HSTCP-LP: A Protocol for Low-Priority Bulk Data Transfer in High-Speed High-RTT Networks

Rice Networks Grouphttp://www.ece.rice.edu/networks

Aleksandar Kuzmanovic Edward W. Knightly

Rice UniversityR. Les Cottrell

SLAC/SCS-Network Monitoring

HSTCP-LP: A Protocol for Low-Priority Bulk Data Transfer in

High-Speed High-RTT Networks

Kuzmanovic, Knightly, and Cottrell

Motivation

Traditional view of service differentiation:– High priority: real-time service– Best-effort: everything else

What’s missing?– Low-priority (receiving only excess bandwidth)– Lower than best-effort!

Non-interactive applications, bulk download»It will last long anyway...

Speeds up best-effort service (e.g., web)


Applications for Low Priority Service

LP vs. fair-share:– Bulk downloads

SLAC->CERN Improve my other

applications

LP vs. rate-limiting:– P2P file sharing

Often rate limited Isolation vs. sharing

T im e

R a te lim it

C a pa c ityA va ila bleba ndw idth

G a in

AB


Problem Formulation & Design Objectives

Low-priority service objectives– Utilize the “excess/available” capacity

What no other flows are using

– TCP-transparency (non-intrusiveness)– Inter-LP flow fairness (fair-share of the available

bandwidth)

Design end- host- based transm ission protocol that em ulates the low- priority service


Origins of the Available Bandwidth

Why is excess bandwidth available when TCP is greedy?

– Time-of-day effects Night- vs. day-time traffic

– Short-lived flows Majority traffic is web browsing

– TCP is imperfect Low-aggregation regimes


TCP fairness

In presence of TCP

cross-traffic:– TCP achieves fairness

A B

T C P 1

T C P 2 T im e

F ull C ap ac ityT C P 1 d e m a n d

T im e

F ull C ap ac ityT C P 2 d e m a n d

T im e

B a n d w id th s h a re

In ter-T C P -fairn es s


Illustration of TCP Transparency

LP flow utilizes only excess bandwidth

– Does not reduce the throughput of TCP flows

A B

T C P

LP T im e

F ull C ap ac ity

T C P d e m a n d

T im e

F ull C ap ac ity

L P d e m a n d

T im e

F ull C ap ac ity


L P flo w u tilize sa v a ila b le b a n d w id th

T C P -tra n s p a re n c y


Fairness Among LP Flows

Inter-LP-fairness is

essential for

simultaneous

file transfers

A B

T C P

LP 1LP 2 T im e

F ull C ap ac ityT C P d e m a n d

T im e

F ull C ap ac ityL P 1 a n d L P 2 d e m a n d s

T im e


In ter-L P -fairn es s


HSTCP-LPA Congestion Control Protocol

Problem– TCP-LP [Infocom03]

AIMD control not

suitable for high speeds

Approach– Add HSTCP [Floyd03] high-speed mechanisms

Challenge– Develop large windows and achieve low-

prioritization at the same time

Lowspeed

Highspeed

Excess bandw idth utilization

Transparency


Early Congestion Indication

For transparency, HSTCP-LP must know of congestion before non-LP flows

Idealized objective: buffer threshold indication

Endpoint inference: one-way delay threshold

)( minmaxmin dddsdi

b uffer thres ho ld


Reverse Cross-Traffic

HSTCP-LP uses one-way packet delays (RFC1323) for congestion indication – Source-destination time stamping– Synchronized clocks not needed

One-way delay: – Eliminates the impact of the reverse cross-traffic

HSTCP-LP can loose Gb/s of available bandwidth if RTT is used

A

B

D a ta pa thA ck pa th


HSTCP-LP Timeline IllustrationC

on

ge

stio

n W

ind

ow

T im e

packet loss • Reach high throughput ...quickly in slow-start• Estimate one-way ...delay and compute ...delay threshold



on

ge

stio

n W

ind

ow

T im e

packet loss

sm oothedone-w ay delayindications

Apply HSTCP response function with early congestion indications



on

ge

stio

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ind

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T im e

packet loss


• HSTCP response ...function above ...Low_Window• TCP-LP response ...function below ...Low_Window• Send 1 packet/RTT



on

ge

stio

n W

ind

ow

T im e

packet loss


HSTCP increase function with early congestion indications


Implementation and Experiments

Linux-2.4.22-web100 kernel: – HSTCP HSTCP-LP

Time stamping, modified congestion control...

Paths:– Stanford, CA Ann Arbor, MI– Stanford, CA Gainesville, FL– Available bitrate ~ 450 Mb/s


Low-Priority Background Data Transfer

HSTCP-LP is highly non-intrusive to other advanced TCP stacks

– Strict prioritization for larger bottleneck queue lengths – Lighter prioritization for (max_delay < 50 ms)


Utilizing Excess Bandwidth

Extensive experiments on a number of high bandwidth-delay production networks– no cross-traffic– periodic UDP cross-traffic– reverse cross-traffic– http://www.slac.stanford.edu/~hadrien

HSTCP-LP utilizes 80-127% of the available bandwidth when compared to other high-speed stacks– 127% when transmission buffer (tqueuelen) is

large


Conclusions

HSTCP-LP: a new protocol for high bandwidth-delay production networks– General low priority service (compared to “best-effort”)

Attractive for low-priority bulk downloads: ftp, web updates, P2P

HSTCP-LP is incrementally deployable– Sender side modification of HSTCP without changes to

routers

Implementation and evaluation in the Internet

http://www.ece.rice.edu/networks/TCP-LP


Questions

http://www.ece.rice.edu/networks/TCP-LP

HSTCP-LP: A Protocol for Low-Priority Bulk Data Transfer in High-Speed High-RTT Networks

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