EE689 Lecture 7 Review of Last Lecture Differentiated Services Networks Performance results

Differentiated Services Keep the core/backbone router stateless Maintain per-flow state at the edges. Mark flows (individual/aggregate) at the edges based on contract profiles. Give better treatment to IN packets and drop OUT packets first at the time of congestion.

2-BIT Proposal Mark packets with Assure/Premium Service tags. Premium Service packets get low delay Assured Service packets get better BW than non-marked packets P packets have higher priority, dropped when out of profile.

Performance Results End-to-end response to packet drops impacts delivered throughput. Flows with same reservations, but different RTTs get different BWs Possible for a flow with no reservation, but better RTT to get more than another flow with reservations.

Performance Results CBR flows can still claim substantial BW - can’t hog all the BW though. Reservations lead to “better best-effort” Service differentiation based on reservations difficult Sharing excess BW difficult - results in loss of service differentiation.

TCP’s Impact Flows with higher target rates fall short and flows with lower rates exceed targets. Multiplicative decrease/additive increase causes this RTT bias inherent in TCP Need better mechanisms for service differentiation

No-OUT OUT packets are more susceptible to be dropped. Every packet drop results in a window decrease Reduce window decreases for higher BW => Don’t send OUT packets?

Inverse-rate drop Drop packets inverse proportion to the reservation Mark packets with reservation level - can keep core stateless Different flows will have packets dropped at different rates Favors higher rate flows

Two-Windows Modify TCP windowing mechanism cwnd = rwnd + ewnd, rwnd = reservation window, ewnd = excess window OUT packet drop ewnd = ewnd/2 IN packet drop cwnd = cwnd/2 Source needs to know how packets are marked - may not work with aggregation

Two-windows Protects reservation level on OUT packet drops More aggressive than current TCP Requires modifications to all end sources.

THREE-DROPS Mark packets IN, OUT-IN, OUT-OUT Maintain state of sending rates of flows at the edge. Mark OUT packets of flows not reaching targets OUT-IN, mark OUT packets of flows exceeding targets OUT-OUT Drop OUT-OUT before OUT-IN Feedback based

Summary Packet Marking and differentiated packet dropping can provide service differentiation Reservation level may not directly correlate to service Improved techniques provide better service differentiation Edge markers can provide substantial improvements