Is Microsoft trying to redefine the meaning of push e-mail? A few days ago the company's chief Steve Ballmer announced
an Exchange Server feature pack to include "Direct Push Technology" - the delivery of e-mail to mobile devices without any action on the part of the user. At least one analyst, Yankee Group's John Jackson, has reason to doubt that Microsoft's new push email technology is really push at all.
In the case of Windows Mobile, the user's device checks back with the server at specified intervals to receive any pending e-mail deliveries. I digged a bit further and found this technical explanation
from the Microsoft Exchange team:
The [mobile] device issues an HTTP request to Exchange, which asks Exchange to report any changes that occur in the mailbox of the requesting user within a specified time limit. The URL of this HTTP request is the same as that of other AirSync commands ("/Microsoft-Server-ActiveSync") with some differing query string parameters. The body of the HTTP request allows the client to specify those folders that Exchange should monitor for changes. Typically, these will be the Inbox, Calendar, Contacts, and Tasks folders. Upon receiving this request, Exchange will monitor the specified folders until either the time limit expires or a change (such as the arrival of a piece of email) occurs in one of those folders, whichever comes first. Exchange will then issue a response to this request that notes in which folders the changes occurred. Of course, this will be empty if the time limit elapsed before any changes occurred. Upon receiving an empty response, the device simply re-issues the request. This loop of issuing a request for change notifications, receiving an empty response, and re-issuing the request for change notifications is called "the heartbeat." Upon receiving a non-empty response, the device issues a synchronization request against each folder in the response. When those complete, it re-issues the request for change notifications.
In the case of RIM (Blackberry), on the other hand, the network server is continually checking with the device -- which remains essentially inactive -- to see where it is. Obviously RIM's approach is less battery-intensive and faster to respond to new incoming e-mail since it is only reacting when the server initiates a connection.
[via News Factor