.: Advanced Linux Networking :.

Broadband is a term that's commonly applied in a couple of different ways. First, it may refer to a networking technology that allows for the simultaneous transmission of multiple types of information, such as video, audio, and digital data. Second, it may refer to a substitute for ordinary dial-up telephone network connections that permits substantially higher speeds (typically 200Kbps or greater). Although 200Kbps doesn't sound like much compared to technologies like Ethernet, it's a substantial improvement over 56Kbps telephone dial-up speeds.

Residential and small business customers frequently use broadband technologies to link to the Internet through an Internet Service Provider (ISP), or occasionally to link multiple sites without running dedicated cables. Typically, broadband connections link a computer that you own to the Internet as a whole. This contrasts with the other network technologies described here, which normally link together a group of computers that you own or administer. Therefore, broadband connections frequently require that you conform to some requirements of the ISP that provides the connection. Many low-end broadband ISPs require that you not run servers, for instance.

In 2002, the most popular forms of broadband are Digital Subscriber Line (DSL) and cable modems. DSL comes in several varieties, such as Asymmetric DSL (ADSL) and Single-Line (or Symmetric) DSL (SDSL), and operates using high-frequency signals over ordinary telephone lines. Cable modems operate over cable TV networks by occupying the bandwidth of one TV channel (often with some additional bandwidth reserved, as well). Broadband through satellite systems, local radio-frequency transmissions, and fiber-optic cabling are also available in at least some areas.

Most broadband connections use an external modem that sports a broadband connector for linking to the broadband network and an Ethernet port for connecting to your computer. You therefore need a supported Ethernet adapter, and you configure that adapter with the standard Linux drivers. The broadband modem itself needs no special drivers, although some ISPs require you to use the Point-to-Point Protocol over Ethernet (PPPoE), which is implemented in Linux via the experimental PPP over Ethernet driver in the Network Device Support menu. (This option requires that you first enable the PPP Support option, discussed shortly in "Dial-Up Devices.") Another PPPoE option is to use the Roaring Penguin PPPoE package, available from http://www.roaringpenguin.com/pppoe/.

Some broadband modems come with USB interfaces rather than Ethernet interfaces. The 2.4.17 Linux kernel supports none of these devices, although Alcatel provides Linux drivers for its Speed Touch USB DSL modem at http://www.alcatel.com/consumer/dsl/supuser.htm. Check with the hardware manufacturer or at http://www.linux-usb.org for updated information on drivers for other USB products.

Some broadband modems, particularly for low-end ADSL accounts, come as internal PCI cards. As with USB devices, support for these is rare. The 2.4.17 kernel includes support for the General Instruments Surfboard 1000, an old one-way cable modem. (One-way means that it only receives data; you must use a conventional telephone modem to send data. One-way broadband services are undesirable and are becoming rare.) Drivers for the Diamond 1MM DSL modem are available from http://www.rodsbooks.com/network/network-dsl.html, but these drivers are an unsupported modification of existing Ethernet drivers and may not work on 2.4.x or later kernels.

If your broadband provider doesn't give you the option of an Ethernet- interfaced modem, buy one yourself and sell the modem your ISP provides on an auction site like eBay (http://www.ebay.com). Be sure you buy a compatible modem, though, and only sell the one your ISP provides if it's given to you or if you must buy it; don't sell a modem your ISP rents to you!

Another type of long-distance connection is a Wide-Area Network (WAN). This type of technology allows connections over dedicated long-distance circuits, often called leased lines because they may be ordinary telephone lines leased from the telephone company. (The phone company doesn't provide a signal on the other end, though; you do.) Such connections often use external devices, known as WAN routers, which link to a Linux computer or local network much as do broadband modems. Another option is to use a dedicated WAN interface card. Linux includes support for a range of such devices in the WAN Interfaces submenu of the Network Device Support menu. As with many other submenus, you must select the first option (WAN Interfaces Support), then select the option corresponding to the device you intend to use.