Transcript Preemptive Strategies to Improve Routing Performance of
Preemptive Strategies to Improve Routing Performance of Native and Overlay Layers
Srinivasan Seetharaman - College of Computing, Georgia Tech Volker Hilt - Multimedia Networking, Bell Labs Markus Hofmann Mostafa Ammar - Multimedia Networking, Bell Labs - College of Computing, Georgia Tech
Multi-Layer Interaction Service overlay networks offer enhanced services by forming a virtual network of specialized nodes They deploy independent routing schemes that are oblivious to underlying native network achieve a specific selfish objective Two main problems: Mismatch of routing objectives Misdirection of traffic matrix estimation
Repeated Game Model Player1: Overlay Routing (OR) Latency-optimized paths between nodes Reacts to changes in link latency by probing periodically, without concern for bandwidth Player2: Traffic Engineering (TE) MPLS-based scheme that solves a linear program ( using GNU LP kit ) to obtain optimal multi-paths using traffic matrix as input Minimize [ Max util = Max a E ( X a /C a ) ]
Repeated Game model (contd.) Native link delays Overlay Link Latencies Native routes Overlay Routing Traffic Engineering Overlay routes Traffic on each overlay link Traffic Matrix Overlay layer traffic Background traffic
Illustration of OR vs TE Shortest latency routes OVERLAY NATIVE
A
Minimize (Max util) 4ms 14ms 4ms
B
23ms 10ms
C
5ms
D
A 2 3ms 3 2ms E 2 10ms 3 2ms B I 2 10ms F 4 2ms 5 4ms 4 2ms 4 2ms C G J 2 10ms D 3 3ms H
Initial State
Numbers on each link represent the avail-bw
Illustration of OR vs TE (contd.) OVERLAY NATIVE
A
4ms 14ms 6ms
B
23ms 10ms
C
5ms
D
A 2 3ms
0
2ms E 2 10ms
0
2ms B I 2 10ms F 4 2ms
1
4ms 4 2ms
2
2ms C G J 2 10ms D
2
3ms H
Overlay traffic introduced Avail-bw changed
Multihop paths A B C A B D
Illustration of OR vs TE (contd.)
A 5ms
14ms
4ms B
23ms 10ms
C
5ms
D
OVERLAY NATIVE SPLIT A 1 3ms 1 2ms E 2 10ms 1 2ms B I 2 10ms F 2 2ms 3 4ms 2 2ms 4 2ms C G J 2 10ms D 2 3ms H
After TE reacts Latency changed
Multihop paths A B C A B D
Illustration of OR vs TE (contd.)
A
5ms 14ms 4ms
B
23ms 10ms
C
5ms
D
OVERLAY NATIVE SPLIT A 1 3ms 1 2ms E 2 10ms 1 2ms B I 2 10ms F
0
2ms
5
4ms
0
2ms 4 2ms C G J 2 10ms
0
3ms D H
0
2ms
After Overlay routing reacts Avail-bw changed
Multihop paths A B C A B C D B C D
Simulation Results TE objective
Round
Overlay objective Overall stability
Past research [Qiu-Sigcomm03] conducted a simulation study of scenarios where there is a conflict of objectives [Liu-Infocom05] analyzed the interaction between OR and TE to show existence of Nash equilibrium General conclusion: The system suffers from prolonged route oscillations and sub-optimal routing costs
Our goal .. is to propose strategies that obtain the best possible performance for a particular layer while steering the system towards a stable state.
Resolving Conflict – Basic Idea Designate leader / follower Leader will act after predicting or counteracting the subsequent reaction of the follower Similar to the Stackelberg approach
Resolving Conflict - Obstacles Incomplete information Unavailable relation between the objectives NP-hard prediction
Resolving Conflict - Simplification Assume: Each layer has a general notion of the other layer’s selfish objective Operate leader such that a.
Follower has no desire to change b.
Follower has no alternative to pick Friendly Hostile Constitutes a preemptive action Use history to learn desired action gradually.
Overlay Strategy - Friendly Native layer only sees a set of src-dest demands
E A Overlay link
1 A B A
B
C B C 1
C Traffic (Mbps)
0 1 2
D
Improve latency of overlay routes, while retaining the same load pressure on the native network!
Load-constrained LP
Overlay Strategy – Friendly (contd.) Acceptable to both OR and TE Stable within a few rounds
Overlay Strategy - Hostile Push TE to such an extent that it does not reroute the overlay links after overlay routing
C
1 Unused overlay link AB
E B
1
D A
Send dummy traffic in an effort to render TE ineffective Dummy traffic injection
Overlay Strategy - Hostile (contd.) Acceptable only to OR TE can’t improve further
Native Strategy - Friendly TE pays no attention to the length of the route!
Native route E
A B A C D E
Next hop
E 1
B
D B 1 Dest itself 2 2 2 1
D
TE should balance load, while ensuring that the path length is almost the same!
Hopcount-constrained LP
Native Strategy - Friendly (contd.) Acceptable to both OR and TE Takes a bit longer to converge
Native Strategy - Hostile Dissuade overlay routing from using certain multihop paths Overused native link
C
1
E
1
B
1
D A
Increase latency of native links that are heavily loaded, without any knowledge of overlay networks Load-based latency tuning
Native Strategy - Hostile (contd.) Takes a bit longer to converge Disrupted overlay routing
Preemptive Strategies: Summary We proposed four strategies that improve performance for one layer and achieve a stable operating point Inflation factor = Steady state obj value with strategy Best obj value achieved Leader Overlay Native Strategy Friendly: Load-constrained LP Hostile: Dummy traffic injection Friendly: Hopcount-constrained LP Hostile: Load-based Latency tuning Inflation Overlay TE 1.082
1.023
1.122
1.992
1.027
1.938
1.184
1.072
Preemptive Strategies: Summary (contd.) Each strategy achieves best performance for the target layer within a few rounds with no interface between the two layers with all information inferred through simple measurements If both layers deploy preemptive strategies, the performance of each layer depends on the other layer’s strategy.