Description: This MIB module manages the charging related
function on the GGSN node of a GPRS system. 

The following diagram illustrates a simplified GPRS 
logical architecture with the interface name 
denotations: 

+==+     +===+     +====+        +====+        +===+ 
|MS|-----|BSS|-----|SGSN|---Gn---|GGSN|---Gi---|PDN| 
+==+     +===+     +====+        +====+        +===+ 
                        \          / 
                         Ga       Ga 
                          \ +==+ / 
                            |CG|
                            +==+ 

Charging information in GPRS is collected for each MS 
by SGSNs and GGSNs that are serving that MS. The GGSN 
collects charging information for each MS based on  
both external data network usage and the GPRS network  
resources.  

Acronyms and terms: 

 APN    Access Point Name
 BSS    Base Station System
 CCA    Credit Control Answer
 CDR    Call Detail Record 
 CID    Charging Identification 
 CG     Charging Gateway 
 CGF    Charging Gateway Functionality  
 CGG    Charging Gateway Group.
 DCCA   Diameter Credit Control Application
 ETSI   European Telecommunications Standards 
        Institute 
 Ga     Name of the interface between SGSN/GGSN and CG 
 Gi     Name of the interface between GGSN and PDN 
 Gn     Name of the interface between GGSN and SGSN 
 G-CDR  Gateway GPRS Support Node-Call Detail Record   
 GGSN   Gateway GPRS Support Node 
 GPRS   General Packet Radio Service 
 GSM    Global System for Mobile communication 
 GTP    GPRS Tunneling Protocol 
 GTP'   GTP enchanced for charging  
 IE     Information Element
 MS     Mobile Station 
 PDN    Packet Data Network
 PDP    Packet Data Protocol 
 SGSN   Serving GPRS support Node 
 TOS    Type of Service. 
 PSD    Persistance Storage Device.
 PTC    Packet Transfer Command.
 EPC    Evolved Packet Core
 PGW    PDN Gateway
 SGW    Serving Gateway
 SPGW   When a single physical EPC Gateway acts as both SGW and
        PGW for a session, then that session is said 
        to be in SPGW mode.