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Network A system of interconnected computers and computerized peripherals such as printers is called computer network. This interconnection among computers facilitates information sharing among them. Computers may connect to each other by either wired or wireless media. A computer network consists of a collection of computers, printers and other equipment that is connected together so that they can communicate with each other.  

Network application
A Network application is any application running on one host and provides a communication to another application running on a different host, the application may use an existing application layer protocols such as: HTTP(e.g. the Browser and web server), SMTP(e.g. the email-client). And may be the application does not use any existing protocols and depends on the socket programming to communicate to another application. So the web application is a type of the network applications. 
There are lots of advantages from build up a network, but the th…


A wide area network (WAN) is a large telecommunications network that consists of a collection of LANs and other networks. WANs generally span a wide geographical area, and can be used to connect cities, states, or even countries. Although they appear like an up-scaled version of a LAN, WANs are actually structured and operated quite differently. This wide area network tutorial serves to explain how WANs are designed/constructed and why their use is beneficial. 

The public switched telephone network (PSTN) refers to the international telephone system that uses copper wires to carry analog voice data. It consists of a collection of individual telephones that are hardwired to a public exchange. The public switched telephone network was formerly known simply as the public telephone network.  

The public switched telephone network is a global system that has developed over several decades. From the early research of Alexander Graham Bell, telecommunications companies evolved the PSTN architecture that provided for yesterday's landline voice communications. One important distinction with the public switched telephone network is that it stands in contrast to private exchange networks. Private branch exchanges and other technologies allowed companies and other parties to create more individual telephone lines that were not represented in the PSTN and public landline architecture. One way to explain this is that individual lines were built into private endpoint systems, so that an individual recipient could have many different individual phone lines using the same public switched telephone network trajectory.  
Today, as smartphones and mobile devices continue to proliferate, wireless telecom networks are taking up market share and PSTN landline technology is diminishing. In some places, less industrialized communities have skipped directly from an underserved or insufficient public switched telephone network architecture directly to the use of cell phones and mobile devices. PSTN has also been known to stand for "pretty standard telephone network," a tongue-in-check expression referring to its slow speed.  

The size of a network is limited due to size and distance constraints. However networks may be connected over a high speed communications link (called a WAN link) to link they together and thus become a WAN. WAN links are usually: 
Leased Line: 
A leased line is a telephone line that has been leased for private use. In some contexts, it's called a dedicated line. A leased line is usually contrasted with a switched line or dial-up line. 

In packet switching network unlike CS network, it is not required to establish the connection initially. The connection/channel is available to use by many users. But when capacity or number of users increases then it will lead to congestion in the network. Packet switched networks are mainly used for data and voice applications requiring non-real time scenarios.  If user-A wants to send data/information to user-C and if user-B wants to send data to user-D, it is simultaneously possible. Here information is padded with header which contains addresses of source and destination.  

This header is sniffed by intermediate switching nodes to determine their route and destination. In packet switching, station breaks long message into packets. Packets are sent one at a time to the network. Packets are handled in two ways, viz. datagram and virtual circuit. In datagram, each packet is treated independently. Packets can take up any practical route. Packets may arrive out of order and may go missing. In virtual circuit, preplanned route is established before any packets are transmitted. The handshake is established using call request and call accept messages. Here each packet contains virtual circuit identifier (VCI) instead of the destination address. In this type, routing decisions for each packet are not needed.  

In circuit switching network dedicated channel has to be established before the call is made between users. The channel is reserved between the users till the connection is active. For half duplex communication, one channel is allocated and for full duplex communication, two channels are allocated. 
It is mainly used for voice communication requiring real time services without any much delay.  

If user-A wants to use the network; it need to first ask for the request to obtain the one and then user-A can communicate with user-C. During the connection phase if user-B tries to call/communicate with user-D or any other user it will get busy signal from the network. 
Comparison between Circuit switching & Packet switching 
As shown above in Packet switched (PS) networks quality of service (QoS) is not guaranteed while in circuit switched (CS) networks quality is guaranteed. PS is used for time insensitive applications such as internet/email/SMS/MMS/VOIP etc. In CS even if user is not talking the channel cannot be used by any other users, this will waste the resource capacity at those intervals. The example of circuit switched network is PSTN and example of packet switched network is GPRS/EDGE.  
Following table summarizes difference between circuit switching and packet switching of type datagram and virtual circuit.  

Packet Switching(Virtual Circuit type)
Dedicated path
No Dedicated path
No Dedicated path
Path is established for entire conversation
Route is established for each packet 
Route is established for entire conversation
Call setup delay
packet transmission delay
call setup delay as well as packet transmission delay
Overload may block call setup
Overload increases packet delay 
Overload may block call setup and increases packet delay
Fixed bandwidth
Dynamic bandwidth
Dynamic bandwidth 
No overhead bits after call setup 
Overhead bits in each packet
overhead bits in each packet 

  • X.25 - This is a set of protocols developed by the CCITT/ITU which specifies how to connect computer devices over an internetwork. These protocols use a great deal of error checking for use over unreliable telephone lines. They establish a virtual communication circuit. It uses a store and forward method which can cause about a half second delay in data reception when two way communications are used. Their speed is about 64Kbps. normally X.25 is used on packed switching PDNs (Public Data Networks). A line must be leased from the LAN to a PDN to connect to an X.25 network. A PAD (packet assembler/disassembler) or an X.25 interface is used on a computer to connect to the X.25 network. CCITT is an abbreviation for International Telegraph and Telephone Consultative Committee. The ITU is the International Telecommunication Union.  
  • Frame Relay - Error checking is handled by devices at both sides of the connection. Frame relay uses frames of varying length and it operates at the data link layer of the OSI model. A permanent virtual circuit (PVC) is established between two points on the network. Frame relay speed is between 56Kbps and 1.544Mbps. Frame relay networks provide a high-speed connection up to 1.544Mbps using variable-length packet-switching over digital fiber-optic media. Frame relay does not store data and has less error checking than X.25.  
  • Switched Multi-megabit Data Service (SMDS) - Uses fixed length cell switching and runs at speeds of 1.533 to 45Mbps. It provides no error checking and assumes devices at both ends provide error checking.  
  • Telephone connections  

o Dial up -Dial-up Internet access is a form of Internet access that uses the facilities of the public switched telephone network (PSTN) to establish a connection to an Internet service provider (ISP) by dialing a telephone number on a conventional telephone line.

o Leased lines - These are dedicated analog lines or digital lines. Dedicated digital lines are called digital data service (DDS) lines. A modem is used to connect to analog lines, and a Channel Service Unit/Data Service Unit or Digital Service Unit (CSU/DSU) is used to connect to digital lines. The DSU connects to the LAN and the CSU connects to the line.  
o T Carrier lines - Multiplexors are used to allow several channels on one line. The T1 line is basic T Carrier service. The available channels may be used separately for data or voice transmissions or they may be combined for more transmission bandwidth. The 64Kbps data transmission rate is referred to as DS-0 (Digital Signal level 0) and a full T1 line is referred to as DS-1

T1 and T3 lines are the most common lines in use today. T1 and T2 lines can use standard copper wire. T3 and T4 lines require fiber-optic cable or other high-speed media. These lines may be leased partially called fractional T1 or fractional T3 which means a customer can lease a certain number of channels on the line. A CSU/DSU and a bridge or router is required to connect to a T1 line. 

  • Integrated Services Digital Network (ISDN) - Comes in two types and converts analog signals to digital for transmission. It is a dial up service  
  • Basic Rate ISDN (BRI) - Two 64Kbps B-channels with one 16Kbps D channel. The D channel is used tor call control and setup.  
  • Primary Rate ISDN (PRI) - 23 B-channels and one D channel.  

A device resembling a modem (called an ISDN modem) is used to connect to ISDN. The computer and telephone line are plugged into it.  

o Switched-56 - A switched line similar to a leased line where customers pay for the time they use the line. Speed is 56Kbps. It is not dedicated and will not work to connect a WAN.  

  • Asynchronous Transfer Mode (ATM) - May be used over a variety of media with both base-band and broadband systems. It is used for audio, video, and data. It uses fixed length data packets of 53 8 bit bytes called cell switching. 5 bytes contain header information. The cell contains path information that the packet is to use. It uses hardware devices to perform the switching of the data. Speeds from 155Mbps to 622 Mbps are achieved. Error checking is done at the receiving device, not by ATM. A permanent virtual connection or circuit (PVC) is established. It may also use a switched virtual circuit (SVC). Service classes:  

o Constant bit rate for data. 

o Variable bit rate for audio or video.  
o Connection less for data.  
o Connection oriented for data. 

ATM can be embedded in other protocols such as ATM-25, T1, T3, OC-1, OC-3, OC-12, and OC-48. Some ATM technologies include: 

o ATM-25 - 25Mbps speed.  
o STS-3 - 155Mbps on fiber or category 5 cable.  
o STS-12 - 620 Mbps on fiber cable for campus wide network.  
o STS-48 - 2.2 Gbps on fiber cable on a MAN.  
o STS-192 - 8.8 Gbps on fiber cable on intercity long distance. This is normally used by phone companies.  

  •  Synchronous Optical Network (SONET) - A physical layer standard that defines voice, data, and video delivery methods over fiber optic media. It defines data rates in terms of optical carrier (OC) levels. The transmission rate of OC-1 is 51.8 Mbps. Each level runs at a multiple of the first. The OC5 data rate is 5 times 51.8 Mbps which is 259 Mbps. SONET also defines synchronous transport signals (STS) for copper media which use the same speed scale of OC levels. STS-3 runs at the same speed of OC-3. Mesh or ring topology is used to support SONET. SONET uses multiplexing. The ITU has incorporated SONET into their Synchronous Digital Hierarchy (SDH) recommendations.  

Broadband is a term frequently used with accessing the Internet using high speeds, usually in excess of 248kbps. In general terms broadband referred to communication technology that can employ different channels of data or data streams by using any medium (air or Physical). Obviously, to transfer data at a higher rate, it requires more bandwidth (or frequencies). With wide band of frequencies, information can be multiplexed and sent on many different frequencies or channels within the band concurrently, allowing more information to be transmitted in a given amount of time.

Broadband can be provided over your phone line, via cable, or via satellite. It involves large volumes of information being carried at high speeds to your PC and vice versa. This allows graphics, music and videos to be experienced in real time by the user. Broadband, therefore, has many features that can be taken advantage of in the home or office: 

  • The connection to the Internet is always on, allowing for instant Internet access and no need to wait for a connection to be made, as in dial up access. 
  • The phone line is unaffected; this means that you can make telephone calls whilst the Internet is on. This is due to the fact that voice and Internet data use different frequencies for transmission. 
  • Normally, you pay a standard monthly fee for unlimited Internet access, and you are not charged for the time you are connected to the Internet. There are certain broadband products now that also offer pay as you go access. 
  • Broadband allows music and videos downloaded at a faster rate. 
  • You can take advantage of instant messaging and online high-speed interactive games. 
  • You can receive uninterrupted real time services, such as Internet radio, streaming video and voice-over-ip, phone calls. 

Cable Broadband: The local cable TV provider provides the broadband cable modem connection. The cable modem should not be confused with dialup access modem. Both are different, and one can't be used in place of other. In fact, they are different animals! The cable Internet connection speed varies with the number of users on the service at a given point in time. Given a given geographical area, users of the broadband cable service share the connection bandwidth among themselves. As a result, the access speed may reduce to a noticeable extent at times. This is likely to occur at peak times, like late in the evenings after the work day is over when many people will be accessing the Internet. The cable company, however, claim the total bandwidth as available to the customer, as if you were the only person accessing the Internet using the cable. But that is clearly not the case. 

A cable, as shown in the diagram, generally runs down your street and, if you choose to connect, a second cable is then run from the main line to your home. If you happen to already have cable TV installed, you won't need to get a professional installer to run this cable to your house – and that may mean savings on your set up fees.  

Broadband cable Internet access requires a cable modem at the customer's premises and a cable modem termination system at a cable operator facility, typically a cable television head end. The two are connected via coaxial cable or a Hybrid Fiber Coaxial (HFC) plant. While access networks are sometimes referred to as last-mile technologies, cable Internet systems can typically operate where the distance between the modem and the termination system is up to 100 miles (160 km). Using Cable Internet, downstream bit rates that can be typically reached at customer end are 30Mbit/s. Upstream traffic typically of range of 384Kbit/s or more at the customer premises. One downstream channel can handle hundreds of cable modems. As the system grows, the cable modem termination system (CMTS) can be upgraded with more downstream and upstream ports. 

  • Both ADSL and wireless users can experience degraded quality and reduced speeds if the customer premises is a long way from the Internet service provider (ISP). The quality issue is something cable surfers don’t need to worry about. 
  • Cable Internet generally has a more constant top speed than thos available with traditional dial-up, DSL technology, or wireless. 
  • Your phone line is free from any interruption. You can make or receive call using your phone line because a cable modem is no way related with your phone line. 

  •  You will need to buy a special cable modem hardware to send or receive information via a fiber-optic cable. 
  • The more people there are sharing the bandwidth, the slower your experience will be the quoted speeds are more like “theoretical maximums” speeds. 
  • If you haven't already connected to cable TV, you may need a professional to do the installation. Laying cable and related hardware increases the initial costs of having Cable modem service. 
  • Many packages place limits on downloads and uploads.  

DSL provides high-speed networking over ordinary phone lines using broadband modem technology. DSL technology allows Internet and telephone service to work over the same phone line enabling a customer to use both Internet and voice simultaneously. 
DSL Internet services are used primarily in homes and small businesses. DSL Internet service works over a limited distance from the exchange and the service quality becomes poor as the distance of the consumer increases from the exchange area where the DSL hub equipment is installed. DSL Internet service can be categorized as either asymmetric or symmetric. 

Asymmetric types of DSL connections provide more network bandwidth for downloading (from the Internet service provider down to the subscriber's computer) than for uploading in the other direction. By reducing the amount of bandwidth available upstream, service providers are able to offer relatively more bandwidth downstream. Asymmetric DSL technology is popular in residential DSL services as home Internet users predominately use downstream bandwidth. Typical asymmetric DSL services support 5 Mbps for downloads and 1 Mbps for uploads. 

 ADSL (Asymmetric Digital Subscriber Line): ADSL allows more data to be sent over existing copper telephone lines (POTS), when compared to traditional analog modem lines. A special filter, called a micro filter, is installed on a subscriber's telephone line to allow both ADSL and regular voice (telephone) services to be used at the same time. ADSL requires a special ADSL modem and subscribers must be in close geographical locations to the provider's central office to receive ADSL service. Typically this distance is within a radius of 2 to 2.5 miles (or 2.5 to 4 kilo meters approximately). 
A typical ADSL system is shown in the figure above. ADSL typically supports data rates of from 640kbps up to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate). 

ADSL2: ADSL2 (ITU G.992.3 and G.992.4) adds more speed and functionality to older ADSL specification. This is achieved as result of better noise reduction, and modulation techniques. 

ADSL2+ (ITU G.992.5) doubles the bandwidth used for downstream data transmission, and achieving rates of 20 Mbps on telephone lines up to a distance of about one mile or 5,000 feet. ADSL2+ equipment is interoperable with ADSL and ADSL2. ADSL2+ will include all the feature and performance benefits of ADSL. 

Wi-Fi creates a network in your home or office a little zone where computers can get broadband Internet. It uses radio waves, just like TV or mobile phones. You may sometimes hear this zone referred to as a WLAN (Wireless Local Area Network). 

A device called a wireless transmitter receives information from the Internet via your broadband connection. The transmitter converts the information into a radio signal and sends it. 

You could think of the transmitter as a mini radio station, broadcasting signals sent from the Internet. The ‘audience’ for these transmissions is the computer (or computers, as more than one can connect at the same time), which receives the radio signal via something called a wireless adapter. 

The whole process, meanwhile, works in reverse, with the computer sending information to the wireless transmitter. It then converts them and sends them via your broadband connection.  
To use Wi-Fi you will need certain equipment: 

  • A wireless transmitter, also known as a Wireless Access Point (WAP) 
  • A Wi-Fi adapter on every computer that will use Wi-Fi 

WiMAX is an IP based, wireless broadband access technology that provides performance similar to 802.11/Wi-Fi networks with the coverage and QOS (quality of service) of cellular networks. WiMAX is also an acronym meaning "Worldwide Interoperability for Microwave Access (WiMAX).WiMAX is a wireless digital communications system, also known as IEEE 802.16, which is intended for wireless "metropolitan area networks". WiMAX can provide broadband wireless access (BWA) up to 30 miles (50 km) for fixed stations, and 3 - 10 miles (5 - 15 km) for mobile stations. In contrast, the Wi-Fi/802.11 wireless local area network standard is limited in most cases to only 100 - 300 feet (30 - 100m). 

With WiMAX, Wi-Fi like data rates are easily supported, but the issue of interference is lessened. WiMAX operates on both licensed and non-licensed frequencies, providing a regulated environment and viable economic model for wireless carriers. 

LTE, or long-term evolution, is a type of mobile broadband that rivals WiMAX. Both services are IP-based and use a technology called orthogonal frequency-division multiplexing (OFDM) access. They also use a type of wireless technology that lets people get high-speed Internet across coverage areas that span miles. 

It refers to third generation of standard mobile phones and mobile telecommunication services fulfilling the International Mobile Telecommunication-2000 (IMT-2000) specifications by the International Telecommunication Union.3G technologies are intended for the true multimedia cell phone typically called smart phones. It allows simultaneous use of speech and data services and higher data rates it comes with enhancements over previous wireless technologies, like high-speed transmission, advanced multimedia access and global roaming. 3G helps to simultaneously transfer both voice data (a telephone call) and non-voice data (such as downloading information, exchanging e-mail, and instant messaging). 

The 3.5G solution promises a data download speed of up to 14Mbps (megabits per second) and an upload speed of up to 1.8Mbps. Compared to that, the mere 384Kbps (kilobits per second) download, and uploads up to 64Kbps that a 3G network now offer. 3.5G rely on the new High-Speed Downlink Packet Access protocol, which are responsible fast transfer speeds over those of 3G. 

4G Technology is basically the extension in the 3G technologies with more bandwidth and services offers in the 3G. 4G technologies are the future technologies that are mostly in their maturity period. The expectation for the 4G technologies is basically the high quality audio/video streaming over end-to-end Internet Protocol. 

a) ATM 
b) ISDN 
c) MPLS 
d) RIP 

a) T1 
b) T3 
c) Frame Relay 
d) Cable Modem  

 a) Frame Relay 
b) ISDN 
c) RIP 
d) ATM  

a) Frame Relay 
b) ISDN 
c) RIP 
d) ATM  

a) Automated Teller Machine 
b) Asynchronous Transfer Mode 
c) Asynchronous Transfer Method 
d) Autonomous Transfer Mode 

a) T1 
b) T3 
c) E1 
d) E3 

a) Frame Relay 
b) ISDN 
c) MPLS 
d) RIP 

a) ADSL 
b) HDSL 
c) FDSL 
d) SDSL   

a) POP 
b) Central Office 
c) Demac 
d) Central Jack 


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