Contention Question

I understand that 50:1 contention means that up to 50 people are sharing
bandwidth, but sharing how much exactly? Does it mean that if all 50 are on
a 512 connection you could potentially have download speeds of 10Kbps, or am
I completely misunderstanding it?

On Fri, 10 Oct 2003 23:39:56 +0100, "s7uar7" <(E-Mail Removed)>
wrote:

>I understand that 50:1 contention means that up to 50 people are sharing
>bandwidth, but sharing how much exactly? Does it mean that if all 50 are on
>a 512 connection you could potentially have download speeds of 10Kbps, or am
>I completely misunderstanding it?

You are most right, yes you are sharing bandwidth with others at a
ratio of 50:1 and the lowest bandwidth possible is 10Kbps.

It isn't 50 users sharing one 512k connection, it is much larger
bandwidths shared between much larger sets of users. The sizes we are
typically talking about 12mbps shared between 1200 users.

It tends to work out quite well.
--
Andy Norman (E-Mail Removed)
http://www.norman.cx/
Replace the fish with my first name to reply

s7uar7 wrote:
> I understand that 50:1 contention means that up to 50 people are sharing
> bandwidth, but sharing how much exactly? Does it mean that if all 50 are on
> a 512 connection you could potentially have download speeds of 10Kbps, or am
> I completely misunderstanding it?

IIUC, the contention is for the backhaul connection between your
exchange and your ISP. The connection between you and your exchange will
be a real 512K (or whatever speed you have paid for), however at the
exchange there will be up to 50 connections multiplexed into the logical
pipe back to your ISP.

Working out exactly how much bandwidth that equates to is not easy since
they don't typically advertise the capacity of the backhaul connection.
I would expect it to be in the order of 8Mbs or more allocated to each
50 users. As with most things related to telecomms its based on
statistical probabilities - 8Mbs would only be enough for 16 odd users
to use concurrently and get the full 512K - the reality however is that
since each users usage is "bursty" in nature, it's not likely that
everyone that shares the connection will require their full capacityat
the same time. Hence it works rather well and it appears that we each
get the 512K we expect.

You may see degradation if you are unlucky enough to be sharing with 20
P2P file transfer junkies however!

--
Cheers,

John.

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On Sat, 11 Oct 2003 04:08:55 +0100, John Rumm
<(E-Mail Removed)> wrote:

>however at the
>exchange there will be up to 50 connections multiplexed into the logical
>pipe back to your ISP.

the 50 is a ratio, not a number. If there were 50 connections it would
be a 512k channel they were linked too, its more likely to be a large
number in a bigger channel - 137 in a 1.4 M channel for example :-)

Phil

Phil Thompson wrote:

>>however at the
>>exchange there will be up to 50 connections multiplexed into the logical
>>pipe back to your ISP.
>
>
> the 50 is a ratio, not a number. If there were 50 connections it would
> be a 512k channel they were linked too, its more likely to be a large
> number in a bigger channel - 137 in a 1.4 M channel for example :-)

Yup I appreciate that (that was why I said "logical pipe") - was just
sticking to 50 to keep it simple! ;-)

Since ADSL in the UK runs over BTs ATM network I would expect it to
ultimately running on 622Mbs links. However I expect that an ISP can
purchase less backhaul connectivity than that, since with a 50:1 ratio
622Mbs is a hell of a lot of subscribers!

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article <CuThb.6527$(E-Mail Removed)>,
John Rumm <(E-Mail Removed)> wrote:
>Since ADSL in the UK runs over BTs ATM network I would expect it to
>ultimately running on 622Mbs links. However I expect that an ISP can

622Mbps in just the maximum access circuit you can buy to CellStream. ISPs
buy access circuits into their own premises and PVCs between them and BW
Wholesale to deliver their customers' traffic. That doesn't mean tha BT
runs 1 x 622Mbps circuit into the ATM cloud per exchange - the access
circuits will depend on need per exchange.

>purchase less backhaul connectivity than that, since with a 50:1 ratio
>622Mbs is a hell of a lot of subscribers!

ISP "fat pipes" come in 10, 155 and 622Mbps, I believe.

Zane

John Rumm <(E-Mail Removed)> wrote in
news:CuThb.6527$(E-Mail Removed):

> Phil Thompson wrote:
>
>>>however at the
>>>exchange there will be up to 50 connections multiplexed into the
>>>logical pipe back to your ISP.
>>
>>
>> the 50 is a ratio, not a number. If there were 50 connections it
>> would be a 512k channel they were linked too, its more likely to be a
>> large number in a bigger channel - 137 in a 1.4 M channel for example
>> :-)
>
> Yup I appreciate that (that was why I said "logical pipe") - was just
> sticking to 50 to keep it simple! ;-)
>
> Since ADSL in the UK runs over BTs ATM network I would expect it to
> ultimately running on 622Mbs links. However I expect that an ISP can
> purchase less backhaul connectivity than that, since with a 50:1 ratio
> 622Mbs is a hell of a lot of subscribers!
>

Just a question of curiosity. I noticed that Plus Net offers a package with
a 20:1 contention ratio. Is the difference between 50 and 20 noticable in
real live or is it perceived? I understand that possibly during peak hours
and when the US come on-line that this too has an effect of download speed.

One2Go

One2Go <(E-Mail Removed)> wrote:

: Just a question of curiosity. I noticed that Plus Net offers a package with
: a 20:1 contention ratio. Is the difference between 50 and 20 noticable in
: real live or is it perceived? I understand that possibly during peak hours
: and when the US come on-line that this too has an effect of download speed.

20:1 is based on BT's business ADSL product.

It have seen articles which say that, with the numbers of ADSL customers at
present, no part of the network is running at anything near 50:1
ratio. I think that the same article said that, if the ratio exceeds ~15-20:1
in reality (as opposed to just in theory), there is likely to be an outcry
- they reckoned that BT should be working towards this sort of figue being
a practical upper limit!

In article <Xns94165A07EA396one2go@212.135.5.86>, (E-Mail Removed)
says...
> John Rumm <(E-Mail Removed)> wrote in
> news:CuThb.6527$(E-Mail Removed):
>
> > Phil Thompson wrote:
> >
> >>>however at the
> >>>exchange there will be up to 50 connections multiplexed into the
> >>>logical pipe back to your ISP.
> >>
> >>
> >> the 50 is a ratio, not a number. If there were 50 connections it
> >> would be a 512k channel they were linked too, its more likely to be a
> >> large number in a bigger channel - 137 in a 1.4 M channel for example
> >> :-)
> >
> > Yup I appreciate that (that was why I said "logical pipe") - was just
> > sticking to 50 to keep it simple! ;-)
> >
> > Since ADSL in the UK runs over BTs ATM network I would expect it to
> > ultimately running on 622Mbs links. However I expect that an ISP can
> > purchase less backhaul connectivity than that, since with a 50:1 ratio
> > 622Mbs is a hell of a lot of subscribers!
> >
>
> Just a question of curiosity. I noticed that Plus Net offers a package with
> a 20:1 contention ratio. Is the difference between 50 and 20 noticable in
> real live or is it perceived?

Apparently, at the moment, we're not running at anything like a 50:1
contention ratio, so _ATM_ it's probably not worth getting 20:1.

> I understand that possibly during peak hours
> and when the US come on-line that this too has an effect of download speed.

It's nothing to do with the speed of the rest of the net, the contention
ratio is (as I understand it) from your exchange.

If the entire net grinds to a halt, it won't make any difference if you're
on 20:1 or 50:1.

Pete.

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Pete Smith <(E-Mail Removed)> wrote in
news:(E-Mail Removed) :

> In article <Xns94165A07EA396one2go@212.135.5.86>, (E-Mail Removed)
> says...
>> John Rumm <(E-Mail Removed)> wrote in
>> news:CuThb.6527$(E-Mail Removed):
>>
>> > Phil Thompson wrote:
>> >
>> >>>however at the
>> >>>exchange there will be up to 50 connections multiplexed into the
>> >>>logical pipe back to your ISP.
>> >>
>> >>
>> >> the 50 is a ratio, not a number. If there were 50 connections it
>> >> would be a 512k channel they were linked too, its more likely to
>> >> be a large number in a bigger channel - 137 in a 1.4 M channel for
>> >> example
>> >> :-)
>> >
>> > Yup I appreciate that (that was why I said "logical pipe") - was
>> > just sticking to 50 to keep it simple! ;-)
>> >
>> > Since ADSL in the UK runs over BTs ATM network I would expect it to
>> > ultimately running on 622Mbs links. However I expect that an ISP
>> > can purchase less backhaul connectivity than that, since with a
>> > 50:1 ratio 622Mbs is a hell of a lot of subscribers!
>> >
>>
>> Just a question of curiosity. I noticed that Plus Net offers a
>> package with a 20:1 contention ratio. Is the difference between 50
>> and 20 noticable in real live or is it perceived?
>
> Apparently, at the moment, we're not running at anything like a 50:1
> contention ratio, so _ATM_ it's probably not worth getting 20:1.
>
>> I understand that possibly during peak hours
>> and when the US come on-line that this too has an effect of download
>> speed.
>
> It's nothing to do with the speed of the rest of the net, the
> contention ratio is (as I understand it) from your exchange.
>
> If the entire net grinds to a halt, it won't make any difference if
> you're on 20:1 or 50:1.
>
> Pete.
>

Thanks for the information.