bekdik
Honorary Master
How does shaping affect contention?
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Why does Telkom shape?
- Thread starter alaincraven
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stoke
Honorary Master
Contention = e.g. 100 people per 1MB's.
Shaping = Prioritising the traffic on a line.
i.e. Not related at all.
i.e. Your question does not make any sense.
The more contended a line is, then - well - the more we're being ripped of by the line provider, cos if everyone started to us the line at the same time, the line would fail dismally to provide any of us with any service.
Shaping = Prioritising the traffic on a line.
i.e. Not related at all.
i.e. Your question does not make any sense.
The more contended a line is, then - well - the more we're being ripped of by the line provider, cos if everyone started to us the line at the same time, the line would fail dismally to provide any of us with any service.
Based on a study a few years ago in the US by an ISP consortium.
90% of the BW is consumed by 10% of the users
The remaining 10% of bandwidth is shared betweeen the other 90% of the users.. That is why typically most ISP's aren't concerned about the 10% that are eating up the BW.
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As far as contention ratios..
In your office, if you have a 24 port 10/100 switch with 23 users and 1 server. What is your contention ratio to the server? 23:1.. 1 user could actually kill all the BW to server. Does it happen often? not really, if it does, you typically scream at the admin, unless you are the admin then you go slap the user..
Does that make sense?
90% of the BW is consumed by 10% of the users
The remaining 10% of bandwidth is shared betweeen the other 90% of the users.. That is why typically most ISP's aren't concerned about the 10% that are eating up the BW.
*********************
As far as contention ratios..
In your office, if you have a 24 port 10/100 switch with 23 users and 1 server. What is your contention ratio to the server? 23:1.. 1 user could actually kill all the BW to server. Does it happen often? not really, if it does, you typically scream at the admin, unless you are the admin then you go slap the user..
Does that make sense?
Due to capping the effective line speed is about 9Kbit over a monthly average, which gives a virtual 1:55 contention ratio for a 512Kbit link. This ratio of course is totally artificial as it assumes 100% saturation by all users and has nothing to do with the real contention ratio you experience before the cap hits.
As paarlberg rightly pointed out it is only a small percentage of the users that scoff bandwidth, so as you have more subscribers the rate at which you need to add capacity decreases per subscriber. Considering the number of ADSL users I can quite easily imagine contention of 1:200 or even higher being used by Telkom, especially since capping eliminates those high usage users pretty quick.
As paarlberg rightly pointed out it is only a small percentage of the users that scoff bandwidth, so as you have more subscribers the rate at which you need to add capacity decreases per subscriber. Considering the number of ADSL users I can quite easily imagine contention of 1:200 or even higher being used by Telkom, especially since capping eliminates those high usage users pretty quick.
bekdik
Honorary Master
So does this mean that if I shape the bandwidth I can increase the user contention and so get more people paying for the same infrastructure?
Shaping and Contention are not really related.
Shaping is usually used to ensure that an aggressive protocol does not congest the lines.
Contention is sharing the backend capacity between a number of users.
In theory shaping is only supposed to kick in when the lines are congested, while contention is always there – just you only notice it if everyone is surfing at the same time.
So contention is what will enable you to save money on infrastructure, while shaping keeps your bandwidth hogs from degrading the whole network.
The trouble is that Telkom seem to have done their shaping backwards, usually you assign priority to latency sensitive protocols such as VoIP or streaming data and not to email and http which are not very sensitive to small delays.
Shaping is usually used to ensure that an aggressive protocol does not congest the lines.
Contention is sharing the backend capacity between a number of users.
In theory shaping is only supposed to kick in when the lines are congested, while contention is always there – just you only notice it if everyone is surfing at the same time.
So contention is what will enable you to save money on infrastructure, while shaping keeps your bandwidth hogs from degrading the whole network.
The trouble is that Telkom seem to have done their shaping backwards, usually you assign priority to latency sensitive protocols such as VoIP or streaming data and not to email and http which are not very sensitive to small delays.
stoke
Honorary Master
Nail on the head fellow. Not totally unexpected - this is backward africa is it not.pookfuzz said:
paarlberg said:
ping xxx.xxx.xx.86
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to xxx.xxx.xx.86, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 297/310/345 ms
That is over SAIX at 6AM SA time.
stoke said:Nail on the head fellow. Not totally unexpected - this is backward africa is it not.
Shaping can also include limiting the length of time that a subscriber or group of subscribers can chew up your bandwidth..
In cisco it would be this..
traffic-shape group 150 48000 48000 48000 1000
You can get a full decription on Cisco's site for each of them and how they affect the speeds.. Basically that example would allow bursts for 1000ms and then they would be throttled back to 48k.. This would be applied to an interface on the router and to a specified group, this could include 1 IP or a full range or even multiple ranges. It would depend on how access-list 150 in the example above would be configured..
Juice
Expert Member
pookfuzz said:
My problem is that shaping paints bandwidth hogs and gamers with the same brush. Because they have no way of differentiating between a P2P (well-documented and generally accepted hog) application and an on-line game. I thought shaping routes high priority traffic at the cost of low priority traffic and effectively introduces significant packet loss. I'm not even sure that it is done in such a sensible fashion any more, because even in the weeeeee hours of the morning, your P2P application will still only achieve 6kb/s on SAIX's shaped service. That would imply that the shaped traffic is passing through ports that have been deliberately throttled to only allow traffic through at a specific transfer rate. That's not prioritisation of traffic, in my opinion. That's more akin to sabotage. And I am annoyed because my pathetically small amount of WoW traffic has to suffer the same punishment as P2P traffic.
In all honesty, I'm failing to see the point of low caps AND port-shaping. Certainly this only amounts to a double whammy, both designed to filter out so-called 'abuse', but unfortunately spreading collateral damage to low-volume users like me.
Does anyone know HOW shaping works?
Juice
There are a number of ways in which shaping can be implemented. As paarlberg said it can be used to set a hard throughput limit on traffic, allow bursting based on time or consumption.
Usually shaping (if done sensibly) works from the total available capacity and assigns percentages or minimums to specific protocols, routes or clients. If one group does not use all the capacity assigned to it that capacity then spills over into the other groups. Bursting allows brief exceptions to the shaping rules, basically giving a connection a head start. Bursting can also work with a pooling type mechanism, the idea being that you can save up capacity while you are idle.
Of course the real question is how does Telkoms shaping work. It appears to simply limit throughput and not care if the there is free capacity - a very crude way to do shaping. In reality nobody really knows how Telkom have done it, we can only guess. Much like the contention ratios Telkom refuses to disclose I suspect how the shaping is done is also a dirty secret where the truth would cause outrage.
My guess is either Telkom lack the skill/equipment to setup shaping correctly, don't understand how it should work or have made a business decision to cripple it.
This shaping appears to take place at the ADSL perimeter as ADSL to ADSL connections do not appear to suffer shaping.
Usually shaping (if done sensibly) works from the total available capacity and assigns percentages or minimums to specific protocols, routes or clients. If one group does not use all the capacity assigned to it that capacity then spills over into the other groups. Bursting allows brief exceptions to the shaping rules, basically giving a connection a head start. Bursting can also work with a pooling type mechanism, the idea being that you can save up capacity while you are idle.
Of course the real question is how does Telkoms shaping work. It appears to simply limit throughput and not care if the there is free capacity - a very crude way to do shaping. In reality nobody really knows how Telkom have done it, we can only guess. Much like the contention ratios Telkom refuses to disclose I suspect how the shaping is done is also a dirty secret where the truth would cause outrage.
My guess is either Telkom lack the skill/equipment to setup shaping correctly, don't understand how it should work or have made a business decision to cripple it.
This shaping appears to take place at the ADSL perimeter as ADSL to ADSL connections do not appear to suffer shaping.
stevedavies
Member
Juice said:
Juice: the low cap and port shaping are not designed to filter out abuse. Or not primarily.
They are designed to make sure ADSL makes a mountain of money for a small cost.
And that it can't be used to replace an even more expensive Diginet connection.
And so that VOIP can't be used to replace an even more even more expensive international / long distance voice call.
Sorry - did you expect a product that would meet your broadband needs?
Steve
arf9999
MyBroadband Member
pookfuzz said:
The shaping seems to be present only on international bandwidth. Even outside of the ADSL network - i.e. on IS's network it seems fine.
koffiejunkie
Executive Member
I chat to my sis in Austin every couple of nights on Skype, using 192kbit ADSL on my side, while my house mate is browsing and doing his gentoo emerge updates. This is 64kbit up. Only occasionally does she complain about my voice on her side breaking up.