When the elementary streams are in a form of packetized elementary streams they are multiplexed (grouped) by the MPEG-2 multiplexer with all other special information to form a resulting contiguous byte data stream. Figure below depicts a principle of multiplexing in the MPEG-2 systems layer.
As can be seen from Figure an output multiplexed signal contains a lot of other information [21]:
The MPEG-2 multiplexer can produce two types of multiplex streams: a programme or transport stream. The programme stream (PS) is intended for the storage and retrieval purposes of digital content from storage medium (e.g. DVD) and it relies on error-free environments. Unlike the programme stream the transport stream (TS) enables to multiplex more programmes and is not so much susceptible to errors because it is protected by FEC (Forward Error Correction) code. Therefore, TS is suitable for broadcasting via terrestrial or satellite environments. The other difference is that TS consists of transport packets with fixed length of 188 bytes.