Sep 2024 – Oct 2025 · 1 yr 1 mo · Seoul, South Korea · On-site

• Head of Product Group (Product Managers, Software Engineers/QA, Infrastructure Engineers, Tech Support).

Oct 2023 – Sep 2024 · 11 mos · Seoul, South Korea · On-site

Mar 2023 – Oct 2023 · 7 mos · Seoul, South Korea · On-site

Jan 2019 – Oct 2022 · 3 yrs 9 mos

• Worked on Cloudflare’s edge proxy handling all incoming traffic, which implements HTTP 1.1 (plaintext, TLS), HTTP/2 (TCP+TLS) and HTTP/3 (UDP+QUIC) and other protocols.
• HTTP/2 Upload speed improvement. Blog: “Delivering HTTP/2 upload speed improvements” (https://blog.cloudflare.com/delivering-http-2-upload-speed-improvements/)
• gRPC Support: PoC and writing a software specification, tech lead of the project. Blog: “Road to gRPC” (https://blog.cloudflare.com/road-to-grpc/)
• quiche - QUIC protocol stack (https://github.com/cloudflare/quiche)
• Implemented quiche's congestion control algorithms: CUBIC (draft-ietf-tcpm-rfc8312bis), BBR (draft-cardwell-iccrg-bbr-congestion-control), PRR (RFC6937), HyStart++ (draft-ietf-tcpm-hystartplusplus, later RFC9406)
• Deployed CUBIC and Hystart++ to Cloudflare QUIC services: Blog: “CUBIC and HyStart++ Support in quiche” (https://blog.cloudflare.com/cubic-and-hystart-support-in-quiche/)
• Others: Chromium-style flow control implementation, Delivery Rate Estimation (draft-cheng-iccrg-delivery-rate-estimation-02), Outgoing packet pacing with GSO and SO_TXTIME (https://blog.cloudflare.com/accelerating-udp-packet-transmission-for-quic/), various bug fixes and performance improvements. iCloud Private Relay Proxy: Improving QUIC performance (https://blog.cloudflare.com/icloud-private-relay/)
• Contributor of https://datatracker.ietf.org/doc/html/rfc9406

Nov 2017 – Jan 2019 · 1 yr 2 mos

• After the Neumob acquisition, I worked on migrating the Neumob service and customers onto Cloudflare infrastructure and continued to improve the entire service (protocol, SDK, tests).
• Blog: “A cost-effective and extensible testbed for transport protocol development” (co-author) (https://blog.cloudflare.com/a-cost-effective-and-extensible-testbed-for-transport-protocol-development/)

Mar 2016 – Nov 2017 · 1 yr 8 mos · Sunnyvale, CA

• Faster Mobile Apps. Mobile Edge Cloud, acquired by Cloudflare. (https://blog.cloudflare.com/neumob-optimizing-mobile/)
• Basic architecture design of Neumob, including consumer app (Android, iOS) and enterprise service
• Design & Implementation of NP (Neumob Protocol): UDP-based transport layer protocol designed to provide high performance/less error for wifi and mobile network (2G, 3G, LTE)
• Design & Implementation of NP-Relayd (Neumob Protocol Relay Daemon), a translation layer between NP and TCP in server side
• Design & Implementation of a high scalable API Service for Neumob SDK, for SDK Initialization and Config Update
• Design & Implementation of 1st-gen proxy server for consumer app and enterprise service including basic middle mile optimization
• Design & Implementation of VPN server for Neumob Consumer app
• Performance tuning and improvement including real world traffic
• Setting up 1st-gen production environment (AWS, FreeBSD, Linux, ansible and fluentd)
• Troubleshooting customer issues - identify service issues based on the report/ticket and performance bottleneck, fixing issues by various metric data and log analysis and packet capture, working with other teams
• Design reviews and code reviews with peer engineers
• Writing/managing company patents

Jan 2015 – Feb 2016 · 1 yr 1 mo · Sunnyvale, CA

• Neumob is the leader in app acceleration for a mobile-first world. The Neumob Accelerator SDK speeds up the load times, reliability and performance of mobile apps anywhere in the world, helping app owners keep their hard-won users and drive maximum revenues.
• The company’s innovative, mobile-first infrastructure and global presence combine to dramatically reduce frustrating in-app errors, slow load times, failed uploads and app timeouts, whether an app’s users are hyper-local in one city or located around the world. App owners simply install a 2-line SDK into their app, and instantly gain access to Neumob’s world-class, global app acceleration network.
• For businesses that need to deliver mobile apps to their users faster, more reliably and more securely to any targeted mobile audience, on any network, Neumob is the answer.

Apr 2013 – Jan 2015 · 1 yr 9 mos

• Moved back to US office. Leading CDNetworks CDN/Web performance measurement/optimization effort, working with performance engineers in Korea, Service Delivery, Network Operation, Engineering and Product Management.
• Writing/maintaining internal tool for analyzing CDN performance including competitor. Working with Cedexis for RUM data analysis and Gomez/Keynote for agent-based performance data analysis

Feb 2008 – Jan 2011 · 2 yrs 11 mos

• Dispatched to CDNetworks US Office (San Jose, CA).
• CDN Service Operation of CDNetworks San Jose Office
• Launching Application Delivery Network Project
• Due Diligence for acquisition of Panther Express, Post-Merger Integration (technology, engineering)
• Working with Engineering team of San Jose office, launching new platform based service such as Cloud DNS
• Performance Management of CDN & Application Delivery

Jan 2007 – Jan 2015 · 8 yrs

• Working/Leading with Engineering team - platform development, new product launching (Cloud DNS, DNA, Cloud Storage etc)
• Working with Operation team - service performance evaluation, troubleshooting
• Performance Management of Content/Application Delivery Network
• Technology evaluation/PoC support
• Co-work with KDDI for Mobile Network Analysis, CDN caches and SPDY Accelerator

Apr 2005 – Dec 2006 · 1 yr 8 mos

• Leading R&D Center with the following area.
• Platform development of Nefficient Content Delivery Network
• Streaming (Windows Media, Flash Media)
• Caching
• Global Load Balancing
• HTTP-based streaming system
• Multimedia (VOD/Live) Player
• Customer Portal and log processing
• Multi-national support (Japan, China, US)
• Team has grown up from ~20 (3 teams) to ~40 (5 teams).

Sep 2005 – Sep 2006 · 1 yr · Within 23 wards, Tokyo, Japan

• Dispatched to CDNetworks Japan (Tokyo office).
• Set up basic CDN operation system of CDNetworks Japan with help of Korea office.
• Build system and network for partnership company (ClubIT - later Broadmedia)
• Migration of ~100 US-based CDN customer onto CDNetworks/ClubIT CDN
• High level troubleshooting technical issue of customers
• Launch a new service and localization for Japanese users.

Apr 2001 – Mar 2005 · 3 yrs 11 mos · Gangnam-gu, Seoul, Korea

• Design & implementation of Rewriter Global Load Balancer: HTTP, FTP, Windows Streaming
• Design & implementation of PowerFTP: HTTP based parallel download service, service daemon, logging
• Design & implementation of CacheNet Contents Delivery Network
• System administration and performance optimization on CacheNet CDN (FreeBSD, Windows 2000/2003)
• Leading implementation and deployment of CacheNet Managed CDN: KERIS (edunet)/Kangnam-gu-chong e-learning VOD system (ingang.or.kr)

Feb 1999 – Apr 2001 · 2 yrs 2 mos · Gangnam-gu, Seoul, Korea

• Dedicated server hosting - monitoring tools development, training
• Development of Linux distribution - qLinux (Linux on Windows)
• Development of CacheNet Content Delivery Network

Sep 2000 – Jan 2010 · 9 yrs 4 mos

• Ports committer of FreeBSD ports system. Maintained lots of korean category ports but not limited to. See commit logs: http://freshbsd.org/committer/cjh