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Thread: Need experts advice

  1. #1

    Need experts advice

    Hello Everyone,

    let me start by explaining to you about my internet connection first to give you a better idea, i am subscribed to 15 Mbps download speed and 1 Mbps upload speed, now if i run a speed test i get like 16, 17, 18 Mbps which is really good right, everything seems to be working fine, well not so much to my believe, this is a new connection that i had installed 4 days ago, on the first day the service was working i noticed the Data path was set to Fast/Fast then on the 2nd day it got switched to Interleaved/Interleaved, i understand that this affects only Ping, Latency etc which affects gaming online and shouldn't make a problem for the connection, well in that case is my interleave depth and interleave delay and INP set properly or do you guys think that these values are insane, i spoke to tech support for my ISP many times but they are clueless what is Data path and they say they can't change it from Interleaved to Fast and that its all being done automatically and they can't do that manually, i understand that this is incorrect and that they are just a bunch of uneducated morons and just refusing to help based on company orders cos where i am from (Egypt) so basically companies > ppl around here.

    sorry about the long introduction, below is all the info i could gather that might help you understand things better and let me point out that my connection is ADSL2+, PPPOE, LLC, UBR, these are my connection settings, MTU command test the maximum i could get without fragmentation is 1464 so i was told to add 28 so my MTU set in the router would be 1492, i heard so many stories that MTU for PPPOE LLC should be like 1454, some say 1448, anyway let me know what you guys think, please bare in mind that all my knowledge about broadband or w.e i am talking about here is all from the internet so i am just a n00b here so take it easy on me guys


    Link Status Connected
    Modulation Type ADSL_2plus
    Actual Rate (Up/Down) 1023/20479 kbps
    Attainable Rate (Up/Down) 2282/25712 kbps
    Noise Margin (Up/Down) 24.3/10.6 dB
    Line Attenuation (Up/Down) 12.2/3 dB
    Output Power (Up/Down) 7.9/13.7 dBm
    Data Path (Up/Down) Interleaved/Interleaved
    Interleave Depth (Up/Down) 32/64
    Interleave Delay (Up/Down) 769/596 ms
    INP (Up/Down) 3.7/0.7 symbols
    LinkEncap G.992.3_Annex_K_ATM
    CRC Errors (Up/Down) 0/122
    Annex Type AnnexM
    « SpeedGuide.net TCP Analyzer Results »
    Tested on: 2019.05.06 03:09
    IP address: xxx.xx.xxx.xxx
    Client OS/browser: Windows 7 (Chrome 74.0.3729.131)

    TCP options string: 020405ac0103030201010402
    MSS: 1452
    MTU: 1492
    TCP Window: 66792 (multiple of MSS)
    RWIN Scaling: 2 bits (2^2=4)
    Unscaled RWIN : 16698
    Recommended RWINs: 63888, 127776, 255552, 511104, 1022208
    BDP limit (200ms): 2672kbps (334KBytes/s)
    BDP limit (500ms): 1069kbps (134KBytes/s)
    MTU Discovery: ON
    TTL: 112
    Timestamps: OFF
    SACKs: ON
    IP ToS: 00000000 (0)

  2. #2
    Administrator Philip's Avatar
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    Fast path vs. Interleave is an error correction scheme, if the error rate creeps up the CO/DSLAM may automatically impose Interleave mode to cope with that. Interleave helps resolve errors on longer loops and noisy lines. It rearranges bits before they are transmitted so that errors can be detected and possibly corrected. This Interleave process introduces a few ms delay (10-20ms) that may be an issue for gaming. Both the CO and CPE have to use the same setting, it may be the default used by your CO, or they may be using an automated sync optimization scheme.

    Interleave mode may be imposed automatically by the condition of your line (high error rates, low upstream SNR), software optimizations by your provider to improve DSL stability, or by hardware/firmware upgrades at the DSLAM.

    How to change from Interleave to Fast path to reduce latency:
    - if your line syncs better than the speed you are provisioned for, it usually syncs using fastpath
    - if there are no errors on the line, and no recent/frequent reboots the automated system may switch you to fast path from interleave mode.
    - In some cases technical support may able to manually make changes to customers' sync profile to set either Fast path or Interleave mode.
    Linux is user friendly, it's just picky about its friends...
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  3. #3
    Thanks philip, would you happen to know about the interleave depth, delay and INP values above, is it good or needs to be tuned.

    Can you please give ur opinion about my MTU results posted above, why my rwin is
    Not a multiple.

  4. #4
    Administrator Philip's Avatar
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    Interleave depth - the smaller it is, the closer it would be in behavior to "Fast path" (Fast path would be like Interleave=0). Delay seems too high, I doubt you can tune it on your end though.


    MTU is fine at 1492, the exact RWIN value can't be tuned directly with more recent Windows variants, including Windows 7. RWIN is tuned on the fly, depending on line conditions and your client advertises a different RWIN value in every packet. We can only adjust how aggressive the auto-tuning algorithm is, the default setting of "normal" should work well for your bandwidth. It is adjustable with the TCP Optimizer but it is fine as is.

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