Performance Evaluation of ATM Shortcuts in Overlaid IP/ATM Networks

1. Performance Evaluation of ATM Shortcuts in Overlaid IP/ATM Networks Jim Kurose Don Towsley Department of Computer Science Univ. of Massachusetts, Amherst Victor Firoiu Bay Architecture Lab Nortel Networks

2. Outline • The problem: benefit of ATM shortcuts in IP/ATM • Two methods for network performance comparison • Where are ATM shortcuts beneficial? • Conclusion

3. ATM Shortcuts - What Benefit ? • Facts • Internet ubiquitous • ATM infrastructure widely deployed • Forwarding IP traffic with bw. resv. • Hop-by-hop in IP • ATM shortcuts • Potential benefits of ATM shortcuts • Cut through IP processing • Shorter path in ATM => fewer resv. • Richer ATM netw. => Lower blocking pr. • In this study: evaluate (2) and (3) ATM link IP link ATM shortcut IP router ATM switch

4. Comparing Network Performance • Consider two instances of an IP/ATM network: N1: using IP routing N2: using ATM routing Rr1 r1 r3 Rr3 Rr2 r2 • Define Network Load Ratio R(p): • N1: traffic load (ri)i => flow blocking pr. p1 • N2: traffic load (Rri)i => flow blocking pr. p2 • R(p) is such that p1=p2=p “N2 performs R times better than N1”

5. Computing Network Load Ratio • Algorithm: Pi(r) given by Fixed Point Method • Complexity: O(L2CV2FS) L = no. links F = no. Fixed Point iterations (3..100) C = max. no. flows / link S = no. Inversion iterations (10..50) V = no. nodes • Problems • high computational complexity • computes R(p) only for a given p • need R for a range of p values

6. Simplification: Asymptotic Load Ratio • Observe: for p<0.1, R(Ni,Nj,p)constant (p) • Define: Asymptotic Load Ratio TandemNSFBoneStarComplete

7. Computing Asymptotic Load Ratio • For networks with all links having same capacity C: • where hi = prob(flow traverses link i) • Similar result conjectured for heterogeneous capacities • verified by simulation • Advantages • low complexity O(LV2),L = no. links, V= no. nodes • gives performance comparison for a range of p values

8. Accuracy of Asymptotic Load Ratio • Simulation: generate random networks (Nk)k • Compute NLR: R(Ni,Nj,p) for several p, using Fixed Point • Compute ALR: A(Ni,Nj) using simple method • Compute relative error : • Computation time • NLR: 104s, for each p • ALR: 0.008s

9. Where are ATM Shortcuts Beneficial? • Simulation • Generate random ATM networks • NA = no. nodes, aA = prob(link exists between two nodes) • Generate IP networks: • For each ATM/IP network pair • map IP nodes to ATM nodes • map IP links to shortest path ATM routes • Compute Asymptotic Load Ratio • Results • ALR highly correlated with: • IP to ATM average depth ratio • IP to ATM diameter ratio • ALR not correlated with: ave. degree ratio, no. nodes ratio

10. Simulation Results

11. Conclusion • Proposed two methods for evaluating benefit of ATM shortcuts • low computational complexity • accurate for a wide range of network load • Evaluated IP/ATM topologies where ATM shortcuts increase network capacity • when average route length is decreased • Methodology useful for network designers • asses opportunity for IP/ATM protocols • Future work • extend results for networks with alternate routing • flows with heterogeneous bandwidth requirements