Question about bits and bytes for ADSL

[WayneHu]

Please refer to the following link:

www.cisco.com/univercd/cc/td/doc/product/software/ios121/121relnt/70series/rn70xp.htm+PPPoA+RFC&hl=en]PPPoE & PPPoA[/URL]

[WayneHu]

Sorry! Above post is the wrong Link..

PPPoE, PPPoA

[Kaj]

Re: Question about bits and bytes for ADSL

Originally posted by Jorden
<b>How fast is fast these days?

Asking these questions for a friend of mine, but also for me once I get my ADSL.</b>

1. <b>If I have a 1Mbit download connection at maximum, how long does a 1.5Gigabyte file take to download then? </b>
   
   Ok, get your calculator: you'll get a maximum of 125kByte/sec; when you divide 1500000kByte by 125kByte, the total amount of time will be 12000 seconds, or 200 minutes, or 3 hour and 20 minutes. <b>Theoretically!!</b>
   In real life you have to consider slow connections on the other side and such, but on a local server like a newsserver, these speeds can be reached.
   
2. <b>Are all downloads measured in Kbits or Kbytes per second?</b>
   
   Kilobits. Devide them by 8, and you'll get the speeds in kiloBytes. (hence the capital B)
   
3. <b>Will my PCI NIC be a bottleneck when downloading (from an external ADSL modem), as it only runs at 33Mb/s ?</b>
   
   No, not at all.. since a 10mbit NIC is faster than the ADSL-connection (1mbit ADSL versus 10mbit NIC; note the difference) this won't bother you at all. The maximum throughput of the PCI-bus is 133MB; even a 100Mbit NIC doesn't reach that kind of bandwidth.
   
4. <b>Will ADSL-downloadspeed matter on an ISDN line?</b>
   
   No. An ADSL-connection runs on different carrierwaves and the maximumspeed will be the speed your ISP will give you. Wether you are on an ISDN or an analogue line; it doesn't matter.
   You take a subscription for 1mbit; well, that's what you'll get at maximum.
   KPN wants to sell everyone an IDSN-connection, because that's easier for them to modify the colo's for ADSL. That's all, and it has nothing to do wether the dataconnection is fast or not.

I know that some answers have been given in this thread, but I wanted to make a clear list of answers, ready to pluck.

/edit: removed some typo's

[Rags]

Re: Re: Question about bits and bytes for ADSL

Originally posted by Kaj

[list=1]

[*] <b>Are all downloads measured in Kbits or Kbytes per second?</b>

Kilobits. Devide them by 8, and you'll get the speeds in kiloBytes. (hence the capital B)

Actually when thinking of transfer, the number to divide by is between 9 and 12. There is the transfer overhead (stop bits, etc) that will take some of your thoroughput down.

Rags

[Fat Tone]

Ok, but compression helps too. I have NTL cable (512kb/sec) and will often get average download speeds of over 70kBytes/sec which is better than the theoretical 64KBytes/sec maximum. Of course its often slower than this too.

Tony.

edit/typos

[cjolley]

Jorden,
I have a pretty typical DSL connection:
Rated 384/128, Runs 1,100/96 as per the speed test at dslreports.com.
Your download speed has more to do with the rate that the site can deliver than the rate your connection can read.
If I am connected to a good site my download rate is about 160 KBps.
More typical would be 50 KBps.
Right now I am downloading the RedHat 7.1 CDs at a constant 20 KBps from ftp.redhat.com.
~1.5 Gig & it will take about a day.
Chuck

[WayneHu]

Re: Re: Re: Question about bits and bytes for ADSL

Originally posted by Rags


Actually when thinking of transfer, the number to divide by is between 9 and 12. There is the transfer overhead (stop bits, etc) that will take some of your thoroughput down.

Rags

That's for some old and slow media interface like RS-232C.

1x% overhead is too much for those low error rate and high speed media. Instead of parity bit, Ethernet uses checksum.

ATM cell only has checksum for its header. It relies on the low bit error rate hardware to keep the high effective bandwidth.

In fact, the ATM network has very high speed transition to go through the intermediate nodes. Thus it is unnecessary and inefficient to check the data integrity for those nodes. The reason why the cell header still has to be checked is quite simple. The pass through path is recorded in the cell header and it changes after going though one node to another. Thus it is dangerous that the VPI/VCI fields are wrong in the cell header.

[Jon P. Inghram]

Right now our cable provider (RoadRunner/Cox Cable) in Wichita has the modems capped at 3 Mbit/s down, 256 kbit/s up. Used to be 10 Mb/s down, 750 kbit/s up. There were times soon after we first had the service hooked up, and before the local node got seriously overloaded that we could download at 6 Mbit/s off the local servers. Too bad they've been too cheap up actually upgrade their network... right now we're doing good to average over 1.5 Mbit/s.

[Jorden]

Thanks all

[Rags]

Re: Re: Re: Re: Question about bits and bytes for ADSL

Originally posted by WayneHu


That's for some old and slow media interface like RS-232C.

1x% overhead is too much for those low error rate and high speed media. Instead of parity bit, Ethernet uses checksum.

ATM cell only has checksum for its header. It relies on the low bit error rate hardware to keep the high effective bandwidth.

In fact, the ATM network has very high speed transition to go through the intermediate nodes. Thus it is unnecessary and inefficient to check the data integrity for those nodes. The reason why the cell header still has to be checked is quite simple. The pass through path is recorded in the cell header and it changes after going though one node to another. Thus it is dangerous that the VPI/VCI fields are wrong in the cell header.

That would be all fine and dandy if we didn't live in a real world. I understand that the transfer protocol is much more efficient than the old RS-232, but it's overhead was much more than what I posted, when taken into the real world. What happens in the real world is that there is multiple things that interupt the transfer, and thus the overhead goes up much higher than the continuous theoretical value. And that is just the interuption in the data you are pulling off the internet to your modem, then on top of that overhead you have the small amount of overhead between the modem and nic. So you can see why the value is not a set one, but rather an average of between 1 and 4 b/s.

Rags