Asynchronous Connections

Asynchronous
Connections



Know the commands and procedures necessary to configure
an access server for modem connectivity so telecommuters
can access the central site.


Know the commands and procedures to configure dial-out
connections.


Know the commands used for reverse Telnet.


Understand how to configure the modem for basic
asynchronous operations.


Know the commands and procedures used for the modem
autoconfiguration feature.

As noted in Chapter 22, “Cisco Solutions for Remote Access,”
asynchronous (analog) remote access solutions are extremely
popular, primarily because little preparation is needed on the
remote side of the connection. Unlike Frame Relay, ISDN, and X.25,
asynchronous connections
use standard phone lines and are available virtually everywhere. With cellular modems, these
services are even available on a wireless basis. (This is different from the code division multiple
access (CDMA) and Global System for Mobile Communications (GSM) data connections
briefly noted in Chapter 22.) This wide availability provides a huge advantage over other
remote access solutions and effectively mandates the inclusion of asynchronous connections in
modern implementations. Unfortunately, analog-based modems suffer from low performance
and relatively high cost per kilobyte.
With a digital connection at the service provider’s side of the connection, it is possible to
provide up to 56Kbps of theoretical bandwidth to remote users; however, the Federal Communications
Commission (FCC) limits this to 53Kbps in the United States. Also, asynchronous
connections require a lengthy call-setup time—sometimes more than one minute—
which can substantially affect user and application performance.
Administrators frequently look for other technologies to replace asynchronous modems, or dialup
connections, in order to improve performance. Even with the proliferation of ISDN, DSL, cable
modems, and other technologies, no system has yet successfully dethroned simple dial-up services.