COMPUTER NETWORKSChapter 1. Basic Network Concepts
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Network :- A network is defined as a group of two or more computer systems linked together. A network is a collection of computers, servers, mainframes, network devices, peripherals, or other devices connected to one another allowing for data to be shared and used. A great example of a network is the internet, connecting millions of people all over the world together. Below is an example image of what a home network with multiple computers and other network devices all connected to each other and the Internet. Another Definition of Network:- A network consists of two or more computers that are linked in order to share resources (such as printers and CDs), exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams. Two Types of Network:- 1. Human Network. 2. Computer Network. 1. Human Network:- As human beings, we are all social beings who all share and yearn for the same thing. Connectivity, community, a human connection, a human network. However, in this digital age, what is"Human Connectivity?" or "Human Network?". Well, according to the text book definition of "human network," it is defined as a social structure composed of individuals, business partners, friends or other organizations connected through technology, social media, using devices such as PCs, cell phones, and PDAs. 2. Computer Network:- A computer network is a group of computer systems and other computing hardware devices that are linked together through communication channels to facilitate communication and resource-sharing among a wide range of users. Network Plan:- Network is planned for the purpose of establishing communication link between nodes. Benefit of Network:- 1. Sharing Information. 2. Sharing Resources. 3. Facilitating Centralized Management Managing Software or System. 4. Backing Up Data. Network Classifications:- ->On the basis of Geography All these three differ in terms of physical size only, otherwise hardware structure & architecture are same for all the three. 1. LAN:- (Local Area Network). The computers are geographically close together (that is, in the same building). 2. MAN:- (Metropolitan Area Network). A data network designed for a big town or city. 3. WAN:- (Wide Area Network). The computers are farther apart and are connected by telephone lines or radio waves. -> On the basis of component role 1. Pear to Peer Network:- In a peer-to-peer network, a group of computers is connected together so that users can share resources and information. There is no central location for authenticating users, storing files, or accessing resources. This means that users must remember which computers in the workgroup have the shared resource or information that they want to access. It also means that users must log on to each computer to access the shared resources on that computer. 2. Server based Network:- In a server-based network, the server is the central location where users share and access network resources. This dedicated computer controls the level of access that users have to shared resources. Shared data is in one location, making it easy to back up critical business information. Each computer that connects to the network is called a clientcomputer. In a server-based network, users have one user account and password to log on to the server and to access shared resources. Server operating systems are designed to handle the load when multiple client computers access server-based resources.Windows SBS 2008 is installed and configured as the central server on a server-based network. Windows SBS 2008 provides the central point for authenticating users, accessing resources, and storing information. Network Features:- 1. File Sharing:- 2. Printer Sharing:- 3. Application Services:- 4. E-Mail:- 5. Remote Access:- The particular computer of internet can be remotely accessed sitting far away from their. Chapter 2. Network Topologies & Networking Devices ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Geographical structure of a network in a specific pattern is called Network Topology. Types of Topology:- Network Topology is the schematic description of a network arrangement, connecting various nodes(sender and receiver) through lines of connection. 1. Bus Topology:- Bus topology is a network type in which every computer and network device is connected to single cable. When it has exactly two endpoints, then it is called Linear Bus topology. 2. Ring Topology:- It is called ring topology because it forms a ring as each computer is connected to another computer, with the last one connected to the first. Exactly two neighbours for each device. 3. Star Topology:- In this type of topology all the computers are connected to a single hub through a cable. This hub is the central node and all others nodes are connected to the central node. 4. Mesh Topology:- It is a point-to-point connection to other nodes or devices. All the network nodes are connected to each other. Mesh has (n)(n-2)/2physical channels to link (n) devices. 5. Tree Topology:- It has a root node and all other nodes are connected to it forming a hierarchy. It is also called hierarchical topology. It should at least have three levels to the hierarchy. 6. Hybrid Topology:- It is two different types of topologies which is a mixture of two or more topologies. For example if in an office in one department ring topology is used and in another star topology is used, connecting these topologies will result in Hybrid Topology (ring topology and star topology). Network control device:- 1. Hub:- Hub is one of the basic icons of networking devices which works at physical layer and hence connect networking devices physically together. Hubs are fundamentally used in networks that use twisted pair cabling to connect devices. They are designed to transmit the packets to the other appended devices without altering any of the transmitted packets received. They act as pathways to direct electrical signals to travel along. They transmit the information regardless of the fact if data packet is destined for the device connected or not. 2. Switches:- Switches are the linkage points of an Ethernet network. Just as in hub, devices in switches are connected to them through twisted pair cabling. But the difference shows up in the manner both the devices; hub and a switch treat the data they receive. Hubworks by sending the data to all the ports on the device whereas a switch transfers it only to that port which is connected to the destination device. A switch does so by having an in-built learning of the MAC address of the devices connected to it. Since the transmission of data signals are well defined in a switch hence the network performance is consequently enhanced. Switches operate infull-duplexmode where devices can send and receive data from the switch at the simultaneously unlike in half-duplex mode. The transmission speed in switches is double than in Ethernet hub transferring a 20Mbps connection into 30Mbps and a 200Mbps connection to become 300Mbps. Performance improvements are observed in networking with the extensive usage of switches in the modern days. 3. Routers:- Routers are network layer devices and are particularly identified as Layer- 3 devices of the OSI Model. They process logical addressing information in the Network header of a packet such as IP Addresses. Router is used to create larger complex networks by complex traffic routing. It has the ability to connect dissimilar LANs on the same protocol. It also has the ability to limit the flow of broadcasts. A router primarily comprises of a hardware device or a system of the computer which has more than one network interface and routing software. 4. Bridge:- A bridge is a computer networking device that builds the connection with the other bridge networks which use the same protocol. It works at the Data Link layer of the OSI Model and connects the different networks together and develops communication between them. It connects two local-area networks; two physical LANs into larger logical LAN or two segments of the same LAN that use the same protocol. 5. Repeaters:- Active Hub are smarter than the passive hubs. They not only provide the path for the data signals in fact they regenerate, concentrate and strengthen the signals before sending them to their destinations. Active hubs are also termed as ‘repeaters’. 6. Gateway:- Gateway is a device which is used to connect multiple networks and passes packets from one packet to the other network. Acting as the ‘gateway’ between different networking systems or computer programs, a gateway is a device which forms a link between them. It allows the computer programs, either on the same computer or on different computers to share information across the network through protocols. A router is also a gateway, since it interprets data from one network protocol to another. Others such as bridge converts the data into different forms between two networking systems. Then a software application converts the data from one format into another. Gateway is a viable tool to translate the data format, although the data itself remains unchanged. Gateway might be installed in some other device to add its functionality into another. 7. Modems:- Modem is a device which converts the computer-generated digital signals of a computer into analog signals to enable their travelling via phone lines. The ‘modulator-demodulator’ or modem can be used as a dial up for LAN or to connect to an ISP. Modems can be both external, as in the device which connects to the USB or the serial port of a computer, or proprietary devices for handheld gadgets and other devices, as well as internal; in the form of add-in expansion cards for computers and PCMCIA cards for laptops. Configuration of a modem differs for both the external and internal modem. For internal modems, IRQ – Interrupt request is used to configure the modem along with I/O, which is a memory address. Typically before the installation of built-in modem, integrated serial interfaces are disabled, simultaneously assigning them the COM2 resources.For external connection of a modem, the modem assigns and uses the resources itself. This is especially useful for the USB port and laptop users as the non-complex and simpler nature of the process renders it far much more beneficial for daily usage. Chapter 3. Transmission Media ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Transmission media is defined as wire cable which carries data on it. It can be wireless also. Two Types of Transmission media:- 1. Guided Media 2. Un-Guided Media 1. Guided Media:- It is the transmission media in which signals are confined to a specific path using wire or cable. The types of Bounded/ Guided Media are discussed below. Wire Cable Transmission-> * Twisted Pair. * UTP (Unshielded Twisted Pair). * SIP (Shielded Twisted Pair). * Co-Axial Cable. * Optical Fiber. Optical Fiber - .................................. Optical Fiber Structure:- Structure of Optical Fiber is in three layers - 1. Core. (u1) - in middle of the cable. 2. Cladding. (u2) - upper layer of cable after core. 3. Buffer Coating. - it is a coating to make cable covered to isolated with environment lights or reflection to do not entered in it or in cable from outside. Condition between core and cladding is reflective index of core is greater than cladding. => u1>u2 (Condition) Light Source for Fiber:- The signal is in the form of digital data, data is made of bit, every bit is converted into burst of light with the speed of coming bit one by one on cable of suitable light source. Two Light Source is used to transmit data on Optical Fiber Cable:- 1. LED - Surface Emission & Edge Emission. 2. LASER - Fabry Parat Resonator Cavity & DFB (Distributed Feed Back) Propagation Mode:- OFC ( Optical Fiber for Communication) - This cable takes intense light from suitable light source which is actually data bit in the form of light waves. Two types of Propagation Mode:- 1. Single Mode. 2. Multi-Mode. 1. Single Mode:- In single mode of propagation, the reflective index value is constant throughout the thickness of core. 2. Multi-Mode:- In this case the reflective index of the core keeps changing starting from central axis to outer along diameter. This change in reflective index is of two types. 1.Abrupt changing which is step index. 2. Continues change which is called graded index. Advantages of Optical Fiber:- 1. Long distance data transmission. 2. Large information capacity. 3. Small size and low weight. 4. Immunity to electrical interface enhance safety. 5. Increase signal security. Disadvantages of Optical Fiber:- The only one disadvantage of optical fiber in communication is that the setup to build a optical fiber communication between somewhere is very costly. 2. Un-Guided Media:- Unguided or wireless media sends the data through air (or water), which is available to anyone who has a device capable of receiving them. Types of unguided/ unbounded media are discussed below : *.Radio Transmission :- Its frequency is between 10 kHz to 1GHz. It is simple to install and has high attenuation. These waves are used for multicast communications. *.Micro Wave Transmission:- It travels at high frequency than the radio waves. It requires the sender to be inside of the receiver. It operates in a system with a low gigahertz range. It is mostly used for unicast communication. There are 2 types of Microwave Transmission : 1.Terrestrial Microwave 2.Satellite Microwave Wireless Transmission-> * Wireless link can be implemented by using a. Electro-Magnetic Waves. b. IR Wave. Wireless communication band:- 1. Microwave Communication - Wavelength = 1mm Frequency = 300MHz - 300 GHz ( wavelength = 0.1 cm) Frequency band:- L = 1 - 2 GHz S = 2 - 4 GHz C = 4 - 8 GHz X = 8 - 12 GHz KU = 12 - 18 GHz K = 18 - 26 GHz KA = 26 - 40 GHz 2. Satellite Communication - Frequency Band: - f = 3 - 300 GHz Up Link = 6 GHz DN Link = 4 GHz 3. Cellular Communication - Triband :- 850 MHz 950 MHz 1900 MHz Quad Band:- 850 MHz 950 MHz 1800 MHz 1900 MHz Gap between the forward channel and reverse channel is 45 MHz and channel bandwidth is 200 KHz. Access Method:- The term access represents, intercepting the waves and the information derivation from that. Method of Accessing:- 1. TDMA (Time Division Multiple Access) 2. FDMA (Frequency Division Multiple Access) 3. CDMA (Code Division Multiple Access) 4. SDMA (Space Division Multiple Access) 5. PDMA (Power Division Multiple Access) The channel bandwidth is very scarce, every body wants to use it for communication but the use of channel is not available to everybody at all time; so there have been develop many access methods to make the channel available for everybody. Chapter 4. Network - Reference Model ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The most important Network Reference Model are:- 1. TCP/IP (Transfer Control Protocol/Internet Protocol). 2. OSI (Open System Interconnect). 1. TCP/IP Definition:- TCP/IP is transmission control protocol and internet protocol. Protocols are set of rules which govern every possible communication over the internet. These protocols describe the movement of data between the host computers or internet and offers simple naming and addressing schemes. 4 Layers of TCP/IP Model:- 1. Application Layer. 2. Transport Layer. 3. Network Layer. 4. Subnet Layer. 2. OSI Definition:- To ensure national and worldwide data communication ISO (ISO stands for International Organization of Standardization) developed this model. This is called a model for open system interconnection (OSI) and is normally called as OSI model. OSI model architecture consists of seven layers. It defines seven layers or levels in a complete communication system. Note:- Network Reference Model gives an structure of a network and its working concept that how the network is able to fulfill the requirement of user. Interlayer Communication:- Every layer in the ISDN protocol stack has to communicate with the other layers with which it is in contact: layer 1 interacts with layer 2 which in turn interacts with layer 1 and layer 3 and finally layer 3 which interacts with layer 2 and something which sits above it. The way how this communication is done is also specified in the above referenced ITU Recommendations and it is done by so called ``primitives'' which separate the layers logically from each other in a well defined manner. Data Encapsulation:- For the purpose of data security extra data are attached with the main data is called Data Encapsulation. Horizontal Communication:- Communication of data between same layer of OSI Model is called Horizontal Communication. Vertical Communication:- Communication of data between different layers of OSI Model is called Vertical Communication. 7 Layers Of OSI Model:- 1. Application Layer. 2. Presentation Layer. 3. Session Layer. 4. Transport Layer. 5. Network Layer. 6. Data Link Layer. 7. Physical Layer. 1. Application Layer:- The application layer is Hardware based. The application software, which is used for communication makes application layer of OSI Model. Other part are also included in this application software, it decides how the data is generated, processed & routed. Function of Application Layer:- Work in association with operating system & its main function is - a. Authentication. b. Security. c. Network Access. d. Error Control. 2. Presentation Layer:- In this layer data reformatting and encryption is done. 3. Session Layer:- It maintains connectivity between computer to computer and computer to mobile or mobile to mobile for exchange of data. 4. Transport Layer:- In this layer total data is splinted into packets. 5. Network Layer:- The conversion of logical address into physical address is the duty of Network Layer. It is also used for switching action and routing of the data. The Internet Protocol is the main feature of this layer. 6. Data Link Layer:- The processing and obstruction removal is the duty of this layer. 7. Physical Layer:- It is hardware transmission media cable which gives physical links between two nodes. It can be guided or unguided both. Comparison of the OSI and TCP/IP Reference Model ...................................................... OSI(Open System Interconnection) 1. OSI is a generic, protocol independent standard, acting as a communication gateway between the network and end user. 2. In OSI model the transport layer guarantees the delivery of packets. 3. Follows vertical approach. 4. OSI model has a separate Presentation layer and Session layer. 5. OSI is a reference model around which the networks are built. Generally it is used as a guidance tool. 6. Network layer of OSI model provides both connection oriented and connectionless service. 7. OSI model has a problem of fitting the protocols into the model. 8. Protocols are hidden in OSI model and are easily replaced as the technology changes. 9. OSI model defines services, interfaces and protocols very clearly and makes clear distinction between them. It is protocol independent. 10. It has 7 layers. TCP/IP(Transmission Control Protocol / Internet Protocol) 1. TCP/IP model is based on standard protocols around which the Internet has developed. It is a communication protocol, which allows connection of hosts over a network. 2. In TCP/IP model the transport layer does not guarantees delivery of packets. Still the TCP/IP model is more reliable. 3. Follows horizontal approach. 4. TCP/IP does not have a separate Presentation layer or Session layer. 5. TCP/IP model is, in a way implementation of the OSI model. 6. The Network layer in TCP/IP model provides connectionless service. 7. TCP/IP model does not fit any protocol. 8. In TCP/IP replacing protocol is not easy. 9. In TCP/IP, services, interfaces and protocols are not clearly separated. It is also protocol dependent. 10. It has 4 layers. Chapter 5. TCP/IP Fundamentals ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Protocol :- Protocol is defined as rules & regulations of network communications. For a communication to take place the two ends must agree on a protocol. The Protocol defines following things:- 1. What is Communicative? 2. How it is Communicated? 3. When it is Communicated? In this way we find three distinguished elements of protocol:- 1. Syntax. 2. Semantics. 3. Timing. The Internet Protocol suffers from two types of major protocol:- 1. Lack of error control. 2. Lack of assistant mechanism. Examples of some important protocol used in networking:- 1. SLIP (Serial Line Internet Protocol). 2. PPP (Point to Point Protocol). 3. ARP (Address Resolution Protocol). 4. IP (Internet Protocol). 5. ICMP (Internet Control Message Protocol). 6. TCP (Transmission Control Message). 7. UDP (User Datagram Protocol). 1. SLIP :- This was developed for serial communication system between two nodes containing serial ports. It was also used for modem connection. Later on this protocol was modify into PPP mostly person computer used this protocol. The internet protocol packet is encapsulated and then routed on the transmission media. 2. PPP :- This protocol is used for establishing link between home computer and server computer and also between home computer and ISP (Internet Service Provider). It provides the services of physical layer. PPP provides services as follow:- 1. Format of the frame which is to be exchanged between two devices. 2. How to negotiate between two devices. 3. Network layer and data encapsulation. 4. Devices Authentication. 5. Connection over multiple links. 6. Network Address Configuration. 7. PPP is byte oriented. 3. ARP :- It is a protocol for mapping an Internet Protocol address (IP address) to a physical machine address that is recognized in the local network. 4. IP :- An IP address is a fascinating product of modern computer technology designed to allow one computer (or other digital device) to communicate with another via the Internet. IP addresses allow the location of literally billions of digital devices that are connected to the Internet to be pinpointed and differentiated from other devices. In the same sense that someone needs your mailing address to send you a letter, a remote computer needs your IP address to communicate with your computer. 5. ICMP :- It is an error-reporting protocol network devices like routers use to generate error messages to the source IP address when network problems prevent delivery of IP packets. The ICMP is divided in two broad categories:- 1. Error Reporting Messages. 2. Query Message. Note:- ICMP is used by Network Devices link Routers. It sends the error message and also it remains the Query Message. 6. TCP :- It is a standard that defines how to establish and maintain a network conversation via which application programs can exchange data. TCP works with the Internet Protocol (IP),which defines how computers send packets of data to each other. Together TCP and IP are the basic rules defining the Internet. It is a connection oriented. It creates a virtual connection between two TCPs. In addition TCP usage flow control and error control mechanism at the transport level. It is reliable. Services provided by TCP:- 1. Process to Process Communication. 2. Stream delivered services. 3. Sending and receiving buffers. 4. Full duplex communication. 7. UDP :- It provides process to process communication between host to host. It is connectionless, unreliable transport protocol. UDP has fixed size header of 8 byte. UDP has 4 fields:- 1. Source Port Number. 2. Destination Port Number. Both of these are 16 bits long. 3. Length :- It is a 16 bit field that defines the total length of UDP, Header + Data. 4. Checksum :- This field is used for deleting the error over the entire datagram. IP Addressing:- Addressing means knowing the address of host and visitors. In a network many devices can exist. Some of them are nodes, switches, routers, client, server, host. Each one of them is assigned a specific IP Address for the purpose of distinguished identity to them. IP Address Classes:- Class A:- 1.0.0.0 to 126.255.255.255 . Subnet Mask Address is 255.0.0.0 Class B:- 128.0.0.0 to 191.255.255.255 . Subnet Mask Address is 255.255.0.0 Class C:- 192.0.0.0 to 233.255.255.255 . Subnet Mask Address is 255.255.255.0 Class D:- 224.0.0.0 to 239.255.255.255 . It is used only for testing of the network. Class E:- It is reserved for future use. Subnet:- A large network can be divided into small networks. Each of these small network is called subnet and they will have unique subnet address. This is called subnetting. The unique subnet gives masking effect that means directly one node cannot reach to the other node to the other subnet. Registered Address:- Registered address are public. They are visible on the network. It allocated to ISP which assigned them to its Customers. Unregistered Address:- It is private. It is not exposed to anyone and outside the company or home network. IPv4 :- It is sometimes known as decimal noted IP Address. It is 32 bit long. 2^3 * 4 = 32 bit. IPv6 :- It is hexa-decimal type IP Address. It is 128 bit long. 2^4 * 8 = 128 bit. |