CSE 6590 Fall 2010 Routing Metrics for Wireless Mesh Networks 1 4 October, 2015

2 Wireless Mesh Networks Mostly static nodes Limited bandwidth Ample energy supply Possibly multi-radio/multi-channel/multi-rate

3 New Routing Metrics for WMNs Motivation Limited bandwidth require efficient routing Goals High throughput Low end-to-end delay

4 Intra Flow Interference  Nodes on the path of the same flow compete with each other for channel bandwidth Causes throughput to decrease sharply Increases delay at each hop Increases bandwidth consumption

5 Inter Flow Interference A node which transmits also contends for bandwidth with the nodes in the neighbouring area of its path. Leads to bandwidth starvation Some nodes may never get to transmit

04/10/ Routing Protocols for Mesh Networks

04/10/ On Demand Routing Originally designed for mobile ad hoc networks e.g., DSR, AODV Flood-based route discovery when source needs to communicate with destination Good for maintaining network connectivity under frequent changes in topology High overhead is unnecessary in networks with static nodes

04/10/ Table-Driven (Proactive) Routing Proactively maintain and update routing tables Broadcast route update messages Periodically Topology changes Lower overhead than on-demand routing in static networks Cannot cope with frequent metrics changes Route flapping High message overhead Two approaches: Source routing Hop-by-hop routing

04/10/ Source Routing Example protocol: LQSR Source nodes put entire path in packet header Large packet headers waste network bandwidth Does not scale

04/10/ Hop-by Hop Routing Distance-vector routing (slow convergence ) Link-state routing (fast convergence) Packet only carries destination address Small overhead Scalable Preferable, especially link-state routing

04/10/ Least Cost Path Routing Routing protocols route packets along minimum weight paths Performance of minimum weight paths impact the performance of routing protocols Characteristics of path Path length Link packet loss ratio Link capacity Intra-flow interference Inter-flow interference Capture as many characteristics as possible Note: In multi-channel multi-radio networks, channel assignment and routing must work together for optimal performance.

04/10/ Routing Metrics for WMNs Hop Count Expected Transmission Count (ETX) Expected Transmission Time (ETT) Weighted Cumulative ETT (WCETT) Metric of Interference and Channel Switching (MIC) The metrics evolved, each incorporating features of the previous ones

ETX 13 Expected number of transmissions required for successfully receiving a packet over that link. ETX = 1 / (P f. P r ) P f : packet delivery ratio in forward direction P r : packet delivery ratio in backward direction To get P f and P r : sending one probe packet per second. ETX is an additive metric Path cost = sum of link costs on that path

ETT 14 Expected transmission time ETT = ETX x (S / B) S: average packet size B: data rate

WCETT 15 Weighted cumulative expected transmission time Addresses the issue of channel reuse along a path

WCETT (2) 16

04/10/ Loop Free Routing - Isotonicity Definition The order of the weights of two paths must be preserved when we append or prefix a common third path on the two paths

MIC 18 Metric of Interface and Channel switching Improves upon WCETT

MIC (2) 19

MIC (3) IRU (Interference-aware Resource Usage) The aggregated channel time of all the neighbouring nodes (include end points of link l) consumed by the transmission on link l Captures path length, link capacity, loss ratio and inter-flow interference CSC (Channel Switching Cost) Captures intra-flow interference 20

04/10/ Routing Metrics for WMNs

04/10/ Performance Evaluation Single Channel Compare MIC, ETT and hop count Simulation parameters One radio per node All radios configured to the same channel 1000m x 1000m, 100 nodes, 20 flows

04/10/ Single Channel ─ Results

04/10/ Performance Evaluation Multiple Channels Compare MIC, ETT, WCETT and hop count Simulation parameters 2 radios per node Each can be configured to 1 of 3 channels 1000m x 1000m, 100 nodes, 20 flows

04/10/ Multiple Channels ─ Results

References 26 “Wireless Mesh Networking” book, section 1.8.