1. 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 - Multimedia Networking, Bell Labs
Mostafa Ammar - College of Computing, Georgia Tech

2. 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

3. 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 = MaxaE ( Xa/Ca ) ]

4. Repeated Game model (contd.)
Overlay
Routing
Overlay Link
Latencies
Overlay routes 
Overlay layer
traffic
Native link
delays 
Traffic on each overlay link
The frequency of looping depends on the probing mechanism
Traffic
Engineering
Native
routes 
Background traffic
Traffic Matrix

5. Illustration of OR vs TE
14ms C
Shortest latency routes A
4ms
4ms B
5ms
10ms D
OVERLAY
23ms
NATIVE 2 E F 4
10ms
2ms C 3 3 4
2ms 4 3
Minimize (Max util)
2ms
2ms
Numbers on each link represent the avail-bw
2ms
3ms A B 5 G H
4ms 2 2 3 3
3ms
3ms
6ms
2ms I 2 J 2 D
10ms
10ms
Initial State

6. Illustration of OR vs TE (contd.)
14ms C
Multihop paths
A  B  C
A  B  D A
6ms
4ms B
5ms
10ms D
OVERLAY
23ms
NATIVE 2 E F 4
10ms
2ms C 4
2ms 2 2
2ms
2ms
2ms
3ms A B 1 G H
4ms 2 2 1 2
6ms
3ms
3ms
2ms I 2 J 2 D
10ms
10ms
Overlay traffic introduced
Avail-bw changed

7. Illustration of OR vs TE (contd.)
14ms C
Multihop paths
A  B  C
A  B  D A
4ms
5ms B
5ms
10ms D
OVERLAY
23ms
NATIVE 2 E F 2
10ms
2ms C 1 1 2
2ms
2ms 4 2
2ms
2ms
3ms
SPLIT A B 3 G H
4ms 1 1 1 2
3ms
3ms
6ms
2ms I 2 J 2 D
10ms
10ms
Latency changed
After TE reacts

8. Illustration of OR vs TE (contd.)
14ms C
Multihop paths
A  B  C
A  B  C  D
B  C  D A
4ms
5ms B
5ms
10ms D
OVERLAY
23ms
NATIVE 2 E F
10ms
2ms C 1 1 4
2ms
2ms
2ms
2ms
3ms
Traffic going from node A to D cannot be split into components that go to C and that which goes to D
SPLIT A B 5 G H
4ms 1 1 3
3ms
6ms
3ms
2ms I 2 J 2 D
10ms
10ms
After Overlay routing reacts
Avail-bw changed

9. Simulation Results TE objective Overlay objective Overall stability
Round
Clear conflict
Duration of suboptimality is longer for TE
Lot of oscillations observed

10. 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

11. Our goal .. is to propose strategies that
obtain the best possible performance for a particular layer
while steering the system towards a stable state.

12. 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

13. Resolving Conflict - Obstacles
Incomplete information
Unavailable relation between the objectives
NP-hard prediction

14. Resolving Conflict - Simplification
Assume: Each layer has a general notion of the other layer’s selfish objective
Operate leader such that
Follower has no desire to change  Friendly
Follower has no alternative to pick  Hostile
Constitutes a preemptive action
Use history to learn desired action gradually.
Follower is forced

15. Overlay Strategy - Friendly
Native layer only sees a set of src-dest demands
Improve latency of overlay routes, while retaining the same load pressure on the native network!
Load-constrained LP C
Overlay link
Traffic (Mbps)
A ® B
A ® C 1
B ® C 2 E 1 B 1 D A

16. Overlay Strategy – Friendly (contd.)
Acceptable to both OR and TE
Stable within a few rounds

17. Overlay Strategy - Hostile
Push TE to such an extent that it does not reroute the overlay links after overlay routing
Send dummy traffic in an effort to render TE ineffective
Dummy traffic injection C E 1
Unused overlay link AB B 1 D A
- Unused by real overlay traffic
- Non-overlapping with overlay links under use

18. Overlay Strategy - Hostile (contd.)
TE can’t improve further
Acceptable only to OR

19. Native Strategy - Friendly
TE pays no attention to the length of the route!
TE should balance load, while ensuring that the path length is almost the same!
Hopcount-constrained LP
Native route
Next hop
Total Hops
A ® B E 2
A ® C D
D ® E B
All others
Dest itself 1 C E 1 B 1 D A

20. Native Strategy - Friendly (contd.)
Acceptable to both OR and TE
Takes a bit longer to converge

21. Native Strategy - Hostile
Dissuade overlay routing from using certain multihop paths
Increase latency of native links that are heavily loaded, without any knowledge of overlay networks
Load-based latency tuning
Overused native link C E 1 1 B 1 D A

22. Native Strategy - Hostile (contd.)
Disrupted overlay routing
Takes a bit longer to converge

23. 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
Inflation
Leader
Strategy
Overlay TE
Friendly: Load-constrained LP
Hostile: Dummy traffic injection
1.082
1.023
1.122
1.992
Native
Friendly: Hopcount-constrained LP
Hostile: Load-based Latency tuning
1.027
1.938
1.184
1.072

24. 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.