How to determine an appropriate APN and s8 protocol type

Question

What information used by MME to determine an appropriate APN-OI and S8 protocol type (PMIP or GTP) when the MME and PDN GW are located in different PLMNs?

And if the HSS provides the identity of a statically allocated PDN GW, or the HSS provides the identity of a dynamically allocated PDN GW and the Request Type indicates "Handover", no further PDN GW selection functionality is performed means PDN Gw is chosen which is mentioned in subscriber information by HSS ?

Comments

Let me answer the first part only -

HSS also contains information about the (Packet Data Networks) PDNs to which the user can connect. This could be in the form of an access point name (APN)  or a PDN address.

So in short APN is provided by the HSS and it identifies a GGSN or P-GW. It includes an APN network identifier which defines the Packet Data Network (PDN) to which the UE requests connectivity, and may also include an APN operator identifier which defines in which Public Land Mobile Network (PLMN) the P-GW or GGSN is located, according to LTE World.  To accomplish this, the APN structure is comprised into two parts: a network identifier and an operator identifier.

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Thank you sir,
So APN-OI is used to find out the P-GW or GGSN PLMN.
If P-Gw belongs to Other PLMN. then s8 will use PMIP or GTP? when PMIP will come into picture.

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I have only answered first part, second part of the question is still to be answered :)