Transcript Hardware - Computer and Information Science

Hardware
– Internet is a network of
interconnected
Host Computers or Hosts
– Each host is assigned a unique
IP address,
e.g. 146.245.1.13
IP Stands for Internet Protocol
Computers Communicate
Through PACKETS
Analogy to letters sent by regular mail
Contain:
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A source address
A destination address
Sequencing Information
Error Control Information
•
Source is IP address of computer
sending
Destination is IP address of destination
computer
Data sent across internet is usually
divided into multiple packets
Packets may arrive at destination out
of order
Internet is a Complex
Network of Computers
Router, a special kind of host,
ensures that packets reach their
destination.
Communication
• Server is a host on the Internet that
manages network resources
and fulfills requests from clients.
• Many types of servers: Web
servers, e-mail servers
Database servers and file servers;
single server may provide
multiple services.
• Web server stores web pages and
delivers them to clients upon
request
Web browser uses the hypertext
transfer protocol (HTTP) to request
and Transfer pages from a Web
server.
Common Protocols
FTP File Transfer Protocol
POP Post Office Protocol
(for sending email)
SMTP Simple Mail Transfer
Protocol (for receiving email)
Communication Media
Bits, Bytes,
Kilobytes, Megabytes, Gigabyte,
Terabytes
MICRO-MINIATURIZATION;
MOORE’s LAW
ASCII – American Standard Code for
International Intechange
256 What is so special about this
number?? And 1024??
Communications Media
/ Cont.
Bandwidth: how much data can be
transferred through a medium in
fixed amount of time?
bps = Bits per second; MHZ = Mega
Hertz = 1000’s cycles per second
Kbps; Mbps, Gbps, Tbps;
Copper wire used for POTS (Plain old
telephone system)
Advantages: available, reliable, ease
of installation
Disadvantage: Speed
Communication Media/ Cont.
Hence Fiber Optic Cable:
flexible glass fiber; thinner
and lighter;
Yet with much wider bandwidth; Uses
bursts of light to represent bits,
rather than electronic bits
interpreted by computers as bits.
Optical Modem (modem stands for
modulator – demodulator) translates
digital signals from computers into
light through a process called
modulation
Fiber Optic Cable/
Cont.
•
Light is transmitted over the fiberoptic cable to the receiver’s
optical modem
•
Converts the light back into
electrical signals through a process
called demodulation
Recent New Optical
Technology Called
Opto-Chip
• Able to convert most basic
particle of light, PHOTON into
electric current.
• Process allows tremendous
amounts of data to be sent over
fiber-optic networks through
particles 100 times smaller than
the diameter of a human hair.
Opto-Chip/ Cont.
• Further enhancements allow
multiple wavelengths to be
transmitted over a single fiber.
• Repeaters amplify signals, thereby
countering deterioration
of signals over distance over copper
and fiber-optic networks.
• Fiber optic networks are also more
complicated and expensive to
develop and maintain. Must be
carefully cut and polished.
Storage Area Network
(SAN) Provides high
capacity,
Reliable data storage on a network;
Fault Tolerant.
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Stores multiple terabytes.
High speed fiber-optic line
Data collected in logical groups
Large volume storage, may provide
Backup and recovery
Redundant copies stored using
“mirror” technology”
– SAN uses fiber-channel technology
– Operates at transfer rates of 100 Mbps
Most Home Users Use
ISP (internet service
providers)
(SEE TABLE)
•
Modem is employed
Takes DIGITAL SIGNAL (Computer)
–
Converts into ANALOG SIGNAL
(Modem into telephone line)
Converted back into DIGITAL SIGNAL
(Line into Modem and Recipient
Computer)
Digital Subscriber Line
(DSL)
• Offers high bandwidth over
standard copper telephone lines
• xDSL refers to many forms
• ADSL means assymmetric
– Slower Upstream (Sending) than
Downstream (Receiving)
• SDSL means symmetric
– Same upstream and downstream
– Up to 3Mbps.
DSL / cont.
• HDSL high speed DSL
– Also same upstream and
downstream
– Rates up to 1,544 Mbps
– Users within 4500 feet of a
central office
– offers rates 13 Mbps to 55 Mbps
• VDSL very high speed DSL.
More DSL
•Transformns copper
Telephone Wire into High
Speed Digital Connection
•Does not require any
additional rewiring
•Exploits existing wiring;
•Takes advantage of
bandwidths unused
•Gives 3 information
carrying lines:
–1 internet to home computer
–1 transports from home to
internet
–1 for regular phone and
faxes.
•Still More DSL
• Much faster speeds than Modem
over Telephone
• Requires Hardware at the local
telephone company’s central office
• Speed decreases over distance
• Fastest DSL is within a few
thousand feet of central office.
• Voice Over DSL (VoDSL)
takes advantage of high bandwidth
of DSL – voice services over single
line
Broadband
• Category of high bandwidth
Internet Service provided mainly
by Cable TV and Telephone
Companies to home users.
• Can handle Voice, Data and Video
• Enables Video-Conferencing, RealTime Voice and Streaming-Media
Applications.
• Eliminates need to dial in to an ISP
CABLE MODEM
• Perhaps most popular form of more
advanced service being adopted by
the public.
• Transmission over same cable that
brings Television to home/business.
• UNLIKE DSL, bandwidth is shared
with many users.
• Can reduce bandwidth available to
many people in one building or
neighborhood.
• Can typically offer downstream rate
between 384 Kbps and 1.5 Mbps
and upstream of 128 Kbps.
• Elimnates need for extra phone line
for computer in home
Integrated Services
Digital Network
• Provides High-speed connections
to the Internet over both digital and
standard telephone lines.
• Transfer speeds up to 128Kbps.
• Uses Hardware called
terminal adaptor (TA) and
ISP that provides ISDN.
• Limited availability and Expensive.
• Uses 3 Channels
– Basic Rate Interface (BRI)
– Two Bearer (B) Channels supporting
data transfers at 64 Kbps.
– Data Channel (D) is used to transmit
Routing Information.
– Each B Channel may be used for
Voice or Data Communication and
Combined for Maximum (128Kbps)
rate.
T-1 and T-3 Lines
• T-1 is a dedicated connection that
supports data rates of 1.544 Mbps.
• Made up of 24 channels
– Each channel supports 64 Kbps
• T-3 Line Supports data rates of 43
Mbps and is made up of 672
channels that each support 64Kbps.
• T-1 and T-3 can be used for both
voice and data communication.
– Like a “hub” – used for large
organizations