Tolong jelaskan mengenai verifikasi reachability GSN dari Struktur Jaringan Inti GPRS dalam bahasa sunda

update, contona pindahna langganan ti hiji SGSN kanu lianna.

GTP' : pikeun mindahkeun data tagihan ti GSN ka fungsi panagihan.

GGSNs and SGSNs (collectively known as GSNs) listen for GTP-C messages on UDP port 2123 and for GTP-U messages on port 2152.  This communication happens within a single network or may, in the case of international roaming, happen internationally, probably across a GPRS Roaming Exchange (GRX).

The "Charging Gateway Function" (CGF) listens to GTP' messages sent from the GSNs on UDP port 3386.  The core network sends charging information to the CGF, typically including PDP context activation times and the quantity of data which the end user has transferred.  However, this communication which occurs within one network is less standardised and may, depending on the vendor and configuration options, use proprietary encoding or even an entirely proprietary system.