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Mark Claypool, Feng Li and Jae Chung

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1 Mark Claypool, Feng Li and Jae Chung
BBR' - An Implementation of Bottleneck Bandwidth and Round-trip Time Congestion Control for ns-3 Mark Claypool, Feng Li and Jae Chung In Proceedings of the Workshop on ns-3 (WNS3) Mangalore, India, June 2018

2 Revisit model of congested link
Introduction TCP dominant protocol on Internet Yesterday Designed in an era of limited resources – low network bandwidths, small queues Packet loss a sign of congestion Today Router queues can be large (buffer bloat) Packet loss can be from wireless errors Revisit model of congested link

3 Congestion and Bottlenecks

4 Congestion and Bottlenecks

5 Congestion and Bottlenecks

6 Congestion and Bottlenecks

7 Congestion and Bottlenecks
Bandwidth-Delay Product

8 Estimating Optimal Point

9 Estimating Optimal Point
To see both max BW and min RTT  Must probe on both sides of BDP!

10 Estimating Optimal Point
N. Cardwell, Y. Cheng, C.S. Gunn, S.H. Yeganeh, and V. Jacobson. BBR: Congestion-Based Congestion Control,Communications of the ACM, 60(2), February 2017. BBR – Bottleneck Bandwidth and Round-trip time Model network Each ACK, update max BW and min RTT Control sending based on model Probe for max BW and min RTT Pace near estimate BW Keep inflight near BDP Goal: high throughput with small bottleneck queue

11 Outline Introduction (done) BBR (next) BBR’ Validation Evaluation
Conclusions

12 BBR – Walk towards max BW, min RTT

13 BBR – STARTUP: exponential search

14 BBR – DRAIN: drain queue built up in STARTUP

15 BBR – PROBE_BW: explore max BW, drain, cruise

16 BBR – PROBE_RTT: check if min RTT changed

17 BBR – State Machine 2 Phases of probing
Warm-up Steady-state 2 Phases of probing Increase inflight to get max BW Lower inflight to get min RTT  Apply during Warm-up and Steady-state Warm-up Startup – ramp up quickly (ala Slow Start) Drain – drain built up queue Steady-state ProbeBW – cycle pacing rate to probe BW ProbeRTT – if needed, coordinated dip to probe RTT

18 BBR – Median Latency versus Buffer Size
BBR vs. CUBIC. Synthetic bulk download. 8 flows, bottleneck 128 Kb/s, RTT 40 ms

19 BBR – Mean Goodput versus Loss Rate
BBR vs. CUBIC. Synthetic bulk download. 1 flow, bottleneck 100 Mb/s, RTT 100 ms

20 BBR Status Status of BBR v1.0 Actively working on BBR v2.0
Deployed widely at Google Open source for Linux TCP and QUIC Documented in IETF Internet Drafts ACK aggregation (e.g., WiFi) Packet loss signals Dynamics of sharing with loss- based congestion control FreeBSD NetFlix

21 ns – The Network Simulator
Discrete event simulators ns-1 (LBNL) – 2001 ns-2 (DARPA) – 2010 ns-3 (NSF and INRIA) – present Educational and Research use Yearly workshop (WNS3) Share ideas, code, research Does not support BBR! Implementation of BBR for ns-3

22 Outline Introduction (done) BBR (done) BBR’ (next) Validation
Evaluation Conclusions

23 BBR’ Implementation Protocol states BDP computation
N. Cardwell, Y. Cheng, S. H. Yeganeh, and V. Jacobson. BBR Congestion Control, IETF Draft, July 2017. Y. Cheng, N. Cardwell, S. H. Yeganeh, and V. Jacobson. Delivery Rate Estimation, IETF Draft, July 2017. Developed based on specifications: Protocol states Solution: state machine BDP computation Solution: compute each ACK Delivery rate estimation Solution: hook to record when send Packet pacing Solution: “hijack” at TCP layer

24 BBR’ Implementation BBR’ APP TCP BBR’: On ACK, update RTT & BW
BBR’: Compute & set pacing rate BBR’: Compute BDP & set cwnd Device ready to send?  Callback to APP APP: call send() TCP: enqueue packet TCP: timer triggers paced send BBR’: on send, book-keeping TCP: actually send TcpBbr BulkSend- Application BbrStateMachine TCP TcpSocketBase TcpSocketState

25 BBR’ Implementation BBR’ APP TCP BBR’: On ACK, update RTT & BW
BBR’: Compute & set pacing rate BBR’: Compute BDP & set cwnd Device ready to send?  Callback to APP APP: call send() TCP: enqueue packet TCP: timer triggers paced send BBR’: on send, book-keeping TCP: actually send TcpBbr BulkSend- Application BbrStateMachine PktsAcked() 1 TCP TcpSocketBase TcpSocketState

26 BBR’ Implementation BBR’ APP TCP BBR’: On ACK, update RTT & BW
BBR’: Compute & set pacing rate BBR’: Compute BDP & set cwnd Device ready to send?  Callback to APP APP: call send() TCP: enqueue packet TCP: timer triggers paced send BBR’: on send, book-keeping TCP: actually send TcpBbr BulkSend- Application BbrStateMachine PktsAcked() 1 TCP TcpSocketBase TcpSocketState SetPacingRate() 2

27 BBR’ Implementation BBR’ APP TCP BBR’: On ACK, update RTT & BW
tcb → m_cwnd APP 3 BBR’: On ACK, update RTT & BW BBR’: Compute & set pacing rate BBR’: Compute BDP & set cwnd Device ready to send?  Callback to APP APP: call send() TCP: enqueue packet TCP: timer triggers paced send BBR’: on send, book-keeping TCP: actually send TcpBbr BulkSend- Application BbrStateMachine PktsAcked() 1 TCP TcpSocketBase TcpSocketState SetPacingRate() 2

28 BBR’ Implementation BBR’ APP TCP BBR’: On ACK, update RTT & BW
tcb → m_cwnd APP 3 BBR’: On ACK, update RTT & BW BBR’: Compute & set pacing rate BBR’: Compute BDP & set cwnd Device ready to send?  Callback to APP APP: call send() TCP: enqueue packet TCP: timer triggers paced send BBR’: on send, book-keeping TCP: actually send TcpBbr BulkSend- Application BbrStateMachine PktsAcked() 1 TCP TcpSocketBase TcpSocketState DataSend() SetPacingRate() 4 2

29 BBR’ Implementation BBR’ APP TCP BBR’: On ACK, update RTT & BW
tcb → m_cwnd APP 3 BBR’: On ACK, update RTT & BW BBR’: Compute & set pacing rate BBR’: Compute BDP & set cwnd Device ready to send?  Callback to APP APP: call send() TCP: enqueue packet TCP: timer triggers paced send BBR’: on send, book-keeping TCP: actually send TcpBbr BulkSend- Application BbrStateMachine PktsAcked() 1 TCP TcpSocketBase TcpSocketState Send() DataSend() SetPacingRate() 5 4 2

30 BBR’ Implementation BBR’ APP TCP BBR’: On ACK, update RTT & BW
tcb → m_cwnd APP 3 BBR’: On ACK, update RTT & BW BBR’: Compute & set pacing rate BBR’: Compute BDP & set cwnd Device ready to send?  Callback to APP APP: call send() TCP: enqueue packet TCP: timer triggers paced send BBR’: on send, book-keeping TCP: actually send TcpBbr BulkSend- Application BbrStateMachine PktsAcked() 1 TCP TcpSocketBase TcpSocketState Send() DataSend() SetPacingRate() 5 4 2 SendDataPacket() 6

31 BBR’ Implementation BBR’ APP TCP BBR’: On ACK, update RTT & BW
tcb → m_cwnd APP 3 BBR’: On ACK, update RTT & BW BBR’: Compute & set pacing rate BBR’: Compute BDP & set cwnd Device ready to send?  Callback to APP APP: call send() TCP: enqueue packet TCP: timer triggers paced send BBR’: on send, book-keeping TCP: actually send TcpBbr BulkSend- Application BbrStateMachine PktsAcked() 1 TCP TcpSocketBase TcpSocketState Send() DataSend() SetPacingRate() 5 4 2 (Timer) SendDataPacket() 6 PacePackets() 7

32 BBR’ Implementation BBR’ APP TCP BBR’: On ACK, update RTT & BW
tcb → m_cwnd APP 3 BBR’: On ACK, update RTT & BW BBR’: Compute & set pacing rate BBR’: Compute BDP & set cwnd Device ready to send?  Callback to APP APP: call send() TCP: enqueue packet TCP: timer triggers paced send BBR’: on send, book-keeping TCP: actually send TcpBbr BulkSend- Application BbrStateMachine Send() 8 PktsAcked() 1 TCP TcpSocketBase TcpSocketState Send() DataSend() SetPacingRate() 5 4 2 (Timer) SendDataPacket() 6 PacePackets() 7

33 SendDataPacketReal()
BBR’ Implementation BBR’ tcb → m_cwnd APP 3 BBR’: On ACK, update RTT & BW BBR’: Compute & set pacing rate BBR’: Compute BDP & set cwnd Device ready to send?  Callback to APP APP: call send() TCP: enqueue packet TCP: timer triggers paced send BBR’: on send, book-keeping TCP: actually send TcpBbr BulkSend- Application BbrStateMachine Send() 8 PktsAcked() 1 TCP TcpSocketBase TcpSocketState Send() DataSend() SetPacingRate() 5 4 2 (Timer) SendDataPacket() 6 PacePackets() 7 SendDataPacketReal() 9

34 SendDataPacketReal()
BBR’ Implementation BBR’ tcb → m_cwnd APP 3 BBR’: On ACK, update RTT & BW BBR’: Compute & set pacing rate BBR’: Compute BDP & set cwnd Device ready to send?  Callback to APP APP: call send() TCP: enqueue packet TCP: timer triggers paced send BBR’: on send, book-keeping TCP: actually send TcpBbr BulkSend- Application BbrStateMachine Send() 8 PktsAcked() 1 TCP TcpSocketBase TcpSocketState Send() DataSend() SetPacingRate() 5 4 2 (Timer) SendDataPacket() 6 PacePackets() 7 SendDataPacketReal() 9

35 Outline Introduction (done) BBR (done) BBR’ (done) Validation (next)
Evaluation Conclusions

36 Verification: BBR’ – Basic Bottleneck
Single flow. Bottleneck: 10 Mb/s, 22 ms RTT BBR’ works as expected (based on specification)

37 Verification: BBR’ – Basic Bottleneck
(Estimated versus Actual) BBR’ accurately infers RTT and BW

38 Validation: BBR’ versus BBR – Steady State
Single flow. Bottleneck: 10 Mb/s, 40 ms RTT BBR’ looks similar to BBR

39 Validation: BBR’ versus BBR – Bwidth Increase
Single flow. Bottleneck: 40 ms RTT. Time 20: 10 Mb/s  20 Mb/s BBR’ looks similar to BBR

40 Validation: BBR’ versus BBR – Bwidth Decrease
Single flow. Bottleneck: 40 ms RTT. Time 40: 20 Mb/s  10 Mb/s BBR’ looks similar to BBR

41 Outline Introduction (done) BBR (done) BBR’ (done) Validation (done)
Evaluation (next) Conclusions

42 Evaluation: BBR’ vs. CUBIC – Wired
BBR’ has similar Throughput, but lower RTT

43 Evaluation: BBR’ vs. CUBIC – Wireless
5 km Evaluation: BBR’ vs. CUBIC – Wireless Results for 4G LTE similar to wired

44 Evaluation: BBR’ vs. CUBIC – Wireless
0 – 20 km Evaluation: BBR’ vs. CUBIC – Wireless BBR’ has similar Throughput, but lower RTT with distance

45 Apoova Lad and Chengle Zhang for early work
Conclusions Evolution of networks needs evolution of TCP BBR promising, but needs more vetting ns-3 network simulator great for vetting, but no BBR BBR’ – Implementation of BBR for ns-3 Use existing CC code base Integrate with other NS layers Validation – looks like BBR Evaluation compared to CUBIC Similar throughputs Lower RTTS Acknowledgements Apoova Lad and Chengle Zhang for early work

46 Future Work Incorporate more BBR features
Application limited flows Adverse Internet conditions – packet reordering, ACK loss Adjustments of BBR parameters Pacing Gain rates Evaluation over more network conditions Competing protocol stacks Wireless (WiFi and LTE) Queue sizes (small, super large)

47 Mark Claypool, Feng Li and Jae Chung
BBR' - An Implementation of Bottleneck Bandwidth and Round-trip Time Congestion Control for ns-3 Mark Claypool, Feng Li and Jae Chung In Proceedings of the Workshop on ns-3 (WNS3) Mangalore, India, June 2018

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