Multicast Algorithms in Service

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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

1

Dario Pompili*, Luca Lopez^, Caterina Scoglio+

*dario@ece.gatech.edu
,
^lopez.luca@gmail.com
,
+caterina@eece.ksu.edu


*Broadband and Wireless Networking Laboratory

Georgia Institute of Technology, Atlanta, GA 30332, USA


^Dipartimento di Informatica e Sistemistica

University “La Sapienza,” Rome 00184, Italy


+Department of Electrical and Computer Engineering

Kansas State University, Manhattan, KS 66506, USA

Multicast Algorithms in Service
Overlay Networks


Infocom 2006, April 23
-
29

2

D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

2

Outline


An Introduction to Overlay Networks


Native Network vs. Virtual Overlay Network


Unicast vs. Multicast Transmissions


Multicast Applications


Proposed Overlay Multicast Algorithms: DIMRO
and DIMRO
-
GS


Performance Evaluation


Conclusions and Future Work




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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

3

An Introduction to Overlay Networks


Overlay routing enhances IP network reliability and performance by
forwarding traffic through intermediate overlay nodes [1
-
3]. This way,


It can bypass congestion


It can overcome transient outages



Past research [4,5] focused on techniques for:


Building overlay networks


Evaluating their performance



[1] H. Zhang, J. Kurose, and D. Towsley, “Can an overlay compensate for a careless
underlay?” in
Proceedings of IEEE INFOCOM 2006
, Barcelona, Spain, Apr. 2006

[2] Y. Zhu, C. Dovrolis, and M. Ammar, “Dynamic overlay routing based on available
bandwidth estimation: A simulation study,”
To appear in the Computer Networks Journal
,
2006

[3] S. Y. Shi and J. S. Turner, “Routing in overlay multicast networks,” in Proceedings of
IEEE INFOCOM 2002, New York, NY, USA, June 2002

[4] D. Andersen, H. Balakrishnan, M. Kaashoek, and R. Morris, “Resilient overlay networks,”
in
Proceedings of ACM Symposium on Operating Systems Principles
, Banff, Canada, Oct.
2001

[5] A. Nakao, L. Peterson, and A. Bavier, “A routing underlay for overlay networks,” in
Proceedings of ACM SIGCOMM
, Karlsruhe, Germany, Aug. 2003

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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

4

Native Network vs. Virtual Overlay Network


We consider two layers of network infrastructure:


The
native network
, which includes end
-
systems, routers, links,
and the associated routing functionality, and provides best
-
effort
datagram delivery between its nodes


The
virtual overlay network
, which is formed by a subset of the
native layer nodes interconnected through overlay links to
provide enhanced services.




Overlay links are
virtual
in the sense that they are IP
tunnels over the native network


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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

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Unicast vs. Multicast Transmissions


Unicast transmissions:



The sender transmits data to a single receiver and, if multiple receivers
want to receive the same data content, the sender has to transmit
multiple copies of data


Multicast transmission:


The sender transmits only one copy of data that is delivered to multiple
receivers


A challenging objective in multicasting is to minimize the
amount of network resources to compute multicast trees

Unicast

Multicast

3 copies of
the same
message

Only 1 copy
of the
message

S

R
2

R
3

R
3

R
2

S

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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

6

Multicast Applications


We present two algorithms to build virtual multicast trees on an overlay
network for as many applications as:


Live video, software and file distribution, replicated database, web site
replication, videoconference, distributed games, file sharing, periodic delivery

Source Specific

Group Shared

Real
-
time

Live video distribution

Videoconference,
distributed games

Non Real
-
time

Software and file distribution, replicated
database, server and web site replication,
periodic data delivery (sport scores,
magazines, newspapers)


File sharing,
collaborative
groupware, replicated
database

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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

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Proposed Overlay Multicast Algorithms


DIMRO: DIstributed Multicast algorithm for Internet Resource
Optimization



It builds virtual source rooted multicast trees for source specific
applications


It takes the virtual link available bandwidth into account to avoid traffic
congestion and fluctuation, which cause low network performance



DIMRO
-
GS:
DIstributed Multicast algorithm for Internet
Resources Optimization in Group Shared applications


It constructs a virtual shared tree for group shared applications by
connecting each member node to all the other member nodes with a
source rooted tree computed using DIMRO



Both DIMRO and DIMRO
-
GS algorithms offer service differentiation,
i.e., they provide QoS at application
-
layer without IP
-
layer support

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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

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DIMRO: Objectives


Most of the algorithms in the literature focus on computing multicast
trees for real
-
time applications (delay sensitive)


Bandwidth is often taken into account only as a constraint


Optimization involves only one tree, and not all trees for different
multicast groups



DIMRO optimizes the overlay network performance when multiple
multicast comunications should take place



The objective is to exploit the network resource in an efficient way



The available bandwidth on each virtual link plays a key role in the
multicast tree research

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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

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DIMRO: Motivations


If the overlay available bandwidth
is not esplicitely taken into
account the risk is to:


Overload some link


Leave some other link
unexploited



Load balancing is NOT achieved
if cost does not explicitely take
available bandwidth on links into
account

R
1A

S
A

R
2A

R
1B

R
2B

S
B

R
3B

Overloaded Link

Unexploited Link

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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

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DIMRO: Steps of the Algorithm

1.
Receivers are order according to decreasing
requested bit rates

2.
The optimum path between the sender and the
receiver with the highest requested rate is
computed

3.
Then, paths connecting other receivers are
computed, according to the decreasing order

4.
The k
th

receiver r
k

is connected to the sender s by
using that path p(s,r
k
) that minimizes the following
objective function:










)}
,
(
)
,
{(
1
)
,
(
k
r
s
p
v
u
uv
uv
k
a
r
s
p
f


R
1

1024 Kbps

R
2

512 Kbps

R
3

256 Kbps

S

0

0

0

0

0

0

Step

1

Step

1

Step

1

Step

2

Step

3

Step

3

uv
uv
uv
uv
k
uv
uv
uv
B
B
B
F
b
B







)
(

B
uv
: total bandwidth of virtual link (u,v)


b
uv
: available bandwidth of virtual link (u,v)


F
k
: cumulative rate by the k
th

receiver R
k


a
uv
: binary variable that equals 0 if link (u, v)
already belongs to the tree, 1 otherwise


V and E: number of vertexes and edges in the
overlay network, respectively







T
v
u
T
v
u
a
uv
)
,
(
,
1
)
,
(
,
0
)
,
|,
|
|,
(|
B
F
E
V



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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

11

DIMRO
-
GS: the Algorithm


DIMRO
-
GS (Group Shared DIMRO) is the extension of DIMRO to
the multicast shared tree case


For M group members, the virtual shared tree is set up by building M
virtual source rooted trees, each one having a different group
member as root and all the other members belonging to the tree


Each source rooted tree is built using DIMRO


If each group member has the same bandwidth requirement, the first
step of DIMRO is skipped.


When M source rooted trees are computed, the virtual shared tree is
completed



DIMRO computational complexity: O(M ∙ |V| ∙ |E|)


It builds the virtual multicast tree by computing for as many as M times
the spanning tree using the Bellman
-
Ford algorithm, whose complexity
is O(|V| ∙ |E|)



DIMRO
-
GS computational complexity: O(M2 ∙ |V| ∙ |E|)


It runs DIMRO M times

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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

12

Simulation Scenario


A random overlay network has been
generated following the Waxman’s
model [6], with parameters
(
α
,
β
)


The bandwidth capacity B
uv

of each
virtual link (u, v) is randomly
generated using a uniform distribution
with mean
B

= 100Mbps


Two different one hundred node
random overlay networks are
generated. Network 2 has a higher
number of links than Network 1


Two metrics are used to compare the
competing algorithms, the
Rejection
Rate

and the
Network Load


α

β

B

nodes

Network
1

0.2

0.4

100Mbps

100

Network
2

0.3

0.6

100Mbps

100









)
,
(
Re
#
Re
#
Re
v
u
uv
Trees
quested
Trees
jeted
Rate
jection
[6] B. M. Waxman, “Routing of multipoint connections,”
IEEE Journal on Selected
Areas in Communications
, vol. 6, no. 9, pp. 1617

1622, December 1988


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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

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DIMRO: Performance Evaluation in Network 1


In Network 1, the DIMRO
Rejection Rate
is lower than the
Rejection Rate
of
the Optimal solution of the Steiner Tree Problem (OSTP) with c
uv
= 1


The DIMRO
Network Load
is the same as the OSTP
Network Load
until the
Rejection Rate
is the same. Then, since DIMRO rejects less trees, its
Network
Load
becomes higher than the OSTP one

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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

14

DIMRO: Performance Evaluation in Network 2


In Network 2, the DIMRO
Rejection Rate
is significantly lower than the OSTP
Rejection Rate

(less
unavoidable
bottlenecks exist). Since Network 2 has a
higher number of links, the number of possible paths between two nodes
increases; thus, it is easier for DIMRO to avoid bottlenecks


A lower
Network Load
with a higher
Rejection Rate
proves that OSTP does
not efficiently use the available network resources

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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

15

DIMRO
-
GS: Performance Evaluation in Network 1


When the
Number of Requested Trees
increases, the FTM
Rejection Rate
becomes significantly higher than the one of DIMRO
-
GS, since FTM uses a
higher amount of network resources


In fact, when the
Number of Requested Trees
increases, the FTM
Network
Load
becomes significantly higher than the DIMRO
-
GS
Network Load

16

D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

16

DIMRO
-
GS: Performance Evaluation in Network 2


Network resources
saturate
later when DIMRO
-
GS is used, which causes a
lower
Rejection Rate


In Network 2, DIMRO
-
GS achieves a lower
Rejection Rate
and
Network Load


Note that in Network 1 bottlenecks do not allow to efficiently exploit all
network resources


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D. Pompili, L. Lopez, C. Scoglio, Multicast Algorithms in Service Overlay Networks, Infocom 2006

17

Conclusions and Future Work


Two algorithms for multicast applications in service overlay networks were
presented



The first builds virtual source rooted multicast trees for source specific
applications



The second constructs a virtual shared tree for group shared applications



Their objective is to achieve traffic balancing on the overlay network so as to
avoid traffic congestion and fluctuation, which cause low network performance



The algorithms actively probe the underlay network and compute virtual
multicast trees by dynamically selecting the least loaded available paths on the
overlay network



Future research will focus on dynamic multicast groups, and on the
interactions between overlay and underlay networks