How the always-on functionality works in LTE?

Question

I know a little bit that always-on means the user will always be connected to the network. How can it possible when the user is moving how it will have the same IP-address or if some other funda is there. I want to know. If you can give me details description.

Answer 1

The LTE system and EPC adopt the "Always-ON" concept whereby a bearer is established and an IP address is allocated to the mobile terminal when the power to the terminal is ON. This IP address is always allocated to the terminal so that servers on the service provision side can provide IP services the same as in a fixed communications network without having to be aware that the access network is actually a mobile communications network. The always-on bearer is situated inside the EPC (between the S-GW and P-GW), but if a non-communicating state continues, the radio bearer (mobile terminal - eNodeB-S-GW) is released to make more efficient use of radio resources. This means that, when an attempt to communicate reoccurs, only the radio bearer has to be re-established to reopen the communications link, which shortens the connection delay.

Answer 2

This is about the Default Bearer, and even more about the signaling part of default bearer between UE and Radio.
As soon as eNB/eUTRAN notices the UE is not transmitting any data it switches its state from CONNECTED to IDLE.
But the eUTRAN also assures the EPC side that the UE is still connected.

The UE has the same IP address allocated on the initial Attach procedure. EPC is aware of existing bearers, they are just not kept on the radio/eUTRAN side.

When the traffic is sent/recived for this UE, the establishemtn procedure happens only on the Radio/eUTRAN side.

There are many timers on the Radio/eUTRAN side that could help you understand the above, but as I'm not Radio person, please look them up yourself.