placing relay nodes for intra-domain path diversity
DESCRIPTION
Placing Relay Nodes for Intra-Domain Path Diversity. Meeyoung Cha Sue Moon Chong-Dae Park Aman Shaikh Proc. of IEEE INFOCOM 2006. Speaker 游鎮鴻. Outline. Introduction and Motivation Related Work Penalty Quantification Placement Algorithms Evaluation Conclusions and Comments. - PowerPoint PPT PresentationTRANSCRIPT
Placing Relay Nodes forIntra-Domain Path Diversity
Meeyoung ChaSue MoonChong-Dae ParkAman ShaikhProc. of IEEE INFOCOM 2006
Speaker 游鎮鴻
Outline
Introduction and Motivation Related Work Penalty Quantification Placement Algorithms Evaluation Conclusions and Comments
Routing Instability in the Internet
Link and router failures are frequent. Routing protocols are used to detect such failures and
route around them. Convergence time is in the order of seconds or minutes. End-to-end connections experience long outages.
How to increase reliability and robustness of mission-critical services against temporary end-to-end path outages?
Path Diversity and Overlay Networks
Take advantage of path diversity provided by the network topology.
Overlay path – use a node inside the network to relay packets over an alternate path that is different from the default routing path. ex) RON [Anderson et al., SOSP 2001]
Detour [Savage et al., IEEE Micro 1999]
Idea: use disjoint overlay paths along with the default routing path to route around failures.
Objective
Previous work has focused on selecting good relay nodes assuming relay nodes are already deployed
As an ISP, we consider the problem of placing relay nodes well
Assumptions:· Intra-domain setting [Shortest Path First Routing]
· Relays are simply routers with relaying capability
· Overlay paths use single relay node
disjoint overlay path
default path
relays
Disjoint overlay path gives maximum robustness against single link failures!
Path Diversity – Disjoint Overlay Path
Destination(egress router)
ISP Network
Origin(ingress router)
Path Diversity – Disjoint Overlay Path
Completely disjoint overlay paths are often not possible.
- Existing path diversity: Equal Cost Multi-Paths (ECMP)
Intra-PoP
AR
AR BR
BR
BR
BR AR
AR
Inter-PoP
(PoP: Point of Presences, AR: Access Router, BR: Backbone Router)
Impact of ECMP on Overlay Path Selection
We may need to allow partially disjoint paths.
Such overlap makes networks less resilient to failures. We introduce the notion of penalty to quantify the quality degradation of overlay paths when paths overlap.
o d
r
default path
overlay path
Partially Disjoint Overlay Path
0.5
0.5
0.25
0.25
0.5 0.75
0.125
0.125
0.875
0.125
1.0o d
Impact of a single link failure on a path- Prob. of a packet routed from o to d encounters a failed link l = P[ path od fails | link l fails ]
Penalty for Overlapped Links
Consider overlay path (ord) is used with default one (od).
Penalty – the fraction of traffic carried on the overlapped link
o d
r
Penalty for Overlapped Links (cont.)
Penalty of relay and relay set
Penalty of a relay r for OD pair (o,d) Po,d(r) = P[ both ord and od fail | single link failure ]
Penalty of a relay set R of size k sum of minimum penalty of all OD pairs using relays ∑o,d min( Po,d(r) | r ∈ R )
How to find a relay set R of size k with minimum penalty
Optimal solution exhaustive search, 0-1 integer programming (IP)
Greedy selection heuristic start with 0 relays iteratively make greedy choice (minimal penalty) repeat until k relays are selected
Local search heuristic start with k set of random relays repeat single-swaps if penalty is reduced
Placement Algorithms
Performance evaluation Number of relays vs. penalty reduction Comparison with other heuristics (random, degree)
Sensitivity to network dynamics Based on topology snapshot data, do relays selected
remain effective as topology changes? Based on network event logs, what is the fraction of
traffic protected from failures by using relays?
Evaluation Overview
Performance Evaluation
Relay Node Properties
Node degree, Hop count, Path weight
5% of nodes are selected as relays
10% of nodes are selected as relays
Sensitivity to Network Dynamics
Relays are relatively insensitive to network dynamics.
complete protectionfor 75.3% failures
less than 1% of trafficlost for 92.8% failures
(failu
re e
vents
)
Hypothetical Traffic Loss from Failure Event Logs
Conclusions This is the first work to consider relay placement for path
diversity in intra-domain routing.
They quantify the penalty of using partially disjoint overlay paths; and propose two heuristics for relay placement.
They evaluate their methods on diverse dataset. Their heuristics perform consistently well (near-optimal). A small number of relay nodes (≤10%) is good enough. Relays are relatively insensitive to network dynamics.
Comments
Evaluations are abundant. The comparison to Degree method is not a
good example.
Reference
http://an.kaist.ac.kr/~mycha/