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

2

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

Introduction

4

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

5

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

6

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

7

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

8

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

9

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

Multipath Routing for Point-to-Point Video Delivery

11

A Point-to-Point Video Network

L in k s ta te = ( b an d w id th , d e lay )

(15 ,6

)

(1 0 ,8 ) C lien tM u ltim ed ia s e r v er

( 2 0 ,7 )

(10,5)

(10,10)

( 8 ,1 3 )

(1 5 ,7 )

(5 ,1 3 )

(10 ,1 2 )

(20 ,6

)

( 1 0 ,1 4 )

(15 ,7

)

v 0 v 6

v 5

v 4

v 3

v 2

v 1

12

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

13

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

14

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

15

An Example

s

v1

v3

v2 v5

v4

t

(20,6)

(10,5)

(15,7)

(8,13)

(20,7)

(10,8)

(15,6)(10,12)

(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)

16

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

17

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

18

High Success Rate

19

High Bandwidth Achieved

20

Low Average Delay

21

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

22

An example

s t

Upper hierarchy

Lower hierarchy

Server Scheduling Algorithm

24

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

25

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

26

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

27

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

28

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

29

General Case of Scheduling

;)()(1

1min

K

iii pdpw

BD

Video timet1 tK-1t2t0 t3 . . .

p1

pK

p2

p1p1

p1

p3

p2

p2

. . . . . .

i

lliii pdpdpw

Bt

1

))()()((1

30

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

31

Rescheduling Achieves a Delay Comparable to the Shortest Path

Extension to Point-to-Multipoint Video Delivery

33

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

34

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

35

An Examples

UsersBase layer tree 1

Base layer tree 2

Enh. layer tree 1

36

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

37

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

38

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

39

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

40

An Example on Layerings

UsersBase layer tree 1

Base layer tree 2

Enh. layer tree 1

41

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

42

High Success Rate

43

High Average Bandwidth

44

Slightly Higher Cost

45

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

Questions and Answers

Thank you!