End-to-end Asymmetric End-to-end Asymmetric Link Capacity EstimationLink Capacity Estimation

Ling-Jyh Chen, Tony Sun, Guang Yang, M.Y. Sanadidi, Mario GerlaLing-Jyh Chen, Tony Sun, Guang Yang, M.Y. Sanadidi, Mario GerlaDept. of Computer Science, University of California at Los AngelesDept. of Computer Science, University of California at Los Angeles

DefinitionDefinition CapacityCapacity: maximum IP-layer throughput that a flow can

get, without any cross traffic. Available BandwidthAvailable Bandwidth: maximum IP-layer throughput that

a flow can get, given (stationary) cross traffic.

Previous Work on Capacity EstimationPrevious Work on Capacity Estimation Per-hop based

pathchar: use different packet sizes to probe the per-hop link capacity

clink, pchar: variants of pathcharNettimer: use “packet tailgating” technique

End-to-end basedPathrate, Sprobe, CapProbe

These approaches are either one-way based or unable to estimate asymmetric link capacities.

Estimating Asymmetric LinksEstimating Asymmetric Links Asymmetric links are becoming popular (e.g.

DSL, cable modems, and satellite links). Knowing the capacity of BOTH direction links is

important for applications.

Related work: ALBP [Yu et al, ICC’03] employs a multi-packet delay

model to estimate “per-hop” capacity of asymmetric links.

Our ContributionOur Contribution We propose an end-to-end asymmetric link

capacity estimation technique, called AsymProbeAsymProbe.

AsymProbe is CapProbe based:round trip methodpacket pair basedsimple, fast, and accurate

Packet Pair DispersionPacket Pair DispersionT3

T2 T3

T3

T1

T3

Narrowest Link

20Mbps 10Mbps 5Mbps 10Mbps 20Mbps 8Mbps

Capacity = (Packet Size) / (Dispersion)

Issues: Compression and ExpansionIssues: Compression and Expansion

• Queueing delay on the first packet => compression

• Queueing delay on the second packet => expansion

CapProbe CapProbe (Rohit et al, SIGCOMM’04)(Rohit et al, SIGCOMM’04) Key insight: a packet pair that gets through with zero queueing

delay yields the exact estimate. CapProbe uses “Minimum Delay Sum” filter.

CapacityCapacity

Proposed Approach: AsymProbeProposed Approach: AsymProbe

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)','max('

22

11

21

2

22

1

11

TPC

TPC

TTTCPT

CPT

AsymProbe: ExampleAsymProbe: ExampleC1 C2 P1 P2 T1 T2 C'1 C'2

1000kbps

500kbps

1500 bytes 100 bytes 12 ms 1.6 ms 1000.00 kbps 66.67 kbps

1500 bytes 300 bytes 12 ms 4.8 ms 1000.00 kbps 200.00 kbps

1500 bytes 500 bytes 12 ms 8 ms 1000.00 kbps 333.33 kbps

1500 bytes 700 bytes 12 ms 11.2 ms 1000.00 kbps 466.67 kbps

1500 bytes 900 bytes 12 ms 14.4 ms 833.33 kbps 500.00 kbps

1500 bytes 1100 bytes 12 ms 17.6 ms 681.82 kbps 500.00 kbps

1500 bytes 1300 bytes 12 ms 20.8 ms 576.92 kbps 500.00 kbps

1500 bytes 1500 bytes 12 ms 24 ms 500.00 kbps 500.00 kbps

500kbps

1000kbps

100 bytes 1500 bytes 1.6 ms 12 ms 66.67 kbps 1000.00 kbps

300 bytes 1500 bytes 4.8 ms 12 ms 200.00 kbps 1000.00 kbps

500 bytes 1500 bytes 8 ms 12 ms 333.33 kbps 1000.00 kbps

700 bytes 1500 bytes 11.2 ms 12 ms 466.67 kbps 1000.00 kbps

900 bytes 1500 bytes 14.4 ms 12 ms 500.00 kbps 833.33 kbps

1100 bytes 1500 bytes 17.6 ms 12 ms 500.00 kbps 681.82 kbps

1300 bytes 1500 bytes 20.8 ms 12 ms 500.00 kbps 576.92 kbps

1500 bytes 1500 bytes 24 ms 12 ms 500.00 kbps 500.00 kbps

C=P/TC=P/T

AsymProbe AlgorithmAsymProbe Algorithm AsymProbe has four phases:

Phase 1: the probing phase (P1=Pmax ; P2=Pmax ) (=> CapProbe)

Phase 2: the probing phase (P1=Pmax ; P2=Pmin)

Phase 3: the probing phase (P1=Pmin ; P2=Pmax )

Phase 4: the decision phase

AsymProbe AlgorithmAsymProbe Algorithm The decision phase:

IssuesIssues AsymProbe is able to estimate asymmetric link capacities when

the “asymmetric ratio” is larger than Pmin /Pmax and smaller than Pmax /Pmin.

AsymProbe can not estimate “extremely asymmetric” links.

Pmax is limited by MTU.

Pmin is limited by the supported system time resolution.

Packet SizeNarrow Link Capacity

100 Mbps 10 Mbps 1 Mbps

500 bytes 0.04 ms 0.4 ms 4 ms

1000 bytes 0.08 ms 0.8 ms 8 ms

1500 bytes 0.12 ms 1.2 ms 12 ms

SimulationSimulation AsymProbe: A <-> B; Cross Traffic: C <->B E->D: 1.5Mbps; D->E: 128kbps

Simulation ResultsSimulation Results Pmax=1500 bytes ; Pmin=100 bytes

EmulationEmulation

Pmax=1500 bytes ; Pmin=500 bytes

Emulation ResultsEmulation Results

Internet ExperimentsInternet Experiments P1=1500 bytes, P2=500 bytes Supported “asymmetric ratio” = 3:1

Application – TCP ProbeApplication – TCP Probe The concept of AsymProbe can be integrated

with other data transmission protocols, e.g. TCP. TCP packet size:

forward direction: TCP data 1500 bytes reverse direction: TCP ACK 40 bytes

According to AsymProbe algorithm: If , then T1>T2

TCP Probe estimates the capacity of the forward direction link If , then T1<T2

TCP Probe estimates the capacity of the reverse direction link

401500

Re

verse

forward

CC

401500

Re

verse

forward

CC

TCP ProbeTCP Probe

DelAck

TCP Probe:

CapProbe:

More details in [Anders et al, GI’05]

TCP Probe ApplicationTCP Probe Application

Vertical handoff usually results in a dramatic change in the path capacity.

Service agility using “Fast Rate Adaptation” (FRA) algorithm FRA forces TCP to enter Slow Start when detecting a handoff from

LOW to HIGH

Service Agility – TCP ProbeService Agility – TCP Probe

Unit: bps

TCP Probe with “fast rate adaptation” Vertical handoff from 10Mbps to 100Mbps

SummarySummary We propose an end-to-end asymmetric link

capacity estimation technique, called AsymProbe. We evaluate AsymProbe by simulation and

Internet experiments. The concept of AsymProbe can be integrated with

other data transmission protocols. We present a passive capacity estimation

technique, called TCP Probe, which integrates AsymProbe with TCP.

Thanks!Thanks!

CapProbe:CapProbe: http://nrl.cs.ucla.edu/CapProbe/