Path Diversity with Forward Error Correction (PDF) System for Packet Switched Networks

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

Agenda

IntroductionMotivationProposed System

Overview Architecture Redundant Path Selection

SimulationsConclusion & Comments

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

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

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

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

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

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.

System Architecture

Router

Sender Receiver

Relay Node

Physical Network

Overlay Network

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

System Overview

Sender Receiver



3. Sender instructs relay nodes to execute traceroute from themseleves to receiver.


(S, Rec, 201us)

(S, RN_B, 73us)

(S, RN_C, 51us)

(S, RN_A, 100us)

Relay Node A

Relay Node C

Relay Node B

Sender Receiver



3. Sender instructs all relay nodes to execute traceroute from themseleves to receiver.


Command (traceroute, receiver)



Relay Node A

Relay Node C

Relay Node B

Sender Receiver



3. Sender instructs all relay nodes to execute traceroute from themseleves to receiver.


(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)

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

Sender Receiver





Relay Node A

Relay Node C

Relay Node B

Setup Command (flowID, recvIP, recvPort)

Sender Receiver





Relay Node ASetup Command (flowID, recvIP, recvPort)

FlowID RecvIP RecvPort

…. …. ….

…. …. ….

flowID recvIP recvPort

…. …. ….

Sender Receiver





Relay Node AData (flowID, recvIP, recvPort)

FlowID RecvIP RecvPort

…. …. ….

…. …. ….

flowID recvIP recvPort

…. …. ….

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


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.


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)


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


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


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

Simulation 1

AS Interconnections

Routers Interconnections

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

Simulation

Flat Topology






Simulation

Flat Topology






Simulation

Flat Topology






Simulation

Flat Topology






Simulation

Flat Topology






Simulation

Flat Albert Barabasi

1500 Nodes

2967 Edges

H-Albert-Barabasi I

1500 Nodes

2997 Edges

H-Albert-Barabasi II

1500 Nodes

4337 Edges

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

Simulation Results

The latency decreases as # of participating nodes increase because more choice of redundant paths

Initial latency = 1.7

Decrease gradually beyond 20%

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)

Simulation - NS

……

……

Default path : 11 links

Redundant path : 18 links

Sender Receiver

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

Results

Case 1

Case 3

Case 2

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.

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

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.

Documents

Path Diversity with Forward Error Correction (PDF) System for Packet Switched Networks