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COMPUTER NETWORKS NOTE
What is a Host? A host is a computer, connected to other computers for which it provides data or services over a network. In theory, every computer connected to a network acts as a host to other peers on the network. In essence, a host reflects the logical relationship of two or more computers on a network. To simplify this, suppose you want to download an image from another computer on your network. That computer is “hosting” the image and therefore, it is the host computer. On the other hand, if that same computer downloads an image from your computer, your computer becomes the host computer. Your computer can be a host to other computers. Likewise, your router can be a host to other routers. But a host must have an assigned IP address. Therefore, modems, hubs, and switches are not considered hosts because they do not have assigned IP addresses. What is network bandwidth? Network bandwidth is a measurement indicating the maximum capacity of a wired or wireless communications link to transmit data over a network connection in a given amount of time. Typically, bandwidth is represented in the number of bits, kilobits, megabits or gigabits that can be transmitted in 1 second. Synonymous with capacity, bandwidth describes data transfer rate. Bandwidth is not a measure of network speed -- a common misconception. How does bandwidth work? The more bandwidth a data connection has, the more data it can send and receive at one time. In concept, bandwidth can be compared to the volume of water that can flow through a pipe. The wider the pipe's diameter, the more water can flow through it at one time. Bandwidth works on the same principle. The higher the capacity of the communication link, the more data can flow through it per second. What is a Client? A client is a computer hardware device or software that accesses a service made available by a server. The server is often (but not always) located on a separate physical computer. What is a Server? A server is a physical computer dedicated to run services to serve the needs of other computers. Depending on the service that is running, it could be a file server, database server, home media server, print server, or web server.
What is a packet? In networking, a packet is a small segment of a larger message. Data sent over computer networks*, such as the Internet, is divided into packets. These packets are then recombined by the computer or device that receives them. Suppose Alice is writing a letter to Bob, but Bob's mail slot is only wide enough to accept envelopes the size of a small index card. Instead of writing her letter on normal paper and then trying to stuff it through the mail slot, Alice divides her letter into much shorter sections, each a few words long, and writes these sections out on index cards. She delivers the group of cards to Bob, who puts them in order to read the whole message. What Does Frame Mean? In networking, a frame is a unit of data. A frame works to help identify data packets used in networking and telecommunications structures. Frames also help to determine how data receivers interpret a stream of data from a source. Advertisements Techopedia Explains Frame One way to define frames in networking is that the frame is a primary data unit within Level 2, or the data link layer of the OSI model. By contrast, Level 3, or the networking layer of the OSI model uses the packet as a primary data unit. Frames and packets may have different terminology attached to their use depending on the context or industry in question. In general, the frame is a formatting resource for data that needs to be split up into recognizable pieces in order to be interpreted by a receiver. What is Local Host? When you call an IP address on your computer, you try to contact another computer on the internet, but when you call the IP address 127.0.0.1, you are communicating with the local host. Localhost is always your computer. Your computer is talking to itself when you call the local host. Your computer does not always directly identify the local host. Within your network, localhost has a separate IP address like 192.168.0.1. (for most cases) which is different from the one you use on the internet. This is usually dynamically assigned by the internet service provider (ISP). Localhost can be seen as a server that is used on your computer. This term is generally used in the context of networks. Localhost is not just the name for the virtual server but it is also its domain name. Just like .example, .test, or .invalid, ., .localhost is a top-level domain reserved for documentation and testing purposes. While accessing the domain, a loopback is triggered. If you access “http://localhost” in the browser, the request will not be forwarded to the internet through the router. It will instead remain in your system. Localhost has the IP address 127.0.0.1. This refers back to your server.
Crosstalk A disturbance caused by electromagnetic interference, along with a circuit or a cable pair. A telecommunication signal disrupts a signal in an adjacent circuit and can cause the signals to become confused and cross over each other. What Is Attenuation in Networking? When used by networking professionals, the word attenuation refers to the loss of signal strength due to external or internal factors. Let’s explore how attenuation occurs and what options are available to increase signal strength. Attenuation is the loss of signal strength in networking cables or connections. This typically is measured in decibels (dB) or voltage and can occur due to a variety of factors. It may cause signals to become distorted or indiscernible. An example of this is Wi-Fi signal and strength getting noticeably weaker the further that your device is from the router. When measuring attenuation in a wired network, the greater the signal strength over a long distance, the more effective the cable is. Less efficient cables will struggle with signal attenuation, and networking administrators may need to adjust the cable or insert amplifiers or repeaters in order to boost the signal strength. However, the more signal amplifiers applied, the slower the signal speed will become between endpoints, due to the extra components that have been added. Attenuation Versus Amplification While attenuation is the loss of signal strength, amplification boosts the strength of a signal. However, amplification can also affect the noise in the transmission, potentially degrading the quality of the signal. Noise can come in the form of electromagnetic frequencies, electrical currents, wire leakage or wireless signals. In computer networking, internal software can help reduce the overall noise so that the signal isn’t too distorted. Management of both attenuation and amplification is among the key skills and troubleshooting tasks of networking professionals. Distortion describes an interruption of transmitting signals that cause an unclear reception. Distortion is commonly found in sound generated or received by a computer, video, or display signals and data cables such as network cables.
What is Computer Networking? Computer networking refers to connected computing devices (such as laptops, desktops, servers, smartphones, and tablets) and an ever-expanding array of IoT devices (such as cameras, door locks, doorbells, refrigerators, audio/visual systems, thermostats, and various sensors) that communicate with one another. Please visit- https://www.cisco.com/c/en_in/solutions/enterprise-networks/what-is- computer-networking.html#~q-a What Does Web Mean? The Web is the common name for the World Wide Web, a subset of the Internet consisting of the pages that can be accessed by a Web browser. Many people assume that the Web is the same as the Internet, and use these terms interchangeably. However, the term Internet actually refers to the global network of servers that makes the information sharing that happens over the Web possible. So, although the Web does make up a large portion of the Internet, but they are not one and same. What’s difference between The Internet and The Web? The Internet is a global network of networks while the Web , also referred to formally as World Wide Web (www) is a collection of information that is accessed via the Internet. Another way to look at this difference is that the Internet is infrastructure while the Web is served on top of that infrastructure. Alternatively, the Internet can be viewed as a big Web that stores. At a high level, we can even think of the Internet as hardware and the Web as software! Difference Between The Internet and The Web Feature Internet WWW Definition A global system of interconnected computer networks that use TCP/IP protocol to link devices worldwide. A system of interlinked hypertext documents and multimedia content accessible via the Internet.. Scope All types of digital communication such as gaming, chatting, file sharing, email, etc. Specifically refers to the collection of web pages and websites accessible via web browsers. Components Hardware(servers, routers, devices), protocols(TCP/IP, FTP, SMTP, etc) and various services. Websites, web pages, web servers and hyperlinks that are used to navigate between them.
It consists of 2 separately insulated conductor wires wound about each other. Generally, several such pairs are bundled together in a protective sheath. They are the most widely used Transmission Media. Twisted Pair is of two types: Unshielded Twisted Pair (UTP): UTP consists of two insulated copper wires twisted around one another. This type of cable has the ability to block interference and does not depend on a physical shield for this purpose. It is used for telephonic applications. Shielded Twisted Pair (STP): This type of cable consists of a special jacket (a copper braid covering or a foil shield) to block external interference. It is used in fast-data-rate Ethernet and in voice and data channels of telephone lines. Coaxial Cable It has an outer plastic covering containing an insulation layer made of PVC or Teflon and 2 parallel conductors each having a separate insulated protection cover. The coaxial cable transmits information in two modes: Baseband mode(dedicated cable bandwidth) and Broadband mode(cable bandwidth is split into separate ranges). Cable TVs and analog television networks widely use Coaxial cables. Optical Fiber Cable Optical Fibre Cable uses the concept of refraction of light through a core made up of glass or plastic. The core is surrounded by a less dense glass or plastic covering called the cladding. It is used for the transmission of large volumes of data. The cable can be unidirectional or bidirectional. The WDM (Wavelength Division Multiplexer) supports two modes, namely unidirectional and bidirectional mode. Stripline Stripline is a transverse electromagnetic (TEM) transmission line medium invented by Robert M. Barrett of the Air Force Cambridge Research Centre in the 1950s. Stripline is the earliest form of the planar transmission line. It uses a conducting material to transmit high- frequency waves it is also called a waveguide. This conducting material is sandwiched between two layers of the ground plane which are usually shorted to provide EMI immunity. Microstripline In this, the conducting material is separated from the ground plane by a layer of dielectric. Stripline Stripline is a transverse electromagnetic (TEM) transmission line medium invented by Robert M. Barrett of the Air Force Cambridge Research Centre in the 1950s. Stripline is the earliest form of the planar transmission line. It uses a conducting material to transmit high-
frequency waves it is also called a waveguide. This conducting material is sandwiched between two layers of the ground plane which are usually shorted to provide EMI immunity. Microstripline In this, the conducting material is separated from the ground plane by a layer of dielectric. Factors Considered for Designing the Transmission Media Bandwidth: Assuming all other conditions remain constant, the greater a medium’s bandwidth, the faster a signal’s data transmission rate. Transmission Impairment : Transmission Impairment occurs when the received signal differs from the transmitted signal. Signal quality will be impacted as a result of transmission impairment. Interference: Interference is defined as the process of disturbing a signal as it travels over a communication medium with the addition of an undesired signal. Network Devices: Network devices, also known as networking hardware, are physical devices that allow hardware on a computer network to communicate and interact with one another. For example Repeater, Hub, Bridge, Switch, Routers, Gateway, Brouter, and NIC, etc.
1. Repeater – A repeater operates at the physical layer. Its job is to amplifies (i.e., regenerates) the signal over the same network before the signal becomes too weak or corrupted to extend the length to which the signal can be transmitted over the same network. When the signal becomes weak, they copy it bit by bit and regenerate it at its star topology connectors connecting following the original strength. It is a 2- port device. 2. 2. Hub – A hub is a basically multi-port repeater. A hub connects multiple wires coming from different branches, for example, the connector in star topology which connects different stations. Hubs cannot filter data, so data packets are sent to all connected devices. In other words, the collision domain of all hosts connected through Hub remains one. Also, they do not have the intelligence to find out the best path for data packets which leads to inefficiencies and wastage. **3. Types of Hub
- Active Hub:-** These are the hubs that have their power supply and can clean, boost, and relay the signal along with the network. It serves both as a repeater as well as a wiring center. These are used to extend the maximum distance between nodes. 5. Passive Hub:- These are the hubs that collect wiring from nodes and power supply from the active hub. These hubs relay signals onto the network without cleaning and boosting them and can’t be used to extend the distance between nodes. 6. Intelligent Hub:- It works like an active hub and includes remote management capabilities. They also provide flexible data rates to network devices. It also enables an administrator to monitor the traffic passing through the hub and to configure each port in the hub.
card is a layer 2 device which means that it works on both the physical and data link layers of the network model.
Difference between Unicast, Broadcast and Multicast in Computer
Network
The cast term here signifies some data(stream of packets) is being transmitted to the recipient(s) from the client(s) side over the communication channel that helps them to communicate. Let’s see some of the “cast” concepts that are prevailing in the computer networks field. What is Unicast? This type of information transfer is useful when there is a participation of a single sender and a single recipient. So, in short, you can term it a one-to-one transmission. For example, if a device having IP address 10.1.2.0 in a network wants to send the traffic stream(data packets) to the device with IP address 20.12.4.2 in the other network, then unicast comes into the picture. This is the most common form of data transfer over networks. What is Broadcast? Broadcasting transfer (one-to-all) techniques can be classified into two types: Limited Broadcasting: Suppose you have to send a stream of packets to all the devices over the network that your reside, this broadcasting comes in handy. For this to achieve, it will append 255.255.255.255 (all the 32 bits of IP address set to
- called Limited Broadcast Address in the destination address of the datagram (packet) header which is reserved for information transfer to all the recipients from a single client (sender) over the network.
Direct Broadcasting: This is useful when a device in one network wants to transfer packet stream to all the devices over the other network. This is achieved by translating all the Host ID part bits of the destination address to 1, referred to as Direct Broadcast Address in the datagram header for information transfer. What is Multicast? In multicasting, one/more senders and one/more recipients participate in data transfer traffic. In this method traffic recline between the boundaries of unicast (one-to-one) and broadcast (one-to-all). Multicast lets servers direct single copies of data streams that are then simulated and routed to hosts that request it. IP multicast requires the support of some other protocols like IGMP (Internet Group Management Protocol), Multicast routing for its work. Also in Classful IP addressing Class D is reserved for multicast groups. Types of Network Topology: Bus, Ring, Star, Mesh, Tree Diagram Network topologies describe the methods in which all the elements of a network are mapped. The topology term refers to both the physical and logical layout of a network. Types of Networking Topologies Two main types of network topologies in computer networks are 1) Physical topology 2) Logical topology Physical topology This type of network is an actual layout of the computer cables and other network devices Logical topology Logical topology gives insight’s about network’s physical design. Different types of Physical Topologies are: P2P Topology Bus Topology
Difference between LAN, MAN and WAN LAN stands for local area network. It is a group of network devices that allow communication between various connected devices. Private ownership has control over the local area network rather than the public. LAN has a short propagation delay than MAN as well as WAN. It covers smaller areas such as colleges, schools, hospitals, and so on. MAN stands for metropolitan area network. It covers a larger area than LAN such as small towns, cities, etc. MAN connects two or more computers that reside within the same or completely different cities. MAN is expensive and should or might not be owned by one organization. WAN stands for wide area network. It covers a large area than LAN as well as a MAN such as country/continent etc. WAN is expensive and should or might not be owned by one organization. PSTN or satellite medium is used for wide area networks. Basis LAN MAN WAN Full-Form LAN stands for local area network. MAN stands for metropolitan area network. WAN stands for wide area network. Geographic Span Operates in small areas such as the same building or campus. Operates in large areas such as a city. Operates in larger areas such as country or continent. Ownership LAN’s ownership is private. MAN’s ownership can be private or public. While WAN also might not be owned by one organization. Transmission Speed The transmission speed of a LAN is high. While the transmission speed of a MAN is average. Whereas the transmission speed of a WAN is low. Propagation delay The propagation delay is short in a LAN. There is a moderate propagation delay in a MAN. Whereas, there is a long propagation delay in a WAN. Congestion There is less While there is more Whereas there is more
Basis LAN MAN WAN congestion in LAN. congestion in MAN. congestion than MAN in WAN. Design & Maintenance LAN’s design and maintenance are easy. While MAN’s design and maintenance are difficult than LAN. Whereas WAN’s design and maintenance are also difficult than LAN as well MAN. Fault tolerance There is more fault tolerance in LAN. While there is less fault tolerance. In WAN, there is also less fault tolerance. Medium CN What is the OSI Model? OSI stands for Open Systems Interconnection, where open stands to say non-proprietary. It is a 7-layer architecture with each layer having specific functionality to perform. All these 7 layers work collaboratively to transmit the data from one person to another across the globe. The OSI reference model was developed by ISO – ‘International Organization for Standardization‘, in the year 1984. The OSI model provides a theoretical foundation for understanding network communication. However, it is usually not directly implemented in its entirety in real-world networking hardware or software. Instead, specific protocols and technologies are often designed based on the principles outlined in the OSI model to facilitate efficient data transmission and networking operations Data Flow In OSI Model When we transfer information from one device to another, it travels through 7 layers of OSI model. First data travels down through 7 layers from the sender’s end and then climbs back 7 layers on the receiver’s end. Data flows through the OSI model in a step-by-step process: Application Layer: Applications create the data. Presentation Layer: Data is formatted and encrypted. Session Layer: Connections are established and managed.
Physical Layer – Layer 1 The lowest layer of the OSI reference model is the physical layer. It is responsible for the actual physical connection between the devices. The physical layer contains information in the form of bits. It is responsible for transmitting individual bits from one node to the next. When receiving data, this layer will get the signal received and convert it into 0s and 1s and send them to the Data Link layer, which will put the frame back together. Functions of the Physical Layer Bit Synchronization: The physical layer provides the synchronization of the bits by providing a clock. This clock controls both sender and receiver thus providing synchronization at the bit level. Bit Rate Control: The Physical layer also defines the transmission rate i.e. the number of bits sent per second. Physical Topologies: Physical layer specifies how the different, devices/nodes are arranged in a network i.e. bus, star, or mesh topology. Transmission Mode: Physical layer also defines how the data flows between the two connected devices. The various transmission modes possible are Simplex, half-duplex and full-duplex. Data Link Layer (DLL) – Layer 2 The data link layer is responsible for the node-to-node delivery of the message. The main function of this layer is to make sure data transfer is error-free from one node to another, over the physical layer. When a packet arrives in a network, it is the responsibility of the DLL to transmit it to the Host using its MAC address. Logical Link Control (LLC) Protocol Data Unit Logical Link Control (LLC) is a sublayer that generally provides the logic for the data link as it controls the synchronization, multiplexing, flow control, and even error-checking functions of DLL (Data Link Layer). DLL is divided into two sublayers i.e. LLC sublayer and MAC (Medium Access Control) sublayer. The basic model of LLC protocols is modeled after the HDLC (High-Level Data Link Control). These protocols are unacknowledged connectionless service, Connection-oriented service, and acknowledged connectionless service. All of these protocols use the same PDU (Protocol Data Unit) format as shown –
This PDU format basically contains 4 different fields given below –
- Destination Service Access Point (DSAP) Field – DSAP is generally an 8-bit long field that is used to represent the logical addresses of the network layer entity meant to receive the message. It indicates whether this is an individual or group address.
- Source Service Access Point (SSAP) Field – SSAP is also an 8-bit long field that is used to represent the logical addresses of the network layer entity meant to create a message. It indicates whether this is a command or response PDU. It simply identifies the SAP that has started the PDU.
- Information Field – This field generally includes data or information.
- Control Field – This field identifies and determines the specific PDU and also specifies various control functions. It is an 8 or 16-bit long field, usually depending on the identity of the PDU. It is used for flow and error control. There are basically three types of PDU. Each PDU has a different control field format. These are given below – Information (I) – It generally includes 7-bit sequence number (N(S)) and also a piggybacked sequence number (N(R)). It is used to carry data or information. Supervisory (S) – It generally includes an acknowledgment sequence number (N(R)) and also a 2-bit S field for three different PDU formats i.e. RNR (Receive Not Ready), RR (Receive Ready), and REJ (Reject). It is generally used for flow and error control.
