Upload/download effects on each other

Telocity_2001 · Post by **Telocity_2001** » Wed Feb 28, 2001 8:40 pm

Hi,
I'm new to this forum! This may be a redundant question, but I'd just like to know why does uploading affects your downloads, and vice versa? For example, I may be downloading at 30.xxk/s, and when I start an upload the download transfer rate decreases. Your help is greatly appreciated! I really want to understand this. Thanks in advance for all your inputs. CHeers!

Best regards,
Abe

Kip Patterson · Post by **Kip Patterson** » Wed Feb 28, 2001 8:52 pm

Welcome to Speedguide!

Uploads and downloads are not independant. Each requires acknowledgement packets. At best the minimum upload traffic is just over 2% of the download, and in some circumstances can be greater.

Kip Patterson

Bababooey · Post by **Bababooey** » Wed Feb 28, 2001 11:15 pm

It's about 3% for me.

martialcomp · Post by **martialcomp** » Wed Feb 28, 2001 11:20 pm

Yep, high upstream usage does slow the downstream. I have had customers go from 30-40 kilo bytes per second while a file is being sent, to over 200 kilo bytes per second when the file being sent was completed. The systems are not symetrical.

BandwidthBandit · Post by **BandwidthBandit** » Wed Feb 28, 2001 11:36 pm

Originally posted by Kip Patterson:
Welcome to Speedguide!

Uploads and downloads are not independant. Each requires acknowledgement packets. At best the minimum upload traffic is just over 2% of the download, and in some circumstances can be greater.

Kip Patterson

Is this true with all connections (ie.T1,T3) or just residential connections?

Roger3554 · Post by **Roger3554** » Thu Mar 01, 2001 5:12 pm

Regardless of the type of connection (cable, DSL, T1, T3) the far end device will send acknowledgement packets back to the near end PC. Since these packets being received at the near end, they will occupy a small amount of downstream bandwidth. I don't know what percentage that amounts to.

The same is true in the other direction. When you are downloading a file you will be using a small amount of upstream bandwidth because you will be sending acknowledgement packets back to the other end. This is a characteristic of TCP/IP and is not dependent on the type of connection.

If you are uploading a file and you are limited to 128Kbps you could easily be using all or nearly all of your upstream bandwidth. If you are downloading at that same time, your machine may have to wait to send the acknowledgement packets to the far end so your down load speed suffers.

Cable modems use a separate frequency band for upstream and downstream. If it weren't for the acknowledgment packets, etc. being sent in the opposite direction of the file transfer the upstream and downstream would be independent. This is more of a problem for asymmetric systems such as cable modems and ADSL than for T1 or T3 systems that have the same bandwidth in both directions.