Network+

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■    Specialized equipment is required at the phone company and at the remote computer.


■    Not all ISDN equipment can connect to every other type of equipment.


■    ISDN is a type of dial-up connection and, therefore, the connection must be initiated.

Other Digital Options


Digital connections provide one main benefit to remote access users: increased bandwidth over older technologies. The digital nature of ISDN and other digital connection types makes them excellent choices for remote access connections. Some of the more important types are:


■    xDSL


■    Frame relay


   T-series


   Asynchronous Transfer Mode (ATM)


■    FDDI

xDSL Technology


xDSL is a general category of copper access technologies that is becoming popular because it uses regular POTS phone wires to transmit digital signals, and is extremely inexpensive compared with the other digital communications methods. xDSL implementations cost hundreds of dollars instead of the thousands that you would pay for a dedicated, digital point-to-point link (such as a T1). They include digital subscriber line (DSL), high data-rate digital subscriber line (HDSL), single-line digital subscriber line (SDSL), very high data-rate digital subscriber line (VDSL), and asymmetric digital subscriber line (ADSL), which is currently the most popular. It is beyond the scope of this book, however, to cover all of the DSL types.


ADSL is winning the race because it focuses on providing reasonably fast upstream transmission speeds (up to 640Kbps) and very fast downstream transmission speeds (up to 9Mbps). This makes downloading graphics, audio, video, or data files from any remote computer very fast. The majority of web traffic, for example, is downstream. The best part is that ADSL works on a single phone line without losing voice call capability. This is accomplished with what is called a splitter, which enables the use of multiple frequencies on the POTS line.

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