Table 2-9 Common DSL Services Compared

Service Supports User Typical Typical Typically
Type Existing Installation Downstream Upstream Marketed
  Telephone Option Speeds Speeds To
  Line        
           
ADSL Yes Yes 384Kbps to 128Kbps to Home, small
      6Mbps 768Kbps business
           
SDSL Not typical No 144Kbps to Same as Larger busi-
      2.0Mbps downstream ness and
        speed corporate
           

 

 

A device known as a DSL modem is used to connect your computer to DSL service. DSL modems connect to your PC through the RJ-45 (Ethernet) port or the USB port. The rear of a typical DSL modem that uses an Ethernet (RJ-45) connection is shown in Figure 2-8.

 

  RJ-45 connection RJ-11 connection
        to computer to telephone line
                 
Power connection                
                                         
                                         
                                         

 

 

RJ-11 cable

 

RJ-45 cable

 

Figure 2-8The rear of a typical DSL modem with a power port (top left), RJ-45 data port to thePC (top center), and an RJ-11 telephone line port (top right). The RJ-45 cable is shown at bottom left, and the RJ-11 cable is shown at bottom right.

 

To prevent interference with DSL from ordinary telephony devices (telephones and fax machines), a DSL vendor might use a separate line dedicated for DSL, or might require the use of a device called a microfilter on each telephone jack that is used for devices other than the DSL modem (see Figure 2-9).


Chapter 2: Networking 55

 

  Two-outlet  
modular adapter  
RJ-11 line cord   Existing
   
    RJ-11
    wallplate
DSL modem Microfilter  
   

 

 

Data Line Telephone
RJ-45 RJ-11

 

Figure 2-9A typical self-installed DSL setup. The DSL vendor supplies the DSL modem (center)and microfilters that attach between telephones and other devices and the wall outlet (right).

 

 

Dial-Up

 

Dial-up networking (DUN) is the oldest method for home and small businesses to connect to the Internet. Dial-up connections are often referred to as analog connections because the device used to make the connection is an analog modem, which connects to the Internet through an ordinary telephone line. Every time you connect to the Internet with a dial-up modem, you are making a network connection.

 

Most laptops include a built-in analog modem, but desktops that use analog modems must either use an external modem that connects via USB or serial (COM, RS-232) ports or an internal modem that uses an expansion slot. Figure 2-10 illustrates a typical dial-up modem for a desktop computer.

 

An Internet service provider (ISP) provides a connection between the user with an analog (dial-up) modem (or other connectivity device) and the Internet. ISPs that provide dial-up access have sev-eral modems and dial-up numbers that their customers can access.

 

The maximum download speed in the US is 53Kbps with a so-called 56K modem, with the maximum upload speed at 33.6Kbps. Line quality can greatly degrade both download and upload speeds.

 

A DUN connection can be creating using Windows or with special setup software provided by the ISP.


56 CompTIA A+ Quick Reference

 

 

32-bit PCI slot

 

RJ-11 telephone jacks

 

Figure 2-10A typical internal dial-up modem for a desktop computer. This example plugs into aPCI slot.

 

 

Fiber

 

A growing number of DSL and cable vendors are using fiber optic lines to deliver content, such as AT&T U-verse, Verizon FiOS, and others. Speeds available with all-fiber connections can be as high as 150Mbps.

 

Satellite

 

Satellite Internet providers, such as HughesNet (previously known as DirecWAY, and, before that, as DirecPC), StarBand, and WildBlue use dish antennas similar to satellite TV antennas to receive and transmit signals between geosynchronous satellites (these orbit the earth at a distance of 22,000 miles over the equator) and computers. In some cases, you might be able to use a dual-purpose satellite dish to pick up both satellite Internet and satellite TV service.

 

Satellite Internet services use external devices often called satellite modems to connect the com-puter to the satellite dish. They connect to the USB or Ethernet (RJ-45) port in a fashion similar to that used by DSL or cable modems.

 

Download and upload speeds and the amount of data that can be downloaded per day vary by provider and service type. For example, HughesNet offers three residential plans with maximum download speeds ranging from1Mbps to 2Mbps, maximum upload speeds range from 200Kbps to 300Kbps, and daily download limits from 250MB to 450MB.


Chapter 2: Networking 57

 

Because of satellite Internet’s high price per unit of download and upload speed, upfront equip-ment expense, and poor latency (which affects online gameplay and time-sensitive business opera-tions such as real-time stock analysis and trading), satellite Internet is recommended only when other forms of broadband Internet are not available.

 

ISDN

 

ISDN (Integrated Services Digital Network) was originally developed to provide an all-digital method for connecting multiple telephone and telephony-type devices, such as fax machines, to a single telephone line and to provide a faster connection for teleconferencing for remote computer users. A SOHO-based connection can also provide an all-digital Internet connection at speeds up to 128Kbps. Line quality is a critical factor in determining whether any particular location can use ISDN service. If an all-digital connection cannot be established between the customer’s location and the telephone company’s central switch, ISDN service is not available or a new telephone line must be run (at extra cost to you!).

 

Cellular (Mobile Hotspot)

 

Some smartphones can share their GSM (Global System for Mobile Communications) data con-nection with other devices via Wi-Fi. 3G provides a maximum download speed of 56Mbps, and 4G provides a maximum download speed of 100Mbps.