Transcript Document 7791294

Achieving Dependable Bulk
Throughput in a Hybrid Network
Guy Almes <[email protected]>
Aaron Brown <[email protected]>
Martin Swany <[email protected]>
Joint Techs Meeting
Univ Wisconsin -- 17 July 2006
Outline
Observations:
on user needs and technical opportunities
 on TCP dynamics

Notion of a Session Layer
the obvious application
 a stronger application

Phoebus as HOPI experiment
deployment
 early performance results

Phoebus as an exemplar hybrid network
On User Needs
In a variety of cyberinfrastructure-intensive
applications, dependable high-speed wide-area
bulk data flows are of critical value
Examples:



Terabyte data sets in HPC applications
Data-intensive TeraGrid applications
Access to Sloan Digital Sky Survey and similar very
large data collections
Also, we stress ‘dependable’ rather than
‘guaranteed’ performance
As science becomes more data-intensive, these
needs will be prevalent in many science
disciplines
On Technology Drivers
Network capacity increases, but user
throughput increases more slowly

Source: DOE
The cause of this gap relates to TCP
dynamics
On TCP Dynamics
Consider the Mathis Equation for Reno
MTU
Speed 
RTT * loss
Focus on bulk data flows over wide areas
How can we attack it?




Reduce non-congestive packet loss (a lot!)
Raise the MTU (but only helps if end-to-end!)
Improve TCP algorithms (e.g., FAST, Bic)



RTT is still a factor
Use end-to-end circuits
Decrease RTT??
Situation for running example
The Transport-Layer Gateway
A session is the end-to-end chain of segmentspecific transport connections


In our early work, each of these transport connections
is a conventional TCP connection
Each transport-level gateway (depot) receives data
from one connection and pipes it to the next
connection in the chain
Session
User Space
Session
Transport
Transport
Transport
Network
Network
Network
Data Link
Data Link
Data Link
Physical
Physical
Physical
The Logistical Session Layer
Obvious Application
Place a depot half-way between hosts A
and B, thus cut the RTT roughly in half
MTU
Speed 
max( RTT1,RTT2 ) * loss
Bad news: only a small factor
Good news: it actually does more

MTU1
MTU 2
Speed  min(
,
)
RTT1 * loss 1 RTT2 * loss2
Obvious Application: With one depot to reduce RTT
Stronger Application
Place one depot at HOPI node near the
source, and another near the destination
Observe:

Abilene Measurement Infrastructure:



2nd percentile: 950 Mb/s median: 980 Mb/s
MTU = 9000 bytes; loss is very low
Local infrastructure:


MTU and loss are good, but not always very good
but the RTT is very small
But with HOPI we can do even better
The HOPI Project
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
The Hybrid Optical and Packet Infrastructure
Project (hopi.internet2.edu)
Leverage both the 10-Gb/s Abilene backbone
and a 10-Gb/s lambda of NLR
Explore combining packet infrastructure with
dynamically-provisioned lambdas
Stronger application: depots near each host
Backbone:
large RTT
9000-byte MTU
very low non-congestive loss
GigaPoP / Campus:
very small RTT
some 1500-byte MTU
some non-congestive loss
Two Conjectures
Small RTT does effectively mask
moderate imperfections in MTU and loss
End-to-end session throughput is (only a
little less than) the minimum of component
connection throughputs
MTU1
MTU 2
Speed  min(
,
,
RTT1 * loss 1 RTT2 * loss2
MTU 3
)
RTT3 * loss3
Phoebus
Phoebus aims to narrow the performance
gap by bringing revolutionary networks like
HOPI to users

Phoebus is another name for the mythical
Apollo in his role as the “sun god”
Phoebus stresses the ‘session’ concept to
enable multiple network/transport
infrastructures to be catenated
Phoebus builds on an earlier project called
the Logistical Session Layer (LSL)
Experimental Phoebus
Deployment
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Place Phoebus depots at each HOPI node
Ingress/egress spans via ordinary
Internet2/ Abilene IP infrastructure
Backbone span can use either/both of:
10-Gb/s path through Abilene
 dynamic 10-Gb/s lambda

Initial test user sites:
SDSC host with gigE connectivity
 Columbia Univ host with gigE connectivity

Initial Performance Results
In very early tests:
SDSC to losa: about 900 Mb/s
 losa to nycm: about 5.1 Gb/s
 nycm to Columbia: about 900 Mb/s
 direct: 380 ± 88 Mb/s
 Phoebus: 762 ± 36 Mb/s

In later tests with a variety of file sizes,
SDSC to losa performance became worse
Initial Performance Results
Bandwidth Comparison
600
Megabits/second
500
400
300
200
100
0
32
64
128
256
512
1024
Transfer Size in Megabytes
Direct
Phoebus
2048
4096
Initial Test Results
What about the three components?
SDSC to losa depot: 429-491 Mb/s
 losa depot to nycm depot: 5.13-5.15 Gb/s
 nycm depot to Columbia: 908-930 Mb/s

Whatever caused that weakness in the
SDSC-to-losa path did slow things down
Plans for Summer 2006
‘Experimental production’ Phoebus,
reaching out to interested users
Improve access control and
instrumentation:

Maintain a log of achieved performance
Test use of dynamic HOPI lambdas
Evaluate Phoebus as a service within
newnet
Test use of Phoebus internationally
Comments on Backbone Span
Backbone could ensure flow performance
between pairs of backbone depots
Backbone could provide a Phoebus
Service in addition to its “IP” service
Relatively easy to use dynamic lambdas
within the backbone portion of the
Phoebus infrastructure
Alternatively, the backbone portion could
use IP, but a non-TCP transport protocol!
Comments on the Local
(Ingress and Egress) Spans
Near ends, we have good, but not perfect,
local/metro-area infrastructure
Relatively hard to deploy dynamic
lambdas
Small RTTs allow high-speed TCP flows to
be extended to many local sites in a
scalable way
Thus, Phoebus leverages both:
innovative wide-area infrastructure and
 conventional local-area infrastructure

Phoebus can thus extend the value of
multi-lambda wide-area infrastructure to
many science users on high-quality
conventional campus networks
Ongoing Work
Phoebus deployment on HOPI
We’re seeking project participants!
 Please email for information

ESP-NP
ESP = Extensible Session Protocol
 Implementation on an IXP Network Processor
from Intel
 The IXP2800 can forward at 10 Gb/s

Acknowledgements
UD Students:

Aaron Brown, Matt Rein
Internet2:

Eric Boyd, Rick Summerhill, Matt Zekauskas, ...
HOPI Testbed Support Center (TSC) Team

MCNC, Indiana Univ NOC, Univ Maryland
San Diego Supercomputer Center:

Patricia Kovatch, Tony Vu
Columbia University:

Alan Crosswell, Megan Pengelly, the Unix group
Dept of Energy Office of Science:

MICS Early Career Principal Investigator program
End
Thank you for your attention
Questions?