In Roaming Scenarios two different roaming architectures are defined:
- Roaming with Home Routed traffic
- Roaming with Local Breakout
In first case: UE is latched to visited network (Other PLMN) and using E-UTRAN, MME, S-GW of Visited Network but P-GW will belong to his Home Network (S8-Interface). So here the UE is still connected to his Home PDN-GW.
In Second case: UE is latched to visited network (Other PLMN) and using E-UTRAN, MME, S-GW and P-GW too. So here UE is not connected to his Home PDN-GW. This is where Local BreakOut Happens.
Local Breakout: comes in to picture in second scenario explained above. It enables visitor networks to breakout Internet sessions into home network, instead of routing back to Home networks.
Role of Diameter S9 interface:
- S9 interface lies between the H-PCRF and the V-PCRF (Policy Charging and Rules Function)
- These functions use Diameter to exchange information about the quality of service a roaming customer should get as well as charging information once Local Breakout has begun.