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AyeUp
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Upstream 4 channels?

I've noticed a change in my upstream now locking on to 4 channels and wonder if this is indicative of things to come? (faster uploads maybe?)

The other thing I have noticed is that one channel locks on to 16qam where as the rest are 64qam, is there any reason for that or is it a fault?

channels.PNG

JM
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Sephiroth
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Message 2 of 16
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Re: Upstream 4 channels?

I have the same (had the same since mid-summer). My postcode is RG41.

My understanding is that the 4 channels precede a move to the upstream being 10% of the downstream as a standard offering. My further understanding is that when all 4 channels can reliably operate at 64QAM, the segment is ready for upgraded upstream speed.

My Power Levels & SNR sticky explains all that.

Seph - ( DEFROCKED - My advice is at your risk)

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Adduxi
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Message 3 of 16
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Re: Upstream 4 channels?

Still on 2 16 qam here, BT postcode, and have been for as long as I can remember.

I'm guessing the 16 qam for noise reasons? Perhaps the infrastructure over here in Northern Ireland is older as it's ex NTL ?

Just wondering if there is a roadmap for future infrastructure upgrades anywhere, but knowing how close to their chest VM keep things, I would suspect not  Smiley Happy

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Sephiroth
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Message 4 of 16
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Re: Upstream 4 channels?

It doesn't get much older at street level than my ex-NTL cabling in RG41.

I think they are trialling various areas.

Seph - ( DEFROCKED - My advice is at your risk)

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Message 5 of 16
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Re: Upstream 4 channels?

Hello AyeUp

 

Thank you for your post and well spotted, just so you are aware the 25Mz channel is at 16QAM by design it is not because of any performance problems.

 

Thank you 

Nicola

Virgin Media Forum Team
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Sephiroth
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Message 6 of 16
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Re: Upstream 4 channels?


Nicola_C wrote:

Hello AyeUp

 

Thank you for your post and well spotted, just so you are aware the 25Mz channel is at 16QAM by design it is not because of any performance problems.

 

Thank you 


Nicola

Have I got hold of the wrong end of the stick?  If 3 US channels have 64QAM and 1 has 16QAM (the more noise prone channel), isn't there a throughput constraint?  I know the symbol rate is the same at both modulations, but the 16QAM channel will become congested faster than the 64QAM channel, thus slowing the whole upstream experience for the user at that time.   If that's right, what's the point of putting anyonme one a 16AM channel?

 

Seph - ( DEFROCKED - My advice is at your risk)

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Ignition
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Message 7 of 16
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Re: Upstream 4 channels?

No throughput constraint from this. CMTS scheduler balances load.

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Sephiroth
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Re: Upstream 4 channels?


Ignition wrote:

No throughput constraint from this. CMTS scheduler balances load.


That's the bit that I'm on about.  The CMTS balances the load, but the 16QAM symbol size is then the limiting resource.  What have I misunderstood?

 

Seph - ( DEFROCKED - My advice is at your risk)

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bambamboyo
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Message 9 of 16
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Re: Upstream 4 channels?


Sephiroth wrote:

Nicola_C wrote:

Hello AyeUp

 

Thank you for your post and well spotted, just so you are aware the 25Mz channel is at 16QAM by design it is not because of any performance problems.

 

Thank you 


Nicola

Have I got hold of the wrong end of the stick?  If 3 US channels have 64QAM and 1 has 16QAM (the more noise prone channel), isn't there a throughput constraint?  I know the symbol rate is the same at both modulations, but the 16QAM channel will become congested faster than the 64QAM channel, thus slowing the whole upstream experience for the user at that time.   If that's right, what's the point of putting anyonme one a 16AM channel?

 

I am in RG4, Reading/Caversham with 4 upload channels the same as you - the 25800000 channel has massive problems and has had 35 T3 timeouts in the last 24 hours.  It looks like there is noise on the upstream part of the network in the area.  My Hub 3 seems to cope reasonably well, but my neighbour with an old Superhub 1 has constant reboots on the hub (our up/down signal levels are both well in spec) and I think this is all caused by the constant T3 timeouts.

Can this issue with the upstream channel @ 25800000Hz be raised with networks to be looked at?


 

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Sephiroth
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Message 10 of 16
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Re: Upstream 4 channels?


bambamboyo wrote:

Sephiroth wrote:

Nicola_C wrote:

Hello AyeUp

 

Thank you for your post and well spotted, just so you are aware the 25Mz channel is at 16QAM by design it is not because of any performance problems.

 

Thank you 


Nicola

Have I got hold of the wrong end of the stick?  If 3 US channels have 64QAM and 1 has 16QAM (the more noise prone channel), isn't there a throughput constraint?  I know the symbol rate is the same at both modulations, but the 16QAM channel will become congested faster than the 64QAM channel, thus slowing the whole upstream experience for the user at that time.   If that's right, what's the point of putting anyonme one a 16AM channel?

 

I am in RG4, Reading/Caversham with 4 upload channels the same as you - the 25800000 channel has massive problems and has had 35 T3 timeouts in the last 24 hours.  It looks like there is noise on the upstream part of the network in the area.  My Hub 3 seems to cope reasonably well, but my neighbour with an old Superhub 1 has constant reboots on the hub (our up/down signal levels are both well in spec) and I think this is all caused by the constant T3 timeouts.

Can this issue with the upstream channel @ 25800000Hz be raised with networks to be looked at?


 


I have seen many stats on this forum where the 25.8 meg upstream channel is 64QAM.  So it is not 16QAM by design, but when it is 16QAM it is because of local conditions that are either known to the network engineers and thus configured at the CMTS, or dynamically set by the CMTS according to the measured noise level.

As to RG4 vs RG41 (where I live):  The Reading hub site has c. 30 CMTS servers (actually huge modems).  Each CMTS has several line cards, each of which serves one or more optical nodes out in the street.  An RG4 user might be on the same CMTS as an RG41 user but they tend to allocate on a locality basis for maintenance purposes.

So, poor upstream on 25.8 meg in RG4 will be an entirely local thing and not have anything to do with noise in RG41.  Local noise can be anywhere in your segment, often at the optical node (but unlikely if the area has been upgraded which RG has if you are on 4 US channels); often at a street cabinet amplifier. Noise is difficult to pinpoint and if it is causing real problems, like T4 events across the locality, then VM engineers come out and fix it after diagnosis.  If it's only T3 events, then there are no drop-outs and although they want to have all US frequencies enabled at 64QAM, there is nothing drastic that needfs to happen.

The Hub 3 does not report T3 events in the US stats; I only have the network log to go by and my US is working perfectly fine.  Btw, the reason that the RG area is on 4 upstreams, is that it is one of the pilot areas for the upcoming 10% of downstream speed for upstream; they need a clean upstream in the area for that.

HTH.

 

Seph - ( DEFROCKED - My advice is at your risk)