External cable modems connect computers to the internet via USB or Ethernet ports, while internal cable modems are PCI cards installed inside computers. Set top box integrated cable modems provide internet access through televisions. Cable modems use hybrid fibre-coaxial (HFC) infrastructure and consist of a tuner to connect to the cable line, a demodulator to process signals, a modulator to transmit upstream data, and a central processing unit to control operations.

1. Cable ModemsAdam RudderowTED 111www.wireless-thing.com

2. External Cable Modemsa small box that can provide a computer with an Internet connection through either usb or ethernet. most cable modems do come with USB ports installed as well as the usual Ethernet port

3. Internal Cable ModemsInternal cable modems come in form of a PCI (Peripheral Component Interconnect) bus card for PC'sDisadvantage:If cable modem is powered down just itself, computer would be powered down as well

4. Set Top Box Integrated Cable ModemsCommonly used for services like interactive TV and Internet via your televisionMany companies use this type of cable modem to supply Internet access to your computer

5. Downstream/UpstreamDownstream data is transmitted from the Internet towards the computer that requested itUpstream data is data that is sent or "uploaded" from a computer towards the Internethttp://www.tvcinc.com/products/cm550.jpg

6. CATV Infrastructures Cable Access Television, sometimes known as Community Antenna TelevisionModems use CATV infrastructures that partly consist of HFC (Hybrid Fibre-Coax)http://www.microsens.pl/gifs_all/catv_node.gif

7. Typical Cable Modem Componentswww.talkbroadband.com

8. TunerConnects to the CATV outletDigital modulated signals and then forwards them towards the demodulatorCan be attached to a diplexer, which enables the tuner to use a range of frequencies for both the downstream and upstream traffic

9. DemodulatorFour main functions:QAM (Quadrature Amplitude Modulation)A/D converter (Analog to Digital)Error correctionMPEG (Moving Picture Experts Group) synchronizer

10. Demodulator (Cont’d)QAM takes radio-frequency signal and changes it so the A/D converter can process itA/D converter converts signal into a digital signal of 0's and 1'sError correct module then compares the data received to a known standard, fixing errors in transmissionMPEG synchronizer is then used to sequence and organise data groups into their correct order

11. ModulatorThree main functions:To insert data that is ready for error correctionQAM (Quadrature Amplitude Modulation)D/A conversion (digital to analog)

12. Modulator (Cont’d)AKA Burst modulatorConverts digital data back into analog radio frequency signals so that they are ready for transmission

13. MAC (Media Access Control) Acts as the interface between parts of various network protocols Either the CPU of the cable modem or the CPU of the computer is used to take some pressure away from the MAC because of the complexity of its functions.

14. CPU (Central Processing Unit) The brain that controls all of the activity inside the cable modem itselfwww.novopc.com

15. Citationshttp://www.talkbroadband.com/articles/19/1/How-do-Cable-Modems-Work%3Fhttp://www.howstuffworks.com/cable-modem.htm/printablehttp://www.ehow.com/how-does_4962579_how-cable-modems-work.html