In IPTV, the receiver only receives the selected channel. To change channels, the set-top box sends a request to the content server, which then sends a new data stream to the client with the selected channel.
IPTV uses two transmission modes depending on the network: Multicast and Unicast.
What are Multicast and Unicast transmission modes?
Multicast transmission distributes all programs, which are copied and split by routers until they reach the receivers subscribed to the content. These receivers then decide whether or not to watch the programs they are receiving. This model requires more processing power from network components and is used in closed networks such as hotels, businesses, and CATV networks.
The main advantage of Multicast mode is that an unlimited number of clients can receive the same program without increasing bandwidth.
Unicast transmission mode transmits as many copies of the program or programs across the network as there are receivers that have requested to view them (if a receiver has not requested it, it does not receive the program). This method requires more network bandwidth because the total bandwidth required is cumulative, depending on how many receivers request to view the program.
 
Interarrival packet time (IPTV) – Time between packet arrivals
: In an optimal IPTV transmission, all packets arrive at their destination within a relatively constant, short time. This function verifies this continuity in the reception of packets from the selected transport stream.
Generally, the graph's measurements should be concentrated near small time values. A spread of values ​​along the time axis may indicate a network problem.
 
The Interarrival Packet Time graph shows the percentage of IP packets as a function of the time between packets.

More information