5G/LTE Call Process: Big Tech Technical Interview Prep

This course contains the use of artificial intelligence.

Understand 5G/LTE call processing from the device

Learn how a UE discovers a cell, establishes a radio connection, registers with the network and prepares its data path. Kihong Kim connects these steps using diagrams and the actual names of RRC/NAS messages and fields. Over 25 years of experience in device validation and commercial launch provide the practical context.

Build a clear model of the UE–Network Interface

Each procedure identifies the starting state, the communicating entities, the important fields and the expected response. RRC Connection completion and NAS registration completion are explained separately. Control procedures are connected to the resulting EPS Bearer or PDU Session data path.

Lessons 1–3: LTE

Follow LTE Architecture, Cell Search, System Information, Cell Selection and Cell Reselection, Random Access and RRC Connection. Continue through Attach, Authentication, Security and Default EPS Bearer setup, then Paging, Service Request and Mobility.

Lessons 4–6: NSA EN-DC

Connect the existing LTE access to NR Measurement, SgNB Addition and the SCG configuration visible to the UE. Read PSCell, NR Random Access, BWP and bearer-path settings, followed by SCG changes, release and Failure Information.

Lessons 7–12: 5G SA

Start with NR Cell Search, MIB and SIB1, then connect RRC establishment, 5GS Registration, Authentication and Security. Understand PDU Session setup and modification, state transitions, Service Request, Mobility and LTE Interworking.

From a concept to a message field

For example, learn why q-RxLevMin = −53 represents −106 dBm and how measurement values and applicable conditions affect Cell Selection. Publicly decoded examples, standard field illustrations and available LTE records are identified separately. Newly captured NSA/SA lab logs are not claimed.

Instructor: Kihong Kim

KT (1999.03–2020.05): Sr. Technical Program Manager; mobile device HW/SW validation and commercial launch, device–network interoperability analysis, iPhone commercialization in Korea and OTA service work.

AT&T (2020.06–2021.10): Senior Engineer; pre-launch network interoperability validation of new devices and services.

Keysight Technologies (2021.10–2022.09): Senior Lead Engineer; 5G, IMS, VoIP and E911 system validation and protocol test scenarios.

Samsung Electronics America (2022.10–2025.04): Technical Architect / Program Lead; 5G device and service quality for major US operators, coordinating customer, development and quality requirements.

Course format and scope

12 lessons with English slides and narration. Protocol message and field names retain their English standard form. The course explains fundamental call processing; new equipment labs and captured NSA/SA logs are not included. VoLTE/IMS, Data Throughput, Band Combination and OFDM performance analysis are covered in the separately available VoLTE/IMS & 5G/LTE Throughput course. This call-process course focuses on UE access, registration, sessions and mobility.

Turn a call flow into a technical-interview explanation

Use the message examples to state the UE starting condition, identify the last confirmed step and expected response, and explain what evidence you would check next. Practise a 60-90 second answer in your own words, then consider how your approach changes when the observations or assumptions change. This is especially relevant to cellular/modem, device validation and interoperability roles.

Kihong Kim brings 25 years of mobile communications experience and firsthand experience across more than 100 job interviews, including Apple interviews through the final stage and Google TPM interviews. His examples help you connect technical knowledge with your own experience and reasoning.

The course content reflects the instructor's personal experience and knowledge and does not constitute official training or endorsement by any past employer.