How roaming works in LTE?

Question

when a ue attaches on visited network(roaming scenario), what are the core network nodes and interface involved. Details of complete signalling flow will be appreciable.

Answer 1

When the user is in roaming and latched to visited network (other Network PLMN) it will be connected to E-UTRAN, MME and S-GW of the visited LTE Network. However, LTE/SAE allows the P-GW of either the visited or the home network to be used, as shown in below:

The user will go to his home P-GW through visited network for the home operator's services. The interface between S-GW and P-GW is S5/S8.

S5: If the devices are in the same network.
S8: If they are in different networks (Mainly in Roaming scenarios)

So these interfaces are logical entities if the user is not in roaming and have same operator network. The operator can integrate both S-GW and P-GW in to a single device. Like these S5/S8 interface will get vanishes altogether.

Comments

Thanks Hiteshwar for your reply. I still have one related query. What are all  scenarios when visited network PGW is used rather than home network PGW ?

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This one is Local Breakout scenario. In this it enables visitor networks to breakout Internet sessions into home network, instead of routing back to User Home networks.