internet - How does uni-directional packet data transfer work?

When we speak of the Internet data transfers and protocols, the normal process (that I'm aware of) is this:

• A request is sent to the server (some data uploaded)
• The server processes the request (on remote server)
• The response is sent back to the client (data downloaded)

However, how does a satellite TV's set-top-box go about updating its firmware? I am aware that it just fetches (or downloads data) directly from satellite, which is then deflated and installed on the system. But how does it manage to make the request for the download, since it can never transmit data up to the satellite as a "request".

This uni-directional data transfer baffles me, and I'd be glad if someone could explain the protocol please.

The model you describe is just the traditional way the web works, but is not the only communication protocol used. Now I can't say for sure exactly what your provider is doing, but assuming they're using a traditional IP network the most common way of doing unidirectional communication is to use the UDP protocol on top of IP (in a previous life I worked a lot with satellite communications and we did everything over UDP).

The provider likely broadcasts updates to all clients and then the software on the set top box , which is always listening for updates, checks if it should accept the update and then responds accordingly.

It uses Broadcasting. It is a channel (a Frequency, an ip address for internet analogy) preconfigured by the manufacturer to communicate and in this case send firmware updates to the receiver. Like Sat channels send audio and video data to your receiver.

It doesn't need to send a request because the channel is always emitting the firmware file, i think they send the file in a loop with a begining sequence preset. So the receiver looks for the begining sequence and start copying from that point.

Check this wikipedia page for more information : https://en.wikipedia.org/wiki/Broadcasting_(networking)