This MIB module manages the GPRS Tunnelling Protocol
(GTP) on GGSN and SGSN.
        
GPRS provides wireless access to packet data network on
the GSM infrastructure.
        
The following diagram illustrates a simplified GPRS
logical architecture with the name of inter-node
interface:
        
+---------------------------------------------+         
|  a PLMN                 +======+   +======+ |
|                         | SGSN |   | AAA  | |
|                         +======+   +======+ |
|                            |           |    |
|                            Gn         SGi   |
|                            |           |    |
|+====+   +====+ +=====+ +======+    +======+ |    +===+
|| TE |-R-| MT |-| BSS |-| SGSN |-Gn-| GGSN |-|-Gi-|PDN|
|+====+   +====+ +=====+ +======+    +======+ |    +===+
|                                        |    |  
|                                        |    | 
+----------------------------------------|----+ 
                                         Gp
                                         |
                +-----------------------------+
                | +====+   +=====+   +======+ |   
                | | MS |---| BSS |---| SGSN | |
                | +====+   +=====+   +======+ |  
                |                             | 
                |                other PLMN   |
                +-----------------------------+
        
GTP is the protocol between GSN nodes (GSN peers) in
the GPRS backbone network. It includes both the GTP
signalling and data transfer procedures.
        
GTP is used both on the Gn interface, i.e. the interface
between GSN peers with in a PLMN, and the Gp
interface between GSN peers in different PLMNs.
        
SGSN is the serving GPRS support node, it responsible 
for the delivery of data packets from and to the MS 
within its service area.
        
GGSN is the gateway GPRS support node, it provides 
interworking with external PDN and is connected with 
SGSNs via an IP-based GPRS backbone network.
        
The GTP protocol is implemented only by SGSNs and GGSN.
        
A PDP Context is an information set maintained by MS 
and GSNs which describes the mobile wireless service
call or session.
        
A Qos Profile is associated with each PDP context which
defines multiple attributes like precedence, delay, 
reliability, peak throughput and mean throughput.
Based on the precedence, delay and mean throughput an
user is classified into one of the three Qos classes:
Best Effort, Normal and Premium.
        
Mean throughput is measured at the Gi and R reference 
points in units of octets per second. It specifies the 
average rate at which data is expected to be 
transferred across the GPRS network during the 
remaining lifetime of an activated PDP context.
        
A MAP converting GSN is responsible for converting GTP
messages to and from MAP messages.  This helps in the
communication with HLR.
        
Acronyms and terms:
        
 APN    Access Point Name
 BSS    Base Station Subsystem
 CG     Charging Gateway
 COA    Change of Authorization
 ETSI   European Telecommunications Standards Institute
 GDM    GTP Director Module
 Gi     Reference point between GPRS and an external 
        packet data network.
 Gn     the interface between GSNs within a PLMN 
 Gp     the interface between GSNs in different PLMNs 
 GGSN   Gateway GPRS Support Node
 GPRS   General Packet Radio Service
 GSM    Global System for Mobile communication
 GSN    GPRS Support Node
 G-PDU  GTP PDU 
 HLR    Home Location Register
 MAP    Mobile Application Protocol
 MME    Mobility Management Entity
 MS     Mobile Station = TE + MT
 MT     Mobile Termination
 NMS    Network Management System
 PDN    Public Data Network
 PDP    Packet Data Protocol
 PDU    Protocol Data Unit
 PGW    PDN Gateway
 PLMN   Public Land Mobile Network
 R      Reference point between a non-ISDN compatible 
        TE and MT. 
 SAE    System Architecture Evolution
 SGSN   Serving GPRS Support Node
 SGW    Serving Gateway
 TE     Terminal Equipment
 T-PDU  the payload of G-PDU
 VRF    Virtual routing and forwarding
 AAA    Authentication, Authorization and Accounting
 eNodeB Evolved Node B
 RNC    Radio Network Controller