Broadband

Posted by : Unknown Saturday, June 29, 2013

BROADBAND

Definition:

Broadband is a communication carriers or media. With broadband, multiple signals can travel on the same media at the same time.

What exactly broadband?

Communication carriers or media, for example wires or cables,

are of two types: broadband and base band . Base-band is where only one signal passes through the media at a time. So, with broad band, multiple signals can travel on the same media at the same time. The classic example of this is the cable that carries multiple TV channels to your television set.

We will define broadband as internet access through non-traditional media (other than dial-up over telephone lines)with downstream speeds of at least 64 KBPS . We say a lower limit of 64 KBPS because a dial-up modem on a telephone line can deliver up to 56 KBPS downstream.

). When we talk of non-traditional media ,we ‘re actually talking of only two options currently-Internet over cable and digital subscriber line(DSL).when we talk of DSL,we’re actually talking of a number of technologies like ADSL, SDSL, HDSL, IDSL, and VDSL, all of which deliver internet connects at varying speeds over existing telephone connections without using the all-too-familiar dial –up modem the most common DSL implementation in India today is ADSL or asynchronous DSL.

ADSL can deliver from 1.5-9 Mbps down stream (to the user) and 16-640 kbps upstream (user requests to web servers).

Ideally, when we talk of broad band,we refer to connections to the home ,and not to the workplace.Why is that ? typically home user will have more data sent down to him in the form of downloaded software or stream music or vedio,than data sent back to the net.On the other hand,bussiness will need to send more data out into the net,in the form of data served from web servers they host or software and data transferred to business partners . Asymmetric technologies like ADSL and internet over cable can’t support this need to transfer data out on to the net.So,corporates would ideally opt for symmetric options-leased lines or the like-here data transfer rate are high in both directions.

However not all businesses need to transfer huge amounts of data out with most Indian web site being hosted at separated data center the roll of the corporate Internet connections becomes limited to sending and receiving e-mail and browsing the web in such a situation broadband can use d as a corporate solution also .

Another advantage of broadband is that it does not tie up your telephone line and,consequently doesn’t saddle you with heavy telephone bills.On the flip side ,while usage charges for broadband tend to be low ,the cost of equipment ,like a DSL or cable modem,can be pretty high. Citing these savings in telephone charges ,some ISPs offer 32 kbps connects as an option. Does this qualify as broadband ?the band width is not at all broad in this case and you may actually take more time to down load software or brows the web than you would on a good dial-up connections but then you do save a packet on telephone charges.

How do you choose between service providers? You may not have much of choice here.it’s your cable TV provider who will double up as your internet over cable provider in the of DSL,too,the market has not big enough for competition yet most service providers currently operate in mutually exclusively territories.

What about the choice between cable and DSL? Here again ,the story is more or less the same .if you’re lucky enough to have a choice between cable and DSL,and with other things like back bone and gateway bandwidths of service provider being equal,DSL may work out to be better and with cable in the long run. This is because cable is a shared media. This is ,the cable that comes to your house runs to your neighbor’s. As more and more users are added to the segment of cable that you’re on , the available bandwidth will get shared between all of them.

Why Broadband?

Imagine yourself going for a movie to the races ,and the shop where you usually order weekly groceries ,simultaneously. All this ,while you are on a train en route to home after a hectic day at work’s this a scene from a latest holly wood block buster ? is it Arthur c Clarke’s 2020/belive it or not, it’s now and it’s here, thanks to broadband.

Here’s how broadband fits into our lives.

Enabling convergence:

Increasingly ,all forms of electronic information –telephony, data traffic and TV and radio-are being converted into digital format,making it possible for a single network to handle all of them. also ,there’s continuing demand to transport more information,more quickly. the result is a need for a communication links with huge bandwidth .broadband is a possible answer.

Broad connectivity options

High-speed internet access and remote LAN access are just the beginning of broadband. Other applications that will be made possible include videoconferencing, desk-top-desk video, interactive CAD, and collaborative working.3G wireless networks (based on broadband ) will lead to applications such as mobile multimedia, mobile videoconferencing, etc.

Disaster control and management :

The Gujarat earthquake is a case in point of where broadband wireless networks could have been deployed. Ad hoc wireless broadband networks would have come in handy in Gujarat when all means of communication failed, especially for sending multimedia information. This could be online help from a surgeon to a medic who’s providing aid to disaster victims; or schedules, distribution plans, and remote monitoring of relief material.

Military and defense:

Wireless broadband networks would enable military to exchange multimedia information while on the move. In many tactical scenarios, the effective use of these networks may become the difference between victory and defeat.

Mobile videoconferencing:

For the busy business managers of the future and for telecommuting workers operating from anywhere, wireless broadband data communication may become a great asset.

Remote monitoring of industrial plants:

Engineers can monitor industrial plants right from their mobile handset, rather than go to the plant or its monitoring station.

As you can see, broadband access can lead to more useful applications for end users and new revenue generation models for network operators providing broadband services.

GETTING READY FOR BROADBAND:

If you live in any of the major cities, then you couldn’t have missed the colorful pipes lying by the roadside everywhere. These pipes will carry fiber optic cable that will form the backbone for providing broadband access to homes and offices. All equipment used with this fiber-optic backbone would vary depending upon the broadband technology used. Currently, three such technologies, called Ethernet,cable modems, and xDSL, are being used.

The three technologies use different types of cables for their communication. Ethernet uses Cat 5 cabling, cable modems use coaxial cables, and DSL uses single pair copper cables. Due to this, all equipment has to have the proper termination to be able to join the fiber backbone.

Broadband over Ethernet:

The setup for this is similar to a typical Ethernet setup, and the speed would also be in the order of 10/100 Mbps. The typical subscribers for this would be large companies needing VPN connectivity among their various office locations. The termination at the subscriber end would be an Ethernet switch with RJ45 ports capable of taking Cat 5 cabling. The switch \would be connected to a router, which would in turn to be hooked to the broadband service provider. In some cases, it might be more convenient to have need-to-end fiber-optic connectivity form the broadband service provider to the subscriber.

Cable modem setup:

A cable TV network was originally meant for audio and video broadcast. To provide data over the same network, meaning Net access, extra equipment needs to be added both at the subscriber’s and at the cable operator’s end. At the subscriber’s end, cable modems are installed. These would connect to what’s called an Optical Node(O/N) over coaxial cables. If there are several O/Ns, then they would all terminate into an Optical Shelf(O/S) over optical fiber cable.

The O/S terminates into a device called the CMTS (Cable Modem Termination System), again over fiber cabling. This is the most important and the costliest device in the setup as it’s responsible for both upstream and downstream transfer of data from the Internet. As we see, this setup is a mix of coaxial and fiber cabling. This sort of a setup is known as HFC, or Hybrid Fiber-Coaxial setup. However, it can also be done purely on coaxial or fiber.

DSL setup:

There are many flavors of DSL, which we’ll cover in a separate article. Here, we’ll focus on ADSL (Asymmetric Digital Subscriber Line), which is becoming popular among broadband service providers. In a typical ADSL setup, the subscriber would have either a DSL modem or as router. These devices have the same interface as used in Ethernet networks. This could be directly connected to a computer with a network card, if it’s home; or to a hub or a router if it’s an office.

The other end of the DSL modem or router would connect to a DSLAM( Digital Subscriber Line Access Multiplexer) thorough a plain single pair copper cable, which is essentially an ordinary telephone line. The DSLAM would be the termination point for all the subscribers in a particular area. This would in turn terminate into what’s called a DSL. Aggregator over a high-speed digital fiber link called OC-3. This aggregator in turn would connect into the broadband service provider’s network over a fiber cable.

A DSLAM could lie in a subscriber’ place, such a commercial building, where several offices need a DSL connection. It could also lie tat a telephone exchange, from where the copper cabling that’s spread out for voice will also start carrying data traffic.

The choice of whether to use DSL, cable modem, or Ethernet depends largely upon the cost. For the time being, cable modems are used mostly for homes, while DSL and Ethernet are used mostly for offices. However, as broadband technologies become widespread, their costs will come down and they will become affordable even for the home user. In California, for example, most new apartment buildings are geared with DSL or other broadband technology. That may not happen so soon here.

HOW DSL WORKS:

Digital Subscriber Line (DSL) give you broadband access over your existing copper telephone wires. A DSL connection to the Internet is a high-speed,’alway on’(you don’t need to dial up your ISP each time you want to connect) connection that lets you use your telephone lines for making and receiving calls and for Internet access simultaneously.

DSL is also known as xDSL, with the ‘x’ standing for various kinds of DSL technologies. These technologies differ in the connect speed and connection (asymmetric or symmetric) they provide. A point to note in DSL technology, whatever the favor, is that there’s a trade-off between speed and distance.

DSL flavors:

Some popular kinds of DSL are:

ADSL Asymmetric Digital Subscriber Line, as the name suggests, is an asymmetric connection, that is, it provides higher speeds for downstream (from the Internet to the user) data than for upstream (from the user to the Internet) data. This kind of Net usage pattern is seen most in homes and among individual users, where downstream data usually includes graphics, audio. And video, while there isn’t much data to transfer upstream. Downstream speeds for ADSL range from 1.5-9 Mbps, while upstream speeds are up to 1.5Mbps, for a distance of 18,000 feet from the service provider’s premises.

ADLS LITE: This is a lower speed version of ADSL and provides downstream speeds of up to 1Mbpos and upstream speeds 512 kbps, at a distance of 18,000 feet from the service provider’s premises. It is intended to simplify DSL installation at the user’s end.

R-ADSL: The Rate-Adapt Digital Subscriber Line provides the same transmission rates as ADSL, but an R-ADSL modem can dynamically adjust the speed of the connection depending on the length and quality of the line.

HDSL: The high Bit-Rate Digital Subscriber Line provides a symmetric connection, that is , upstream speeds and downstream speeds are the same, and rage from 1.544 MBPS to 2.048 Mbps at a distance of 12,000-15,000 feet. Symmetric connections are more useful in applications like videoconferencing, where data sent upstream is as heavy as data sent downstream. HDSL-II, which will provide the same transmission rates but over a single copper-par wire, is also round the block.

IDSL: The ISDN Digital Subscriber Line provides up to 144 kbps transmission speeds at a distance of 18,000 feet (can be extended),and uses the same techniques to transfer data as ISDN lines. The advantage is that, unlike ISDM\N, this is an ‘always on’ connection.

SDSL: The Single-line Digital Subscriber Line provides symmetric transmissions at rates similar to HDSL. The difference is that it uses a single copper-pair wire to do so (while HDSL uses two or three), and operates at a maximum distance of 10,000 feet from the service provider’s premises.

VDSL : The Very High Bit-rate Digital Subscriber Line is the fastest of all xDSL flavors and provides transmission rates of 13-52 Mbps downstream and 1.5-2.3 Mbps upstream over a single copper-par wire, at a distance of 1,000-4,500 feet from the service provider’s premises.

How DSL works:

. To illustrate how DSL works, we’ll use the example of an ADSL connection from your home to your service provider’s central office (CO).

In DSL, voice and data get transferred simultaneously over your existing twisted-pair copper telephone lines by using different frequency ranges on the same line. Voice is transferred on lower frequency bands and data on higher ones.

The technology to do this resides in the DSL transceiver or modem that’s installed both at your end and at the end of your service provider. A DSL modem on your end sends data over the telephone line to your service provider’s CO. At the CO, a DSL Access Multiplexer (DSLAM) terminates and aggregates incoming ADSL lines. It redirects the voice traffic to the public switched telephone network (PSTN) and the data to a high-speed digital line that connects to the Internet.

For both these methods to work, you need to install low-pass filters of splitters called POTS (Plain Old Telephony Service) splitters, with your DSL MODEM. These separate low frequency voice signals from high frequency data signals, Os that one doesn’t interfere with the other, and you get simultaneous access to telephone and Internet services. Such a splitter would be installed at the CO too. Since human voice can be transmitted below a frequency of 4 kHz, most low-pass filters block access above 4 kHz.

Transmitting data with DSL:

Transmitting digital data over an analog (telephone) line is a complex process, and various problems can arise. In copper lines, distortion is higher on higher frequencies, and since digital data requires higher frequencies, transmitting it is a challenge. There are also problems like thermal nose, crosswalk (Interference between nearby cables), and attenuation (signal loss because signal power diminishes as it travels across a medium, especially for long distances). DSL modems use a process called modulation to address some of these problems. Modulation also enables the transfer of large amounts of digital data, which is what makes DSL a high-bandwidth solution.

Simply speaking , modulation is a method by which a data signal is transferred from one point to another over long distance. The data signal is first put on top of what’s called the carrier signal, which is stronger either in amplitude or frequency. The resulting encoded signal is then sent and recovered at the receiving end by a process called demodulation.

DSL uses either Carrierless Amplitude Phase (CAP) or Discrete MultiTone (DMT) to modify the carrier signal. Both of these use the same modulation technique-Quadrature Amplitude Modulation (QAM)-but implement it in different ways.

UNDERSTANDING CABLE MODEMS:

You will agree that accessing the Internet through normal modems, be it from office or home, is not the easiest thing in the world to do. One of the alternatives that’s becoming popular among home users is a cable modem.

Cable Internet means accessing the Internet through the same cable that brings TV channels like Star, Zee, and MTV into your homes. The two main devices, which make this possible, are a Cable Modem Termination System (CMTS), which has to be installed at your cablewallah or broadband service provider’s end, and a cable modem, which has to be installed in your home. Cable modems come in three different flavors:

External cable modems:

The most common type of cable modem available today, this is small device, similar to ordinary dial-up external modems. But that’s where the similarity ends. One side of the cable modem connects to the coaxial cable coming from your local cable operator, and the other side connects to your PC through an Ethernet interface. So you’ll need an additional network card inside your PC to connect this. An Ethernet cable will connect your PC to the cable modem. An obvious advantage of the Ethernet interface is that you can easily connect more computers to the cable modem by attaching a hub to it.

Internal cable modems:

These cable modems fit inside your PC and usually have a PCI interface. They’re cheaper than external cable modems, and being PCI, will only fit inside an ordinary desktop PC. Mac and notebook users will probably need an external cable modem.

Set-top box:

You may have seen set-top boxes (STBs) from companies like Jadoonetand Samsung, which allow you to access the Internet using your TV and a keyboard. Till now, these boxes contained a regular modem that would dial to an ISP and connect over normal telephone lines, but the cable modem is also available in set-top boxes now.

Inside a cable modem:

Although the various types of cable modems we’ve mentioned are different in appearance, they all contain the same key components needed to make them work. Let’s look at these components and see how they function.

Tuner:

Internet data travels in the form of radio frequency signals over a cable network. Therefore, a cable modem needs something to be able to send sand receive these signals. That’s what a tuner does. It sits inside the cable modem and connects to the cable coming from your cable operator. This cable has to go through a splitter before it reaches the cable modem, which separates your Internet data from normal TV programs. Internet data is transmitted at different frequencies for uploading (upstream) and downloading (downstream). For this, the tuner contains duplexes, which allows it to handle both downstream (between 42-850 MHz) and upstream frequencies (between 5-42 MHz). The tuner receives digitally modulated QAM signals and passes them on to the demodulator.

Demodulator:

This part of a cable modem converts radio-frequency signals received from the tuner into signals that can be fed to an analog to digital (A/D) converter. This in turn converts these analog signals into a series of 0s and 1s.

Modulator:

The modulator does the reverse of what demodulator does. It converts digital computer data (upstream data sent form your PC to the Internet) into radio-frequency signals, which can be transferred over the cable.

MAC:

The MAC (Media Access Control) mechanism sits between the upstream and downstream data paths. It’s used to share the media in a controlled and reasonable way, so that all users are bale to access the Internet without an yours faithfully problems. For example, the cable modem service provider can control the bandwidth assigned to a particular cable modem using its MAC address.

Interface:

The interface, which can be Ethernet, PCI, or USB, transfers data between your PC and the cable modem. STBs don’t have a PC interface, but connect directly to your cable operator’s cable. You then attach your TV and a keyboard to the STB to access the Internet.

Conclusion

Using broadband network we can get high-speed communication services and to upgrade the speed of Internet backbones. And it is multi connection high-speed service .It supports interactive and switched two-way transmission also.