LTE : Part 1 : Connection with the Network

How does UE remains connected to the Network in LTE


APN : Access Point Name

It identifies the PDN ( the packet data network ) to which UE will communicate .
APN also helps in identifying the type of service. ( default, mms, internet etc).

Check the APN settings of your phone, you will see in APN
 > type
 > IPv4/Ipv6

APN name will be  like  airtel.mnc078.mcc405.gprs


PDN is packet data network , which will provide that type of service ....MMS , internet , IMS

P-GW  is PDN gateway, which is last node of LTE network, it is gateway/server/computer which will provide the service promised by the APN which UE used.


PDN address : It is the IP address which UE has to get identity in the PDN network.


Now since LTE is only PS network, so you should always need connection with the some PDN.
Hence when we attach with LTE network for the first time, we will be activating some APN.

That APN is known as default APN.

Bearer :  It is name given to identify two end points in LTE network.

 EPS bearer : Between  UE and P-GW
 S5/S8 bearer : Between S-GW and P-GW
 E-RAB : Between UE and S-GW
 Radio Bearer : Between UE and eNB
 S1 Bearer : Between eNB and S-GW.


So now in brief, when you bootup

You will try to attach to network, and also try to get the default APN up.
Now when these two things are done , we are connected to network.

but as cellular technologies are mainly for moving devices, we will face problem, when our device has moved to other location.

Hence when we focus on LTE we focus on two parts.  SIGNALLING : this helps in keeping both UE and Network in contact.

Then is DATA part, which helps in moving packets from UE to Network and vice-versa.

We will see first SIGNALLING and then DATA part.