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Author Topic: Swapping OR Modems - results....  (Read 20043 times)

Bestgear

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Re: Swapping OR Modems - results....
« Reply #15 on: March 09, 2013, 08:52:48 PM »

Hi

Interesting stuff...but it still does not explain to me why different modems perform differently on the same line.

I tried a ECI b/i on a friends line that had been used with an unmolested early huawei and it surprised me and sync was 15MB less! His line length was just 103m.

Unless I am reading your graph wrong, the 612 I tested should have out performed the b/r on my (confirmed) 434m line but it could not get near it (circa 11mb less).

I will get another virgin huawei tomorrow and retest my line and report back.

Weird....


BG
« Last Edit: March 09, 2013, 08:59:02 PM by Bestgear »
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c6em

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Re: Swapping OR Modems - results....
« Reply #16 on: March 09, 2013, 09:26:09 PM »

I also configured it as a router (rather than having my 1841 do PPPoE) and it works very well - I can only wonder why BT did not sell/provide an all in one modem router solution (obvioulsy model LAN ports and wireless). Thinking here is that if the 612 router was ok as a basic firewall, loosing more kit saves power (have a few separate APs to cover the house).

I don't have VDSL so cannot comment from personal experience but....
I'd imagine that having an all in one modem/router is 'pushing the envelope' a bit in terms of getting the CPU etc to manage the VDSL signal/bit swaps/margin/sync whatever, and act as a wireless access point, and manage the DCHP/routing stuff at 1G speeds, and run the firewall....not forgetting all the other housekeeping stuff running in the background.
By separating out the modem only bit the BT unit can cope with managing the line only aspect on its own without running into capacity problems.

For an all-in-one "home gateway" type application unit which could manage everything with ease at full VDSL and LAN/wireless speeds I'd guess we need to start looking at a netbook level of computing power to be available.....and methinks this sort of stuff is simply not yet available in the domestic mass market.

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burakkucat

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Re: Swapping OR Modems - results....
« Reply #17 on: March 10, 2013, 02:21:19 AM »

I'd imagine that having an all in one modem/router is 'pushing the envelope' a bit in terms of getting the CPU etc to manage the VDSL signal/bit swaps/margin/sync whatever, and act as a wireless access point, and manage the DCHP/routing stuff at 1G speeds, and run the firewall....not forgetting all the other housekeeping stuff running in the background.

That is in agreement with my understanding of the situation. Beattie's wizards at Grimbledon Down, having performed their experiments, decided to provide the service (for all CPs/ISPs to sell) from an Ethernet (WAN) port. Hence the definition of the modem as the active NTE for VDSL2 based services. This concept follows the precedence of the technology of the earlier Megastream and Kilostream services.
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Bestgear

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Re: Swapping OR Modems - results....
« Reply #18 on: March 10, 2013, 08:56:07 AM »


I'd imagine that having an all in one modem/router is 'pushing the envelope' a bit

Using the 612 as a modem/router rather than just as a modem did not exhibit any loss of throughput on my line, so should be an ok zero cost option for those that dont want a HH (for whatever reason).

What is hard work for a router is when it is managing VPN and firewall rules (ACLs not just simple NAT usually). Wireless is usually handled by a separate chipset, and are just hung off the LAN side.

It is amusing to see the quality and performance of home vdsl kit really - when you consider that even a lot of cisco kit of not that long ago would struggle to traverse the bandwidth we have in home vdsl!

Personally, I use a wee cisco router so I can have vpns and proper control of rules... and of course ditching the HH3 means that I loose the BT public wifi service without switching off my opt-in!

BG
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c6em

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Re: Swapping OR Modems - results....
« Reply #19 on: March 10, 2013, 09:47:21 AM »


Concidentially someone on the Plusnet forums has just today posted to the effect that their experiments on using the 612 as a modem/router rather than a modem only does indeed affect the download speeds  - they are obviously close to the cabinet if they are getting 74Mbps download achieved.
Their conclusion is the same - the 612 simply cannot cope.
http://community.plus.net/forum/index.php/topic,112626.msg969073/boardseen.html#new
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burakkucat

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Re: Swapping OR Modems - results....
« Reply #20 on: March 10, 2013, 07:18:00 PM »

Not being a VDSL2 service user, I cannot comment on usage of the Huawei HG612 as a modem/router for that FTTC based product.

However I have now used a HG612, a HG610 and a HG622 on a 'sync speed restricted by E- + D-side length' ADSL2+ service. Of the three, I rate the HG622 the best, then the HG612 and finally the HG610 in performance terms.

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asbokid

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Re: Swapping OR Modems - results....
« Reply #21 on: March 11, 2013, 01:46:44 PM »

The results are surprising and the reverse of what was previously understood from ADSL.

I'm going to re-do these tests in greater depth.  Resetting the linecard chipset between modems (to eliminate DLM issues), testing each modem multiple times, and best matching the line-profile used by BT, as much as we understand it.

Any suggestions for conducting new tests would be appreciated :-)

Cheers, a
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les-70

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Re: Swapping OR Modems - results....
« Reply #22 on: March 11, 2013, 04:36:08 PM »

1. You might try adding some cross talk e.g.  if you have short untwisted section with an extra modem running at the same time.

2. If you have access to more than one of the same type of modem (perhaps you still have a few HG622) it would be interesting to test a few of them to see the variance in "identical" modems

  I had, with help from two neighbors four DG834gv4's all running the same firmware.  The sync was at about 16Mb/s and consistently varied between them.  One was best -  :) mine as it happens and one worst 1MB/s slower also mine  :( . The other two were about 0.3 and 0.6 Mb/s slower than the best one. A rough variation of plus and minus 0.5Mb/s on the same chipset. 

   
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npr

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Re: Swapping OR Modems - results....
« Reply #23 on: March 11, 2013, 06:26:43 PM »

Any chance of simulating aluminium phone lines?
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asbokid

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Re: Swapping OR Modems - results....
« Reply #24 on: March 11, 2013, 07:28:43 PM »

Thanks guys, keep the ideas coming!

Cross-talk can be simulated with Gaussian noise from an arbitrary waveform generator - the Hantek DDS-3x25. [1] Though it's not straightforward connecting the generator with its 50ohm coax (unbalanced) output to a balanced twisted pair with 100ohm impedance.   Experiments continue  ???

Certainly various levels of attenuation, including those found in aluminium pairs, can be modelled with passive attenuators (low-noise resistor-based pads).  [2]

Another 'issue' is the time that a line is left to stabilise after synchronising.  Five minutes, ten? Sixty?  It's limited only by patience!

cheers, a

[1] http://www.hantek.com/english/news_list.asp?unid=13
[2] http://insidehuaweima5616msan.wordpress.com/2012/11/13/simulating-loop-characteristics-to-test-cpe/
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NewtronStar

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Re: Swapping OR Modems - results....
« Reply #25 on: March 11, 2013, 08:24:30 PM »

will the SNR be taken in to consideration during tests as you know after 3 pm this seems to start to get lower in the evenings & syncing each modem at different times of the day can cause 1-2 Mbps a of difference in throughput, you need some sort of minium like 2Mbps steps in the graphs  ;)
« Last Edit: March 11, 2013, 08:34:26 PM by NewtronStar »
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benji09

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Re: Swapping OR Modems - results....
« Reply #26 on: March 11, 2013, 08:40:17 PM »

  Just reading the above, and if I understood the point mentioned correctly, my information from my past, BT lines, unless they are loaded junction plant, which I doubt now exist, had an impedance of 1K2. Unloaded cable is just one great capacitor, which makes it a terrible transmission line. Unless we go back to the stone age and use old fashioned cadmium copper wires separated a few inches apart, having inductance and capacitance etc in a matched situation then the line would provide a 600ohm impedance. So using 100 ohm as a test line may not be totally accurate
« Last Edit: March 11, 2013, 08:43:13 PM by benji09 »
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asbokid

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Re: Swapping OR Modems - results....
« Reply #27 on: March 11, 2013, 09:28:58 PM »

Hi Benji09,

Ooh, thanks! Glad someone knows what they're talking about!

The plan is to replicate for VDSL2 modems some earlier tests for ADSL performed by Mattias Ernelli, an intern at Telenor, a Scandinavian telco.

Ernelli used an arbitrary waveform generator (AWG) to inject artificial noise into the loop under test. This from page 46 of his thesis [1]



Ernelli is using two 1:1 100ohm baluns to connect the noise generator.  I must admit, it's an area about which I know next to nothing  :-[   How does it work?!  Any clues?!

EDIT: there's a short Application Note from Agilent on ADSL Copper Loop Measurements. [2].  The authors of the note write:

Quote
The system impedance in the POTS band is 600 Ω and in the ADSL band is 100 Ω. Meanwhile, a measurement instrument like a network analyzer typically is unbalanced and it has 50 Ω port impedance. You need to use a BALUN to match both of the system impedances. For example, a 50:100 BALUN should be chosen to measure cables in the ADSL band.

cheers, a

[1] http://www.ee.kth.se/php/modules/publications/reports/2008/XR-EE-KT_2008_003.pdf
[2] http://cp.literature.agilent.com/litweb/pdf/5968-1196E.pdf
« Last Edit: March 12, 2013, 04:35:07 PM by asbokid »
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dazzlew

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Re: Swapping OR Modems - results....
« Reply #28 on: March 13, 2013, 01:18:05 PM »

Wonderful stuff asbokid.. really interesting research.

By chance do you know if the Revision of the HG612 make any difference as I've just come across a 3B, I already have a 2B version.
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asbokid

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Re: Swapping OR Modems - results....
« Reply #29 on: March 13, 2013, 01:27:33 PM »

Hi Dazzlew,

Ernelli's thesis is brilliant.   As for the two modems, performance seems to be identical.  The 3B has physical modifications to the heatsink / BGA fabrication to try and defeat the earlier overheating problems.  Seems to work.  Other than that, between the 2B and 3B, there's no obvious difference in xDSL performance.

cheers, a

EDIT: heck, it's Typo Tuesday!
« Last Edit: March 13, 2013, 05:19:49 PM by asbokid »
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