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EPC EUTRAN LTE Notes RF

IMTx: NET02x (4G Network Essentials) – Mobility Management – 4. Changing MME and SGW

These are my lecture notes from IMT’s NET02x (4G Network Essentials) course, I thought I’d post them here as they may be useful to someone. You can find my complete notes here.

As we’ve seen earlier, the eNB needs a connection to an MME and a S-GW.

However different eNBs may connect to different S-GWs or different MMEs, and our UE may connect to any eNB, so we need a way to handover between S-GWs and MMEs.

Handover to new S-GW

Let’s take a look at a scenario where a UE is moving from one eNB to another, and each of the two eNBs is in a different S-GW.

At the start we have a connection from the MME to the S-GW, a GTP-C tunnel for control information and a GTP-U tunnel (called the S5/58 bearer) that carriers the user data over GTP-U between the P-GW and the S-GW.

As the UE moves to the eNB in TA2 we need the MME to modify the tunnel from the P-GW to the S-GW to change it from connecting the P-GW to the old S-GW and instead connecting the P-GW to the new S-GW.

The MME establishes a new tunnel for control to the new S-GW, and sends a message to the new S-GW to modify the tunnel from the P-GW to the old S-GW to point to the new S-GW.

Handover to new MME

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