Thursday, March 15, 2018

APN-OI Replacement

                       APN-OI Replacement

Helps MME select the corresponding PGW based upon the APN-OI replacement value received from HSS in Update Location Answer.

PGW is selected using DNS NAPTR query using APN-FQDN.
FQDN consists of APN-NI + APN-OI

Traffic can be diverted to the specific PGW when there are multiple PGWs with same MCC-MNC in the home network or if the UE is roaming in visiting network and to home-route the traffic to its home PGW.

In the normal scenario, PGW-FQDN constructed by MME based upon the APN value(NI) received from UE and MCC/MNC(OI) based upon the IMSI.
FQDN= <APN-NI>.apn.epc.<APN-OI>

If it is required not to select the default PGW by MME, APN-OI replacement field is required and to be provided by HSS to force MME to select the specific PGW of its choice instead of default PGW.


1. When UE is roaming and traffic needs to divert to home PGW then home HSS needs to send Visiting-PLMN allowed flag as false and APN-OI replacement value as home MCC-MNC (mncxxx.mccxxx.gprs) along with OI tag if need to route to the specific PGW host.

Then MME creates APN-FQDN using above information and sends DNS NAPTR query to get the home PGW IP to forward the Create Session Request.

Note: if APN-OI replacement value is set by HSS in UE’s subscription Profile, then this is applicable for all the APN’s UE is subscribed to.