Stratum is a proposal for an open source client-server "overlay" protocol that enables thin clients. It is currently used by Electrum. While originally announced right before 2012, the protocol has not yet been completed and proposed as a BIP for standardisation.
The stratum protocol was extended to support pooled mining as a replacement for obsolete getwork protocol in late 2012. Developed behind closed doors, the mining service specification was initially announced via Slush's pool's website. Shortly thereafter, alternative "cheat sheet" style documentation was provided by BTCGuild. As the extension lacks a formal BIP describing an official standard, it has further developed only by discussion and implementation.
Tables showing miner/server support for Stratum mining protocol:
|Server||get transactions||dynamic difficulty||job frequency||resume|
|HHTT||No||No (User selected difficulty)||30s||No|
|50BTC||No||No (User selected difficulty)||5s||No|
|Ozcoin||No||Yes or user selected||30s||No|