TCP/IP Tutorial and Technical Overview - IBM Redbooks

peer layer). The dashed line represents the propagation through the provider
over a period of time.
Session services and operations
WSP is designed to function above transaction services, and also directly on
datagram services without using the WTP layer. This means WSP can
communicate with WDP (see 18.9.1, “Wireless Datagram Protocol (WDP)” on
page 672) or with WTP (see 18.9.4, “Wireless Transaction Protocol (WTP)” on
page 679), depending on the architecture of the application. Figure 18-13 shows
two sessions from a WAP client to a WAP server.
One WAE application (represented by the dashed line) uses services from the
session layer (WSP), the transport layer (WDP), and the network layer in the
WAP client when it sends a message over the wireless network to the WAP
proxy. In the WAP proxy, the equivalent peer layers are also used to reach the
receiving WAE.
The other WAE application (represented by the solid line) uses additional
services from the transaction layer (WTP). This is because an additional class of
services is required for particular transactions (see 18.9.4, “Wireless Transaction
Protocol (WTP)” on page 679).
Figure 18-13 Client/server connection flow showing two WSP sessions
686 TCP/IP Tutorial and Technical Overview
WAP client WAP server
WAE
WSP
WTP WDP
Bearer
Wireless
Network
WAE
WSP
WTP WDP
Bearer