LTE Call Flow – Explained!

The LTE call flow travels over the various components of the network and goes through a series of predetermined steps to finish the end-to-end signalling process. This process begins at the user equipment (UE) and continues to the other parts of the network.

The LTE call flow travels over the various components of the network and goes through a series of predetermined steps to finish the end-to-end signalling process. This process begins at the user equipment (UE) and continues to the other parts of the network

The fundamental building blocks:

• User equipment
• Tablets, mobile phones
• IoT
• LTE eNodeB
• Core network elements
• MME, PGW, HSS and SGW are the acronyms for these.
• These elements can set up signalling and sessions by communicating through various interfaces, such as S1, S6a and

The eNodeB and the UE initiate the communication by requesting a Radio Resource Connection (RRC LTE). It extends to the fundamental components of the network, which communicate with one another via message passing.

LTE Call Flow

1. (MIB, SIB): Elements of the Master Information Block (MIBs) and the System Information Block (SIBs) make it possible for UE to locate itself on the network and sync with it.
2. Random Access Preamble (RAP): This is the first message sent from the UE to the eNB. Its purpose is to achieve uplink synchronisation to obtain the resource for the third message.
3. Request to attach to the PDN sent by eNodeB: The eNodeB will send its first message to the core network, in which it will pass the connect request to the MME. This message is transmitted through the S1AP interface and includes the initial UE message.
4. Authentication request and information: The MME will contact the HSS, and the HSS will then send the security MME. This security tuple will contain K-ASME, XRES, RAND, AUTN etc.
5. Genuine response: The user equipment (UE) is responsible for transmitting the genuine response value, which was derived from the essential K-ASME, XRES, RAND, AUTN etc.
6. Completion of Security Mode: The security mode command MME transmits the encryption and integrity protection algorithms and the critical selection identifier (KSI-ASME). The response message from the UE is sent back to the MME, ciphering it with NAS and protecting its integrity.

7 . Response to the session: Message of acknowledgement sent from the MME to the SGW, indicating that the (GTP-C) tunnel has been established.

8. RRC Reconfig: To activate the default radio bearer, the eNodeB will send an RRC message.
9. Flowing data: At this point, the user equipment (UE) has successfully established a connection to the network, and the data that has been buffered will be sent to the UE via the Data Radio bearer.

Conclusion

Hence, understanding the LTE call flow is important if you want a career in this line. Hope this blog comes in handy!