PE Computer Engineering case studies

PE Computer Engineering · Put your knowledge to work in context.

The PE Computer Engineering credential is a professional engineering license offered in the United States through the state licensing boards that make up the National Council of Examiners for Engineering and Surveying (NCEES). It is intended for engineers who design, integrate, verify, and maintain computing systems and who want the legal authority and professional standing that a PE license carries. The PE Computer Engineering case studies are 5 cases and about 5,350 words.

Tail-Latency Regression After a NUMA and Power-Management Change

A 2U dual-socket server (2 × 16 cores, four NUMA nodes after sub-NUMA clustering was enabled) runs a Java event-ingest service that receives about 120,000 messages per second in 8 KB batches from a 25 GbE NIC. Before a BIOS and kernel upgrade, p50 and p99 end-to-end latency were 1.2 ms and 4 ms.

986 words, about 5 min 2

Timing Closure Under Pressure on a 200 MHz Capture Path

A Kintex-7 FPGA must close timing at 200 MHz for an ADC capture path and also hosts a 100 MHz housekeeping bus driven by an external microcontroller. After a debug core (ILA) was added to chase a field issue, the implementation report shows worst negative slack of −1.8 ns and 312 failing endpoints, against 40 before the debug core.

1,151 words, about 6 min 3

Retry Amplification Takes Down a Payments Platform

A payments platform runs three services - checkout, inventory and a ledger - behind one load balancer. Checkout calls inventory with a 200 ms timeout, up to three retries with exponential backoff from a 100 ms base and no jitter, and no circuit breaker; the HTTP client library also retries once on connection failure.

1,047 words, about 5 min 4

Single-Stream Throughput and an MTU Black Hole on a 38 ms WAN

A mining site connects to a data centre over a 1 Gbps carrier Ethernet service with a committed rate of 400 Mbps and a measured round-trip time of 38 ms. An engineering team is migrating nightly seismic files of 20–60 GB each from the site to the data centre using a single TCP stream with default Linux settings; the observed transfer rate is about 190 Mbps, even though the carrier's own throughput test, run with eight parallel streams, shows 900 Mbps.

1,096 words, about 5 min 5

Cold-Temperature Brownouts in a LoRaWAN Sensor

A battery-powered LoRaWAN sensor is powered by a single 3.6 V Li-SOCl2 AA cell and reports every 15 minutes. The radio draws 118 mA for 90 ms per transmission at +20 dBm; between transmissions the board draws 6 µA.

1,070 words, about 5 min