IBB blocks in flight across all streams of one session. Each stream keeps
its own window as well; this is what stops the streams from adding theirs
up. Without it every stream holds window blocks at once, the stanzas pile
up in the one XMPP connection's send queue, and a small page's first block
waits behind every large download's full window. Twice the default stream
window, so a stream alone runs exactly as fast as it did before.
IBB blocks in flight across all streams of one session. Each stream keeps its own window as well; this is what stops the streams from adding theirs up. Without it every stream holds
windowblocks at once, the stanzas pile up in the one XMPP connection's send queue, and a small page's first block waits behind every large download's full window. Twice the default stream window, so a stream alone runs exactly as fast as it did before.