Question : Why a company need T1 over DSL?

From my knowledge, I know T1 has SLA, a dedicated line and reliable. But both download/upload are 1.544 mbps. Whereas DSL, like I have at my home is download/upload -> 5M/800k.

It looks like DSL has more bandwidth over T1. So I think if I download a big file, it would be so much faster at my place. So why we need to pay so much for T1? Can anyone explain to me in great detail, thank you!

Answer : Why a company need T1 over DSL?

Yes - the aggregation is happening at the DSLAM in the Telephone Exchange.  This Wikipedia Article explains it fairly well:

http://en.wikipedia.org/wiki/Digital_subscriber_line_access_multiplexer

A T1 line won't go through a DSLAM - as that is for DSL lines.

Upload / Download speed requirements can vary from compnay to company depending on their use.

If you have a company that sends more mail than it receives or sends out large graphics to people, then a faster outbound speed (upload) would be better than inbound (download) speed.

On the other hand, if a company spends it's day browsing the web and downloading items from it, then download speed would be more interesting speed.

I am on an up to 24mb download speed with an up-to 2.5mb upload speed.  When I got connected, I was more interested in having the best upload speed possible as I host mail, so download speed was not as useful to me.  I ended up with 1.9Mb upload and about 9Mb download.  I am very happy!