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Digital TV broadcasting


As known, there are few methods of delivering television programming to consumers: over-the-air TV, satellite TV and cable TV. We are interested only in the last one for now. Through time and technology development a few more methods were invented: traditional IPTV and IPTV/OTT. This article covers the transition from cable TV to IPTV and IPTV/OTT, the factors that caused it, its advantages and disadvantages as well as their stream transmission diagrams.

Let's take a look at the cable TV first.

Cable TV

Cable TV is a method of delivering television programming to consumers via radio frequency signals transmitted through cables. Earlier people used to install antennas in their appartments and houses to receive the TV signal, but gradually operators switched to this type of TV signal transmission. So, what are the advantages of cable TV?

  • providing more TV channels. Thus, it is possible to broadcast more TV channels, which is undoubtedly beneficial for both the subscriber and the operator.
  • no need to install an antenna
  • higher level of anti-interference capability

Let's have a look at the delivery signal diagram (see Diagram 1):

Diagram 1. Cable TV signal transmission

So, how does the stream gets transmitted to the viewer?

  • Step 1:

TV signal is transmitted from the satellites and/or TV tower to the satellite dish.

  • Step 2:

It is then transferred to the demultiplexer, where it is "split" into a number of channels, i. e. one stream comes in, and several come out. At the same stage, unnecessary channels are eliminated from the input stream, for example, those that do not fit the given time zone or do not match the language criteria. Thus, the signal supplied at the input is MPTS (Multi Programm Transport Stream), and at the output — several SPTS (abbr. Single Program Transport Stream). This is where descrambling of the locked channels takes place as well.

  • Step 3:

Output streams then become an input for the multiplexer, where the reverse to demultiplexing process happens — several single streams merge into one. Thus, the input — several SPTS and the output — one MPTS. This is also where stream gets scrambled for the protection purposes.

  • Step 4:

The stream is subsequently delivered to the viewer's TV through the cable. TV signal also gets descrambled with the built-in CAM module in TVs.

Cable TV is "attached" to the address due to the cable run. That means that a subscriber can watch TV only within his home and only on the TV screen to which this very cable is connected to. Cable TV is in great request in HoReCa industry and in medical clinics due to its limited access to the translated content. Further with the development of the Internet new methods of TV signal delivery appear.

A few examples of cable TV providers: Xfinity (USA), Directv (USA, Latin America and the Carribean), Bell Canada (Canada).


To get an access to the Internet and to watch TV you needed two different cables. Technology development made it possible to transmit TV stream through IP protocol. This made it possible to transmit the TV signal over the same cable as Internet access. Thus, there is no need for a separate cable for television, which simplifies the task for both operators and viewers, and also saves viewers from unnecessary wires at home. IPTV provided subscribers with:

  • more various TV channels, in contrast to cable TV
  • better video and audio content quality
  • traffic economy for the operators
  • release from the need of holding an additional cable for TV
  • recording of the aired programs: the set-top box (STB), included in the IPTV service provided by the operator, is capable of recording TV programs according to a preliminary schedule. If you miss your favorite TV show or an episode of the TV series, you can watch it at any time suitable for you.

TV stream delivery in IPTV model looks as follows (see Diagram 2):

Diagram 2. IPTV signal transmission

  • Step 1:

TV signal is transmitted from the satellites and/or TV tower to the satellite dish.

  • Step 2:

The stream is then transferred to the headend that functions as a demultiplexer (splits one stream into several) and a descrambler as well. So that one stream carries one TV channel. Then the streams are sent by multicast to the router.

  • Step 3:

Router being located in the apartment building or a house receives all the TV channels through IP network. The streams are delivered on demand to the STB afterwards.

  • Step 4:

TV stream is further transmitted to the set-top box (STB) of the viewer, that is placed in his house or apartment. Router sends the channels on demand. That means that if a viewer turns on Canal+ then the router sends this Canal+ to the STB. Usually there are multiple viewers watching the same channel simultaneously. In this case, router splits the signal and delivers it to multiple STBs.

  • Step 5:

Finally the stream is delivered to the TV screen.

The process of TV signal delivery was in some way simplified, however, it is still "attached" to the viewer's address.

For more information about IPTV, see IPTV.


Internet development entailed development of the methods of delivering the TV signal to the end-user. In addition, set of services provided by set-top boxes began to expand. This allowed users to watch movies and live streams, rewind the broadcast, etc. Furthermore, as demand on different devices and gadgets increased, people began to purchase various smartphones, tablets, PCs, laptops, etc. Also Netflix, YouTube, etc. start to appear. So that now it's possible to transmit the TV signal over the Internet. Due to the peculiarities of the Internet, it became possible to perform recording in the archive and organize cloud storage of data. This freed users from downloading content every time to a separate device to watch it. Thus, IPTV/OTT provided even more convenient services for subscribers:

  • more different channels, not only local ones.
  • watching content from different devices: Smart TV, smartphone, PC, etc.
  • watching movies and streams.
  • viewing management: rewinding and pause of TV programs, watching programs from the archive, etc.
  • no need for cables, since the signal is transmitted over the Internet.
  • cloud storage.
  • no need to download content for each device to watch it.

TV signal transmission in IPTV/OTT looks as follows (see Diagram 3):

Diagram 3. IPTV/OTT signal transmission

  • Step 1:

TV signal is transmitted from the satellites and/or TV tower to the satellite dish.

  • Step 2:

Stream is then transferred to the headend that functions as both demultiplexer and multiplexer.

  • Step 3:

It is further delivered to the ingest server.

  • Step 4:

TV signal becomes an input for a transcoder afterwards. Transcoder converts the stream into different formats to adapt to consumer's internet connection speed. That process is called multi-bitrate.

  • Step 5:

Stream copy is then recorded and stored in archive for managing the viewing itself (watching the programs from the archive, rewind and pause, etc.).

  • Step 6:

And later on it is delivered to restreamer and converted into different protocols to be processed by diffeerent devices. Also stream protection is arranged with the help of DRM (Digital Rights Management) and subscriber's authorization.

  • Step 7:

Finally, restreamer delivers the stream to various devices (Smart TVs, STBs, smartphones, tablets, PCs, etc.).

You have probably noticed that most operators provide IPTV/OTT services. It turned out to be more beneficial. Now you can watch movies and broadcasts not only on TV screen, but also on a smartphone, PC or laptop, etc. Thus, IPTV/OTT got rid of this address "attachment" so that it allows viewers to watch the content regardless of their location and hence, expand the broadcast geography. Therefore, it does not matter where the viewer is: at home, at friend's house or on vacation somewhere abroad. The viewer always has an opportunity to watch television as long as Internet access is enabled.

For more information about IPTV/OTT, see IPTV/OTT.