Basic Networking Term

What is Network?

A computer network is a digital telecommunications network for sharing resources between nodes, which are computing devices that use a common telecommunications technology.
Data transmission between nodes is supported over data links consisting of physical cable media, such as twisted pair or fibre-optic cables, or by wireless methods, such as Wi-Fi, microwave transmission, or free-space optical communication.

Why we need network?

• The big reason to have a network as per above definition is to share resources. We want to share information or share some kind of resource with someone else.
• Now what is a resource in the old days.
• A common example of a resource would be a printer.
• If you had an office with 100 people in the office, you could buy a printer for every workstation or for every PC.
• And that's what they had to do before the days of networking. They either had to have a printer for every computer or have no printers or what they had to do is do something like this where they copy a file onto a floppy disk and then go over to the printing station and then print it manually.
• It makes much more sense to have a centralized resource in this case a printing resource and share that resource amongst the people in the office.
• So rather than having let's say 100 printers for 100 people you only let's say have 10 printers.
• So, you've reduced the cost by creating a shared resource a resource that can be shared by what are called clients. So, we have client devices or PCs in this example that are sharing a resource in this case a printer.

Why are we doing this?

• We are trying to share a resource between what in this definition is called a node and they define that as a computing device. So, a node is a computing device, and there are many types of computing devices.
• We could have Windows laptops.
• We could have Mac books.
• We could have phones.
• We could have servers.
• Those are often the devices that most consumers will think about.
• But in networking, we have specialized devices such as hubs, switches, routers, and firewalls.

Network Types

• Biggest network that we know of today, unless you know about aliens having a bigger network somewhere out there in space is the Internet.
• So, the Internet is the biggest network that we have on Earth today.
• But a network doesn't have to be very big.
• A small network would simply consist of two computers.
• For Example: We have two window laptops, most basic form a computer network will use something like a cable.
• Cable can be of many types such as copper ethernet cable, called as UTP or unshielded twisted pair copper cable or RJ45 cable, which is mostly used in old laptop nowadays.
• Now a Network Interface Card or NIC is how we connect to the physical network or wireless network.
• It's basically a card that's either inserted into a laptop or is built into a laptop that has what's called a MAC address or Media Access Control address on Ethernet which is the technology that we generally use today on wireless devices.
• We can consider an example of two mobile devices now, where we don’t have any RJ45 or USB port to connect cable. Also, it will be not efficient for user to use cable.
• So, to transfer data between two mobile devices nowadays, we use WIFI or Bluetooth, and data is transmitted through the medium air.
• This type of network is wireless network.

What is Server?

• In computing, a server is a computer program or a device that provides functionality for other programs or devices, called “clients”.
• This architecture is called the client-server model, and a single overall computation is distributed across multiple processes or devices.

So, servers provide functionality to clients and that begs the question what is a client?

• A client is a piece of computer hardware or software that accesses a service made available by a server. The server is often on another computer system in which case the client accesses the service by way of a network.
• Google as an example will have thousands upon thousands upon thousands of servers to service the requests from millions of clients. So, they will have many servers to service or provide a service to the clients.
• When you go to the Google Website, and you type in a request that's querying databases and retrieving information from databases to give you an answer about some query that you've made.
• So, the server is providing a service to a client.
• Now on a server, one physical computer will be listening on different port numbers for different protocols.

What is a protocol?

• It's basically a set of rules used for communication between devices.
• A server is not as clever as that. It has to listen on specific port numbers for specific protocols.
• If you want to get a web page your browser is automatically configured or programmed to talk to port 80 or to port for 443.
• If you're using an application like FTP the application is automatically going to talk to the server on Port 21 and the server is listening on Port 21.
• So, a server can run multiple services and provide multiple services to clients

Networking 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, router, access point and NIC, etc.

• 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 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 it bit by bit and regenerate it as it is. It is a 2-port device.
• 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.

Types of Hubs

• 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.
• 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.
• 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.

• Bridge – A bridge operates at the data link layer. A bridge is a repeater, with add on the functionality of filtering content by reading the MAC addresses of the 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 the source station and the frame specifies which route to follow. The host can discover the frame by sending a special frame called the discovery frame, which spreads through the entire network using all possible paths to the destination.

• 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, which makes it very efficient as it does not forward packets that have errors and forward good packets selectively to the correct port only.  In other words, the switch divides the collision domain of hosts, but the broadcast domain remains the same.

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

• Gateway – A gateway, as the name suggests, is a passage to connect two networks that may work upon different networking models. They work as 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 switches or routers. A gateway is also called a protocol converter.

• NIC – NIC or network interface card is a network adapter that is used to connect the computer to the network. It is installed in the computer to establish a LAN.  It has a unique id that is written on the chip, and it has a connector to connect the cable to it. The cable acts as an interface between the computer and the router or modem. NIC card is a layer 2 device which means that it works on both the physical and data link layers of the network model.

• Access Point - While an access point (AP) can technically involve either a wired or wireless connection, it commonly means a wireless device. 
• An AP works at the second OSI layer, the Data Link layer, and it can operate either as a bridge connecting a standard wired network to wireless devices or as a router passing data transmissions from one access point to another
• Wireless access points (WAPs) consist of a transmitter and receiver (transceiver) device used to create a wireless LAN (WLAN). 
• Access points typically are separate network devices with a built-in antenna, transmitter, and adapter. 
• APs use the wireless infrastructure network mode to provide a connection point between WLANs and a wired Ethernet LAN. 
• They also have several ports, giving you a way to expand the network to support additional clients. 
• Depending on the size of the network, one or more APs might be required to provide full coverage.