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CABLE TELEVISION

CABLE TELEVISION. -Many people already get their telephone and internet service over the cable, and the cable operator are actively working to increase their market share. Topics:- 1)Community antenna television 2)Internet over cable 3)Spectrum allocation 4)Cable modems 5)ADSL versus Cable.

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CABLE TELEVISION

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  1. CABLE TELEVISION -Many people already get their telephone and internet service over the cable, and the cable operator are actively working to increase their market share. Topics:- 1)Community antenna television 2)Internet over cable 3)Spectrum allocation 4)Cable modems 5)ADSL versus Cable Networking(Chepter-2)

  2. Community Antenna Television • The system initially consisted of a big antenna on top of a hill to pluck the television signal out of the air, an amplifier, called head end, to strengthen and a coaxial cable to deliver it to people’s homes. • In the early years cable television was called community antenna television It was very mom-and-pop operation; anyone handy with electronics could set up a service for his town and the users would chip in to pay the costs. • As the number of subscribers grew, additional cables were spliced onto the original cable and amplifiers were added as needed. • In 1974,Time,Inc.,started a new channel, Home Box Office (HBO) • This development gives rise to two changes: • 1) Large corporation began buying up existing cable systems and laying new cable to acquire new subscribers 2) There was now a need to connect multiple system often in distant cities in order to distribute the new cable channels Networking(Chepter-2)

  3. Internet over cable • Over the course of the years the cable between various cities were replaced by high-bandwidth fiber. • A system with fiber for the long-haul runs and coaxial cable to the houses is called an HFC (Hybrid Fiber Coax) system. • The electro-optical converters that interface between the optical and electrical parts of the system are called fiber nodes. • Because the bandwidth of fiber is so much more than that of coax, a fiber node can feed multiple coaxial cables. • Now, many cable operator have decided to get into the Internet access business, and often the telephony business as well. • The differences the cable plant and telephone plant have an effect on what has to be done to achieve these goals. • However the another difference between the HFC system and the telephone system that is much harder to remove. Networking(Chepter-2)

  4. Internet over cable • In HFC, a single cable is shared by many houses, where as in the telephone system, every house has its own private local loop. • All the programs are broadcast on the cable and it does not matter whether there are 10 or 10000 viewers. • But when the same cable used for internet access ,it matters a lot with users because of their needs to access internet. It will affect the bandwidth. • While in telephone system there are no such problems. Downloading a large file over an ADSL (Asymmetric Digital subscriber line) line does not reduce your bandwidth. • But on the other hand the bandwidth of coax is much higher than that of twisted pairs. • This Problem is tackled by splitting up long cable and connect each one directly to a fiber node. • The bandwidth from the head end to each fiber node is effectively infinite, so as long as there are not too many subscribers on each cable segment. Networking(Chepter-2)

  5. Spectrum Allocation Networking(Chepter-2)

  6. Cable Modems • Internet access requires a cable modem, a devices that has two interfaces on it: One to computer and one to the cable network. • In past cable operator has the cable modem and cable company technician will installed it, but now in market, customer buy the cable and installed it themselves. • The larger cable operators termed up with a company called CableLabs to produce to produce a cable modem standard and to test products for compliance. • This standard, called DOCSIS (Data Over Cable Service Interface Specification) is just starting to replace proprietary modem. • The European version is called EuroDOCSIS. • The modem-to-computer interface is straightforward. • It is normally 10-Mbps Ethernet (or occasionally USB) at present. • When a cable modem is plugged in and powered up, it scans the downstream channels looking for the special packet periodically put out by the headend to provide system parameters to modems that have just come on-line. • Upon finding this packet, the new modem announces its presence on one of the upstream channels. Networking(Chepter-2)

  7. Cable Modems • These assignments can be changed later if the headend deems it necessary to balance the load. • The modem then determines its distance from the headend by sending it a special packet and seeing how long it takes to get the response, it is called ranging. • Distance is important to accommodate the way the upstream channels oprate and to get the timing right, they are divided in time in minislots. • After completed ranging and gotten its upstream channel, downstream channel and minislots assignments, it is free to start sending packets. • The 1st packet it sends is one to the ISP requesting an IP address, which is dynamically assigned using a protocol called DHCP and also requests and gets an accurate time of day from the headend. Networking(Chepter-2)

  8. ADSL versus Cable • Cable uses coax ; ADSL uses twisted pair. Capacity of coax is hundreds of times more than twisted pair. • ADSL providers give specific statements about the bandwidth; Cable providers do not make any claims because the effective capacity depends on how many people are currently active on the user’s segment. • ADSL system acquires more users, their increasing numbers have little effect on existing users, since each user has a dedicated connection; With cable, as more subscribers sign up for Internet service, performance for existing users will drop. • Everyone has a telephone, but not all users are close enough to their end office to get ADSL; On the other hand, not everyone has cable, but if you do have cable and the company provides Internet access, you can get it. • ADSL is inherently more secure than cable; Any cable user can easily read all the packets going down the cable. Networking(Chepter-2)

  9. ADSL versus Cable • ADSL provider offer a choice of ISPs and sometimes they are even required to do so by law; This is not always the case with cable operators. Networking(Chepter-2)

  10. CABLE TELEVISION NAME ROLL NO. • ANAND SONI 08SQMCA53 GUIDED BY :- PRITESH UPADHYAY Networking(Chepter-2)

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