1. End-host Perspectives on Congestion Management Murari Sridharan muraris@microsoft.com CONEX BOF, IETF 76, Hiroshima

2. Its all about the apps Apps have diverse needs – P2P, VoIP, TV, online apps, games Filling the pipe while being TCP fair High-speed congestion control, Autotuning the receive window, host OS (including app) bottlenecks Low priority scavenger service Protocols changes to reduce latency Multipath transport to maximize link capacity, improve resiliency

3. End-host view of the network Mostly works as expected Establishing connectivity is sometimes problematic Largely remains a black box – Congestion, bottleneck capacity is implicitly inferred Network seems change/risk averse Imposes complex usage requirements – Volume caps, pay-per-use, metered data plans …

4. Networks view of the end-hosts End-hosts cannot be trusted, need to be explicitly controlled Application performance needs can be inferred and improved upon by inspecting packets on the wire End-hosts typically establish connectivity to well-known servers And the reality is …

5. Splitting at the seams Devices, Devices, Devices … – IGDs/NATs/Firewalls/DPI devices/Load balancers/Soft switches Layering violations, RFC non-conformance, no future proofing – Backwards compatibility Thanks to deep packet inspection you cant even touch padding bits! – Hampered ECN deployment New protocols hard or impossible to deploy – No changes to protocol on the wire – Takes time for apps to move to using new APIs Not all apps need TCP, but only TCP passes reliably E2E – Tunneling, feedback loops & TCP over TCP issues Network traffic management is a nightmare due to increased appetite for large volumes

6. CONEX: Things to consider Lets please stop inferring each other. – How can the end-host learn about network policy? – Explicit feedback to/from the network – OS has tons of context than the small amount reflected in the packets Wireless/Cellular network operators are moving towards usage based models – Tactically, policy based routing/interface selection is the high-order bit How does the end-host learn about the network policy?

7. CONEX: Things to consider Incremental deployment & incentives Bottleneck is largely within the home and/or last mile – Congestion exposure doesnt add any benefit but shouldnt make it worse Primal-dual congestion control – Performance is a function of source rate controller, AQM, marking thresholds, congestion measure – Measure of congestion, feedback of congestion measure, and use of congestion measure by the source controller are all important. Beyond TCP – UDP(DCCP) + ECN