Faster Is Better

Faster Is Better

With all the types of physical networking standards covered in this book, there have been options for different speeds. Even Ethernet has several options. With WAN options, there are many more variations for speed, and DSL is no exception.

DSL standards come in many flavors to meet different needs. (Most of the standards come from the ITU, which also owns most of the modem standards.) For instance, DSL has limits on how long the local loop can be. (The length of the local loop is simply the length of the combined cables that stretch from a house to the CO.) Some DSL variants allow the local loop to be much longer than some other DSL variants, whereas others only allow for a shorter local loop. The distances tend to range from less than a mile to 45 miles. For the standards with a shorter local loop, the transmission rates tend to be much higher, which is a simple design tradeoff.

The speeds for DSL can go as high as 50 Mbps, but you must have a short local loop to the CO. The slower DSL speeds are approximately 384 Kbps, but that allows you to have a much longer local loop.

Interestingly, the speed at which data goes from the Internet to the home is faster than the other directiona feature called asymmetric transmission rates. As it turns out, a lot more data goes toward a PC at home than in the reverse direction for most TCP/IP applications. For instance, when you ask for a web page, the HTTP request might be a few hundred bytes, but the web page might be millions of bytes of data. So, rather than send at the same speed in both directions, it's better to have more bandwidth toward the home, where most of the bandwidth is needed.