CABLE, ISDN, DSL, AND SATELLITE


Most connections to the Internet are accessed through an Internet Service Provider (ISP). A local or national ISP provides an IP address that can be used to gain access to the Internet. Although many individuals and businesses still use a 56Kbps analog dial-up connection to access the Internet, broadband services, such as cable, ISDN, and DSL, are becoming increasingly popular (and somewhat more affordable) based on their high transmission speeds and instant accessibility. See Table 22.2 for a quick reference of Internet technology connection types and associated speeds.

Table 22.2: Internet Connection Types and Speeds

Connection Type

Average Connection Speed

Telephone modem

14.4–56Kbps

Cable modem

1–2Mbps

ISDN

128Kbps

DSL

1.5Mbps and higher

Satellite

400Kbps

T1 line

1.544Mbps

Cable

Broadband cable modem connections seem to be the Internet connectivity tool of choice for today’s home users. All you really need for this technology is a cable modem, an NIC, RJ-45 cable, a coaxial cable, and an ISP. This technology allows Internet access speeds of around 1.5Mbps. It provides a connection similar to that of cable television. The signal is always at the end of the cable wire, waiting to be accessed; in other words, the connection is always available. There is no need to reconnect to the ISP every time you want to access the Internet.

A traditional cable modem uses two connections. It connects to a wall-mounted incoming cable connection with a coaxial cable and connects to a computer system, hub, or router using a standard 10BaseT Ethernet cable with an RJ-45 connector.

The previously mentioned cable connection speed of approximately 1.5Mbps is much faster than that of a 56Kbps telephone modem. Cable is also faster than ISDN, which has a speed of approximately 128Kbps and currently competes with speeds by DSL.

Integrated Services Digital Network (ISDN)

ISDN is a baseband transmission technology that is well suited for the transmission of audio and video at rates of up to 128Kbps. ISDN utilizes an adapter that is included with an ISDN router in place of a standard analog modem.

There are two types of ISDN services typically available by ISPs or local phone carriers: basic rate interface and primary rate interface.

Basic Rate Interface (BRI): BRI is an ISDN technology made up of two 64Kbps B channels that carry data and voice and a 16Kbps D channel that is responsible for control information. BRI implementations are common for small-business and home use.

Primary Rate Interface (PRI): PRI is an ISDN technology that is used with larger businesses, such as ISPs and telecommunication companies. PRI is made up of 23 B channels and one D channel. PRI typically utilizes the bandwidth capabilities of a T1 connection.

ISDN has for the most part been replaced with DSL technology, which is described next.

Digital Subscriber Line (DSL)

DSL is a connection technology that uses regular copper wire telephone lines, or Plain Old Telephone Service (POTS), to bring access speeds of up to 6.1Mbps to homes or businesses. In actuality, DSL offers upload speeds of up to 128Kbps and download speeds of 1.5Mbps for individual connections. DSL utilizes a modem for a highly sophisticated modulation process and is well suited for high-speed transmission of audio and video.

DSL has provided major competition to the cable modem and is commonly used in locations that cable service or access is not offered.

Unlike using less secure cable modem services, DSL is not a shared service connection. To be more specific, you do not share your DSL connection with your neighbors, as cable subscribers do.

DSL implements two types of speeds. An upload speed, or ‘upstream speed,’ and a download speed, or ‘downstream speed.’ The upload speed represents how fast you can transmit information to other locations or computers connected to the Internet. The download speed represents how fast you can download such things as files, programs, or music to your system from other systems on the Internet.

As well as these two types of speeds, there are two separate forms of DSL technology available that can offer different speeds. They are ADSL (Asymmetric DSL) and SDSL (Symmetric DSL), which are described next.

Note

DSL is a connection technology that uses existing POTS wires. It requires a special modem and typically requires that a signal splitter be installed in the home or office. DSL is a technology that can be remotely activated.

ADSL (Asymmetric DSL)

ADSL is by far the most commonly used form of DSL today. ADSL works simultaneously with voice over existing telephone lines. It works asymmetrically, meaning that the speed used for downstream receiving transmissions is far greater than the speed used for upstream sending. ADSL was developed with the home and small-business user in mind. The ADSL conceptual theory is based on the fact that the typical end user will download far more information than they will be sending.

It supports receiving data rates (downstream rate) from 1.5–9.0Mbps and sending data rates (upstream rates) from 16–640Kbps.

Remember for the exam, asymmetric means that transmission rates are not the same in both directions.

SDSL (Symmetric DSL)

SDSL is well suited for business applications and programs that require and depend on the same speed for sending and receiving data. In other words, with SDSL, your upstream speed is identical to your downstream speed. SDSL can support data rates up to 3Mbps.

SDSL operates on the same phone wires that are used for normal voice communication. But because SDSL technology works at higher frequencies than that of normal voice, it can exist on the same media without interfering.

Remember for the exam, symmetric means that transmission rates are the same in both directions.

SATELLITE

A satellite is a wireless communications device that orbits the earth, acting as a receiver/transmitter for such things as Internet connectivity and GPS (Global Positioning Systems). A satellite Internet connection is similar to a satellite TV connection in that a satellite signal is transmitted to a receiver and the signal is decoded on the satellite subscriber’s end. Most satellite Internet connections are considered asynchronous, with upstream speeds for a single system averaging 50–150Kbps and up to 1,200Kbps for downloads or ‘downstreaming.’

Satellite connections are ideal for those who are located out of the range of cable and DSL service providers. In order to use a satellite Internet connection, you will need a satellite dish antenna, a transceiver (for transmitting and receiving), and a two-way satellite Internet service provider.

In general terms, here’s how it works:

  • The satellite dish antenna is mounted on or near your home or business.

  • The satellite dish antenna is connected to a satellite modem (transceiver) with a coaxial cable.

  • The satellite modem communicates with your PC through an Ethernet or USB connection.

  • Information is transmitted to and received from a two-way geosynchronous satellite that orbits approximately 22,300 miles above the equator.

  • The geosynchronous satellite communicates with a provider facility that is connected to the Internet.

Using an Internet satellite connection is not always perfect or guaranteed; it is not uncommon that such things as solar interference and periods of rain fade (signal loss caused by inclement weather) cause signal degradation or loss of connection.




The A+ Certification & PC Repair Handbook
The A+ Certification & PC Repair Handbook (Charles River Media Networking/Security)
ISBN: 1584503726
EAN: 2147483647
Year: 2003
Pages: 390

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