The Direct Push Process

6/2/2010

Direct push traffic resembles small HTTP requests to an Internet Web site that takes a long time to issue a response. The content of the packets is typically encrypted by using Secure Sockets Layer (SSL), which makes identifying direct push traffic by sniffing difficult.

The following steps provide an overview of the direct push process:

1. The client issues an HTTP message known as a ping request to an Exchange server, asking that the server report any changes that occur in the user’s mailbox within a specified time limit.
   In the ping request, the client specifies the folders that Exchange should monitor for changes. Typically these are the Inbox, Calendar, Contacts, and Tasks.
2. When Exchange receives this request, it monitors the folders specified until one of the following occurs:
   • The time limit expires. The time limit is determined by the shortest time out in the network path.
     If this occurs, Exchange issues an HTTP 200 OK response to the client.
   • A change occurs in one of the folders, such as the arrival of mail.
     If this occurs, Exchange issues a response to the request and identifies the folder in which the change occurred.
3. The client reacts to the response from the Exchange server in one of the following ways:
   • If it receives an HTTP 200 OK response indicating that no error occurred, it re-issues the ping request.
   • If it receives a response other than HTTP 200 OK, it issues a synchronization request against each folder that has changed. When the synchronization is complete, it re-issues the ping request.
   • If it does not receive a response from the Exchange server within the time specified, it lowers the time interval in the ping request and then re-issues the request.

See Also

Concepts

How the Direct Push Technology Works