(Re-posting from Network Engineering SE, turns out this was actually off-topic there.)
Having moved to a new house I hired with an ISP a broadband internet plan. The technician told me I live really close (< 40m) from the street cabinet, and also the ISP runs a fiber optic cable up to the cabinet, so my signal quality should be excellent. I hired 25mbps downstream and 2.5mbps upstream, the technician said I could ask for an increase up to the ISP maximum which is 50mbps (upload: 5mbps).
In terms of speed and uptime I'm indeed getting what I'm paying for, however, the ping latency leaves much to be desired. I was left wondering why there is so much difference between a full FTTH setup and mine.
I read on many places that ADSL and its descendants use something called interleaving, which if I understand correctly is an error correction technique to improve reliability over the wire, at the expense of response time (latency). The DSL channel mode (is that correct?) can be either fastpath or interleaved. If interleaved, the interleave depth is adjustable, which in turns means the interleave delay will be higher or lower. This setting can be different for upstream and downstream.
Since my DSL status seems quite good, I called my ISP and requested to disable interleave over my line in order to improve latency. But the operator had no clue what I was talking about. A visit was scheduled; when the technician came by, he also didn't appear to have much of a clue what exactly I was requesting, either. I tried to explain the best I could, despite knowing very little myself. He sort of understood, but said that this setting was something that was enforced not on the DSLAM, but somewhere higher up in the hierarchy (perhaps on the B-RAS?) and he himself could not change that, only the ISP themselves (in my country, ISP's technicians are usually outsourced - that is, he is actually employed by another company). He also concluded that this interleave delay setting was probably changed automatically by the system, and it was probably not possible to set/override it manually.
I searched a little more and found information about something called DLM, which appears to be a form of automated line management that can increase or decrease, among other things, the interleave delay. I found many references of people successfully being able to disable interleave for ADSL, but nothing conclusive about VDSL.
Before calling my ISP again, I wanted to get my facts straight.
So, my questions are:
- Did I understand everything correctly up to this point?
- What additional info about any of these concepts would help me (or anyone) to better understand this matter?
- I have VDSL2. Is it possible for my ISP to actually disable interleave for my internet, or is it not? Where is it done? How exactly is it done? (can it be done remotely by a support operator?)
- How much of an improvement should I expect in latency? My stats are as follows:
- ping my DSL default gateway (which is probably the B-RAS): 19.7ms
- ping CloudFlare DNS (
1.1.1.1): 25.8ms - average ping to gameservers located on my country: 37ms (mean average)
- average ping to gameservers in the US: 180ms (ditto)
- DSL line status:
near-end interleaved channel bit rate: 27495 kbps near-end fast channel bit rate: 0 kbps far-end interleaved channel bit rate: 2593 kbps far-end fast channel bit rate: 0 kbpsnear-end FEC error fast: 0 near-end FEC error interleaved: 28 near-end CRC error fast: 0 near-end CRC error interleaved: 0 near-end HEC error fast: 0 near-end HEC error interleaved: 0 far-end FEC error fast: 0 far-end FEC error interleaved: 0 far-end CRC error fast: 0 far-end CRC error interleaved: 0 far-end HEC error fast: 0 far-end HEC error interleaved: 0
Downstream: relative capacity occupation: 100% noise margin downstream: 19.8 dB output power upstream: 5.1 dbm attenuation downstream: 7.3 dB
Upstream: relative capacity occupation: 100% noise margin upstream: 32.5 dB output power downstream: 13.4 dbm attenuation upstream: 1.6 dB
(...) attain upstream: 41866 attain downstream: 116124
(...) Interleave Depth: 1575
atur chan interleave delay: 7 atur chan prev tx rate: 2593 kbps atur chan curr tx rate: 2593 kbps atur chan crc block len: 32773 Adsl Standard: VDSL2 Adsl Type: ANNEX_B
