On Thu, Jan 12, 2017 at 09:13:23AM -0500, Greg Sanders via bitcoin-dev wrote:
> BIP125 is the standard way to signal:
> https://github.com/bitcoin/bips/blob/master/bip-0125.mediawiki
> 
> Should explain everything you need.

Additionally some miners mine full replace-by-fee, which has no limitations on
nSequence. My implementation (for v0.13.2) is here:

    https://github.com/petertodd/bitcoin/tree/replace-by-fee-v0.13.2

and is identical to Bitcoin Core modulo the nSequence stuff being removed, and
a special service bit added to allow full-rbf nodes to preferentially peer with
each other to make sure replacement transactions get propagated.

In practice full-RBF works fairly well, so while it's even faster to use the
nSequence signalling specified in BIP-125, doing so is not mandatory so long as
you can et your replacement transaction to a full-RBF node.

-- 
https://petertodd.org 'peter'[:-1]@petertodd.org