Asynchronous Dial-Up

Asynchronous dial-up
is traditional modem-based access over the public analog phone network.
The primary advantage of asynchronous dial-up is that it is available virtually everywhere.
Unfortunately, its greatest limitation is bandwidth, which is currently limited to less
than 56 kilobits per second (Kbps). In addition, asynchronous dial-up connections require a
negotiation period, during which time traffic must be buffered and the user experiences delay.
Because hotels, homes, and customer sites are already supplied with the traditional level of
connectivity, dial-up connections are primarily suited to those members in the workforce who
are mobile. Such connections are a substantial benefit when compared to the other remote
access technologies, each of which must be predefined or preprovisioned.
Given the universal availability of analog circuits, most designers find that they still require
dial-up installations to be a part of their remote access solution. Typically, ISDN installations
lend themselves to a dual role—as an ISDN Primary Rate Interface (PRI) that can terminate
23 analog connections, or an assortment of ISDN B channels (user data bearer channels) and
analog connections. This ability to service both ISDN digital connections and asynchronous
dial-up connections can greatly ease facilities, configuration, and administration burdens.
Analog circuits are best suited for short-duration, low-bandwidth applications. Examples of
this type of traffic include terminal emulation and e-mail services. Limited file-transfer and
client/server-based application activity could also use this connection.