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Author Topic: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems  (Read 969 times)

Weaver

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ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« on: October 02, 2020, 02:25:07 PM »

I have a heap of VMG 1312-B10A units which I am using as modems with ADSL2 and which have our very own Johnsonís custom firmware in them and with no wireless. My questions:
  • Is there any performance difference between the two used as mere modems, with ADSL and no wireless?
  • Any other advantages / disadvantages? Price ? Availability ?
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Alex Atkin UK

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #1 on: October 02, 2020, 03:42:37 PM »

I'd think you of all people would be the expert on this by now.
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Weaver

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #2 on: October 02, 2020, 03:47:11 PM »

Hardly, because I donít know anything much about the 8924-B10A. Is the DSL hardware the same for example ? Iím thinking about future problems getting hold of more 1312-B10As that are new or new-ish given that they have not been in production for a while now.
« Last Edit: October 02, 2020, 03:49:30 PM by Weaver »
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meritez

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #3 on: October 02, 2020, 03:56:01 PM »

Sorry to go off at a tangent, any thoughts on the VMG1312-T20B as a replacement for the B10A?

Looks like the B10D/B10A replacement, the AA wiki is unpopulated, and the Zyxel product page is not sure if it offers just 2.4ghz wifi or 5ghz as well?

https://www.zyxel.com/uk/en/products_services/Wireless-N-VDSL2-Gateway-with-USB-VMG1312-T20B/

if it offers 5ghz 802.11n that would be a nice touch, though I'm not sure on the chipset.

https://support.aa.net.uk/Router_-_VMG1312-T20B

lovely blank page above
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Weaver

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #4 on: October 02, 2020, 04:50:31 PM »

Iím afraid I donít know anything about that model. A couple of requirements: it would have to be supported by our good friend johnson; I donít know about the software vs hardware compatibility between that model and the others. It would also have to have the good DSL input filter that is present in the B10A models and lacking in the B10Ds, from what I have read. As this is a modem-only situation, I wonít be using wireless.

Is the 8924-B10A still in production?
« Last Edit: October 02, 2020, 04:53:37 PM by Weaver »
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hushcoden

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #5 on: October 02, 2020, 06:35:01 PM »

Quote
if it offers 5ghz 802.11n that would be a nice touch, though I'm not sure on the chipset.
VMG1312-B10A/D have a Broadcom chipset while the VMG1312-T20B is a Mediatek
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Alex Atkin UK

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #6 on: October 03, 2020, 12:24:30 AM »

Hardly, because I donít know anything much about the 8924-B10A. Is the DSL hardware the same for example ? Iím thinking about future problems getting hold of more 1312-B10As that are new or new-ish given that they have not been in production for a while now.

I thought the idea was that the DSL hardware WAS the same thus why they are both equally recommended?  Same with the 8925 except its missing the filtering.  But hey, I could have misunderstood as the thread discussing this is so darn long.
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Weaver

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #7 on: October 03, 2020, 01:48:15 AM »

Agreed, the thread is daunting. Maybe they do have the same DSL hardware.
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siofjofj

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #8 on: October 03, 2020, 10:55:41 AM »

I have a VMG8924-B10A on the shelf, and posted some details about its hardware here https://forum.kitz.co.uk/index.php/topic,24975.msg419850.html#msg419850 along with a PCB photo.

Basically, like the VMG1312-B10A, it has the BCM63168 chipset. It also has additional RF filtering at the input, visible in the PCB photo as the common mode choke labelled 'UMEC UT34297B' (datasheet http://umec.com.tw/file/Product/file/15-21D.pdf). As you know, the VMG1312-B10A also has this additional common mode input filtering, however for this modem it appears to be a different unlabelled component (see PCB photo in https://forum.kitz.co.uk/index.php/topic,21772.msg375799.html#msg375799).

The VMG8924-B10A is long discontinued too I'm afraid. The VMG8924-B10D is still in production I think, but I have no idea what chipset this has or whether it has the input common-mode filter. There is also the slightly more recent (but still discontinued) VMG3925-B10B, which has the BCM63168 chipset but no common-mode filter, and the currently manufactured VMG3925-B10C which is similar (and is currently supplied by Andrews and Arnold). Finally there is the VMG3926 which has the BCM63168 chipset and the common-mode filter (see https://forum.kitz.co.uk/index.php/topic,18246.msg324172.html#msg324172), but I have never seen this for sale in the UK.

For what it's worth, I see no significant difference in ADSL2+ performance between my TP-Link Archer VR600v1 (BCM63168 chipset, no common-mode filter) and my Zyxel VMG8924-B10A (BCM63168 chipset, with common-mode filter). Possibly this is because the Mk4 VDSL SSFP filter I have fitted to my NTE5C master socket (like the Mk3 version for the NTE5A I had before Openreach changed it) also has a common-mode filter built into it (called a REIN filter by Openreach). I know you don't use landline telephones so don't need a filter, however you could perhaps try fitting one to see if you benefit from the common-mode choke within (this is indeed wired between the incoming line and the DSL connection, so the usual statement that the DSL connection is wired straight though a DSL filter is not quite true for these faceplates).

Edit: I just measured the inductance of each leg of the common-mode choke in my spare VDSL Mk3 SSFP, and got 1.0 mH for each. This compares with 4.7 mH for each leg of the choke in the VMG8924-B10A (according to the datasheet I linked to above), suggesting more aggressive filtering for the one in the modem.
« Last Edit: October 03, 2020, 12:04:17 PM by siofjofj »
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Alex Atkin UK

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #9 on: October 03, 2020, 07:29:46 PM »

Possibly this is because the Mk4 VDSL SSFP filter I have fitted to my NTE5C master socket (like the Mk3 version for the NTE5A I had before Openreach changed it) also has a common-mode filter built into it (called a REIN filter by Openreach). I know you don't use landline telephones so don't need a filter, however you could perhaps try fitting one to see if you benefit from the common-mode choke within (this is indeed wired between the incoming line and the DSL connection, so the usual statement that the DSL connection is wired straight though a DSL filter is not quite true for these faceplates).

Thanks for this, I had been wondering if I should replace the faceplate on one of my lines because my old ADSL Nation filter failed so I moved the MK3 onto the line I use with telephones, leaving no filter on the second line at all.  Seems it could be worth getting another MK3 after all even though I do not have a landline on the second line?
« Last Edit: October 03, 2020, 07:34:19 PM by Alex Atkin UK »
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siofjofj

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #10 on: October 03, 2020, 07:53:26 PM »

Thanks for this, I had been wondering if I should replace the faceplate on one of my lines because my old ADSL Nation filter failed so I moved the MK3 onto the line I use with telephones, leaving no filter on the second line at all.  Seems it could be worth getting another MK3 after all even though I do not have a landline on the second line?
Possibly, though hard to say for sure. If you have a weak signal due to a long metallic path, but little common-mode noise, then the filter just adds more attenuation without significantly helping with regard to noise, making the overall SNR worse and reducing sync speed. On the other hand, if you have a strong signal but tons of common-mode noise, the additional attenuation is insignificant however the noise reduction is very beneficial, giving a higher SNR. The effect of noise bursts also need to be considered, as it could be that the filter reduces sync rate under normal conditions, but also reduces the number of CRCs that occur during noise bursts.

When the Mk3 SSFP was introduced, which differs from the Mk2 only by a higher inductance common-mode choke, a number of people getting nearly 80Mb/s on VDSL2 observed a decrease in sync speed when changing to the Mk3. This was due to the added attenuation of the higher frequency tones caused by the Mk3. Openreach seem to know this, as if you compare the VDSL Mk4 faceplate with the G.Fast faceplate you will note that the G.Fast variant has fewer turns of wire on the choke. In fact, the common mode choke in the G.Fast Mk4 variant looks very similar to that in the Mk2, while the one in the VDSL Mk4 variant looks the same as that in the Mk3.

Basically, I'd say there are too many variables to give an answer that is accurate for all situations. The only thing that can be done is to try the different faceplates and see what results you get. I only suggested it here in case Weaver ends up not being able to get the Zyxel modems with integral filter, so he could compensate somewhat by adding one externally with a SSFP.

Edit: Thinking about it, Weaver's lines are long and rural. The signal is therefore heavily attenuated, yet I can't imagine there are many noise sources along it. I wouldn't be surprised if Weaver's lines benefit from having no common-mode filter at all. It might be worth trying the VMG3925-B10B in this case, which has the good BCM63168 chipset but no filter (Johnson also has a custom firmware for it).
« Last Edit: October 03, 2020, 08:09:33 PM by siofjofj »
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Weaver

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #11 on: October 03, 2020, 11:57:58 PM »

Thank you so much for your generous reply, very helpful indeed.
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Alex Atkin UK

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #12 on: October 05, 2020, 07:39:16 PM »

Possibly, though hard to say for sure. If you have a weak signal due to a long metallic path, but little common-mode noise, then the filter just adds more attenuation without significantly helping with regard to noise, making the overall SNR worse and reducing sync speed. On the other hand, if you have a strong signal but tons of common-mode noise, the additional attenuation is insignificant however the noise reduction is very beneficial, giving a higher SNR. The effect of noise bursts also need to be considered, as it could be that the filter reduces sync rate under normal conditions, but also reduces the number of CRCs that occur during noise bursts.

I switched to a NTE5C (shhhh don't tell Black Sheep) with a MK4 and my speed actually has gone down because of the re-sync (was going to happen eventually as its gotten colder so the SNR has dipped).  I guess time will tell if it reduces errors or not.

The fun part will be removing it again if I need to as the Kelly Communications guy who fitted the second NTE put it too close my first one to press the side of the faceplate.  :no:  So I guess I wont be replacing the MK3 as I will have to remove that to get the MK4 off.

I'm honestly just clutching at straws now while waiting for the delayed FTTP rollout.  At least it looks neater and the MK4 seems to make a more stable connection to the RJ11 plug than the MK3 which seems loose.

In relation to speed reduction, I noticed no difference on my main line when going from the ADSL Nation filter to the MK3, 76Mbit on both.
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j0hn

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #13 on: October 05, 2020, 07:57:26 PM »

At least it looks neater and the MK4 seems to make a more stable connection to the RJ11 plug than the MK3 which seems loose.

That's because it's an rj45 socket.
I used an rj45 to rj11 cable for my patch lead for a few years.

In the end i just cut the rj45 plug off and connected directly to the idc connectors on the master socket.
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siofjofj

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Re: ZyXEL VMG 1312-B10A vs VMG 8924-B10A as modems
« Reply #14 on: October 05, 2020, 08:10:00 PM »

I switched to a NTE5C (shhhh don't tell Black Sheep) with a MK4 and my speed actually has gone down because of the re-sync (was going to happen eventually as its gotten colder so the SNR has dipped).  I guess time will tell if it reduces errors or not.
Agreed. I would imagine, with the exception of some extreme cases with perhaps a lot of local interference, any differences will be relatively small.

The fun part will be removing it again if I need to as the Kelly Communications guy who fitted the second NTE put it too close my first one to press the side of the faceplate.  :no:  So I guess I wont be replacing the MK3 as I will have to remove that to get the MK4 off.
...
At least it looks neater and the MK4 seems to make a more stable connection to the RJ11 plug than the MK3 which seems loose.
Functionally speaking, I personally prefer the Mk3 design, and would rather Openreach hadn't changed my Mk3 to the Mk4. The Mk3 faceplate is so much more secure, being held on with two screws, while my Mk4 one wouldn't stay on at all to begin with until I warmed and then bent the securing clips outwards. I agree that the Mk4 is more aesthetically pleasing though, and understand the reasons for changing to the screwless design.
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