Network Border PatrolCelio Albuquerque, Brett J. Vickers and Tatsuya

Suda

Jaideep VaidyaCS590F Fall 2000

Need• End to End Congestion Control /

Avoidance Mechanisms not enough.• Unresponsive flows• Rogue TCP stacks

• Network level mechanisms - Necessary Evil

• Try to push as much to the border of the network as possible

Essential Idea• Core Stateless Congestion Avoidance

Mechanism

• Exchange of feedback between Edge Routers

• Per-flow rate monitoring at Egress Routers

• Per-flow rate control at Ingress Routers

Goals• Eliminate congestion collapse resulting

from undelivered packets

• When combined with fair queueing, achieve approximately max-min fair bandwidth allocations for competing network flows

NBP Egress Router

NBP Ingress Router

Feedback Control Algorithm

• Decides how and when feedback packets are exchanged between edge routers.

• Necessary for discovering source, communicate per-flow bit rates & detect network congestion by estimating RTT

• BFFs can be generated asynchronously. (RTT cannot be calculated in this case)

FeedBack Packets

Rate Control Algorithm• Regulates rate at which each flow

enters the network. Converge on set of per-flow transmission rates, preventing congestion collapse. Maximize link utilization.

• Similar to TCP congestion control (Slow start and Congestion avoidance phases)

• Handles synchronous and asynchronous packets differently

Rate Control Algorithm contd.

• Activated on receipt of feedback packet.• Synchronous feedback

• Update baseRTT• Calculate mrc (minimum rate change)• Change rate based on phase

• Aysnchronous feedback• Use old mrc and modify rate based on

current phase

Results from Simulation Experiments

• Preventing congestion collapse

Results from Simulation Experiments

• Max-min fairness

Fairness Results• NBP by itself is not able to provide

fairness.• With WFQ or CSFQ, NBP provides

approximate fairness, and avoids congestion collapse

• Results with WFQ are better than results with CSFQ.

• CSFQ’s fairness mechanism engages only when congestion is detected

• CSFQ is an approximation of WFQ

Implementation Issues• Scalable Flow Classification• Scalable inter-domain deployment• Scalable fairness• Incremental Deployment• Multicast• Multi-path routing• Integrated or Differentiated service

Conclusion• Pros

• Good paper. Limitations noted.• Stop gap solution. Adequate for goals noted.

• Cons• Incremental deployment not easy.• Deployment based on whether we expect

QoS technology to be available soon.• Overload is directly proportional to number

of flows. Would not work well with HTTP 1.0 (more number of flows)

Questions?