MAX_CONCURRENT_STREAMS

The streams the internal port takes on one HTTP/2 connection at a time, which it advertises (SETTINGS_MAX_CONCURRENT_STREAMS, Netty's default made explicit). The JDK client neither queues a request past a peer's limit nor opens another connection for it: it fails the request, unsent, with IOException: too many concurrent streams (JDK 21 and 25 alike). So the node's senders on one connection keep within it between them: its HttpSignalSender sends at most HttpSignalSender.DEFAULT_CONCURRENCY requests to a node at a time, and its HttpClusterChannel keeps the rest (HttpClusterChannel.DEFAULT_STREAMS), a forward past them waiting for a stream.