We have a subsystem of specialized code dedicated to networking as a server with clients (ingress). It lives in src/mongo/transport.

Notable classes include (but are not limited to):

• ServiceExecutor (and derived classes)
• ServiceStateMachine
• ReplyBuilderInterface

We should probably also briefly explain traffic capture (TrafficRecorder) that lives in src/mongo/db.

Since ingress networking is mostly invisible to the system at large, we can document it as a single section in src/mongo/transport/README.md.

This is intended to be abstract documentation, describe relationships and state transitions not code in common language.