(3)                  (2)
              .-------^------..------------^------------------.
 ,-(1)-----.                               _____
; ________  :            L4S  -------.    |     |
:|Scalable| :               _\      ||__\_|mark |
:| sender | :  __________  / /      ||  / |_____|\   _________
:|________|\; |          |/   -------'       ^    \1|condit'nl|
 `---------'\_|  IP-ECN  |          Coupling :     \|priority |_\
  ________  / |Classifier|                   :     /|scheduler| /
 |Classic |/  |__________|\   -------.     __:__  / |_________|
 | sender |                \_\ || | ||__\_|mark/|/
 |________|                  / || | ||  / |drop |
                      Classic -------'    |_____|


(1) Scalable sending host
(2) Isolation in separate network queues
(3) Packet identification protocol