Transcript section 18 Networking at Home the Office and Globe This lesson includes the following sections: • Data Communication with Standard Telephone Lines and Modems • Digital.

section 18
Networking at Home
the Office and Globe
This lesson includes the following sections:
• Data Communication with Standard
Telephone Lines and Modems
• Digital Telephone Lines
• Networks in the Home
Data Communications over Standard
Telephone Lines
• Networks commonly use dedicated media to transmit
data. However, the public telephone system can also be
used for data communications.
• Telephone system – called plain old telephone system
(POTS)
• Standard phone lines transmit data much more slowly
than network media, but devices such as modems make
phone lines practical for data transmission over long
distances.
• Many people and businesses use modems to exchange
data, and to establish connections with office networks.
Data Communications over Standard
Telephone Lines - Modems
•
First modem for personal computers is developed by
Hayes Microcomputer Products, Inc., in 1978.
•
Most telephone lines attached to home and businesses
are analog, not digital.
•
Because PCs transmit and receive data in digital
format, a device called a modem is needed to convert
digital data to analog format for transmission over
phone lines.
Data Communications over Standard
Telephone Lines - Modems (Cont.)
•
When receiving data from another computer, the
modem converts it from analog format to digital
format.
•
Modem (modulator-demodulator)
•Modulation phase: turn the digital signals into
analog signals
•Demodulation phase: analog signals are
converted into digital signals
The analog signal
(audible)
is sent through
telephone lines.
011010001
Digital signal
This modem converts
digital to analog.
MODEM
MODEM
011010001
Digital signal
This modem converts
analog to digital.
Data Communications over Standard
Telephone Lines - Choosing a Modem
•
Modem can be
•A simple circuit board, i.e., an expansion card
•An external device that plugs into a serial port
•A PC Card (previously called PCMCIA Card)
•Software model: replace most the hardware in a
hardware modem with an application program.
•Easy upgrade
•
Current model can make phone call while connecting
to the internet
Internal
Modem
External
Modem
在這部外接數據機的背面，是將它連接到電腦、電
話插座、與電話的接線。
內接數據機插入電腦的擴充槽之一
這部筆記型電腦配備有PC卡型式的數據機。這數據機附有行
動電話，所以使用者不需使用電話線就可以登入網路。
Data Communications over Standard
Telephone Lines - Choosing a Modem
•
Another type of modem that is increasing in use is the
cable modem.
•It connects the computer to the internet through
the cable TV system.
Data Communications over Standard
Telephone Lines - Choosing a Modem
•
Transmission speed - the speed at which the modem
sends data - which is measured in bits per second.
•
Data compression, the technology the modem uses to
shrink data so it can be transmitted faster.
•
Error correction, the method the modem uses to
ensure data is sent and received without errors.
•
Internal versus external, which describes whether or
not the modem fits inside the PC case.
Data Communications over Standard
Telephone Lines - Uses for a Modem
Modems are primarily used for file transfer, or sending
files to a remote computer
• Sending a file to another computer is called
uploading.
•
Receiving a file from another computer is called
downloading.
The files are transmitted by file transfer protocol (FTP)
Data Communications over Standard
Telephone Lines - Uses for a Modem
Modem communication
•
Full-duplex: data can be travel in both directions at
the same time.
•
Half-deplex: data can be sent in both directions but
only one direction at a time.
大多數的現代數據機與網路連線是全雙工的。但偶
爾也會使用半雙工傳輸來連接電腦。
Using Digital Telephone Lines
•
Telephone lines has throughput limitation.
•
Thus, telephone companies are now installing digital
telephone lines, which are dedicated to transmitting
data in digital format.
•
Digital phone lines transmit data at much higher
speeds than standard analog phone lines.
•
Often, data travels across analog lines and digital
lines. In such cases, data may need to be converted
from one format to another multiple times before
reaching its destination. (As shown in Next Figure)
傳送資料時，電腦傳送數位訊號到數據機，然後它將類比訊
號傳送到轉換站機，然後它又傳送數位訊號到另一個轉換站。
然後這程序顛倒，直到它抵達接收的電腦為止。
Using Digital Telephone Lines (Cont.)
•
The transformation from analog to digital lines will
affect most users in:
•Need a different phone – a digital one
•Does not need a modem to send data. Instead, you
need an adapter
•Can send data much more quickly
利用地區數位電話線，由傳送電腦到接收電
腦的資料可保持為數位格式。
Using Digital Telephone Lines Common Digital Services
The most commonly used digital telephone services are:
•
ISDN, T1, and T3
•
DSL
•
ATM
•
Cable Modem
Using Digital Telephone Lines –
ISDN, T1, and T3
•
Integrated Services Digital Network (ISDN) is a system
that replaces analog phone services with digital services.
•
Basic rate ISDN (BRI) offers three channels on one
phone line: two 64 or 56 Kbps channels for data and one
19Kbps channel for control. BRI transmits data up to
128 Kbps.
•
Primary rate ISDN (PRI) offers 24 channels at 64 Kbps,
(In the U.S.) a total bandwidth of 1.544 Mbps. This is T1
service. In Europe, PRI service provides 31 data
channels.
Using Digital Telephone Lines –
ISDN, T1, and T3 (Cont.)
•
Using even more channels, T3 service offers up to 672
channels of 64 Kbps each for a total of 44.736 Mbps.
Using Digital Telephone Lines DSL Technologies
•
Digital Subscriber Line (DSL) service is outpacing
ISDN services since it is less expensive in terms of
hardware, setup, and monthly costs.
•
Two key points that make DSL attractive are its speed
and medium.
•Standard DSL offers speeds of 52 Mbps
theoretically.
•DSL can use POTS lines, the standard copper
wire used for telephone communications.
Using Digital Telephone Lines DSL Technologies (Cont.)
•
Several types of DSL service are available, reaching
transmission speeds up to 51.84 Mbps.
•Asymmetric DSL (ADSL)
•Rate adaptive DSL (RADSL)
•High-bit-rate DSL (HDSL)
•ISDN DSL (IDSL)
•Symmetric DSL (SDSL)
•Very-high-bit-rate DSL (VDSL)
Using Digital Telephone Lines - ATM
• Asynchronous transfer mode (ATM) digital service is
offered as a high-bandwidth, efficient means for
transferring multimedia content, data, and voice over
phone lines.
• Initially, ATM is proposed for different kinds of data
(voice, data, video) on the telephone system. However,
it can also implemented on computer LANs and
WANs.
• Some types of ATM service can reach transmission
speeds of 10,000 Mbps.
Using Digital Telephone Lines Cable Modem Connections
•
Cable modems allow users to connect their PCs to
the Internet via the local cable television system.
•
Cable companies offer Internet service by
combining television and data signals and
distributing them over the cable system.
•
Cable modem service can achieve speeds of 27 Mbps.
纜線數據機系統結合一般的有線電視網路，與連接到網際網
路的廣域網路
Networks in the Home
•
Because more homes now have multiple computers,
home networks are gaining in popularity. Home
networks offer the same advantages to home users as
to a business.
•
Home networks are typically based on existing
telephone or wireless technologies.
•
Popular PC operating systems, such as Windows and
the Mac OS, provide simple networking tools that
are adequate for running a home network.
有數百萬的家庭目前有多部PCs。新的科技讓家庭可以在家
中使用現有的媒體(例如電話線)與現成的作業系統(例如視窗)
而建立網路
Section 7b review
•
Explain how computer data travels over telephone
lines.
•
Explain a modem's function.
•
List four features you should consider when
evaluating modems.
•
Differentiate four types of digital telephone services.
•
Describe one potential use for a home network.
.