Presented by:
Ankita Mor

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Internet Access via Cable TV Network
Need for Cable TV Networks!!
Internet is a Logical, Global Meta Network of computer networks.
The number of internet users is increasing tremendously.
The graph below shows increase in no. of active users in India from 2000-09 i.e 2-million in 2000 to 52 million in 2009
Internet was initially accessed using ADSL technology i.e telephone lines.
Many problems like slow speed ,lower bandwidth ,cost etc.
Traffic congestion on the already slow transmission lines.
Cable TV Networks:
An alternative due to economic cost, higher bandwidth and higher speed.
High penetration in almost all homes in the country.
Technology already implemented in US, but in India we are in initial stages.
Traditional Cable Networks
Started as video service provider.
CATV used to receive signals from TV stations and distribute them, via co-axial cables.
Used co-axial cable end to end.
Large number of amplifiers
are required.
Unidirectional:-from head-end
to subscriber.
Changes in Cable network
Initially designed to deliver TV signals in one direction.
To provide TV services Cable Operators had to recreate a portion of the over-the-air radio frequency (RF) spectrum within a sealed coaxial cable line.
Operators had to upgrade the network so that signals could flow in both directions.
Replaced existing one way amplifiers with two way amplifiers to separate the upstream and downstream signals and amplify each direction separately in the right frequency range.
Modern Cable Networks
Also called as hybrid fiber-coaxial(HFC) network.
Used combination of fiber-optic and co-axial cable.
Modulation and demodulation done at distribution hubs.
Less amplifiers required.
Bidirectional communication
Setup for transfer by Cable TV Network
Cable network for data transmission requires-
1.Cable modem(CM):installed on subscriber premises. Similar to ADSL technology.
2.Cable modem transmission system(CMTS):
Installed inside distribution hub
Receives data from Internet and sends it to the subscriber.
Also receives data from subscriber and passes it to Internet.
Headend: CMTS (Cable Modem Termination System)
One Headend supports @ 2000 Cable Modem Users on a single TV Channel
CMTS interfaces the CATV network to the Internet
CMTS output channel combined with TV video signals
CATV Network to Subscriber via coaxial cable
One-to-Two splitter: One signal to Set Top Box (STB), other to Cable Modem
Cable Modem
One Modem can support up to 16 users in a local-area network
PC/Ethernet Card
Cable Modem connected to PC via ethernet, USB, PCI Bus, etc
Bandwidth Distribution
Even in HFC system, last part of network is coaxial cable.
It has bandwidth ranges from 5 to 750 MHz
The cable company has divided it into three bands:
Downstream Video band:54 to 550 MHz, more than 80 channels
Downstream data band:550 to 750 MHz,33 channels
Upstream data band:5 to 42MHz,6 channels
6-MHz channels each for upstream and downstream data
Cable Modem
Upstream Communication:
The CM checks downstream channels for specific packet sent by CMTS.
The CMTS sends it to CM, allocating the upstream and downstream channels.
CM finds distance from CMTS by ranging and establishes synchronization for time sharing
CM sends packet to ISP for internet address.
CM and CMTS exchange packets for security parameters.
CM sends unique identifier to CMTS
Communication starts in allotted upstream channel.
Data rate <=12 Mbps
QPSK is used for modulation as lower frequencies more susceptible to noise and interference.
Downstream Communication:
Communication is much simpler.
64-QAM is used for modulation.
Theoretical downstream data rate is 30 Mbps ,actual limit is 10Mbps.
No contention as only one sender.
CMTS sends the packet with address of receiving CM , using downstream channel
Cable TV Services
A typical cable television system will usually contain four types of programming service. They include:
1. Basic Cable
2. Expanded Basic
3. Pay Cable Television
Video on Demand
4. Enhanced Information Services
High Speed Internet Access
High Definition Television
Digital Video Recording
Cable Telephony
Real World Performance
Is based upon other devices connected to it.
For eg:
If connection to remote Internet site itself has speed equivalent to a T1 connection (1.5Mbps), then that is as fast as the data can be served to you, no matter how fast your receiving equipment is.
As usage on your segment grows (as more customers are added) the bandwidth must be shared by more people
Adding more cable network segments is very expensive for the cable operator
Advantages
Can provide Internet access to multiple PC’s
Advanced High speed Internet access service.
No new software required
Integration of modem in the Billing system via router.
High Quality digital signal due to proper signal strength.
Reasonable cost.
Limitations
Cable connections are not available in every neighbourhood.
All Cable Companies may not provide Internet access.
It requires two-way data transfer. So cable equipment needs to be changed.
‘Always on’ feature, one needs a firewall and activation of other security features.
Cable modems connected to the head-end equipment at the cable company is like your computer being connected to a LAN hub. When using a single Ethernet card, this results in other people on your branch of the network being able to 'see' data passing to your computer.
Summary
Cable TV networks solve problems that occur in case of telephone lines for internet access.
High speed without traffic jam and with low cost.
Feasible if certain basic requirements-two way cable network and better-quality cables are met.
The cable TV networks as an alternative is worth considering.