Virtual Distance: A Generalized Metric for Overlay Tree Construction

ISCC’12 July 1 2012

Suat Mercan (Zirve University)&

Murat Yuksel (University of Nevada, Reno)

Outline

• Introduction• Virtual Directional Multicast (VDM)• Virtual Distance• Performance Evaluation• Conclusion

Motivation• Increasing bandwidth (127 Kbps(2000) 4.4 Mbps(2010))

• Increasing Internet usage 360,985,492(2000) - 1,966,514,816 (2010)

• High demand for multimedia applications (Internet TV, tele-conference, online education, youtube)

• A huge amount of internet traffic coming from multimedia (90% of Internet traffic in 2014 according to Cisco)

• This trend is calling efficient and scalable mechanisms to transfer content to many receivers from a single source

Motivation• Various types of multimedia applications

• Sensitivity of these applications differs against various network performance metrics– delay is crucial for video conferencing which includes interactivity– jitter is important for video streaming– bandwidth is for HDTV

Our Work• Responding to these varying application-specific requirements or

sensitivities is a key point

• We define and use the concept of virtual distance for constructing overlay trees

• We aim to find the most appropriate parent for a peer according to the application’s purpose

• Calculating the virtual distance based on different criteria, but without protocol modification, makes the overlay multicast protocol satisfy different quality expectations for different apps

• Our key goal is to automatically calculate overlay multicast trees such that they can be seamlessly customized to applications’ performance goals.

Virtual Direction Multicast (VDM)

Virtual Direction Multicast• We embed the virtual distance method in our previous overlay multicast

tree protocol, VDM.• VDM:

– Tree based– Source is alone at the beginning– Tree extends with new joins. – Want to use minimum resource as satisfying end user

Directionality

P C P C P C

CASE I CASE II CASE III

Join

CASE I

Join

CASE III

CASE I

Join

CASE III

CASE II

Reconnection

• Each node knows its grandparent• When parent leaves, join process starts at grandparent

Virtual Distance

Virtual Distance

• Round Trip Time (RTT) is used to calculate distances• What about loss rate?• Delay and loss rate between two nodes may be uncorrelated

because of background and cross traffic on routers• A peer might experience high loss rate on a good path in terms

of delay• Sensitivity of multimedia applications differs against various

network performance metrics• This requires to take other factors into account when building

overlay tree

Virtual Distance

delay=100msloss=1%

delay=50msloss=2%

Delay-basedVDM-D

Loss-basedVDM-L

Virtual Distance

• A key property of VDM is the capability of virtualizing the underlying network in different ways

• It is possible to establish “virtual directions” based on performance metrics

• Different values of these metrics may produce different virtual distances and thus different overlay tree

• We can establish target specific overlay trees to improve some specific performance metrics

Sample Measurement from Akamai website

Information from iPlane Dataset

• Inter-PoP measurement data sample from iPlane• Three points A, B, C• d1 = distance (A-B) d2 = distance (B-C) • l1 = loss(A-B) l2 = loss(B-C)• d1/d2 and l1/l2 are inversely correlated for 44%

Performance Evaluation

Performance Evaluation

• We evaluate the performance of VDM-D (delay-based) and VDM-L (loss-based) in order to show the efficiency of the virtual distance concept

• We analyze protocol behaviors as we vary the churn rate in the overlay network

Simulation Setup

• NS-2 (Network simulator)• 792 nodes in physical network• 200 nodes in overlay network• Degree of each node between 2-5• Each physical link is assigned error rate between 0% - 2%• Run 5,000s• Under different churn rates (1% - 20%)• Run each simulation 10 times

Simulation Results

Stretch Loss

VDM optimizes the loss when the virtual distance is based on

loss.

VDM optimizes the stretch when the virtual distance is based on delay.

Virtual Distance

Conclusions

• Our key goal is to automatically calculate overlay multicast trees such that they can be seamlessly customized to applications’ performance goals.

• VDM-D uses delay for distance estimation, and improves stress and stretch while giving higher loss rate

• VDM-L achieves better performance in terms of loss rate

Thank you!