On Selfish Routing in Internet-like Environments

thoughtlessskytopNetworking and Communications

Oct 29, 2013 (3 years and 10 months ago)

103 views

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



Questions?