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4.1.4.2
 
Offline charging 
Offline charging is used for users who only pay for their services periodically, e.g. once a 
month. Offline charging is based on IMS nodes that report accounting information. This 
is done by sending Accounting-Requests (ACR) and the corresponding Accounting-
Answers (ACA). These messages are based on the Diameter protocol and carry AVP just 
like online charging. The ACR messages are sent to the Charging Data Function (CDF) 
which responds with an ACA.
4.1.5
 
WAP PUSH
This background information is based on [[41], [42]] 
4.1.6
 
Architecture 
With the term push we mean that a server push information to a mobile terminal without 
any requests from the terminal. We can therefore say that the push technology is server-
initiated.
Figure 4-3 WAP Push Architecture 

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4.2 TMMS Service based on IMS: : Design 
Page 49 of 93 
From figure Figure 4-3 we can see that in WAP the push technology has three important 
nodes. These are the Push Initiator (PI)), the Push Proxy Gateway (PPG) and a WAP 
mobile terminal. A PI pushes content and delivery instructions to a PPG using the Push 
Access Protocol (PAP). Further on the PPG pushes the content to the right mobile 
terminal using the WAP Push Over-the-Air (OTA) protocol. This protocol runs on top 
of either HTTP or Wireless Session Protocol (WSP) and are of that reason called OTA-
HTTP and OTA-WSP. Since our services use OTA-HTTP, we will focus on this. 
Further readings about the OTA-WSP can be done in [[41], [42]]. OTA-HTTP uses as 
the name imply HTTP for communication between the PPG and the mobile terminal. It 
uses HTTP POST to deliver content to the terminals. OTA-HTTP is a connection-
oriented service and sets up a TCP connection before any content can be pushed from 
the PPG and the mobile terminal. There are two different methods to set up a TCP 
connection. The first one is called PPG Originated TCP (PO-TCP), and in this case a 
TCP connection is established by the PPG towards the terminal. In this method it is 
assumed that the terminal has IP connectivity with the network and that this IP address 
is known to the PPG. The other method is Terminal Originated TCP (TO-TCP). In this 
method the TCP connection is established from the terminal towards the PPG. 
Summarized the core features of the OTA-HTTP are: 
ƒ
IP connectivity procedure 
ƒ
TCP connection procedure 
ƒ
Registration – PPG becomes aware of the terminal’s current capabilities 
and preferences 
ƒ
Content push – Delivery of content from PPG to terminals using HTTP 
POST method. 
In addition of mentioned features, OTA-HTTP provides mechanisms for identifying and 
optionally authenticates both PPG and the mobile terminal during registration and 
delivery.