As we discussed in the body of this chapter, DVB-S is set up to carry MPEG-2 TS streams encapsulated with 16 bytes of Reed–Solomon FEC to create a packet
that is 204 bytes long (Fig. A4.4). DVB-S embodies the concept of “virtual channels” in a manner analogous to ATM; virtual channels are identified by PIDs (one can think of the DVB packets as being similar to an ATM cell, but with different length and format). DVB packets are transmitted over an appropriate network. The receiver looks for specific PIDs that it has been configured to acquire (directly in the headend receiver for terrestrial redistribution purposes or in the viewer’s set-top box for a DTH application or in the set-top box via an IGMP join in an IPTV environment).
Specifically, to display a channel of IPTV digital television, the DVB-based application configures the driver in the receiver to pass up to it the packets with a set of specific PIDs, for example, PID 121 containing video and PID 131 containing audio (these packets are then sent to the MPEG decoder which is either hardware- or software-based). So, in conclusion, a receiver or demultiplexer extracts ESs from the TS in part by looking for packets identified by the same PID.