Wireless Mesh Networks

1. Wireless Mesh Networks Myungchul Kim mckim@icu.ac.kr

2. - IEEE Communications Magazine, pp. 523-530, Sept 2005 Introduction Mesh routers and mesh clients Multi-hop communications with much lower transmission power Mesh router with multiple wireless interfaces Mesh client with a single wireless interface Customers without wireless NICs can access WMN through for example, Ethernet Advantages: low up-front cost, easy network maintenance, robustness, reliable service coverage, etc. The available MAC and routing protocols are not scalable; throughput drops significantly as the number of nodes or hops in WMNs increases. A Survey on WMNs

3. Network architecture Infrastructure/backbone WMNs Fig 1. Network architecture and critical design factors

4. Client WMNs Actually the same as a conventional ad hoc network Routing and self-configuration Hybrid WMNs Fig 2 Network architecture and critical design factors

5. The characteristics of WMN Supports ad hoc networking: self-forming, self-healing and self-organization Multi-hop wireless networks Minimal mobility and dedicated routing and configuration Mobility of end nodes Mesh routers integrate heterogeneous networks, wireless and wired Power-consumption constraints are different Compatible and interoperable with other wireless networks Network architecture and critical design factors

6. Critical design factors Radio techniques Directional and smart antennas, multiple input and multiple output (MIMO) systems, and multi-radio/multi-channel systems Refconfigurable radios, frequency agile/cognitive radios, software radios Scalability Mesh connectivity: network self-organization and topology control algorithms are needed Broadband and QoS Security: no centralized trusted authority to distribute a public key in a WMN Ease of use Compatibility and interoperability Network architecture and critical design factors

7. Network capacity The guideline to improve the capacity of ad hoc networks: a node should only communicate with nearby nodes [1]. Througput capacity can be increased by deploying realying nodes. -> utilizing the node mobility -> transmission delay and buffer Nodes need to be grouped into clusters. Layered communication protocol Physical layer Advanced physical-layer technques: congnitive radios dynamicaly capturing the unoccupied spectrum Enable the programmability of all advanced physical layer techniques Open research issues: improve the trasmission rate and the performance of physical-layer techniques and utilize the cross layer design between MAC and the physical layer Advances and research challenges

8. MAC layer in WMN More than one-hop communcations Distributed for multipoint-to-multipoint communication Network self-organization Mobility is low Single-channel MAC and Multi-channel MAC Single-channel MAC Modifying existing MAC protocols Cross-layer design: directional antenna-based MACs and MACs with power control -> hidden terminal problem Proposing innovative MAC protocols: how to design a distributed TDMA MAC protocols overlaying CSMA.CA? Advances and research challenges

9. Multi-channel MAC Multi-channel single-transceiver MAC Multi-channel multi-transceiver MAC Multi-radio MAC Open research issues: scalable MAC, MAC/physical cross-layer design, network integration in the MAC layer Routing layer Optimal routing protocol features Multiple performance metrics: how about hop-count? Scalability Robustness: link failures or congestion, load balancing Efficient routing with mesh infra Advances and research challenges

10. Routing layer (con’t) Routing protocols with various performance metrics Link quality source routing (LQSR) Link quality metrics Expected transmission count (ETX) Multi-radio routing Weighted cumulative expected transmission time (WCETT) Link quality metric and the minimum hop-count Multi-path routing Better load balancing and high fault tolerance Hierarchical routing Clusters Advances and research challenges

11. Routing layer (con’t) Geographic routing Position information of nodes in the vicinity and the destination node Delivery is not guaranteed even if a path exists between source and destination Open research issues Scalability Better performance metrics Routing/MAC cross-layer design Efficient mesh routing Advances and research challenges

12. Transport layer Reliable data transport Non-congestion packet loss Unknown link failure due to wireless channels and mobility in mesh clients Network asymmetry: TCP is critically dependent on ACK Large RTT variations Ad hoc transport protocol (ATP) Rate-based and quick-start Congestion detection is a delay-based approach -> congestion cause No retransmission timeout Congestion control and reliability are decoupled Real-time delivery A rate control protocol (RCP) is needed to work with UDP Advances and research challenges

13. Transport layer (con’t) Open research issues Cross-layer solution to network asymmetry Adaptive TCP on various wireless networks Application layer Internet access Distributed information storage and sharing Information exchange across multiple wireless networks Improve existing applications layer protocols Propose new application-layer protocols for distributed information sharing Develop innovative applications for WMNs Advances and research challenges

14. Network management Mobility management Distributed mobility management Power management Network monitoring Security Factors such as distributed network architecture, vulnerability of channels and nodes in the shared wireless medium, and the dynamic change of network topology An AAA centralized server? No central authroity for managing security keys An open issue: A distributed authentication and authorization sheme with secure key management Advances and research challenges

15. Cross-layer design One approach is to improve the performance of a protocol layer by taking into account parameters in other protocol layers. Another approach is to merge several protocols into one component. Advances and research challenges