Determining the Optimal Configuration for the Zone Routing Protocol

1. Determining the Optimal Configuration for the Zone Routing Protocol By M. R. Pearlman and Z. J. Haas Presentation by Martti Huttunen martti.huttunen@ee.oulu.fi

2. Introduction • Zone Routing Protocol • A hybrid proactive-reactive protocol • Single configuration parameter: Zone radius • The research problem • To find an optimal value for the zone radius • To use minimal control traffic • Parameters reflecting performance • Node velocity and density, network span and traffic

3. Classes of routing protocols • Proactive routing • Routing table is updated continuously • Pro: small (and stable) delay • Con: amount of control traffic • Reactive routing • Routes are traced as they are required • Pro: less route queries • Con: highly variable delays

4. Routing Protocols 1/2 • Distributed Bellman-Ford • Problems: Slow convergence and amount of control traffic • Optimizations such as DSDV do not fully solve problems • Link-state protocols • OSPF: frequent changes in topology result in high control traffic • OLSR: uses multicasting (vs. point-to-point) to reduce control traffic • Global periodic topology updates are not well suited to larger or more dynamic networks

5. Routing Protocols 2/2 • Wireless Routing Protocol • Each node constructs a minimum spanning tree using its neighbors’ spanning trees • Problem: All nodes must be able to store a full routing table and its construction is costly • Source-initiated protocols • TORA: also destination floods its information • Queries are very costly to the network • AODV: uses source routing to limit flooding • Full path transmission might result in large control packets

6. The Zone Routing Protocol • A hybrid proactive-reactive protocol • Proactive routing is used in the transmission range of the node • Reactive routing is performed only on selected nodes • Elimination of loops • The configuration is adaptive: traffic is analyzed and zone range modified accordingly

7. Intrazone Routing • Intrazone routing is proactive, termed IARP • IARP may utilize any proactive algorithm • In this paper, split-horizon version of the distance vector algorithm is used • To achieve functional coverage, a node should have sufficient amount of neighbors • Adjusting zone radius requires the capability of adjusting transmitter power • On the other hand, having a large routing zone might result in excessive control traffic • The amount of proactive control traffic depends only on zone membership vs. network size

8. Interzone Routing • Intrazone routing is reactive, termed IERP • Improves from flooding algorithms by utilizing the known zone topology • Increases probability of a node being able to provide a route • Helps in estimating propagation in (probable) cases where the destination is not in the current zone • Bordercasting is used • May be implemented via unicasting or selective multicasting • Problem: How to actually derive border information?

9. Interzone Routing Sequence • Is destination inside zone? • Yes -> Reply • Bordercast a routing request • Peripheral (border) nodes will continue sequence • Once the reply arrives, deliver it to the source • Each node appends its information to the request • Information is used to source-route the reply • A full path is provided • Routing information should be cached if possible • Multiple routes may be discovered • Example selection metrics: number of hops, delay

10. Interzone Routing Problems • Once the request leaves initial zone, the request may be reflected back • Results in very quick flooding of the network • Early termination process is required • Intermediate nodes must be able to receive bordercasted messages • Intermediate nodes will terminate queries they have already received • Nodes must be able to either eavesdrop routing requests or broadcasting must be applied

11. Evaluation Procedure • OPNET simulation - network parameters • Number of nodes N • Node density d (average nr. of neighbors/node) • Relative node velocity n (rate of new neighbor entry) • Measurements • Amount of control traffic vs. data • The optimal zone radius r (in hops) • IARP/node/s = n * IARP-update/neighbor (r , d) • BER is approximated to increase drastically at certain transmitter range

12. Evaluation Results – IARP traffic • Procedure consists of delivering topology changes • Simulation results show exponential growth r ^ n (roughly) • The n denotes number of neighbors

13. Evaluation Results – IERP traffic/query • Each node receives d packets per query • Data is effectively flooded over network • The early termination process limits traffic • Traffic decreases as a mostly linear function of r, as zones cover more nodes • Simulation shows that with networks d < 6, the average traffic decreases • This is because of network getting partitioned -> queries do not reach all nodes -> networks with d < 5 are ignored (!) • Also, when zones are dense, traffic increases • Detecting redundant queries becomes increasingly difficult • IERP/s = IERP-update/query/node (r , d) * N * (Rinitial + Rseq) • Rinitial = rate of new route queries, Rseq = Route update rate • Effects of node velocity?

14. Evaluation Results – total performance • As r increases, the rate of IERP queries decreases • Intrazone communication is more dominant • The node density curve is parabolic • As Rused >> Rfailure, the curve gets more steep and the minimum point more evident • The estimation of this information requires specific algorithms • 2 options provided: min searching and traffic adapting

15. Traffic estimation: Min searching • r is adjusted periodically to find optimal value • Requires statistics of transmitted data and control information • These statistics are compared to the previous value • The comparison is used to determine if the direction of change was correct • A history of statistical values is kept per r value • Very sensitive to node velocity as converges slowly • Thresholds in traffic property changes trigger a new estimation

16. Traffic estimation: Traffic adaptive • r is adjusted according to the ratio of IARP/IERP traffic • As zones grow too large, IARP traffic becomes dominant • Does not require “triggering” as such, but is a continuous process • No extra traffic, analysis is based on required transactions • Oscillates on small r values • Simulation shows adaptive algorithm to be superior in terms of generated control traffic

17. Conclusions • The ZRP is a flexible and scalable solution • As IERP is triggered only on demand, the node velocity has little effect on control traffic and on the optimal zone radius • If traffic is periodic (vs. continuous), the performance is less affected by failed routes and node velocity • In these cases zone radius should be smaller • A less dense network with mobile nodes performs better with a larger zone radius

18. Achievements • Intra- and interzone routing is well applicable to heterogeneous networks • Natural selection of zones: different radio networks • Scales to very large networks • In WLAN-scale solutions is also sufficiently simple

19. Critique • Bordercasting is vital for IERP efficiency • Performance in less dense networks is questionable • Actual determination of IARP zone depends on the properties of the radio network used • Some IERP queries might be necessary to achieve full intrazone topology • Unicasted bordercasting is not very effective -> multi- or broadcasting should be available • Not very suitable for smallest devices • Various statistics and tables required