A Study of Bandwidth-sharing Mechanisms in Connection-oriented Networks Ph.D. Dissertation presented...
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A Study of Bandwidth-sharing Mechanisms in Connection-oriented Networks
Ph.D. Dissertation presented by
Xiangfei ZhuDepartment of Computer Science
University of VirginiaFeb 19, 2008
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 2
Outline
Quick overview Hypothesis and Metrics Contributions and Publications
Motivation Proposed mechanisms
BA-n BA-First VBDS Immediate-request
Related work Summary
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 3
Hypothesis
Well-designed algorithms employing immediate-request and book-ahead bandwidth-sharing mechanisms will lead to efficient utilization of modern high-speed connection-oriented networks
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 4
Metrics
Service provider-oriented metrics Utilization Always possible to achieve high utilization if there are no user-oriented
performance requirements
User-oriented metrics Call blocking probability: book-ahead mechanisms for session-type requests Delay: book-ahead mechanisms for data-type requests
Combined metrics Session type: express call blocking probability as a function of utilization Data type: express mean transfer delay as a function of utilization
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 5
Key contributions
Two book-ahead mechanisms for session-type requests Analytical and simulation models for these two schemes Models can be used as tools to test design choices and parameter values
A book-ahead mechanism for data-type requests Overcomes a disadvantage of using circuit-switched networks for file transfers
(when compared to packet switching)
Design and deployment of a wide-area, high-speed, optical dynamic circuit network Demonstrated the readiness of off-the-shelf switches for actual service offerings
Measurements of actual end-to-end call setup delays and per-switch processing delays Useful to other researchers for modeling purposes
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 6
Publications
X. Zhu and M. Veeraraghavan, " Analysis and Design of Book-ahead Bandwidth-Sharing Mechanisms," accepted by the IEEE Transactions on Communications (TCOM).
X. Zhu, M. E. McGinley, T. Li, and M. Veeraraghavan, "An Analytical Model for a Book-ahead Bandwidth Scheduler," Proc. of IEEE Global Telecommunications Conference (Globecom) 2007, Washington, DC, Nov. 2007.
X. Zhu, X. Zheng, and M. Veeraraghava, "Experiences in implementing an experimental wide-area GMPLS network," IEEE Journal on Selected Areas in Communications (JSAC), vol. 25, pp. 82-92, Apr. 2007.
X. Zhu, X. Zheng, M. Veeraraghavan, Z. Li, Q. Song, I. Habib, and N. S. V. Rao, “Implementation of a GMPLS-based network with end host initiated signaling,” in Proc. Of IEEE International Conference on Communications (ICC) 2006, Istanbul, Turkey, Jun. 2006.
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 7
Why the renewed interest in connection-oriented networks? Internet – connectionless packet-switching
Pros: efficient (high utilization) Cons: low quality of service (bandwidth, delay, jitter, etc. )
Resurgence of interests in connection-oriented networks: Top-down driver: large-team scientific projects require
predictable high-speed network services Bottom-up driver: advances in optical circuit-switching
technologies
Various connection-oriented testbeds are being deployed around the world NSF Experimental Infrastructure Network (EIN)
program ESnet4 (US), CA*net4 (Canada), UKLight (UK),
SURFnet (Netherlands), JGN2 (Japan) Internet2 Dynamic Circuit network
Terascale Supernova Initiative (TSI)http://www.phy.ornl.gov/tsi/
Large Hadron Collider (LHC)http://www.phys.ufl.edu/~matchev/LHCJC/lhc.html
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 8
Internet2 deployment of Dynamic Circuit network
Backbone picture reprinted from http://www.internet2.edu/pubs/networkmap.pdfIP NetworkDynamic Circuit Network
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 9
Why revisit the topic of bandwidth sharing in connection-oriented networks?
Existing mechanisms Immediate-request (IR) mode: used in the telephone network Leased-line mode: used in high-speed connection-oriented networks, such as
SONET and WDM Can these mechanisms be used in connection-oriented networks in new
context (high-speed + new apps)? IR mode: cannot achieve high utilization with low call blocking probability when
channel density is low Channel density in the telephone network is on the order of 100 or more Channel density in high-speed testbeds is on the order of 10
Leased-line mode: poor temporal sharing, expensive and inefficient Cannot be used because the number of universities involved in these projects is large
Better utilizationBetter service quality
Leased linesImmediate
request
New bandwidth-sharing mechanisms are needed!
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 10
What mechanisms exist for sharing resources in other contexts?
Reservation systems Reservation phase before resource usage e.g., book flight tickets, make medical appointments, etc.
Queueing systems On-demand service e.g., bank teller, grocery store checkout, etc. Two types of queueing system based on waiting space
Bufferless queueing – no waiting space e.g., street parking
Buffered queueing – has waiting space e.g., bank teller, grocery store checkout
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 11
idleidle
Are these mechanisms suitable for bandwidth sharing?
Reservation systems Yes, book-ahead mode
Queueing systems Bufferless queueing – Yes, immediate-request call-blocking mode Buffered queueing – No
X1 X2 X3 H1 H2
H3 H4 H5
H6 H7 H8
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 12
Two types of book-ahead systems
Classification based on request type Session-type requests
Specify desired bandwidth and duration e.g., remote visualization and remote instrument control
Data-type requests Specify size of data to be transferred e.g., file transfers
File size known at the sending end
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 13
Proposed mechanisms
Bandwidth Sharing in high-speed connection-oriented networks
Immediate-requestBook-ahead
BA-n/BA-First VBDS (Varying-Bandwidth Delayed Start)
Low-to-moderate per-channel ratehigh per-channel rate
session-type requests data-type requests
BA-n BA-First
Users specify a set of call-initiation time options
Users accept any call-initiation time
Deployed a testbed
Implemented software
Measured call-setup delays
Analytical model
Simulation model
Comparison with IR
Analytical model
Simulation model
Comparison with IR
Simulation model
Comparison with packet switching
Published in TCOM Published in Globecom
Published in JSAC
Published in ICC
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 14
Channel available for H timeslots starting at any one of the n call-initiation times? Yes, accept request No, reject request
Analytical model for the BA-n scheme
X XSwitch1 Switch2
scheduler
A call specifies: - Bandwidth: 1 channel
- Holding time: H timeslots
- Set of n call-initiation times: {s1, s2,…, sn}
m channels
Assumptions: Call arrival process is Poisson
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 15
Discrete-time Markov Chain model
System state: vector X with K components (x1, x2, …xK) xi: number of reserved channels in the ith interval 0≤xi ≤ m
Challenges Non-homogeneous system
Transition rates at time interval boundaries are infinite, but finite at other times Mixed system
Call arrival process: continuous Call holding time: discrete
A user can reserve any timeslots in the reservation window
Key insights Embedded DTMC at time interval boundaries Discretize time into very “small” timeslots to use geometric distribution to approximate (exponential) call
interarrival time distribution Timeslots should be small enough to make the probability of more than 1 call arriving in a timeslot negligible Any call arrival rate can be downgraded to a small call arrival rate by changing the time unit
e.g., 36 call/hour -> 0.01 call/second
(x1, x2, …xK)m: link capacity in channels
K: reservation window in timeslots
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 16
Simulation model
Limitation of the analytical model – does not scale with m Recall that the state space is defined as
Size of the state space: (m+1)K
Simulation model Support larger values of m Relax assumptions used in the analytical model
Call-initiation time options: uniform distribution → bell-shaped distribution
Per-call bandwidth: single channel → multi channels Path length: single link → multi links
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 17
Model validation and verification
Model validation Our models are for an initial design and
implementation of BA systems Therefore, no real-world measurements Model validation technique – peer/expert reviews
Real system measurements “available” for input parameters Example:
Real-system measurements for telephony applications - Poisson call arrival process
Same pattern likely in video-conference calls
Model verification Compare analytical model results with simulation model results
[Jain91] R. Jain, The Art of Computer Systems Performance Analysis: Techniques for Experimental Design, Measurement, Simulation, and Modeling, New York, Wiley-Interscience, 1991.[Pace02] D. K. Pace and J. Sheehan, “Subject matter expert (SME)/peer use in m&s v&v,” in Proc. of the Foundations, Lauarel, MD, Oct. 2002.
“Three validation techniques Expert intuition Real system measurements Theoretical results” [Jain91]
“Qualitative validation has to be used when adequate acceptable real world data do not exist to permit quantitative validation and is based mainly on SME (Subject Matter Expert) and peer view” [Pace02]
“Three aspects of model validation Assumptions Input parameter values and distributions Output values and conclusions” [Jain91]
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 18
Key results from the BA-n study
BA-n scheme outperforms IR scheme when per-channel rate is high e.g., when m=10
With the IR mode, high utilization achievable but at a cost 23% call blocking probability at 80% utilization 46% call blocking probability at 90% utilization
With the BA-3 mode, high utilization achievable with low call blocking probability 0.1% call blocking probability at 80% utilization 2% call blocking probability at 90% utilization
Reservation window size (K) dependence on call holding time (H) K/H does not need to be large e.g., when m=10, to achieve 90% utilization with 2% call blocking probability,
K=4H.
Multi-link scenario BA-n scheme outperforms IR Fairness achieved with “trunk reservation”
Between long-path and short-path calls
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 19
Roadmap
Bandwidth Sharing in high-speed connection-oriented networks
Immediate-requestBook-ahead
BA-n/BA-First VBDS
high per-channel rate
session-type requests data-type requests
BA-n BA-First
calls specify a set of call-initiation time options
calls accept any call-initiation time
Analytical model
Simulation model
Comparison with IR
Analytical model
Simulation model
Comparison with IR
Simulation model
Comparison with packet switching
Published in TCOM Published in Globecom
Published in JSAC
Published in ICC
Deployed a testbed
Implemented software
Measured call-setup delays
Low-to-moderate per-channel rate
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 20
m channels
Is a channel available in the entire reservation window? Yes, accept request No, reject request
Analytical model for the BA-First scheme
X XSwitch1 Switch2
scheduler
A call specifies: - Bandwidth: 1 channel
- Holding time: H timeslots
- Set of n call-initiation times: {s1, s2,…, sn}
- Any call-initiation time
1 timeslot
Assumptions: Call arrival process is Poisson
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 21
System state
Use “bins” to represent reservation intervals If the ith bin is not full, all bins after it must be empty
The system state is expressed as a 2-tuple (i, n) i – index of the first bin that is not full n – number of reserved channels in the ith bin A special case is (K, m), which denotes the state in which all bins are full
Call arrivals
m
n
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 22
m
n
The state of the system changes in two cases A call arrives:
e.g., (i, n)->(i, n+1) if n<m-1; (i, n)->(i+1, 0) if n=m-1 and i<K A time-interval boundary is encountered
e.g., (i, n)->(i-1, n) if i>1 The model is a CTMC but it is non-homogeneous
The system behavior at the timer-interval boundaries is different from its behavior at other times
There is an embedded time-homogeneous DTMC if we only look at the system at the time-interval boundaries
Call arrivals
Call arrivals
CTMC
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 23
m
n
The transition probability can be calculated by counting the number of calls (denoted by a) that arrived in the past time interval, and calculating the probability that a calls arrive in a interval
A: number of call arrivals in the current interval FA(a) is the Cumulative Distribution Function of A
GA(a) is the Probability Mass Function of A
The transition probability from state (i, n) to state (j, q) is 1-FA(mK-1) if i=1 & (j,q)=(K,m), i.e., mK or more calls arrived
GA(m(j-1)+q) if i=1 & (j,q)≠(K,m), i.e., m(j-1)+q calls arrived
1-FA(m(K-i+1)+m-n-1) if i≠1 & (j,q)=(K,m), i.e., m(K-i+1)+m-n or more calls arrived
GA(m(j-i+1)+q-n) if i≠1 & (j,q)≠(K,m), i.e., m(j-i+1)+q-n calls arrived
j
q
Call arrivals
Call arrivals
Embedded DTMC
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 24
Performance metrics
Call blocking probability
Link utilization
Mean scheduling delay - two parts Integral part: number of intervals before scheduled service interval Fractional part: delay within the arrival interval
Call arrivals
integral partfractional part
m
n
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of Virginia 25
IR v.s. BA schemes
Example To achieve a 90% utilization
with a call blocking probability less than 10% BA-First schemes are needed
when m<59
To achieve a 90% utilization with a call blocking probabilityless than 20% BA-First schemes are needed
when m<32
Use of the model -
Test design choices and parameter values
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 26
Parameters: 1) link capacity in channels, m = 2 or 8 2) reservation window size, K = 2, 4, 8, or 16
To run a system at 100% offered load with a 4% or less call blocking probability If m=2, K should be 8 time units If m=8, the number is only 4 time units
Is larger value of K always better? If m=8, call blocking probability and utilization plots for K=4, 8 and 16 overlap But mean scheduling delay increases significantly as K increases
Use of the model -
Select an appropriate reservation window size
Increasing reservation window size beyond a certain level is actually detrimental to system performance!
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 27
Use of the model -
An approximate solution for M/D/m/p system
Solutions exist for M/D/1, M/D/m (approximation) systems No existing solution for M/D/m/p system BA-First model (m, K) ≈ M/D/m/m(K+1) queuing model at moderate-to-high loads
Why? Call-arrival process: both Poisson Call holding time: both deterministic Reservation window is effectively “waiting space”
1/2
fractional part
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 28
We modeled the BA-First mechanism using a non-homogeneous CTMC
We extracted an embedded DTMC and solved it for steady-state probabilities
We obtained solutions for metrics such as call blocking probability, link utilization, and mean scheduling delay
We demonstrated the use of the model as a design tool for book-ahead systems
We demonstrated the use of the model as a solution for M/D/m/p queueing system at moderate-to-high loads
Key results from the BA-First study
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 29
Roadmap
Bandwidth Sharing in high-speed connection-oriented networks
Immediate-requestBook-ahead
BA-n/BA-First VBDS
high per-channel rate
session-type requests data-type requests
BA-n BA-First
calls specify a set of call-initiation time options
calls accept any call-initiation time
Analytical model
Simulation model
Comparison with IR
Analytical model
Simulation model
Comparison with IR
Simulation model
Comparison with packet switching
Published in TCOM Published in Globecom
Published in JSAC
Published in ICC
Deployed a testbed
Implemented software
Measured call-setup delays
Low-to-moderate per-channel rate
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 30
Book-ahead scheme for data-type requests
Data-type requests: specify size of data to be transferred
Drawback of using circuits for file transfers With fixed-bandwidth allocation, file transfers cannot take advantage of bandwidth
freed by the completion of other transfers
Fixed-Bandwidth Delayed Start (FBDS) Fixed-bandwidth allocation with rate set to maximum rate
Varying-Bandwidth Delayed Start (VBDS) Assign different bandwidth levels for different time ranges
File transfer request =(File Size, Maximum rate, [Requested start time])
Can be provided by file server
Limited by various constraints at end hosts, such as disk-access speed
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 31
VBDS
Idea of VBDS Upon receiving a reservation request, VBDS scheduler returns a Time-
Range-Channel (TRC) vector {(Bk, Ek, Ck, k=1,2,…)} Bk: start time of the kth time range
Ek: end time of the kth time range
Ck: set of channels allocated to the transfer in the kth time range
Scheduler maintains channel-availability function γ(t)
Cost of VBDS Switches need to be reprogrammed multiple times within a transfer
Switch programming time is considered in the analysis Switches need to maintain channel availability function
Reduce the number of changes in channel-availability function Discretize time
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 32
VBDS example
Assumptions: 4-channel link with per-channel rate 10Gbps Unit of time discretization: 100ms Switch programming time: 1 unit
A file transfer request specifies (5GB, 20Gbps, 50) (50, 60, {4}) – 1.125GB (60, 70, {2, 4}) – 2.375GB (70, 75, {2, 4}) – 1.5GB
(File Size, Maximum rate, Requested start time)
0 10 20 30 40 50 60 70 80 … ∞
Ch
an
ne
l ava
ilab
ility
γ(t
)4
3
2
1
Time
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 33
Numeric results
Compare VBDS, FBDS, and Packet switching (PS)
Nor
mal
ized
Del
ayA
vera
ge th
roug
hput
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 34
Key results from the VBDS study
Circuit-switched network with VBDS achieves similar performance as packet-switched networks for moderate-to-large files Significant: at high speeds, circuit switching cost << packet switching cost
VBDS favors large files when compared to packet switching Packet switching: newly arriving transfers “cut in” VBDS: Not so. Allocated bandwidth remains dedicated to ongoing transfers
We do not recommend using circuit-switched network for small files Scheduling and circuit setup overheads
Cost Circuit switching: setup overhead (unsuitable for small files) Packet switching: congestion control algorithm (lower throughput for moderate-to-large
files)
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 35
Roadmap
Bandwidth Sharing in high-speed connection-oriented networks
Immediate-requestBook-ahead
BA-n/BA-First VBDS
high per-channel rate
session-type requests data-type requests
BA-n BA-First
calls specify a set of call-initiation time options
calls accept any call-initiation time
Analytical model
Simulation model
Comparison with IR
Analytical model
Simulation model
Comparison with IR
Simulation model
Comparison with packet switching
Published in TCOM Published in Globecom
Published in JSAC
Published in ICC
Deployed a testbed
Implemented software
Measured call-setup delays
Low-to-moderate per-channel rate
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 36
Immediate-request bandwidth sharing
Deployed a wide-area experimental network with immediate-request mode of bandwidth sharing - CHEETAH
State-of-the-art in 2004 Control-plane protocols are standardized by IETF - GMPLS
protocol suite Vendors have implemented these protocols in high-speed optical
circuit switches No deployed network uses these functions No signaling protocol client for end hosts to enable the creation
of end-to-end high-speed circuits
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 37
CHEETAH network
Switches: Sycamore SN16000 Intelligent Optical switch Robust implementation of GMPLS control-plane protocols Support standardized Ethernet-SONET mapping
Atlanta, GA
zelda1
zelda2
zelda3
Raleigh, NC
OC192card
ControlCard
GbE/10GbE
card
SN16000
H wukong
Oak Ridge, TN
To Cray X1
zelda4
zelda5
HH
OC192card
ControlCard
GbE/10GbE
card
SN16000
H
HH
OC192card
ControlCard
GbE/10GbE
card
SN16000OC-192 OC-192
End hosts: general-purpose Linux PCs with two NICs and CHEETAH end-host software
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 38
IR mode of sharing in CHEETAH
Designed and implemented an end-host software package based on the GMPLS architecture Stand-alone circuit request tools Integrated into applications such as Squid (an open-source web proxy
software)
Ran experiments of IR mode call setups and releases
Measured end-to-end circuit setup delays and per-switch signaling message processing delays Measurements useful to other researchers for modeling purposes
Demonstrated the readiness of off-the-shelf switches for actual service offerings
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 39
Related work
Research papers on book-ahead bandwidth sharing Most of these papers use simulations None of them considers book-ahead calls with multiple acceptable options Our results show that a book-ahead mechanism that specifies only one call-
initiation time may perform worse than an immediate-request mechanism
File transfers List scheduling: all proposed algorithms use fixed allocations Bin packing: cannot break a block into pieces to fit into bins TCP improvements: determine fair share for a flow faster and more
accurately, while we determine share for a flow during setup
Optical connection-oriented testbeds e.g.: ESnet4, NSF DRAGON, CA*net4, UKLight, JGN2, etc. Focus: implementation & inter-domain usage Our work: mixed study of IR and BA; theoretical modeling + implementation
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 40
Summary
High-speed connection-oriented networks should support a combination of bandwidth-sharing services
Greater sharingBetter service quality
IP servicesLeased
linesImmediate
request
BA-n/BA-First VBDS
Existing services:
New services:
For video telephony, transfers of moderate-sized files
For reservations that specify file size (large file transfers)
For reservations that specify desired bandwidth and duration
For serving as “wires” between switches to create networks that offer other services
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 41
Future work
Routing issue in reservation phase Currently assume a linear topology in multi-link scenarios Multiple route options should be exploited
Distributed implementation Necessary for inter-domain scheduling
Service providers do not share network topology information with each other
Validate models against real measurements A long-term future work item after deployment & user base build-up
Questions from Form G111
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 43
Questions from Form G111 -
Defining the problem
In the context of new optical circuit-switched technologies and new application requirements, what bandwidth-sharing mechanisms can lead to efficient utilization of modern high-speed connection-oriented networks?
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 44
Questions from Form G111 -
Analysis of previous and related work
Research papers on book-ahead bandwidth sharing Most of these papers use simulations None of them considers book-ahead calls with multiple acceptable options Our results show that a book-ahead mechanism that specifies only one call-
initiation time may perform worse than an immediate-request mechanism
File transfers List scheduling: all proposed algorithms use fixed allocations Bin packing: cannot break a block into pieces to fit into bins TCP improvements: determine fair share for a flow faster and more accurately,
while we determine share for a flow during setup
Optical connection-oriented testbeds e.g.: ESnet4, NSF DRAGON, CA*net4, UKLight, JGN2, etc. Focus: implementation & inter-domain usage Our work: mixed study of IR and BA; theoretical modeling + implementation
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 45
Questions from Form G111 -
Success criteria
Has the student adequately defined the measure(s) of success to be used to evaluate the work? Is there a well defined metric with a goal? Does the metric adequately represent the desired success criteria?
Success criteria Session-type BA requests
BA-n: better performance than IR BA-First: a model that scales to m>100
Data-type BA requests At least the same performance as packet switching
IR mode Stable network deployment and software implementation
Metrics Session type: express call blocking probability as a function of utilization Data type: express mean transfer delay as a function of utilization
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 46
Questions from Form G111 -
Solution
Is the approach taken well executed? Does it appear to be correct? Is the work technically challenging? Does the student utilize appropriate professional standards?
A combination of analytical, simulation, and experimental methods. Two book-ahead mechanisms for session-type requests
Analytical and simulation models for these mechanisms One book-ahead mechanism for data-type requests
A simulation model for this mechanism A wide-area testbed for experimental study of the immediate-request
mechanism Testbed deployment Software implementation Experimentation and measurements
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 47
Questions from Form G111 -
Innovation and risk
Two new Markov chain models for book-ahead bandwidth-sharing schemes (first Markov chain models for book-ahead schemes)
An approximate solution for the M/D/m/p queueing system
One of the first deployments of a wide-area high-speed dynamic circuit network
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 48
Questions from Form G111 -
Broader implications(Social, economic, political, technical, ethical, business, etc.)
Demonstrated the readiness of off-the-shelf circuit switches for actual service offering (business and technical)
Designed efficient bandwidth-sharing algorithms for high-speed connection-oriented networks Circuit switches are less complex than packet switches, which
means Less expensive (economic) Consume less power (environmental)
Backup slides
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 50
Assumptions Link capacity m = 1 Advance-reservation horizon K = 3 Number of classes L = 2 Holding time for class-1 calls h1 = 1 Holding time for class-2 calls h2 = 2 Number of options n = 1
System transition happens at the end of each timeslot Example: state (0, 0, 1)
A call arrives and reserves the third timeslot -> state (0, 1, 1) Pr=(1/3)pr1 A call arrives and reserves the first timeslot -> state (1, 1, 0) Pr=(1/3)pr1 No call arrives or the arrived call is blocked -> state(0, 1, 0) Pr=1-(2/3)pr1
Current time t t+k
1
# o
f rese
rved
ch
an
nels
Time
(Backup slides) BA-n - Example of the analytical model for the BA-n scheme
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 51
Define a left shift operator : If , .
Define a K-component vector , where
The transition probability from state x to state y is
p: the probability that a call arrives during a time slot rj: the probability that an incoming call belongs to class j qi,j: the probability that a class-j call is admitted with a initiation time of the ith timeslot Bx: the probability that an incoming call is blocked when the system is in state x
First row: a class-j call is admitted with an initiation time of the ith timeslot Second row: no call arrives or a call arrives but is blocked Third row: all other states
(Backup slides) BA-n –
DTMC model – Transition probability matrix
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 52
Use Hypergeometric probability mass function to calculate Bx and qi,j A large set of N elements, known to have d defective elements The probability of having k defective units in a random batch of n
elements, drawn without replacement from the large set
Define dj: number of “ineligible” timeslots for class-j calls Mapping:
A total of (K+1-hj) candidate timeslots: corresponds to N dj ineligible timeslots: corresponds to d defective units e.g.: the first t options are all rejected: corresponds to a batch of n elements are all
defective (k=n) After we obtain the transition matrix
Calculate the steady-state probabilities Calculate average call blocking probability and utilization
(Backup slides) BA-n –
To compute qij and Bx
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of Virginia 53
BA-all clearly outperforms IR BA-1 is worse than IR
Reason: “gaps” are caused by advance reservations Analogy: if a doctor spends exactly 1 hour with each patient, patients arriving in the middle of an hour will
cause gaps (time period shorter than 1 hour) Restricted call-initiation times
Call-initiation time options are restricted to fall on call holding time boundaries Restricted BA-n mechanisms clearly outperform IR Performance of restricted BA-n is almost as good as BA-all
(a) Call blocking probability (b) Utilization
(Backup slides) BA-n –
Comparison of blocking probability and utilization
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 54
Provide insight into how to select the advance-reservation horizon (K ) Longer K means better performance Longer K also means greater storage and computation needs
The performance improvement is small after K reaches a certain value
(number of class L=1, call holding time H = 200, offered load = 100%)
(Backup slides) BA-n – Dependence of reservation window size on number of channels and call holding time (1)
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 55
BA-all with Number of channels m =2 Call holding time H =300 Offered load = 100%
The ratio K/H instead of K determines the call blocking probability. K/H values for different values of m corresponding to 3 values of call blocking probability
Call blocking probability 2% 5% 10%
m=2 14 6 4
m=5 5 4 3
m=10 4 3 2
(Backup slides) BA-n – Dependence of reservation window size on number of channels and call holding time (2)
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 56
Consider a system designer who wants to know the payoff by increasing the reservation window size Assume we want to run the system with 1% call blocking probability e.g., m=4, by increasing K from 2 to 4, the system load/channel can be increased from
75% to 93% This is quite significant in that it allows for a 24% increase in the number of endpoints
multiplexed on to the link
m=4
(Backup slides) BA-First –
Numerical results – system design
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 57
(Backup slides) VBDS –
Why prefer using connection-oriented networks for file transfers The cost of high-speed circuit switches are lower than high-speed packet switches
High-speed memories for route table lookup and packet buffering Rich set of features such as policing and shaping
The simulated PS system is an idealized system in which buffers are assumed to be infinitely large In reality packet loss will occur due to congestions Mechanisms, such as TCP’s congestion control schemes, are required to recover from
these packet losses with retransmissions and rate adjustments Transport protocols designed for circuits, such as Circuit-TCP (C-TCP) are more efficient
Take advantage of the information on the fair share of a flow Disabling TCP’s Slow Start and AIMD algorithm
Item Cisco 12416 Sycamore SN16000
Base system $130,000 $183,500
10x1GbE card $169,830 $63,500
1x10GbE $125,000 $65,500
1xOC192 $225,000 $37,500
A system with 6 pieces 10xGbE +6 pieces 1x10GbE + 3 pieces OC192
(Total 120Gbps client data rate)
$2,573,970($21,000/Gbps)
$1,084,700($9,000/Gpbs)
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of Virginia 58
(Backup slides) VBDS –
VBDS favors large files when compared to PS
Packet switching: newly arriving transfers “cut in”
VBDS: Not so. Allocated bandwidth remains dedicated to ongoing transfers
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 59
(Backup slides) IR -
Erlang-B formula
Cannot achieve high utilization with low call blocking probability when m is small
Call blocking probability (PB) against the link capacity expressed in channels (m)
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 60
(Backup slides) IR -
GMPLS control plane
Purpose of Generalized Multi-Protocol Label Switching (GMPLS) control plane Dynamic bandwidth sharing (distributed) Provisioning (configure the switches for the circuit/VC)
Three components Link management protocol OSPF-TE routing protocol RSVP-TE signaling protocol
Bandwidth sharing mode Immediate-request (cannot specify a future call-initiation time or call
holding time in protocols) Calls are accepted or rejected - “call blocking"
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 61
(Backup slides) IR -
CHEETAH concept
Provide on-demand circuit service as an add-on to the connectionless service provided by the Internet
Hybrid circuits: GbEthernet-SONET-GbEthernet
2/19/2008
Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 62
Architecture
Based on the RSVP-TE code from KOM/DRAGON About 40K lines of C++ code
What I did: Modified the code to inter-operate with the Sycamore SN16000 Added admission control, session management, user interface, etc. Integrated code for DNS lookup from our partner CUNY Designed and implemented APIs for general applications About 4K lines of new code
(Backup slides) IR -
CHEETAH end-host software development
Application
DNS client
RSVP-TE module
TCP/IP
C-TCP/IPNIC 1
NIC 2
End HostCHEETAH software
Internet
SONET circuit-switched network
CircuitGateway
CircuitGateway
Application
DNS client
RSVP-TE module
TCP/IP
C-TCP/IPNIC 1
NIC 2
End HostCHEETAH software
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 63
(Backup slides) IR -
CHEETAH end-host software architecture
DNS lookup – to support our scalability goal
Five steps of circuit setup Message parsing
RSVPD Route determination
Left to the edge switch CAC Date-plane configuration
Route/ARP table update Message construction
RSVPD
DNS server
RSVP-TE Daemon(RSVPD)
DNS lookupCHEETAH daemon (CD)
socket
CD API socket
User space
Kernel spaceC-TCP
C-TCP API
End host
Circuit-requestor
RSVP-TE
messages
DNS client
CAC
Route/ARP table update
RSVPD API
CHEETAH software
CD API can be integrated into web servers, FTP servers, etc., so that “elephant” flows are automatically handled via a dynamically created dedicated circuit/VC
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Ph.D. Dissertation Defense Department of Computer Science, University
of Virginia 64
(Backup slides) IR -
End-to-end signaling delay measurements
Signaling delays incurred in setting up a circuit between zelda1 (in Atlanta, GA) and wuneng (in Raleigh, NC) across the CHEETAH network.
Observations: Delays for setting up SONET circuits for rates in the original SONET hierarchy are small
(166ms) Delays for hybrid Ethernet-SONET circuits are much higher (1.6s) (vendor implementation)
The measured delay can be used for analytical and simulation models for related research
Circuit type End-tend circuit setup delay (s)
Processing delay for Path message at
the NC SN16000 (s)
Processing delay for Resv message at
the NC SN16000 (s)
OC-1 0.166103 0.091119 0.008689
OC-3 0.165450 0.090852 0.008650
1Gb/s EoS 1.645673 1.566932 0.008697
Round-trip signaling message propagation plus emission delay between GA SN16000 and NC SN16000: 0.025s