Wi-Fi Network:

Wi-Fi is a family of radio technologies commonly used for wireless local area networking (WLAN) of devices. It is based on the IEEE 802.11 family of standards. Devices that can use Wi-Fi technologies include desktops and laptops, smart phones and tablets, smart TVs, printers, digital audio players, digital cameras, cars and drones.

Compatible devices can connect to each other over Wi-Fi through a wireless access point as well as to connected Ethernet devices and may use it to access the Internet. Such an access point (or hotspot) has a range of about 20 meters (66 feet) indoors and a greater range outdoors.

Hotspot coverage can be as small as a single room with walls that block radio waves, or as large as many square kilometers achieved by using multiple overlapping access points.

Wi-Fi most commonly uses the 2.4 gigahertz (12 cm) UHF and 5 gigahertz (6 cm) SHF ISM radio bands; these bands are subdivided into multiple channels. Each channel can be time-shared by multiple networks.

These wavelengths work best for line-of-sight. Many common materials absorb or reflect them, which further restricts range, but can tend to help minimize interference between different networks in crowded environments.

Wi-Fi is potentially more vulnerable to attack than wired networks because anyone within range of a network with a wireless network interface controller can attempt access. Wi-Fi Protected Access (WPA) is a family of technologies created to protect information moving across Wi-Fi networks and includes solutions for personal and enterprise networks.

To connect to a Wi-Fi LAN, a computer must be equipped with a wireless network interface controller. The combination of computer and interface controllers is called a station.

A service set is the set of all the devices associated with a particular Wi-Fi network. The service set can be local, independent, extended or mesh.

Each service set has an associated identifier, the 32-byte Service Set Identifier (SSID), which identifies the particular network. The SSID is configured within the devices that are considered part of the network, and it is transmitted in the packets. Receivers ignore wireless packets from networks with a different SSID.

Wi-Fi nodes operating in ad-hoc mode refers to devices talking directly to each other without the need to first talk to an access point (also known as base station).

There are many different versions of Wi-Fi: 802.11a, 802.11b, 802.11g, 802.11n (Wi-Fi 4), 802.11h, 802.11i, 802.11-2007, 802.11-2012, 802.11ac (Wi-Fi 5), 802.11adj, 802.11af, 802.11-2016, 802.11ah, 802.11ai, 802.11aj, 802.11aq, 802.11ax (Wi-Fi 6), 802.11ay.

Generation	IEEE Standard	Maximum Link rate
Wi‑Fi 6	802.11ax	600–9608 Mbit/s
Wi‑Fi 5	802.11ac	433–6933 Mbit/s
Wi‑Fi 4	802.11n	72–600 Mbit/s

 

Equipment frequently supports multiple versions of Wi-Fi. To communicate, devices must use a common Wi-Fi version.

Uses:

Wi-Fi technology may be used to provide Internet access to devices that are within the range of a wireless network that is connected to the Internet.

Wi-Fi provides service in private homes, businesses, as well as in public spaces at Wi-Fi hotspots set up either free-of-charge or commercially, often using a captive portal webpage for access. Organizations and businesses, such as airports, hotels, and restaurants, often provide free-use hotspots to attract customers.

Routers that incorporate a digital subscriber line modem or a cable modem and a Wi-Fi access point, often set up in homes and other buildings, provide Internet access and internetworking to all devices connected to them, wirelessly or via cable.

Similarly, battery-powered routers may include a cellular Internet radio modem and Wi-Fi access point. When subscribed to a cellular data carrier, they allow nearby Wi-Fi stations to access the Internet over 2G, 3G, or 4G networks using the tethering technique. Some laptops that have a cellular modem card can also act as mobile Internet Wi-Fi access points.

Wi-Fi also connects places that normally don't have network access, such as kitchens and garden sheds. A number of other "wireless" technologies provide alternatives to Wi-Fi in some cases:

• Bluetooth, short distance network.
• Bluetooth Low Energy, a low-power variant.
• Zigbee, low-power, low data rate, and close proximity.
• Cellular networks, as used by smartphones.
• WiMax, provide wireless internet connection from outside individual homes.

Networking Devices : Repeater, Hub, Bridge, Router, Brouter and Modem

 

NETWORKING DEVICES:

 

A] Repeaters:

 

o   Repeaters are physical hardware devices that have a primary function to re generate the electric signal by:

1.    Reshaping the waveform

2.    Amplifying the waveform

3.    Retiming the signal

 

o   The purpose of a repeater is to extend the line segment beyond its physical limits.

 

o   A line segment is a logical path such as the logical was used by all 802.3 Ethernet types.

 

o   A line segment is given an identification number called a segment number or network number to differentiate it from other segments.

 

o   Typically repeaters are used to connect two physically close buildings together that are too far apart to just extend the segment.

 

o   They can be used to connect floors of a building together that would surface the maximum allowable segment length.

B] Hubs:

 

o   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.

 

o   Hub is a small box that connects together the signal from each individual device, optionally amplifies each signal, and then sends the signal out to all other connected devices.

 

o   Amplification helps to ensure that devices on the network receive reliable information.

 

o   Hubs are also called concentrators or repeaters.

 

o   They come in various sizes the most common being 12 port or 24 port.

 

o   There are three main points to remember about hubs:

 

1.     Many kinds of nodes can be connected to the hub with the networking cables.

2.     All Hubs can be uplink together, either with straight cable or crossover cable depending on whether or not the hub has a uplink port

3.     Performance will decrease as the number of users is increased.

 

o   Hubs cannot filter data, so data packets are sent to all connected devices.

 

o   Also, they do not have intelligence to find out best path for data packets which leads to inefficiencies and wastage.

 

o   When choosing a hub, the main consideration should be performance. Always remember that the network may expand in the future.  Try to buy a hub that has enough ports to allow for expansion without more hardware purchases.

 

Types of Hub:

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

2.    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 distance between nodes.

C] Bridges:

 

o   Bridges are both hardware and software devices.

 

o   They can be standalone devices - separate boxes specifically designed for bridging applications or they can be dedicated PCs with two NIC and bridging software.

 

o   A bridge operates at data link layer. A bridge is a repeater; with add on functionality of filtering content by reading the MAC addresses of source and destination.

o   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:

1.    Transparent Bridges: - These are the bridge in which the stations are completely unaware of the bridge’s existence. That is, 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.

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

D] Router:

 

o   A router is a device that forwards data packets along networks.

 

o   A router is connected to at least two networks, two LANs or WANs, or a LAN and its ISP’s network.

 

o   Routers are located at gateways, the places where two or more networks connect and are the critical device that keeps data flowing between networks and keep the networks connected to the internet.

 

o   When data is sent between locations on one network or from one network to a second network the data is always seen and directed to the correct location by the router.

 

o   They complete this by using headers and forwarding tables to determine the best path for forwarding data packets and they use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.

 

o   Routers are physical devices that join multiple wired or wireless networks together.

 

o   By maintaining configuration information in the routing table, wired or wireless routers also have the ability to filter traffic either incoming or outgoing based on the IP addresses of the senders and receivers.

 

o   Router translates information from one network to another; it is similar to a super intelligent bridge. 

 

o   Routers select the best path to route a message, based on the destination address and origin.

 

o   The router can direct traffic to prevent head on collision and is smart enough to know when to direct traffic along back roads and shortcuts.

 

E] Brouter:

 

o   They are protocol dependent devices.

 

o   When brouter receives a frame to be forwarded to the remote segment, it checks to see if it recognizes the network layer protocol.

 

o   If the brouter does, it acts like a router and finds the shortest path.

 

o   If it doesn't recognize the network layer protocol all it acts like a bridge and forwards the frame to the next segment.

 

o   The key advantage of them is that they have the ability to act as both a bridge and a router.

 

o   It can replace separator bridges and routers, thus, saving money.

F] Modem:

 

o   A modem (modulator-demodulator) is a hardware device that converts data into a format suitable for a transmission medium so that it can be transmitted from computer to computer (over telephone wires).

 

o   A modem modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information.

 

o   The goal is to produce a signal that can be transmitted easily and decoded reliably to reproduce the original digital data.

 

o   A common type of modem is one that turns the digital data of a computer into modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data.

o   Modems are generally classified by the maximum amount of data they can send in a given unit of time, usually expressed in bits per second (symbol bit(s), sometimes abbreviated "bps") or rarely in bytes per second (symbol B(s)).

 

o   Modems can also be classified by their symbol rate, measured in baud. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal.

 

o   There is one standard interface for connecting external modems to computers called RS-232. Consequently, any external modem can be attached to any computer that has an RS-232 port, which almost all personal computers have.

 

 

o   There are also modems that come as an expansion board that you can insert into a vacant expansion slot. These are sometimes called onboard or internal modems.

 

 

Types of Modem:

a)    Dial-Up Modems:

Modems used on dial-up networks convert data between the analog form used on telephone lines and the digital form used on computers. An external dial-up modem plugs into a computer at one end and a telephone line on the other end.

b)    Broadband Modems:

A broadband modem like those used for DSL or cable internet access uses advanced signaling techniques to achieve dramatically higher network speeds than earlier-generation dial-up modems. Broadband modems are often referred to as high-speed modems. Cellular modems are a type of digital modem that establishes Internet connectivity between a mobile device and a cell phone network.

External broadband modems plug into a home broadband router or other home gateway device on one end and the external Internet interface such as a cable line on the other.

The router or gateway directs the signal to all the devices in the business or home as needed. Some broadband routers include an integrated modem as a single hardware unit.

Computer Network Topologies : Bus, Star, Ring, Mesh and Hybrid

 

Networks & Network Topologies:

 

o   A computer network is a digital telecommunications network which allows nodes to share resources.

o   In computer networks, computing devices exchange data with each other using connections (data links) between nodes.

o   These data links are established over cable media such as wires or optic cables, or wireless media such as Wi-Fi.

o   Network computer devices that originate, route and terminate the data are called network nodes.

o   Nodes are generally identified by network addresses, and can include hosts such as personal computers, phones, and servers, as well as networking hardware such as routers and switches.

o   Two such devices can be said to be networked together when one device is able to exchange information with the other device, whether or not they have a direct connection to each other.

 

 

v  NETWORK TOPOLOGIES:

 

o   Network topology is the arrangement of the elements (links, nodes, etc.) of a communication network.

o   Network topology is the topological structure of a network and may be depicted physically or logically. It is an application of graph theory^.

o   Physical topology is the placement of the various components of a network (e.g., device location and cable installation), while logical topology illustrates how data flows within a network.

o   Distances between nodes, physical interconnections, transmission rates, or signal types may differ between two different networks, yet their topologies may be identical.

 

   Bus Topology:

 

o   It is often used when a network installation is a small, simple or temporary.

o   A bus topology is characterized by a main trunk or backbone line with a network computers attached at intervals along the trunk line.

o   This topology type is considered a passive topology because the computers on a bus just sit and listen.

o   When they hear a data on the wire that belongs to them, they accept that data.  When they are ready to transmit, they make sure no one else on the bus is transmitting and they send their packets of information.

o   Typically used coaxial networking cables hooked to each computer using a T- connector.

o   Each end of the network is terminated using a terminator specific to cable type.

o   Bus network are easy to assemble and are easy to extend.

o   They require a fairly limited amount of cabling when compared to other topologies.

o   Bus networks are prone to cable breaks, loose connectors and cable shorts that can be very difficult to troubleshoot.

 

Advantages:

 

1.    The bus is simple, reliable in very small networks, easy to use and easy to understand.

2.    It requires the least amount of cable to connect the computers together and hence it is less expensive.

3.    It is easy to extend a bus. Two cables can be joined into one longer cable with a device called a barrel connector. This makes a long cable and allows more computers to join the network.

 

Disadvantages:

 

1.    Heavy network traffic can slow a bus considerably since only one computer at a time can send a message.

2.    Barrel connector used to extend a bus weakens the electric signal.  Too many of them may prevent the signal from being correctly received all along the bus.

3.    Cable break or loose connector causes reflection and stops all network activity.

Star Topology:

 

o   In a star topology, all the cables run from the computers to a central location, where they all are connected by a device called a hub.

o   Each computer on network communicates with a central hub that resends the message either to all the computers or only to the destination computer.

o   Star Network is easily expandable with the main limiting factor being the number of ports available on the hub.

 

Advantages:

 

1.    It is easy to modify and add new computers to star network without disturbing the rest of the network.

2.    If there is a fault in the network then it can be fixed only by fixing the central hub and not affecting any other computers.

3.    Single computer failure does not necessarily bring down the whole star network.  The hub can detect the fault and can isolate the faulty computer.

 

Disadvantages:

 

1.    If the central hub fails, the whole network fails to operate.

2.    Star networking is expensive because all network cables must be pulled to one central point, required more cable than other network topologies.

Bus Topology vs. Star Topology:

Bus Topology	Star Topology
Has a backbone.	Doesn't have backbone.
Bus network doesn't use any hub.	Star network use central hub.
If the backbone fails, the network will fail.	If hub fails, the network will fail.
Bus network users to Terminator at both end of cable.	As cables are connected to hub there are many Terminators.
It is not much fault tolerant and as it is difficult to find problem in cable.	Star topology network is fault tolerant.  If not is not working then can check Central hub.
In this topology BNC-T connector are used to connect coaxial cable.	In this topology RJ-45 connector are used to connect Central hub and node.
Difficult to add more nodes.	Easy to add more nodes.
Less expensive.	More expensive as hub is used.
More number of collisions occurs.	Less number of collisions occurs.
Not widely used in network.	Widely used in network.
Bus topology is used only in LAN.	Star topology is used in both LAN and WAN.

Ring Topology:

 

o   Ring topology is one in which the network is a loop where data is passed from one workstation to another.

o   In ring topology, each computer is connected to the next computer, with the last one connected to the first.

o   When a message is sent, each of the computers in the network receives the information from its previous one and retransmits it to the next one.

o   The message flow around the ring in one direction.

o   Some ring networks do token passing. A short message called token is passed around the ring.

o   When a computer wants to send a message it modifies and add the token and send it to the destination computer through the ring.

o   Token ring networks are defined by IEEE 802.5 and were primary developed by IBM.

o   The token ring network is designed to transmit a token, are special frame design to go from node to node around the ring.

o   As the frame passes, if workstation needs to transmit data, it modifies the frame, attaches its data and sends it on.

o   If the data is intended for the next workstation on the network, it receives the data and the information stops at that work station.  If it is intended for somewhere else on the network, the data is transmitted around the ring until it finds its intended location.

o   Once the data find its new home, a blank token is transmitted and another workstation can attach data and then that data travels around the ring.

o   There is a token holding timer to prevent a workstation from transmitting too much data.  This protocol ensures all workstations on the network get an opportunity to send a data.

o   Fast token ring networks can transmit up to 1 Gbps.

 

Advantages:

 

·         It include a 4K maximum frame size, longer distance capabilities than Ethernet, and each station is guaranteed  access to a token at some point.

 

 Disadvantages:

 

·         It is difficult to troubleshoot and the failure of one computer on the ring can disrupt the data flow.

·         Also adding or removing computers from this type of topology can disrupt the operation of the network.

Mesh Topology:

 

o   A mesh network topology has a link between each device in the network.

o   In mesh topology each device is connected to every other device on the network through a dedicated point-to-point link.

o   When we say dedicated it means that the link only carries data for the two connected devices only.

o   Let’s say we have ‘n’ devices in the network then each device must be connected with (n-1) devices of the network. Number of links in a mesh topology of n devices would be n (n-1)/2.

 

Advantages:

 

·         No data traffic issues as there is a dedicated link between two devices which means the link is only available for those two devices.

·         Mesh topology is reliable and robust as failure of one link doesn’t affect other links and the communication between other devices on the network.

·         Mesh topology is secure because there is a point to point link thus unauthorized access is not possible.

·         Fault detection is easy.

 

Disadvantages:

 

·         Amount of wires required to connect each system is tedious and headache.

·         Since each device needs to be connected with other devices, number of I/O ports required must be huge.

·         Scalability issues, because a device cannot be connected with large number of devices with a dedicated point to point link.

Hybrid Topology:

A combination of two or more topology is known as hybrid topology. For example a combination of star and mesh topology is known as hybrid topology.

 

Advantages:

 

1. We can choose the topology based on the requirement for example, scalability is our concern then we can use star topology instead of bus technology.

2. Scalable as we can further connect other computer networks with the existing networks with different topologies.

 

Disadvantages:

 

1. Fault detection is difficult.

2. Installation is difficult.

3. Design is complex, so maintenance is high, thus, expensive.