CHAPTER - 4

INTERNET NETWORK

Network

• A computer network is simply a group of computers that are so connected that resources can be shared and information can be exchanged.

• exchange information • share resource

• wired & wireless

Need of Networking

• Resource sharing• Reliability• Financial benefits• Better communication medium• Access to remote database

Types of Networks

• Local Area Network (LAN)• Metropolitan Area Network (MAN)• Wide Area Network (WAN)• Value-Added Network (VAN)• Backbone• Campus Area Network (CAN)• Home Area Network (HAN)• Wireless/Mobile Networks

Local Area Network

• within a room/floor/building/organization• usually less than 1 km in diameter

Advantages of LAN

• sharing of expensive resources such as color laser printers• high-speed exchange of essential information between key people in an organization• increase the range of potential applications• increase productivity and profitability

Disadvantages of LAN

• financial cost of networking hardware• requires memory space in each computer• complex• lack of control• security system must be implemented in order to protect confidential data• memory intensive programs(RDBMS) are particularly vulnerable to networking because of memory requirement

Characteristics of LAN

• restricted geographical area• relatively high speed than WAN• private networks

• e.g. Computer Lab

Metropolitan Area Network

• larger than LAN but smaller than WAN• e.g. cable TV networks

Characteristics of MAN

• 5-50 KM• generally not owned by a single organization (biz. purpose)• large companies/universities with multiple buildings• acts as a high-speed network to allow sharing of regional resources

Wide Area Network

• nationwide or worldwide (public network)• it may also enable LANs to communicate with each other

Characteristics of WAN

• ensure high-quality, reliable service for end users• separate each user’s session• use public transmission media such as telephone lines, microwave link and satellite links

Functions of WAN

• Remote data entry

• Centralizing information

• Facilitating communications

Types of WAN

• Hierarchical Networks : configure computers in a hierarchy (client-server)

• Distributed Data-processing Networks : peer-to-peer

Nodes

• A node is any device connected to a computer network. • Nodes can be computers, personal digital assistants (PDAs), cell phones, or various other network appliances.

Host/Server

• The most powerful type of computer on the network, that does all  the processing for the user.

Workstation

• It is a personal computers on network that is operated by network users. • Each workstation process its own files using its own operating system.

Bandwidth• refers to the difference between the highest and lowest frequencies of a transmission channel • In networking, bandwidth or throughput defines the net bit rate (bit/s, kbit/s, Mbit/s, Gbit/s, etc.)

Broadband vs. Baseband•Bandwidth can be divided into channels thus channel is simply a portion of bandwidth that can be used for transmitting data.two ways of allocating the capacity of bounded transmission media are:Baseband & Broadband. •Transmission use entire bandwidth for single channel.• Allow the division of bandwidth into multiple channels.

Interoperability• Network Interoperability is the continuous ability to send and receive data between interconnected networks providing the level of quality expected by the end user customer.

Network Administrator• an individual that is responsible for the maintenance of  computer hardware and software systems that make up a computer network• generally mid-level support staff within an organization and do not typically get involved directly with users

Functions of Network Admin• Initial network planning• Frequency allocation, predetermined traffic routing to support load balancing• Cryptographic key distribution authorization• Configuration management• Fault management• Security management• Performance management• Bandwidth management• Accounting management

Network Management• a service that employs a variety of tools, applications and devices to assist human network managers in monitoring and maintaining networks• There exist a wide variety of software and hardware products that help in managing a network by sending them alerts when they recognize problems.• Upon receiving these alerts, management entities are programmed to react by executing operator notification, event logging, system shutdown and/or automatic attempts at system repair• Simple Network Management Protocol (SNMP)

Network Security• Physical Security Holes : unauthorized physical access

• Software Security Holes : privileged software

• Inconsistent Usage Holes : When a system administrator assembles ineffective hardware and software such that the system is seriously flawed from a security point of view

Protection Methods• Authorization : access only those resources they are authorized• Authentication : username & password• Encrypted Smart Cards : Punch card • Biometric Systems : Thumb impression, retina eyes• Firewall : Protection Layer1. Packet Filter2. Application Gateway3. Circuit-level Gateway4. Proxy Server

Network Components

Chassis

RepeaterRegenerates and propagates all electrical

transmissions between 2 or more LAN segmentsAllows extension of a network beyond physical length

limitationsLayer 1 of the “OSI model”

HigherLayers

Physical

HigherLayers

PhysicalPhysicalRepeater

Network A Network B

Repeater

Bridge/Hub/SwitchConnects 2 or more LAN segments and uses data link

layer addresses (e.g.MAC addresses) to make data forwarding decisions

Copies frames from one network to the otherLayer 2 of the “OSI model”

Bridge/Hub/Switch

Physical 1 Physical 2

Data Link Data Link

HigherLayers

Physical

HigherLayers

Physical

Data Link23-01-88-A8-77-45

Data Link53-F1-A4-AB-67-4F

Node in Network A Node in Network B

Switch & Router

RouterConnects 2 or more networks and uses network layer

addresses (like IP address) to make data forwarding decisions

Layer 3 of the “OSI model”

Router

A node in Network B

HigherLayers

Physical

HigherLayers

PhysicalPhysical 1

Data Link

Physical 2

Data Link Data Link

A node in Network A

Data Link

Network145.65.23.102

Network137.22.144.6 Network Network

Gateway/TunnelConnects 2 or more networks that can be of different

types and provides protocol conversion so that end devices with dissimilar protocol architectures can interoperate

Gateway

137.22.144.6

145.65.23.102

Netware

TCP/IP

Gateway

Probe• Remote Network MONitoring : to monitor the LAN

RSM & Terminal Server• Router Switch Module(RSM): A router installed as a card in a switch to perform routing between VLANs

• Terminal Server: A specialized system that connects terminals to a network

Logical Devices• A Digital Field Meter(DFM) monitors logical devices to diagnose power supply, resource and temperature exceptions.

• Fan• Temperature Sensor• Processor• Memory• Power Supply• Voltage Sensor

Network Adapters• A logical or physical component of a network device that connects the device to a network.

• Port: A port has a MAC address but no IP address

• Interface: It may have a MAC address, an IP address, or both.

Logical Links(Virtual LAN)• VLANs are logical links managed by DFM.

• VLAN is a logical subgroup within LAN that is created by software rather than by manually moving cables in the wiring closet.

Client/Server Model • Two parts: Client & Server

Client/Server Model • A client is a single-user workstation running front-end software that knows how to communicate with the server.

• A server is one or more multi-user processors with shared memory.

• Clients rely on servers for services.

Advantages of Client/Server Model • It facilitates the use of graphical user interface(GUI) available on powerful workstations.

• It allows the acceptance of open systems because of the fact that clients and servers can be running on different hardware and software platforms.

Disadvantages of Client/Server Model • If a significant portion of application logic is moved to a server, the server may become a bottleneck in the processing and distribution of data to the clients.

• The server’s limited resources will be in ever-increasing demand by the increasing number of resource consumers.

Application of Client/Server• Novel’s NetWare Operating System: supports TCP/IP protocol

• Windows NT 4.0: supports TCP/IP, IPX, also includes Internet Information Server (IIS). IIS includes both a web server and an FTP server.

• Windows 2000 Server: supports IP, IPX, AppleTalk

• IBM OS/2 Warp: It does not include an Internet server, but it does have a built-in web browser and FTP client.

File Server Model• In this model, the application and the data reside on the file server.

• When a network user needs access the application and data, both are loaded over network onto that user’s workstation.

• Sending the application and data from the server to the workstation puts load on the network.

File Server Model

Communication Media• There are several types of physical channels through which data can be sent from one point to another in a LAN.

• Bounded/Guided Media (Wired)• Unbounded/Unguided Media (Wireless)

• Media differ in the capability for the following reasons:1. Noise absorption: Susceptibility to external noise2. Radiation: Leakage of signal3. Attenuation: decline of magnitude of signal with

distance4. Bandwidth: transmission speed

Guided Media• Wired media

1. Twisted-pair wire : LAN

2. Coaxial cabling : Cable TV

3. Fiber-optic cabling : Broadband

Twisted-pair wire• two insulated copper wires (1 mm thick)

• The purpose of twisting the wires is to ensure that each wire is equally exposed to any external electrical magnetic field that could induce unwanted noise.

• commonly used in local telephone communication and for digital data transmission over short distances up to 1 km. (9600 bps)

Twisted-pair wire

Insulator (Teflon in Cat 5)

Advantages• being the oldest method, trained manpower is easily available

• In a telephone system, signals can travel several kilometers without amplification

• can be used for both analog and digital data transmission

• least expensive

• if a portion of a twisted-pair cable is damaged, the entire network is not shutdown

Disadvantages• easily picks up noise signals

• thin (break easily)

Types of TP Cable• Category 3 : 4 pairs

• Category 5 : 4 pairs but more twisted with Teflon insulation

• Category 6 : Gigabyte Ethernet

Coaxial Cabling• stiff (rigid) copper wire surrounded by an insulating material• The insulator is encased within a cylindrical conductor (braided mesh)• The signal is transmitted by the inner copper wire

Types of Coaxial Cabling• Two types:

1. 50-ohm : digital transmission2. 75-ohm : analog transmission (Cable TV)

Coaxial Cable Implementation

Terms Implementation

10Base2 Thin Ethernet (RG-58), 10MBPS, 185m cable segment

10Base5 Thick Ethernet, 10MBPS, 500m cable segment(bus)

10BaseF

Fiber-optic cable

10BaseT

UTP, uses RJ-45 connectors, Star Topology, 100m length

Thick Ethernet

0.4 inch thick, 1006m

Thin Ethernet

0.2 inch thick, 165m, normally used for office installation

Advantages• better shielding against EMI(Electromagnetic interference) than twisted-pair cable

• can be used for both analog and digital

• higher bandwidth (noise immunity)

• more expensive than TP but easy to handle

• capable of carrying over 50 std 6MHz color TV channels

Security• Cables that employ copper conductors can easily be breached by listening equipment.

• If the main consideration is security, then fiber cable is the only choice to avoid espionage.

Optical Fiber• newest form of bounded media• superior in data handling and security• transmits light signals rather than electric signals• each fiber has an inner core of glass/plastic that conducts light

Optical Fiber• total internal reflection

Optical Fiber• Two light sources:1. LEDs (Light Emitting Diodes)2. LASERs(Light Amplification by Stimulated Emission

Radiation)

Photoelectric diodes

LED/Laser

Types of Optical Fiber• Two types:1. Single-mode fiber (8-10µ (microns) core)2. Multimode fiber (50µ microns core) 1µ = 10-6 m

Laser

LED

Characteristics• Cost: more expensive than copper cable (associated equipments)• Installation: difficult to install• Bandwidth capacity: provides data rates from 100MBPS to 2GBPS• Node capacity: 75 nodes• Attenuation: much lower attenuation but has a different problem, namely, chromatic dispersion• EMI: immune to eavesdropping • Mode of transmission: half duplex

Chromatic Dispersion

Advantages• handle much higher bandwidth with low attenuation

• not affected by power surges, EMI or power failures

• lighter than copper cable

• do not leak light and are quite difficult to tap (excellent security)

Disadvantages• unfamiliar technology requiring skills

• Being unidirectional, two-way communication requires either two fiber cables or two frequency bands on one fiber

• higher cost

Comparison

Factor UTP STP Coaxial Fiber-optic

Cost Lowest Moderate Moderate Highest

Installation Easy Fairly easy Fairly easy Difficult

Bandwidth 1-155 Mbps 1-155 Mbps 100 Mbps 2 Gbps

Attenuation

High (few hundred meter)

High (few hundred meter)

Lower (few kilometer)

Lowest (tens of kilometer)

EMI Most vulnerable to EMI and eavesdropping

Less vulnerable than UTP

Less vulnerable than UTP

Not affected by EMI or eavesdropping

Unguided Media• signals are not guided through a solid medium (Air)

• Radio wave (including VHF and microwave links)• Satellite links• VSATs(Very Small Aperture Terminals)• Infrared and millimeter waves

Radio Waves• frequencies between 10 KHz and 1 GHz• broadcast omnidirectionally or unidirectionally• The power of the Radio Frequency (RF) signal is determined by the antenna and trans-receiver.

Characteristics• easy to generate• travel long distances• penetrate buildings easily• omnidirectional• At low frequency, radio waves pass through obstacles easily, but the power falls off sharply with distance from source.• At high frequency, radio waves tend to travel in straight lines and bounce off obstacles.• absorbed by rain

Microwave Transmission• Above 100 MHz, the waves travel in straight lines and can, therefore, be narrowly focused.• Concentrating all the energy into a small beam using a parabolic antenna gives a much higher signal to noise ratio, but the transmitting and receiving antennas must be accurately aligned with each other.• uses repeaters at intervals of about 25-30 km to amplify weak signal

Microwave Transmission• do not pass through buildings well• Multipath Fading (delayed waves may arrive out of phase)• The higher the towers are, the further apart they can be.

Characteristics• transmission depends on weather and frequency. (10GHz)• widely used for long-distance telephone communication, cellular telephones, television distribution• inexpensive as compared to fiber-optic system (congested area)• 16 Gbps

Types• Two Types:

1. Terrestrial2. Satellite

Terrestrial Microwave Systems• use directional parabolic antennas to send and receive signals• Relay towers and repeaters are used to extend signals• used whenever cabling is cost-prohibitive such as in hilly areas or crossing rivers etc.

Characteristics• Frequency range : 4-6 GHz and 21-23 GHz• Cost : inexpensive for short distance but expensive for long distance• Installation: difficult due to Line-of-sight requirements• Bandwidth capacity: 1-10 Mbps• Attenuation: affected by atmospheric conditions (rain and fog)• EMI: vulnerable to EMI, jamming and eavesdropping

Satellite Microwave Systems• one antenna is on the satellite in geo-synchronous orbit about 36,000 km above the equator (can reach the most remote places)• the transmitted frequency is different from the receiving frequency to avoid interference

Characteristics• Frequency range: 4-6 GHz and 11-14 GHz• Cost: The cost of building and launching a satellite is extremely high• Installation: extremely technical and difficult • Bandwidth capacity: 1-10 Mbps• Attenuation: depends on frequency, power, antenna size and atmospheric conditions. Higher frequency microwaves are more affected by rain and fog

Advantages and Limitation• visible from any point• transmission and reception costs are independent of the distance• a transmission station can receive its own transmission (testing)

• cost of placing the satellite• a signal sent to a satellite is broadcast to all receivers within the range (security measures need to be taken)

VSATs• Very Small Aperture Terminals (1m wide antennas)• the micro-stations do not have enough power to communicate directly with one another, hence • a special ground station, the hub, with a large high-gain antenna is needed to relay traffic between VSATs

Light Wave Transmission• connect two LANs in two buildings via lasers mounted on their roof-tops• Coherent optical signaling using lasers is inherently unidirectional. So, each buildings needs its own Laser and photo detector

Advantages and Disadvantages• Advantages:1. bandwidth is very high at very low cost2. easy to install3. does not require any license

• Disadvantages:1. cannot penetrate rain or thick fog2. heat from sun causes convection currents

Infrared and Millimeter Waves• used for short-range communication (remote control in TV)• directional, cheap and easy to build but do not pass through solid objects• Security if Infrared systems against eavesdropping is better than that of radio systems• No government license is needed (radio systems must be licensed)

Fiber-optics communication

Factor LED Laser

Data rate Low High

Mode Multimode Multimode or single-mode

Operating distance 3 Km 30 Km

Lifetime Long life Short life

Temperature sensitivity

Minor Substantial

Cost Low Substantial

• Light Source: LED/Laser• Transmission medium: Fiber-optic cable• Detector: converter

Types of Network• Client/Server Computer Network

• Peer-to-peer (P2P) Computer Network

Client/Server• Two-tier architecture• Server accepts client requests, process them and return the requested information to the client.

Client/Server• Characteristics of Client:1. Activates Master Computer2. Initiates requests3. Waits for and receive replies4. Connects to one or more number of servers at one time5. Typically interacts directly with end-users using a GUI

• Characteristics of Server:1. It waits for requests from clients2. Upon receipt of requests, it process them and then

offers replies3. It usually accepts connections from a larger number of

clients.4. It does not interact directly with end-users.

Peer To Peer(P2P) Computer Network Direct system exchange of resources between linked peers in network

The most used in the world

Basically different from the Client-server architecture

• e.g. Telephony Traffic

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Architecture of P2PPeer to peer is a type of network infrastructure where each computer is both server

and client. In this case, the computers connected to the network share their resources .

• Distributed Architecture • Decentralized architecture

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P2P Network administration

In a typical peer-to-peer, there is no administrator .So,

each user manages his own post. On the other hand all users

can share their resources as they wish. If we consider one of

the posts as a server, it is intended to share resources, if not it

consumes resources from other posts

Types of P2P• three categories:

1. Collaborative/Distributed computing: Science and Biotech org.

2. Instant messaging: MSN Messenger or AOL (real-time chat)

3. Affinity communities: search other user’s computers for information and files like Napster

4. Napster was the name given to two music-focused online services. It was originally founded as a pioneering peer-to-peer file sharing Internet service that emphasized sharing audio files, typically music, encoded in MP3 format.

Working of P2P• each computer typically runs both client and server software• Once you have downloas and install P2P client, you can log into a Central Indexing Server (indexes all users who are connected to the server means who are online)• P2P client will contain an area where you can search for a specific file.• The utility queries the index server to find other connected users with the requested file.• Once the file download is complete, the connection will be broken.

Addressing in Internet• Each device in a network must have a unique address to be identified.

• two types of addressing schemes:1. IP (Internet Protocol) addressing : 192.168.10.51

2. DNS (Domain Name System) addressing : www.google.com

IP Address

• two version of IP Address:1. IPv4 : 32-bit address2. IPv6 : 128-bit address

0-255 0-255 0-255 0-255

Octet (4)

Period (3)

• two types of IP Address:1. Static IP2. Dynamic IP : DHCP

IPv4 ClassesA, B, C : Mostly used classesD : MulticastE : Broadcast

Class Leftmost bits Start address Finish address

A 0XXX 0.0.0.0 127.255.255.255

B 10XX 128.0.0.0 191.255.255.255

C 110X 192.0.0.0 223.255.255.255

D 1110 224.0.0.0 239.255.255.255

E 1111 240.0.0.0 255.255.255.255

Domain Name System (DNS)• purpose of DNS is to translate domain names into IP addresses

Domain Name System (DNS)• domain name space (tree) is divided into three different sections:

1. Generic domains2. Country domains3. Inverse domains

Generic Domains• define registered hosts according to their generic behavior (3 chr)

Label Description

com Commercial organization

edu Educational institutions

gov Government institutions

int International organizations

mil Military groups

net Network support centers

org Nonprofit organizations

Country Domains• 2 character country abbreviations

Label Description

us USA

in India

uk UK

ca Canada

au Australia

fr France

Inverse Domains• used to map an address to a name (rDNS)

Resolving Names to Addresses• HOSTS.txt was used earlier (managed by Stanford Research Institute International (SRI) • In 1983, Paul Mockapetris introduce the concept of DNS• The root of DNS database on the Internet is managed by the Internet’s Network Information Center (InterNIC).

• The top-level domains were assigned organization wise, and by country.

Workgroup vs Domain• Workgroup (P2P) , Domain (Client/Server)• In a domain, user accounts are defined & managed in a central database (Security Accounts Manager)• By default, each domain is a separate entity and do not share information and resources.• To allow users to access resources in another domain, you need to establish a trust between the two domains.

Network Topologies• Topology is the method in which networks are physically connected together.• It determines the complexity and cost.

• Bus• Ring• Star• Mesh

Bus Topology• simplest & oldest used LAN design (passive topology)• e.g. Ethernet 10Base2 (thinnet)• can be found in Client/Server system

Advantages & Disadvantages• Advantages:1. simple, reliable, easy to use (small-sized LANs)2. requires least amount of cable (less expensive)3. it is easy to extend a bus (connector)

• Disadvantages:1. spend a lot of its bandwidth with the computers

interrupting each other instead of communicating2. difficult to troubleshoot

Ethernet• 1973 by Bob Metacalfe (IEEE standard called 802.3 CSMA/CD)

Collision Domain• a section of a network where data packets can collide with one another when being sent on a shared medium• the larger the collision domain, the more likely it is that collision will occur

CSMA/CD• Carrier Sense Multiple Access with Collision Detection

LocalTalk• a data link protocol built into the Macintosh (Apple computer)

• it forms a part of the AppleTalk protocol suite (provide file and printer sharing services)

• AppleTalk Network Layer

Ring Topology• active network, no termination, each node act as a repeater• can be found in P2P networks

Nearest Active Upstream Neighbor

Nearest Active Downstream Neighbor

Advantages & Disadvantages• Advantages:1. every computer is given equal access to the token2. continues to function in a slower manner rather than

fail completely

• Disadvantages:1. Failure of one computer affects the whole network2. difficult to troubleshoot3. Adding or removing computers disrupts the network

IBM Token Ring• IBM created IEEE 802.5 standard known as Token Ring• it uses a special packet known as Token• Multi-station Access Unit (MSAU)

Fiber Distributed Data Interface(FDDI)• another ring-based network but implemented without hubs• uses multimode fiber-optic cables to implement very fast, reliable networks

Fiber Distributed Data Interface(FDDI)• used as a backbone to connect LANs and computers

Working of FDDI• The possessor of the token is allowed to put a new token onto the ring as soon as it finished transmitting its frames.

Wrapping

Star Topology• Hybrid hub can accommodate several types of cable (Hybrid Star)• e.g. Ethernet 10BaseT• Active Hub(regenerates & require power) and Passive Hub (not req.)

Advantages & Disadvantages• Advantages:1. easier to modify or add new computers2. easy to troubleshoot3. robust4. use several types of cable

• Disadvantages:1. if the central hub fails, the whole network fails to

operate2. cabling cost

Asynchronous Transfer Mode(ATM)• newest topology, can carry voice & data over network wire or fiber• transmits all packets as 53-byte cells • Quality of Service (QoS)• extremely high-speed (25-622Mbps or 2.488Gbps)

Working of ATM• ATM communicates with cells rather than transmitting frames.

• Instead of specifying the source and destination addresses of the stations communicating, an ATM cell indicates the path the data will flow through.

• every station is always transmitting (empty cells)

Mesh Topology• most often used in large backbone networks in which failure of a single switch or router can result in a large portion of a network going down (expensive)

Intranet• a network that connects the computer and networks within an organization by using the hardware and software that is used on the Internet (TCP/IP protocol)

• secure & can have thousands of users

Intranet(HCL)

Intranet(Wipro)Interne

t

Extranet