Hi, for realtime multi player online game, you can use three solution, web socket, web rtc and signalr.
The main performance is for server code not web socket or other network solution.
Assume that you have a big world with 500 online player that each 100ms all player must be update and get other player information,this means a
for with 500x500 repeat in each every 100ms(also I ignored other server side calculations), so It is clear that you must focusing to sever side optimization, for example using quad tree algorithm to reduce
for iterations .