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Layers of OSI Model

When most non-technical people hear the term “seven layers”, they either think of the popular Super Bowl bean dip or they mistakenly think about the seven layers of Hell, courtesy of Dante’s Inferno (there are nine). For IT professionals, the seven layers refer to the Open Systems Interconnection (OSI) model, a conceptual framework that describes the functions of a networking or telecommunication system.

Model of gathering information
This project is aimed at developing a decision-theoretic approach to information gathering from a large distributed network of information sources. The project is motivated by the rapid growth in on-line information sources such as digital libraries, independent news agencies, government agencies, as well as human experts providing a variety of services. A continued expansion of these services is expected over the next 5-10 years. In addition, improved information retrieval (IR) and information extraction (IE) techniques are becoming available, allowing a system not only to locate but also to extract necessary information from unstructured textual documents. The large number of information sources that are currently emerging and their different levels of accessibility, reliability and associated costs present a complex information gathering planning problem that a human decision maker cannot possibly solve.

Application layer protocols and service examples - Telnet - DNS - FTP - DHCP

Telnet
In a nutshell, Telnet is a computer protocol that was built for interacting with remote computers.

The word “Telnet” also refers to the command-line utility “telnet”, available under Windows OS and Unix-like systems, including Mac, Linux, and others. We will use the term “Telnet” mostly in the context of the telnet client software.

DNS
The Domain Name System (DNS) is the phonebook of the Internet. Humans access information online through domain names, like nytimes.com or espn.com. Web browsers interact through Internet Protocol (IP) addresses. DNS translates domain names to IP addresses so browsers can load Internet resources.

FTP
The File Transfer Protocol (DHCP) is a standard network protocol used for the transfer of computer files between a client and server on a computer network. FTP is built on a client-server model architecture using separate control and data connections between the client and the server.

DHCP
Dynamic Host Configuration Protocol (DHCP) is a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device's IP address can even change while it is still connected.

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The IP addresses can be classified into two. They are listed below.

1) Static IP addresses

2) Dynamic IP addresses

What is public IP address?

A public IP address is the address that is assigned to a computing device to allow direct access over the Internet. A web server, email server and any server device directly accessible from the Internet are candidate for a public IP address. A public IP address is globally unique, and can only be assigned to a unique device.

Special Addresses of Global Significance

Private Addresses

Reserved Addresses

nternet Protocol hierarchy contains several classes of IP Addresses to be used efficiently in various situations as per the requirement of hosts per network. Broadly, the IPv4 Addressing system is divided into five classes of IP Addresses. All the five classes are identified by the first octet of IP Address.

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Network Devices

(Hub, Repeater, Bridge, Switch, Router, Gateways and Brouter)

1. Repeater – A repeater operates at the physical layer. Its job is to regenerate the signal over the same network before the signal becomes too weak or corrupted so as to extend the length to which the signal can be transmitted over the same network. An important point to be noted about repeaters is that they do not amplify the signal. When the signal becomes weak, they copy the signal bit by bit and regenerate it at the original strength. It is a 2 port device.

2. Hub –  A hub is basically a multiport 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, collision domain of all hosts connected through Hub remains one.  Also, they do not have intelligence to find out best path for data packets which leads to inefficiencies and wastage.

Types of Hub

Active Hub:- These are the hubs which have their own power supply and can clean, boost and relay the signal along with the network. It serves both as a repeater as well as wiring centre. These are used to extend the maximum distance between nodes.

Passive Hub :- These are the hubs which collect wiring from nodes and power supply from 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.

3. Bridge – A bridge operates at data link layer. A bridge is a repeater, with add on the functionality of filtering content by reading the MAC addresses of source and destination. It is also used for interconnecting two LANs working on the same protocol. It has a single input and single output port, thus making it a 2 port device.

Types of Bridges

Transparent Bridges:- These are the bridge in which the stations are completely unaware of the
bridge’s existence i.e. whether or not a bridge is added or deleted from the network, reconfiguration of
the stations is unnecessary. These bridges make use of two processes i.e. bridge forwarding and bridge learning.

Source Routing Bridges:- In these bridges, routing operation is performed by source station and the frame specifies which route to follow. The hot can discover frame by sending a special frame called discovery frame, which spreads through the entire network using all possible paths to destination.

4. Switch – A switch is a multiport bridge with a buffer and a design that can boost its efficiency(a large number of ports imply less traffic) and performance. A switch is a data link layer device. The switch can perform error checking before forwarding data, that makes it very efficient as it does not forward packets that have errors and forward good packets selectively to correct port only.  In other words, switch divides collision domain of hosts, but broadcast domain remains same.

5. Routers – A router is a device like a switch that routes data packets based on their IP addresses. Router is mainly a Network Layer device. Routers normally connect LANs and WANs together and have a dynamically updating routing table based on which they make decisions on routing the data packets. Router divide broadcast domains of hosts connected through it.

other Devices

6. Gateway – A gateway, as the name suggests, is a passage to connect two networks together that may work upon different networking models. They basically work as the messenger agents that take data from one system, interpret it, and transfer it to another system. Gateways are also called protocol converters and can operate at any network layer. Gateways are generally more complex than switch or router.

7. Brouter – It is also known as bridging router is a device which combines features of both bridge and router. It can work either at data link layer or at network layer. Working as router, it is capable of routing packets across networks and working as bridge, it is capable of filtering local area network traffic.

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network protocol

A network protocol  defines rules and conventions for communication between network devices. Network protocols include mechanisms for devices to identify and make connections with each other, as well as formatting rules that specify how data is packaged into sent and received messages.

Internet Protocols

The Internet Protocol (IP) family contains a set of related (and among the most widely used) network protocols. Beside Internet Protocol itself, higher-level protocols like TCP, UDP, HTTP, and FTP all integrate with IP to provide additional capabilities. Similarly, lower-level Internet Protocols like ARP and ICMP also coexist with IP. In general, higher-level protocols in the IP family interact more closely with applications like web browsers, while lower-level protocols interact with network adapters and other computer hardware.

Wireless Network Protocols

Thanks to Wi-Fi, Bluetooth, and LTE, wireless networks have become commonplace. Network protocols designed for use on wireless networks must support roaming mobile devices and deal with issues such as variable data rates and network security.

Network Routing Protocols

Routing protocols are special-purpose protocols designed specifically for use by network routers on the internet. A routing protocol can identify other routers, manage the pathways (called routes) between sources and destinations of network messages, and make dynamic routing decisions. Common routing protocols include EIGRP, OSPF, and BGP.

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Transmission Mediums in Computer Networks

Data is represented by computers and other telecommunication devices using signals. Signals are transmitted in the form of electromagnetic energy from one device to another. Electromagnetic signals travel through vacuum, air or other transmission mediums to move from one point to another(from sender to receiver).

Electromagnetic energy (includes electrical and magnetic fields) consists of power, voice, visible light, radio waves, ultraviolet light, gamma rays etc.

Transmission medium is the means through which we send our data from one place to another. The first layer (physical layer) of Communication Networks OSI Seven layer model is dedicated to the transmission media, we will study the OSI Model lat

Factors to be considered while selecting a Transmission Medium

1. Transmission Rate

2. Cost and Ease of Installation

3. Resistance to Environmental Conditions

4. Distances

Network Topology list

Key Terms to Know

Mesh Topology

Star Topology

Bus Topology

Ring Topology

Tree Topology

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Computer Networks

A computer network consists of two or more computing devices that
are connected in order to share the components of your network.

Fundamental Elements of a Network

the modern data network has become a critical asset for many industries. Most basic data networks are designed to connect users and enable them to access various resources,
All data networks are comprised of these elements, and cannot function without them.

1. Hardware

The backbone of any network is the hardware that runs it. Network hardware includes network cards, routers or network switches, modems and Ethernet repeaters. Without this hardware, computers have no means of accessing a network.

1. Software

In order for the hardware to interact with the network, it needs software to issue commands. The primary form of networking software is protocols

1. Client Devices

Client devices are the computers and mobile devices connected to the network. Client devices are vital components of a network, as without clients requiring access the network is essentially pointless. In order to classify as a client device, a computer or mobile device must be able to connect to the network and utilize it. Depending on the network, client devices may also require specialized software to establish a connection.

1. Connection Media

Without connections, a network cannot function. The medium used to connect the nodes of a network varies with the type of network.