XMPPs actually been really good at this for quite some time; despite XML being a bit verbose, it compresses very well and it's had TCP like stream management at

XMPPs actually been really good at this for quite some time; despite XML being a bit verbose, it compresses very well and it's had TCP like stream management at the application protocol layer for ages, among other things. It was pretty bad at low-bandwidth connections in the early 2000s, but now there are people running it over extremely low bandwidth high frequency radio, so a janky phone connection is no problem.