How does cable internet work

Internet access via cable connection

In addition to radio reception, cable network operators also offer Internet access and a telephone connection. Since the cable networks were actually only developed and set up for the transmission direction, the cable networks had to be made suitable for return channels. The TV cable is therefore considered to be "the alternative" to DSL.
The availability of cable TV networks varies greatly from region to region. There are no nationwide valid offers.

The cable connection

Residents of single-family, semi-detached and terraced houses can easily conclude a contract with the cable provider. This is usually not a problem for residents of apartment buildings either.
The introduction of the Internet in the cable network will not change anything for the television viewer. Modifications may only be necessary when a customer orders an Internet connection. For example, the antenna socket in the apartment must be replaced if it does not yet have a data connection. It is an antenna socket with an additional socket on which an F connector with screw fastening fits. The F connector is also used in satellite technology. The screw connection prevents accidental removal or loose contacts. The sockets for TV and radio remain unchanged. A bandpass is integrated into the new socket, which separates the return channel from the television and radio signals.
In addition to the antenna socket, the antenna amplifier in the house must also be replaced if it does not support the high frequency range. A technician from the cable company will replace the socket and the amplifier.
The customer receives a special cable modem that his cable operator provides. It is connected to the data socket of the antenna socket via a coaxial cable. The modem is then usually near the television. From there, a connection to the router or the computer must be established.

restrictions

The TV cable network is a "shared medium". This means that although Internet access is offered via cable connections with several hundred Mbit / s, download rates can drop drastically at peak times because the architecture of the cable network means that many participants have to share the total bandwidth. Only the network operator knows how high the total bandwidth is in the customer's service area.
The bandwidth specification is somewhat more precise for TV cable than for DSL. While the cable length and quality play a role with DSL, the bandwidth with TV cable is mainly influenced by the number of users who use it at the same time. In the case of TV cable, the advertised speed is often actually achieved. Amplifiers ensure that the necessary signal quality reaches every customer.
The participants share the advertised bandwidth in a network segment. That can be several dozen customers. Since mainly private households are supplied with it, this limitation is not a problem. The normal state of an Internet connection in private households is idle.

Transmission technology

Because of the different transmission methods and techniques used, it is difficult to go into the details of the technology. Each provider uses different equipment.

In order to make the frequency spectrum usable for Internet access, the TV channel grid is subdivided with a combination of frequency and time multiplex.
In the receiving direction (downlink), transmission is carried out in radio mode (broadcast). This means that all participants on the same cable harness receive the same signal. The customer's cable modem then filters out the packets that are directed to the customer's own subscriber address. Access to the channels is controlled via time slots. This is assigned to the cable modem by the CMTS (in the head station).

Transmission speed

The cable network is a so-called "shared medium". This means that all participants on a cable strand have to share the bandwidth available there.
In the case of a cable network offer with 100 Mbit / s, the cable modem is limited to this value.
With cable connections with the DOCSIS-3 standard, the cable modems typically work at up to 400 Mbit / s.

With a transmission capacity of 10 GBit / s for 100 to 200 connections, 50 to 100 MBit / s per connection can be guaranteed. This very quickly results in "up to 50 or 100 Mbit / s".

Why is the uplink less than the downlink?

In the transmission direction, i.e. from the modem to the head-end station, there is the problem of input noise from the distributed antenna sockets. The noise is increased by the amplifiers in the cable network because the signal is not regenerated, only the level is increased. In order for the information from the cable modem to reach the CMTS at all, a more robust, but less efficient modulation method must be used in the sending direction. In addition, the frequency range in the sending direction is smaller than in the receiving direction.

Overview: cable modem technology

Other related topics:

Product recommendations

Everything you need to know about communication technology.

Communication technology primer

The communication technology primer is a book about the basics of communication technology, transmission technology, networks, radio technology, mobile communications, broadband technology and Voice over IP.

I want that!

Everything you need to know about communication technology.

Communication technology primer

The communication technology primer is a book about the basics of communication technology, transmission technology, networks, radio technology, mobile communications, broadband technology and Voice over IP.

I want that!