TCP/IP Modal

TCP/IP originated out of the investigative research into networking protocols that the US Department of Defense (DoD) initiated in 1969. In 1968, the DoD Advanced Research Projects Agency (ARPA) began researching the network technology that is called packet switching.
The original focus of this research was that the network is able to survive the loss of subnet hardware, with existing conversations not being broken off. In other words, DoD wanted connections to remain intact as long as the source and destination nodes were functioning, even if some of the machines or transmission lines in between were suddenly put out of operation. The network that was initially constructed as a result of this research to provide a communication that could function in wartime., then called ARPANET, gradually became known as the Internet. 
The TCP/IP protocols played an important role in the development of the Internet. In the early 1980s, the TCP/IP protocols were developed. In 1983, they became standard protocols for ARPANET. Because of the history of the TCP/IP protocol suite, it's often referred to as the DoD protocol suite or the Internet protocol suite.

Network Access Layer – The lowest layer of the TCP/IP protocol hierarchy. It defines how to use the network to transmit an IP datagram. Unlike higher-level protocols, Network Access Layer protocols must know the details of the underlying network (its packet structure, addressing, etc.) to correctly format the data being transmitted to comply with the network constraints. The TCP/IP Network Access Layer can encompass the functions of all three lower layers of the OSI Reference Model (Physical, Data Link and Network layers). 
As new hardware technologies appear, new Network Access protocols must be developed so that TCP/IP networks can use the new hardware. Consequently, there are many access protocols - one for each physical network standard. Access protocol is a set of rules that define how the hosts access the shared medium. Access protocol has to be simple, rational and fair for all the hosts. Functions performed at this level include encapsulation of IP datagrams into the frames transmitted by the network, and mapping of IP addresses to the physical addresses used by the network. One of TCP/IP's strengths is its universal addressing scheme. The IP address must be converted into an address that is appropriate for the physical network over which the datagram is transmitted. 

Internet layer – Provides services that are roughly equivalent to the OSI Network layer. The primary concern of the protocol at this layer is to manage the connections across networks as information is passed from source to destination. The Internet Protocol (IP) is the primary protocol at this layer of the TCP/IP model. 

Transport layer – It is designed to allow peer entities on the source and destination hosts to carry on a conversation, just as in the OSI transport layer. Two end-to-end transport protocols have been defined here TCP and UDP Both protocols will be discussed later.

Application Layer – includes the OSI Session, Presentation and Application layers. An application is any process that occurs above the Transport Layer. This includes all of the processes that involve user interaction. The application determines the presentation of the data and controls the session. There are numerous application layer protocols in TCP/IP, including Simple Mail Transfer Protocol (SMTP) and Post Office Protocol (POP) used for e-mail, Hyper Text Transfer Protocol (HTTP) used for the World-Wide-Web, and File Transfer Protocol (FTP). Most application layer protocols are associated with one or more port number.

Introduction to Computer Network

Broadcast Networks In computer networking, you will come across terms such as broadcasting and broadcast network. This article aims at providing you information such as what a broadcast network is, how it’s done and a brief introduction to multicasting.

What is A Broadcast Network? Have you ever heard of TV broadcasting? What does that mean? A TV program is broadcasted which means it's sent to everyone who has permission to receive and watch the program. Similarly, in a broadcast network, messages are sent and those messages are received by all computers in the network. How A Broadcast Network Works? The messages, termed as packets according to networking terminology, travel across the single shared medium for communication and are received by all computers. These messages will have address information regarding the intended recipient. Each computer, as it receives these packets, will analyze them and find out if it’s meant for them. If not, they simply ignore these packets. If they are the intended recipient, the packet is processed. This method can be applied in the following ways A packet sent to a single computer A packet sent to all computers in the network A packet sent to a select subgroup computer in a network We discussed how the broadcast network works for a single computer. For all computers in the network, the only difference is that, instead of one computer processing the packet, all computers will process the packet. This method is called broadcasting. The third method is sending the packet to a subgroup in a network. The subgroup can have 2 or more computers and each computer may be part of any number of subgroups. This is called multicasting. The first bit is reserved to indicate multicasting in a packet and the remaining n-1 bit in the address field is used to indicate the group to which the packet is to be sent. Point-To-Point Network A point-to-point network, compared to a broadcast network has many connections between computers. Often times, for a message to reach its destination, it has to traverse a number of intermediate computers. It’s kind of like a hierarchy like if you need to reach the president, you have to go through a number of other officials. We use broadcast networks for geographically small networks and point-to-point networks for larger networks.

In the case of point-to-point networks, routing algorithms play a major role in deciding the routes that the packet must take in order to reach the destination in the minimum amount of time. LAN - Local Area Network A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings. In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet. In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization. They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring. WAN - Wide Area Network As the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth. A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address. A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances. LAN, WAN and Home Networking Residences typically employ one LAN and connect to the Internet WAN via an Internet Service Provider (ISP) using a broadband modem. The ISP provides a WAN IP address to the modem, and all of the computers on the home network use LAN (so-called private ) IP addresses. All computers on the home LAN can communicate directly with each other but must go through a central gateway, typically a broadband router, to reach the ISP. Other Types of Area Networks While LAN and WAN are by far the most popular network types mentioned, you may also commonly see references to these others: Wireless Local Area Network - a LAN based on WiFi wireless network technology Metropolitan Area Network - a network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity such as a government body or large corporation. Campus Area Network - a network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus. Storage Area Network - connects servers to data storage devices through a technology like Fibre Channel. System Area Network - links high-performance computers with high-speed connections in a cluster configuration. Also known as Cluster Area Network.

OSI Modal

Learn what the Open Systems Interconnection (OSI) reference model is and how its seven layers of functions provide vendors and developers with a common language for discussing how messages should be transmitted between any two points in a telecommunication network. OSI (Open Systems Interconnection) is a reference model for how applications can communicate over a network. 

A reference model is a conceptual framework for understanding relationships. The purpose of the OSI reference model is to guide vendors and developers so the digital communication products and software programs they create will interoperate, and to facilitate clear comparisons among communications tools. Most vendors involved in telecommunications make an attempt to describe their products and services in relation to the OSI model. And although useful for guiding discussion and evaluation, OSI is rarely actually implemented, as few network products or standard tools keep all related functions together in well-defined layers as related to the model. 

The TCP/IP protocols, which define the Internet, do not map cleanly to the OSI model. Developed by representatives of major computer and telecommunication companies beginning in 1983, OSI was originally intended to be a detailed specification of actual interfaces. Instead, the committee decided to establish a common reference model for which others could then develop detailed interfaces, which in turn could become standards. OSI was officially adopted as an international standard by the International Organization of Standards (ISO). OSI layers The main concept of OSI is that the process of communication between two endpoints in a telecommunication network can be divided into seven distinct groups of related functions or layers. Each communicating user or program is at a computer that can provide those seven layers of function. So in a given message between users, there will be a flow of data down through the layers in the source computer, across the network and then up through the layers in the receiving computer. The seven layers of function are provided by a combination of applications, operating systems, network card device drivers and networking hardware that enable a system to put a signal on a network cable or out over Wi-Fi or other wireless protocol).

The seven Open Systems Interconnection layers are :

 Layer 7: The application layer.
This is the layer at which communication partners are identified (Is there someone to talk to?), network capacity is assessed (Will the network let me talk to them right now?), and that creates a thing to send or opens the thing received. (This layer is not the application itself, it is the set of services an application should be able to make use of direct, although some applications may perform application layer functions.) 

Layer 6: The presentation layer.
This layer is usually part of an operating system (OS) and converts incoming and outgoing data from one presentation format to another (for example, from clear text to encrypted text at one end and back to clear text at the other). 

Layer 5: The session layer.
This layer sets up, coordinates and terminates conversations. Services include authentication and reconnection after an interruption. On the Internet, Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) provide these services for most applications.

Layer 4: The transport layer. 
This layer manages packetization of data, then the delivery of the packets, including checking for errors in the data once it arrives. On the Internet, TCP and UDP provide these services for most applications as well. 

Layer 3: The network layer. 
This layer handles the addressing and routing of the data (sending it in the right direction to the right destination on outgoing transmissions and receiving incoming transmissions at the packet level). IP is the network layer for the Internet. 

Layer 2: The data-link layer. 
This layer sets up links across the physical network, putting packets into network frames. This layer has two sub-layers, the Logical Link Control Layer and the Media Access Control Layer. Ethernet is the main data link layer in use.

Layer 1: The physical layer. 
This layer conveys the bit stream through the network at the electrical, optical or radio level. It provides the hardware means of sending and receiving data on a carrier network.