@startuml

skinparam backgroundColor white

entity Initiator
entity Responder
Initiator -> Responder: Open connection

== Establish that both sides support multistream-select ==

note over Initiator, Responder: Both sides may send initial multistream id simultaneously
Responder -> Initiator: Send multistream protocol id
Initiator -> Responder: Send multistream protocol id
note over Initiator, Responder: If anything other than multistream id is received, abort


== Negotiate protocol to use ==


loop until success, or Initiator gives up and closes channel
  Initiator -> Responder: Send protocol id for desired protocol
  alt protocol is supported by Responder
    Responder -> Initiator: Echo back protocol id to indicate agreement
  else protocol is not supported
    Responder -> Initiator: Send "na" (not available)
  end
end

== Use negotiated protocol ==

Initiator -> Responder: Send protocol-specific message
Responder -> Initiator: Send protocol-specific reply

@enduml