30 October 2013
1
On Selfish Routing in Internet
-
like
Environments
paper by
Lili Qiu, Yang Richard Yang, Yin Zhang, Scott Shenker
presentation by
Ed Spitznagel
30 October 2013
2
Selfish Routing
•
Selfish routing: allowing hosts to choose routes
themselves (e.g. source routing) or use overlay
routing networks (e.g. Detour, RON)
–
routing decisions designed to optimize host
-
based or
overlay
-
based metrics, rather than system
-
wide metrics
30 October 2013
3
Selfish Routing
•
Theoretical results have shown that selfish routing
can result in “suboptimal system behaviour”
–
“price of anarchy” (latency of selfish routing vs.
globally optimal) can be unbounded for general latency
functions [Roughgardern and Tardos]
•
Does this happen in Internet
-
like environments?
30 October 2013
4
Outline
•
Models and Methodology
•
Selfish Source Routing
•
Selfish Overlay Routing
•
Selfish Routing vs. Traffic Engineering
•
Conclusion
30 October 2013
5
Network Model
•
Physical network: directed graph
G = (V, E)
where latency
of each link is a function of its load
•
Demands: Network traffic is partitioned into traffic
demands
•
Overlays: an overlay consists of overlay nodes, directed
overlay links, and a set of demands originated from the
overlay nodes.
–
paper considers the fully connected overlay topology only
•
Users: originators of traffic. Their objective is to minimize
latency.
30 October 2013
6
Network Model
•
Route Controller: controls the network
-
level
routing.
–
OSPF routing: three methods for weight assignment are
used:
Hop
-
count
Random
-
weight
Optimized
-
compliant: weights are set to minimize network
cost, assuming all traffic is compliant.
–
MPLS routing: uses multi
-
commodity flow routing
30 October 2013
7
Routing and Traffic Equilibria
•
Evaluate each selfish routing scheme by
computing its performance at traffic equilibria
•
Game
-
theoretic approach: equilibrium is a state
where no user can improve his traffic’s latency
•
Computed directly by algorithms in the appendix
(faster than using simulation techniques)
30 October 2013
8
Routing
•
Routing on the physical network
–
Source Routing: results in selfish routing of the type most often
studied
–
Optimal Routing: routing that achieves minimal average latency
over all traffic demands
•
Overlay routing
–
Overlay Source Routing: selfish routing through overlay nodes
–
Overlay Optimal Routing: routing through the overlay that
achieves minimal average latency
•
Compliant routing: follow the routes determined by the
network
-
level routing protocol
30 October 2013
9
Network Topologies
•
A real tier
-
1 ISP (referred to as
ISPTopo
) with ~100
backbone routers connected via OC48 and OC192 links
•
Other ISP topologies as mapped by Rocketfuel:
•
Random power
-
law topologies generated using BRITE
30 October 2013
10
Traffic demands
•
Real traffic demands: measured on
ISPTopo
for
three randomly chosen hours in November 2002
•
Synthetic traffic demands: randomly map POPs in
ISPTopo
to non
-
leaf nodes in the Rocketfuel
topology.
•
Load scale factor: scale up demands so that, when
all traffic is compliant and routed based on
shortest hop
-
count
, the max link utilization is
100∙
F
%, where
F
is the load scale factor
30 October 2013
11
Link Latency Functions
•
Several link latency functions are used:
•
“To avoid the discontinuity when the load approaches
capacity, we approximate the M/M/1 or M/D/1 function
with a linear function beyond 99% utilization”
–
(not sure if this makes sense)
30 October 2013
12
Performance Metrics
•
Average latency
•
Maximum link utilization
•
“Network cost” metric:
–
cost for a link with load
x
and capacity
c
is:
–
cost of a network is the sum of its links’ costs
30 October 2013
13
Outline
•
Models and Methodology
•
Selfish Source Routing
•
Selfish Overlay Routing
•
Selfish Routing vs. Traffic Engineering
•
Conclusion
30 October 2013
14
Selfish Source Routing
•
Are Internet
-
like environments among the worst cases?
30 October 2013
15
Selfish Source Routing
•
Effect of network load
on average latency:
30 October 2013
16
Selfish Source Routing
•
User latency for all topologies, using M/M/1 latency
function
30 October 2013
17
Selfish Source Routing
•
User latency for
ISPTopo
, varying the latency function
30 October 2013
18
System
-
wide cost for selfish source routing
•
Effect of network load
on max link utilization:
30 October 2013
19
System
-
wide cost for selfish source routing
•
Effects of network topologies:
•
selfish routing: highest max link utilization, highest network cost
•
selfish routing may make a network more prone to overload,
especially when failures occur
30 October 2013
20
System
-
wide cost for selfish source routing
•
Effects of latency functions:
–
results for different latency functions are qualitatively
the same
30 October 2013
21
Outline
•
Models and Methodology
•
Selfish Source Routing
•
Selfish Overlay Routing
•
Selfish Routing vs. Traffic Engineering
•
Conclusion
30 October 2013
22
When every node is in the overlay
•
ISPTopo, using OSPF for network
-
level routing
•
three choices of OSPF weight assignments
•
3 of the 4 curves overlap
30 October 2013
23
When every node is in the overlay
•
Again, but with other topologies
•
Selfish routing achieves latency close to optimal (and
usually better than compliant routing)
•
...but at the cost of higher maximum link utilization
30 October 2013
24
When not every node is in the overlay
•
ISPTopo
, overlay covers edge nodes only
•
curves almost completely overlap
–
Internet backbone is fairly well
-
connected and well
-
provisioned
30 October 2013
25
When not every node is in the overlay
•
Random partial coverage: latency similar to full coverage;
full coverage has higher max link utilization
30 October 2013
26
Interactions Among Competing Overlays
•
Competing demands at the same nodes, using
same underlying network
•
Foreground and background traffic at 50% each
Different topologies
Different methods for computing
OSPF weights
30 October 2013
27
Can Many Overlays Coexist Well?
•
Results for
ISPTopo
, with various multiple
-
overlay configurations:
30 October 2013
28
Outline
•
Models and Methodology
•
Selfish Source Routing
•
Selfish Overlay Routing
•
Selfish Routing vs. Traffic Engineering
•
Conclusion
30 October 2013
29
Selfish Routing vs. Traffic Engineering
•
Traffic engineering: adjust physical routing based
on network traffic patterns (traffic matrix)
•
Selfish routing will then adjust the traffic matrix in
response to that…
•
… which causes the traffic engineering to produce
a new routing matrix
•
And the process repeats…
30 October 2013
30
Selfish Routing and OSPF optimizer
•
Optimizer chooses link weights for OSPF
•
Selfish routing + traffic engineering: considerably
worse performance than either one alone
30 October 2013
31
Selfish Routing and MPLS optimizer
•
Better, perhaps due to MPLS’s finer
-
grained control (can adjust
routing matrix without reducing available resources, unlike OSPF)
•
Almost as good as using only selfish routing or only TE
•
MPLS TE requires solving very large linear programming problem
30 October 2013
32
Conclusion
•
Unlike the worst
-
case scenarios, selfish routing in
Internet
-
like environments achieves close to optimal
–
often at the cost of overloading certain links
–
can become worse due to interaction with traffic engineering
•
Future work
–
investigate how the multi
-
AS nature of Internet affects routing
performance
–
dynamics of selfish routing (how equilibria are reached)
–
better understanding of interactions between traffic engineering
and selfish routing
–
study of selfish routing with other metrics (loss, throughput)
30 October 2013
33
End of Presentation
•
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