[aleprok]

Push server requires constant connection with the client and the server pushes new information to clients without requiring the client to first ask for updates. Polling requires the client to ask for updates, but does not require constant connection. The connection with polling server is required only while the poll is happening.

Push server basically does not require much at all download bandwith, when polling requires bandwith for each update request. But push server requires open connection per active client, which might be in the millions at the same time. Pull server does not need active connections to be open all the time. Only when a request happens. For example web servers use pull method to service more clients with less cpu and memory usage because the connections are actually only open when http request/reply happens. Games and chats use push method to move information to the server and to push information given by another client to other clients. But for the server to push data to clients the server at least needs to have the ip address of the client with udp or open socket with tcp.