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Ye Wang, Xuan Li, Dongtao Liu, Maoke Chen
ICCT2006Guilin, China
Optimizing Cost and Performance
for Concurrent Multipath Transferring
using extended shim6
Guilin, ChinaICCT2006
Content
Introduction• CMT, shim6, traffic optimization
Modeling, Analysis, and Algorithm• lower cost when performance satisfied
• higher performance when cost restricted
• cost-performance tradeoff (higher NPR)
Simulation ResultsConclusion & Future Work
Guilin, ChinaICCT2006
Introduction – CMT
Concurrent Multipath Transferring• Multimedia / P2P / Distributed Computing / FTP / …
Site
ISP1CERNET2
ISP1CERNET2
ISP2NSFCNET
ISP2NSFCNET
ISP3…
ISP3…
Remote Site
2001:250::4321/64
2001:da8::5678/64
2001:9ef::0246/64
2001:980:ffe:1::42
Guilin, ChinaICCT2006
Introduction – CMT
Possible CMT • multiple TCP connections
– not applicable for general applications
• SCTP– far beyond deployment
– little work for end sites’ demand
• TCP with extended shim6– incremental deployable
– more applicable
– simple way to achieve traffic optimization
Guilin, ChinaICCT2006
Introduction – shim6
Sender A
shim6 Network Paths
ULP
IP
Src ULID(A)Dst ULID(B)
Src L(A)Dst L(B)
Receiver B
shim6
ULP
IP
Src ULID(A)Dst ULID(B)
Src L(A)Dst L(B)
Site Multihoming by IPv6 Intermediation• Separate Identifier (host ID) from Locator (IP address)
Guilin, ChinaICCT2006
Introduction – traffic optimization
Communication Solicitation of End Sites• Performance Maximization + Cost Minimization
Big Challenging for Internet• more than “best effort”
• transferring in Layer 4, forwarding in Layer 3
Our proposal: TCP CMT using extended shim6• intermediation in Layer 4.5
• traffic (re)distribution on multiple Locator pairs
• shim6 + TCP trigger
Guilin, ChinaICCT2006
Introduction – traffic optimization
Related Works• Augmenting TCP
– TCP-Reno, AQM/ECN, RED, XCP, VCP, etc.
• SCTP: Stream Control Transmission Protocol– much more powerful than TCP
– aim at better QoS for general purpose transferring
• Smart routing– distribute traffic “optimally” in Layer 3
– long-term mechanism
– gateway-side traffic control
Guilin, ChinaICCT2006
Modeling – Definitions
Path i (i: 1~n): locator pair iTraffic • traffic volume through Path i:
ISP Pricing and Site Cost• *flow pricing, lease pricing, flat-rate pricing• pricing via Path i by according ISP: • site cost:
Site Performance• bandwidth:• Equivalent Bandwidth:
Natural Price Ratio• NPR:
Internet
6 paths (n=6)
ISP11
ISP12
ISP13
ISP21
ISP2
2
1
n
i ii
C p m
im
ip
ii
mb
t
1
n
ii
mb
t
bu
C
Guilin, ChinaICCT2006
Modeling
Problem Statement• For what and not for what
– How to (re)distribute TCP cwnd? care
– How to rebuild TCP recv window? care
– Which locator pairs to use? careless, depends on shim6
– Deal with fast retransmission? careless at present, depends on TCP-sub
• 1. Optimize cost when performance satisfied
• 2. Optimize performance when cost restrained
• 3. Higher NPR
1
min min1
min ( min )
. ( )
n
i ii
ni
i
p m C
mst B b B
t
1
max max1
max ( max )
. ( )
ni
i
n
i ii
mb
t
st p m C C C
1 1
1
max max{ } max{ / }
n n
i i ii i
n
ii
m p mb
uC t m
Guilin, ChinaICCT2006
Analysis
EB
Typical demands for “at-least” bandwidth
or“at-most” cost
NPR
Cost
A simple metric of how well the traffic is distributed
PerformanceNPR
Cost
“optimalpoint”
Goal: enhance performance and minimize cost
“EB min”
“Cost max”
Cost
Guilin, ChinaICCT2006
Analysis
• Lemma – Timing pricing and lease pricing both call for performance maximization
• Assumption– Paths are ordered by price (p1<p2<…<pn)
• Theorem – N locator pairs, p1<p2<…<pn,
max{ u } = max{ M / [ max{ mi/bi } * sum( pi*mi ) ] } min max { mi/bi } mi/bi = const = t b = b1 (1 + m2/m1 + m3/m1 + … + mn/m1)If mk>0, b = b1 + b2 + … + b(k-1) + b1*mk/m1( good for split and rebuild window, good performance )
or min{ sum( pi*mi ) }m1 = m …( bad performance )
or heuristic algorithm
Guilin, ChinaICCT2006
Algorithms – 1
Lower cost when performance satisfied1. b(i) m(i) / t (i = 1..N);
2. B Bmin; i 1;
3. if B > b(i), then m(i) b(i) * t; else m(i) B * t, end;
4. B B – b(i), i i + 1
5. if i <= n goto 3); else end.
Guilin, ChinaICCT2006
Algorithms – 2
Higher performance when cost restricted• Heuristic
– reduce throughputs when deficit
– improve performance when surplus
1. b(i) m(i) / t (i = 1..n);
2. let C sum( p(i) * m(i) ) (i = 1..n);
3. Cdelta Cmax – C;
4. if Cdelta < 0 then m(i-1) m(i) * 105% (i = 2..n); else m(i+1) m(i) * 95% (i=1..n-1);
Guilin, ChinaICCT2006
Algorithms – 3
Higher NPR• similar as Algorithm 2, but use another metric for judgment
• cut half load of Path i when
• enlarge sub-window of Path i when
• Relative Agio:
• Quick metric:
2
1 1 1
1 1
( )1 1
/( )
n n n
i i i ii i i
n n
i i ii i
m p m mU
t n tm n p m
1
i
ii
i i
mmtU
p p t
iU U
iU U
1 j i jij
i i
p p pr
p p
2
1.. ,
1i i
iik k
k n k i
mU U m
p tn m r m
Guilin, ChinaICCT2006
Simulation Results
Simulation in ns-2• modified TCP agent + multiple modified IP agents
• network topology: 3-ISP multihoming (+ N paths)
• over 1000 runs
Site
ISP1CERNET2
ISP1CERNET2
ISP2NSFCNET
ISP2NSFCNET
ISP3…
ISP3…
Remote Site
Guilin, ChinaICCT2006
Simulation Results
High-bandwidth demand for CMT
Guilin, ChinaICCT2006
Simulation Results
Constant-bandwidth demand for CMT
Guilin, ChinaICCT2006
Simulation Results
Optimize cost when bandwidth satisfied
Guilin, ChinaICCT2006
Simulation Results
Optimize bandwidth when cost restrained
Guilin, ChinaICCT2006
Simulation Results
Optimize Natural Price Ratio
Guilin, ChinaICCT2006
Conclusion and Future Work
Contribution• A case study on future IPv6 Internet technology (shim6)
• Optimize CMT for the cost and performance of multihomed end sites within the TCP layer
Status• Good attempt in theory and simulation-based study
• Little practice (shim6 has not yet been deployed), Only a best-effort way
Stepping forward• Develop real-system (shim6 prototype + UDP + algorithms)
• Better congestion control mechanism (retransmission and reordering)
• Study on site-ISP games
Thank you!
Ye Wang, Xuan Li, Dongtao Liu, Maoke Chen