Principles of Communications Week 6 L10/L11 8&10 Nov, 2022 - Scheduling and Queue Management

I am going to loop back around to flow and congestion control, because these things go together like strawberries and cream, or meta and verse:-)

Flow control can be open loop (call setup with a traffic descriptor and an associated admission control algorithm), or closed loop, based on feedback (dupack, packet loss/timeout, or explicit congestion notification).

Packet forwarding can be FIFO, or Round Robin, or weighted according to some request (management, setup, payment, etc - out-of-band). If it is round robin, we get fairness quite naturally, and some degree of protection against misbehaviour of other flows. If the flows are policed (because they gave a descriptor in open loop, or because they implement congestion avoidance and control), then we get more protection against misbehaviour of other flows of packets. If the router implements an Active Queue Management scheme (like RED), as well as a schedule (like round robin), then we get more protection (even against our own misbehaviour).

A neat example of use of scheduling in a different layer is in the new web protocol, QUIC, in browsers - this paper illustrates nicely how one can improve rendering of pages by changing the order that components flow through the layers of HTTP, QUIC, to/from UDP/IP...