Description: 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