1. Wireless Mesh Networks

2. Introduction Wireless mesh network architecture
Why Wireless mesh network?
When Wireless mesh networks?
Routing background
Problems in existing routing protocols
Problems in frequency allocation

3. Existing wireless networking technologies

4. Wireless Mesh Networks
A wireless mesh network (WMN) is a communications network made up of radio nodes organized in a mesh topology.
Wireless mesh networks often consist of
mesh clients
mesh routers
Mesh routers contain additional routing functionality due to the presence of wireless interface card in them
Nodes have two functions:
Generate/terminate traffic
Route traffic for other nodes

5. Characteristics of Wireless mesh networks
Multihop Wireless network.
Support for adhoc networking and capability of self forming, self healing and self organization.
Mobility dependence on the type of mesh node.
Multiple types of network access.
Dependence of power consumption constraints on the type of mesh nodes

6. Why WMN? Multi-hop wireless network
Support for ad-hoc networking, and capability of self-forming, self healing and self organization.
Multiple types of network access
Mobility dependence on the type of mesh nodes
Compatibility and interpretability with existing wireless technologies

7. Compatibility and inter operatability with existing wireless networks
Dedicated routing and configuration
Mobility

8. Types of WMN
Infrastructure/ Backbone WMN
Client WMN
Hybrid WMN

9. Infrastructure/Backbone WMN
Mesh routers form an mesh infrastructure among themselves.
Provides backbone for clients and enables integration of WMNs with existing wireless networks and Internet through gateway/bridge functionalities.
Clients connect to mesh router with wireless link or Ethernet

10. Infrastructure/Backbone WMN

11. Client WMN
Client nodes constitute peer-to-peer network, and perform routing and configuration functionalities as well as provide end-user applications to customers, ”mesh routers are not required”
Multi-hop routing.
Client nodes have to perform additional functions such as routing and self-configuration.

12. Client WMN

13. Hybrid WMN A combination of infrastructure and client meshing.
Infrastructure provides connectivity to other networks such as the Internet, Wi-Fi, WiMAX, cellular, and sensor networks;
Mesh clients can access the network through mesh routers as well as directly meshing with other mesh clients.
The routing capabilities of clients provide better connectivity and coverage

14. Hybrid WMN

15. Protocol Design Physical Layer Mac Layer Network Layer Transport Layer
Application Layer

16. Physical Layer
Orthogonal frequency multiple access (OFDM) has significantly increased the speed of IEEE from 11 mbps to 54 mbps.
Ultra-wide band (UWB) can achieve much higher rate for short-distance applications.
MIMO can increase system capacity by three times or even more.
Frequency agile or cognitive radios can achieve much better spectrum utilization.

17. MAC Layer Differences between WMNs MACs and Wireless Networks MACs
MACs for WMNs are concerned with more than one hop communication
MAC must be distributed and collaborative, and must
work for multipoint-to-multipoint communication.
Network self-organization is needed for better collaboration between neighboring nodes and nodes in multi-hop distances.
Mobility affects the performance of MAC.

18. Routing Layer Features of routing protocol for WMNs:
Multiple Performance Metrics
Hop-count is not an effective routing metric.
Other performance metrics, e.g., link quality and round trip time (RTT), must be considered.
Scalability
Routing setup in large network is time consuming.
Node states on the path may change.
Scalability of routing protocol is critical in WMNs.

19. Routing Layer Robustness
WMNs must be robust to link failures or congestion.
Routing protocols need to be fault tolerant with link failures and can achieve load balancing.
Adaptive Support of Both Mesh Routers and Mesh Clients
Mesh routers : minimal mobility, no constraint of power consumption, routing is simpler
Mesh clients : mobility, power efficiency, routing is complicated
Need to design a routing protocol that can adaptively support both mesh routers and mesh clients.

20. Transport layer: research issues
Cross-layer Solution to Network Asymmetry
Routing protocol can select an optimal path for both data and ACK packets.
MAC layer and error control may need to treat TCP data and ACK packets differently.
Adaptive TCP
WMNs will be integrated with the Internet and various wireless networks such as IEEE , , , etc.
Same TCP is not effective for all networks.
Applying different TCPs in different networks is a complicated and costly approach, and cannot achieve satisfactory performance.

21. Application layer Applications supported by WMNs: Internet Access
Advantages of WMNs: low cost, higher speed, and easy installation.
Distributed Information Storage and Sharing
Data sharing between nodes within WMNs
Query/retrieve information located in distributed database servers.
Information Exchange across Multiple Wireless Networks.
Cellular phone talks Wi-Fi phone through WMNs,
Wi-Fi user monitors the status of wireless sensor networks.

22. WMN Standards WPAN: Bluetooth, Zigbee WiFi: 802.11a, b, g, n
WiMAX:

23. WMN Standards IEEE 802.16a WMAN Mesh
“mesh mode” in addition to the point-to-multipoint(PMP) mode defined in IEEE
Operating in the licensed and unlicensed lower frequencies of 2–11 GHz, allowing non-line-of-sight (NLO) communications, spanning up to a 50 km range.
Supporting multihop communications.

24. WMN Standards 802.11s WLAN Mesh
Multi-hop capability added to g/a/b
Auto configure on power up
Multi-channel multi-radio operation
Topology discovery
MAC Path selection protocol
Modified forwarding for QOS and mesh control

25. Routing Layer Features of routing protocol for WMNs:
Multiple Performance Metrics
Hop-count is not an effective routing metric.
Other performance metrics, e.g., link quality and round trip time (RTT), must be considered.
Scalability
Routing setup in large network is time consuming.
Node states on the path may change.
Scalability of routing protocol is critical in WMNs.

26. When WMN? Broadband home networking
Community and neighborhood networking
Enterprise networking
Wireless mesh networks
Transportation systems
Building automation
Health and medical systems
Security surveillance systems

27. Mesh vs. Ad-Hoc Networks
Wireless Mesh Networks
Multihop
Nodes are wireless, some mobile, some fixed
It relies on infrastructure
Most traffic is user-to-gateway
Multihop
Nodes are wireless, possibly mobile
May rely on infrastructure
Most traffic is user-to-user

28. Mesh vs. Sensor Networks
Wireless Mesh Networks
Wireless Sensor Networks
Bandwidth is generous (>1Mbps)
Some nodes mobile, some fixed
Normally not energy limited
Resources are not an issue
Most traffic is user-to-gateway
Bandwidth is limited (tens of kbps)
In most applications, fixed nodes
Energy efficiency is an issue
Resource constrained
Most traffic is user-to-gateway

29. Ad Hoc Networks
An ad-hoc network is a wireless local area network (LAN) that is built spontaneously as devices connect.
Instead of relying on a base station to coordinate the flow of messages to each node in the network, the individual network nodes forward packets to and from each other.

30. Contd… Formed by wireless hosts which may be mobile.
Don’t need a pre-existing infrastructure/backbone.
Routes between nodes pottentially contain multiple hopes.

31. Why MANET?? Ease, speed of deployment
Decreased dependence on infrastructure.
Can be used in many scenerios where deployment of wired network is impossble
Lots of military applications

32. History of Ad Hoc networks
In situations where networks are constructed and destructed in ad-hoc manner, mobile ad-hoc networking is an excellent choice.
The idea of mobile ad-hoc or packet radio networks has been under development since 1970s. Since the mid-90s, when the definition of standards such as IEEE (what we think of as WiFi or just ) helped cause commercial wireless technology to emerge, mobile ad-hoc networking has been identified as a challenging evolution in wireless technology.

33. Characteristics of Ad Hoc networks
Every node is responsible for forwarding packets to other nodes
Nodes themselves implement security function among themselves
Topology changes continuously as nodes are highly mobile.
Purpose Specific
Dynamic
No master-slave relationship (Every node is a router)

34. Types of MANET’s Fully symmetric environment
Asymmetric characteristics
Asymmetric responsibilities

35. Fully symmetric environment
All nodes have identical capabilities and respoonsibilities

36. Asymmetric capabilities
Transmission range and radios may differ
Battery life at different nodes may differ
Processing capacity may be different at different nodes
Speed of movement different

37. Asymmetric responsibilities
Only some nodes may route packets
Some nodes may act as leader for nearby nodes e.g. cluster haed

38. Other variants
Traffic characteristics may differ (bandwidth,realibility, unicast/multicast/broadcast )
Mobility patterns may be different (Little/ Highly mobile)
Mobility characteristics may differ (speed, direction of movement, pattern of movement)

39. Challenges Limited wireless transmission range
Broadcast nature of wireless medium
Packet losses due to transmission errors
Environmental issues
Mobility induced route changes
Mobility induced packet losses
Battery constraints

40. Characteristics of Ad Hoc networks
Connectivity among the hosts changes with time
Nodes are low power devices, low CPU process capability, and low memory.
Due to above reasons; the existing routing protocols are highly unstable.

41. Routing protocols Proactive: Reactive:
Determine route independent of traffic pattern
Used in traditional wired network
Reactive:
Discover/ maintain routes only if needed.

42. Tradeoff of proactive vs reactive
Proactive has low while reactive has high latency
Reactive have low overhead while proactive have high overhead

43. Metrics for Ad Hoc routing
Number of hops
Distance
Latency
Load balancing for congested loads
cost

44. Wireless Standards for Mobile Ad Hoc networks
802.11g
802.11n

45. 8002.11b Developed in July 1999 Maximum bandwidth=11 Mbps
Uses 2.4 GHZ Frequency range
Low cost

46. 802.11a Developed in 2001 Maximum bandwidth= 54 Mbps
Uses 5 GHZ frequency band
Much faster than b

47. 802.11g Developed in 2003 Modified version of 802.11b
Maximum bandwidth =54Mbps
Uses frequency range=2.4 GHZ

48. 802.11n Used for faster and long distance communication
Not formally published and approved yet.

49. Applications Personal area network Civilian environment
Emergency operations
Sensor networks