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COMPUTER NETWORKS
UNIT I:
Introduction: Network Types, LAN, MAN, WAN, Network Topologies Reference models - The OSI Reference Model- the TCP/IP Reference Model - A Comparison of the OSI and TCP/IP Reference Models, OSI Vs TCP/IP, Lack of OSI models success, Internet History. Physical Layer – Introduction to Guided Media- Twisted-pair cable, Coaxial cable and Fiber optic cable and unguided media: Wireless-Radio waves, microwaves, infrared.
NETWORK: Network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network.“Computer network’’ to mean a collection of autonomous computers interconnected by a single technology. Two computers are said to be interconnected if they are able to exchange information.The connection need not be via a copper wire; fiber optics, microwaves, infrared, and communication satellites can also be used.
USES OF COMPUTER NETWORKS
1. Business Applications to distribute information throughout the company ( resource sharing). sharing physical resources such as printers, and tape backup systems, is sharing information client-server model. It is widely used and forms the basis of much network usage. communication medium among employees. email ( electronic mail ), which employees generally use for a great deal of daily communication. Telephone calls between employees may be carried by the computer network instead of by the phone company. This technology is called IP telephony or Voice over IP ( VoIP ) when Internet technology is used. Desktop sharing lets remote workers see and interact with a graphical computer screen doing business electronically, especially with customers and suppliers. This new model is called e-commerce ( electronic commerce ) and it has grown rapidly in recent years. 2.Home Applications
peer-to-peer communication person-to-person communication electronic commerce entertainment.(game playing,)
3.Mobile Users Text messaging or texting Smart phones, GPS (Global Positioning System) m-commerce NFC (Near Field Communication) 4.Social Issues
With the good comes the bad, as this new-found freedom brings with it many unsolved social, political, and ethical issues. Network Definition – A group of computers which are connected to each other and follow similar usage protocols for the purpose of sharing information and having communications provided by the networking nodes is called a Computer Network. A network may be small where it may include just one system or maybe as large as what one may want. The nodes may further be classified into various types. These include:
- Personal Computers
- Servers
- Networking Hardware
- General Hosts Networking can be classified into three types:
- Types of Computer Networks
- Topology
- Interpreters
All are in detail further below 1.Types of Computer Networks There are five main types of Computer Networks: 1.LAN (Local Area Network) – Systems connected in a small network like in a building or a small office It is inexpensive It uses Ethernet or Token-ring technology Two or more personal computers can be connected through wires or cables acting as nodes Transfer of data is fast and is highly score 2.PAN (Personal Area Network) –
- Tree Topology – In this type of topology nodes are connected in the form of a tree. The function of the central node in this topology may be distributed
- Line Topology – in this topology all the nodes are connected in a straight line
- Hybrid Topology – When two more types of topologies combine together, they form a Hybrid topology
1.Bus Topology
- The bus topology is designed in such a way that all the stations are connected through a single cable known as a backbone cable.
- Each node is either connected to the backbone cable by drop cable or directly connected to the backbone cable.
- When a node wants to send a message over the network, it puts a message over the network. All the stations available in the network will receive the message whether it has been addressed or not.
- The bus topology is mainly used in 802.3 (ethernet) and 802.4 standard networks.
- The configuration of a bus topology is quite simpler as compared to other topologies.
- The backbone cable is considered as a "single lane" through which the message is broadcast to all the stations. Advantages of Bus topology:
- Low-cost cable: In bus topology, nodes are directly connected to the cable without
passing through a hub. Therefore, the initial cost of installation is low.
- Moderate data speeds: Coaxial or twisted pair cables are mainly used in bus-based networks that support upto 10 Mbps.
- Familiar technology: Bus topology is a familiar technology as the installation and troubleshooting techniques are well known, and hardware components are easily available.
- Limited failure: A failure in one node will not have any effect on other nodes. Disadvantages of Bus topology :
- Extensive cabling: A bus topology is quite simpler, but still it requires a lot of cabling.
- Difficult troubleshooting: It requires specialized test equipment to determine the cable faults. If any fault occurs in the cable, then it would disrupt the communication for all the nodes.
- Signal interference: If two nodes send the messages simultaneously, then the signals of both the nodes collide with each other.
- Reconfiguration difficult: Adding new devices to the network would slow down the network.
- Attenuation: Attenuation is a loss of signal leads to communication issues. Repeaters are used to regenerate the signal.
2.Ring Topology:
- Ring topology is like a bus topology, but with connected ends.
- The node that receives the message from the previous computer will retransmit to the next node.
- The data flows in one direction, i.e., it is unidirectional.
- The data flows in a single loop continuously known as an endless loop.
- It has no terminated ends, i.e., each node is connected to other node and having no termination point.
- The data in a ring topology flow in a clockwise direction.
- Coaxial cable or RJ-45 cables are used to connect the computers.
- Hubs or Switches are mainly used as connection devices in a physical star topology.
- Star topology is the most popular topology in network implementation. Advantages of Star topology:
- Efficient troubleshooting: Troubleshooting is quite efficient in a star topology as compared to bus topology. In a bus topology, the manager has to inspect the kilometers of cable. In a star topology, all the stations are connected to the centralized network. Therefore, the network administrator has to go to the single station to troubleshoot the problem.
- Network control: Complex network control features can be easily implemented in the star topology. Any changes made in the star topology are automatically accommodated.
- Limited failure: As each station is connected to the central hub with its own cable, therefore failure in one cable will not affect the entire network.
- Familiar technology: Star topology is a familiar technology as its tools are cost- effective.
- Easily expandable: It is easily expandable as new stations can be added to the open ports on the hub.
- Cost effective: Star topology networks are cost-effective as it uses inexpensive coaxial cable. 7. High data speeds: It supports a bandwidth of approx 100Mbps. Ethernet 100BaseT is one of the most popular Star topology networks. Disadvantages of Star topology
- A Central point of failure: If the central hub or switch goes down, then all the connected nodes will not be able to communicate with each other.
- Cable: Sometimes cable routing becomes difficult when a significant amount of routing is required.
4.Tree topology
- Tree topology combines the characteristics of bus topology and star topology.
- A tree topology is a type of structure in which all the computers are connected with each
other in hierarchical fashion.
- The top-most node in tree topology is known as a root node, and all other nodes are the descendants of the root node.
- There is only one path exists between two nodes for the data transmission. Thus, it forms a parent-child hierarchy. Advantages of Tree topology
- Support for broadband transmission: Tree topology is mainly used to provide broadband transmission, i.e., signals are sent over long distances without being attenuated.
- Easily expandable: We can add the new device to the existing network. Therefore, we can say that tree topology is easily expandable.
- Easily manageable: In tree topology, the whole network is divided into segments known as star networks which can be easily managed and maintained.
- Error detection: Error detection and error correction are very easy in a tree topology.
- Limited failure: The breakdown in one station does not affect the entire network.
- Point-to-point wiring: It has point-to-point wiring for individual segments. Disadvantages of Tree topology
- Difficult troubleshooting: If any fault occurs in the node, then it becomes difficult to troubleshoot the problem.
- High cost: Devices required for broadband transmission are very costly.
- Failure: A tree topology mainly relies on main bus cable and failure in main bus cable will damage the overall network.
- Reconfiguration difficult: If new devices are added, then it becomes difficult to reconfigure.
5.Mesh topology:
- Mesh technology is an arrangement of the network in which computers are interconnected with each other through various redundant connections.
- There are multiple paths from one computer to another computer.
- It does not contain the switch, hub or any central computer which acts as a central point of communication.
- The Internet is an example of the mesh topology.
- Mesh topology is mainly used for WAN implementations where communication failures
- The combination of various different topologies is known as Hybrid topology.
- A Hybrid topology is a connection between different links and nodes to transfer the data.
- When two or more different topologies are combined together is termed as Hybrid topology and if similar topologies are connected with each other will not result in Hybrid topology. For example, if there exist a ring topology in one branch of ICICI bank and bus topology in another branch of ICICI bank, connecting these two topologies will result in Hybrid topology. Advantages of Hybrid Topology:
- Reliable: If a fault occurs in any part of the network will not affect the functioning of the rest of the network.
- Scalable: Size of the network can be easily expanded by adding new devices without affecting the functionality of the existing network.
- Flexible: This topology is very flexible as it can be designed according to the requirements of the organization.
- Effective: Hybrid topology is very effective as it can be designed in such a way that the strength of the network is maximized and weakness of the network is minimized. Disadvantages of Hybrid topology:
- Complex design: The major drawback of the Hybrid topology is the design of the Hybrid network. It is very difficult to design the architecture of the Hybrid network.
- Costly Hub: The Hubs used in the Hybrid topology are very expensive as these hubs are different from usual Hubs used in other topologies.
- Costly infrastructure: The infrastructure cost is very high as a hybrid network requires a lot of cabling, network devices, etc.
3 REFERENCE MODELS: Computer Network Models A communication subsystem is a complex piece of Hardware and software. Early attempts for
implementing the software for such subsystems were based on a single, complex, unstructured program with many interacting components. The resultant software was very difficult to test and modify. To overcome such problem, the ISO has developed a layered approach. In a layered approach, networking concept is divided into several layers, and each layer is assigned a particular task. Therefore, we can say that networking tasks depend upon the layers.
1.OSI Model: 1.OSI stands for Open System Interconnection is a reference model that describes how information from a software application in one computer moves through a physical medium to the software application in another computer. 2.OSI consists of seven layers, and each layer performs a particular network function. 3.OSI model was developed by the International Organization for Standardization (ISO) in 1984, and it is now considered as an architectural model for the inter-computer communications. 4.OSI model divides the whole task into seven smaller and manageable tasks. Each layer is assigned a particular task. 5.Each layer is self-contained, so that task assigned to each layer can be performed independently. Characteristics of OSI Model:
The OSI model is divided into two layers: upper layers and lower layers. 1.The upper layer of the OSI model mainly deals with the application related issues, and they are implemented only in the software. The application layer is closest to the end user. Both the end user and the application layer interact with the software applications. 2.An upper layer refers to the layer just above another layer. The lower layer of the OSI model deals with the data transport issues. The data link layer and the physical layer are implemented in hardware and software. The physical layer is the lowest layer of the OSI model and is closest to the physical medium. The physical layer is mainly responsible for placing the information on the physical medium.
Line Configuration: It defines the way how two or more devices can be connected physically. Data Transmission: It defines the transmission mode whether it is simplex, half-duplex or full- duplex mode between the two devices on the network. Topology : It defines the way how network devices are arranged. Signals: It determines the type of the signal used for transmitting the information.
2.Data-Link Layer:
- This layer is responsible for the error-free transfer of data frames.
- It defines the format of the data on the network.
- It provides a reliable and efficient communication between two or more devices.
- It is mainly responsible for the unique identification of each device that resides on a local network. It contains two sub-layers: 1. Logical Link Control Layer 2. Media Access Control Layer
1.Logical Link Control Layer It is responsible for transferring the packets to the Network layer of the receiver that is receiving. It identifies the address of the network layer protocol from the header. It also provides flow control.
2.Media Access Control Layer A Media access control layer is a link between the Logical Link Control layer and the network's physical layer. It is used for transferring the packets over the network.
Functions of the Data-link layer:
Framing: The data link layer translates the physical's raw bit stream into packets known as Frames. The Data link layer adds the header and trailer to the frame. The header which is added to the frame contains the hardware destination and source address.
Physical Addressing: The Data link layer adds a header to the frame that contains a destination address. The frame is transmitted to the destination address mentioned in the header.
Flow Control: Flow control is the main functionality of the Data-link layer. It is the technique through which the constant data rate is maintained on both the sides so that no data get corrupted. It ensures that the transmitting station such as a server with higher processing speed does not exceed the receiving station, with lower processing speed.
Error Control: Error control is achieved by adding a calculated value CRC (Cyclic Redundancy Check) that is placed to the Data link layer's trailer which is added to the message frame before it is sent to the physical layer. If any error seems to occurr, then the receiver sends the acknowledgment for the retransmission of the corrupted frames.
Access Control: When two or more devices are connected to the same communication channel, then the data link layer protocols are used to determine which device has control over the link at a given time.
3.Network Layer:
It is a layer 3 that manages device addressing, tracks the location of devices on the network. It determines the best path to move data from source to the destination based on the network conditions, the priority of service, and other factors. The Data link layer is responsible for routing and forwarding the packets. Routers are the layer 3 devices, they are specified in this layer and used to provide the routing services within an internetwork. The protocols used to route the network traffic are known as Network layer protocols. Examples of protocols are IP and Ipv6.
Functions of Network Layer:
contains the address known as a service-point address or port address. The responsibility of the network layer is to transmit the data from one computer to another computer and the responsibility of the transport layer is to transmit the message to the correct process. 2.Segmentation and reassembly: When the transport layer receives the message from the upper layer, it divides the message into multiple segments, and each segment is assigned with a sequence number that uniquely identifies each segment. When the message has arrived at the destination, then the transport layer reassembles the message based on their sequence numbers. 3.Connection control: Transport layer provides two services Connection-oriented service and connectionless service. A connectionless service treats each segment as an individual packet, and they all travel in different routes to reach the destination. A connection-oriented service makes a connection with the transport layer at the destination machine before delivering the packets. In connection-oriented service, all the packets travel in the single route. 4.Flow control: The transport layer also responsible for flow control but it is performed end-to- end rather than across a single link. 5.Error control: The transport layer is also responsible for Error control. Error control is performed end-to-end rather than across the single link. The sender transport layer ensures that message reach at the destination without any error.
5.Session Layer:
It is a layer 3 in the OSI model. The Session layer is used to establish, maintain and synchronizes the interaction between communicating devices. Functions of Session layer: 1.Dialog control: Session layer acts as a dialog controller that creates a dialog between two processes or we can say that it allows the communication between two processes which can be either half-duplex or full-duplex. 2.Synchronization: Session layer adds some checkpoints when transmitting the data in a sequence. If some error occurs in the middle of the transmission of data, then the transmission will take place again from the checkpoint. This process is known as Synchronization and recovery.
6.Presentation Layer:
- A Presentation layer is mainly concerned with the syntax and semantics of the information exchanged between the two systems.
- It acts as a data translator for a network.
- This layer is a part of the operating system that converts the data from one presentation format to another format.
- The Presentation layer is also known as the syntax layer.
Functions of Presentation layer: 1.Translation: The processes in two systems exchange the information in the form of character strings, numbers and so on. Different computers use different encoding methods, the presentation layer handles the interoperability between the different encoding methods. It converts the data from sender-dependent format into a common format and changes the common format into receiver-dependent format at the receiving end. 2.Encryption: Encryption is needed to maintain privacy. Encryption is a process of converting the sender-transmitted information into another form and sends the resulting message over the network. 3.Compression: Data compression is a process of compressing the data, i.e., it reduces the number of bits to be transmitted. Data compression is very important in multimedia such as text, audio, video.
7.Application Layer:
An application layer serves as a window for users and application processes to access network service. It handles issues such as network transparency, resource allocation, etc. An application layer is not an application, but it performs the application layer functions. This layer provides the network services to the end-users. Functions of Application layer: 1.File transfer, access, and management (FTAM): An application layer allows a user to access the files in a remote computer, to retrieve the files from a computer and to manage the files in a remote computer. 2.Mail services: An application layer provides the facility for email forwarding and storage. Directory services: An application provides the distributed database sources and is used to provide that global information about various objects.
TCP/IP model:
- The TCP/IP model was developed prior to the OSI model.
- The TCP/IP model is not exactly similar to the OSI model.
1.IP Protocol: IP protocol is used in this layer, and it is the most significant part of the entire TCP/IP suite. Following are the responsibilities of this protocol: 2.IP Addressing: This protocol implements logical host addresses known as IP addresses. The IP addresses are used by the internet and higher layers to identify the device and to provide internetwork routing. 3.Host-to-host communication: It determines the path through which the data is to be transmitted. 4.Data Encapsulation and Formatting: An IP protocol accepts the data from the transport layer protocol. An IP protocol ensures that the data is sent and received securely, it encapsulates the data into message known as IP datagram. 5.Fragmentation and Reassembly: The limit imposed on the size of the IP datagram by data link layer protocol is known as Maximum Transmission unit (MTU). If the size of IP datagram is greater than the MTU unit, then the IP protocol splits the datagram into smaller units so that they can travel over the local network. Fragmentation can be done by the sender or intermediate router. At the receiver side, all the fragments are reassembled to form an original message. 6.Routing: When IP datagram is sent over the same local network such as LAN, MAN, WAN, it is known as direct delivery. When source and destination are on the distant network, then the IP datagram is sent indirectly. This can be accomplished by routing the IP datagram through various devices such as routers. 7.ARP Protocol:
45. me Ministers of India | List of Prime Minister of India (1947-2020) ARP stands for Address Resolution Protocol. ARP is a network layer protocol which is used to find the physical address from the IP address. The two terms are mainly associated with the ARP Protocol: 1.ARP request: When a sender wants to know the physical address of the device, it broadcasts the ARP request to the network. 2.ARP reply: Every device attached to the network will accept the ARP request and process the request, but only recipient recognize the IP address and sends back its physical address in the form of ARP reply. The recipient adds the physical address both to its cache memory and to the datagram header 8.ICMP Protocol: ICMP stands for Internet Control Message Protocol. It is a mechanism used by the hosts or routers to send notifications regarding datagram problems back to the sender. A datagram travels from router-to-router until it reaches its destination. If a router is unable to route the data because of some unusual conditions such as disabled links, a device is on fire or network congestion, then the ICMP protocol is used to inform the sender that the datagram is undeliverable.
An ICMP protocol mainly uses two terms: 1.ICMP Test: ICMP Test is used to test whether the destination is reachable or not. 2.ICMP Reply: ICMP Reply is used to check whether the destination device is responding or not. The core responsibility of the ICMP protocol is to report the problems, not correct them. The responsibility of the correction lies with the sender. ICMP can send the messages only to the source, but not to the intermediate routers because the IP datagram carries the addresses of the source and destination but not of the router that it is passed to.
Transport Layer: The transport layer is responsible for the reliability, flow control, and correction of data which is being sent over the network. The two protocols used in the transport layer are User Datagram protocol and Transmission control protocol. User Datagram Protocol (UDP) It provides connectionless service and end-to-end delivery of transmission. It is an unreliable protocol as it discovers the errors but not specify the error. User Datagram Protocol discovers the error, and ICMP protocol reports the error to the sender that user datagram has been damaged.
UDP consists of the following fields: Source port address: The source port address is the address of the application program that has created the message. Destination port address: The destination port address is the address of the application program that receives the message. Total length: It defines the total number of bytes of the user datagram in bytes. Checksum: The checksum is a 16-bit field used in error detection. UDP does not specify which packet is lost. UDP contains only checksum; it does not contain any ID of a data segment.
