David,
[DS] Let me clarify why ATSSS introduces a new point of failure. First
here's the common network topology today without ATSSS. In this example
the Client is a smartphone, and the user is browsing a website hosted by
WebServer.
[Client] ----- { cellular } ------- [WebServer]
\------------{ Wi-Fi } ------------/
The client has (at least) two IP addresses: IP_Client_cell and
IP_Client_WiFi.
The WebServer has IP_Server.
My understanding of most of today's QUIC deployments is that the client
is not connected to the webserver but to a CDN or edge node that serves
as a proxy to the webserver.
Thus the setup is
[Client] ----- { cellular } ------- [Edge] ---------[WebServer]
\------------{ Wi-Fi } -------/
Now let's assume the Client is happily browsing using QUICv1 over one
interface, if that network goes down, QUIC will automatically migrate to
the other network and the web browsing will not fail. The client can
send packets to IP_Server on any interface and as long as one interface
works they will reach the server.
Now let's introduce ATSSS:
[Client] ----- { cellular } ------- [ATSSS Proxy] -------- [WebServer]
\------------{ Wi-Fi } ------------/
The ATSSS Proxy has IP_ATSSS.
The packets sent by the client are not sent to IP_Server here, they're
sent to IP_ATSSS.
If the ATSSS proxy becomes unreachable mid connection, the client's
connection will break - because it's sending to IP_ATSSS not IP_Server.
The client will detect the failure of the ATSSS proxy and will then be
able to switch to non-ATSSS to directly reach the webserver/edge node.
Since the client uses the ATSSS for multiple applications, a failure of
the ATSSS proxy will be quickly detected.
My point is that in this scenario ATSSS reduces reliability by adding a
point of failure.
I don't see a difference between the failure of an Edge node and an
ATSSS proxy. Both can be deployed with enough redundancy to limit the
impact of failures. The only difference is that ATSSS nodes will
probably be deployed by network operators while Edge nodes are deployed
by CDN providers.
Olivier
