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Providing Controlled Quality
Assurance in Video Streaming
across the Internet
Yingfei Dong, Zhi-Li Zhang and Rohit RakeshComputer Networking and Multimedia Research Group
Dept. of Computer Science and EngineeringUniversity of Minnesota
Motivations
The Internet: Service-Oriented Network Service Requirement: End-to-End QoS
Service Delivery System: Content Distribution Networks
On-Demand Large Stored Video Streaming
--- High Bandwidth requirements
oWide-Area Stored Video Delivery System
Common Approach --- Proxy Server System
Proxy Content Delivery Architecture
Proxy Server + VPN
Virtual Private Network(VPN)
Network- Layer VPN
not Leased-Lines, but Service Level
Agreements,
Coarse-grain average :
T3 VPN, 99.9% available, 120 ms average RTT monthly average
No rate guarantee for individual flows No packet loss/delay guaranteeApplication-level Traffic Management is needed.
System Constraints and Challenge
Constraints Limited Buffer Space v.s. Huge Video Volume
Streaming from central servers is required.
Aggregate B/W v.s. Individual Flow Requirement Bandwidth management must be present.
Stringent Timing v.s. No Delay/Loss GuaranteeReliably prefetching is necessary.
Challenge Quality Assurance across Best-Effort Networks
Outline
Motivations and Background Staggered Two-Flow Streaming Control Bandwidth Sharing Conclusion and Current Work
Objective and Approaches Objective and Approaches
Controlled Quality Assurance in streaming
on the best-effort Internet by exploiting
Application Information, such as the priority
structure in videos (frame-dependency), and flow rate
Coarse-grain bandwidth assurance of VPN
Storage / processing capacity of proxy servers
Priority Structure in Videos
Two flows in a video session: A Reliable Flow for essential data (e.g., I frames) An Unreliable Flow for enhanced data (e.g., P/B)
Segment and Staggered Delivery
The Reliable Flow is one segment ahead
Staggered Two-Flow Streaming
Reliable Flow: I-frame segments, prefetched and cached at proxy.
Unreliable Flow: P/B-frames segments, real-time delivery subject to adaptation when congestion in the soft VPN pipe.
Merging both flows at Proxy Server, then send to clients
Prefetching Cache
Illustration
To user
k
k+1
Unreliable Delivery
Reliable Prefetching
k
k+1
k
k
Proxy ServerCentral Server best-effort VPN
Merging
k
Competition!!
Interesting Issues
Data Plane Issues Bandwidth Competition Unreliable-Flow Unreliable-Flow Rate Adaptation
Control Plane Issues Application-aware Resource Management
e.g., Admission Control, VPN management, Video placement and migration
Implementation Issues
Application-Aware Controlled Bandwidth Sharing
Stable and Predictable transport protocolsControlled TCP (cTCP)
Application-aware throughput control: A variant of TCP Reno using a simple TCP model to regulate the injection rate.
Rate-Controlled UDP(rUDP) Generating Piece-wise CBR traffic:
Extending UDP on FreeBSD with a periodical injection mechanism limited by a leaky-bucket
Both are implemented in FreeBSD kernel.
TCP: reliable but not fit to our setting
Sliding Window (W) Injection Control
W packets per RTT
AIMD Fluctuation: Greedily Increase,
back off to half when loss Fairness regardless of flow
requirements
Packet losses even when sufficient B/W
cTCP: a variant of TCP Reno
Flow Target Rate TcTCP
Target Window Size Wtarget
using a simple TCP bandwidth model to limit the injection to the flow requirement
If packet loss
else
MSS
RTTTW
cTCP
75.0
target
MSS
RTTTW
cTCP target
No slow-start.
No packet losses when given sufficient B/W.
Two cTCP Flows v.s. Two TCP Flows
On a 64KBps link, the 1st flow with a target rate 13KBps starts12 seconds earlier than the 2nd flow with a target rate 27KBps
Experimental EnvironmentExperimental Environment
Controlled Testbed on FreeBSD4.1 3 PCs on a dedicated Gbps Ethernet switch A central server and a proxy server A bandwidth-and-delay control unit emulates
a VPN pipe in between, running IP Dummynet Testing Video: a 60-minute MPEG-2 video clip
Target Rate of I frames, 52 KBps Target Rate of P/B frames, 200 KBps
Multiple Sessions: cTCP/rUDP v.s. TCP/rUDP
RXs in TCP or cTCP rUDP Losses
A video session of two flows (cTCP/rUDP or TCP/rUDP)
Multiple Sessions (Arrival / Departure): cTCP/rUDP v.s. TCP/rUDP
C = 5 • 1.1 • Max_Rate
Starting with 4 sessions;
Then, add one more;
Later, terminate two.
Compare the variations of packet RXs and losses
Summary of Controlled BW Sharing
Practical quality assurance of the essential data
over best-effort networks
None / Low Packet Losses
Stable, Predictable System Performance
Providing chances for applying simple application-aware
traffic management
TCP-firendly: do not grab BW from others
Patent Pending
Current and Future Work
Quality Assurance issues in Service-Oriented Networks
Scalability in data plane
Aggregation at the levels of video, session, and flow.
Network parameters sharing among sessions.
Service-Oriented B/W Management in control plane
Application-ware admission control
Proxy Placement utilizing the topology info.
Proxy Caching and Video Placement / Migration.
High-Quality VOD on Cable Broadband Networks.