Transcript Slide 1

End-to-end Asymmetric
Link Capacity Estimation
Ling-Jyh Chen, Tony Sun, Guang Yang, M.Y. Sanadidi, Mario Gerla
Dept. of Computer Science, University of California at Los Angeles
Definition


Capacity: maximum IP-layer throughput that a flow can
get, without any cross traffic.
Available Bandwidth: maximum IP-layer throughput that
a flow can get, given (stationary) cross traffic.
Previous Work on Capacity Estimation

Per-hop based
 pathchar:
use different packet sizes to probe
the per-hop link capacity
 clink, pchar: variants of pathchar
 Nettimer: use “packet tailgating” technique

End-to-end based
 Pathrate,

Sprobe, CapProbe
These approaches are either one-way
based or unable to estimate asymmetric
link capacities.
Estimating 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 Contribution

We propose an end-to-end asymmetric link
capacity estimation technique, called
AsymProbe.

AsymProbe is CapProbe based:
 round
trip method
 packet pair based
 simple, fast, and accurate
Packet Pair Dispersion
T1
T3
Narrowest Link
T2
20Mbps
10Mbps
T3
5MbpsT3
10Mbps
T3
20Mbps
Capacity = (Packet Size) / (Dispersion)
8Mbps
Issues: Compression and Expansion
• Queueing delay on the first packet => compression
• Queueing delay on the second packet => expansion
CapProbe (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.
Capacity
Proposed Approach: AsymProbe
T1 
P1
C1
T2 
P2
C2
 T '  max(T1 ' , T2 ' )
 C '1 
P1
T'
C '2 
P2
T'
AsymProbe: Example C=P/T
C1
1000
kbps
500
kbps
C2
500
kbps
1000
kbps
P1
P2
T1
T2
C'1
C'2
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
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
AsymProbe 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 Algorithm

The decision phase:
Issues

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 Size
Narrow 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
Simulation


AsymProbe: A <-> B; Cross Traffic: C <->B
E->D: 1.5Mbps; D->E: 128kbps
Simulation Results

Pmax=1500 bytes ; Pmin=100 bytes
Emulation

Pmax=1500 bytes ; Pmin=500 bytes
Emulation Results
Internet Experiments


P1=1500 bytes, P2=500 bytes
Supported “asymmetric ratio” = 3:1
Application – 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:
C forward

1500
40

1500
40
 If C
, then T1>T2
TCP Probe estimates the capacity of the forward direction link
Re verse
C forward
 If C
, then T1<T2
TCP Probe estimates the capacity of the reverse direction link
Re verse
TCP Probe
CapProbe:
DelAck
TCP Probe:

More details in [Anders et al, GI’05]
TCP 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 Probe
TCP Probe with “fast rate adaptation”
 Vertical handoff from 10Mbps to 100Mbps

Unit: bps
Summary




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!
CapProbe: http://nrl.cs.ucla.edu/CapProbe/