CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [442]
Figure 25-16 The New Connection Wizard
Figure 25-17 Connection options in Network Connections
PPP Dial-up links to the Internet have their own special hardware protocol called Point-to-Point Protocol (PPP). PPP is a streaming protocol developed especially for dial-up Internet access. To Windows, a modem is nothing more than a special type of network adapter. Modems have their own configuration entry in the Network Connections applet.
Most dial-up “I can’t connect to the Internet”–type problems are user errors. Your first area of investigation is the modem itself. Use the modem’s properties to make sure the volume is turned up. Have the user listen to the connection. Does she hear a dial tone? If she doesn’t, make sure the modem’s line is plugged into a good phone jack. Does she hear the modem dial and then hear someone saying, “Hello? Hello?” If so, she probably dialed the wrong number! Wrong password error messages are fairly straightforward—remember that the password may be correct but the user name may be wrong. If she still fails to connect, it’s time to call the network folks to see what is not properly configured in the Dial-up Networking settings.
ISDN
A standard telephone connection comprises many pieces. First, the phone line runs from your phone out to a network interface box (the little box on the side of your house) and into a central switch belonging to the telephone company. (In some cases, intermediary steps are present.) Standard metropolitan areas have a large number of central offices, each with a central switch. Houston, Texas, for example, has nearly 100 offices in the general metro area. These central switches connect to each other through high-capacity trunk lines. Before 1970, the entire phone system was analog; over time, however, phone companies began to upgrade their trunk lines to digital systems. Today, the entire telephone system, with the exception of the line from your phone to the central office, and sometimes even that, is digital.
During this upgrade period, customers continued to demand higher throughput from their phone lines. The old telephone line was not expected to produce more than 28.8 Kbps (56 K modems, which were a big surprise to the phone companies, didn’t appear until 1995). Needless to say, the phone companies were very motivated to come up with a way to generate higher capacities. Their answer was actually fairly straightforward: make the entire phone system digital. By adding special equipment at the central office and the user’s location, phone companies can now achieve a throughput of up to 64 K per line (see the paragraphs following) over the same copper wires already used by telephone lines. This process of sending telephone transmission across fully digital lines end-to-end is called integrated services digital network (ISDN) service.
ISDN service consists of two types of channels: Bearer, or B, channels and Delta, or D, channels. B channels carry data and voice information at 64 Kbps. D channels carry setup and configuration information and carry data at 16 Kbps. Most providers of ISDN allow the user to choose either one or two B channels. The more common setup is two B/one D, usually called a basic rate interface (BRI) setup. A BRI setup uses only one physical line, but each B channel sends 64 K, doubling the throughput total to 128 K. ISDN also connects much faster than modems, eliminating that long, annoying, mating call you get with phone modems. The monthly cost per B channel is slightly more than a regular phone line, and usually a fairly steep initial fee is levied