TCP/IP Tutorial and Technical Overview - IBM Redbooks

This kind of transaction, where the server is the initiator of the connection with a
WAP client, is a new feature. It is designed under the name push initiator, as
illustrated in Figure 18-5.
Because the WAP client is located in the WAP domain and the server is in the
Internet, both do not share the push initiator protocol. Therefore, again, gateway
support is needed to provide this functionality. A gateway that performs pushing
is called a push proxy gateway (PPG).
WAP
Domain
Figure 18-5 Push technology
If the push initiator wants to send out information to WAP clients, it contacts the
push proxy gateway (PPG). It uses traditional Internet protocols together with the
push access protocol (PAP). The PPG forwards the pushed content to the WAP
domain, where it is transmitted over the air using the push over-the-air protocol
(OTA).
The PPG might have the capability to tell the push initiator about the state of the
delivery of the message to the client. But this can take some time, because the
WAP client might not be online. If the client is online, it can accept or reject the
pushed content.
The PAP uses XML messages, which can be tunneled through HTTP through
the Internet.
18.6.2 Push proxy gateway (PPG)
The PPG is the access point for content pushes from the Internet to the mobile
network. It does everything that is necessary for this kind of operation, such as:
► Authentication
► Security
WAP
Client
Push
over-the-Air
Protocol
Push Proxy
Gateway
Push
Access
Protocol
Push
Initiator
Internet
Chapter 18. Wireless Application Protocol 665