What Is Dial-Up Networking?
Applies To: Windows Server 2008
What is dial-up remote access?
Dial-up remote access is a remote access technology that is available as part of Routing and Remote Access included in Windows Server® 2008.
Organizations require a simple solution that allows employees to remotely access their corporate e-mail accounts and shared files from home or from other locations outside the corporate network. Dial-up remote access provides the solution by enabling a remote access client to use the wide area network (WAN) infrastructure to connect to a remote access server.
Dial-up remote access vs. VPN
Windows Server 2008 remote access provides two different types of remote access connectivity: dial-up remote access and virtual private network (VPN) remote access.
With dial-up remote access, a remote access client uses the telecommunications infrastructure 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.
With virtual private network remote access, a VPN client uses an IP network, such as the Internet, to create a virtual point-to-point connection with a remote access server acting as the VPN server. After the virtual point-to-point connection is created, the rest of the connection parameters can be negotiated.
Demand-dial routing is not a technology, but a process by which packets are forwarded across a Point-to-Point Protocol (PPP) link. Demand-dial routing is used by remote access technologies—dial-up remote access and VPN, as well as routing technologies—unicast routing, multicast routing, and network address translation (NAT). For more information about demand-dial routing, see What Is Demand-Dial Routing?.
Components of a dial-up remote access connection
A dial-up remote access connection contains the following components:
Remote access client
Remote access server
Components of a Dial-up Remote Access Connection
Remote access client
Remote access clients running Windows Server 2008, Windows Server 2003, Windows XP, Windows 2000, Windows NT 4.0, Windows Millennium Edition, and Windows 98 can connect to a remote access server running Windows Server 2008. Almost any PPP remote access client, including UNIX and Macintosh, can connect to a remote access server running Windows Server 2008.
Remote access server
The remote access server running Windows Server 2008 accepts dial-up connections and forwards packets between remote access clients and the network to which the remote access 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 most common methods for dial-up remote access include:
Public Switched Telephone Network (PSTN)
Integrated Services Digital Network (ISDN)
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 the analog signal reaches the PSTN switch, it is converted to a digital signal. The analog-to-digital conversion introduces noise on the connection known as quantization noise.
When a remote access 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 no analog-to-digital conversion when the remote access server sends information to the remote access client. Because there is no quantization noise in the path back to the remote access client, there is a higher signal-to-noise ratio and, therefore, a higher maximum bit rate.
With this technology, called V.90, remote access clients can send data at 33.6 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 following must be true:
The remote access client must be using a V.90 modem.
The remote access server must be using a V.90 digital switch and 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 access client.
PSTN Connection with V.90