multipath routing for video delivery over bandwidth-limited networks s.-h. gary chan jiancong chen...
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Multipath Routing for Video Delivery over Bandwidth-Limited Networks
S.-H. Gary Chan Jiancong Chen Department of Computer Science
Hong Kong University of Science and Technology
Clear Water Bay, Kowloon
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Outline
Introduction Multipath routing heuristic for point-to-point video d
elivery Scheduling algorithm at the server to achieve the the
oretical minimum start-up delay Extension to point-to-multipoint layered video deliv
ery Conclusion
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Introduction
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Research Motivation Deliver quality video services over bandwidth-
limited networks (e.g., the Internet) Video application requirements
High bandwidth Low start-up delay or network transmission cost
Traditional routing based on single path approach (e.g., the shortest path routing) is no longer sufficient to meet the bandwidth requirement QoS routing
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Negotiating and Guaranteeing QoS in the Internet Integrated services/Resource Reservation Protocol
(RSVP) Multi-protocol label switching (MPLS) Differentiated services model (DiffServ) Traffic engineering Constraint-based routing
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Constraint-Based Routing Compute routes subject to multiple constraints
Distribution of link state information Route computation
Goals Select routes that can meet certain QoS requirements Increase utilization of the network
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Meeting Bandwidth Requirement with Low Delay: Multipath Routing The video data is transmitted over multiple paths in
the network Increasing the overall aggregate delivery bandwidth Routing to meet the bandwidth requirement
The end host needs to do reassembly Increasing the start up delay Server scheduling to reduce the delay
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Previous Work on Multipath Routing Search multiple paths and select the best one
E.g., selective probing Find multiple paths for a connection (e.g., disjoint
paths routing) Mainly designed for reliability rather than high aggregate
bandwidth
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Our Work A multipath heuristics for point-to-point video delivery
Low delay and buffer requirement Efficient
Given a set of path lengths The theoretical minimum delay achievable A scheduling algorithm to achieve that
For point-to-multipoint communication with heterogeneous bandwidth requirement
How the multicast trees should be constructed to minimize the cost of the tree-aggregate
The corresponding number and bandwidth of the video layers
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Multipath Routing for Point-to-Point Video Delivery
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A Point-to-Point Video Network
L in k s ta te = ( b an d w id th , d e lay )
(15 ,6
)
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v 0 v 6
v 5
v 4
v 3
v 2
v 1
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Multipath Problem Formulation: Bandwidth-Constrained Delay-Optimized Problem
Given: A source s A destination t Bandwidth requirement B
B less than the max-flow of the network
Find routing and scheduling algorithms to achieve Bandwidth no less than B Minimum delay
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Desirable Properties of Routing Algorithms Efficient
Similar complexity as the shortest path routing Fast route convergence
Achieving high end-to-end bandwidth Preferably the max-flow of the network
Amendable to the current Internet routing
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A Multipath Routing Heuristics1. Find the max-flow sub-graph G’ of the network
2. Find the shortest-path in the sub-graph G’
3. If the aggregated bandwidth of the path(s) found is sufficient, return
4. Subtract the bandwidth from G’ along the path just found
5. Repeat steps 2 to 4
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An Example
s
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v2 v5
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(10,5)
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(8,13)
(20,7)
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(15,7)s
v1
v3
v2 v5
v4
t
(20,6)
(10,5)
(15,7)
(8,13)
(20,7)
(10,8)
(15,6)
(10,14)
(10,10)
(5,13)
(10,12)
(15,7)
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Simulation Model Hierarchical network
3-hierarchy nodes: backbone routers, border routers and intra-domain routers
Random links System parameters
Network size Network density Connectivity, etc
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Comparison with the Traditional Approaches Shortest path Shortest-feasible path
Remove the links with insufficient bandwidth Run the shortest path algorithm over the residual network
Performance measures Success rate in meeting the bandwidth requirement Bandwidth achieved End-to-end delay, given by the longest path
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High Success Rate
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High Bandwidth Achieved
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Low Average Delay
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Hierarchical routing Logical hierarchical topology as in the Internet State information
Only full local information is maintained Remote state information is partially maintained
Compute multiple routes in the regions in parallel Reduce computation complexity, processing time, and
storage
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An example
s t
Upper hierarchy
Lower hierarchy
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Server Scheduling Algorithm
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Problem Formulation Given a set of path lengths What is the theoretical minimum start-up delay
achievable if video data can be scheduled? Guarantee continuity
Find a data scheduling algorithm at the server to achieve such minimum delay No other algorithms can achieve lower delay while
maintaining stream continuity
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A Simple Case Two paths with the same bandwidth of B/2 but
different delays d1 and d2 (d1 < d2) Without server scheduling, the start-up delay equals
the delay of the longer path, i.e., d2
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The Theoretical Minimum Delay Data production and consumption curves
The difference is the buffer requirement
In the example, the minimum start-up delay is (d1+d2)/2
minimized delay
Data
d1 d2 Time0
Slope=B/2
Slope=B
original delay
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The Idea Don’t indiscriminately multiplex video packets
along all the paths The server sends the video prefixes along the shorter
paths The client plays back the prefixes with stream
continuity Before the data from the longest path arrives
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The Scheduling Algorithm The video sequence is partitioned into segments All the segments are transmitted in parallel over the
multiple paths The earlier segments are transmitted over the shorter
paths
To path 1 To path 1
To path 2Video data
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General Case of Scheduling
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An Exact Solution Solving the Multipath Problem A network with unit link bandwidth Multipath is disjoint paths With scheduling, the problem is to find the shortest-
disjoint paths (SDP) Bandwidth requirement: B units Find the B-shortest-disjoint paths
The sum of their delays is minimum The shortest-disjoint paths algorithm is well known
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Rescheduling Achieves a Delay Comparable to the Shortest Path
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Extension to Point-to-Multipoint Video Delivery
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A Video Multicast System A server and multiple clients
The clients have different bandwidth requirements A link is characterized by its bandwidth and cost
Find multiple multicast trees spanning the multicast group Meeting the heterogeneous bandwidth requirements of the members With minimum cost of the tree-aggregate
Assignment of video layers A base layer and several enhancement layers The number of video layers, and Their respective bandwidths
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A Simple Case All the users have the same requirement B Multiple trees are used to span all the users
With minimum cost of the tree-aggregate If all the bandwidth requirements are met
A single video layer with bandwidth B Otherwise, layered video can be used
The higher layers serve users with increasing end-to-end bandwidth
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An Examples
UsersBase layer tree 1
Base layer tree 2
Enh. layer tree 1
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Problem Formulation: Bandwidth-Constrained Cost-Optimized Problem Given
A source s A set of destinations Y (= {y1, y2,…, yn}) Bandwidth requirement B (= {b1, b2,…, bn} )
Find multiple trees T to achieve Bandwidth no less than bi for yi
Minimum cost of the aggregated “mesh” The corresponding number and bandwidth of the layers, and
along which trees a layer transmits Multiple trees
To find a min-cost tree (Steiner tree) is NP-hard To construct such multiple trees is even harder
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Two Heuristics: Multipath Extension Based on point-to-point multipath heuristic First meet the bandwidth requirement of each user with the
multipath heuristics Aggregate the paths Construct trees out of the paths-aggregate
Each tree has a certain bandwidth equal to the bandwidth of the bottleneck link
There is at least one tree spanning all the users
Complexity: O(m|V|3) Bandwidth-first approach
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Min-Cost Tree Extension First find a min-cost multicast tree spanning all the
users Add branches to the tree until all the bandwidth
requirements are met Closest receivers Forming new trees
Complexity: O(mB|V|2) Cost-first approach
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Bandwidth Assignment of Layers
1. Group the trees spanning the same set of users
2. Arrange these groups according to decreasing number of users covered
The previous set of users is the superset of the latter
3. The aggregate bandwidth of the first tree-group is the bandwidth of the base layer
4. The aggregate bandwidth of the 2nd group is the bandwidth of the enhancement layer 1, and so on
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An Example on Layerings
UsersBase layer tree 1
Base layer tree 2
Enh. layer tree 1
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Simulation Results Hierarchical network Comparing with a single-tree approach
(shortest path tree) Performance measures
Success rate of meeting the bandwidth requirements of the users
Average bandwidth achieved Cost
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High Success Rate
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High Average Bandwidth
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Slightly Higher Cost
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Conclusion Video routing over a bandwidth-limited network Multi-path heuristic
Achieve high end-to-end bandwidth with low delay Video scheduling algorithm at the server
Reduce the start-up delay to the theoretical minimum Extension to multicast environment
Meeting heterogeneous bandwidth requirements Minimum cost of the tree-aggregate
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Questions and Answers
Thank you!