Computer Networking – Basic
Before you start proceeding with the tutorial on computer network, it is important to understand the terms that you will see throughout this guide regarding networking.
Common networking terms:
Each device on a network, is called a node. A node may be a computer, laptop or printer or any input and output device.
A network host is a computer or other device connected to a computer network. A network host may offer information resources, services, and applications to users or other nodes on the network.
Network Interface Card(NIC):
A network interface card is a computer circuit board or card that is installed in a computer that connects to the network.
Network operating system (NOS):
It is an operating system that coordinates the activities of multiple computers across a network. It is designed to runs on a server and enables the server to manage data, users, groups, security, applications, and other networking functions.
LAN (Local Area Network):
A local area network (LAN) is a computer network that interconnects computers within a limited area such as a home, school, computer laboratory, or office building, using network media.
WAN (Wide Area Network):
A wide area network (WAN) is a network that covers a broad area (i.e., any telecommunications network that links across metropolitan, regional, national or international boundaries) using leased telecommunication lines.
A protocol is a set of rules and standards that basically define a language that devices can use to communicate.
IP (Internet Protocol):
The Internet Protocol is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internet working, and essentially establishes the Internet.
TCP (Transmission Control Protocol)
Transmission control protocol (TCP) is a network communication protocol designed to send data packets over the Internet. TCP is a transport layer protocol in the OSI layer.
FTP (File Transfer Protocol):
The File Transfer Protocol (FTP) is a standard network protocol used to transfer computer files from one host to another host over a TCP-based network, such as the Internet.
DNS (Domain Name System):
The Domain Name System (DNS) is a distributed naming system for computers, services, or any resource connected to the Internet or a private network. The DNS translates Internet domain and host names to IP addresses. DNS automatically converts the names we type in our Web browser address bar to the IP addresses of Web servers hosting those sites.
A computer network is a set of computers and computerized peripherals connected together for the purpose of sharing resources.
Computers may connect to each other by wired media or wireless media.
Types of Networks:
Generally networks are classified based on their geographical span –
1) LAN (Local Area Network):
A local area network (LAN) is a computer network that interconnects computers within a limited area such as a home, school, computer laboratory, or office building, using network media. In a LAN computers in the network can be from few to hundreds.
LAN provides a useful way of sharing resources between end users. Resources like Printers, File Servers, Scanners and internet is easy sharable among computers. LAN can be wired or wireless or in both forms at once.
The most popular local area networking protocol today is Ethernet.
2) MAN (Metropolitan Area Network):
A metropolitan area network (MAN) is computer network larger than a local area network, covering an area of city or a large campus. It is used by big organization to connect all of its offices within city.
A Metropolitan Area Networks bridges a number of LAN with a fiber-optical links which act as a backbone, and provides services similar to what Internet Service Provider (ISP) provide to Wide Area Networks and the Internet.
2) WAN (Wide Area Network):
A wide area network (WAN) is a network that covers a broad area (i.e., any telecommunications network that links across metropolitan, regional, national or international boundaries) using telephone systems, fiber-optic cables, and satellite links or leased lines. The Internet is also a WAN which is the largest WAN in a world.
Network topology is the arrangement of the various elements (links, nodes, etc.) of a computer network. Essentially, it is the topological structure of a network and may be depicted physically or logically.
Network topologies are categorized into the following basic types:
Point-to-point (PTP) topology connects two nodes directly together using a single piece of cable. The example of pure point to point links is two computers communicating via modems.
2) Bus Topology:
Bus topology is the cheapest way of connecting computers used by small organization in which device are connected to a single cable. In Bus Topology, each node is directly connected to a cable.
- Bus Topology is less expensive.
- It is easy to use and understand.
- It’s easy to connect a computer or device.
- It is easy to extend a network.
- In a heavy network, it becomes slow.
- The entire network shuts down if there is a break in the main cable.
3) Star Topology:
In a star network all nodes are connected to a device, which may be a hub, a router or a switch. This central device is acting as a server and other nodes are as clients. Every communication is pass through this central device. In star network, devices typically connect to the hub with Unshielded Twisted Pair (UTP).
- Unlike Bus Network, the failure of a single node or cable doesn’t affect the entire network.
- Easy to add another workstation to the network.
- By using centralized networking device, it reduces cost.
- Failure of the central device will causes the whole network failure.
4) Ring Topology:
In ring topology,each node is connected to exactly two other nodes, creating a circular network structure. Each packet is sent in one direction on a ring until it reaches its final destination.
- It eliminates the cost of using central host.
- It continue to function after capacity is exceeded but the speed will be slow.
- Failure of any node in the network, can affect the whole network.
- To add or remove any node will disrupts the network.
5) Mesh Topology:
A mesh network uses a network topology in which each node (called a mesh node) relays data for the network. In this type, a host is connected to one or two or more than two hosts. All nodes cooperate in the distribution of data in the network.
- Main advantage of mesh topology is fault tolerance, mean if there is any cable breaks then traffic can be routed through different path.
- As it uses multiple pathways, if required additional cabling and network interfaces.
- It is very hard to manage.
6) Tree Topology:
It is also known as Hierarchical Topology. A tree topology is essentially a combination of bus topology and star topology. This topology divides the network in to multiple levels/layers of network
It has a root node, intermediate nodes, and ultimate nodes. This structure is arranged in a hierarchical form and any intermediate node can have any number of the child nodes.
An example of this network could be cable TV technology. Other examples are in dynamic tree based wireless networks for military, mining and otherwise mobile applications.
- It is scalable. Secondary nodes allow more devices to be connected to a central node.
- Point to point connection of devices.
- Having different levels of the network makes it more manageable hence easier fault identification and isolation.
- Maintenance of the network may be an issue when the network spans a great area.
- Since it is a variation of bus topology, if the backbone fails, the entire network is crippled.
7) Hybrid Topology:
Hybrid topology is the interconnection of two or more basic topologies, each of which is laid out so the resulting network does not display a standard topology. Internet is the best example of largest Hybrid topology.
Introduction to OSI Reference Model
The OSI model defines the basic building blocks of computer networking, and is an essential part of a complete understanding of modern TCI/IP networks.
Network Model Overview:
An understanding of the concepts of the OSI model is absolutely necessary for someone learning the role of the Network Administrator or the System Administrator.
There is a set of rules for the communication process for one computer to send information to another computer and for that computer to receive and understand this information. There is a standard that ensure that every devices and products can communicate with each other over any network. This set of standards is called a model.
The OSI Model was developed by the International Organization for Standardization (ISO) in 1978 and was published in 1984. Open System Interconnect is an open standard for all communication systems.
This model is divided into 7 layers, and each layer has a distinctive job in the communication process. Here is a look at each layer from a top-down –
Here is a look at each layer from a top-down –
1) Application Layer:
This layer supports application and end-user processes. This layer interacts with software applications that implement a communicating component. This layer ensures that effective communication with another application program in a network is possible. This layer provides application services for file transfers, e-mail, and other network software services.
This layer is responsible for providing interface to the application user. This layer encompasses protocols which directly interacts with the user.
Some of the better-known Application layer protocols are
- DNS (Domain Name System) for resolving Internet domain names.
- FTP (File Transfer Protocol) for file transfers.
- SMTP (Simple Mail Transfer Protocol) for e-mail.
- SMB (Server Message Block) for file sharing in Windows networks.
- NFS (Network File System) for file sharing in Unix networks.
- Telnet for terminal emulation.
2) Presentation Layer:
The presentation layer takes the data from the application format, and then transforms data into the form that the application accepts. This layer formats and encrypts data to be communicated in different formats via different sources.
3) Session Layer:
The session layer controls the dialogues (connections) between computers. It establishes, manages and terminates the connections between the local and remote application. It provides for full-duplex, half-duplex, or simplex operation, and establishes checkpointing, adjournment, termination, and restart procedures.
4) Transport Layer:
The Transport layer is primarily concerned with end-to-end connection reliability. The transport layer controls the reliability of a given link through flow control, segmentation/desegmentation, and error control. Transport layer can keep track of the segments and retransmit those that fail.
The transport layer also provides the acknowledgement of the successful data transmission and sends the next data if no errors occurred. The transport layer creates packets out of the message received from the application layer. Packetizing is a process of dividing the long message into smaller messages.
5) Network Layer:
Network Layer Handles routing of data across network segments. The network layer establishes the route between the sender and receiver across switching points, which are typically routers. Network Layer provides data routing paths for network communication and for that it selects and manages the best logical path for data transfer between nodes.
6) Data Link Layer:
The data link layer provides a reliable link between two directly connected nodes, by detecting and possibly correcting errors that may occur in the physical layer. It makes sure each packet created by the networking layer is transmitted successfully. If an error occurs during transmission, it is corrected and retransmitted.
The data link layer is divided into two sublayers:
Media Access Control (MAC) layer – responsible for controlling how devices in a network gain access to data and permission to transmit it.
- Logical Link Control (LLC) layer – controls error checking and packet synchronization.
- The Point-to-Point Protocol (PPP) is an example of a data link layer in the TCP/IP protocol stack.
This layer is responsible for reading and writing data from and onto the line. Link errors are detected at this layer.
7) Physical Layer:
The physical layer consists of the basic networking hardware transmission technologies of a network. It defines the electrical and physical specifications of the data connection. It defines the relationship between a device and a physical transmission medium.
The physical layer is responsible for various encoding and signaling functions that transform the data from bits that reside within a computer or other device into signals that can be sent over the network.