Types of Internet connectivity

 When you connect to the Internet, you might connect through a regular modem, through a local-area network connection in your office, through a cable modem or through a digital subscriber line(DSL) connection. DSL is a very high-speed connection that uses the same wires as a regulartelephone line.

Here are some advantages of DSL:

You can leave your Internet connection open and still use the phone line for voice calls.

The speed is much higher than a regular modem

DSL doesn't necessarily require new wiring; it can use the phone line you already have.

The company that offers DSL will usually provide the modem as part of the installation.

But there are disadvantages:

A DSL connection works better when you are closer to the provider's central office. The farther away you get from the central office, the weaker the signal becomes.

The connection is faster for receiving data than it is for sending data over the Internet.

The service is not available everywhere.

(Franklin n.d.)

How Cable Modems Work

Extra Space

You might think that a television channel would take up quite a bit of electrical "space," orbandwidth, on a cable. In reality, each television signal is given a 6-megahertz (MHz, millions of cycles per second) channel on the cable. The coaxial cable used to carry cable television can carry hundreds of megahertz of signals -- all the channels you could want to watch and more. (For more information, see How Television Works.)

In a cable TV system, signals from the various channels are each given a 6-MHz slice of the cable's available bandwidth and then sent down the cable to your house. In some systems, coaxial cable is the only medium used for distributing signals. In other systems, fiber-optic cable goes from the cable company to different neighborhoods or areas. Then the fiber is terminated and the signals move onto coaxial cable for distribution to individual houses.

(Franklin n.d.)

How do you access the Internet other than dial-up if you live too far from a phone company office forDSL and there is no cable TV on your street? Satellite Internet access may be worth considering. It's ideal for rural Internet userswho want broadband access. Satellite Internet does not usetelephone lines or cable systems, but instead uses a satellite dish fortwo-way (upload and download) data communications. Upload speed is about one-tenth of the 500 kbps download speed. Cable and DSL have higher download speeds, but satellite systems are about 10 times faster than a normal modem.

Firms that offer or plan to offer two-way satellite Internet include StarBand, Pegasus Express, Teledesic and Tachyon. Tachyon service is available today in the United States, Western Europe and Mexico. Pegasus Express is the two-way version of DirecPC.

Two-way satellite Internet consists of:

Approximately a two-foot by three-foot dish

Two modems (uplink and downlink)

Coaxial cables between dish and modem

The key installation planning requirement is a clear view to the south, since the orbiting satellites are over the equator area. And, like satellite TV, trees and heavy rains can affect reception of the Internet signals.

Two-way satellite Internet uses Internet Protocol (IP) multicasting technology, which means up to 5,000 channels of communication can simultaneously be served by a single satellite. IP multicasting sends data from one point to many points (at the same time) by sending data in compressed format. Compression reduces the size of the data and the bandwidth. Usual dial-up land-based terrestrial systems have bandwidth limitations that prevent multicasting of this magnitude.

Some satellite-Internet service still requires you to have a dial-up or cable modem connection for the data you send to the Internet. The satellite data downlink is just like the usual terrestrial link, except the satellite transmits the data to your computer via the same dish that would allow you to receive a Pay-Per-Viewtelevision program.

So, if you are in a rural area and you want broadband access to the Internet, satellite Internet may be for you!

(Franklin n.d.)

Most of us are familiar with a normal business or residential line from the phone company. A normal phone line like this is delivered on a pair of copper wires that transmit your voice as an analog signal. When you use a normal modem on a line like this, it can transmit data at perhaps 30 kilobits per second (30,000 bits per second).

The phone company moves nearly all voice traffic as digital rather than analog signals. Your analog line gets converted to a digital signal by sampling it 8,000 times per second at 8-bit resolution (64,000 bits per second). Nearly all digital data now flows over fiber optic lines, and the phone company uses different designations to talk about the capacity of a fiber optic line.

If your office has a T1 line, it means that the phone company has brought a fiber optic line into your office (a T1 line might also come in on copper). A T1 line can carry 24 digitized voice channels, or it can carry data at a rate of 1.544 megabits per second. If the T1 line is being used for telephone conversations, it plugs into the office's phone system. If it is carrying data it plugs into the network's router.

A T1 line can carry about 192,000 bytes per second -- roughly 60 times more data than a normal residential modem. It is also extremely reliable -- much more reliable than an analog modem. Depending on what they are doing, a T1 line can generally handle quite a few people. For general browsing, hundreds of users are easily able to share a T1 line comfortably. If they are all downloading MP3 files or video files simultaneously it would be a problem, but that still isn't extremely common.

A T1 line might cost between $1,000 and $1,500 per month depending on who provides it and where it goes. The other end of the T1 line needs to be connected to a web server, and the total cost is a combination of the fee the phone company charges and the fee the ISP charges.

A large company needs something more than a T1 line. The following list shows some of the common line designations:

DS0 - 64 k­ilobits per second

ISDN - Two DS0 lines plus signaling (16 kilobytes per second), or 128 kilobits per second

T1 - 1.544 megabits per second (24 DS0 lines)

T3 - 43.232 megabits per second (28 T1s)

OC3 - 155 megabits per second (84 T1s)

OC12 - 622 megabits per second (4 OC3s)

OC48 - 2.5 gigabits per seconds (4 OC12s)

OC192 - 9.6 gigabits per second (4 OC48s)

Wireless MAN-Advanced for WiMAX-2, also known as IEEE 802.16m, has been approved by The Institute of Electrical and Electronics Engineers (IEEE), the standard for the next generation of WiMax, which may deliver downstream speeds of more than 300 mbps. At the CEATAC trade show in Tokyo last year, Samsung demonstrated a pre-standard 802.16m network that achieved a speed of 330 mbps.

A significant majority of carriers that have committed to building so-called 4G (fourth-generation) networks have chosen LTE (Long-Term Evolution), which shares some underlying characteristics with WiMax but comes from a different standards body. We are delighted that IEEE has recognized the completion of this comprehensive technical effort that has involved hundreds of creative and diligent professionals from over twenty countries during the last four years.

IEEE 802.16m incorporates innovative communications technologies like multi-user MIMO for sending more than one stream of data, multicarrier operation and cooperative communications. It also supports femto-cells, self-organizing networks, and relays according to the IEEE. The new standard is backward compatible with the current WiMax.

WiMax is used for stationary or nomadic wireless broadband in many parts of the world. The 802.16e mobile WiMax standard was approved in the middle of the past decade, well before LTE and powered the first national network in the US using a next-generation technology.

(Anubha 2011)

Wednesday, December 8, 2010

What is the Difference Between GSM and CDMA?

One of the basic things that differentiates GSM (based on TDMA) and CDMA is the way the carve up bandwidth.

Each bit of radio spectrum used by a handset has to be shared with other people in the area. It is more or less the same as multiplexing for normal data land lines.

The major difference between GSM/TDMA and CDMA is in the way they divide up those signals between multiple users.

GSM/TDMA uses a Time Division method. TDMA, in fact, stands for Time Division Multiple Access. Simply put, this means that each device on the local network is allocated a time slice where it "owns" the bandwidth, and it can send/receive its data.

So lets just pick a number and say there are 30 available time slices in a given cycle. Each phone would then get 1/30th of every cycle that it could send and receive data (aka, voice).

CDMA uses a different method, called Code Division Multiple Access. The specifics of how it breaks the cycle up are beyond me, but how it works out is that the phones only get a slice of the bandwidth cycle when they actually need one. So if you are not talking, and the other person is not talking, nothing is transmitted.

With GSM/TDMA, each phone is transmitting and receiving during its slices of the bandwidth cycle, whether it needs it or not.

Since most coversations are comprised largely of silence, the end result is that CDMA phones have to transmit less data. They don't have to send silence, like GSM/TDMA phones do.

This means a few things. More CDMA calls can be fit into a given amount of frequency spectrum (ie. it is more efficient for the network), less radiation is being created from the phone towards the user (you only get radiation when you are talking, basically), and battery power is conserved since the handset only transmits when it actually has something to send.

There are other differences, too, that I can't get into. For one, it is harder to implement a CDMA network. The tower placement is more difficult. Dealing with hills is more difficult than with GSM/TDMA. Things like that.

But in general, CDMA is vastly superior technology. Not surprising since Qualcomm's version of it (that which is used in CDMA and WCDMA phones) is newer technology, even if the basics were in use by the US military as far back as the 40s.

The important thing for me, though, is the SIM card. Had CDMA implemented the use of a SIM card (something it very easily could have done), then the North American market would be very different today, and there would be more CDMA networks in other countries. The SIM card allows people to easily switch phones, and that helps the market.

(Saeed n.d.)

TDMA, which predates the more advanced GSM technology standard, has been incorporated into GSM. TDMA is no longer in use by the major U.S. cell phone service carriers.

(Fendelman n.d.)

• 1. Dial-up connection is the one which the PC connects to the internet (WAN) by dialing up through a phone line.

  2. Dial-up connection speed limit is limited to 56kbps.

  3. In Dial-up connection you dail up to the internet using phone line so the charges as per the local call per minute or based on the operator charges. It is basically phone call charges.

  4. In Dial-up connection the phone line will busy when connect to internet so no body can call to your number when you are connected to Internet.

  5. Dial-up connection uses analog transmission there by it is difficult to attain high speed so surfing the interenet for wathing videos or playing online games is difficult.

  6. In Dial-up connection, the analog signal must be translated to digital and viceversa, hence it will be slower. It uses built-in modem to connect and does not require a special router

  7. Dial-up connection is more secured than broadband connection.

(http://www.differencebetween.co.in n.d.)