What is Wifi technology? How does it work?

- Wifi has emerged as a very popular technology. 

- This technology has enabled the electronic devices to exchange information between them and to share the internet connection without using any cables or wires. 

- It is a wireless technology. 

- This technology works with the help of the radio waves. 

- The Wifi is defined as a WLAN (wireless local area network) product by the wifi alliance that is based on the standards defined by IEEE (802.11 standards). 

- Most of the WLANs are based upon these standards only and so this technology has been named as wifi which is the synonymous with the term WLAN. 

- The wifi-certified trademark might be used by only those wifi products which have the complete certification for the wifi alliance inter-operability. 

- A number of devices now use wifi such as the PCs, smart phones, video game consoles, digital cameras, digital audio players, tablet computers and so on. 

- All these devices can connect to the network and access internet by means of a wireless network access point. 

- Such an access point is more commonly known as a ‘hotspot’. 

- The range of an access point is up to 20 m. 

- But it has a much greater range outside.  

- An access point can be installed in a single room or in an area of many square miles. 

- This can be achieved by using a number of overlapping access points. 

- However, the security of the wifi is less compared to the wired connections for example Internet.

- This is so because a physical connection is not required by an intruder. 

- The web pages using SSL have security but the intruders can easily access the non-encrypted files on the internet. 

- It is because of this, that the various encryption technologies have been adopted by the wifi. 

- The earlier WEP encryption was weak and so was easy to break.

- Later, came the higher quality protocols such as the WPA2 and WPA. 

- The WPS or the wifi protected set up was an optional feature that was added in the year of 2007. 

- This option a very serious flaw which is that it allowed the recovery of the password of the router by an attacker.

- The certification and the test plan has been updated by the wifi alliance for ensuring that there is resistance against attacks in all the devices that have been newly certified.

- For connecting to a wifi LAN, a wireless network interface controller has to be incorporated in to the computer system.

- This combination of the interface controller and the computer is often called as the station. 

- The same radio frequency communication channel is shared by all the stations.

- Also, all the stations receive any transmission on this channel. 

- Also, the user is not informed of the fact that the data was delivered to the recipient and so is termed as the ‘best–effort delivery mechanism’. 

- For transmitting the data packets, a carrier wave is used. 

- These data packets are commonly known as the ‘Ethernet frames’. 

- Each station regularly tunes in to the radio frequency channel for picking up the transmissions that are available. 

- A device that is wifi enabled can connect to the network if it lies in the range of the wireless network. 

- One condition is that the network should have been configured for permitting such a connection. 

- For providing coverage in a large area multiple hotspots are required. 

- For example, wireless mesh networks in London. 

- Through wifi, services can be provided in independent businesses, private homes, public spaces, high street chains and so on. 

- These hotspots have been set up either commercially or free of charge. 

- Free hotspots are provided at hotels, restaurants and airports. 

Explain the concept of inter-networking?

- The practice in which one computer network is connected with the other networks is called inter-networking. 

- The networks are connected with the help of gateways. 

- These gateways are used since they offer a common method for routing the data packets across the networks.

- The resulting system in which a number of networks are connected is called the inter-network or more commonly as the internet. 

- The terms “inter” and “networking” combine together to form the term “internet working”.  

- Internet is the best and the most popular example of the inter networking. 

- Internet has formed as a result of many networks connected with the help of numerous technologies. 

- Many types of hardware technologies underlie the internet. 

- The internet protocol suite (IP suite) is the inter networking protocol standard responsible for unifying the diverse networks. 

- This protocol is more commonly known as the TCP/ IP. 

- Two computer local area networks (LANs) connected to one another by means of a router form the smallest internet but not the inter network. 

- Inter networking is not formed by simply connecting two LANs together via a hub or a switch. 

- This is called expansion of the original local area network. 

- Inter networking was started as a means for connecting the disparate networking technologies. 

- Eventually, it gained widespread popularity because of the development needs of connecting many local area networks together through some kind of WAN (wide area network). 

- “Catenet” was the original term that was used for the inter network. 

- Inter network includes many types of other networks such as the PAN or personal area network. 

- Gateways were the network elements that were originally used for connecting various networks in predecessor of the internet called the ARPANET. 

- Today, these connecting devices are more commonly known as the internet routers. 

- There is a type of interconnection between the various networks at the link layer of the networking model. 

- This layer is particularly known as the hardware centric layer and it lies below the TCP/ IP logical interfaces level. 

Two devices are mainly used in establishing this interconnection:

Ø  Network switches and

Ø  Network bridges

- Even now this cannot be called as inter networking rather, the system is just a single and large sub-network. 

- Further, for traversing these devices no inter networking protocol is required. 

- However, it is possible to convert a single network in to an inter network. 

- This can be done by making various segments out of the network and also making logical divisions of the segment traffic using the routers. 

- The internet protocol suite has been particularly designed for providing a packet service. 

- This packet service offered by the IPS is quite unreliable. 

- The elements that maintain a network state and are intermediate in the network are avoided by the architecture. 

- The focus of the architecture is more on the end points of the active communication session.

- For a reliable transfer of the data, a proper transport layer protocol must be used by the applications. 

- One such protocol is the TCP (transmission control protocol) and it is capable of providing a reliable stream for communication. 

- Sometimes a simpler protocol such as the UDP (user datagram protocol) might be used by the applications. 

- The applications using this protocol carry out only those tasks for which reliable data delivery is not required or for which realtime is required. 

Examples of such tasks include voice chat or watching a video online etc. Inter networking uses two architectural models namely:

1. OSI or the open system interconnection model: This model comes with 7 layer architecture that covers the hardware and the software interface.
2. TCP/ IP model: The architecture of this model is somewhat loosely defined when compared with the OSI model. 

Introduction to Frame Relay

Frame relay is a synchronous HDLC protocol based network. Frame Relay is a standardized wide area networking technology that specifies the physical and logical link layers of digital telecommunications channels using a packet switching methodology. Data is sent in HDLC packets, referred to as "frames".
Frame relay technology was developed to specifically address these needs :
- A higher performance packet technology.
- Simpler network management.
- More reliable networks.
- Lower network costs.
- Integration of traffic from both legacy and LAN applications over the same physical network.

Advantages of Frame Relay

Frame Relay offers an attractive alternative to both dedicated lines and X.25 networks for connecting LANs to bridges and routers. The success of the Frame Relay protocol is based on the following two underlying factors:
- Because virtual circuits consume bandwidth only when they transport data, many virtual circuits can exist simultaneously across a given transmission line. In addition, each device can use more of the bandwidth as necessary, and thus operate at higher speeds.
- The improved reliability of communication lines and increased error-handling sophistication at end stations allows the Frame Relay protocol to discard erroneous frames and thus eliminate time-consuming error-handling processing.

These two factors make Frame Relay a desirable choice for data transmission; however, they also necessitate testing to determine that the system works properly and that data is not lost.

Network Bridging

Bridging is a forwarding technique used in packet-switched computer networks. Unlike routing, bridging makes no assumptions about where in a network a particular address is located. Instead, it depends on flooding and examination of source addresses in received packet headers to locate unknown devices. Once a device has been located, its location is recorded in a table where the MAC address is stored so as to preclude the need for further broadcasting. The utility of bridging is limited by its dependence on flooding, and is thus only used in local area networks.
A network bridge is a device which connects two parts of a network together at the data link layer (layer 2 of the OSI model).

Situations Where Bridging Is Appropriate :
- Connecting Networks.
- Filtering/Traffic Shaping Firewall.
- Network Tap.
- Layer 2 VPN : Two Ethernet networks can be joined across an IP link by bridging the networks to an EtherIP tunnel or a tap(4) based solution such as OpenVPN.
- Layer 2 Redundancy : A network can be connected together with multiple links and use the Spanning Tree Protocol to block redundant paths.

Advantages :
- Self-configuring.
- Isolate collision domain.
- Reduce the size of collision domain by micro segmentation in non-switched networks.
- Transparent to protocols above the MAC layer.
- LANs interconnected are separate, and physical constraints such as number of stations, repeaters and segment length don't apply.
- Helps minimize bandwidth usage.

Disadvantages :
- It does not limit the scope of broadcasts.
- It does not scale to extremely large networks.
- Buffering and processing introduces delays.
- Bridges are more expensive than repeaters or hubs.

Bridges - Basic Hardware Component

A bridge device filters data traffic at a network boundary. Bridges reduce the amount of traffic on a LAN by dividing it into two segments.A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges do send broadcasts to all ports except the one on which the broadcast was received.

Bridges inspect incoming traffic and decide whether to forward or discard it. Bridges serve a similar function as switches, that also operate at Layer 2. Traditional bridges, though, support one network boundary, whereas switches usually offer four or more hardware ports. Switches are sometimes called "multi-port bridges" for this reason.

Bridges come in three basic types:
- Local bridges: Directly connect local area networks (LANs)
- Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers.
- Wireless bridges: Can be used to join LANs or connect remote stations to LANs

Today, bridges are slowly but surely falling out of favor. Ethernet switches offer similar functionality; they can provide logical divisions, or segments, in the network. In fact, switches are sometimes referred to as multi-port bridges because of the way they operate.

Quick Tech Tip : Metropolitan Area Networks - MANs

A metropolitan area network, or MAN is basically a bigger version of LAN. MAN is a computer networks usually spanning a campus or a city, which typically connect a few local area networks using high speed backbone technologies. A MAN supports both data and voice. A MAN just has one or two cables and does not contain switching elements.
A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities. MANs can also depend on communications channels of moderate-to-high data rates. A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking of local networks. Metropolitan area networks can span up to 50km, with the devices being used such as modem and wire/cable devices.
The standard that has been adopted for MANs is called DQDB (Distributed Queue Dual Bus). DQDB consists of two unidirectional cables or buses to which all other computers are connected. Each bus has a head-end which initiates transmission activity.
There are three important features which discriminate MANs from LANs or WANs:
1. The network size falls intermediate between LANs and WANs. A MAN typically covers an area of between 5 and 50 km range. Many MANs cover an area the size of a city, although in some cases MANs may be as small as a group of buildings.
2. A MAN, its communications links and equipment are generally owned by either a consortium of users or by a network service provider who sells the service to the users.
3. A MAN often acts as a high speed network to allow sharing of regional resources. It is also frequently used to provide a shared connection to other networks using a link to a WAN.

Quick Tech Explanation: Local Area Networks - LANs

Local Area networks, generally called LANs, are privately owned networks within a single building or campus of up to a few kilometers in size. Most local area networks are built with relatively inexpensive hardware such as Ethernet cables, network adapters, and hubs. Wireless LAN and other more advanced LAN hardware options also exist as a part of modern LANs.
The most common type of local area network is an Ethernet LAN. If you look at size of LAN's, the smallest home LAN can have exactly two computers; a large LAN can accommodate many thousands of computers. Many of the larger LANs are divided into logical groups called subnets.

LANs are distinguished from other kinds of networks by three characteristics:
1. Size: LANs have a size limit and cannot expand beyond this size, essentially meaning that it is possible to plan and design for the worst case transmission time.
2. Topology: This is the geometric arrangement of devices on the network. For example, devices can be arranged in a ring or in a straight line. In a bus network, one machine is master and is allowed to transmit. An arbitration mechanism is needed to resolve conflicts when two or more machines want to transmit simultaneously.
In ring network, each bit propgates around on its own, not waiting for the rest of the packet to which it belongs.
3. Protocols: The rules and encoding specifications for sending data. The protocols also determine whether the network uses a peer-to-peer or client/server architecture.
4. Media: Devices can be connected by twisted-pair wire, coaxial cables, or fiber optic cables. Some networks do without connecting media altogether, communicating instead via radio waves.

Most LANs connect workstations and personal computers. Each node (individual computer) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data. Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions.

LANs are capable of transmitting data at very fast rates, much faster than data can be transmitted over a telephone line; but the distances are limited, and there is also a limit on the number of computers that can be attached to a single LAN.

Introduction to Routers

A computer networking device which forwards data packets across a network toward their destinations, through a process of routing is known as Router. In companies and large corporations, a central computer system acts as a router to connect all of the company's computers to one network. This allows group participation and collaboration on large projects or just to connect all of the company's resources at one central location. It also aids in reliable communication between employees working on different floors in the building or in different countries.

1. Router is required to connect multiple networks, like your LAN to the Internet.
2. Routers store large tables of networks and addresses, then using algorithms to determine the shortest routes to individual addresses within those networks.
3. Routers not only facilitate intra-network communications, but also play a role in overall network performance.
4. Routers help in delivering the information faster.
5. Routers also protect LAN from Internet.
6. Router blocks any packet that has a destination address outside of the LAN. If the destination address is valid, the router could check the Packet for an error. If there is an error, the router could discard the Packet and send a message to the originating address.
7. Routers have address translation and filtering capabilities.