Is this true about the B\width available on Adsl??

beomont

Got this of the Alcatel website(the usb modems that eircom are providing for the trial)

"Unlike cable modems, ADSL is not shared among users and so its speed and capacity are not affected by how many subscribers are using the service at the same time. The line is there for you and you alone."

Just wondering if this is in fact true as a mate of mine who has been on the Ntl service since it started did say something about a ratio of people to one connection on the cable service.
Another question I would like to ask is if you were to get more bandwidth on your adsl connection like 1mbit or 1.5 does your ping times go down or is there a ceiling on it??

Red Moose

NOpe, AFAIK there is a similar contention ratio on ADSL, e.g., in the UK in summer 2000 when BT introduced it was initially at 50:1, so if everyone was using it, it would actually be slower than 56k in theory anyway.

Essentially I would say that a comment like that is just marketing nonsense - after all, they are telling the truth because it is *your* line going into the house, which you pay specific rental for *cough* DACS box *cough*, whereas the cable box is all routed through a big box somewhere on the street near you.

Bandwidth, as in 1MBit, etc., will not affect ping. You can get sub 200ms pings on a 33.6 modem, and get 300ms+ on a 56k........ISDN has only 64k bandwidth but way better pings, so it's obviously somethign to do with the specific type of line, probably

Dustaz

Im not 100% sure, but afaik Cable bandwith is shared before it hits the 'exchange' while xDSL is shared at the exchange.
So if theres noone on the net apart from you and your neighbour and he decides to host a warez server, your bandwith dies if your using cable but not if you are using DSL. Whereas if Irelands internet traffic is heavy, your in trouble no matter which system you use.
Hmm, Not sure if im absolutly correct here so, I should probably let someone explain it better:)

No idea about the second question, but all the other trialists i saw had similar pings to mine on game servers, but im not sure whether anyone on the trials got a 1mb line.

Fergus

With ADSL, you have dedicated bandwidth between you and the exchange (into the DSLAM), and I believe from there to the ISP's point of presence. However, at that stage you are sharing a fixed pipe with as X other users. Typically the ratio of available bandwidth to each user's rated DSL speed os 1-24, 1-50 or even 1-100.

Ping time is affected by a number of factors. The speed of the DSL line will affect how long the packet takes to get from you to the first router ('hop'). There's also latency while the router decides the next path for the packet. And then depending how busy that path is, it might have to wait a bit longer. Then there is the total number of hops to get to the far end and back. The more hops there are, the less the speed of your local connection is going to matter.

Boston

in england its 50:1 and a 2mbit pipe while here its 25:1 with a 1mbit pipe. you decide which is better

rardagh

This is a partially-true statement to the extent that there is a direct connection from the DSLAM to the DSL CPE over the copper loops.

However, it is not totally true because (to an extent) there is theoretical 'spectrum' contention within the copper bundles. This is why you will find that some European Regulatory Authorities allow an incumbent OLO to limit their DSL deployment to a percentage of the lines in every x hundred pair bundle. Furthermore, in order to alleviate the potential of this latent problem impacting more-rather-than-less, the ODTR has (as have most other EU NRAs) sought to impose a spectrum mask on the DSL CPEs being deployed. This 'trick' has proven in other countries to effectively limit the range of services available to the customer as the incumbent seeks to exagerrate the impact of this spectrum congestion - in fact in Ireland it is impossible for an OLO to deploy VDSL currently because the ODTR has not sanctioned a CPE Spectrum Mask that is suitable for VDSL.

The Other Areas of contention have already been previously stated, including:

1. The DSLAM itself
2. The Transit link from the DSLAM to the Core network of the OLO or Eircom
3. The 'Internet' link of the OLO or Eircom
4. Any Router, NAT box, firewall etc. through which your data passes

Each of these 4 points can be addressed directly by the telecom operator, however the higher the contention ratio at each level typically the higher the operating margin for the provision of service. This is why in some countries, service prcing differentiation is based on 'the level of contention' you are willing to pay for; 1:1 = Expensive , 50:1 = Less Expensive.

PiE

Well, using my hyper-technologically-advanced-uber-computer's memory I've worked out that 25:1 on a 1mb pipe is EXACTLY THE SAME as 50:1 on a 2mb pipe! Imagine that.

Boston

Originally posted by PiE
Well, using my hyper-technologically-advanced-uber-computer's memory I've worked out that 25:1 on a 1mb pipe is EXACTLY THE SAME as 50:1 on a 2mb pipe! Imagine that.

when you dont know what your talking about, id advise you not to make stupid comments,

24:1 over 1mbit is vastly different to 50:1 over 2mbit

i will not take the time to explain it to you as you clearly lack the ability to graps the significant of what i would say.

Try not to be smart me again for your own good. if you really do seak to understand it, then i suggest you post a tread in the net/comms forum. if your not to rude about it someone like hubson might actually answer you, and inlighten you to the realities of this world we live in.

Ps: Now thats a stinging reply

hudson806

bundle. Furthermore, in order to alleviate the potential of this latent problem impacting more-rather-than-less, the ODTR has (as have most other EU NRAs) sought to impose a spectrum mask on the DSL CPEs being deployed. This 'trick' has proven in other countries to effectively limit the range of services available to the customer as the incumbent seeks to exagerrate the impact of this spectrum congestion

Although its true that many telcos have used the issue to stall CLEC DSL deployments, its important to stess that sensible spectral management is still absolutely essential to avoid Crosstalk(particularly FEXT) problems in the future. In the case of VDSL, this is particularly true, as its frequency range directly overlaps with G.dmt DSL and G.Lite DSL frequencies.

Originally posted by «Bo§ton»


when you dont know what your talking about, id advise you not to make stupid comments,

24:1 over 1mbit is vastly different to 50:1 over 2mbit.

You're confusing the ratio with the size of the backhaul:- the backhaul (1Mb or 2Mb determines the ratio: it isn't really an additional parameter the way that you seem to think it is. In reality, the ratio and the bandwidth are two separate issues:

1./ In general, the more bandwidth shared , the better: 100 people sharing 1Mb/s should get a better service than 50 people sharing 512kb/s simply because the impact of individual bandwidth hogs will be smaller.

2./ The ratio makes a far greater impact though: 50:1 is always slower than 24:1, all other things being equal. However, due to (1) the more users sharing the service, the better it will be.

In short, saying 50:1 over 2Mb vs. 24:1 over 1Mb is nonsense:- it makes far more sense to compare ratios at a given speed - and 512k@50:1 is worse than 512k@25:1.

Finally, in an attempt to get this back on topic: The issue of these ratios is what separates DSL from cable modem services: Its not all that easy to set up ratios with the current cable modem standards. The usual strategy with cable modems is to just have them all terminate at a 'head-end', which is basically a big router hooked into the Internet. When the traffic begins to look a bit congested at that point, more bandwidth is added (or not added if they want to minimize costs...)

So, in short, Alcatel's website is probably right, but only to a point since its still easy to have crap ADSL services and really good cable modem services

Dustaz

I think i speak for a fair amount of people when i say "huh?" to rardagh and hudsons posts
n1 for the simplified version tho hudson:)

PiE

Cough.

Boston

Originally posted by hudson806


Although its true that many telcos have used the issue to stall CLEC DSL deployments, its important to stess that sensible spectral management is still absolutely essential to avoid Crosstalk(particularly FEXT) problems in the future. In the case of VDSL, this is particularly true, as its frequency range directly overlaps with G.dmt DSL and G.Lite DSL frequencies.



You're confusing the ratio with the size of the backhaul:- the backhaul (1Mb or 2Mb determines the ratio: it isn't really an additional parameter the way that you seem to think it is. In reality, the ratio and the bandwidth are two separate issues:

1./ In general, the more bandwidth shared , the better: 100 people sharing 1Mb/s should get a better service than 50 people sharing 512kb/s simply because the impact of individual bandwidth hogs will be smaller.

2./ The ratio makes a far greater impact though: 50:1 is always slower than 24:1, all other things being equal. However, due to (1) the more users sharing the service, the better it will be.

In short, saying 50:1 over 2Mb vs. 24:1 over 1Mb is nonsense:- it makes far more sense to compare ratios at a given speed - and 512k@50:1 is worse than 512k@25:1.

well thats what i was trying to say, though i did leave out the 512k part i was acting on a level stardard. in which case 24:1 is going to be better for obvious reasons. i only included the size of the pipe because it had allreeady been mentioned what it was in england and i wanted to state what it is here.

JamworkS

Bandwidth, as in 1MBit, etc., will not affect ping. You can get sub 200ms pings on a 33.6 modem, and get 300ms+ on a 56k........ISDN has only 64k bandwidth but way better pings, so it's obviously somethign to do with the specific type of line, probably

For example, AFAIK ISDN is digital so, unlike 56k it doesn't need to convert the signal (Modulate/Demodulate) making it faster (at some point), besides that ISDN installation go to different part in the exchange instead of the one with all the voice+data routers. But I still can't think of the 4 months delay in the installation of an ISDN line.


JamworkS.

d-j-k

Are you sure about ISDN going to a different part of the exchange?!

ISDN is provided by the normal circuit switched network. In a digital exchange your line card is provided with a 64K circuit. The line card encodes the voice signals ( a bit like a PC sound card) from your line as data and pass it thru to the switching system. All ISDN does is replace the analogue line card, actually with a much simpler one. You are basically given access to the raw 2X B channels 64K + 1 D (signalling channel) data channels rather than being given an analogue line card. I think the hiSpeed box uses the D-channel for maintenence/monitoring/remote setup etc, so i'm not sure if you can access it thru it.

AFAIK, in a modular digital switching system (exchange) like the 2 systems used by eircom. Alcatel E-10 and Ericsson AXE, changing a line to ISDN litterally involves someone going to a rack of line cards, sliding out the analogue one and sliding in an ISDN one. Some newer cards are even dual purpose and can handle either analogue "plain old telephone service" or ISDN protocalls. Changing over is a matter of just telling the line card to provide Euro-ISDN instead of POTS.

It is true that in the olden days ISDN was provided by a different part of the exchange. Eircom and many other telco's throughout the world were working with 2 different technologies. Older crossbar (electromechanical) and electronic but non-digital switches alongside full modern digital switches. Usually an old exchange was parented by a digital one which provided access to the "rest of the world" and if a customer requested ISDN they were re-routed to the digital part of the exchange. However, Eircom have had 100% digitalisation for quite some time and in reality had very few electromechanical exchanges since ISDN launched. The delays are totally unexplainable!! Perhaps a lack of resources? or some inefficiencies.. but they can hardly argue that it's down to a technical inability to supply it!

Go to www.alcatel.com or www.erricson.com and look up AXE and E-10 and you'll find out what those switches "should" be able to do. (software update dependent)

cmkrnl

Originally posted by «Bo§ton»
in england its 50:1 and a 2mbit pipe while here its 25:1 with a 1mbit pipe. you decide which is better

Not quite, for the business ADSL tarriff the contention ratio is 20:1. That said I have never experienced congestion in 12 months of using my 2Meg DSL connection from Easynet.


greg

Boston

well holdon wait a minute, the bog standard adsl from bt is 50:1 and only come in one form. bitstream adsl on the other hand can he allmost anything that they agree on.

DeVore

/me slaps forehead.

50 over 2mbit is OBVIOUSLY and CONSIDERABLY better then 25 over 1mbit.


Break it down, Hammertime...

Do you think :
1 user sharing 1 56k line is better then
2 users sharing 2 x 56k lines?

Of course it is, because you are likely to be using it at different (microsecond level) times. Remember, maxing a line out is kinda hard to do without something like Quake and even then programs like Roger Wilco can squeeze enough for voice over.

Ok, more blatantly:

would you rather be 1 user on 56K or one of 10 *POSSIBLE* users on a half a meg line? the very worst case is that all 10 are on and fighting for bandwidth equally (routers dont really prioritse warez/quake packets over other packets).

Ok, if the math doesnt convince you and you cant see the logic, then let me tell you some anecdotal evidence:
12 (twelve) people work relatively fine off a SINGLE ISDN LINE in Spin here. Browsing and general usage isnt really affected.

I dunno, sometimes the armchair experts here really amaze me. I could go into normal distribution graphs of internet usage and how doubling the number of POSSIBLE users would only slightly increase the peak load on the line.
However I think I might as well show them to my dog Fluffles.

And I dont have a dog.

DeV.

Boston

a but you see you potential max speed is only 512k so you have to share that either 50 ways or 25 ways, which is better.

it all depends on what you take into account and what you discard

cmkrnl

Originally posted by «Bo§ton»
well holdon wait a minute, the bog standard adsl from bt is 50:1 and only come in one form. bitstream adsl on the other hand can he allmost anything that they agree on.

Not quite.

The 512k USB delivered IPstream is delivered @ 50:1 contention. The Ethernet delivered 512/1024/2048 IPStream is @ 20:1 contention.


You paints your monet ;-).



greg

cmkrnl

Originally posted by «Bo§ton»
a but you see you potential max speed is only 512k so you have to share that either 50 ways or 25 ways, which is better.

it all depends on what you take into account and what you discard

Not quite, the contention is for the BFP at the back of the DSLAM, i.e an E3 or a DS3. Not the connection down the copper from the exchange. Unless one has a substantial number of users running their connection flat out, you will not notice the contention.

All connections at both contention ratios terminate on the same DSLAM and are packet shaped at the relevant QoS level.


greg

Boston

Originally posted by cmkrnl


Not quite.

The 512k USB delivered IPstream is delivered @ 50:1 contention. The Ethernet delivered 512/1024/2048 IPStream is @ 20:1 contention.


You paints your monet ;-).



greg

thats interesting, i wasnt aware they were selling an ethernet version, i knew they were trialing a 1mb version in london that was ethernet. have you got anymore details about it.

Also, im aware that few the level of use is a factor, but not to that extent imho but a las im not as well up on this as either you or hubson. but but of you seem to have differing views

oscarBravo

The brother in London has ADSL. He pays £300/qtr for it, with 512k down (I think), no caps (although he heard a 1GB/day rumour), and no setup fee. He got a 4-port Ethernet hub included in the deal.

I don't know if he had the option to pay a setup charge and so reduce his quarterly costs.

cmkrnl

Originally posted by «Bo§ton»


thats interesting, i wasnt aware they were selling an ethernet version, i knew they were trialing a 1mb version in london that was ethernet. have you got anymore details about it.

BTIgnite deliver IPStream DSL on ethernet at 512/1024/2048 on an Efficient Networks 5861 DSL router with a 256k back channel. The ISP I am with (EasyNet) provides ethernet only & provides real addresses (in my case a /29). However the router can do NAT & packet filter based firewalling should you feel the need.

Also, im aware that few the level of use is a factor, but not to that extent imho but a las im not as well up on this as either you or hubson. but but of you seem to have differing views

What he says is correct, Potential contention problems is ultimately caused by the lack of capacity on the ATM circuit coming out of the DSLAM back to the ISP. If this is kept large enough & upgraded when one reaches say 35-40% sustained utilisation. The average DSL user will never see contention. I can sustain > 200K/Sec downloads here from various parts of net, however over a 24 hour period my average utilisation is in single digit figures /sec. It would take 17 2 Meg DSL users running flat out to fill an E3. However that is not the full story. Any decent QoS software running on the DSLAM will take the number of connections into a/c & make sure that everyone gets a decent bite at the cherry. Start throttling the 256k back channel for those 17 users & it'll choke their tcp transfers real quick.

The DSL method of bandwidth sharing is IMHO superior to that offered by cable, as one will not have a situation when some haX0r running a warez site can bring everyone else on the same network to a crawl.



greg