What’s the Difference Between ADSL and SDSL?

Every industry has its jargon and IT is no exception. In this post we want to tell you about two terms used in connection with broadband connections – ADSL and SDSL.
ADSL stands for Asymmetric Digital Subscriber Line and SDSL means Symmetric Digital Subscriber Line, with the difference related to the speeds for uploading and downloading. Asymmetric has different upload and download speeds, but they are the same with Symmetric. In ADSL, the download speed is several times faster than the upload speed, which makes it more practical for most uses, e.g. viewing internet pages. 

An analogy is to think of a major road going into a town or city with a total of 10 lanes; 4 active traffic lanes and a hard shoulder each way. Most people will be going in during the morning and out in the evening, so having the same number of lanes means there will be traffic jams during the morning and again in the evening when commuters leave. If you could have an uneven number of lanes in the morning and evening then you could reduce the jams, i.e. by having more lanes going in during the morning and more coming out in the evening. 

ADSL is like having this uneven number of lanes – but only in one direction. So great when everyone is going the same way but not if you need both directions. ADSL is fine for ordinary usage such as the internet at home (mainly downloading) but not so good if you have to upload data to a server frequently, such as you might do with remote workers or a cloud computing arrangement.

So organisations using cloud computing services for vital operations would need an SDSL line but ADSL is fine when there is less need for speed and capacity. SDSL is more expensive which is why ADSL is usually the default option unless requirements indicate otherwise. 

There is also a third route – bonded ADSL. This involves merging two ADSL lines together which provides some additional capacity but doesn’t offer the same apparent speed as an SDSL line.

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