[WXC/VFX] Interleaving and VFX

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Niel

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#15171 8-Aug-2007 07:09

Does turning interleaving off affect VFX quality, and if so in what way? Actual experience answers much appreciated. Thanks.

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#81547 8-Aug-2007 10:26

I have interleaving turned off on our Xnet FS/FS connection where we have 2 VFX lines. I did this purely to lower latency in the connection so you get less delay with VFX conversations.

Turning off the interleaving lowered the latency by 30 or 40ms in my case. While you probably wouldn't notice this small change, I found an unexpected benefit:

Download Speed was increased by around 20%!

If you have a good line with minimal errors and are close to the exchange, there's no reason not to turn off interleaving. However, if you are more than about 3km from the exchange, I wouldn't recommend it. Also, if your Attenuation is high, I wouldn't recommend it.

Niel

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#81550 8-Aug-2007 10:40

Thanks, the kind of answer I was after. Putting 2 and 2 together, it is my understanding that your speed goes up because you can acknowledge the TCP/IP packets with less delay. So sending acknowledgements faster means you receive the next packet faster.

I want to turn it off primarily for reducing VFX delay. It will help with internaltional calls to the other side of the world. Will have to wait 'till tonight to send an e-mail to WxC, hope one of their team reads this and initiates the process so long...

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Griven

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#81554 8-Aug-2007 11:01

Hello Niel,

Interleaving has been requested off on your connection, please allow 2-3 working days for this to complete.

Nicholas Cuc

Network Support
WorldxChange Communications
www.xnet.co.nz

Niel

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#81575 8-Aug-2007 14:00

Great, the kind of customer serveces you don't get every day! Was hoping you could do it so it will be done before the weekend so I have time to play with it.

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coffeebaron

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#81602 8-Aug-2007 17:44

I tried my DSL connection with interleaving switched off, and although there was a noticeable improvement in responsiveness of my connection, it did have some adverse effects. My connection would drop out quite regularly, and I had an increase in data errors. I am 5km + from the exchange, so I guess this was expected.

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Fraktul

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#81610 8-Aug-2007 18:24

Niel: Thanks, the kind of answer I was after. Putting 2 and 2 together, it is my understanding that your speed goes up because you can acknowledge the TCP/IP packets with less delay. So sending acknowledgements faster means you receive the next packet faster.

Pretty much correct - google "bandwidth delay product" for more information on this.

If you are looking at it solely from a view to improve VoIP quality with VFX then it is of questionable benefit - yes it will lower latency but the 30-50ms this lowers your latency by is probably not going to reduce the perceived voice quality by much.

The exception is international calls and possibly mobile, where the total path latency between A and B party may be at or near the point where it begins to interfere with natural speech patterns (this difference in perceptual quality based on latency is not linear).

Remember if turning interleaving off comes at the price of say 2-5% packet loss this is a poor trade off. The effects of packetloss will not be able to be concealed if 2-3+ consecutive packets are lost, meaning you will generally lose a syllable or more out of a word.

If you can turn off interleaving without experiencing and packet loss however there is no reason not to really, it just requires that you look at your modem connection characteristics and decide if the SNR is acceptable or you for you to take the risk. Even then its a try and see approach sometimes.

grant_k

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#81613 8-Aug-2007 19:09

Here are the stats from my FS/FS Xnet connection:
====================================================
System up Time: 543 Hours 39 Minutes 44 Seconds
CPU Load: 2.92%

WAN Port Statistics:
Link Status: Up
Upstream Speed: 608 kbps
Downstream Speed: 7360 kbps
Node-Link Status TxPkts RxPkts Errors Tx B/s Rx B/s Up Time
1-PPPoA Up 4748232 4942742 0 1701 1246 543:39:24

LAN Port Statistics:
Interface: Status TxPkts RxPkts Collisions
Ethernet 100M/Full Duplex 4713698 4570834 0

noise margin upstream: 12.0 db
output power downstream: 20.0 dbm
attenuation upstream: 7.0 db

noise margin downstream: 10.5 db
output power upstream: 0.0 dbm
attenuation downstream: 20.0 db
====================================================

The interesting facts here are:

* 0 Errors in 543 Hours (about 23 days)
* Downstream Attenuation of 20dB which tells me that I am 1.45km from the exchange

This is obviously a very good quality connection which has experienced NO errors during the past 23 days. Hence an excellent candidate for Interleaving to be turned Off.

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Fraktul

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#81617 8-Aug-2007 20:07

SNR is probably more useful than attenuation :)

Yes, looks pretty good and should be fine with interleaving turned off.

Regarding no errors - this is probably meaning no non-recoverable errors, so this does not necessarily mean that you would likewise see no errors under a non interleaved connection as the whole point of interleaving is the distribution of cells over a greater time period to reduce the chance of non-recoverable errors :)

grant_k

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#81622 8-Aug-2007 20:23

Fraktul: SNR is probably more useful than attenuation :)

Thanks for the tip Fraktul. I wasn't sure whether SNR or Attenuation was the most important.

From some info I had earlier, anything above 10dB is supposed to be OK. Would you agree with that?

Fraktul: Regarding no errors - this is probably meaning no non-recoverable errors, so this does not necessarily mean that you would likewise see no errors under a non interleaved connection as the whole point of interleaving is the distribution of cells over a greater time period to reduce the chance of non-recoverable errors :)

Interleaving has been turned off for about six months -- in fact since about one day after we got connected with Xnet.

Given that the above figures represent the situation with Interleaving already turned Off, do you think the 0 errors actually means that no CRC errors were detected on the line during the past 23 days, or is it still 0 non-recoverable errors as you stated above for the Interleaved case?

Niel

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#81625 8-Aug-2007 20:45

If it is basic info (as you listed), then take it as zero non-recoverable errors. If you have a detailed status screen, it will separate it into all the different types of errors.

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Fraktul

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#81640 8-Aug-2007 21:30

As Niel states its probably 0 non-recoverable as its only non recoverable errors you are really concerned about when it comes down it it.

There are two things which are of primary importance, the signal strength (output less attenuation) and the SNR (difference between between the signal and noise strengths).

If the signal strength is too low then regardless of how much noise there is the modem or other signal processor will not be able to extract information. Likewise if there is too little different between the strength of the signal and the strength of the noise (SNR) no information may be extracted or it may contain errors.

>=10db SNR is desirable for ADSL/ADSL 2+ yes.

ajobbins

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#81740 9-Aug-2007 15:02

Would I be better of with Interleave off? I don't really know how to read these stats properly.

Line Mode	G.DMT	Line State	Show Time
Latency Type	Interleave	Line Up Time	00:04:48:18
Line Coding	Trellis On	Line Up Count	1

Statistics	Downstream	Upstream
Line Rate	7616 Kbps	160 Kbps
Attainable Line Rate	8576 Kbps	1072 Kbps
Noise Margin	12.9 dB	30.0 dB
Line Attenuation	29.0 dB	18.5 dB
Output Power	19.8 dBm	3.1 dBm
K (number of bytes in DMT frame)	239	6
R (number of check bytes in RS code word)	16	16
S (RS code word size in DMT frame)	1	16
D (interleave depth)	32	2
Super Frames	1017513	1017511
Super Frame Errors	0	0
RS Words	69190914	4324421
RS Correctable Errors	1199	0
RS Uncorrectable Errors	0	0
HEC Errors	0	0
OCD Errors	0	0
LCD Errors	0	0
Total Cells	310706845	0
Data Cells	1416630	0
Bit Errors	0	0
Total ES	0	0
Total SES	0	0
Total UAS	17	0

grant_k

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#81754 9-Aug-2007 15:46

Hi Adam,

The stats for your line are even better than mine, especially regarding the Noise Margins, so you should have no problems whatsoever in going to Interleaving Off.

The Downstream Attenuation figure also tells you that you are 2.1km from the exchange.

Finally, there are zero uncorrectable errors, so everything is looking good

It's a pity you aren't on Xnet's Flood (FS/FS) plan, then your speeds would totally rock. It's an extra $16 per month though and I guess you aren't too worried about having a slow Upload Speed?

ajobbins

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#81756 9-Aug-2007 15:57

FS/FS would be nice but its 50% more expensive and I don't really think that I would benefit from a faster upload speed really except maybe if I kept my VFX on G711u. G729a sounded terrible when I was on Woosh DSL but sounds alot better (Via my iTalk lines) on Xnet so I have asked to have my VFX line changed over to 729a again.

It's also looking likley I may have to opt for a static IP so that will add to the cost too.

grant_k

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#81760 9-Aug-2007 16:04

adamj: It's also looking likley I may have to opt for a static IP so that will add to the cost too.

WxC are not currently charging any extra for this, and in my case haven't been since I joined in Jan this year. Admittedly, that is on the Flood plan, I'm not sure if the same policy applies to River.

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