How Does It Work?

How Does It Work?

Introduction ][ What Is A Cable Modem? ][ How Does It Work? ][ Advantages And Disadvantages ][ Transmission Of Data ][ What Is MAC? ][ What Standards Exist? ][ Bibliography/Links ][ Copyright Notice ][ From The Author ][ Assignment Questions

Typical Use And Installation Of A Cable Splitter And Internet/TV

As I briefly mentioned before, the cable modem works the same as a traditional analog modem, but the three different types all work slightly differently.

An external modem has to be connected to an ethernet card that either is or needs to be installed inside your PC. While these cards are fairly cheap, most computers don't have them, so they have to be purchased separately. One advantage of having on of these cards is that you can set up your own network as well as having your cable modem.

The internal cable modem works the same as an external modem, but it has to be connected differently. The way to connect the internal cable modem is through a PCI bus card. These are cheaper than ethernet cards, but they have their drawbacks. The first drawback is that they can only be used on your PC, and you also can't set up an ethernet network. The cable may also cause problems because it isn't isolated from the mains cable.

The interactive set-top box works differently from the internal and external modems, because it has to operate the cable TV channels as well as the internet. A return channel is also included in this method. This is usually the telephone line, and it allows you to surf the internet on your TV screen.

Cable modems operate on a cable TV channel, just like a TV channel. Each channel can accommodate for about 1000 cable modems. If more cable modems are required then more channels are added to the head-end.

When a cable modem transmits or receives data, and this is done in timeslots. The three types of timeslots are reserved, contention, and ranging slots.

A reserved slot can only be used by the cable modem that it is assigned to. The assigning of reserved slots is done by the head-end. These types of timeslots is usually used for long data transmissions.

A contention slot can be used by all cable modems for transmitting data. If two cable modems try to transmit in the same contention slot then the data will collide and it will be lost. If this happens then the head-end will signal that no data was received and then the cable modems will try again at some other random time.

Ranging slots are used to compensate for the time differences between cable modems. The head-end measures the difference in time and tells one of the cable modems a positive or negative value to adjust their internal clock by. This is supposed to prevent the collision of data.

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