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A metropolitan area network (MAN) is a high-speed network that connects local area networks in a metropolitan area such as a city or town and handles the volume of communications activity across that region. A MAN typically includes one or more LANs, but covers a smaller geographic area than a WAN. A MAN usually is managed by a group of users or by a single network provider that sells the service to the users. Local and state governments, for example, regulate some MANs. Telephone companies, cable television operators, and other organizations offer users with connections to the MAN.
A wide area network (WAN) is a network that covers a huge geographic area (such as a city, country, or the world) using a communications channel that combines many types of transmission media such as telephone lines, cables, and radio waves. A WAN can be one large network or can consist of two or more LANs connected together. The Internet is the world's largest WAN.
Typically, a WAN consists of a number of interconnected switching nodes. A transmission from any one device is routed through these internal nodes to the particular destination device. These nodes (including the boundary nodes) are not concerned with the content of the data. Their purpose is to provide a switching ability that will move the data from node to node until they reach their destination.
In a circuit-switched network, a dedicated transmission path is created between two stations through the nodes of the network. That path is a connected sequence of physical links between nodes. On each link, a logical channel is dedicated to the connection. Data send by source, passes through dedicated path rapidly. At each node, received data are routed or switched to the proper outgoing channel. Common example of circuit switching is the telephone network.circuit-switching.jpg
Circuit switching in telephone network 
Packet-switched network is quite different. In this scenario, it is not necessary to dedicate transmission capacity along a path through the network. Rather, data is transmitted in a sequence of small chunks, called packets. Each packet passes through the network from one node another. At each node, the entire packet is received, stored briefly and then forward to next destination. Common uses are terminal-to-computer and computer-to-computer communications.packet-switching.jpg
Packet switching in telephone network 
Frame Relay is a standardized WAN technology. Network provider uses Frame Relay for voice and data as an encapsulation method, used between LANs over a WAN. Each end-user takes leased line to a frame-relay node. The frame-relay network controls the transmission over a consistently-changing path transparent to all end-users. Frame Relay has become one of the most widely used WAN protocols.Frame_relay.jpg
Frame relay diagram 
Asynchronous Transfer Mode (ATM) uses fixed length packets, called cells, which works in the range of 10s and 100s of Mbps as compared to 2 Mbps target of frame relay. ATM can offer a constant-data-rate path even though it is using a packet-switching method and also extends circuit switching to allow several channels with the data rate on each channel dynamically set on demand.
ATM diagram 
The Topology is the geometric representation of the relationship of the links and the linking devices (Nodes) in a Network.
2.1 NETWORK TOPOLOGY
A network topology refers to the arrangement of the computers and devices in a communications network.
2.2 TYPES OF NETWORK TOPLOGY
There are five different types of network topologies which help to communicate two or more devices by linking them, which are following:
2.2.1 MESH TOPOLOGY
Every device has a dedicated point-to-point link to every other device in a "Mesh Topology". The term "dedicated" means that the link carries traffic only between the two devices it connects.
Advantages of Mesh Topology
There are several advantages of Mesh Topology which are following:
Use of dedicated links guarantees that each connection can carry its own load. This technique eliminates traffic problems as in case of shared link.
Mesh Topology is robust because if one link fails, it does not affect other.
Security & Privacy are major components due to dedicated links.
Point-to-point connection makes fault identification easy and recovery is very rapid.
Disadvantages of Mesh Topology
There are several disadvantages of Mesh Topology which are following:
Amount of cabling makes installation & reconfiguration very difficult and huge wiring can be greater than the available space.
Number of I/O ports required.
Hardware required to connect each link can be prohibitively expensive.
Mesh Topology Diagram 
Wireless Mesh Networks
Wireless Mesh Networks are based on the radio frequencies and was originally developed by army to be able to communicate. Reliability factor is very high in any kind of Mesh Network. There are three types of wireless mesh networks; Fixed wireless, Peer-to-peer and Node to Node.
Mesh Topology Real Time Implementation
Mesh topology has following real time implementation in many fields:
The Naval Postgraduate School, Monterey CA, demonstrated a third configuration multi-radio wireless mesh network for border security. In a 2007 pilot system, aerial cameras kept aloft by balloons relayed real time high resolution video to ground personnel via a mesh network [9-1].
A MIT Media Lab project developed the XO-1 single-radio laptop or "OLPC" for under-privileged schools in developing nations and uses mesh networking (based on the IEEE 802.11s standard) to create a robust and inexpensive infrastructure. The instantaneous connections made by the laptops are claimed by the project to reduce the need for an external infrastructure such as the Internet to reach all areas, because a connected node could share the connection with nodes nearby. Greenpacket has implemented a similar concept with its application called SONbuddy [9-2].
Software defined radio
Many mesh networks operate across multiple radio bands. For example Firetide and Wave Relay second configuration dual radio mesh networks have the option to communicate node to node on 5.2 GHz or 5.8 GHz, but communicate node to client on 2.4 GHz (802.11). This is achieved by using Software Defined Radio (SDR) [9-3].
2.2.2 STAR TOPOLOGY
Star networks are one of the most well-known computer network topologies. In its simplest form, a star network consists of one central "Switch, Hub or Computer" which performs as a router to transmit data. If the central node is "Passive", the originating node must be able to bear the reception of an echo of its self transmission, delayed by the two-way transmission time plus any delay created in the central node. An active star network has an active central node that typically has the means to prevent echo-related troubles.
The star topology reduces the possibility of network failure by linking all of the systems to a central node. When applied to a bus-based network, hub rebroadcasts all transmissions received from any peripheral node to all nodes on the network, sometimes including the originating node. All peripheral nodes may thus exchange data with all others by transmitting to, and receiving from, the main hub only. The breakdown of a transmission line linking any peripheral node to the central device will result in the separation of that peripheral node from all others, but the rest of the systems will be working smoothly.
Star Topology Diagram 
Advantages of Star Topology
Easy to set up and to expand.
Any connecting node to hub will have very little effect on the network, whereas on a ring network it would all fail with one fault.
Easy to detect faults and recovery is very rapid.
Data Packets are sent speedily as they do not have to pass through any unnecessary nodes.
Disadvantages of Star Topology
Expensive to install.
If the host computer fails the entire system is affected.
Star Topology Real Time Implementation
Star topology is being used in Local Area Networks (LANs) either it is in home or small home-office or office network. In office, Star topology is used to share resources in efficient manner like a single networking printer can be shared among various numbers of connected devices to a HUB.
Star Topology real time implementation 
2.2.3 TREE TOPOLOGY
Tree Topology is a mixture of the bus and the Star Topology. The tree like structure allows having many servers on the network and can branch out the network in different ways. This is mostly helpful for colleges, universities and schools so that each of the branches can recognize the relevant systems in their own network and yet join to the big network in some way.
A Tree Structure suits best when the network is broadly spread and hugely divided into many branches. Like other network topologies, the Tree Topology has its advantages and disadvantages. A Tree Network may not suit small network environments and it may be resulted into waste of cable to use it for small networks. Tree Topology has a few limitations and the configuration should match those limitations.
Tree Topology Diagram 
Advantages of Tree topology
A Tree Topology is implemented by many network vendors and even hardware vendors.
A point to point connection is possible with Tree Networks.
All the computers have instant access to the larger networks.
Best topology for branched out networks.
Tree Topology Limitations
The length of the network depends on the type of cable that is being used for connections.
Tree Topology network is completely dependent on the trunk which is the main spine of the network. If that fails then the entire network would breakdown.
Since the Tree Topology network is large, it is difficult to configure and may also get complex after a certain point.
Tree Topology Features
There will be at least three levels of chain of command in the Tree Network Topology and they all communicate based on the root node.
It has two kinds of topology integral in it which is the star and the linear way of connecting to nodes.
The Tree Topology works by taking into account the total number of peripheral nodes present in the network. It does not matter how much nodes are there on each level. Nodes can be attached to any level of the hierarchy and there are no limitations.
The higher levels in the chain of command are likely to perform more functions than the lower levels in the network.
Tree Topology Real Time Implementation
Cable TV network is the best example of tree topology. Main cable from main office is divided into many branches and each branch is divided into smaller branches and so on. Hubs are used when cable is divided.
2.2.4 BUS TOPOLOGY
In Bus topology, all computers are connected to a "single cable" or "backbone", by a transceiver either directly or by using a short drop cable. All ends of the cable should be terminated, that is connected to a device such as a computer or terminator. Most bus topologies use coaxial cables. Thick-net cable works as a central backbone cable and thin-net cable is used to connect nodes.
Huge number of computers on a bus network will influence network performance. Since only one computer can send data at a time. More computers on the network, there will be waiting to send data. A line crack at any point along the trunk cable will result in total network breakdown.
Computers on a bus only listen for data being sent they do not move data from one computer to the next, this is called passive topology.
Bus Topology Diagram 
Advantages of Bus Topology
Easy to put into operation and extend.
Requires a lesser amount of cable length than a star topology.
Well appropriate for temporary or small networks not requiring high speeds.
Primarily less expensive than other topologies
Disadvantages of Bus Topology
Difficult to administer and troubleshoot at any stage.
Restricted cable length and number of stations.
If there is a problem with the cable, the entire network breakdown.
Maintenance costs may be higher in the long run.
Performance degrades as additional computers are connected.
Low security because all computers on the bus can see all data transmissions of others.
Proper termination is required.
If one node fails, the whole network will fail.
If additional computers are attached, the amount of data travelling causes the network to slow down.
2.2.5 RING TOPOLOGY
In a Ring Topology, computers are connected by a single loop of cable. The data signals moves around the loop in only one direction, passing through each node on the network. Ring topology is an active topology because each node boosts the signal before passing it on to the next node.
One technique of transmitting data around a ring is known as token passing. The token is passed from computer to computer until it gets to a computer that has data to send.
If there is damage in line or if there is adding or removing a device anywhere in the ring, this will bring down the network. In an attempt to provide a solution to this trouble, some network implementations (such as FDDI) support the implementation of a double-ring. If the primary ring breaks, or a device fails, the secondary ring will be used as a backup.
Ring Topology Diagram 
Advantages of Ring Topology
Data is quickly transmits without a 'bottle neck'.
The transmission of data is comparatively simple as packets travel in one direction only.
Adding additional nodes has very little impact on bandwidth
It stops network clash because of the media access method or architecture required.
Disadvantages of Ring Topology
All stations are connected through wire and to add a station, entire network must shut down temporarily.
It is difficult to troubleshoot.
Data packets have to pass through every node between the sender and recipient. Therefore this makes it slower.
If any of the nodes fail then the ring is broken and data cannot be passed on to next node on the network.
In electronics, a "Multiplexer or Mux" is a device that takes one of many analog or digital input signals and outputs it into a single output line. This process is termed as "Multiplexing". An electronic multiplexer helps for several signals to share one expensive device or other resource, for example one A/D converter or one communication line, instead of having each device for every input signal. An electronic multiplexer can be considered as a multiple-input, single-output switch.
An analog multiplexer is a special kind of analog switch that connects one signal chosen from several inputs to a single output.
A digital multiplexer is a set of corresponding switches, with selector that chooses one of the input digital channels to outputs into the single digital output channel. The selector chooses one of the input channels according to the demand it receives digitally. It is possible to make easy multiplexer circuits from standard AND and OR gates but usually multiplexers/data selectors are accessible as standard i.c. packages such as the general TTL 74LS151 8-input to 1 line multiplexer or the TTL 74LS153 Dual 4-input to 1 line multiplexer. Multiplexer circuits with a lot higher number of inputs can be acquired by cascading together two or more smaller devices.300px-Multiplexer2.png
Multiplexer Diagram 
The Multiplexer is a very helpful combinational device that has its utilization in several different applications such as signal routing, data exchanges and data bus control. When used with a demultiplexer, parallel data can be transferred in serial shape via a single data link such as a fibre-optic cable or telephone line. They can also be applied to switch either analogue, digital or video signals, with the switching current in analogue power circuits limited to below 10mA to 20mA per channel in order to decrease heat dissipation.
In electronics, a "Demultiplexer or DEMUX" is a device which takes single input signal and choosing one of many data-output-lines, which is linked to the single input. A multiplexer is frequently used with a corresponding demultiplexer on the receiving end. A demultiplexer can be considered as a single-input, multiple-output switch. A demultiplexer is in this circumstance a device that receives a single input signal that carries many channels and break ups the channels over multiple output signals.300px-Demultiplexer.png
Demultiplexer Diagram 
The fundamental purpose of a multiplexer: combining multiple inputs into a single data stream. On the receiving side, a demultiplexer divides the single data flow into the original multiple signals.
One cost-saving exercise for multiplexers is connecting a multiplexer and a demultiplexer jointly called mul-dex over a single communication channel (by linking the multiplexer's single output to the demultiplexer's single input). In this scenario, the expenditure of implementing separate channels for each data source is more costly than the cost of executing the multiplexing / demultiplexing functions. At the receiving end of the data link, a corresponding demultiplexer is usually required to split single data flow back down into the original flows.
In some cases, the far end arrangement may have more functionality than a ordinary demultiplexer and so, at the same time as the demultiplexing still survives logically, it may not at all really happen physically, such as in network address translation where many IP private network users are multiplexed over a single public IP address.
5. INTERNET PROTOCOL
The Internet Protocol is a set of rules for sending information / data between PCs on the Internet. Each computer / node that uses the Internet Protocol has one IP address that identifies it on the network to all other devices on the planet. Nowadays, there are two types of versions of the Internet Protocol. One is known as IP Version 4 (IPv4) and the other one is called IP Version 6 (IPv6).
5.1 IP ADDRESS
An IP address is a number given to each Personal Computer on the internet. Some computers may also have the same IP address to communicate. These IP addresses are known as "Static IP addresses". Some computers change their IP address from time to time to communicate and are called "Dynamic IP addresses".
5.2 IP VERSION 4
With IPv4, each IP address consists of four numbers, called octets. They start from 0 to 255. To give an IP address to a PC, one takes 4 such numbers. To translate between an IP address and the name of the PC, a system called "Domain Name System" is used. It can translate between the name and the IP Address.
An IPv4 address has the following appearance:
5.3 IPV4 SUBNETTING
At initial stages of development of the IPs, network administrators broke an IP address in two parts which are "Network number portion" and "Host number portion". The highest order octet in an address was called the network number and the rest of the bits were known as rest field or host identifier and were used for host numbering within a network. This method soon became inadequate as time passed. In 1981, the Internet addressing specification was revised and Classful network design implemented for a larger number of individual network assignments. The first three bits of the most important octet of an IP address was defined as the class of the address. Three classes (A, B, and C) were established for universal unicast addressing. Depending on the class derived, the network identification was built on octet boundary segments of the entire IP address.
5.4 IP VERSION 6
IPV6 uses 16 octets (128 bits). So instead of 4 numbers there are now having 16 numbers. IPv6 addresses are generally written as hexadecimal numbers. They are separated by colons (:), so an IPv6 address might be appeared as follows:
5.5 TYPES OF IP ADDRESS
IP addresses are generally categorized in two types which are following:
5.5.1 Public IP Addresses
A public IP address is allocated to every PC that connects to the Internet where each IP is unique. Therefore, two computers with the same public IP address all over the Internet cannot exist. This addressing method makes it possible for the PCs to locate each other online and exchange information/data. The public IP address is allocated to the PC by the ISP as the PC is connected to the Internet gateway. A public IP address can be either "Static or Dynamic". A static public IP address does not alter and is used mainly for hosting WebPages or services on the Internet. Whereas, a dynamic public IP address is selected from a pool of existing addresses and varies each time one connects to the Internet. Thus, when it is re-connected it gets a new IP dynamically.
5.5.2 Private IP Addresses
An IP address is called Private if the IP number remains within one of the IP address ranges allocated for private networks such as a Local Area Network (LAN). The Internet Assigned Numbers Authority (IANA) has allocated the following three blocks of the IP address space for private local networks:
10.0.0.0 - 10.255.255.255 (Total Addresses: 16,777,216)
172.16.0.0 - 172.31.255.255 (Total Addresses: 1,048,576)
192.168.0.0 - 192.168.255.255 (Total Addresses: 65,536)
Private IP addresses are generally used for assigning numbers to the PCs in a private network including home, school and business LANs in airports and hotels which makes it easy for the PCs in the network to communicate with each other. PCs / Devices with private IP addresses cannot communicate directly to the Internet. Similarly, PCs / Devices outside the LAN cannot communicate directly to a PC / device with a private IP. It is feasible to connect two private networks with the assist of a router or a similar device that supports Network Address Translation.
6. WORLD WIDE WEB (WWW)
Many people use the terms World Wide Web and Internet interchangeably, the World Wide Web actually is a service of the Internet. While the Internet was developed in the late 1960s, the World Wide Web appeared in the early 1990s. Since then, it has grown phenomenally to become one of the more broadly used Internet services. The World Wide Web or Web consists of a worldwide set of electronic documents. Each electronic document on the Web is called a Web page, which can include text, graphics, animation, audio, and video. Additionally, Web pages typically have built-in connections to other documents.
Some Web pages are static; others are dynamic. Visitors to a static Web page cam watch the same content. With a dynamic Web page, by contrast, visitors can modify some or all of the viewed content such as desired stock quotes, weather for an area, or ticket availability for flights.
7. HYPER TEXT TRANSFER PROTOCOL (HTTP)
HTTP stands for Hyper Text Transfer Protocol, the underlying protocol used by the World Wide Web. HTTP explains how messages / data are formatted and transmitted, and what actions Web servers and browsers should take in reaction to various commands. When a URL is entered in the browser, this actually sends an HTTP command to the Web server directing it to get and sends the requested Web page
The other important standard that controls how the World Wide Web works is HTML, which covers how Web pages are formatted and shown.
8. WWW vs HTTP
HTTP is an acronym for Hypertext Transfer Protocol. This is the most famous protocol in use today. It is the communication standard used by your web browser in order to communicate with the server of the website that we are viewing. WWW or the World Wide Web is a prefix to a certain name in order to recognize that it is a web site that we are visiting.
There are many accessible protocols in the internet today and in order to differentiate which one is to use, they are allocated specific protocol names that should be there when connecting to a web site or any other source of data. Some protocols that are acknowledged by browsers are: HTTP, HTTPS, FTP, NEWS, and FILE. Although most sites are simply web servers, some sites host multiple services in a single domain name and in order to recognize which one is trying to access and must specify the protocol that the service uses.
Most websites appear in a certain format, mostly it is www.anything.com. The word at the end recognizes the site as commercial, the word in the middle is the domain name, and the WWW in the starting indicates that it is a website and it uses the HTTP protocol. It is, therefore, unnecessary to have "http://www.anything.com" since the WWW tells the browser to use HTTP when it is already in use. But because the majority of people are already used to having a URL written this way, it is left as is by most experts.