Why not max speed on ADSL when line capability > connection speed?

[Bryn]

I'm hoping someone can shed light on the issue of ADSL speeds. I sort of understand that you cannot receive maximum theoretical speed of your connection because of inefficiencies or something, ie. don't hope for 512KB/s download speed on a 4Mbps connection.

What I don't understand is why we don't receive the full speed we pay for if our line is capable of faster speeds. My line is capable of 6Mbps. What technical limitation is preventing me from receiving 4096kbps?

 

[zll]

Um. Your line is 6 mbps but you are wondering what is preventing your from receiving 4 mbps? I think you mean 6?

If you mean 6, you can have a 6 meg line and a 4 meg account, in which case your line is limited by the account speed. If you want max speed on your line you have to have an account that matches it.

 

[Gtx Gaming]

10-15% tcp overheads , why 4096kps line only downloads at 430kbs odd

 

[elriconess]

Why does Telkom not introduce something like Broadband Max?

here's an introductory video:

[video=youtube;3HgXcwK93CQ]http://www.youtube.com/watch?v=3HgXcwK93CQ[/video]

 

[MickZA]

If your line is actually syncing at 6mbs (as opposed to merely capable of) you should get close to theoretical 4mbs throughput speeds when using a TI or IS 4mbs uncapped account from my experience, can't comment on other ISP's 4mbs uncapped offerings.

 

[Bryn]

Um. Your line is 6 mbps but you are wondering what is preventing your from receiving 4 mbps? I think you mean 6?

If you mean 6, you can have a 6 meg line and a 4 meg account, in which case your line is limited by the account speed. If you want max speed on your line you have to have an account that matches it.

Let me rephrase. My line is capable of 6mb. I have a 4mb internet connection. Why can't I receive a full 4096kbps? What is causing the inefficiency when line speed is not an issue?

 

[Bryn]

10-15% tcp overheads , why 4096kps line only downloads at 430kbs odd

Why the 'overheads' when the line is faster than the internet account?

 

[Bryn]

If your line is actually syncing at 6mbs (as opposed to merely capable of) you should get close to theoretical 4mbs throughput speeds when using a TI or IS 4mbs uncapped account from my experience, can't comment on other ISP's 4mbs uncapped offerings.

I think syncing is the correct term. My router DSL status has 6144 down and 640 up. Loading a capped account confirms this potential speed.

I don't receive speeds anywhere near 512KB/s on my main 4Mbps account. It's unshaped btw. I'd just like to know why we don't receive 97+% of our internet connection speed if it's not being limited by the line.

You understood my question best though. Thanks for the info.

 

[MickZA]

Pictures worth a thousand words - TI 4mbs uncapped on a 6mbs line:

 

[grok]

Let me rephrase. My line is capable of 6mb. I have a 4mb internet connection. Why can't I receive a full 4096kbps? What is causing the inefficiency when line speed is not an issue?

In layman's terms your line is capped at 4mbps max & then there's overheads eating into that 4mbps meaning you won't ever get the full speed your line is syncing at. You'll only ever get the full 4mbps when Telkom lets you sync at 6mbps while using a 4mbps ISP account.

Example:

Due to k@k service from Telkom, my 4mbps line currently only syncs at 2mbps max. I have both a 130gb capped & 1mbps uncapped ISP account that I use for backup when I run out of the 130.

When on the capped ISP I get ~180kbps max (sync speed of 2mbps, minus overheads), but when on the 1mbps account it sometimes goes up to ~140kbps ('cos the speed my line syncs at is higher than the speed of my ISP account).

Or something like that ..

 

[Bryn]

In layman's terms your line is capped at 4mbps max & then there's overheads eating into that 4mbps meaning you won't ever get the full speed your line is syncing at. You'll only ever get the full 4mbps when Telkom lets you sync at 6mbps while using a 4mbps ISP account.

Example:

Due to k@k service from Telkom, my 4mbps line currently only syncs at 2mbps max. I have both a 130gb capped & 1mbps uncapped ISP account that I use for backup when I run out of the 130.

When on the capped ISP I get ~180kbps max (sync speed of 2mbps, minus overheads), but when on the 1mbps account it sometimes goes up to ~140kbps ('cos the speed my line syncs at is higher than the speed of my ISP account).

Or something like that ..

I think I'm more confused than before.

Firstly, my line syncs at 6mb and gets that speed with my Afrihost capped account. I assume 'overheads' are not from my ISP but an inherent DSL limitation. Why then must my 4mb uncapped unshaped account (or any account less than the line sync speed) not achieve full 4096kbps on a line syncing at 6mb? There's a whole 2Mbps of line capacity to waste on getting my bandwidth to me.

Secondly, your capped speed makes sense, but how can you get 140KB/s when 128KB/s is as high as 1mb goes, ignoring overheads? Every uncapped ISP claims to deliver the lower of your line or account speed. Is it some sort of error?

 

[MickeyD]

On a capped account you will always receive full line speed (less tcp overheads). You are limited by your data cap.

On an uncapped account you are limited by the lower of your line speed (6) or ISP account (4)m less tcp overheads. This is to ensure that the ISP can make some form of profit from your contented data account.

 

[Chevron]

I think I'm more confused than before.

Firstly, my line syncs at 6mb and gets that speed with my Afrihost capped account. I assume 'overheads' are not from my ISP but an inherent DSL limitation. Why then must my 4mb uncapped unshaped account (or any account less than the line sync speed) not achieve full 4096kbps on a line syncing at 6mb? There's a whole 2Mbps of line capacity to waste on getting my bandwidth to me.

Secondly, your capped speed makes sense, but how can you get 140KB/s when 128KB/s is as high as 1mb goes, ignoring overheads? Every uncapped ISP claims to deliver the lower of your line or account speed. Is it some sort of error?

This could be due to shaping, over subscribed dsl exchange or slow download server.

 

[prodigyX]

Bear in mind that when you sync at 6mb, but pay for 4mb, your ISP is using "shaping" software to keep it at 4mb. This is why sometimes it 'spikes' up past 4mb but then 'settles' at around 4mb. Under perfect conditions (not taking congestion etc. into account), the final speed it settles at is completely up to your ISP. I would imagine in your situation, if you tested various 4mb accounts from different ISPs on your 6mb line, your average speed might be slightly different (and one of the accounts might actually give you the speed you expect).

To summarize, if you're not happy with the speed of your 4mb account on your 6mb line, try another ISP.

 

[grok]

I think I'm more confused than before.

..
Secondly, your capped speed makes sense, but how can you get 140KB/s when 128KB/s is as high as 1mb goes, ignoring overheads? Every uncapped ISP claims to deliver the lower of your line or account speed. Is it some sort of error?

Don't know the exact reason, might be what was said below but I have seen it spike to ~180 on occasion. Usually not that high though.

Bear in mind that when you sync at 6mb, but pay for 4mb, your ISP is using "shaping" software to keep it at 4mb. This is why sometimes it 'spikes' up past 4mb but then 'settles' at around 4mb. Under perfect conditions (not taking congestion etc. into account), the final speed it settles at is completely up to your ISP. I would imagine in your situation, if you tested various 4mb accounts from different ISPs on your 6mb line, your average speed might be slightly different (and one of the accounts might actually give you the speed you expect).

 

[Bryn]

On a capped account you will always receive full line speed (less tcp overheads). You are limited by your data cap.

On an uncapped account you are limited by the lower of your line speed (6) or ISP account (4)m less tcp overheads. This is to ensure that the ISP can make some form of profit from your contented data account.

It's an unshaped account though.

This could be due to shaping, over subscribed dsl exchange or slow download server.

The server is definitely fine (tried SSL news, torrents & Nvidia driver downloads). A Telkom techie set my line to sync at 6mb precisely because it was the fastest good connection I could achieve on my 8mb exchange.

In any case, I can definitely achieve speeds above 4Mbps with capped accounts, so there is room to spare.

Bear in mind that when you sync at 6mb, but pay for 4mb, your ISP is using "shaping" software to keep it at 4mb. This is why sometimes it 'spikes' up past 4mb but then 'settles' at around 4mb. Under perfect conditions (not taking congestion etc. into account), the final speed it settles at is completely up to your ISP. I would imagine in your situation, if you tested various 4mb accounts from different ISPs on your 6mb line, your average speed might be slightly different (and one of the accounts might actually give you the speed you expect).

To summarize, if you're not happy with the speed of your 4mb account on your 6mb line, try another ISP.

So then there's nothing stopping me from receiving proper 4Mbps if my line syncs above that? It's an unshaped and unthrottled uncapped account so it's not like my ISP can blame any factor other than their system.

I'll call them and ask for the 4096kbps that's being paid for.

 

[MickeyD]

It's an unshaped account though.

I'll bet dollars that it is still a contented product, just less so.

 

[Bryn]

I'll bet dollars that it is still a contented product, just less so.

Well, the product description describes the account as completely unshaped 24/7. I know that I have no line issues, so an ISP has no right to manipulate the performance negatively in any way with the exception of ensuring the paid-for speed is not exceeded.

 

[MickeyD]

Well, the product description describes the account as completely unshaped 24/7. I know that I have no line issues, so an ISP has no right to manipulate the performance negatively in any way with the exception of ensuring the paid-for speed is not exceeded.

Shaping and contention are 2 different things...

 

[Logo]

On a capped account you will always receive full line speed (less tcp overheads). You are limited by your data cap.

On an uncapped account you are limited by the lower of your line speed (6) or ISP account (4)m less tcp overheads. This is to ensure that the ISP can make some form of profit from your contented data account.

Capped and uncapped has nothing to do with the overhead, the overhead doesn't change on which account you are as they both use the same network. Overhead is the result of the routing, header and encryption bits that form part of your data packets you send out over the network. Without this you won't have a network. It also has nothing to do with contention ratios as you state later. Contention ratio is the ISP selling 100mb capactity 200 people at 1mbps again nothing to do with network overhead.

To the OP and to MickeyD you can read up on network overhead and the maximum possible throughput at this link http://pflog.net/dsl_overhead/

In short OP the overhead forms part of the data and is not stripped out of the packets when being transmitted between source and destination therefor you will never get full line speed. The downloaders you use are right at the end of the line and only receive the actual data packet and they only count this in your data throughput speeds while the ISPs count the headers in to your throughput speed. on ADSL you are looking at overhead of about 15 to 20 percent. Some ISPs allow for this in that they allow the line to "burst" over the threshold for a short period of time, this is to aid with small downloads such as normal browsing and email downloads, but as soon as a large file is being downloaded you will see it spike in the beginning and then settle down to whatever speed your account is set to.