Class_notes_InternetTechnology

Introduction to Networks

What is a computer Network?

A network is any collection of independent computers that communicate with one another over a shared network medium. When these computers are joined in a network, people can share files and peripherals such as modems, printers, tape backup drives, or CD-ROM drives

Every network includes:

At least two computers Server or Client workstation.Networking Interface Card's (NIC)A connection medium, usually a wire or cableNetwork Operating system software, such as Microsoft Windows NT or 2000

Types of Networks

LANs (Local Area Networks)

LANs are networks usually confined to a geographic area, such as a single building or a college campus.

WANs (Wide Area Networks)

Wide area networking combines multiple LANs that are geographically separate

Internet

The Internet is a system of linked networks that are worldwide in scope and facilitate data communication services such as remote login, file transfer, electronic mail, the World Wide Web and newsgroups.

Intranet

An intranet is a private network utilizing Internet-type tools, but available only within that organization i.e. for large organizations.

MANs (Metropolitan area Networks)

This refers to a network of computers with in a City.

VPN (Virtual Private Network)

VPN uses a technique known as tunneling to transfer data securely on the Internet to a remote access server on your workplace network.

OSI Reference Model

Seven layers of OSI Model:

The Open Systems Interconnection model (OSI model) is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers

ISO OSI Layering Architecture

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

Application Protocol

Transport Protocol

Presentation Protocol

Session Protocol

Host A Host BApplication

Layer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

Router Router

Layer 1: Physical Layer

Functions:

Transmission of a raw bit streamForms the physical interface between devicesWhich modulation technique (bits to pulse)?How long will a bit last?Bit-serial or parallel transmission?Half- or Full-duplex transmission?How many pins does the network connector have?How is a connection set up or torn down?

Layer 2: Data Link Layer

Functions:Provides reliable transfer of information between two adjacent nodesCreates frames from bits and vice versaProvides frame-level error controlProvides flow controlThe data link layer provides the network layer with what appears to be an error-free link for packets

Layer 3: Network Layer

Functions:Responsible for routing decisionsDynamic routingFixed routingPerforms congestion control

Layer 4: Transport Layer

Functions:Hide the details of the network from the session layerProvides reliable end-to-end communicationPerform end-to-end flow controlPerform packet retransmission when packets are lost by the network

Layer 5: Session Layer

May perform synchronization between several communicating applications

or logical transmissions Groups several user-level connections into a single “session”

Examples:

Banking session

Network meetings

Layer 6: Presentation Layer

Performs specific functions that are requested regularly by applications

Examples:

encryption

ASCII to Unicode, Unicode to ASCII

LSB-first representations to MSB-first representations

Layer 7: Application Layer

Application layer protocols are application-dependent

Implements communication between two applications of the same type

Examples:

FTP

HTTP

SMTP (email)

Overview of Layers:

Introduction to TCP/IP Networks:

They are based on an open specification that is not controlled by any vendor.

What Is TCP/IP?

TCP stands for Transmission Control Protocol and IP stands for Internet Protocol. The term TCP/IP is used to refer to a group of protocols related to the TCP and IP protocols such as the User Datagram Protocol (UDP), File Transfer Protocol (FTP), Terminal Emulation Protocol (TELNET), and so on.

TCP/IP Layering Architecture:

HostHost--toto--NetNet

Internet/NetworkInternet/Network

ApplicationApplication

TransportTransport

A simplified model The network layer:

Hosts drop packets into this layer, layer routes towards destination- only promise- try my best

The transport layer:reliable byte-oriented

stream

TCP/IP Protocol Architecture:

Application Protocol

Transport Protocol (TCP)

ApplicationLayer

TransportLayer

NetworkLayer

Host-to-Net Layer

Host AApplication

Layer

TransportLayer

NetworkLayer

Host-to-Net Layer

Host A Host BApplication

Layer

TransportLayer

NetworkLayer

Host-to-Net Layer

NetworkLayer

Host-to-Net Layer

NetworkLayer

Host-to-Net Layer

IPIP IP

1) Physical layer:Physical interface between data transmission deviceCharacteristics of transmission mediumSignal levelsData rates

2) N/W Access Layer: Exchange of data between end system and networkDestination address provisionInvoking services like priority

3) Internet Layer (IP):Systems may be attached to

different networksRouting functions across

multiple networksImplemented in end systems and routers

4) Transport Layer (TCP) Reliable delivery of dataOrdering of delivery

5) Application Layer Support for user applications

Ex. http, SMPT

Local-Area Network

Connect computers within a limited physical area such as an office, classroom, or building

Wide-Area NetworkWANs typically connect fewer computers than LANs and normally operate at lower speeds than LANs. WANs, however, provide the means for connecting single computers and many LANs over large distances.

LAN Topologies

Many LAN technologies have been invented but how specific technologies are similar and how they differ. Each network is classified into a category according to its topology or general shape

The four basic topologies are:

1.Bus Topology

2. Ring Topology

3. Mesh Topology

4. Star Topology

Bus Topology:

Bus topology usually consists of a single cable to which computers attach

The ends of a bus network must be terminated to prevent electrical signals from reflecting back along the bus.

Any computer attached to a bus can send on the cable and all computers receive the signal because all computers attach directly to the cable.

The computers attached to a bus network must coordinate to ensure that . only one computer sends a signal at any time

Ring Topology:Ring topology arranges for computers to be connected in a closed loop

I. A cable connects the first computer to a second computer, another cable connects the second computer to a third, and so on, until a cable connects the final computer back to the first.

II. name ring arises because one can imagine the computers and the cables connecting them arranged in a circle.

III. In practice, the cables in a ring network do not form a circle.

Ring topology requires a computer to connect to a small device that forms the ring

I. this is needed for the ring to continue operation even if some of the computers are disconnected

Mesh Topology:

A network that uses a mesh topology provides a direct connection between each pair of computers

The chief disadvantage of a mesh arises from the cost: •A mesh network connecting n computers requires:

•The important point is that the number of connections needed for a mesh network grows faster than the number of computers

Star Topology:

In star topology, all computers attach to a central pointThe center of a star network is often called a hubA typical hub consists of an electronic device

• That accepts data from a sending computer and delivers it to the appropriate destination

In practice, star networks seldom have a symmetric shape (hub is located an equal distance from all computers)

• Instead, a hub often resides in a location separate from the computers attached to it

Network Interface Card

A Network Interface Card (NIC) is a device that plugs into a motherboard

and provides ports for the network cable connections. It is the computer's

interface with the LAN.

Protocol:

In networking and Communications, the formal specification that defines the procedures to be followed when transmitting and receiving data.

Protocols define the format, timing, sequence and error checking used on the network.

HTTP- Hypertext Transfer Protocol is the stateless protocol used for data transfer within WWW.

IP Address:

A 32-bit address assigned to a computer that uses the TCP/IP protocols. The sender must know the IP address of the destination computer before sending a packet.

This is like a phone number for the computer.

A program on one computer communicates with a program on another computer, by connecting to its IP address.

The 32-bit address is usually represented as four 8-bit decimal numbers separated by periods.

Example: www.utm.edu (IP address is 208.47.4.80)

Communication Technologies

Communication Hardware…

Communication Network…

Communications Networks:

Activity associated with distributing or exchanging information.

Telecommunications –

Technology of communications at a distance that permits information to be created any where and used everywhere with little delay

It involves

– Data: digital and analog– Voice: spoken word– Video: telecommunication imaging

Essentials for Communications:

Must have a message Message must have a transmitter Message must have a medium Message must be understood Message must have some level of security

(Flow Diagram)

Source Transmitter Transmission Receiver Destination

Source System Destination System

Workstation/PC Workstation/PCMedium

Network:point to point or point to multiple point connected mediaA network is a group of computers connected together.low cost, reliable, and efficient means of communicating at a distance.

Node:Anything connected to the networkUsually a computerA printer or a scanner

Segment: Any portion of a network that is separated by a switch, bridge or a router from another part of a network.

Backbone: The main cabling of a network that all of the segment connect to.Backbone is capable of carrying more information than the individual segments.

Simplex: Information flows in only one direction

Half-duplex: Information flows in two directions, but only in one direction at a time.

Full-duplex: Information flows in two directions at the same time

Basic Signal Terminologies

Bit- binary digit, either 0 or 1

Baud- one electronic state change per second

Bit rate- a method for measuring data transmission speed (bits/second)

Mbps- millions of bits per second (data speed; measure of bandwidth = total information flow over a given time) on a telecommunication medium

8 bits = 1 byte

Mb- million bits (quantity of data)

MB- million bytes (quantity of data)

Gbps- Billion bits per second (data speed)

Teraflops- trillion operations per second

Data rate- bits per second

Bandwidth- bandwidth or signal in cycles per second or hertz

Noise- Average level of noise over the communication path.

Error rate- rate at which errors occur where error in 1 or 0 bit occurs

Communication Hardware:

Transmission medium-

Guided Medium: waves are guided along a solid medium path (twisted pair, coaxial cable, and optical fiber).

Unguided medium: waves are propagated through the atmosphere and inner/outer space (satellite, laser, and wireless transmissions)

Conductive: twisted pairs and coaxial cables

Electromagnetic: microwave

Light: lasers and optical fibers (need clear line of sight)

Wireless – inner/outer space, satellite (Omni directional)

Hubs:

A place where data converges from one or more directions and is forwarded out in one or more directions.

Seen in local area networks

Gateways:A gateway is a network point that acts as an entrance to another network. In terms of routing, the network consists of gateway nodes and host nodes. Host nodes are computer of network users and the computers that serve contents (such as Web pages).Gateway nodes are computers that control traffic within your company’s network or at your local internet service provider (ISP)

Routers:A router is a device or a software in a computer that determines the next network point to which a packet should be forwarded toward its destination.Allow different networks to communicate with each otherA router creates and maintain a table of the available routes and their conditions and uses this information along with distance and cost algorithms to determine the best route for a given packet.A packet will travel through a number of network points with routers before arriving at its destination.

Bridge:A bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or token ring).A bridge examines each message on a LAN, "passing" those known to be within the same LAN, and forwarding those known to be on the other interconnected LAN (or LANs).

Difference between (Bridge, Router, Gateway):Bridge: device to interconnect two LANs that use the SAME logical link control protocol but may use different medium access control protocols.Router: device to interconnect SIMILAR networks, e.g. similar protocols and

workstations and servers.

Gateway: device to interconnect DISSIMILAR protocols and servers, and Macintosh and IBM LANs and equipment

(Bridge Diagram)

Switches:

Allow different nodes of a network to communicate directly with each other.Allow several users to send information over a network at the same time

without slowing each other down.

Modulation:

In a modem, the MODULATION process involves the conversion of the digital computer signals (high/low, on/off or logic 1 and 0 states) to audio-frequency tones.

Demodulation:The DEMODULATION process converts the audio tones back into digital signals that a computer can understand directly.

Internet Technology:Internet technology refer-

ArchitectureServices

Architecture-wise:

Service-wise (applications):

Electronic mailRemote terminalFile transferNewsgroupsFile sharingResource distributionWorld Wide WebVideo conferencingGames

Packet:A small, self-contained parcel of data sent across a computer network.Each packet contains a header that identifies the sender and recipient, and a payload area that contains the data being sent.All messages sent on a network such as the Internet are broken into small chucks called packets.

To From Payload / Data

208.47.4.80:80 10.11.1.115 GET /index.html

Header


To From


To


From


To Payload / Data


From


To Payload / Data


From


To

GET /index.html

Payload / Data


From


To

GET /index.html

Payload / Data


From


To

10.11.1.115 GET /index.html

Payload / Data


From


To

208.47.4.80:80 10.11.1.115 GET /index.html

Payload / Data


From


To

When the web server receives this request, it will send the web page back to my computer by breaking it down into smaller parts and sending each part in a packet

Part 1 of web page

Part 2 of web page

10.11.1.115 208.47.4.80

10.11.1.115 208.47.4.80

To From Payload / Data

Packet 1

Packet 2

The Client/Server:

clients

Nodes that use the network's resources are called clients (usually

computers), and nodes that manage the sharing of resources are called

servers.

Servers are specialized computers with their own operating systems and

network administration software.

Client Server

http

Performance: Latency and Bandwidth:

Latency – How long minimum communication takes in seconds (s)– Round trip vs. single trip– More difficult to overcome than bandwidth

Bandwidth – Number of bits per time unit usually seconds (bps)

bandwidth

latency

link

Architectural Approaches:

Connection orientedConnectionless

Connection-oriented– Circuit switched

(Persistent connection set up between sender and receiver

Example: telephone system)Connectionless

– Packet switched

(Data partitioned into packets and sent individually from sender to receiver and reassembled at receiver.)

Switching Schemes:

(1) Circuit Switching

(2) Message Switching (Store-and-Forward)

(3) Packet Switching (Store-and-Forward)

Circuit Switching:

Provides service by setting up the total path of connected lines hop-by-hop

from the origin to the destination

Example: Telephone network

Properties:

Point-to-point communicationSeparate steps for circuit creation, use, and terminationPerformance equivalent to an isolated physical path

Message Switching:

Each message is addressed to a destinationWhen the entire message is received at a router, the next step in its journey

is selected; if this selected channel is busy, the message waits in a queue until the channel becomes free

Thus, the message “travel (hope)” from node to node through a network while allocating only one channel at a time

Packet Switching:

Messages are split into smaller pieces called packetsThese packets are numbered and addressed and sent through the network

one at a time.Allows Pipelining

Comparison of Switching Technologies:

(Circuit switched)

AdvantagesOnly route onceLatency and bandwidth constant

DisadvantagesIdle resources unavailable for other connectionsLarge setup timeSingle point of failure

(Packet switched)

Advantages Efficient use of wires Small startup overhead

Disadvantages Route each packet Per packet overhead Bursty

Netiquette & Ethics

Etiquette:

Is the practice of good manners.being polite and helpful.being kind and not aggressive.Being mindful of the fact that others may see things differently than oneself.

Netiquette:

Is etiquette for the Internet.Being polite to others.Important there are no facial clues or body-language to help us understand

another person, as there is in face to face meetings.

Ten Commandments Of Computer Ethics:

1. Not Use A Computer To Harm Other People.

2. Not Interfere With Other People’s Computer Work.

3. Not Snoop Around In Other People’s Computer Files.

4. Not Use A Computer To Steal.

5. Not Use A Computer To Bear False Witness.

6. Not Copy Or Use Proprietary Software For Which You have Not Paid.

7. Not Use Other People’s Computer Resources Without Authorization

8. Not Appropriate Other People’s Intellectual Output.

9. You Shall Think About The Social Consequences Of The Program

10. You Shall Always Use A Computer to respect for your fellow humans.

Publishing and Browsing the Web

What is World Wide Web?

The World Wide Web (WWW) is a global interactive, dynamic, cross platform, graphical hypertext information system that runs on the Internet.

Internet Standard Domain Names:

Edu: educational organizationsCom: commercial organizationsGov: government institutionsMil: military groups Net: major network support centre'sOrg: organizations other than the aboveInt: international organizations

Web Browser:

A Web Browser is special software such as Netscape, Mosaic or Internet Explorer. These browsers allow a user to view Web pages delivered from a client server (Web Site) situated at a particular URL on the World Wide Web

Search Engines on the WWW:

Tools on the WWW used to search and find web sites related to a particular topic.

provide for searching using keywords and boolean operators.

Popular ones are Alta Vista, Infoseek, HotBot,Web Crawler, Lycos and Yahoo.

Over 600 search engines working at present.

Web Page:

A web Page is a single document written in HTML ( Hypertext Markup Language ) that includes the text of the document, its structure, any links to other documents and graphic images and other media.

Homepage:

Homepage is a Hypertext document a server will serve as default.

URL:

A URL is the space of a web browser where the address of a website is written

Web Protocol and Language:

HTTP (Hyper Text Transfer Protocol)

– The simple protocol used to transfer a World Wide Web page from one computer to another.

– A web client opens up a connection to a web server and sends GET PAGENAME and then the web server sends back the page text (usually HTML) over the connection.

HTML (Hyper Text Markup Language)

– The source form used for documents on the World Wide Web. HTML embeds commands that determine formatting along with the text to be displayed (e.g., to move to a new line or indent text).

Uniform Resource Locator (URL):

Method of accessing Internet Resources. URLs are used by web browsers to connect you directly to a specific document or homepage on resource is physically located.

Example URL:Example URL:

http://www.nic.in:80/nicnet.html

Host AddressHost AddressPortPort

Path/DocumentPath/Document

Data Communication:

1) Coaxial cable

Widely installed for use in business and corporation Ethernet and other types of LANs.Consists of inter copper insulator covered by cladding material, and then covered by an outer jacket

:Physical Descriptions:

Covered by sheath material Outer conductor is braided shielded (ground)

Separated by insulating material

Inner conductor is solid copper metal

•Applications:– TV distribution (cable TV); long distance telephone transmission; short

run computer system links– Local area networks

•Transmission characteristics:– Can transmit analog and digital signals– Usable spectrum for analog signaling is about 400 Mhz– Amplifier needed for analog signals for less than 1 Km and less

distance for higher frequency– Operation of 100’s Mb/s over 1 Km.

2) Twisted Pair Cables:

•Physical description:– Each wire with copper conductor– Separately insulated wires– Twisted together to reduce cross talk– Often bundled into cables of two or four twisted pairs– If enclosed in a sheath then is shielded twisted pair (STP) otherwise

often for home usage unshielded twisted pair (UTP). Must be shield from voltage lines

•Application:– Common in building for digital signaling used at speed of 10’s Mb/s

(CAT3) and 100Mb/s (CAT5) over 100s meters. – Common for telephone interconnection at home and office buildings– Less expensive medium; limited in distance, bandwidth, and data rate.

3) Optical Fibers:

•Physical Description:– Glass or plastic core of optical fiber = 2to125 µm– Cladding is an insulating material– Jacket is a protective cover– Laser or light emitting diode provides transmission light source

•Applications:– Long distance telecommunication– Greater capacity (2 Gb/s over 10’s of Km)– Smaller size and lighter weight– Lower attenuation (reduction in strength of signal)– Electromagnetic isolation (not effected by external electromagnetic

environment.– Greater repeater spacing (fewer repeaters, reduces line regeneration

cost)

4) Wireless Transmission:

•Frequency range (line of sight):– 26 GHz to 40 GHz: for microwave with highly directional beam as

possible– 30 MHz to 1 GHz: for Omni directional applications– 300MHz to 20000 GHz: for infrared spectrum; used for point to point

and multiple point application (line of sight)

•Physical applications:– Terrestrial microwave – long haul telecommunication service

(alternative to coaxial or optical fiber)– Few amplifier and repeaters– Propagation via towers located without blockage from trees, etc (towers

less than 60 miles apart)

Data Security:

Need for Security:

1. Network layer security

TCP/IP can be made secure with the help of cryptographic methods and protocols that have been developed for securing communications on the Internet.

Ex: Electronic mail security (E-mail)

2. Pretty Good Privacy (PGP)

PGP provides confidentiality by encrypting messages to be transmitted or data files to be stored using an encryption algorithm such 3DES or CAST-128.

Email messages protection ways:

•Signing an email message to ensure its integrity and confirm the identity of its sender.•Encrypting the body of an email message to ensure its confidentiality.

•Encrypting the communications between mail servers to protect the

confidentiality of both the message body and message header.

3. Multipurpose Internet Mail Extensions (MIME):

MIME transforms non-ASCII data at the sender's site to Network Virtual Terminal (NVT) ASCII data

It delivers it to client's Simple Mail Transfer Protocol (SMTP) to be sent through the Internet.

The server SMTP at the receiver's side receives the NVT ASCII data and delivers it to MIME to be transformed back to the original non ASCII data.

Example-

I. Secure/Multipurpose Internet Mail Extensions (S/MIME)

Firewalls:

A firewall controls access between networks. It generally consists of gateways and filters which vary from one firewall to another. Firewalls also screen network traffic and are able to block traffic that is dangerous.

Types of firewalls:

1. Packet filters

Packet filters are one of several different types of firewalls that process network traffic on a packet-by-packet

basis. Their main job is to filter traffic from a remote IP host, so a router

is needed to connect the internal network to the Internet. The router is known as a screening router, which screens

packets leaving and entering the network.

2. Circuit-level gateways

The circuit-level gateway is a proxy server that statically defines what traffic will be allowed.

Circuit proxies always forward packets containing a given port number.port number is permitted by the rules set

3. Application-level gateways

An application-level gateway is a proxy server operating at the TCP/IP application level.

A packet is forwarded only if a connection is established using a known

protocol.

Malicious software and antivirus:

1. Malware

Commonly, a computer user can be tricked or forced into downloading software onto a computer that is of malicious intent. Such programs are known as malware and come in many forms, such as viruses, Trojan horses, spyware, and worms.

2. Viruses

Viruses are programs that can replicate their structures or effects by infecting other files or structures on a computer. The common use of a virus is to take over a computer to steal data.

3. Trojan horse

A Trojan horse (commonly known as a Trojan) is a general term for malicious software that pretends to be harmless so that a user willingly allows it to be downloaded onto the computer.

4. Spyware

The term spyware refers to programs that surreptitiously monitor activity on a computer system and report that information to others without the user's consent.

5. Worms

Worms are programs that can replicate themselves thoughout a computer network, performing malicious tasks throughout.

6. Botnet

A botnet is a network of "zombie" computers that have been taken over by a "bot" that performs large-scale malicious acts for the creator of the botnet.

Antivirus:

Antivirus programs and Internet security programs are useful in protecting a computer or programmable device from malware.

Such programs are used to detect and usually eliminate viruses.A user would pay for antivirus software. A computer users now can, and do, download from a host of free security applications on the Internet.

Buffer overflow attacks:A buffer overflow is an attack that could be used by a cracker to get full

system access through various methods.By essentially cracking a computer using brute force.Most security applications and suites are incapable of adequate defense

against these kinds of attacks.

Ex- Through remote control process.

Client-Server Architecture:

A network architecture in which each computer or process on the network is either a client or a server.

Components of Client-Server Architecture:

• Client• Server• Communication Network

Tier Architecture of Client Server model:

2-Tier Architecture :

2-tier architecture is used to describe client/server systems where the client requests resources and the server responds directly to the request, using its own resources. This means that the server does not call on another application in order to provide part of the service.

3-Tier Architecture :

• In 3-tier architecture, there is an intermediary level, meaning the architecture is generally split up between:

• A client, i.e. the computer, which requests the resources, equipped with a user interface (usually a web browser) for presentation purposes

• The application server (also called middleware), whose task it is to provide the requested resources, but by calling on another server

• The data server, which provides the application server with the data it requires

Multi-Tiered Architecture :

WWW

Definition:

All the resources and users on the Internet that are using the Hypertext Transfer Protocol (HTTP)

History:

1969 - RFCs begun by S. Crocker1972 - Email by Ray Tomlinson & Larry Roberts1970’s - TCP by Vint Cerf & Bob Kahn1980s – Hardware Explosion (LANs, PCs, and workstations)1983 – Ethernet by Metcalfe1985 – Internet used by researchers and developers

Development of Internet:

Internet evolved from ARPANET. It includes

first operational packet network

applied to tactical radio & satellite nets also

had a need for interoperability

led to standardized TCP/IP protocols

Model diagram of WWW:

CGI

User

CLIENT

HTTP

TCP/IP

SERVER

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