Title: Multipath Routing for Video Delivery over BandwidthLimited Networks
1Multipath 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
2Outline
- Introduction
- Multipath routing heuristic for point-to-point
video delivery - Scheduling algorithm at the server to achieve the
theoretical minimum start-up delay - Extension to point-to-multipoint layered video
delivery - Conclusion
3Introduction
4Research 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
5Negotiating 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
6Constraint-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
7Meeting 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
8Previous 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
9Our 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
10Multipath Routing for Point-to-Point Video
Delivery
11A Point-to-Point Video Network
12Multipath Problem Formulation Bandwidth-Constrain
ed 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
13Desirable 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
-
14A Multipath Routing Heuristics
- Find the max-flow sub-graph G of the network
- Find the shortest-path in the sub-graph G
- If the aggregated bandwidth of the path(s) found
is sufficient, return - Subtract the bandwidth from G along the path
just found - Repeat steps 2 to 4
15An Example
16Simulation Model
- Hierarchical network
- 3-hierarchy nodes backbone routers, border
routers and intra-domain routers - Random links
- System parameters
- Network size
- Network density
- Connectivity, etc
17Comparison 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
18High Success Rate
19High Bandwidth Achieved
20Low Average Delay
21Hierarchical 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
22An example
Upper hierarchy
Lower hierarchy
23Server Scheduling Algorithm
24Problem 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
25A Simple Case
- Two paths with the same bandwidth of B/2 but
different delays d1 and d2 (d1 lt d2) - Without server scheduling, the start-up delay
equals the delay of the longer path, i.e., d2
26The Theoretical Minimum Delay
- Data production and consumption curves
- The difference is the buffer requirement
- In the example, the minimum start-up delay is
(d1d2)/2
27The Idea
- Dont 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
28The 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
29General Case of Scheduling
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30An 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
31Rescheduling Achieves a Delay Comparable to the
Shortest Path
32Extension to Point-to-Multipoint Video Delivery
33A 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
34A 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
35An Example
s
36Problem 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
37Two 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(mV3)
- Bandwidth-first approach
38Min-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(mBV2)
- Cost-first approach
39Bandwidth Assignment of Layers
- Group the trees spanning the same set of users
- Arrange these groups according to decreasing
number of users covered - The previous set of users is the superset of the
latter - The aggregate bandwidth of the first tree-group
is the bandwidth of the base layer - The aggregate bandwidth of the 2nd group is the
bandwidth of the enhancement layer 1, and so on
40An Example on Layering
s
41Simulation 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
42High Success Rate
43High Average Bandwidth
44Slightly Higher Cost
45Conclusion
- 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
46Questions and Answers