ADSL Sync Rate Mystique

[waslap]

Hi,
Can someone that understands Telkom's ADSL well give me some insight into my experience with the following anomaly with their service. I've been on 10Mb for a couple of years in Centurion and my modem synced anywhere between 6 and 8 Mbit most of the time which I accepted due their 'up to 10Mb' claim. I always assumed it was due to distance from exchange and line quality that I did not get 10Mb. I then moved to Faerie Glen and retained my 10Mb package for 4 months or so but sync rate was seldom more than 6Mb and hardly ever less than 5Mb so I decided to move to the 4Mb package the reasoning being that there's little sense in paying for an up to 10Mb if I only get half that and from my experience with the line by now, when moving to 4Mb I should always get 4Mb. Not so! Now that I'm on the 4Mb package I hardly ever get more than 3Mb sync rate which leads me to believe that the sync rate is shaped by Telkom to achieve some QoS of some sort. Is that correct ? Bear in mind that they are not my ISP so there is probably further shaping involved on that level but that's not what I'm trying to understand here? I'm merely trying to understand whether Telkom will dynamically change sync rates to accommodate current loads e.g. on the backhaul ?
Thanks

 

[FartyMarty]

Hi,
Can someone that understands Telkom's ADSL well give me some insight into my experience with the following anomaly with their service. I've been on 10Mb for a couple of years in Centurion and my modem synced anywhere between 6 and 8 Mbit most of the time which I accepted due their 'up to 10Mb' claim. I always assumed it was due to distance from exchange and line quality that I did not get 10Mb. I then moved to Faerie Glen and retained my 10Mb package for 4 months or so but sync rate was seldom more than 6Mb and hardly ever less than 5Mb so I decided to move to the 4Mb package the reasoning being that there's little sense in paying for an up to 10Mb if I only get half that and from my experience with the line by now, when moving to 4Mb I should always get 4Mb. Not so! Now that I'm on the 4Mb package I hardly ever get more than 3Mb sync rate which leads me to believe that the sync rate is shaped by Telkom to achieve some QoS of some sort. Is that correct ? Bear in mind that they are not my ISP so there is probably further shaping involved on that level but that's not what I'm trying to understand here? I'm merely trying to understand whether Telkom will dynamically change sync rates to accommodate current loads e.g. on the backhaul ?
Thanks

doubt it, coincidence maybe

 

[Pada]

Can you please post your ADSL statistics here - like current sync rates, SNR margins & line attenuation?

Telkom would many times restrict the sync rates when they don't have enough capacity, but this is typically just limiting everyone to sync at up to 4Mbps.

If you're too far from the DSLAM/exchange, then your SNR margins would probably be low and then the modem would automatically sync at a slower speed where the SNR margins are slightly higher.
If the downstream line attenuation is above 50dB, then getting a stable 4Mbps ADSL connection is quite small.
If your downstream line attenuation is below 40dB, then you shouldn't have any issues syncing at 4Mbps at all!

Shaping and congestion related problems are completely unrelated to fluctuating/lower sync rates.
Like many of us would sync/connect at 4Mbps, and only be able to download at 512kbps or slower speeds during the day, due to congestion.
So if your ADSL modem stays connected at 4Mbps, but your download speeds varies a lot (and is slow), then test with another ISP account to rule out shaping on your original ISP account. If all of your ISP accounts perform poorly, then its most likely congestion on Telkom's infrastructure.

 

[waslap]

I booted my modem yesterday. It synced to 4096 for a while, then dropped to 3776 for some time and I went to work this morning and tonight its 1856. There's no filter or telephone hooked up. This is used only for ADSL. As I said previously, when I was on 10Mb, I got on average of 5Mb. I must say though that something that could play its part is that the severe rain in Pretoria was also in the midst of all of this and it could be that it plaid a part in my deteriorated sync speed but if so, how do I convince Telkom of this ?


Downstream Upstream
SNR Margin: 22.0 12.0 db
Line Attenuation: 47.0 24.5 db
Data Rate: 3776 512 kbps

SNR Margin: 18.5 12.0 db
Line Attenuation: 47.0 24.0 db
Data Rate: 1856 512 kbps

 

[Pada]

What brand & model of an ADSL modem is that?

It appears to me like it tries to establish a connection with a very high SNR margin. Like with the D-Link modems, you can set the minimum SNR margin, which may fix your issue!

Unfortunately there is definitely something wrong with your line, because the SNR margin and data rate shouldn't fluctuate THAT much!
Try removing all filters and other devices that may be connected to the Telkom landline and then connect the only modem, directly (without any filters) and see if the data rate is 4096kbps again.

Another thing to check is that the ADSL mode can be either G.DMT or ADSL2+, and that it supports all the bin ranges in the entire frequency spectrum. Not all modems allow you to configure the latter.

 

[slvR]

I'm facing the same issues. Telkom says that they can't find any problems.