PATH DIVERSITY WITH FORWARD ERROR CORRECTION SYSTEM FOR PACKET SWITCHED NETWORKS

Thinh Nguyen and Avideh Zakhor

IEEE INFOCOM 2003

AGENDA Motivation System Description Redundant Path Selection Simulation Results Conclusion

MOTIVATION

- Packet loss and end-to-end delay- Solutions – (1) Layered, error-resilient video codecs

(2) Retransmission

(3) Use of edge architectures

Assume single fixed path between sender and

receiver.

PERFORMANCE OF FEC

Depends heavily on the correlation of packet loss between multiple paths.

So the question is – Are there sufficient disjoint paths between a pair of senders and receivers???

MOTIVATION Theoretical Results –

RS(30,23), packet size-500 bytes, sending rate-800 kbps

Optimal rate partition using two paths.

MOTIVATION

Ratio of irrecoverable loss probabilities of the uni-path scheme to multi-path scheme.

SYSTEM ARCHITECTURE

SYSTEM ARCHITECTURE Contd. Sender first executes traceroute from itself to

all the participating nodes and receiver. It also sends setup packet to all participating

nodes instructing them to execute traceroute. Sender Computes optimal redundant path After redundant path is choosen, sender

sends the setup packet to the selected relay node instructing it to forward packets to the receiver.

SYSTEM ARCHITECTURE Contd. Setup Packet = flow ID + IP Address + Port Number Use UDP to send all the packets between

nodes.

REDUNDANT PATH SELECTION To measure latency, bandwidth and packet

loss –

(1) Use of Probing tools – inc complexity

(2) Passive Probing

Assumption made in this system –

Two paths with absolute lowest loss rates is

not needed.

REDUNDANT PATH SELECTION Sender runs this algorithm. Get information using traceroute tool. Input

is names of the routers and roundtrip delays.

Network Topology – - G(V,E) .- Weights denote the latencies b/w

participating nodes.

REDUNDANT PATH SELECTIONRelay node is computed as-

(1) Compute a set of nodes that result in minimum number of joint links between the default Internet path and all redundant paths.

(2) Choose k’ that results in minimum weight associated with the corresponding redundant path.

SIMULATION RESULTS

Simulation Topologies

Used Brite s/w to generate Alber-Barabasi topologies.

Flat Topology Two level Hierarchial Topology

SIMULATION RESULTS

To estimate average latency, hop counts and degree of disjointness –

(1) Choose a set of participating nodes randomly.

(2) Choose a pair of sender and receiver.(3) Use the redundant path selection algorithm

proposed to find redundant and default paths for the given configuration.

Default path – low latency.

SIMULATION RESULTS(1) Percentage of shared links between redundant and default

paths

SIMULATION RESULTS(2) Latency of redundant path over the latency of default path

SIMULATION RESULTS(3) Number of hops of the redundant path over the number hops of the default

path

SIMULATION RESULTS

(4) Cumulative distribution of shared links for various network topologies

SIMULATION RESULTS

NS SIMULATIONS:Link capacity – 2 Mbs

Packet Loss Rate is considered in 3 scenarios –

(1) Sender streams the video to the receiver at 800kbps on the default path.

(2) Sender streams the video to the receiver on both paths at 400kbps each.

(3) Same as (2) with a shared link between both paths.

SIMULATION RESULTS

Sending Packets using traditional default path

SIMULATION RESULTS

Both redundant and default path without shared link

SIMULATION RESULTS

Both redundant and default path with one shared link

SIMULATION RESULTS

Avg. loss rate of using one path over both with various number of shared links between them.

CONCLUSION

- Simulations show that only 10% of participating nodes are required for the proposed path redundant selection scheme to effectively find a redundant path.

- DRAWBACKS OF THE PROPOSED SYSTEM-

(1) Performance depends on the information given by traceroute.

(2) Some ASes do not report information about their networks.

REFERENCES

Path Diversity for Enhanced Media Streaming.John G. Apostolopoulos and Mitchell D Trott, Streaming Media Systems Group.

Thank You