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A simple program contains video and audio. These are "elements" that make up a program or "service". When we convert these elements into digital streams, they are called "elementary streams".
The next step is to cut the elementary streams up into small "packets" of data for transport. These packets (many times for multiple services) are then woven into a combined "transport stream" for transmission.
When the elementary streams are packetized, they are assigned a "Packet ID" (PID). All packets with the same PID belong to the same elementary steam. There will be one PID for a particular video stream, another PID for another video stream, another PID for a specific audio stream, etc.
The video and audio PIDs are grouped together into a "Service" . This service is assigned a "Service ID" (SID). So, each program will have a SID. The SID will be associated with the PIDs for the elementary streams that make up the service.
The next step is to cut the elementary streams up into small "packets" of data for transport. These packets (many times for multiple services) are then woven into a combined "transport stream" for transmission.
When the elementary streams are packetized, they are assigned a "Packet ID" (PID). All packets with the same PID belong to the same elementary steam. There will be one PID for a particular video stream, another PID for another video stream, another PID for a specific audio stream, etc.
The video and audio PIDs are grouped together into a "Service" . This service is assigned a "Service ID" (SID). So, each program will have a SID. The SID will be associated with the PIDs for the elementary streams that make up the service.