Wireless Mesh Networks MiNEMA Winter School 2009 Dr Johnathan - PowerPoint PPT Presentation

Wireless Mesh Networks MiNEMA Winter School 2009 Dr Johnathan Ishmael ishmael@comp.lancs.ac.uk

Talk Overview  Middleware for Network Eccentric and Mobile Applications Garbinato, Benoît; Miranda, Hugo; Rodrigues, Luís (Eds.) 2009, Approx. 465 p., Hardcover ISBN: 978-3-540-89706-4  Chapter 7: Wireless Mesh Networks

Talk Overview  Chapter 7: Wireless Mesh Networks  Defining  What & Why  Building  Testing  Additional Research Challenges

Defining Wireless Mesh Networks What is a Wireless Mesh Network?

What is a WMN?  A Wireless Mesh Network is a form of multi-hop wireless network providing a low cost, distributed network infrastructure

Why Wireless Mesh Networks? (1)  Provide connectivity to places without existing infrastructure  Ubiquitous Access  Digital Divide

Why Wireless Mesh Networks? (2)  Goals of WMNs:  Provide a network which can deliver high bandwidth- low latency services  Provide Ubiquitous connectivity  Remain cost effective in low density / sparsely populated areas

Why Wireless Mesh Networks? (3)  Other uses:  Specialised Scenarios (Security, Emergency/Disaster)

What is a WMN?  A Wireless Mesh Network is a form of multi-hop wireless network providing a low cost, distributed network infrastructure

Multi-hop Wireless Networks Hybrid Wireless Network Multi-hop Wireless Wireless Wireless Sensor Ad hoc Networks Networks Networks Wireless Mesh Networks

Traditional Wireless Access Point Access Point Connected to the Internet Internet connection (Gateway) Wireless coverage area Wireless Network Client

Ad-hoc Wireless Network  As Ad-hoc nodes are Wireless Network Client added coverage is extended

Wireless Mesh Network Internet connection (Gateway)  As Ad-hoc nodes are Wireless Network Client added coverage is extended Dedicated Mesh Node

Ad-hoc Vs Mesh Vs Wired Ad-hoc Wireless Mesh Wired Wireless Communication Wireless Communication Wired Communication Dynamic Topology Static Topology Static Topology Infrastructure-less Infrastructure based Infrastructure based Battery Powered Usually Mains Powered Mains Powered Temporary in Nature Usually Permanent Permanent No services Decentralised Services Centralised Services

Low Cost?  Ease & Simplicity:  Rapid, scalable deployment without the need for existing infrastructure  Zero administration:  Self-healing: Continuous re-configuration as routes are broken  Price:  Low install cost, low administration cost, low cost to end user

Distributed Network Infrastructure?  In order to function, Wireless Mesh Networks require infrastructure type services such as:  DNS/DHCP  Access Control  Traffic Shaping  Gateway Selection  In a wired network this would be centralised  Yet, without a single point of authority or infrastructure

What is a WMN?  A Wireless Mesh Network is a form of multi-hop wireless network providing a low cost, distributed network infrastructure

Building Wireless Mesh Networks What components are required to make a Wireless Mesh Network?

What Components make a WMN?  The components of a Wireless Mesh Network Application span a large range of Presentation the OSI model Session Transport  No single component Network really “makes” a Wireless Mesh Network Data Link Physical  A concise overview of each layer...

Physical Layer (1)  Choosing the right radio technology  Power usage  Range  Data rate  Antennas  What Antennas? – Directional?  Smart Antennas  Multiple Antennas (MIMO)

Physical Layer (2)  Greater throughput, greater resilience, lower latency & less power  Choosing the correct Physical Layer components depends upon the Application of the network  IPTV solution compared to Disaster Scenario  Research Topics  MIMO-based physical layers for WMNs  Higher physical layer capacity  Ability to operate in high interference levels  Ability to operate in flexible radio bands (Cognitive Radio)

Medium Access Control (MAC) Layer (1)  Wireless MAC layer manages communications between devices in a shared communication channel  Correct operation vital for WMNs due to large number of nodes and the multi-hop nature

Medium Access Control (MAC) Layer (2)  What does the MAC Layer provide?  Collision Avoidance  Energy Conservation  Interference Resistance  Rate Adaption

Medium Access Control (MAC) Layer (3) Time New New Contention Contention Window Window (8 slots) (5 slots) D S D I I I Station 1 RTS Data Defer Access F F F S S S S S Station 2 Defer Access I I CTS Ack F F S S New Old Contention Contention Window Window (1 Slot) (9 slots) D D RTS I I Station 3 F F Defer Access (Based on RTS) S S Defer Access (Based on CTS) Defer Access Station 4 (Hidden from Station 1)

Medium Access Control (MAC) Layer (4)  Research Topics  MAC incompatibilities with higher level protocols  Dual-Multi Channel MAC

Network Layer  Provide functional and procedural means to transfer variable length data from a source to a destination  Routing  Addressing  Quality of Service

Routing Metrics Internet connection (Gateway)  As Ad-hoc nodes are Wireless Network Client added coverage is extended Dedicated Mesh Node

Routing & Routing Metrics (1)  Selects the “best” available path between two hosts on a network  Routing protocols determine a cost for each potential path available and use the lowest cost path  The cost for each path is based on a routing metric

Routing & Routing Metrics (2)  What metrics?  Stable (Uptime)  Most throughput (Bandwidth)  Lowest latency (Round Trip Time)  Cost effective (Access Network Cost)  High power availability (Battery Power)  Routing Protocols based on application and network environment

Routing & Routing Metrics (3)  What makes a good routing protocol?  Ensuring route stability (no route flapping)  Lowest cost paths actually have good performance  AODV by default uses minimum hop count  Efficient (low cost) algorithms for calculating minimum cost paths  Loop free

Routing & Routing Metrics (4)  Protocols divided into (at least) three camps:  Proactive (Table-driven) e.g.:  DSDV (Destination-Sequenced Distance Vector)  OLSR (Optimized Link State Routing Protocol)  Reactive (On-demand) e.g.:  AODV (Ad-hoc on-demand Distance Vector)  DSR (Dynamic Source Routing)  Hybrid e.g.:  ZRP (Zone Routing Protocol)  Some more examples of routing protocols.....

Routing & Routing Metrics (5) And..... And..... And..... And..... And..... And.....       B.A.T.M.A.N. BGR AWDS TBRPF CBRP  ABAM      QuaSAR DREAM Babel WAR  CEDAR  ADMR     RDMAR GLS   CGSR WRP DART AMRIS     SrcRR LAR   DFR CHAMP DDR AMROUTE     SSR GPSAL   DBF GB FSR AQM     PLBR ZHL   DSDV IERP GSR BEMRP     VRR GPSR   Guesswork LBR HARP CAMP     TORA GFG   HSR LMR HSR CBM   ARPAM  SFT    IARP LQSR HSR DCMP HRPLS  FACE      LCA LUNAR LANMAR HSLS DDM ISAIAH       MMRP MOR OORP ATR PARO DSR-MB       ZRP OLSR EADSR MPRDV ALARM FGMP       And many more! Source: http://en.wikipedia.org/wiki/Ad_hoc_routing_protocol_list

Routing & Routing Metrics (6)  Research Topics  Multiple Radio Cards  (Yet more) New metrics  Cross-layer design  Dynamic Channel Assignment

Transport Layer (1)  Responsible for encapsulating application data in datagrams (or vice-versa)  Services include:  Same Order Delivery  Error correction / Segment retransmission  Flow Control  Congestion Avoidance  Ports  Can be connection-orientated (TCP) or connectionless (UDP)  We‟ll focus on TCP...

Transport Layer (2)  TCP performs poorly on WMNs Link Rate Optimal UDP TCP Throughput ACK (Mbps) Throughput (Mbps) (Mbps) Overhead % 6 5.3 4.6 13.2 12 10.3 8.4 18.4 18 14.9 12.0 19.4 24 19.3 16.4 14.5 36 26.8 22.6 15.7 48 32.9 26.9 18.2  Impact of TCP ACKs traversing multiple hops on the network

Transport Layer (3)  Poor congestion control, TCP can‟t differentiate the different between congestion and poor link quality Channel TCP Throughput Optimal UDP TCP Condition (Mbps) Throughput (Mbps) Underutilisation(%) Very bad 0.08 0.87 90.8 Bad 3.37 6.07 44.5 Average 14.5 18.6 22.0 Very Good 26.9 32.9 18.2 Link rate of 48Mbps

Transport Layer (4)  Within a WMN transport layer goals are to provide:  End-to-end reliability  High throughput  Capability to handle network asymmetry  Handle dynamic nature of network

Transport Layer (5)  Research Topics:  Improve performance (cross-layer)  ...without deviating from TCP... or  Do we need a new transport layer protocol for WMNs?  Awareness of link quality, link failure and dynamic nature of the network