VoLTE/IMS & 5G/LTE Throughput: Big Tech Interview Prep

This course contains the use of artificial intelligence.

Google Cloud Text-to-Speech provides the English narration. AI tools assisted with translation, script preparation, and diagrams. The course is based on the instructor's original Korean material and professional telecommunications and mobile-device experience.

VoLTE/IMS & 5G/LTE Data Throughput: Real-World Analysis & Big Tech Interview Prep

Built on 25 years of telecommunications and mobile-device technical and analysis experience, this course connects VoLTE/IMS call processing with practical 5G/LTE Data Throughput analysis. Learn how procedures fit together, which conditions a theoretical maximum assumes, and what to inspect when actual performance differs. Each topic connects diagrams, protocol fields, and calculation examples to a clear analysis sequence.

Follow the complete VoLTE/IMS signaling and media paths

Start with the UE, LTE/EPC, and IMS functions and their protocol layers. Trace SIP delivery separately from RTP media delivery. Then examine IMS Registration, authentication and security, registration refresh and de-registration, originating and terminating call setup, SDP negotiation, and Bearer configuration. Compare SIP headers and response codes with the corresponding request and procedure stage. Connect SDP addresses, Ports, and Codecs to the media that should actually arrive.

Build the Throughput model from OFDM resources

Begin with OFDM and the time-frequency resource grid, then connect Bandwidth, Resource Blocks, MCS, and MIMO to the amount of data that can be transmitted. Use LTE UE Category limits to understand theoretical rates and compare them with the UE's supported Band Combination and current configuration. Distinguish antenna capability, the supported maximum Layer count, and the Rank actually used for transmission.

Investigate the six practical Throughput factors together

Work through Aggregated Bandwidth, allocated PRB, MCS, DL/UL MIMO, BLER, and CQI. A high CQI or MCS alone does not determine the delivered rate. Check the MCS Table, actual resources, active Component Carriers, Layer count, retransmissions, transmission opportunities, and test conditions. Calculation examples show how changing one condition changes the expected rate. LTE and NR differences, CA/Band Combinations, and US carrier Band examples are connected to practical capability checks.

Explain the gap between theoretical and measured performance

First establish the measurement layer and time interval. Then compare the theoretical assumptions with current grants, TBS, successful reception, and application data. Separate radio-resource limitations from retransmissions, traffic supply, TCP behavior, and device or test-system bottlenecks. Plan a comparison test that changes a specific condition and identifies the next evidence needed.

Turn practical analysis into technical-interview answers

The course includes role-relevant practice questions and answers for telecommunications, modem, and cellular positions at companies such as Apple, Google, and Meta. Explain why equal Bandwidth can produce different speeds, why DL 4×4 support does not imply Rank 4, and why high CQI and MCS can coexist with low Throughput. Practice answers that state the conditions, identify relevant measurements, and propose a useful next test.

Learn through 12 lessons with diagrams, message examples, and calculations

Lessons 1–6 cover VoLTE/IMS registration, security, call setup, SDP/Bearers, Codecs and RTP, session features and SRVCC, emergency calls, and abnormal procedures. Lessons 7–12 cover OFDM, UE Category, MIMO, LTE resource calculations, CA and Band Combinations, carrier Bands, NR Throughput, and integrated NSA/SA performance diagnosis. The translated narration, slide transitions, and visual emphasis follow the same teaching sequence.

Instructor Kihong Kim has worked on mobile-device HW/SW verification and commercialization at KT, device and service network interoperability at AT&T, 5G/IMS/VoIP/E911 testing at Keysight Technologies, and device/service quality and technical-issue coordination for US carriers at Samsung Electronics America.

This course is intended for mobile-device development, validation, and performance-analysis professionals and engineers preparing for related technical interviews. Basic familiarity with LTE/5G architecture and common telecommunications terminology is helpful. Study using the supplied slide decks and message/calculation examples; separate measurement equipment or paid analysis tools are not required.