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Author Topic: HEC errors, non-reporting and PTM vs ATM on ADSL2  (Read 3709 times)

burakkucat

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #15 on: October 08, 2016, 12:20:46 AM »

Yes, my TalkTalk circuit is MPF (using the Openreach terminology) i.e. LLU (using Ofcom terminology). The TalkTalk MSAN will accept my CPE connecting in any one of G.992.1, G.992.3 and G.992.5 modes. G.992.5 is pointless due to the line length involved. Hence G.992.3 is my preferred mode.

The little niggle is telling me that I conducted an invalid experiment and I should try again. I fully expect the experiment to fail -- Kitz has spelt out the reasons in quite simple terms, above -- but as a scientist I must perform the experiment properly.  :)
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Weaver

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #16 on: October 08, 2016, 12:40:02 AM »

I just assumed that BT MSANs might not speak PTM, for whatever reason. I forgot, originally, about the fact that this is a non-BT MSAN/DSLAM.
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ejs

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #17 on: October 08, 2016, 08:29:14 AM »

PTM definitely wouldn't work on 20CN because it does not exist for ADSL1!
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kitz

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #18 on: October 08, 2016, 12:08:14 PM »

Maybe Im missing something, but I'm not quite sure how you are going to connect to an ATM DSLAM using PTM and without a PVC. :(

ADSL1 /2/2+ use ATM DSLAMs

BT uses VC-MUX (Virtual Circuit Multiplexing) on its DSLAMs although I think TT may use the older LCC which still needs a VCI
Layer 2 is 'dumb' routing - no IP addressing - hence why the need for a virtual circuit (PVC) and use of virtual paths.
Here in the UK when setting up a router with ATM we use VPI 0 and VCI 38.

--

FTTC uses IP DSLAMs. Still layer 2 routing but uses designated VLANs. 
When setting up a PTM connection we have to input the VLAN info - see IEEE 802.1q which is ethernet specific.

As soon as you select PTM it should ask for VLAN info - See my setup guide here.  Note also Openreach uses 802.1p which is a QoS extension for 802.1q.  I think both BT and TT have to be set at 1 because of IPTV services.

--
The way you configure ATM and PTM are different.
An ATM DSLAM will be expecting the Virtual Circuit ID (VCI) to handshake, its not going to understand any IEEE 802.1x info.
The mode protocols are different and you cant mix and match from one protocol suite with bits from another.
Its kinda like asking an FTP client to be able to read HTTP traffic.
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burakkucat

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #19 on: October 11, 2016, 12:00:18 AM »

I would like to use the statement "It takes two to tango" as an analogy.

Let us assume that the "two" so referenced, above, each have a wide repertoire of dance steps and are equally matched in that respect. Let us further assume that numbers "one" and "two" come together to perform a dance. Number one attempts to performs a tango but number two attempts to perform a military two-step.

I think Weaver will appreciate the analogy.

The TalkTalk MSAN is configured only to use ATM for G.992.{1|3|5} modulation. (The preceding sentence is number one's tango.)

My CPE, a ZyXEL VMG1312-B10D, can be configured to use G.992.{1|3|5} modulation and, furthermore, for G.992.{3|5} modulation it can be configured to use PTM. (The preceding sentence is number two's military two-step.)

I finally repeated the experiment (see replies 3, 4, 6, 8, 10 & 15, above) under well defined conditions. The experiment, as predicted, failed. Synchronisation was readily achieved between the ATU-C and the ATU-R but no higher level data transfer was possible . . . as it takes two to tango.  :)
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Weaver

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #20 on: October 11, 2016, 01:04:43 AM »

Burakkucat was thinking about the U-interface in G.992.x terminology, the DSL link, its protocol stack options and the possible configurations of the two devices.

I was thinking about the V-interface, beyond the ATU-C, expecting it to be just as likely to fail because of config- or capabilities-incompatibility there.

But given the close ties between G.992.3 and VDSL2, I was prepared for a surprise if all the kit might be willing.
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Weaver

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #21 on: October 11, 2016, 01:11:49 AM »

This all started from me grasping at straws as to why my HEC error counts disappeared one day, became "n/a", and never came back.

I wonder how your favourite ISP gets hold of this kind of status info, how many of the mechanisms are lurking in standards docs somewhere, how much is in manufacturers’ specs and how much is BT proprietary cunningness?
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