Routing Metrics for Wireless Mesh Networks CSE 6590 Fall 2010 27 December, 2017

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

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

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

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

Routing Protocols for Mesh Networks 27/12/2017

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 27/12/2017

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 27/12/2017

Source Routing Example protocol: LQSR Source nodes put entire path in packet header Large packet headers waste network bandwidth Does not scale 27/12/2017

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 27/12/2017

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. 27/12/2017

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 27/12/2017

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

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

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

WCETT (2)

WCETT Example

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 27/12/2017

MIC Metric of Interface and Channel switching Improves upon WCETT

MIC (2)

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

Routing Metrics for WMNs 27/12/2017

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 27/12/2017

Single Channel ─ Results 27/12/2017

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 27/12/2017

Multiple Channels ─ Results 27/12/2017

References “Wireless Mesh Networking” book, section 1.8.