the bandwidth. Looks like a win to me.
Click to expand...

I suppose it shows that the higher frequency VDSL2 bands can be a bit unreliable on longer lines like mine (I don't have a shorter FTTC line to test on).

Using the D1 band only is a way to make a VDSL2 connection more reliable, by restricting the downstream frequency range to ~0-4mhz (since the higher frequencies have a lower SNR).

Also, the download rate seems very steady with only the D1 band in use. With all downstream bands active, the download rate can dip 10-20mbps sometimes.

I've be interested to know if anyone else has had similar experiences with VDSL2 / FTTC and if so, did you find any ways to mitigate the packet retransmission / packet loss?

FTTP should solve any problems with packet loss/ retransmission, but for many, this upgrade is years away...
 
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