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Old March 23rd 15, 12:38 PM posted to uk.telecom.broadband
Martin Brown
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Posts: 343
Default Packet loss seems to have increased, how to diagnose?

On 23/03/2015 10:27, wrote:
Graham J wrote:
My son and I both felt recently that "the internet seemed a bit slow".

Well a disconnect/reconnect of the 2820n to the phone line seems to
have fixed it. It's renegotiated its speed up a bit too. :-)

Sadly, re-syncing the ADSL modem or rebooting the router will cure a lot
of things, but then you never know why the problem occurred in the first

Rebooting the modem is always worth a try before considering any other
more serious sort of fault. Some tend to get unreliable after a month or
two continuous running and/or large throughput.

Yes, I know, but still I do at least now have a responsive internet
connection. Next time, if I have the patience, I may try a bit more
diagnosis (if there is a next time of course!).

Sometimes modems or lines get themselves into strange states where the
statistics report unrealistic values. Several of mine have a habit of
showing a noise margin of zero when they get themselves into trouble.

As regards ping, the first IP address to try would be the Default
Gateway shown in the router. On a 2820n this is called GW IP, in the
WAN1 Status section.

Yes, OK, I did try 'nearby' IPs such as the ISP's DNS. They all
showed the same level of packet loss.

I suspect it is data loss on your ADSL link.

I presume from the ping latency you are on interleaved and some packets
are suffering enough corruption to be unrecoverable.

This is the first router in the chain between you and the rest of the
internet, and is generally operated by your ISP. If pinging it is
unreliable then you should take it up with your ISP. However be sure
that you don't have other network traffic using some of the available
bandwidth - this may delay ping responses (by design, ping has a very
low priority). The 2820 will show you a traffic graph to allow you to
identify whether there is any other usage.

If this is reliable, but other addresses (such as are
not, then it's an issue for your ISP. Try several different addresses
from services that likely to have high availability.

It was (I am almost certain) a bad ADSL connection between me and the
ISP, not an issue with ISP connectivity beyond.

Your 11dB SNR margin is not ideal. Having rebooted, what is it now?

It's showing 8 now. I still have the slightly improved speed, it's
4.7Mb/s as opposed to the 4.0Mb/s I was getting before.

That figures. You can trade noise margin for more speed and if you sync
in the afternoon when MW interference is lowest you get the fastest
connection with a slight risk of degradation after dark.

Conversely you can get a slower more stable connection by syncing well
after dark. Using the diurnal variation in SNR to alter the sync rate.

Martin Brown