Definition
A mining channel is the logical pipe over which a Stratum V2 connection carries jobs and shares between a downstream miner and an upstream server. A single transport connection can multiplex several channels, and the protocol defines three types, each suited to a different point in the mining topology. Understanding which channel type a device uses explains how much of the work it does locally versus how much an upstream node does on its behalf.
Standard, extended, and group channels
A standard channel is opened by an end mining device and is limited to standard jobs with a fixed merkle root; the device may only vary the version, nonce, and nTime fields. This is the lightweight path that keeps firmware simple. An extended channel is used by proxies and more capable nodes: it carries an extranonce_prefix and extranonce_size so a downstream node can subdivide the search space further, and the spec requires upstream servers that provide work to support extended channels. A group channel bundles many standard or extended channels so a single NewExtendedMiningJob can address them all at once, cutting broadcast overhead.
Shares ride the channel
Work results travel back on the same channel. Standard channels use SubmitSharesStandard (channel id, sequence number, job id, nonce, nTime, version), while extended channels use SubmitSharesExtended, which adds the extranonce needed to reconstruct the full coinbase. The server replies with aggregated success acknowledgements or per-share error messages.
The standard-channel restriction is what the spec calls header-only mining, and the whole channel scheme is encrypted by the Noise protocol handshake.
In Simple Terms
A mining channel is the logical pipe over which a Stratum V2 connection carries jobs and shares between a downstream miner and an upstream server.…