Internet Access via Cable TV Network

Internet Access via Cable TV Network

Seminar byAnkur Desai

Anisha NayakAnish Kumar

Department of Electronics and Communication Engineering,

Gogte Institute of Technology

ContentsDifferent Types of Internet AccessCable TV NetworksWorking of Cable InternetCable ModemCable Modem Terminating SystemDSL vs Cable InternetAdvantagesDisadvantagesConclusion

Different ways of Internet AccessDial-up connectionISDNDSL (ADSL and SDSL)Cable TV NetworkWireless Network (Wimax, Wifi, EVDO,

HSDPA and UMTS)T1 and T3 linesOptical Fibre lineSatellite

Cable TV NetworkCable TV Network is made up of

coaxial cable lines that bring television signals to TV.

Each television channel is given a 6-megahertz channel on the cable.

Cable TV Networks are high bandwidth networks i.e. 550 to 750 MHz by their very nature of design.

These networks were traditionally built as one way networks carrying 60-100 Cable TV channels downstream i.e. from Headend to the Subscriber.

Working of Cable InternetInternet over cable is a technology and service that uses

the existing cable TV networks to bring Internet data to PC at a very high speed.

Instead of getting an Internet connection through your telephone wire, you get a connection through your cable network (the same place your cable TV Connection comes from).

Internet delivery over Cable TV requires a two-way network since information of selected website, etc. has to be transmitted to the Headend, from where it would be directed to the website of interest.

Higher frequencies flow toward the subscriber and the lower frequencies go in the other direction.

Working of Cable InternetThe television and the Internet

transmission take place simultaneously on the same cable but at different frequencies.

This allows the user to view TV and access Internet at the same time

Working of Cable InternetWhen a cable company offers Internet access over the

cable, Internet information can use the same cables because the cable modem system puts downstream data (data sent from the Internet to an individual computer) into a 6-MHz channel. On the cable, the data looks just like a TV channel. So Internet downstream data takes up the same amount of cable space as any single channel of programming.

One downstream channel can handle hundreds of cable modems.

Upstream data (information sent from an individual back to the Internet ) requires even less of the cable's bandwidth, just 2 MHz, since the assumption is that most people download far more information than they upload

Working of Cable InternetHence setting up of a robust two-way Cable TV

network is the first requisite before deploying Cable Modems on a Cable TV network. This is done by upgrades to the amplifiers in the cable distribution network etc.

Cable Network

Equipments RequiredPutting both upstream

and downstream data on the cable television system requires two types of equipment:

1. A cable modem at the customer end

2. A cable modem termination system (CMTS) at the cable provider's end

Cable ModemFor Cable Internet access on PC, a Cable

Modem is required at user’s end.A cable modem is an external device that

connects to the computer to provide high-speed data access via cable TV networks.

It has two connections; one to the TV cable wire and the other to a computer.

A Cable Modem sends and receives data to and from the Internet by using the existing coaxial cable network.

Cable ModemThe modem translates cable signals the same way

a telephone modem translates signals from a telephone line.

Cable modems translate radio frequency (RF) signals to and from the cable plant into Internet Protocol (IP), the communications protocol spoken by all computers connected to the Internet.

At the customer premise, a high quality two way splitter is installed on the Cable TV line, with one output connected to the Cable Modem and the second output connected to the TV.

Cable Modem

Tuner: The tuner will contain a diplexer, which allows the tuner to make use of one set of frequencies (generally between 42 and 850 MHz) for downstream traffic, and another set of frequencies (between 5 and 42 MHz) for the upstream data.

Cable ModemDemodulator: The most common demodulators have four functions.A Quadrature Amplitude Modulation (QAM) demodulator

takes a radio-frequency signal that has had information encoded in it by varying both the amplitude and phase of the wave, and turns it into a simple signal that can be processed by the analog-to-digital (A/D) converter.

The A/D converter takes the signal, which varies in voltage, and turns it into a series of digital 1s and 0s.

An Error correction module then checks the received information against a known standard, so that problems in transmission can be found and fixed.

MPEG Synchroniser: The network frames, or groups of data, are in MPEG format, so an MPEG synchronizer is used to make sure the data groups stay in line and in order.

Cable ModemModulator: In cable modems that use the cable system for upstream traffic, a modulator is

used to convert the digital computer network data into radio-frequency signals for transmission. It consists of:

1. A section to insert information used for error correction on the receiving end 2. A QAM modulator 3. A digital-to-analog (D/A) converter 

MAC: The MAC sits between the upstream and downstream portions of the cable

modem, and acts as the interface between the hardware and software portions of the various network protocols. All computer network devices have MACs.

CPU: In the case of a cable modem the tasks are more complex than those of a

normal network interface card. For this reason, in most cases, some of the MAC functions will be assigned to central processing unit (CPU).

Cable Modem Terminating SystemThe Internet signals are in the digital

domain and these need to be interfaced to the Analog Cable TV Network. This interface is termed Cable Modem Termination System (CMTS) and typically serves 2000 – 3000 Cable Modems and is connected to a high-speed data link. A typical CMTS consists of an Input interface, Router, Cable Modem card and a powerful Microprocessor. 

At the cable provider's head-end, the CMTS provides many of the same functions provided by the DSLAM in a DSL system.

Cable Modem Terminating SystemThe CMTS takes the traffic coming in from a group of

customers on a single channel and routes it to an Internet service provider (ISP) for connection to the Internet.

At the head-end, the cable providers will have, or lease space for a third-party ISP to have, servers for accounting and logging, Dynamic Host Configuration Protocol (DHCP) for assigning and administering the IP addresses of all the cable system's users.

The downstream information flows to all connected users, just like in an Ethernet network -- it's up to the individual network connection to decide whether a particular block of data is intended for it or not.

Cable Modem Terminating SystemOn the upstream side, information is sent from the user to

the CMTS -- other users don't see that data at all. The narrower upstream bandwidth is divided into slices of time, measured in milliseconds, in which users can transmit one "burst" at a time to the Internet. The division by time works well for the very short commands, queries and addresses that form the bulk of most users' traffic back to the Internet.

A CMTS will enable as many as 1,000 users to connect to the Internet through a single 6-MHz channel. Since a single channel is capable of 30 to 40 megabits per second (Mbps) of total throughput, this means that users may see far better performance than is available with standard dial-up modems.

As the system grows, the CMTS can be upgraded with more downstream and upstream ports.

DSL vs Cable:Speed (advantage - Cable): Cable boasts faster speed than

DSL Internet in theory. However, cable does not always deliver on the promise in everyday practical use.

Popularity (advantage - Both): In the US, cable Internet enjoys significantly greater popularity than DSL, although DSL has been closing the gap recently. Outside the US, DSL continues to hold the edge.

Customer Satisfaction (advantage - DSL): US cable services generally rate lower than DSL in customer surveys.

Security (advantage - Both): Cable and DSL implement different network security models. Historically, more concerns have existed with cable security, although cable providers have definitely taken steps to improve security over the past few years. It's likely both DSL and cable are "secure enough" for most people's needs.

Advantages of Cable InternetHigh connection speed Convenient – you are always connected to

the internet Does not affect your phone line. You don’t

need to switch your local phone service provider.

 Unlike ADSL, its performance doesn't depend on distance from the central cable office.

Disadvantages of Cable IntenetBandwidth is shared over the same cable

line. Connection speed is affected by the number of people using the internet at the same time in your neighborhood.

 Higher security risk than dialup (personal firewall is needed).

 Not available to all cable TV networks. Usually tied with cable TV subscription.

ConclusionCable Internet access is the principal competitor

to DSL and is offered at a range of prices and speeds overlapping that of DSL.

Cable TV has a strong reach to the homes and therefore offering the Internet through cable be a scope for furthering the growth of internet usage in the homes.

The cable is an alternative medium for delivering the Internet Services in the US, there are millions of homes with cable modems, enabling the high-speed internet access over cable.

Referenceshttp://en.wikipedia.org/wiki/

Cable_Internet_accesshttp://en.wikipedia.org/wiki/Cable_modemhttp://en.wikipedia.org/wiki/Internet_Accesshttp://en.wikipedia.org/wiki/

Cable_modem_termination_systemhttp://computer.howstuffworks.com/cable-

modem.htmhttp://www.hathway.com/brodband/

prod_broadband_faq3.asp

Thank you