Transcript Powerpoint - Syzygy Engineering

Communications Technology Division
Glenn Research Center
Satellite Networks & Architectures Branch
SCPS-TP, TCP and Rate-Based Protocol
Evaluation
Cindy Tran, Fran Lawas-Grodek, Bod Dimond and Will Ivancic
[email protected]
216-433-3494
2nd Space Internet Workshop, May 21-22, 2002
1
Presentation Outline
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
• Goals
•
•
•
•
•
TCP Over Wireless Links
Testbed Layout
Test Philosophy
SCPS-TP / TCP /Rate-Based Test Results
Conclusions
2nd Space Internet Workshop, May 21-22, 2002
2
Space-Base Protocol Testing Goal
Communications Technology Division
Glenn Research Center
Satellite Networks & Architectures Branch
• Provide an objective, scientific analysis of currently
available and proposed protocols for space-based
networks.
–
–
–
–
Where do they work?
Where do they fall apart?
How can they be improved or fixed?
What is the state of their maturity?
• Determine which protocol is appropriate for a given
scenario.
• Remove the marketing hype from the space-based
protocol discussions.
2nd Space Internet Workshop, May 21-22, 2002
3
TCP over Satellite/Wireless Links
Communications Technology Division
Glenn Research Center
Satellite Networks & Architectures Branch
• TCP slow start takes a long time to reach equilibrium
– log2 (bandwidth × delay) round-trip times (RTTs)
• poor performance over long fat networks
• particularly for short flows
– on retransmission timeout, TCP enters slow start again
• poor performance over lossy high capacity links
• TCP infers congestion on all packet drops
– even if the loss is due to packet corruption due to noise TCP
congestion avoidance throttles source unnecessarily
• TCP sends a burst of packets when window opens
– this can cause congestion drops in intermediate routers
2nd Space Internet Workshop, May 21-22, 2002
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PUBLIC
INTERNET
Reliable
Transport
Protocol Testbed
Emulated
Topology
Testbed Isolation point
ONE Implementation Diagram
Ka Band Testbed
Net: 10.0.8.x
1
TER2(NetBSD)
IP: 10.0.1.4
10.0.100.4
TER3 (Solaris)
IP: 10.0.1.5
10.0.100.5
10.0.1.x ISINT Terra Network
10.0.100.x Network
TER1 (NetBSD)
IP: 10.0.1.3
10.0.100.3
fffff
3
1
GRC
PBX
2
3
Delay and BER
Facilities
1. TER-rtr1 - 10.0.1.1 (100BaseT Ethernet)
2. TER-rtr2 - 10.0.3.1 (100BaseT Ethernet)
3. TER-rtr3 - 10.0.5.1 (Terra VOIP Circuit)
4. TER-rtr4 - 10.0.7.1 (OC-3 Circuit)
5. TER-rtr5 - 10.0.8.1 (HSSI/RF Circuit)
SPC-demo
(WIN NT/98)
IP: 10.0.2.2
Cisco 7100
O.N.E. DELAY
SIMULATOR
Net: 10.0.3.x
2
Terrestrial Router Interfaces
PSTN
4
SPC1 (NetBSD)
IP: 10.0.2.3
10.0.100.6
SPC2 (NetBSD)
IP: 10.0.2.4
10.2.100.7
SPC3 (NetBSD)
IP: 10.0.2.5
10.0.100.8
Space Router Interfaces
1. SPC-rtr1 - 10.0.2.1 (100Baset Ethernet)
2. SPC-rtr2 - 10.0.3.4 (100Baset Ethernet)
3. SPC-rtr3 - 10.0.6.1 (Space VOIP Circuit)
4. SPC-rtr4 - 10.0.7.2 (OC-3 Circuit)
5. SPC-rtr5 - 10.0.8.2 (HSSI/RF Circuit)
Network
Cisco 7100
5
10.0.100.x
4
TER-demo
(WINNT/98)
IP: 10.0.1.2
SX/14 DELAY
SIMULATOR
Net: 10.0.7.x
10.0.2.x ISINT Space Network
5
SCPS-TP / TCP Testing Philosophy
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
• Tune and baseline protocol on error-free link for each
bandwidth-delay product.
– Both SCPS-TP and TCP where tuned for best performance over the
given delay.
• Record all measurements, not just optimal runs!
• Minimum of 30 runs for congestion friendly protocols and
20 runs for rate-based protocols.
• Measurement time is from SYN to FIN
• Run single flows and multi-flows (3 connections) to ensure
accurate reporting and application of results.
• Capture and save some complete trace files – particularly
when the unexpected is occurring.
2nd Space Internet Workshop, May 21-22, 2002
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Glenn Research Center
Communications Technology Division
Protocol Test Results
2nd Space Internet Workshop, May 21-22, 2002
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Satellite Networks & Architectures Branch
SCPS-TP and TCP Tests
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
• Single Stream Baseline with no congestion
• Multi-Stream with three sources and sinks for congestion
control algorithm testing.
• Solaris Operating System
• 100 BaseT Interfaces
• Binomial Error Distributions
– 1E-8, 1E-7, 1E-6, 1E-5
• Packet Size 1024 Bytes
• Delay
– 10 msec, 250 msec, 500 msec
2nd Space Internet Workshop, May 21-22, 2002
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Rate-Based Protocols
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
• Investigate COTS solutions which tend to be directed at
multicast applications
– MFDP, MDP, Digital Fountain, others
•
•
•
•
Are commercial implementations available and usable?
Are multicast-based implementations overly complex?
Should unicast protocols be developed?
Congestion is controlled by network owner rather than
protocol. Therefore, multi-stream tests where not
considered necessary.
2nd Space Internet Workshop, May 21-22, 2002
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Theoretical Steady State Throughput
Communications Technology Division
Glenn Research Center
Satellite Networks & Architectures Branch
TCP Performance equitation is from Mathis, M. et al, "The Macroscopic Behavior of the Congestion Avoidance
Algorithm",Computer Communications Review, volume 27, number 3, July 1997.
Delay Tolerant
Increasing Delay
2nd Space Internet Workshop, May 21-22, 2002
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Another Example of TCP Steady State Performance
Communications Technology Division
Glenn Research Center
Satellite Networks & Architectures Branch
Don’t Use TCP for long delays.
However, one can still use IP
and a rate-base protocol.
Chart is from “Why not use the Standard Internet Suite for the Interplanetary Internet?”
By Robert C. Durst, Patrick D. Feighery, Keith L. Scott
2nd Space Internet Workshop, May 21-22, 2002
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TCP Throughput at 250 msec RTT
Communications Technology Division
Glenn Research Center
Slow Start
Phenomena
2nd Space Internet Workshop, May 21-22, 2002
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Satellite Networks & Architectures Branch
TCP Standard Deviation for 30 Trials
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
When the first error occurs has a
large effect on TCP throughput as
shown by the standard deviations for
1E-8 and 1E-7
2nd Space Internet Workshop, May 21-22, 2002
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Protocol Throughput
500 msec Delay / 10 Mbyte File, Single Flow
Glenn Research Center
Communications Technology Division
All Rate-Based protocols need work
to reach their full potential.
2nd Space Internet Workshop, May 21-22, 2002
14
Satellite Networks & Architectures Branch
Protocol Throughput
500 msec Delay / 10 Mbyte File, Single Flow
Glenn Research Center
2nd Space Internet Workshop, May 21-22, 2002
Communications Technology Division
15
Satellite Networks & Architectures Branch
Protocol Throughput
250 msec Delay / 10 Mbyte, Single Flow
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
Slight improvement in Congestion Friendly Protocols
At 250 msec vs 500 msec Delay
2nd Space Internet Workshop, May 21-22, 2002
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Protocol Throughput
500 msec Delay / 1 Mbyte File, Single Flow
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
The smaller the file, the more important
the startup algorithms become
– except for EXTREMELY small transactions
such as command and control.
2nd Space Internet Workshop, May 21-22, 2002
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MDP Tuning
(Packet Size 1024 Bytes, Delay 500 msec)
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
Receiver
cannot keep
up and
and hardware
performance
Our Operating
System
Greatest
throughput
achievable
at
degrades
rapidly
at
transmission
settings
could keep rate
up with
the current
MDP
Transmission
settings
of 35 – 40
Mbps
greater
than
40
Mbps
implementation at rates up to 20 Mbps
Rate Setting
2nd Space Internet Workshop, May 21-22, 2002
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Protocol Throughput
SCPS-TP Pure Rate Based – Ack Every Packet, Single Flow
Communications Technology Division
Glenn Research Center
Initialization and
Termination
Increasing Delay
Performance is delay tolerant, but
not completely insensitive to delay.
2nd Space Internet Workshop, May 21-22, 2002
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Satellite Networks & Architectures Branch
Multi-stream Testing of
Congestion-Friendly Protocols
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
• Necessary
– Only truly meaningful test for congestion-friendly protocols (need
to add congestion!)
– Single steam tests provide baseline, but that is all.
• Work in Progress
– Many Problems Getting SCPS to operate correctly in multistreaming configuration.
• Solaris appears to be most stable system.
• BSD is very buggy for both SCPS-TP (all cases) and TCP (over
long delays).
• For single machine operation, SCPS has to be recompiled as
three applications and then performs load sharing which is
undesirable for this emulation.
– Using three steams competing for bandwidth.
• Using three senders and three receivers due to load sharing
occurring in SCPS for single machine sending three streams.
2nd Space Internet Workshop, May 21-22, 2002
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SCPS Gateway
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
• Working on evaluation of SCPS gateway using
MITRE provided code.
– Gateway is operation
– Testing is just beginning
2nd Space Internet Workshop, May 21-22, 2002
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Conclusions
Glenn Research Center
Communications Technology Division
Satellite Networks & Architectures Branch
• Very small transactions such as command and control should see little
difference in performance for TCP or any variant of SCPS-TP or a rate-based
protocol.
• From the single stream tests and preliminary multi-stream tests, there does
not appear to be a significant advantage to deploying SCPS-TP over TCP.
• In extremely errored environments with high RTT delays, a rate-based
protocol is advisable if you properly engineer the network.
– Beware of using rate-based protocols on shared networks unless you can
reserve bandwidth.
• All rate-based protocols need tested work and/or faster machines to reach
their potential.
– For the commercial rate-based protocols tested, this may be due to their
algorithms and coding being optimized for multicast operation.
• New TCP research may dramatically improve TCP operation for near
planetary environments.
– TCP Pacing with Packet Pair Probing, TCP Westwood, TCP Explicit
Transport Error Notification (ETEN).
2nd Space Internet Workshop, May 21-22, 2002
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