Unit IWhat is DATA COMMUNICATION• When we communicate we share information• Sharing can be locally or on to a large distance• Ex. Telephony, Telegraph• Data means information that we want to communicate and is agreed upon by both parties.• Data Communication is defined as the exchange of data between two devices using some form of transmission medium. (Medium can be wired or wireless)

Unit IWhat is DATA COMMUNICATION• For data communication the devices must be a part of communication system.• Communication system consist of• Physical equipments (Hardware)• Programs to monitor communication (Software)

• Ex of Hardware are Transmitter and receiver• Ex of Software is a set of programs that governs

communication. Also called as Protocols

Unit IThe Effectiveness of Data Communication System depends upon four characteristics• Delivery• Accuracy• Timeliness• Jitter• These four parameters decides the efficiency of a data communication system.

Unit I• Delivery : It means that the data should be received by intended or correct device or user. The data must be delivered to the correct destination.• Accuracy: It means that the data should be delivered accurately. The data should not be altered during the transmission or it should not become unusable.• Timeliness: It means that data must be delivered in time. Data delivered late are unusable. This is specially required in audio and video data.

Unit IThe meaning of timely delivery means delivering data as they are produced and also in correct order as it is produced. The delay in data delivery should be minimum. This is called as real time transmission.• Jitter: Jitter refers to the variation in Packet (Small amount of data) arrival time. It is the uneven delay in the delivery of audio and video data.

Unit IComponents of a Data Communication System:

Unit IComponents of a Data Communication System:The data communication system consist of following five components• Message• Sender• Receiver• Transmission Media• Protocol

Unit IComponents of a Data Communication System:• Message: The message is the information (Data) that we want to communicate. The form of information can be Text, Audio, Video, Numbers, Pictures etc.• Sender: It is the device that is capable of transmitting the data. It can be Computer, Laptop, Workstation, Telephone etc.• Receiver: It is the device that is capable of receiving the data. . It can be Computer, Laptop, Workstation, Telephone etc.

Unit IComponents of a Data Communication System:• Transmission Media: It is the physical path using which data travels from sender to receiver. The transmission medium can be wired or wireless. Few examples are Coaxial Cable, Twisted Pair Cable, Radio Waves etc.• Protocol: It is nothing but a set of rules that governs the data communication between two devices. Protocol represents the agreement between the two devices for communication. Without protocol two devices might be connected but not communicating.

Unit IComponents of a Data Communication System:• Transmission Media: It is the physical path using which data travels from sender to receiver. The transmission medium can be wired or wireless. Few examples are Coaxial Cable, Twisted Pair Cable, Radio Waves etc.• Protocol: It is nothing but a set of rules that governs the data communication between two devices. Protocol represents the agreement between the two devices for communication. Without protocol two devices might be connected but not communicating.

Unit IData Flow: There are different ways using which the data flows between two systems. These ways represents the manner in which data can travel from one device to other device. The communication between two devices can be• Simplex• Half Duplex• Full Duplex

Figure Shows these three different ways

Unit IData Flow:

Unit IData Flow:• Simplex: In this mode of communication data can flow in only one direction. Any one of the two connected devices can transmit the data. The other device can only receive the data.

Examples of this mode of communication are Keyboard and Monitor. KB can only transmit data and monitor can only receive the data.

One of the important characteristic is that this mode utilizes the complete capacity of transmission medium for communication.

Unit IData Flow:• Half Duplex: In this mode of communication both the devices can transmit and receive the data. But at a time only one device is allowed to transmit the data.

When one device is transmitting other is receiving and Vice Versa.

Example is Walkie-Talkie Used by Police Persons.Here also the complete capacity of the communication medium is utilized for transmission.

Unit IData Flow:• Full Duplex: In this mode of communication both the devices can transmit and receive the data simultaneously (At the same time).

Here the capacity of communication medium is shared between two stations. This sharing can be using either separate paths or on the basis of time sharing.The example of this type of communication is telephone conversation where both the devices can transmit and receive data at the same time.

Unit INetworks:• A network is a set of more than one devices connected by communication pathways.• The devices connected in a network are also called as NODES.• The communication pathways which connects two nodes in a network are called as LINKS.• A node connected in a network can be a computer, printer, scanner etc.• Also it can be any other device capable of sending and receiving data.

Unit INetwork Criteria:• Any network whether small or large should fulfill certain network criteria • Performance• Reliability• Security

• Performance: The performance of a network can be measured in different ways. One way to measure the performance of a network is using• Transit Time • Response time

Unit INetwork Criteria:• Transit time is the time required for data to travel from one to other device. It should be as minimum as possible.• Response time is the time elapsed between an request and response. It also should be minimum.• The performance of the network also depends upon several factors as• Number of users in a network• Type of transmission media used• Capacity of the hardware used• Efficiency of the software

Unit INetwork Criteria:• All these factors affects the performance of the network in different extents.• Performance of the network is often evaluated with the help of• Throughput• Delay

• Often throughput should be more and delay should be minimum.• But it is observed that if throughput is increased

beyond certain limit the performance degrades.

Unit INetwork Criteria:• Reliability: Reliability of a network is measured using • Frequency of network failure• The time required to recover from failure• The robustness of network against unexpected events.

• Security: This is one of the important criteria for a network. A network should• Protect data from unauthorized access• Protect data from damage• Implement policies for data loss and recovery from

breaches.

Unit INetwork Attributes: (Physical Structures)• Two important network attributes are• Type of connection• Physical Topology

• Type of Connection: In a network we connect two or more devices using communication links.

A communication link is a pathway using which data travels from one to other node in a network.• Two types of connections are possible• Point to Point Link• Multipoint Link

Unit INetwork Attributes: (Physical Structures)• Point to Point Link: In this type of connection there exist a dedicated link between the devices. The entire capacity of the link is used by two connected devices only. Figure below shows point to point link

• The actual connection of the link can be wired or wireless.• The example is communication between TV remote and a TV

Unit INetwork Attributes: (Physical Structures)• Multipoint Link: This type of connection is also called as multi-drop connection. In this type the communication link is shared by more than two devices. All the devices connected to the link uses the same link for all communication. Figure below shows the diagram

Unit INetwork Attributes: (Physical Structures)• In this type of connection the capacity of the communication link is shared by connected devices by two ways• Spatially• Temporally

• In spatial sharing several devices uses the same link simultaneously• In temporal sharing the link is shared on the basis of time i.e. TimeSharing

Unit INetwork Attributes: (Physical Structures)• Physical Topology: This term refers to the way in which the networks are laid down physically. Topology of a network shows the physical arrangement of the nodes in a network. It also shows geometric representation of the relationship between communication links and the nodes that connects to the links. There are four basic topologies

• Mesh• Star• Bus • Ring

Unit INetwork Attributes: (Physical Structures)• Physical Topology: This term refers to the way in which the networks are laid down physically. Topology of a network shows the physical arrangement of the nodes in a network. It also shows geometric representation of the relationship between communication links and the nodes that connects to the links. There are four basic topologies

• Mesh• Star• Bus • Ring

Unit INetwork Attributes: (Physical Structures)• Mesh Topology: In this type of topology there is a dedicated point to point link between all the devices in a network. Every device is connected to every other device in a network using a separate link.• The meaning of dedicated link means that link carries the traffic between only two devices connected to that link.• In order to find the number of links required in a mesh topology following formula is used

No of Links = n(n-1)/2; Where n= No of Nodes

Unit INetwork Attributes: (Physical Structures)• Mesh Topology: In this type of topology there is a dedicated point to point link between all the devices in a network. Every device is connected to every other device in a network using a separate link.• The meaning of dedicated link means that link carries the traffic between only two devices connected to that link.• In order to find the number of links required in a mesh topology following formula is used

No of Links = n(n-1)/2; Where n= No of Nodes

Unit INetwork Attributes: (Physical Structures)• Also in mesh topology each system requires I/O ports to connect to other devices in a network.• The formula for number of I/O ports required in a mesh topology is

No of I/O Ports = n-1 ; Where n= No of NodesFigure below shows diagram for mesh topology

Unit INetwork Attributes: (Physical Structures)• Advantages of Mesh Topology:• Because of dedicated links each link carries its own data load thus eliminating the traffic problems.• Mesh topology is robust. If one link fails it does not affect remaining links in the network.• There is privacy and security in mesh topology because of dedicated links.• Because of point to point link fault identification and isolation is easy.

Unit INetwork Attributes: (Physical Structures)• Disadvantages of Mesh Topology:• Since each device requires a dedicated link to connect to other devices in a network more number of cables and I/O ports are required.• More amount of space is required because of more number of cables.• Because of more number of I/O ports it can be expensive.

• Because of above reasons mesh topology is implemented in limited fashion as a backbone of several computers connected in a hybrid topology.

Unit INetwork Attributes: (Physical Structures)• A good example of Mesh topology is the connection between regional offices of a Telephone Exchange.

Unit INetwork Attributes: (Physical Structures)• Star Topology: In star topology devices in a network are not directly connected to each other.• Each device in a network is connected to a central controller, usually called as HUB.• All the traffic in a network goes through the central controller.• The central controller relays the traffic between all devices in a network.• The link between each device and central controller is a dedicated link.

Unit INetwork Attributes: (Physical Structures)• Figure below shows the diagram for Star topology

• As shown in figure each device connects to the central controller using dedicated point to point link and carries all the traffic between device and central controller.

Unit INetwork Attributes: (Physical Structures)• Advantages of Star Topology: • It is less expensive than mesh topology because of less number of cables and I/O ports.• It is easy to install and reconfigure.• It is robust because if one link fails it does not affects the performance of other links.• Because of point to point links fault identification and isolation is also easy.

Unit INetwork Attributes: (Physical Structures)• Disadvantages of Star Topology: • One of the biggest drawback of star topology is the dependence on central controller. If the central controller fails then entire network is affected.• Also it requires more amount of cabling compared to some other topologies.

• Star topology is popularly used to connect number of computers in a Local Area Network (LAN).

Unit INetwork Attributes: (Physical Structures)• Bus Topology: Bus topology is a example of Multipoint Connection.• In bus topology one long cable acts as a backbone of all the devices in a network.• Figure below shows bus topology

Unit INetwork Attributes: (Physical Structures)• The nodes are connected to the bus cable by drop lines and taps.• Drop line is a cable that connects device with the central bus cable and a tap is a connector used to connect drop line with bus cable.• One of the important aspect of bus topology is the number of devices that can be connected to the bus and the distance between the devices.• This is because as the signal travels along the central cable it becomes weaker and weaker and therefore there is limitation on number of devices and the distance between the taps.

Unit INetwork Attributes: (Physical Structures)•

Unit INetwork Models:• Computer network is collection of heterogeneous entities.• Heterogeneous means the devices that are connected in a network are of different i.e. Computers, Laptops, Mobiles, Printers, Scanners, Hubs, Routers etc. They are also different in nature.• In order to establish communication between these heterogeneous entities we require some common STANDARD, using which they can communicate with each other.

Unit INetwork Models:• The two best known standards in computer networks are• ISO OSI Reference Model• Internet Model (TCP/IP Model)

Unit ICategories of Network:• There are different ways using which we can categories computer networks.• One of the important parameter using which networks are categorized is the distance covered by a network for communication. (Size of the Network)• Based on this parameter networks are classified as• Local Area Network (LAN)• Wide Area Network (WAN)• Metropolitan Area Network (MAN)

Unit ICategories of Network:• Local Area Network (LAN): A local area network is a network that covers a limited distance up to 2 Kilometers.• A LAN usually is privately owned and is used to connect the devices in single office, building or campus.• Depending upon the requirement of and the type of technology used, a LAN can be as simple as connection between two computers in home or it can extend in the premise of a organization.

Unit ICategories of Network:• Figure below shows diagram for LAN

Unit ICategories of Network:• Typically LAN’s are designed to share the resources among the computers or workstations.• The resource that is shared can be Hardware such as a printer, it can be software such as application program or it simply can be data.• In addition to the size, LAN’s are distinguished from other networks on the basis of• Transmission medium• Topology

Unit ICategories of Network:• In general LAN uses same type of transmission medium such as wire cables.• LAN’s are having regular topology. Most common type of topologies are STAR, BUS, RING.• The speed of early LAN’s was limited to 4 to 16 MBPS.• Today LAN’s can operate at a speed up to 100- 1000 MBPS (1 GBPS).• The new trend is of wireless LAN’s where the transmission medium is wireless.

Unit ICategories of Network:• Wide Area Network (WAN): A Wide area network is a large network and is used to connect the devices which are separated by a large distance.• A WAN allows transmission of data such as image, audio, video, text over large geographic areas that may cover a country, continent or even whole world.• A WAN can be as complex as a backbone that connects to the Internet or it can be as simple as a home computer that connects to the Internet using dial up line.

Unit ICategories of Network:• Figure below shows a WAN

Unit ICategories of Network:• As shown in figure a WAN can be• Switched WAN• Point to Point WAN

• A switched WAN is used to connect a end system to the network with the help of a networking device called as Router.• In point to point WAN a Home computer is

connected to the ISP (Internet Service Provider) with the help of lease line (Dedicated) and a MODEM.• A Point to point WAN is often used to provide

Internet Access.

Unit ICategories of Network:• Metropolitan Area Network: A MAN is the intermediate network between LAN and WAN.• The size of the MAN is in between LAN and WAN.• A MAN is designed to cover entire city or town.• It is usually used by the customers which require high speed internet connectivity and the end points of connectivity are spread across the city.• Good examples of MAN are telephone company network that provides connectivity using DSL and cable TV network which now a days provides internet using the same cable.

Unit IInterconnection of Networks: Internetwork• Today it is difficult to identify a LAN, WAN, MAN separately.• All three networks are connected with each other.• When two or more networks are connected with each other it becomes an internetwork.• Figure shows a heterogeneous network made of four WAN and two LAN.

Unit IInterconnection of Networks: Internetwork•

Unit ITHE INTERNET:• The Internet is a organized and structured system.• It has brought wealth of information to our finger tips.• In our day today life we use Internet for different purposes i.e. Sending and Receiving E mail, browsing the information, paying our bills etc.•

Unit ILayered Tasks:• In order to simplify the task of communication between heterogeneous systems, the task of communicating the data is divided into different subtasks. (Layers)• The entity carrying out these subtasks are called as Layers.• Each layer is a combination of some hardware components and a software program.• Each layer is designed to perform certain specific tasks.

Unit ILayered Tasks:• For Ex.

Unit ILayered Tasks:• The network models that are used in computer networks uses layered architecture.• It means that each model consist of several layers that carries specific task or function.• Each layer also provides certain services(Functions) to the layer above it.

Unit IThe OSI MODEL:• Established in 1947 International Standard Organization designs standards for different purposes.• The ISO standard that covers all aspects of data communication is the Open System Interconnection model.• It was introduced in 1970.• An open system is a set of protocols that allows any two systems to communicate with each other regardless of their underlying architecture.

Unit IThe OSI MODEL:• The purpose of OSI is to show how we can allow two systems to communicate with each other without changing the logic of their underlying hardware and software configuration. • The OSI model is not a PROTOCOL, it allows us to understand and design a network model that is flexible, robust and interoperable.• The OSI is a layered framework that allows design of network systems for the communication between any type of systems.

Unit IThe OSI MODEL:• The OSI model consist of SEVEN separate but interrelated layers. Each layer performs a part of process of communicating the data from one system to other.• The Seven layers are• Application• Presentation• Session• Transport• Network•Data Link• Physical

Unit IThe OSI MODEL:• Layered Architecture and Peer to Peer Processes: The Interaction between layers• The OSI model consist of seven ordered layers.• Figure shows a diagram when a message is sent from device A to device B.• While the message travels from device A to device B it passes through many intermediate nodes.• These intermediate nodes usually involves only first three layer of OSI model.

Unit IThe OSI MODEL:•

Unit IThe OSI MODEL:• While designing the OSI model the designers have identified the correlated networking functions and they are grouped into a single layer.• Each layer defines several functions which are different from functions of other layers.• Because of this the architecture has become flexible.• On a single machine each layer uses or calls services from the layer below it.• Between two systems a layer n communicates with layer n on other machine.

Unit IThe OSI MODEL:• The communication between two layers is governed by a set of rules which are agreed upon between them and are called as PROTOCOLS.• The process on each machine in a specific layer communicates with a process on another machine in the same layer. Therefore they are called as peer to peer processes.• The communication between systems is therefore peer to peer communication using a protocol suitable for that layer.

Unit IThe OSI MODEL:•

Unit IThe OSI MODEL:• as shown in figure the data from one machine propagates through 7 layers from top to bottom.• Then it travels through the transmission medium to other machine.• At the destination machine the data travels from bottom layer to top layer and then it is handed over to the user.• Each layer is going to add a header (H7, H6, H5) to the data as it passes vertically through them on same machine.

Unit IThe OSI MODEL:• At data link layer only a header as well as a trailer (T2) is added to the data.• This additional information i.e. Header and Trailer added by each layer on sending machine is for its corresponding layer on destination machine.• This information tells the destination layer what processing it is supposed to do on the data before handing it over to the user.• When data and this additional reaches to the bottom most layer it is converted into electromagnetic signals and transmitted through medium.

Unit IThe OSI MODEL:• Upon reaching at the destination the data is received by bottom most layer and then passes through the upper layers.• At each layer the Header and Trailer is removed by respective layer and finally data is handed over to the user.

Unit IFunctions of the Layers of OSI Model:• There are seven layers of OSI model as• Physical • Data Link• Network• Transport• Session• Presentation• Application

Unit IFunctions of the Layers of OSI Model:• Physical Layer:• The physical layer coordinates the functions that are required for the movement of bit stream from one node to other.• It deals with mechanical and electrical specifications of interface and transmission medium.• It also defines the procedures and functions of devices required for transmission.• Figure shows the position of physical layer

Unit IFunctions of the Layers of OSI Model:• Physical Layer:

• Physical layer also deals with• Physical characteristics of interface and medium• Representation of bits using certain encoding techniques.

Unit IFunctions of the Layers of OSI Model:• Physical Layer:• The data rate of the data to be transmitted is also decided by physical layer. It defines the duration of bits.• It establishes the synchronization of bits between sender and receiver.• It looks after the line configuration.• It looks after physical topology of the network. • It looks after the transmission mode.

Unit IFunctions of the Layers of OSI Model:• Data Link Layer: • It is the job of data link layer to convert raw transmission facility at physical layer into a reliable link.• It represents physical layer in an error free manner to the network layer.

Unit IFunctions of the Layers of OSI Model:• Data Link Layer: • The data link layer is responsible for moving the data frames from one node to other.• Other responsibilities of data link layer are• It divides the packets received from network layer into data frames.• It looks after physical addressing of the frames.• It manages the flow control between two devices connected to the link.• It looks after the error control by detecting lost or damaged frames.• It provides the access control mechanism when the common medium is shared between more than one devices.

Unit IFunctions of the Layers of OSI Model:• Data Link Layer:

Unit IFunctions of the Layers of OSI Model:• Data Link Layer:

Unit IFunctions of the Layers of OSI Model:• Network Layer: • The network layer is responsible for source to destination delivery of a packet, across multiple links.• When two devices are connected to the same link, usually network layer is not required. However when there are multiple links between the source and destination network layer is required for the delivery of a packet.•

Unit IFunctions of the Layers of OSI Model:• Network Layer:

Unit IFunctions of the Layers of OSI Model:• Network Layer: • The responsibilities of network layer are• It looks after the logical addressing of the packet. Data link layer take care of physical addressing, but network layer delivers a packet across network using logical address (IP Address).• When the source and destination are separated using multiple links between them there exists multiple paths from source to destination. In order to deliver a packet to the destination using shortest path network layer performs routing of packets.

Unit IFunctions of the Layers of OSI Model:• Network Layer: •

Unit IFunctions of the Layers of OSI Model:• Transport Layer: • Transport layer is responsible for process to process delivery of the entire message from source to destination.• While network layer looks after delivery of individual packets, transport layer ensures that the entire message is delivered to the destination correctly.• Transport layer sees that the entire message arrives at the destination intact and in order. It also performs error control and flow control for entire message.

Unit IFunctions of the Layers of OSI Model:• Transport Layer: •

Unit IFunctions of the Layers of OSI Model:• Transport Layer: • Following are the other responsibilities of transport layer• In a computer at a time multiple programs are running and each program is running at different memory address. Network layer delivers the packet at correct computer. The transport layer delivers the message to the correct process. This is called as service point addressing.• It looks after the segmentation and reassembling of message at the destination.• It performs connection control i.e. connection oriented or connectionless.

Unit IFunctions of the Layers of OSI Model:• Transport Layer: • It performs end to end flow control.• Transport layer is also responsible for error control. It performs error control for process to process delivery. The error control is usually achieved by retransmission.• Figure shows reliable process to process delivery

Unit IFunctions of the Layers of OSI Model:• Session Layer: The functions provided by first three layers are not sufficient for certain applications. For such applications session layer acts as a network dialog controller and also establishes the synchronization. • Following are the specific responsibilities of session layer• It allows two systems to enter into a dialog using the appropriate transmission mode (Half duplex, Full Duplex)• It allows process to insert checkpoints in a stream of data for synchronization purpose.

Unit IFunctions of the Layers of OSI Model:•

Unit IFunctions of the Layers of OSI Model:• Presentation Layer: It deals with the syntax and semantics of the information that is exchanged between two systems.• Specific responsibilities of presentation layer are• The information exchanged by systems is in different encoding formats. The presentation layer is responsible for interoperability between these different encoding formats.• The presentation layer at the sender changes the format of sender specific data into common format and at the receiver it is converted back into receiver specific data format.

Unit IFunctions of the Layers of OSI Model:• Presentation Layer:• It performs the encryption and decryption of data for providing the privacy.• For Audio and video data which is of large size, it performs compression and decompression to utilize the bandwidth properly.

Unit IFunctions of the Layers of OSI Model:• Presentation Layer:•

Unit IFunctions of the Layers of OSI Model:• Presentation Layer:

Unit IFunctions of the Layers of OSI Model:• Application Layer: The application layer enables the user (Human or Software) to access the network.• It provides different user interfaces to access the services like E Mail, remote file access and transfer etc.• Specific functions handled by Application layer are• It allows a user to log into a remote terminal using virtual terminal facility.• It allows user to access and manage remote files located on other system.• It Provides mail services.• It also provides directory services.

Unit IFunctions of the Layers of OSI Model:•

Unit IFunctions of the Layers of OSI Model:• Summery:

Unit ITCP/IP Protocol Suite:• The TCP/IP protocol suite was developed prior to ISO OSI model.• Therefore the layers of two models do not match exactly.• In original TCP/IP model there are four layers• Host to Network• Internet• Transport• Application

Unit ITCP/IP Protocol Suite:• When TCP/IP is compared with ISO OSI model the Physical and data link layer of OSI are similar to Host To Network Layer of TCP/IP.• The network layer is similar to internet layer• The transport layer is doing the part of the duties of session layer.• Finally the application layer of TCP/IP model performs the functions of Application Presentation and session layers of ISO OSI model.• Therefore here onwards we will assume that TCP/IP contains five layers instead of four.

Unit ITCP/IP Protocol Suite:•

Unit ITCP/IP Protocol Suite:• TCP/IP is a hierarchical model containing interactive modules; each performing a specific functionality.• The protocols in the higher layers are supported by protocols in the bottom layers. • The protocols in the layers of TCP/IP are relatively independent. These protocols can be mixed and matched depending upon the requirement of the system.

Unit ITCP/IP Protocol Suite:• Functions of the Layers:• Host to Network Layer (Physical and Data Link): At this layer TCP/IP does not specify any specific protocol. It supports all the standard and proprietary protocols.• Internet Layer(Network layer): This layer is more commonly called as internetwork layer. At this layer it uses internetworking protocol IP in addition to the four supporting protocols ARP, RARP, ICMP, and IGMP

Unit ITCP/IP Protocol Suite:• Functions of the Layers:• Internetworking Protocol (IP): IP is an unreliable connectionless protocol which tries to give best effort delivery service. The meaning of best effort is that, IP will try to deliver a packet to the destination by considering the unreliability of the underlying layers with no guarantee. It transports packets called as datagram and each datagram is treated separately. IP has no mechanism to track the lost packets, packets that arrives out of sequence. The datagram of same message can arrive at the destination using different routes. Also IP does not keep the track of routes.

Unit ITCP/IP Protocol Suite:• Functions of the Layers:• Internetworking Protocol (IP): IP is an unreliable connectionless protocol which tries to give best effort delivery service. The meaning of best effort is that, IP will try to deliver a packet to the destination by considering the unreliability of the underlying layers with no guarantee. It transports packets called as datagram and each datagram is treated separately. IP has no mechanism to track the lost packets, packets that arrives out of sequence. The datagram of same message can arrive at the destination using different routes. Also IP does not keep the track of routes.