This MIB module defines objects that are used to 
manage GTP Director Module.

In the GPRS network, the APN is the identifier that 
specifies where the user is connecting. The APN 
identifies whether the network is a corporate network 
or a service provider network.  The APN comprises of 
two parts, the network id and the operator id.

The Single Access point feature enables the 
service provider to add new access-points to the GGSN 
without having to provision the HLR. The requests are 
sent by the SGSN to the same virtual APN. A virtual 
APN is not associated with any actual physical 
network.  The GGSN processes the request and forwards 
the packet to the appropriate access-point that is 
specified in the PCO. The Single APN feature is 
supported only in Cisco GGSNs.

The purpose of the GTP-Director is to provide a 
mechanism for service providers using non-Cisco GGSN 
to use the Single APN feature. This would enable the 
service providers to add access-point to the network 
without having to provision the HLR. This will be 
transparent to the SGSN. The mobile user initiates 
a connection request to the SGSN. The access-point 
name specified in the request is the virtual APN. 
The GTP-Director would resolve the access-point name 
and forward the request to the appropriate 
GGSN (real GGSN).

+==+  +===+  +====+   ====   +===+  +====+     +===+
|MS|--|BSS|--|SGSN|--|PLMN|--|GDM|--|GGSN|--Gi-|PDN|
+==+  +===+  +====+   ====   +===+  +====+     +===+
                             | |
                             | |   +====+    
                             | |___|GGSN|------Gi
                             |     +====+       |
                             |                  |
                             |     +====+     +===+
                             |_____|GGSN|--Gi-|PDN|
                                   +====+     +===+

The GTP-Director also provides load balancing across 
GGSNs. The GTP-Director uses the round-robin 
mechanism for providing load balancing.  The 
Cisco GGSNs may use the GTP-Director, but is not 
necessary as they can use IOS-SLB ( Server Load 
Balancing ).

Acronyms and terms:
APN    Access Point Name
BSS    Base Staion Subsystem
GDM    GTP Director Module
GGSN   Gateway GPRS Support Node
Gi     Reference point between GPRS and an external
       packet data network
GPRS   General Packet Radio Service
HLR    Home Location Register
NMS    Network Management System
PCO    Protocol Configuration Options
PDN    Packet Data Network
PDP    Packet Data Protocol
PLMN   Public Land Mobile Network
MS     Mobile Station 
SGSN   Serving GPRS Support Node
TID    Tunnel Identifier