Dial-up remote access is a remote access technology that is available as part of the Routing and Remote Access service (RRAS).
Dial-up remote access provides a simple solution for organizations that want to allow employees to remotely access their corporate e-mail accounts and shared files from home or from other locations outside the corporate network. With dial-up remote access, a remote access client can use the wide area network (WAN) infrastructure to connect to a remote access server. A remote access client uses the telephone system to create a temporary physical circuit or a virtual circuit to a port on a remote access server. After the physical or virtual circuit is created, the rest of the connection parameters can be negotiated. Dial-up networking supports demand-dial routing to help reduce telephone costs.
Components of a dial-up remote access connection
A dial-up remote access connection contains the following components:
Remote access client
Remote access clients running Windows, UNIX, and Macintosh can connect to a RRAS remote access server.
Remote access server
The RRAS remote access server accepts dial-up connections and forwards packets between remote access clients and the network to which the RRAS server is attached.
Dial-up equipment and the WAN infrastructure
The physical or logical connection between the remote access server and the remote access client is facilitated by dial-up equipment installed at the remote access client, the remote access server, and the WAN infrastructure. The nature of the dial-up equipment and WAN infrastructure varies, depending on the type of connection. The following sections describe the most common methods for dial-up remote access.
PSTN, also known as Plain Old Telephone Service (POTS), is the analog phone system designed to carry the minimum frequencies required to distinguish human voices.
Dial-up equipment consists of an analog modem at the remote access client and at least one analog modem at the remote access server. For large organizations, the remote access server is attached to a modem bank containing up to hundreds of modems. Because PSTN was not designed for data transmission, its transmission bit rate is limited compared to other connection methods.
Standard PSTN connection
Digital links and V.90
The maximum bit rate of PSTN depends on the range of frequencies being passed by PSTN switches and the signal-to-noise ratio of the connection. The modern-day analog phone system is only analog on the local loop, the set of wires that connect the customer to the central office (CO) PSTN switch. After reaching the PSTN switch, the analog signal is converted to a digital signal.
When an RRAS server is connected to a CO by using a digital switch based on T-Carrier or ISDN rather than an analog PSTN switch, there is a higher signal-to-noise ratio because of fewer digital to analog conversions and, therefore, a higher maximum bit rate.
With this technology, called V.90, remote access clients can send data at 33.6 kilobits per second (Kbps) and receive data at 56 Kbps. In the United States, the maximum receive bit rate is 53 Kbps due to Federal Communications Commission (FCC) power rules.
To obtain V.90 speeds:
- The remote access client must be using a V.90
- The remote access server must be using a V.90
digital switch and must be connected to PSTN using a digital link,
such as T-Carrier or ISDN.
- There cannot be any analog-to-digital
conversions in the path from the remote access server to the remote
PSTN connection with V.90