Path Diversity with Forward Error Correction (PDF) System for Packet Switched Networks
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Transcript of Path Diversity with Forward Error Correction (PDF) System for Packet Switched Networks
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Path Diversity with Forward Error Correction (PDF) System
for Packet Switched Networks
Thinh Nguyen, Avideh Zakhor
INFOCOM 2003. Twenty-Second Annual Joint Conference of the IEEE Computer and Communications Societies. IEEE , Volume: 1 , 30 March-3 April 2003 Pages:663 - 672 vol.1
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Agenda
IntroductionMotivationProposed System
Overview Architecture Redundant Path Selection
SimulationsConclusion & Comments
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Introduction
Video Streaming is a delay sensitive application
Possible solutions include Layered video codecs Error resilient codecs Forward error correction TCP-friendly protocol Edge architecture
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Introduction
Most schemes assume a single fixed path between the receiver and the sender throughout the session
If congestion happens along that path, video suffers from high loss rate and jitter.
Previous studies show sub-optimal routing path exists.
Path Diversification System with Forward error correction (PDF) is proposed
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Introduction
Recent works and models suggest redundancy path between nodes in the Internet
The Question is whether there exists sufficiently disjoint paths between a pair of senders and receivers on the Internet
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Motivation
Scheme 1 800kbps on default path
Scheme 2 400kbps on default path
400kbps on disjoint, redundancy path
Number of successive lost packets is smaller in scheme 2. Scheme 2 transforms the bursty loss into uniform loss Increase in the FEC efficiency
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Motivation - Experiment
FEC RS(30, 23)
Packet Size 500 bytes
Total Sending Rate 800 kbps
SenderReceiver
Average good time
Average bad time
(1 sec, 10ms)
(1 sec, 10-50ms)
A
B
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Motivation - Experiment
a. Packets divided equally at 15 packets each
b. When the average bad time of B increases, more packets are sent on path A.
a. Multipath can be 15 times higher than unipath
b. Even the loss rate of path B is five times higher than path A, sending packets simultaneously over two paths still benefits.
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System Architecture
Router
Sender Receiver
Relay Node
Physical Network
Overlay Network
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Sender Receiver
Relay Node A
1. Sender executes traceroute from itself to all relay nodes and receiver.
2. Link latencies and router names are obtained.
3. Sender instructs relay nodes to execute traceroute from themseleves to receiver.
4. Send the path information back to the sender
Traceroute
Traceroute
Traceroute
Traceroute
Relay Node C
Relay Node B
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System Overview
Sender Receiver
1. Sender executes traceroute from itself to all relay nodes and receiver.
2. Link latencies and router names are obtained.
3. Sender instructs relay nodes to execute traceroute from themseleves to receiver.
4. Send the path information back to the sender
(S, Rec, 201us)
(S, RN_B, 73us)
(S, RN_C, 51us)
(S, RN_A, 100us)
Relay Node A
Relay Node C
Relay Node B
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Sender Receiver
1. Sender executes traceroute from itself to all relay nodes and receiver.
2. Link latencies and router names are obtained.
3. Sender instructs all relay nodes to execute traceroute from themseleves to receiver.
4. Send the path information back to the sender
Command (traceroute, receiver)
Command (traceroute, receiver)
Command (traceroute, receiver)
Relay Node A
Relay Node C
Relay Node B
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Sender Receiver
1. Sender executes traceroute from itself to all relay nodes and receiver.
2. Link latencies and router names are obtained.
3. Sender instructs all relay nodes to execute traceroute from themseleves to receiver.
4. Send the path information back to the sender
(RN_A, Rec,24us)
(RN_C, Rec,95us)
Relay Node A
Relay Node C
Relay Node B
(RN_B, Rec,130us)
(RN_A, Rec,24us)
(RN_B, Rec,130us)
(RN_C, Rec,95us)
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Sender Receiver
5. The sender, based on the information received , select the redundant path.
6. Sender sends the setup packet to that selected relay node, containing flow ID, IP address and the port number of the receiver.
7. The relay node builds up a table for forwarding packets.
8. Each time, the sender attaches the flow ID in sending packets for relay node to where it should forward to.
Relay Node A
Relay Node C
Relay Node B Default path
Redundant path
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Sender Receiver
5. The sender, based on the information received , select the redundant path.
6. Sender sends the setup packet to that selected relay node, containing flow ID, IP address and the port number of the receiver.
7. The relay node builds up a table for forwarding packets.
8. Each time, the sender attaches the flow ID in sending packets for relay node to where it should forward to.
Relay Node A
Relay Node C
Relay Node B
Setup Command (flowID, recvIP, recvPort)
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Sender Receiver
5. The sender, based on the information received , select the redundant path.
6. Sender sends the setup packet to that selected relay node, containing flow ID, IP address and the port number of the receiver.
7. The relay node builds up a table for forwarding packets.
8. Each time, the sender attaches the flow ID in sending packets for relay node to where it should forward to.
Relay Node ASetup Command (flowID, recvIP, recvPort)
FlowID RecvIP RecvPort
…. …. ….
…. …. ….
flowID recvIP recvPort
…. …. ….
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Sender Receiver
5. The sender, based on the information received , select the redundant path.
6. Sender sends the setup packet to that selected relay node, containing flow ID, IP address and the port number of the receiver.
7. The relay node builds up a table for forwarding packets.
8. Each time, the sender attaches the flow ID in sending packets for relay node to where it should forward to.
Relay Node AData (flowID, recvIP, recvPort)
FlowID RecvIP RecvPort
…. …. ….
…. …. ….
flowID recvIP recvPort
…. …. ….
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Redundant Path Selection
Finding optimal path is difficult and complex Traffic conditions vary rapidly
Use of BGP between ASes. No. of link along the path and their associated latency c
an not be obtained.
OSPF, by periodically probing. Not scalable
Passive Probing tools Measurement process based on the application sending
rates
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Redundant Path Selection
However, Finding two path with absolute lowest loss rates for the proposed PDF system may not be needed
a) Complexity increases, thus not scalable
b) Other paths may still achieve reasonable performance
Performance is still better than uni-path case even one path has five times loss than the other.
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Redundant Path Selection
Denote a network topology as directed graph G=(V,E)
with vertices and edges Vvi E)v,v(e
ji
Vi routers
P(v1, vn) [v1, v2, v3 … vn] : physical path from v1 to vn
Redundant path P(v1, vk) U P(vk, vn)
W(vi, vj) the weight associated with the physical link between vi and vj. (eg. Latency, bandwidth)
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Redundant Path Selection
Step 1 Compute a set of relay nodes O’ that result in the minimu
m number of joint links between the default path and all the redundant paths via a node in O,
O’=arg mink p’(u,k,v) ∩ p*(u,v)
where ,
p’(u, k, v) is redundant path via node k
p*(u,v) is the default path
Ok
Default path
Redundant path
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Redundant Path Selection
Step 2 Choose node k’ that results minimum weight associated
with the corresponding redundant path,
k’=arg minl w(p’(u, l, v))
where , 'Ol Default path
Redundant path
30us
130us
50us
80us
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Redundant Path Selection
Procedure repeated for All remaining relay nodes
for selecting the new redundant path
Advantage
Traceroute only invoke at the start of the session.
Drawback
Information from Traceroute is not complete and accurate
Some ASes hide information from their networks
}'O\O{k
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Simulation 1
AS Interconnections
Routers Interconnections
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Simulation
Flat Topology
1. Randomly choose a set of participating nodes
2. Randomly choose a pair of sender and receiver among all participating nodes
3. Default path is set as the smallest latency between the sender and receiver. (calculated by OSPF)
4. Apply the redundant path selection strategy
5. Repeat 5000 times
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Simulation
Flat Topology
1. Randomly choose a set of participating nodes
2. Randomly choose a pair of sender and receiver among all participating nodes
3. Default path is set as the smallest latency between the sender and receiver. (calculated by OSPF)
4. Apply the redundant path selection strategy
5. Repeat 5000 times
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Simulation
Flat Topology
1. Randomly choose a set of participating nodes
2. Randomly choose a pair of sender and receiver among all participating nodes
3. Default path is set as the smallest latency between the sender and receiver. (calculated by OSPF)
4. Apply the redundant path selection strategy
5. Repeat 5000 times
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Simulation
Flat Topology
1. Randomly choose a set of participating nodes
2. Randomly choose a pair of sender and receiver among all participating nodes
3. Default path is set as the smallest latency between the sender and receiver. (calculated by OSPF)
4. Apply the redundant path selection strategy
5. Repeat 5000 times
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Simulation
Flat Topology
1. Randomly choose a set of participating nodes
2. Randomly choose a pair of sender and receiver among all participating nodes
3. Default path is set as the smallest latency between the sender and receiver. (calculated by OSPF)
4. Apply the redundant path selection strategy
5. Repeat 5000 times
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Simulation
Flat Topology
1. Randomly choose a set of participating nodes
2. Randomly choose a pair of sender and receiver among all participating nodes
3. Default path is set as the smallest latency between the sender and receiver. (calculated by OSPF)
4. Apply the redundant path selection strategy
5. Repeat 5000 times
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Simulation
Flat Albert Barabasi
1500 Nodes
2967 Edges
H-Albert-Barabasi I
1500 Nodes
2997 Edges
H-Albert-Barabasi II
1500 Nodes
4337 Edges
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Simulation Results
Only 2% of total nodes already give less than 10% shared links.
HAB 2 has higher degree of connectivity than HAB 1
Flat topology does not contain routing between ASes
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Simulation Results
The latency decreases as # of participating nodes increase because more choice of redundant paths
Initial latency = 1.7
Decrease gradually beyond 20%
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Simulation Results
(Left) Reduction in latency does not result from fewer links
(Right) P(two or fewer shared link) is 100%(F), 90%(ABII), 85%(AB1)
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Simulation - NS
……
……
Default path : 11 links
Redundant path : 18 links
Sender Receiver
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Parameter
Link Capacity 2Mbs
Propagation Delay 4ms
Random Exponential Traffic Peak Rate 1.8Mbs
Random Exponential Traffic Average Idle Period 8s
Random Exponential Traffic Burst Period 40ms
Video Packet Size 500bytes
RS code Protected RS(30, 23)
3 Scenario
• Sender streams the video to the receiver at 800kbps on default path only
• Sender streams the video to the receiver on both redundant and default path at 400bps for each path with two paths are completely disjoint
• Same as case 2, but with one shared link
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Results
Case 1
Case 3
Case 2
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Results
Effective loss rate = # of irrecoverable packets / total # of packets
Can be 7 times better
Even have 3 shared links (out of 11), the performance is still twice better.
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Conclusion
Path Diversity Scheme (PDF)Heuristic scheme for selecting redundant p
athSimulations done on Internet-like topologie
sNS Simulations for comparing unipath and
multipath scheme
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Comments
PDF performances highly depends on the shared link. Q: what is the performace when the percentage
s of shared link becomes 50%?
Latency incurred in PDF may not be suitable for real time application Q: Considers the end-user throughput in P2P e
nvironment, it most likely exceeds 150ms.