Unit-1:�Introduction to Computer Networks & Internet�

Computer Networks (CN)

GTU #3150710

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Looping

Outline

• What is Computer Network?
• Advantages of Computer Network
• Applications of Computer Network
• Type of Computer Network
• What is Internet?
• The Network Edge & The Network Core
• Transmission Media
• Network Topologies
• Protocol Layers
• Delay, Loss & Throughput

What is Computer Network?

• Computer Network is a system in which multiple computers are connected to each other to share information and resources.

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Wireless

Wired

Network

Devices

Computers

Advantages of Computer Network

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Better Communication

File Sharing

Entertainment

Flexible Access

Advantages of Computer Network

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Inexpensive System

Instant and Multiple Access

Internet Access

Resource Sharing

Applications of Computer Network

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& Many More….

Business & Finance

Email Services

File & Directory Services

Teleconferencing

Types of Computer Network

• Computer networks can be categories by their size as well as their purpose.
• The size of a network can be expressed by the geographic area.
• Some of the different networks based on size are:

Local Area Network

• A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building.

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Metropolitan Area Network

• A metropolitan area network (MAN) is a computer network that interconnects with computer in a metropolitan area like city.
• MAN is a larger than LAN but smaller than the area covered by a WAN.
• It is also used to interconnection of several local area network.

Kudasan

Pethapur

Mansa

Gandhinagar

Wide Area Network

• A wide area network (WAN) is a computer network that exists over a large-scale geographical area.
• A WAN connects different networks, including local area networks (LAN) and metropolitan area networks (MAN).
• It may be located with in a state or a country or it may be interconnected around the world.

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Asia

Africa

America

Types of Computer Networks - Summary

Types of Computer Networks - Summary

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What is Internet?

• The internet is a type of world-wide computer network.
• The internet is the collection of infinite numbers of connected computers that are spread across the world.

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Network Components

What is Protocol?

• Human Protocol(Language)
• “what’s the time?”
• “I have a question”
• Introduction Talk

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• Network Protocol
• Set of rules
• Machines rather than humans.
• All communication activity in Internet governed by protocols.

Protocol is define format, order of message that sent and received among network entities, and actions taken on message transmission and reception.

The Network Edge

• Computers and other devices are connected at the edge (end) of the network.
• These computers are known as hosts or end systems. Router is known as edge router.

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Peer to Peer Network

• Computers are connected together so that users can share resources and information.

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• There is no central server for authenticating users, each of them works as both client and server.
• e.g. Bit Torrent

Client – Server Network

• Client: Request servers for a task.
• Generally called desktop PCs or workstations.
• Server: Receive requests from the clients. Process and response them.
• e.g. Web Server, Email Server

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The Network Core

• Defines the connection of different network segments together and process to transmit data packets across the network.
• It is implemented through the use of switching techniques.

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Switched

Networks

Packet-Switched

Networks

Circuit-Switched

Networks

Circuit Switched Network

• A dedicated channel has to be established before the call is made between users.
• The channel is reserved between the users till the connection is active.
• For half duplex(one way) communication, one channel is allocated and for full duplex(two way) communication, two channels are allocated.
• It is mainly used for voice communication requiring real time services without delay.

Circuit Switched Network – Cont…

• Communication via circuit switching involves three phases:
1. Circuit Establishment
2. Data Transfer
3. Circuit Disconnect

Packet Switched Network

• It is not required to establish the connection initially.
• The connection/channel is available to use by users. But when traffic or number of users increases then it will lead to congestion in the network.
• Packet switched networks are mainly used for data and voice applications requiring non-real time scenarios.

Differences

TRANSMISSION MEDIA

Transmission Media

• A transmission media can be defined as any medium that can carry information from a source to a destination.

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Guided Media

• Guided media are those that provide a wired - channel from one device to another.
• Three Guided media commonly used for data transmission are:

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Twisted Pair Cable

Coaxial Cable

Fiber Optic Cable

Twisted Pair Cable

• Separately insulated
• Twisted together
• It is widely used in different kinds of data and voice infrastructure.
• The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction.
• Two types of twisted pair cable:

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UTP

(Unshielded Twisted Pair)

STP

(Shielded Twisted Pair)

Twisted Pair Cable – Cont…

• UTP(Unshielded Twisted Pair)
• Ordinary telephone wires
• Less expensive
• Weak immunity against noise & interferences
• Most used in two categories: Cat-3 & Cat-5
• Used in laboratory
• STP(Shielded Twisted Pair)
• An extra metallic shield on each pair
• Relatively more expensive
• Better performance than UTP
• Used in exterior network(outside of building).

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Coaxial Cable

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• Outer conductor is braided shield.
• Inner conductor is solid metal.
• Separated by insulating material, and whole cover by plastic cover.
• Used in television, long distance telephone transmission.
• High bandwidth and excellent noise immunity.

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Outer conductor (shield)

Insulator

Inner Conductor

Plastic cover

Fiber Optic Cable

• A fiber-optic cable is made of glass or plastic and transmits signals in the form of light.
• Light travels in a straight line as long as it is moving through a single uniform substance.
• It is surrounded by a cladding of less dense glass or plastic so, difference in density of the two materials must be such that a beam of light moving through the core is reflected off the cladding instead of being refracted into it.
• It use reflection to guide light through a channel.
• Small size & Weight
• Used in high bandwidth network
• High data rate & lower attenuation

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Unguided Media

• Unguided media transmit electromagnetic waves without using a physical conductor.
• This type of communication is often referred to as wireless communication.
1. Radio wave
2. Microwave
3. Infrared Wave

Radio wave

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• Highly regulated
• Omni directional antennas
• Penetrate through walls
• Frequency Range:3KHz – 1GHz.
• It used for multicast communications, AM and FM radios and cordless phones use Radio waves for transmission. 
• Categorized as (i) Terrestrial and (ii) Satellite. 

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Microwave

• Use directional antennas - point to point line of sight communications.
• Microwave communication.
• Used for unicast communication such as cellular telephones, satellite networks.
• Higher frequency ranges cannot efficiently penetrate walls.
• Frequency Range: 1GHz – 300GHz.

Infrared wave

• Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation
• Used on televisions, VCRs, and stereos all use infrared communication.
• Relatively directional
• Cheap, easy to build but they do not pass through solid objects

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NETWORK TOPOLOGIES

Network Topologies

• Network topology is the arrangement of the various components (links, nodes, etc.) of a computer network.
• Types of network topologies :
1. Bus
2. Ring
3. Star
4. Mesh
5. Tree
6. Hybrid

Bus Topology

• Every computer and network device is connected to single cable
• It transmits data only in one direction.
• Cost effective
• Used in small networks
• Easy to expand joining two cables together
• It is used in early LAN connection

Ring Topology

• It forms a ring as each computer is connected to another computer, with the last one connected to the first.
• Transmission is unidirectional & sequential way that is bit by bit.
• Transmitting network is not affected by high traffic or by adding more nodes, as only the nodes having tokens can transmit data.
• Cheap to install and expand.

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Star Topology

• Computers are connected to a single central hub through a cable.
• Fast performance with few nodes and low network traffic.
• Easy to troubleshoot & Easy to setup and modify.
• Only that node is affected which has failed rest of the nodes can work smoothly.
• Hub can be upgraded easily.

Mesh Topology

• Point-to-point connection to other devices or fully connected.
• Traffic is carried only between two connected devices.
• Robust, costly but not flexible.
• Fault is diagnosed easily.
• More cable resource used in setup.

Tree Topology

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• It has a root node and all other nodes are connected to it forming a hierarchy.
• Also called hierarchical topology.
• Mostly used in Wide Area Network – WAN.
• Expansion of nodes is possible and easy.
• Easily managed and maintained.

Hybrid Topology

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• A network structure whose design contains more than one topology is said to be hybrid topology.
• It is a combination of two or more topologies.
• Flexible & reliable as error detection and easy to troubleshoot.
• Scalable as size can be increased easily.

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Comparison of Topologies

PROTOCOL LAYERS

Protocols Layers

• To deals with connecting systems that are open for communication with other systems.
• OSI Layer Model (Open Systems Interconnection)
• Developed by the International Standards Organization (ISO) with seven different layers.
• Physical Layer
• Data Link Layer
• Network Layer
• Transport Layer
• Session Layer
• Presentation Layer
• Application Layer

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Example – Air Plane Travel

ticket (purchase)

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baggage (check)

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gates (load)

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runway takeoff

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airplane routing

ticket (complain)

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baggage (claim)

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gates (unload)

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runway landing

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airplane routing

airplane routing

Departure

Arrival

How OSI Layer Works?

Physical Layer

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• The physical layer is responsible for movements of individual bits from one hop (node) to the next.

Physical Layer – Cont…

• Carries the bit stream over a physical media.
• Physical Layer is concerned with:
• Interface and Medium like guided cables
• Representation of bits
• Data rate
• Synchronization of bits
• Line configuration
• Physical topology
• Transmission mode

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Data Link Layer

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• The data link layer is responsible for moving frames from one hop (node) to the next.

Data Link Layer – Cont…

• Data link layer is concerned with:
• Framing – divide bits stream into data unit (frame)
• Physical addressing
• Flow control – avoid over overwhelming
• Error control – bit loses, retransmission
• Access control

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Network Layer

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• The network layer is responsible for the delivery of individual packets from the source host to the destination host.

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Network Layer – Cont…

• In this layer, packet is combined with header and data.
• In case of data link layer, packet delivers on the same network.
• If two different networks are connected then packet is concern with network layer.
• Network layer is concerned with:
• Logical addressing e.g. 192.168.1.1 (IP Address)
• Routing

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Transport Layer

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• The transport layer is responsible for the delivery of a message from one process to another.

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Transport Layer – Cont…

• This layer ensures that the whole message arrives intact and in order.
• Transport layer is concerned with:
• Service-point addressing (port address)
• Segmentation and Reassembly
• Connection Control
• Flow and Error Control

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Session Layer

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• The session layer is responsible for dialog control and synchronization.

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Session Layer – Cont…

• This layer is network dialog controller – establishes, maintains, synchronizes the interaction among computers.
• Session layer is concerned with:
• Dialog control
• Synchronization

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Presentation Layer

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• The presentation layer is responsible for translation, compression, and encryption.

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Presentation Layer – Cont…

• This layer is concerned with the syntax which refers to order in which data is presented and semantics helps in interpreting a particular pattern.
• Presentation layer is responsible for:
• Translation
• Encryption
• Compression

Application Layer

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• The application layer is responsible for providing services to the user.

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Application Layer – Cont…

• This layer provides various services like:
• Network virtual terminal
• File transfer, access and management
• Mail services
• Directory services

Summary – OSI Layer

Application

Presentation

Session

Transport

Network

Data link

Physical

To allow access to network resource

To translate, encrypt and compress data

To provide reliable process-to-process message delivery and error recovery

To establish, manage and terminate sessions

To move packets from source to destination; To provide internetworking

To transmit bits over a medium; To provide mechanical & electrical specification

To organize bits into frames; To provide hop-to-hop delivery

TCP/IP Reference Model �(Transmission Control Protocol/Internet Protocol)

• It was originally defined as having five layers:
• TCP/IP is a set of protocols developed to allow cooperating computers to share resources across the network.
1. Application Layer
2. Transport Layer
3. Network Layer
4. Data Link Layer
5. Physical Network

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TCP/IP Model Architecture

Comparison

Difference - OSI Model and TCP/IP Protocol Layers

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OSI Model

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TCP/IP Protocol Layer

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Majors between OSI Model and TCP/IP Protocol Layers

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OSI Model

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TCP/IP Protocol Layer

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Protocol Layers: Summary

Delay, Loss & Throughput

• Delay
• As a packet travels from one node (host or router) to the subsequent node (host or router) along this path, the packet suffers from several types of delays at each node along the path.

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Where

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Delay – Cont…

• Processing Delay (d_proc)
• The time required to examine the packets header and determine where to direct the packet.
• To check bit level error
• Determine output link
• Delay in terms of microseconds

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Delay – Cont…

• Queuing Delay (d_queue)
• A time to wait at output link for transmission.
• Depends on congestion level of router.
• If queue is empty, then delay will be zero.
• If queue is full (heavy traffic) then delay will be long.
• Delay in terms of microsecond to millisecond.

Delay – Cont…

• Transmission Delay (d_tran = L/R)
• An amount of time required for the router to transmit the packet.
• It is depending on packet length(L) and transmission rate(R) of link.

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Delay – Cont…

• Propagation Delay (d_prop= d/s)
• A time required to propagate from the beginning of the link to router B.
• Depends on the length of physical medium(d) link and propagation speed(s) of link
• Delay in terms of millisecond.

Sum

• In this problem, we consider sending real-time voice from Host A to Host B over a packet-switched network (VoIP).
• Host A converts analog voice to a digital 64 kbps bit stream on the fly.
• Host A then groups the bits into 56-byte packets.
• There is one link between Hosts A and B; its transmission rate is 2 Mbps and its propagation delay is 10 msec.
• As soon as Host A gathers a packet, it sends it to Host B. As soon as Host B receives an entire packet, it converts the packet’s bits to an analog signal.
• How much time elapses from the time a bit is created (from the original analog signal at Host A) until the bit is decoded (as part of the analog signal at Host B)?

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Solution

• Since this is a packet switched network, the data will be transmitted packet by packet. A packet is 56 byte and the analog to digital conversation rate is 64 kbps.
• Thus the preparing time Tp for a packet is (56*8)/(64*1000)= 0.007 s = 7 ms.
• The transition time Dtrans for a packet is (56*8)/(2*1000*1000) =0.000224 s = 0.224ms. Tprop = 10ms
• Finally, the total time elapses from the time a bit is create until the bit is decoded is Tp+Dtrans+Tprop= 7+0.224+10 = 17.224 ms

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Packet Loss

• Packet loss is the failure of one or more transmitted packets to arrive at their destination.
• The loss of data packets depends on the switch queue/buffer. The loss of data packets increases with the increases in the traffic intensity.
• It affects the performance

of the network.

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Throughput

• Throughput or Network Throughput is the rate of successful message delivery over a communication channel.
• Throughput is measured in bits(data) per second (bit/s or bps)

server, with

file of F bits

send to client

link capacity

R_s bits/sec

link capacity

R_c bits/sec

Client

History of Computer Networks

• 1961-1972 : The development of Packet Switching
• 1972-1980 : Proprietary Network and Internetworking
• 1980-1990 : A Proliferation of Networks
• 1990s : The Internet Explosion
• Recent Developments…

Outline - Revised

• What is Computer Network? Connected each other
• Advantages of Computer Network
• Applications of Computer Network
• Type of Computer Network LAN, MAN, WAN
• What is Internet? Infinite nos. of connected computers across the world
• What is Protocol? Set of Rules
• The Network Edge Host-end system & edge router
• The Network Core Circuit Switched & Packet Switched
• Transmission Media Guided- Wired & Unguided-Wireless
• Network Topologies Bus, Ring, Star, Mesh, Tree, & Hybrid
• Protocol Layers OSI Layer & TCP/IP Layer
• Delay, Loss & Throughput

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