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Author Topic: Availability of L2 Retx (proprietary PhyR or standard G.INP) on upstream?  (Read 2757 times)

Weaver

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Can I ask if any kitizens have L2 retransmission protocol technologies on upstream or downstream or both?

This term covers either the standard G.INP protocol or else the Broadcom-proprietary PhyR in ADSL2/2+ )

I have the PhyR form of L2 retx protocol but only on downstream, not on the upstream for some reason. This is really really annoying, as my upstream is painfully slow and experience from the downstream shows that L2 retx can get me a good bit more speed because the substantial gain in extra reliability achieved by the use of L2 retx can if desired be traded back for yet more speed instead, and I could really do with using L2 retx to speed up the upstream too.
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krypton

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On my line G.INP is enabled in both directions but I don't know how I could help you.
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kitz

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iirc the ITU-T standard for G.INP doesn't support upstream retransmission on adsl2/2+
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Weaver

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@kitz - so perhaps thats related to why I have no proprietary PhyR on upstream for my ADSL2 then? I wish I understood it.
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kitz

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Yup that will be the reason. 
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ejs

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I'm not convinced that that is the reason. There appear to be ADSL only modems that have independent PhyR on/off settings for the upstream and downstream.
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sevenlayermuddle

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A possible disincentive might be,  in order to support retransmission, the modem needs to be able to store the data that might need to be retransmitted.  That might increase manufacturing cost (ram requirements), which might be seen as hard to justify, in cost-conscious consumer appuratus.

The amount of ram needed would be a function of the time it must be retained, pending acknowledgement, and the rate at which it is sent.

Just guessing though. :)
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ejs

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I think G.INP was originally based around using the amount of memory that would have otherwise used for interleaving. Interleaving also needs to store the delay's worth of data in order to re-arrange it.
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krypton

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Please excuse my confusion. The line that I mentioned is running on vdsl2.
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Weaver

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It is an absolutely superb feature. It gives me very very roughly the equivalent of another 3dB of SNRM and about another 5% downstream sync speed. The reliability improvement is absolutely spectacular, looking at the ratio of FEC error count to bad CRCs count when running at 3dB downstream target SNRM and drooping down to about 2dB during part of the day.


I will do some number crunching for all the lines when I am a bit less tired, but here are some numbers for my line 1:

Since Link / Up-time = 5 days 6 min 23 sec = 432383 s

FEC downstream:   178704      CRC downstream :   15
FEC upstream:           46825      CRC upstream:      330

Downstream CRC / FEC   = 8.3937684663E-05    = 1 / 11913.6
Upstream CRC / FEC      = 7.0475174E-03          = 1 / 141.8939393939

This is with an upstream target SNRM of 6dB and target downstream of 3dB. The effectiveness of the combined error correction systems is spectacular, as too is the difference in effectiveness between downstream and upstream, especially given that the target SNRM difference is in the opposite direction.


A question: can I work out how busy the line has been ? How much data has been going through it in both directions?

I thought about looking at the error counts per hour, but then I thought that a busy line and an idle line should not be placed side by side where counts are concerned.

For ADSL2 with ATM, can I take the modems reported "data cells" ATM stats figure and multiply by 53 bytes times 8 bits? There are several cell counters: there is that figure and a total ATM cells figure.

« Last Edit: March 29, 2019, 09:23:41 PM by Weaver »
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ejs

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CRC and FEC counts will be completely unaffected by the amount of traffic going over your Internet connection.
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Weaver

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Just so I understand, that is because there are idle cells screaming through all the time?

I need to have a proper picture of what is going on with ATM here when things are idle. And I also need to understand what it is that a CRC is the CRC of? What does it cover? (And what when theres no user data.) my ignorance here is shameful.  :-[  :(  ???
« Last Edit: March 29, 2019, 09:22:51 PM by Weaver »
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j0hn

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Just so I understand, that is because there are idle cells screaming through all the time?

Basically yes.

I get the similar FEC/ES/rtx_tx when I'm downloading at 40Mb/s over a 6 hour period as I do with just the modem synced (No router/PPP).
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Weaver

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I clearly need to read up on ATM properly.
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kitz

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See Improved impulse noise protection for digital subscriber line (DSL) transceivers

Annex A specifies Support of ITU-T G.998.4 with ITU-T G.992.3  (ADSL2)
Annex B specifies Support of ITU-T G.998.4 with ITU-T G.992.5  (ADSL2+)

Quote
A.1 Specific requirements
For [ITU-T G.992.3], retransmission is defined only for the downstream direction (i.e., DTUs are transmitted only in the downstream direction and the RRC is transmitted only in the upstream direction).

B.1 Specific requirements
For [ITU-T G.992.5], retransmission is defined only for the downstream direction (i.e., DTUs are transmitted only in the downstream direction and the RRC is transmitted only in the upstream direction).


A lot of the constraints do appear to be related to memory, which are far more defined when used with ITU-T G.993.2 (VDSL2) - See Annex C

Quote
C.1 Specific requirements
C.1.1 Memory
The following definitions shall apply:
delay_octetDS,0 = (DDS,0 1) (IDS,0 1)
delay_octetUS,0 = (DUS,0 1) (IUS,0 1).

If retransmission is enabled in the downstream direction,
then delay_octetDS,1 = 2Qtx,DSQDSHDS
otherwise delay_octetDS,1 = (DDS,1 1) (IDS,1 1)

If retransmission is enabled in the upstream direction,
then delay_octetUS,1 = 2Qtx,USQUSHUS
otherwise delay_octetDS,1 = (DUS,1 1) (IUS,1 1)

...etc...
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