Running Linux, 5th Edition - Matthias Kalle Dalheimer [263]
Since some programs try to build up Internet connections from time to time (Netscape is one of those candidates), setting this up can be dangerous for your wallet. If you use this, make sure to check the state of the connection often (as described later in this section).
Try tools that monitor your ISDN connection. The isdn4k-utils package contains a number of those tools, including the command-line tools imon and imontty and X-based tools.
Configure isdnlog to log exactly what you need, and use isdnrep to get detailed reports about the usage of your ISDN line. This works not only for calls to and from computer systems, but also for calls to other ISDN-enabled devices such as phones and fax machines. There is only one caveat: your ISDN board cannot capture outgoing phone numbers for connections being set up by other devices. Most telephone companies provide a service, though, that echoes this phone number back to you and thus lets the ISDN subsystem pick it up. This service is often available for free or for a nominal fee. Ask your telephone company.
For the truly adventurous: experiment with Multilink-PPP. As you know, with ISDN you have at least two lines. If you need extra-high capacity, why not use both? That's what Multilink-PPP does. To use this, you need to turn on the Support generic MP option during kernel configuration, and read the files Documentation/isdn/README.syncppp and Documentation/isdn/syncppp.FAQ in the kernel sources for hints on how to do this. Of course, your provider has to support this, too.
ADSL
The 64-Kbps rate that ISDN supports is nice, but if you want to access multimedia files via the Internet or simply are using the Internet a lot, you may want even more bandwidth. Without drawing additional cables to your house or office, ADSL (Asynchronous Digital Subscriber Line), a variant of DSL (Digital Subscriber Line), is a convenient alternative that gives you up to 128 times (depending on your provider and your type of subscription) the bandwidth of standard dial-up access and is run via your ordinary telephone line. A drawback with ADSL is that it only works within a distance of about 5 to 8 kilometers (3 to 5 miles), depending on cable quality around the next switching station, which makes this service unavailable in rural areas. Typical bandwidths are 0.5 to 8 Mbps (megabits per second) downstream (to your computer—download operations, including viewing web pages and retrieving email) and 0.125 to 1 Mbps upstream (from your computer—upload operations, including sending email). Note that there are other technologies with similar-sounding names, such as SDSL. Although these are fundamentally different on the wire level, setting them up on your Linux box should be no different from ADSL.
ADSL is not dial-up access; once you have logged into your account, you are always connected. Some providers cut your connection after a while (often after 24 hours), upon which you have to log in again in order to regain access.[*]
As we have already mentioned, there are no such things as ADSL cards or ADSL drivers. As far as hardware is concerned, an ADSL connection is just a normal Ethernet connection, using the same cables.
How you connect your Linux box to your ADSL line depends a lot on your ISP. With some ISPs, you rent the necessary equipment, such as an ADSL modem and an ADSL router, as part of your subscription. With others, you have to purchase the necessary hardware yourself, either on the free market or from the ISP. Your ISP can give you all the information you need.
There are two ways to use ADSL: either connecting directly to an ADSL modem or with an intervening ADSL router. If you have an ADSL router (either with a built-in ADSL modem, or in addition to one), you plug your Ethernet cable in there and are ready for action. If you want