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I am correct in believing that no fault on the actual DSL part of a broadband connection would affect latency? By 'DSL part' I am referring to the modem at the customer premises, the copper pair back to the local exchange and the DSLAM at the exchange.
My understanding is that latency is primarily caused by congestion and distance (ie overseas links) and the number of active devices (routers) the data traverses. As the DSL link is not contested, congestion is not happening - assuming no other data traffic from this customer.
[I am trying to get to the bottom of ping times on a friend's ADSL service that are stratospheric 5000-10000ms with nothing else happening on the line. All parameters on the line seem normal (SNR, attenuation etc) and the pings occasionally return to good (30ms) but are bad 99% of the time. ISP hasn't got a clue.]
David G
Posted 2018-02-07T22:25:00.833
Reputation: 111
What do the modems logs show? Traditionally dsl in general has slow latency. But what you are saying is off the maps. Check the phones in the rest of the house, they are supposed to have filter/traps on them. It could explain some of it. But I doubt all. – Tim_Stewart – 2018-02-07T22:30:41.523
BTW, im pretty sure the latency is from the fact that it's going over copper pstn. Switched all the way back to the head-end, DSLAM, plus how many users have concurrent connections to the DSLAM. Etc – Tim_Stewart – 2018-02-07T22:34:31.037
All other phones unplugged (only one anyway and it has a filter). I haven't looked at the modem logs, good suggestion. Tried a second, brand new, good quality modem. – David G – 2018-02-07T22:36:26.770
@Tim_Stewart I don't understand your second comment Tim. The copper pair from each customer is unique back to the local exchange where the DSLAM is located. The point of my question is can there be anything wrong with this unique part that would cause this much latency? If not, then the problem must be further on - ie in the ISP's network. – David G – 2018-02-07T22:39:33.633
Early in my career I installed these, the ISP will ALWAYS blame inside wiring. It's a good place to start checking. Re-terminating at the outlet, and where it connects to the demarc. Try another cat3 jumper between the outlet and dsl modem. My point was that dsl travels (switched on street level) over the same copper PSTN, back to the DSLAM and is then de-multiplexed from voice. (It's traveling on antiquated equipment) – Tim_Stewart – 2018-02-07T23:02:55.660
I take your point - inside wiring is probably very high on the list of causes of problems. Unfortunately in this house the first point where the phone line terminates appears to be behind a wall phone. :-( Anyway my thought is that if the wiring was dodgy, it would be affect more than the latency - if it even can affect the latency? – David G – 2018-02-07T23:23:11.467
Router log may be showing drop outs / time-outs etc. I've never seen adsl with avg latency over 75-100ms... Unfortunately the ISP is only responsible to the demarcation point. If you can prove to the ISP these problems are at the demarc, it is then their responsibility to fix it. Can you home run a temp cable to the demarc? If it's an apartment scenario your landlord is responsible for inside wiring. – Tim_Stewart – 2018-02-08T05:29:08.700
@DavidG Can you please provide a traceroute to something significant but local to your friend and edit your question with the additional info. - Also which country are you in? Yes there are many ways to introduce latency onto adsl at the management layer. – user3788685 – 2018-02-08T19:58:20.427
I will be visiting my friend again tomorrow - will update question then. We are in Australia, just out of Sydney. What are you calling the 'management layer'? Incidentally my friend had some extended periods yesterday (1 hour) when ping times were <20ms and speeds were excellent ?? – David G – 2018-02-08T22:46:06.703