An Overlay Architecture for High Quality VoIP Streams
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Transcript of An Overlay Architecture for High Quality VoIP Streams
An Overlay Architecture for High Quality VoIP Streams
IEEE Trans. on Multimedia 2006
R97725013 翁郁婷R97725015 周克遠
AUTHORS
Yair AmirJohns Hopkins, US Prof.
Claudiu DanilovJohns Hopkins, Assist.
Stuart GooseIEEE Member
David HedqvistChalmers, Sweden,
Stud.
Andreas TerzisIEEE Member
QUALITY ISSUE
INTERACTIVE
Delay CANNOT higher than 100-150 ms Use UDP to deliver VoIP Packets
LOW QUALITY: PACKET LOSS OR DROP
Loss during the Internet Routing Delay and Drop Packet
Note: Currently we allow short delay: Use a buffer on receiver side
> The Cause Factors of VoIP Quality
THE PROTOCOL
Why use UNRELIABLE UDP protocol?
No sufficient time to End-to-end Retransmission
How about BREAK the END-TO-END into HOP-TO-HOP
> The Reason to Use Spines
OVERLAY NETWORK
Virtual Network with Limited Scope Easy to Implement and Control Overhead Signaling Message
> What is Overlay?
THE SPINES Spines DaemonApplications
Open Source Overlay Network Two-level Architecture Each Spines Daemon (Node) is both SERVER and ROUTER
> The Spines Architecture
> The Real-time Recovery Protocol
1. Keep a buffer on each outgoing link
2. Intermediate nodes forward packets as they are received
3. Upon detecting loss, asks the upstream node for Retransmission. A Retransmission Request for a packet is only sent once.
4. When receives a Retransmission Request:If it has the packet, resends itIf not, ignore the request
5. Only the first instance will be forwarded
RECOVERY PROTOCOL
Real-time Recovery Protocol
LOSS RATE PACKET LOSS RATE on Link: p
One Overlay Link with
Two Overlay Nodes
CASE OF CANNOT RECOVERY1. Retransmission Request Loss
p(1–p)p = p2 – p3
2. Retransmission Packet Loss p(1–p)(1–p)p = p2 – 2p3 + p4
3. Else – NegligibleTotal Loss Probability: 2p2 – 3p3 , approximately
> Calculate the Loss Rate of the Real-time Recovery Protocol
p
THE ROUTING
Real Time Routing For Audio Adjust Overlay Routing to avoid Problematic Path Two Parameter: Packet Loss Rate and Latency
> Use a COST FUNCTION to handle the Two-metric Decision
> Calculate the Cost Function of the Routing
COST FUNCTION
THE COST: TRANSMISSION DELAY
ALL CASES
1. Success Transmit: (1 – p)T2. Recovery Transmit: (p – 2p2 + 3p3)(3T + Δ)
3. Packet Loss: (2p2 – 3p3) Tmax
The Cost Function Texp (1 – p)T + (p – 2p2 + 3p3)(3T + Δ) + (2p2 – 3p3) Tmax
• PACKET LOSS RATE on Link: p• Maximum WAITING TIME: Tmax
• ERROR DETECT TIME: Δ
DELAY DISTRIBUTION
ALWAYS CANNOT HANDLE Delay distribution - 1 link, 5% loss
(1–p)
(p – 2p2 + 3p3)
(2p2 - 3p3)
T
(3T+Δ)
Tma
x
Affected on the LOADED COMPUTERS?
APPLICATION LOAD
OVERLAY PROBLEM
INCREASE the PRIORITY
> Overlay Loading Affected by Application Layer
OVERLAY
ADVANTAGE
DISADVANTAGE
CONCLUSION
Segment End-to-end into shorter Overlay Paths Recovery Lost Packets with Limited Time Avoid Problematic Path
Slightly Change the Overall Architecture More Flexibility Easy to Implement and Deployment
Overhead Diminish Margin Utility