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 mailContain:

– 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.

• A protocol defines the steps necessary for computers to communicate

Over the internet.

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 fiber-

optic 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.

• 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 employedTakes 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, Real-

Time 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) andISP 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