Why Does it Take a Long Time to Change Channels on a Digital TV?

A Technical Look into the Reasons

Channel change timing has been the bane of digital TV for years together. Various technological solutions have been proposed and deployed, but all these have been workarounds rather than solutions. The factors contributing to the channel change delay are:

a. Broadcast TV channels are multicast on the network, and the change in channel is effected by the STB 'leaving' the current multicast group on which the current TV channel is broadcast and 'joining' a new multicast group corresponding to the new TV channel. The IGMP protocol is used to leave and join the multicast groups. The request to leave the group is generated by the STB, and sent to the upstream gateway / router. Depending on the whether anyone else in the same network segment has request for the channel or not, the router passes information upstream to the next router. Then the STB generates a request to join the new multicast group corresponding to the new channel. The request is received by the gateway / router, and if any other user connected to the same gateway /router has already joined the group, then the multicast stream is already available in the segment and is additionally now routed to this user also. If no one else in the segment has joined the group, then the request is sent upstream till the time a router that is connected to a segment with the required multicast stream is reached. Then the multicast stream is routed to the user. This network latency is the major contributor to the channel change delay.