TCP/IP Tutorial and Technical Overview - IBM Redbooks

18.6.4 Service indication
The service indication (SI) content type enables the sending of notifications to
users in an asynchronous manner (for example, new e-mails). An SI contains a
short message and a Uniform Resource Identifier (URI), indicating a service.
The message is presented to the user on reception. The user can now select to
either start the service immediately or postpone it for a later execution. If the SI is
postponed, the client stores it in order to enable the user for later SI handling.
18.6.5 Push over-the-air protocol (OTA)
OTA is responsible for transmitting the content from the PPG to the client’s user
agent over the wireless network.
OTA can use a WSP session to deliver the content. However, a WSP session
works in a connection-oriented mode and has to be established by a client prior
to delivery of the pushed content. In this case, where there is no active WSP
session, a session initiation application in the client has to establish the session.
This new function in the client works like a server that listens to session requests
from OTA servers and responds by setting up a WSP session for the push
purpose.
The client can verify the identity information of the OTA server against a list of
such servers before attempting any push session.
18.6.6 Client-side infrastructure
A connection-oriented push requires an active WSP session. As explained in
18.6.5, “Push over-the-air protocol (OTA)” on page 668, the client needs a
special session initiation application (SIA) in order to set up the push session
with the PPG. After receiving a session request from PPG, SIA establishes a
session with the PPG and reports which client applications accept content over
the newly opened session. SIA can also ignore the session request from the
PPG if there is no suitable application available or installed.
When the client receives pushed content, a dispatcher looks at the push
message header to determine its destination application. This dispatcher is
responsible for rejecting content if the destination application is not installed. It is
also responsible for confirming operations to the PPG.
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