How does roaming work?

Since bell/Telus/Rogers and other carrier etc. Sign a roaming agreement how does that work?

Is it like a ran where Telus bell rogers make there own roaming servers where all the traffic is routed to canada? Or is the system abit different then usual. I always used to wonder why the ping is so high on roaming yet the download and upload is so good.

Would love to hear how roaming works.

Ik Verizon has 5G Uw but if Verizon customer was using 5G in Canada he wouldn’t have access to 5G uw unless I’m wrong. Would love to hear yalls opinion!