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  • CNBuB 2015 workshop impressions 16 September 2015
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  • Summer Course at Mekelle Institute of Technology, Ethiopia 10 September 2015
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Wireless mesh networks in communities: some details

Community Networks

Community network (CN) is a term used broadly to indicate the use of networking technologies by, and for, a local community. Free-nets and civic networks indicate roughly the same range of projects and services, whereas community technology centers (CTCs) and telecentres generally indicate a physical facility to compensate for lack of access to information and communication technologies (ICTs).

Ad-hoc networks

In ad-hoc communication networks, the topology of networks is not stored or pre-configured in nodes. Instead, they have to discover it. The basic approach is that a new node may announce its presence and should listen for announcements broadcast by its neighbors. The antenna of a node can “see” several other nodes. Each node learns about nodes nearby and how to reach them, and may announce that it can reach them.

An ad-hoc routing protocol is used to control how nodes decide which way to route packets among devices in a mobile ad hoc network.

Wireless mesh networks, mobility and protocols

A wireless mesh network (WMN) is an ad hoc network made up of radio nodes organized in a mesh topology. A few protocols (MeshNetworks Scalable Routing (MSR), Roofnet Routing (SrcRR)) have been developed specifically for WMNs. Mesh networks can be seen as one type of ad hoc network.

A Mobile ad hoc network (MANET) is a type of ad hoc network where nodes can change locations and configure itself on the fly.  MANET and mesh networks are therefore closely related, but MANET also have to deal with the problems introduced by the mobility of the nodes.

Community Networks applied WMNs

Wireless mesh networks (WMN) receive growing interest for the construction of community networks. For instance, one part of the Athens wireless metropolitan network (AWMN), which covers Athens and the Attica region with roughly 5,00 nodes, has a mesh subnetwork. Moreover, Guifi.net in Catalonia, with more than 15,000 nodes and growing exponentially, has also three mesh subnetworks. Funkfeuer.at is an Austrian wireless and full mesh networking project that covers Wien and several other cities in Austria.

Classify Routing Protocols by Proactive, Reactive and Hybrid

Routing algorithms can be viewed as proactive, reactive, or hybrid. In proactive routing protocols, paths are established regardless of the willingness of a node to transmit data. In reactive (on demand) routing protocols, routing processes are initiated upon requests. In hybrid routing protocols, some of the nodes may implement a proactive routing protocol and others a reactive routing protocol.

Typical MANET Routing Protocols

Proactive routing protocols:

  • Wireless Routing Protocol (WRP): WRP uses improved Bellman-Ford Distance Vector routing algorithm. To adapt to the dynamic features of mobile ad hoc networks, some mechanisms are introduced to ensure the reliable exchange of update messages and reduces route loops.
  • Destination Sequence Distance Vector (DSDV) routing protocol: DSDV is also based on the traditional Bellman-Ford algorithm. But in routing tables of DSDV, an entry stores the next hop towards a destination, the cost metric for the routing path to the destination and a destination sequence number that is created by the destination. Sequence numbers are used in DSDV to distinguish stale routes from fresh ones and avoid formation of route loops.
  • Fisheye State Routing (FSR): It is based on Link State routing algorithm with effectively reduced overhead to maintain network topology information. As indicated in its name, FSR utilizes a function similar to a fish eye. The eyes of fishes catch the pixels near the focal with high detail, and the detail decreases as the distance from the focal point increases. Similar to fish eyes, FSR maintains the accurate distance and path quality information about the immediate neighboring nodes, and progressively reduces detail as the distance increases.
Reactive routing protocols:
  • Dynamic Source Routing (DSR) Protocol: DSR utilizes source routing algorithm. In source routing algorithm, each data packet contains complete routing information to reach its dissemination. Additionally, in DSR each node uses caching technology to maintain route information that it has learnt.
  • The Ad Hoc On-demand Distance Vector Routing (AODV) protocol: In AODV, routing information is maintained in routing tables at nodes. Every mobile node keeps a next-hop routing table, which contains the destinations to which it currently has a route. A routing table entry expires if it has not been used or reactivated for a pre-specified expiration time. Moreover, AODV adopts the destination sequence number technique used by DSDV in an on-demand way.
  • The Temporally Ordered Routing Algorithm (TORA): TORA is based on the concept of link reversal. TORA improves the partial link reversal method by detecting partitions and stopping non-productive link reversals. TORA can be used for highly dynamic mobile ad hoc networks.

WMN Routing Protocols

Reactive Routing Protocols:

  • Dynamic Source Routing Algorithm (DSR): Same as DSR in MANET
  • Ad-hoc On-Demand Distance Vector Routing Algorithm (AODV):  Same as AODV in MANET
  • Link Quality Source Routing Algorithm (LQSR): It is based on DSR algorithm by improving link quality metrics and other related metrics. The metrics are hop count, round trip latency (RTT), packet pair latency and Expected Transmission Count (ETX).To improve the link quality, and LQSR uses link cache instead of route cache.
  • SrcRR Routing Algorithm: It deploys flooding. SrcRR mainly deals with Expected Transmission Count (ETX) metric.
Proactive Routing Protocols:
  • Destination Sequenced Distance Vector Routing Algorithm (DSDV): Same as DSDV in MANET
  • Optimized Link State Routing Protocol (OLSR): In this algorithm, each node broadcasts its link state information to all other nodes in the network. So all nodes can know their 2- hop neighbors. OLSR uses hello messages for link state information. Multi Point Relays (MPR) is important aspect of the OLSR protocol. An MPR for a node N is a subset of neighbors of N which broadcast packets during the flooding process, instead of every neighbor of N flooding the network.
  • Mesh Networking Routing Protocol (MRP): In this protocol each client is chosen a gateway to connect to the internet. If the gateway fails or the node moves, the node will choose a different gateway. All the traffic is assumed to flow through the gateway to the internet.
  • Scalable Routing using heat Protocol: The protocol doesn’t deploy flooding. The basic of Heat is to provide Scalability and robustness. Scalability can be achieved by exchanging local messages .Robustness is achieved by assigning the temperature values such that paths through network areas with high redundancy preferred.
Hybrid Routing Protocols:
  • Hazy-Sighted Link State Routing Algorithm (HSLS): HSLS is a wireless mesh network routing protocol being developed by the CUWiN Foundation. It was invented by researchers at BBN Technologies. HSLS does not flood the network and it is based on the features of proactive, reactive, and suboptimal routing approaches. These strategies are combined by limiting link state updates in time and space.
The following table is a comparison of WMN routing protocols mentioned above:

Other traditional routing protocols:

  • Border Gateway Protocol (BGP) is the protocol backing the core routing decisions on the Internet. It maintains a table of IP networks or ‘prefixes’ which designate network reach-ability among autonomous systems (AS). It is described as a path vector protocol. BGP does not use traditional Interior Gateway Protocol(IGP) metrics, but makes routing decisions based on path, network policies and/or rule-sets. For this reason, it is more appropriately termed a reach-ability protocol rather than routing protocol.
  • Open Shortest Path First (OSPF) is an adaptive routing protocol for Internet Protocol (IP) networks. It uses a link state routing algorithm and falls into the group of interior routing protocols, operating within a single autonomous system (AS).
  • The Better Approach To Mobile Adhoc Networking, or B.A.T.M.A.N., is a routing protocol which is currently under development by the “Freifunk”-Community and intended to replace OLSR. Its crucial point is the decentralization of the knowledge about the best route through the network – no single node has all the data.

Routing protocols used by community networks:

  • Guifi.net barcelona: BGP, OSPF, OLSR, BATMAN
  • Funkfeuer.at: OLSR, OSPF, BGP
  • Athens wireless: OLSR, BGP
  • Berlin Freifunk: OLSR, BATMAN
  • ninux Roma: OLSR

Beneficial for community networks

  • Self-organizing

A mesh network is self-organizing. Because of that, adding new node or relocating existing node is as simple as installing and turning it on. The network discovers the new node and automatically incorporates it into the existing system.

A mesh network is not only inherently reliable, it’s also highly adaptable. If the link-level sensor and data logger are placed too far apart of a solid RF communications link, it is enough to just add one or more repeater nodes to fill the gaps in the network.

In a community network, if one router goes down, messages are sent through an alternate path by other routers. Similarly, if a device or its link in a mesh network fails, messages are sent around it via other devices. Loss of one or more nodes doesn’t necessarily affect the network’s operation. A mesh network is self-healing because human intervention is not necessary for re-routing of messages.

  • Redundancy and scalability

In a mesh network, the degree of redundancy is essentially a function of node density. A network can be deliberately over-designed for reliability simply by adding extra nodes, so each device has two or more paths for sending data. This is a simpler way of obtaining redundancy than is possible in most other types of systems.

A mesh network is also scalable and can handle hundreds or thousands of nodes. Because the network’s operation doesn’t depend on a central control point, adding multiple data collection points or gateways is convenient.

Reliability, adaptability, and scalability are the most important attributes of a wireless network for industrial control and sensing applications. Point-to-point networks can provide reliability, but they don’t scale to handle more than one pair of end points. Point-to-multipoint networks can handle more end points, but their reliability is determined by the placement of the access point and end points.

If environmental conditions result in poor reliability, it’s difficult or impossible to adapt a point-to-multipoint network to increase reliability. By contrast, mesh networks are inherently reliable, adapt easily to environmental or architectural constraints, and can scale to handle thousands of end points

References

A Survey: Routing Protocols for Wireless Mesh Networks, S. Siva Nageswara Rao, Y. K. Sundara Krishna, and K.Nageswara Rao

A Survey of Mobile Ad Hoc network Routing Protocols, Changling Liu, Jörg Kaiser

Routing protocols in wireless mesh networks: challenges and design considerations, Sonia Waharte & Raouf Boutaba & Youssef Iraqi & Brent Ishibashi

http://www.ece.gatech.edu/research/labs/bwn/mesh/

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