MME, SGW, PGW, SGSN selection function

The format that is used for node selection is as follows,
node.epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org

MNC and MCC can be obtained from IMSI
For ex :
If IMSI is 652019876543210
whether MCC is 2/3 digit can be found out from the following link,
click here

For the above mentioned IMSI, MCC is 2 digit and hence we have to append a zero to MNC - '01'
node.epc.mnc001.mcc652.3gppnetwork.org


MME selection function :
MME node selection -
Mmec<MMECode>.mmegi<MMEGroupId>.mme.epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org

MME pool selection -
mmegi<MMEGroupId>.mme.epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org


SGW selection function :
tac-lb<TAC-low-byte>.tac-hb<TAC-high-byte>.tac.epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org

For TAC 9999 and IMSI 652019876543210, hex equivalent of 9999 is 270F,
tac-lb0F.tach-hb27.tac.epc.mnc001.mcc652.3gppnetwork.org
This format can be used by MME/SGSN to find the MME also


PGW selection function :
APN has two parts - APN NI [APN Network Identifier] and APN OI [APN Operator Identifier]

APN NI - <APN-NI>
APN OI - mnc<MNC>.mcc<MCC>

PGW selection uses the following format,
<APN-NI>.apn.epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org

For APN, google.com and IMSI 652019876543210
google.com.apn.epc.mnc001.mcc652.3gppnetwork.org


SGSN selection function :
nri-sgsn<NRI>.rac<RAC>.lac<LAC>.rac.epc.mnc<MNC>.mcc<MCC>.
3gppnetwork.org


Acronyms and what they stand for :
MNC- Mobile Network Code
MCC- Mobile Country Code
EPC - Evolved Packet Core
APN - Access Point Name
NI     - Network Identifier
OI     - Operator Identifier
TAC - Tracking Area Code
NRI  - Network Resource Identifier
LAC - Location Area Code
RAC - Routing Area Code
MME- Mobility Management Entity
SGSN- Serving GPRS Supporting Node