internet access via cable tv l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Internet Access via Cable TV PowerPoint Presentation
Download Presentation
Internet Access via Cable TV

Loading in 2 Seconds...

play fullscreen
1 / 23

Internet Access via Cable TV - PowerPoint PPT Presentation


  • 309 Views
  • Uploaded on

Internet Access via Cable TV. The cable network was designed to deliver TV signals in one direction from the Head-End to the subscribers homes 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

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Internet Access via Cable TV' - giulio


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
changes in the cable network
The cable network was designed to deliver TV signals in one direction from the Head-End to the subscribers homes

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 cable network so that signals could flow in both directions

Changes in the Cable Network
changes in the cable network3
Cable Operators assign a spectrum of signal frequencies to the cable network

One spectrum is used for the signals that move from the Head-End towards the cable subscriber

Another spectrum of signal frequencies are used for the signals that move from the cable subscriber towards the Head-End

Changes in the Cable Network
changes in the cable network4
By replacing existing one way amplifiers with two way amplifiers Cable Operators are able to separate the upstream and downstream signals and amplify each direction separately in the right frequency rangeChanges in the Cable Network
changes in the cable network5
Changes in the Cable Network

A Traditional Cable network

changes in the cable network6
Changes in the Cable Network

A Modern Cable network

how fast is a cable modem
Cable modem speeds vary widely

Depends on the cable modem system

Cable network architecture

Traffic load.

In the downstream direction (from the network to the computer), network speeds can be up to 27 Mbps

BUT, this is an aggregate amount of bandwidth that is shared by users.

How Fast is a Cable Modem?
how fast is a cable modem9
Few computers will be capable of connecting at such high speeds or have exclusive access to the network

A more realistic number is 1 to 3 Mbps.

In the upstream direction (from computer to network), speeds can be up to 10 Mbps.

However, most modem producers have selected a more optimum speed between 500 Kbps and 2.5 Mbps

AND, many cable operators limit the upstream bandwidth to 128 or 384kbs

How Fast is a Cable Modem?
how fast is a cable modem10
An asymmetric cable modem scheme is most common. The downstream channel has a much higher bandwidth allocation (faster data rate) than the upstream,

primarily because Internet applications tend to be asymmetric in nature.

Activities such as World Wide Web (http) navigating and newsgroups reading (nntp) send much more data down to the computer than to the network.

How Fast is a Cable Modem?
how fast is a cable modem11
Mouse clicks (URL requests) and e-mail messages are not bandwidth intensive in the upstream direction.

Image files and streaming media (audio and video) are very bandwidth intensive in the downstream direction.

How Fast is a Cable Modem?
real world performance
The theoretical performance of a Cable Modem is based upon all other devices being able to work at the same speed and performance as the Cable Modem

However, in a similar way that the actual usable bandwidth on a 10Mbps Ethernet connection reduces to a 4Mbps, so too will the performance of a Cable Modem connection be reduced

Real-world performance
real world performance13
The Cable network itself will suffer the same problems of Internet performance as any other Internet Service Provider (ISP)

Although performance to services on the cable network itself can be amazingly fast, access to 'the outside world' will be slowed down by the performance of other connections on the way.

Real-world performance
real world performance14
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

If you connect to a remote Internet site that itself has a connection 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

Real-world performance
who makes cable modems
3Com, Cisco Systems, Com21, General Instrument, Motorola, Nortel Networks, Phasecom, Samsung, Terayon, Toshiba, Zenith

And many others

Who Makes Cable Modems?
cable modem technology
It MOdulates and DEModulates signals

Much more complicated than their telephone counterparts

Cable modems can be part modem, part tuner, part encryption/decryption device, part bridge, part router, part network interface card, part SNMP agent, and part Ethernet hub

Cable Modem Technology
cable modem technology17
Typically, a cable modem sends and receives data in two slightly different fashions

In the downstream direction

he digital data is modulated and then placed on a typical 6 MHz television channel, somewhere between 50 MHz and 750 MHz

64 QAM is the preferred downstream modulation technique, offering up to 27 Mbps per 6 MHz channel

This signal can be placed in a 6 MHz channel adjacent to TV signals on either side without disturbing the cable television video signals.

Cable Modem Technology
cable modem technology18
The upstream channel is more tricky

Typically, in a two-way activated cable network, the upstream (also known as the reverse path) is transmitted between 5 and 42 MHz

This tends to be a noisy environment, with RF interference and impulse noise. Additionally, interference is easily introduced in the home, due to loose connectors or poor cabling

Since cable networks are tree and branch networks, all this noise gets added together as the signals travel upstream, combining and increasing

Due to this problem, most manufacturers use QPSK or a similar modulation scheme in the upstream direction, because QPSK is more robust scheme than higher order modulation techniques in a noisy environment

The drawback is that QPSK is "slower" than QAM.

Cable Modem Technology
cable modem services
The dominant service is high-speed Internet access

This enables the typical array of Internet services to be delivered at speeds far faster than those offered by dial-up telephone modems

Other services will include

access to streaming audio and video servers, local content (community information and services)

access to CD-ROM servers

a wide variety of other service offerings. New service ideas are being developed daily.

Cable Modem Services
cost of cable modem service
In North America, cable operators are packaging high-speed data services much like they do basic cable television service

Typically charging $40 - $60 per month for an Internet service package

Includes software, unlimited Internet access, specialized content and rental of a cable modem

Cost of Cable Modem Service
cost of cable modem service21
At the low end of this pricing scale, a very robust Internet service is available to consumers for about the cost of a dial-up account with a local Internet service provider and a second telephone line

Even at $60 per month, cable is a far better value than ISDN.

Cost of Cable Modem Service
telco return modems
Not really a cable technology

Used more often with Direct Satellite video systems

Satellite down link is used for fast downstream transmission

A telephone modem handles upstream communication over the public telephone network.

"Telco-Return" Modems
support for multiple pcs
A cable modem can provide Intenet access to multiple PCs, if they are connected via a local area network (LAN)

Cable modems typically have an Ethernet output, so they can connect to the LAN with a standard Ethernet hub or router

Each PC must have an assigned IP address

The cable ISP usually sells at a premium of $5-$10 a month per PC

NAT (Network Address Translation) can allow multiple PCs to "hide" behind a single IP Address

Support for Multiple PCs