The real Telkom ADSL

rpm

rpm

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Hi again

I did some calculations to highlight what we are offered at Telkom. It is sold as a 512 kbits/s download connection, but we all know that this is far from the truth. There is a 3 Gig cap, and makes for some interesting Mathematics…lets have a look.

3 Gigabytes = 3*8 gigabits
= 24 Gbits

1 month = 30 days
= 30*24*60*60 seconds
= 2,592,000 seconds

24, 000, 000, 000/2,592,000 = 9259 bits/sec
= 9.259 kbits/s

This tells us that we are actually offered a speed of around 9 kbits/s, 6 times slower than a 56 k modem.

But it gets worse.

The international bandwidth stands at 25 Meg to the best of my knowledge. With over 4000 users, and many business connecting around 10 computers to each connection, the Mathematics is simple:

25,000,000 bits/4000 = 6250 bits/s
= 6.25 kbits/s

This is the real amount of bandwidth we are paying for. And this calculation assumes only 4000 users. There might be many more. 4000 is simply the amount given by Telkom. Apart from the 4000 users, one must remember that many businesses and homes users connect many machines to one line. There are therefore most probably more than 10 000 machines on this 25 Meg connection, which gives an even lower ratio.

Hope this clear up some of the questions on why we have such low speeds, and what we need to fight for.

Regards,

RPM





RPM
[email protected]
 
Correction Mr. RPM.

The official Telkom count was 10 000 ADSL subscribers, last week Wednesday.
[:(]
Admin
 
Hi,

Your first example is not realy applicable in determining the download speeds as in kbits/s, but rather the volume of traffic that you are allowed to transfer in any given month. Had the bandwidth been at the theoretical limit, ie.. 512kbits/s you would be able to transfer the 3gbytes in about 1 hour. However, this is the theory as one has to consider the protocol overheads, propagation delays etc. and will change the figures dramatically. Also keep in mind that the uplink speed is only 128kbits/s and that could also have a bearing on the actual througput. Even so, it should definately not be at the level we are experiencing right now. Typically, you should get about 30-40 kbytes/s transfer and I have seen this on the SA ADSL at some point in time during the early stages of release.

Your second example does however describe one of the main reasons why we are experiencing this unacceptable transfer rate and most of the complaints tends to be around the international transfer rate. If you speak to the ADSL support centre, one of the 1st things you are asked to do, is the speed test. Their speed test is done against a local server and would be quite quick. And that's the point where they say 'no problem found'.

Another more important issue, is the network shaping that Telkom has applied to the ADSL network. I have read earlier about someone else complaining about the socket connections timing out. This is a symptom of Telkom's actions.

The network shaping comes in the form of prioritisation of certain protocols or ports. I am making some assumptions here as the protocol type and destination port should be hidden from the network layer as it is used in the TCP protocol stack. But i am assuming that they may have the means to scan the TCP packets to determine the protocol or destination port. Now this leads to a number of problems.

1) By prioritising certain protocols, they are effectively de-prioritising all others. The protocols I think they have elected to prioritise are HTTP (port 80), FTP (ports 20 or 21) and Mail (Port 110). This means that any other traffic, in particular those not of the protocol type or for the designated destination port, will be de-prioritised. Hence the timeouts on other ports. They have done this deliberately to degrade applications such as Kazaa etc.

2) Now, an application such as Kazaa, is oblivious of this network shaping and so is the TCP stack. The TCP part of TCP/IP is the layer where a reasonable attempt is made to attain reliability. This reliability is achieved by agreeing a sequence number with the destination host and numbering each packet with this sequence number. If the originating host does not receive an ACK (acknowledgement) from the destination host on the sequence number sent, it will retransmit after a certain amount of time. This in itself will cause even more traffic on the network because all the de-prioritised protocols are retrying.

3) Again, i'm making assumptions here, but I believe that there is a sacrifice been made in terms of processing power to implement this network shaping as each packet has to be scanned individually to determine the protocol or port. This could also contribute to delays.

I have many more issues to discuss, but this response is rather long as it is and I will post another topic, or a few, to highlight these.

Regards

A Very Disappointed ADSL Subscriber[V]

PS : I do want to stress that Telkom has confirmed the fact that they are employing network shaping in e-mails to me, however they have refused to provide me with the details of how it is achieved, quoting 'Company Confidential Information'
 
Hi Merlin

Thanks for the informative posting.

I have experienced the port prioritizing first hand. My ping time to New York was as high as 500,000 ms. Amazingly enough it did not ping out, which also happens frequently during daytime. More International bandwidth is a must!

Regards,

RPM


RPM
[email protected]
 
Traffic to USA will suffer a larger propagation delay due to the fact that ADSL is routed via the UK and not the USA as is the case with Dial-up.

I have done some tests for Telkom where I could demonstrate packets being dropped during ping. Ping uses a protocol stack called ICMP and as such will also be subjected to the delays imposed by the network shaping as it does not form part of the selected prioritised protocols.

I have taken some traces on my ADSL line and have experienced an average delay of about 1.2 to 3 seconds during peak. I did the same trace on dialup at the same time and found it to much faster at an average of 450-700 ms. This is quite a difference as the server I did the trace on is based in europe. So one would expect ADSL to have an advantage as it is routed via UK and Dialup via the USA. The delays on ADSL is enough to cause TCP to retransmit, which was evident in the trace where I have seen up to 3 retries.
 
Actually, SAIX dial-up is routed over the SAT3 link to the UK just the same as ADSL. Also, in my experience, FTP is limited to around 10KB/sec most of the time, even for local traffic.

mithrandi
 
*sniff* Rpm is so kewl when he's fighting the good fight :D

/thinsk rpm has mellowed out in his old age :p

*runs* :D
 
As I said before, The Kenyans can be lectured by the Telkom goons in the art of conning and defrauding a whole country , the government and its people and still make them led to believe they get a great/best deal with no guarantee of service. renamed as "Best Effort" Con artists extraordinaire!
 
Merlin said:
Hi,

Your first example is not realy applicable in determining the download speeds as in kbits/s, but rather the volume of traffic that you are allowed to transfer in any given month. Had the bandwidth been at the theoretical limit, ie.. 512kbits/s you would be able to transfer the 3gbytes in about 1 hour. However, this is the theory as one has to consider the protocol overheads, propagation delays etc. and will change the figures dramatically. Also keep in mind that the uplink speed is only 128kbits/s and that could also have a bearing on the actual througput. Even so, it should definately not be at the level we are experiencing right now. Typically, you should get about 30-40 kbytes/s transfer and I have seen this on the SA ADSL at some point in time during the early stages of release.

Your second example does however describe one of the main reasons why we are experiencing this unacceptable transfer rate and most of the complaints tends to be around the international transfer rate. If you speak to the ADSL support centre, one of the 1st things you are asked to do, is the speed test. Their speed test is done against a local server and would be quite quick. And that's the point where they say 'no problem found'.

Another more important issue, is the network shaping that Telkom has applied to the ADSL network. I have read earlier about someone else complaining about the socket connections timing out. This is a symptom of Telkom's actions.

The network shaping comes in the form of prioritisation of certain protocols or ports. I am making some assumptions here as the protocol type and destination port should be hidden from the network layer as it is used in the TCP protocol stack. But i am assuming that they may have the means to scan the TCP packets to determine the protocol or destination port. Now this leads to a number of problems.

1) By prioritising certain protocols, they are effectively de-prioritising all others. The protocols I think they have elected to prioritise are HTTP (port 80), FTP (ports 20 or 21) and Mail (Port 110). This means that any other traffic, in particular those not of the protocol type or for the designated destination port, will be de-prioritised. Hence the timeouts on other ports. They have done this deliberately to degrade applications such as Kazaa etc.

2) Now, an application such as Kazaa, is oblivious of this network shaping and so is the TCP stack. The TCP part of TCP/IP is the layer where a reasonable attempt is made to attain reliability. This reliability is achieved by agreeing a sequence number with the destination host and numbering each packet with this sequence number. If the originating host does not receive an ACK (acknowledgement) from the destination host on the sequence number sent, it will retransmit after a certain amount of time. This in itself will cause even more traffic on the network because all the de-prioritised protocols are retrying.

3) Again, i'm making assumptions here, but I believe that there is a sacrifice been made in terms of processing power to implement this network shaping as each packet has to be scanned individually to determine the protocol or port. This could also contribute to delays.

I have many more issues to discuss, but this response is rather long as it is and I will post another topic, or a few, to highlight these.

Regards

A Very Disappointed ADSL Subscriber[V]

PS : I do want to stress that Telkom has confirmed the fact that they are employing network shaping in e-mails to me, however they have refused to provide me with the details of how it is achieved, quoting 'Company Confidential Information'
Click to expand...

damn, what do you do for a living?! lol
 
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