DSL Speed / ATM

[ShadowKing]

I have Verizon DSL and really like it. I have had about 6 hours of downtime since May, which I think is pretty good.

However, I have a quetion about the technology itself. I get 768k down, 128 up and I was wondering how that worked.

If I am uploading at say 100k then do I still get 768k down or do I then only get 668 down?

I know my modem uses ATM which is an asynchronous techonology. I am assuming that that means that I would get the 768 even when I am uploading at the full 128k.

Just checking with you guys to see if you might know...

[weazel]

basically asynchronous dsl means your upstream bandwidth is lower then your downstream bandwidth. Whereas with sdsl your upstream and downstream are the same 768/768.
Normally you should be able to upload and download at the same time at your quoted speed minus a percentage for overhead. so basically if your uploading at 100k it doesn't take away from your download speed. Just bear in mind that thats in kilobits not kilobytes so roughy 13K up and 77K down, if you round it up.

[Gollo]

[quote]Originally posted by Weazel:
<strong> Just bear in mind that thats in kilobits not kilobytes so roughy 13K up and 77K down, if you round it up.</strong><hr></blockquote>

Wow. If that's the case than I'm getting more than I am paying for. I average anywere from 80 to 90kbps download and between 20 and 30 up. Not bad. (I also have a 768/128 plan).

[tha 4NiK8R]

Ususally with DSL the speed that the ISP says that you will get (ie 768/128) is the speed that they will guarantee you. So if you get more it is likely that you are seeing what you line speed can handle based on distance from the CO. The problem with ADSL is the upload speed is not large enough for you to truly download as fast as your speed is quoted or showing. The reason is Acknowledgements. Most traffic (P2P, etc) are based on TCP and not UDP so there is the overhead of acknowledgements for every packet received. Most ISPs will argue that acks are not large enough to effect you download speed. Well they are wrong...the speed you are truly getting with your 128kbps upload speed is more like 384/128 because of the limitations of the upload and the overhead involved with packet acks. I have 1.5mbps/384kbps adsl and I know that my speed is more like 1.2/384 because of the upload speed. You can really see how bad(or good) your speed is by playing around with some P2P apps or try DCC'ing someone a file while recieving from another source and watch you speed drop like a rock. In the end SDSL is the better deal for your money, if you can get decent speeds in your area (or in my case, my ISP won't give me SDSL).