What are the four major mobility tasks in a 4G LTE network?

Base station association (the mobile identifies itself via IMSI), control-plane configuration (MME and home HSS establish state), data-plane configuration (tunnels from home P-GW to the mobile), and finally mobile handover when the attachment point changes.

* The four LTE mobility tasks: three at attach, one while moving. *

The four tasks:

1. Base station association — the mobile provides its IMSI, identifying itself and its home network
2. Control-plane configuration — the MME and the home HSS establish control-plane state: the home network records that the mobile is in the visited network
3. Data-plane configuration — the MME configures forwarding tunnels for the mobile; visited and home network establish tunnels from the home P-GW to the mobile
4. Mobile handover — the device changes its point of attachment within the visited network

The pattern to recognize: tasks 1–3 happen at attach time (when you arrive in a network), task 4 happens while you move around inside it. And the structure deliberately mirrors the generic mobility model: registration with the home authority (1–2), data path setup through agents (3), and connection migration (4).

Go deeper:

• Mobility management (Wikipedia) — tracking areas, attach, paging and location update in LTE terms.
• System Architecture Evolution (Wikipedia) — the MME/HSS/S-GW/P-GW roles each task touches, and the bearer setup.