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Maintaining Bi-connectivity inOverlay Multicast Networks
Ashutosh Singh
Thesis Supervisor : Prof. Y. N. Singh
Department of Electrical EngineeringIIT Kanpur
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Outline
Introduction
Motivation for Overlay Multicast Networks
Overlay Tree Characterization Overlay Construction and Optimization Schemes
Reliability Enhancement through Bi-connectivity
Proposed approaches toward Bi-connectivity
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Unicast and IP Multicast
Unicast
Sending a packet from one sender to one receiver
Point to point delivery (one host to one client) Multicast:
Sending a packet from one sender to multiplereceivers with a single send operation
Multiple destinations (One Host to Many Clients)
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Example : Unicast
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Example : IP Multicast
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IP Multicast
IP Multicast was introduced in Steve Deerings
PhD Dissertation in 1988 and first widescale
testing done in 1992 at IETF meeting
Allows data to be sent to multiple receivers in
an efficient way
A single datagram is transmitted
Replicated at a network router
Forwarded on multiple outgoing links in order
to reach the receivers6
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Overlay Multicast
Involves receivers in the replication and
forwarding of data
Receivers setup and maintain an applicationlevel distribution infrastructure
Sender transmits a copy to small number of
receivers, which then make copies itself and
forward these on to other receivers
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Example : Overlay Multicast
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IP Multicast : Issues
Requires routers to maintain per group state Scaling constraints
IP Multicast is a best effort Service Provision of higher layer functionalities (reliability,
congestion control & flow control ) more difficult thanin unicast case
IP Multicast calls for changes at the infrastructurallevel
Slow pace of deployment
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Overlay Multicast : Features
End systems participating in a multicast group self-organize in to an overlay using a completelydistributed protocol, on top of which multicast trees
can be constructed End System is an entity that actually takes part in a
self-organizing protocol, could be end host or a proxy
End systems attempt to optimize the efficiency of the
overlay by Adapting to network dynamics
Considering application level performance
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Overlay Multicast : Features
Multicast related features (group membership,
multicast routing & packet duplication) are
implemented at end systems
All packets are transmitted as unicast packets
Provision of higher-layer functionalities simplified
by deploying application intelligence at internal
splitting points of overlay tree
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Overlay Multicast : Performance
Multiple overlay edges traverse the same physical
link , thus redundant traffic on physical links
Communication between end systems involves
traversing other end systems, increasing latency
Though performance penalties are low both from
application and network perspectives
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Overlay Multicast : Architecture
Entity that takes part in self organisation protocol
could be an End Host or Proxy
Peer-to-Peer Architecture:
all functionality is pushed to the end hosts actually
participating
each end host maintains state only for those groups it
is actually participating in completely distributed architecture, small and
medium sized groups
e. g. Audio/video conferencing, virtual class room,
multiparty network games 13
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Overlay Multicast : Architecture
Proxy Based Architecture:
organizations deploy proxies at strategic locations on
the Internet
End hosts attaches to the nearest to receive data
using plain unicast
Overlay is composed of proxies, groups are much
larger
e.g. broadcasting , content distribution
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Overlay Tree Construction
Direct-Tree approach : members explicitly select their parents from among the
members they know e. g. YOID, OVERCAST
Relies on an overlay tree for both control and datatransmission
Mesh-First approach : to support multi sourceapplications first constructing a richer connected mesh
then constructing a reverse shortest path spanning tree of
the mesh (each tree routed at corresponding source) e.g.NARADA
Tree topology for data and mesh topology for controlinformation (group management functions)
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Overlay Tree Characterization
Underlying network G = (N, E) A node n i N denotes a router An edge ( ni , nj ) E denotes a bidirectional physical link
Overlay network, superimposed on G is a tree o = ( s, D, No, Eo )where s is source host,
D is set of receiver hostsNo N is set of nodes in the underlying network G that are
traversed by overlay links
Eo is the set of overlay links Set of hosts Ho = {s} U D and |HO| = n An overlay link eo = (ds , no, .., nls , dr ) Overlay cost = number of underlying hops traversed by all overlay link eo Eo
= ls ( eo )= stress (i) , for every i
ls (e0) denotes the number of router-to-router hops between no, .., nls for theoverlay link e
o ,first and last hops are ignored
Link stress is the total number of identical copies of a packet over the same underlyinglink
Resource usage = delay (i) x stress (i) , for every i
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Sonia Fahmy et al., Characterizing OMNs and their costs , 2007 PurdueUniversity
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Overlay Tree Characterization
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Overlay Multicast
Source
Routers and
underlying links
Receivers
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Metrics: Examples
Overlay link
Source
Receivers
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Link stress on A = 2 RDP of B = (15+15+10)/20 = 2
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Narada:Design Objectives
Self organizing : Overlay Construction should be in fully distributed fashion
robust to dynamic changes in group membership
Self improving Mechanism to gather network information in scalable fashion
Mechanism to incrementally evolve into a better structure
Adaptive to network dynamics: Must adapt to long term variations in path characteristics
Must be resilient to inaccuracies inherent in the measurement
Efficient : Redundant transmission is kept minimal
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Chu et al., A case for End System Multicast, 2003
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Mesh-first approach : Narada
Group Management Component : ensures thatthe overlay remains connected
Member join
Member leave and failure
Repairing mesh partition
Overlay optimization component : ensures thequality of overlay over time
Addition of good links
Dropping of poor links
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Narada : Group Management Each member maintains an updated list of all other members in the group
Let i receive refresh message from neighbor j at is local time t.
Let < k, skj> be an entry in js refresh message
if i does not have an entry for k, then i inserts the entry < k, skj, t > into its table
else if is entry for k is < k, ski, tki> then
if ski>= skj, i ignores the entry pertaining to k else i updates its entry for k to < k, skj, t >
Member join :
member is able to get a list of group members that contain at least onecurrently active group member (bootstrap mechanism)
Joining member randomly selects a few group members from the list availableto it and sends them request
Repeats the process until it gets a response from some member and joins asits neighbor
Starts exchanging REFRESH messages with neighbors
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Narada : Group Management
Member leave and failure : Leaves gracefully:
notifies its neighbors, information is propagated,
continues forwarding packets for some time to minimize transient loss
Abrupt Failure: failure is detected locally and propagated
Each member needs to retain entries for dead members for some time
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A sample overlay topology
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Narada : Group Management
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Repairing mesh partitions : Each member maintains a queue of members that it has
stopped receiving updates for more than Tm time
Deleted member is probed and determined to be dead or a link
is added to it A scheduling algorithm periodically and probabilistically deletes
a member from the head of the queue
Period adjusted so that no entry remains in the queue for more
than a bounded period of time
Probability chosen so that in spite of several members
simultaneously attempting to repair, only a small number of
new links are added
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Narada : Optimization
Adding : Every member periodically probes some random member that is not a
neighbor
new link may be added on the perceived gain in utility in doing so
Dropping : cost of a link between i and j in is perception is the number of group
members for which i uses j as next hop. Consensus cost of its link to every neighbor is computed
Link with lowest consensus cost is dropped if below threshold
Comparison of Narada with IP Multicast :
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Small group
(20 members)
Medium sized group
(128 members)
BW performance
(resources consumed)
Comparable twice
Mean receiver latencies 1.3 1.5 times 2.2 2.8 times
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Narada : Performance Metrics
Latency: measures the end-to-end delay from the source to the receiversas seen by the application
Bandwidth : measures the application level throughput at the receiverand is an indicator of quality of received video
Protocol Overhead: equals to
Resource Usage :
resource usage overlay tree = cost of constituent overlay links
costan overlay link
= cost of constituent physical links
cost a physical link = propagation delay of that link
resource usage IP Multicast = cost of physical links of the native IP Multicast tree
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OMNI Infrastructure
Service providers deploy a set of service nodes (MSNs)
MSNs are organized into an overlay
Degree constrained minimum average latency problem :
Find a directed spanning tree, T of G rooted at the MSN r,satisfying the degree-constraint at each node, such that
i belongs to S ci Lr,i is minimizedWhere S is the set of all MSNs other than source
ci is the number of clients served by MSN i
Lr i
is the overlay latency from root MSN to MSN i
Each MSN i keeps following state information :
Unicast latency between itself and its tree neighbors
Overlay path from root to itself
Si and ^i
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Suman Banerjee, Construction of an efficient OM infrastructure .. , 2003
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OMNI Infrastructure
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OMNI Infrastructure
Initialization Phase: Each MSN measures unicast latency between itself and root, sends
join request to root MSN
Root MSN gathers join requests from all MSNs, creates initial treeusing centralized algorithm and distributes it to MSNs
Overlay latency from root to any other MSN I is bounded by 2 lri log N
Transformation Phase : Local Transformation
Child promote
Parent child swap Iso-level-2 swap
Iso- level- 2 transfer
Aniso-level-1-2 swap
Probabilistic Transformation
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OMNI Infrastructure
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Initialization phase
Parent-child swap
Child-promote
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OMNI Infrastructure
31Aniso-level-1-2 swap
Iso-level-2 swap
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Conferencing Application andOverlay Design
Performance requirements: low latencies , high
bandwidth between source and receivers
Gracefully degradable : can tolerate loss through aquality degradation
Session lengths : long-lived, lasting tens of minutes
Group characteristics : dynamic small group
Source transmission patterns :
source transmits data at a fixed rate
Any member can be the source, usually a single source at a
time 32
Chu et al., Enabling conferencing applications on the I-net using OMA 2004
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Conferencing Application:Large Group
Source based tree approach:
efficient for small group, as group size increases, control
overhead increases very rapidly
Single shared tree approach: scalable, but depth of tree will be high due to out degree
bound and hence high latency. Suitable for non-interactive
application (VOD)
As the number of trees increase, Fault toleranceincreases, delay decreases but protocol overhead
increases.
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Baosong et al.,DualCast: Protocol Design of Multiple shared tree based ALM 2008
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Conferencing Application:Large Group
Multiple shared tree approach (MST):
number of total trees are far less than total number of
sources hence overhead not so large
Tree depth is also not so high hence delay is controlled
Source nodes and listener nodes are treated differently
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Baosong et al.,DualCast: Protocol Design of Multiple shared tree based ALM 2008
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Problem statement
Construction ofan Overlay Multicast Network for
lecture delivery to a medium sized dynamic group
To build a simulator for Overlay Multicasting Networks
To verify the result of various researchers and hence toverify the simulator built
Analyzing specific characteristics of lecture delivery
application and applying them to get improved
optimization algorithm and node failure detecting and
repairing algorithms for better transmission efficiency,
lower overall latency and higher system stability
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Reliability Through Bi-connectivity:Proposed Approaches
Reliability can be achieved by maintaining Bi-
connectivity between any pair ofnodes in the
network
For Mesh-First Protocol: A bi-connected mesh like topologyis created first, on top of that a single or multiple data
delivery trees are built
For Direct-Tree protocol: Two different approaches in each
of which every host gets data feed from two different
paths Connected Leaf-nodes Approach
Child-Grandparent Approach
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Approach 1
Each new node connects to two already existing
nodes in the network
In the beginning when first node comes, there is no
network
Second node joins to this first node
Third node connects to the first and second node forming
a triangle
Fourth node connects to any two of three nodes
Fifth node sees nodes 1 and 4 as having least degree and
connects to the first and fourth node
Continuing this way, a bi-connected mesh is formed
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Approach 1
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Approach 1
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Approach 1: The Basic Concept
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Approach 1 : Node Failure
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Approach 1 : Average Degreeof Nodes
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Average degree of network
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Approach 1 : Average numberof hops required
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Average steps to find path
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Averagesteps
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Approach 2:Connected Child Grandparent
Bi-connectivity in a distribution tree is achieved by
connecting all the nodes to their grandparent
In case grandparent is not available, the node is connected
to its sibling
A 4-level complete binary tree is considered as an example
This is a brute-force approach, a better approach
(Connected leaf nodes approach) needs only half the
number of additional links than this approach
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Approach 2
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Approach 3:Connected Leaf nodes
Bi-connectivity in a distribution tree is achieved by
connecting pairing all leafnodes
Each node pair gets bi-connected, as rings are formed
between any pair of nodes through leaf nodes
A 4-level complete binary tree is considered as an example
For a complete binary tree, the number of additional links
required is (n-1)/2 , where n is the number of nodes in the
network
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Approach 3
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Connected Leaf Nodes VsChild-Grandparent Approach
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Additional links required to achieve biconnectivity
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References
1. Ayman El-Sayed, Vincent Roca, and Laurent Mathy, A surveyofproposalsforanalternativegroupco unicationservice, IEEE Network, special issue onMulticasting: an enabling technology, January/February 2003.
2. Mojtaba Hosseini, Dewan Tanvir Ahmed, Servin Shirmohammadi, and Nicolas D.Georganas, Asurveyofapplication-layermulticastprotocols, IEEECommunications Surveys and Tutorials, 3rd Quarter 2007.
3. Konstantin Andreev, Bruce M. Maggs, Adam Meyerson, and Ramesh K. Sitaraman,
DesigningOverlay MulticastNetworksForStreaming , Symposium onParallelism in Algorithms and Architectures, June7-9, 2003.
4. Sonia Fahmy, and Minseok Kwon,CharacterizingOverlay MulticastNetworksandtheircosts, IEEE/ACM Transaction on Networking, Vol. 15, No. 2, April 2007.
5. Sonia Fahmy, and Minseok Kwon,CharacterizingOverlay MulticastNetworks,11th IEEE International Conference on Network Protocols2003.
6. Suman Banerjee, Seungjoon Lee, Bobby Bhattacharjee, and Aravind Srinivasan,
ResilientMulticastUsingOverlays, IEEE/ACM Transaction on Networking, Vol.14, No. 2, April 2006.
7. Vinay Pai, Kapil Kumar, Karthik Tamilmani, Vinay Sambamurthy, and Alexander E.Mohr,Chainsaw:EliminatingTreesfrom Overlay Multicast , Proceedings ofInternational workshop on Peer-To-Peer Systems (IPTPS) 2005
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References8
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haoping Wang, Xuesong Cao, and Ruimin Hu,A
daptedRouting
Algorith
min
the
Overlay Multicast , Proceedings of 2007 International Symposium on IntelligentSignal Processing and Communication Systems Nov.28-Dec.1, 2007.
9. Tin-Man T. Kwan, and Kwan L. Yeung,On Overlay MulticastTree ConstructionandMaintenance, International Conference on Collaborative Computing:Networking, Applications and Worksharing, 2005.
10. Dejan Kostic, Adolfo Rodriguez, Jeannie Albrecht, and Amin Vahdat, Bullet: HighBandwidthDataDissemination Usingan Overlay Mesh, Symposium on OperatingSystems Principles (SOSP) 2003.
11. Yang-hua Chu, Sanjay G. Rao, Srinivasan Seshan, and Hui Zhang, A CaseforEndSystem Multicast , Proceedings of ACM Sigmetrics 2000.
12. Suman Banerjee, Christopher Kommareddy, Koushik Kar, Bobby Bhattacharjee,Samir Khuller,Construction ofanEfficientOverlay MulticastInfrastructurefor
Real-time Applications, IEEE 2003.13. Christophe Diot, Brian Neil Levine, Bryan Lyles, Hassan Kassem, and Doug
Balensiefen, DeploymentIssuesfortheIPMulticastServiceandArchitecture,
IEEE Network 2000.14. Li Xing-feng, Yan Bao-ping, and Luo Wan-ming,Overlay multicastnetworkoptimizationandsimulation Basedon NaradaProtocol ,10th InternationalConference on Advanced Communication Technology (ICACT) 2008.
15. Radia Perlman,AnalgorithmfordistributedComputationofaspanningTreeinanExtendedLAN ,1985 ACM
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References
16. Yang-hua Chu, Sanjay G. Rao, Srinivasan Seshan and Hui Zhang,Adapted Enablingconferencingapplicationsontheinternetusinganoverlay Multicastarchitecture,
SIGCOMM 2001
17. Li Lao,Jun-Hong Cui, Mario Gerla, Shigang Chen,Ascalableoverlay MulticastArchitectureforLarge-scaleapplications ,IEEE transaction on parallel and distributed
systems April 2007
18. Jianqun Cui,MoreEfficient Mechanism ofTopology-Aware Overlay Constructionin ALM ,
International conference on Networking, Architecture and Storage 200719. Yang Hongyun,Hu Ruiming, Chen Jun, and Chen Xuhui,AReviewofResilient Approachesto
Peer-to-Peer Overlay MulticastforMediaStreaming ,2008 IEEE
20. Thilmee M. Baduge, Akihito Hiromori, Hirozumi Yamaguchi, Teruo Higashino,A distributed
algorithm forconstructing minimum delayspanningtreesunderbandwidthconstraintson
overlaynetworks,wiley intersciencejournals october 2006
21. Shan Baosong, Liaiang Yuan,Zhou Mi and Lou Yihua, DualCast:ProtocolDesignof
MultipleSharedTrees BasedApplication LayerMulticast ,14th IEEE International
Conference on Parallel and Distributed Systems 2008
22. Changlai Du, Hao Yin, Chuang Lin, Yada Hu, VCNF: A SecureVideo ConferencingSystem
BasedonP2PTechnology,10th IEEE International Conference on High Performance
Computing and Communications 2008
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MBone
Mbone was deployment of virtual multicast
network
Unicast encapsulated Multicast packets
received and forwarded
Connectivity through point-to-point IP
encapsulated tunnels
Each tunnel connected 2 endpoints via one
logical links but could cross several routers
Routing decisions made using DVMRP53