During man-made or natural disasters, reliable and efficient communication is crucial for management of emergency services. Tragic events such as the terrorist attacks on September 11th 2001, the Indian Ocean Tsunami in 2004, Hurricane Katrina in the US in 2005 and the Haiti Earthquake in 2010 demonstrated how the current first-responder communications are limited and inadequate for large scale operations.
Interoperability between communication equipment and systems is a critical part of any response. A lack of communication interoperability between different agencies and jurisdictions has severely affected rescue teams and emergency services during recent emergencies and disasters. Due to these issues sometimes the only alternatives were shouting, hand signs, and using runners with written messages.
“The 9/11 commission report noted that a patchwork of incompatible technology and the uncoordinated use of frequency bands were the main reasons for nonexistent or poor interagency communication during emergency response and recovery operations.” (Portmann & Pirzada 2008)
Another issue of emergency/disaster communication is the reliance on current fixed communication infrastructure, such as the landline and mobile phone systems, as well as land mobile radio systems (LMRS), an infrastructure-based system used by emergency services.
In 2005 Hurricane Katrina destroyed or disabled hundreds of wireless base stations, flooded the local offices of agencies, and disconnected vital communications lines. The remaining parts of the network that were functional overloaded and were unable to provide required adequate services.
“First responders were surprised and severely hampered by a near-complete breakdown of the fixed terrestrial communications infrastructure.” (Portmann & Pirzada 2008)
During a crisis or the aftermath of an emergency/disaster, it is important that the responders to the emergency are provided with accurate and up-to-date information. VoIP (voice over ip), Video coverage or other data communication can help provide a considerable aid to the rescue organisers or rescue teams in order to make important decisions. Broadband can allow access to high resolution maps as well as building plans enabling quicker intervention in areas that require it most. (Naudts et al. 2007)
Unfortunately, during an emergency/disaster, it is not possible to depend on the existing network infrastructures, for communication between rescue workers, or requests for help from the public. Because of the need for a fast deployment, redundant, secure, communication network. A WMN has all the characteristics that are required.
Wireless Mesh Network
Wireless Mesh Network (WMN) are communication networks formed from nodes. WMNs can be made up of of mesh clients, mesh routers and gateways. Each node within the network takes the role of not only a host but also a router, forwarding packets for other nodes that are not within range of their destination. The mesh clients are often wireless devices such as PDA’s, laptops and mobile phones. Other than forward traffic between clients mesh routes also provide communication to the gateways which may in turn connect to the Internet. Access to mesh networks is dependent on the nodes working together to create the network.
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WMNs are reliable and offer good redundancy. For example, if a node can no longer operate, or moves out of range, the other nodes can still communicate with each other, either directly or via single or multiple intermediate nodes essentially self-healing the network. WMNs can also self configure by detecting in range nodes and establishing connections. WMNs are capable of being implemented using various wireless technologies including 802.11, 802.15, 802.16, mobile technologies or combinations of more than one type.
Wireless Mesh Networks can be classified as a form of ad-hoc network. They can be deployed to provide connectivity over a certain area, but in a dynamic and cost effective manner. Ad-hoc networks, alternatively, are formed when wireless ad hoc devices are within range of each other. Mesh routers are also more mobile, and can be moved according to the demands of the network. Often the mesh routers are not limited in terms of resources compared to other nodes in the network, and so can be exploited to perform more high resource requirement functions. In this manner, WMNs differs from ad-hoc networks, since their nodes are often constrained by resources.
WMNs can be extended to include thousands of devices, and can be deployed in hours, compared to other networks which can take days or even weeks. They do not require sophisticated planning and site mapping to achieve reliable communications, due to their self-configuration and self-healing properties. Therefore there is no need for expert and costly labour to complete surveys and installation.(Poor 2003)
Wireless Mesh Architecture
There are three basic types of Wireless Mesh Architecture: infrastructure, client, and hybrid. Figure 1 depicts a WMN; the mesh routers provide the backbone infrastructure via wireless connections. Clients access the network hop to the nearest mesh router, which essentially acts as wireless access points. In this type of architecture, the clients have a passive role and do not supply the network with any additional functionality such as routing and forwarding packets.
In client-mesh architecture (Figure 2), the network is made up of only the user/client devices, and no dedicated infrastructure nodes such as mesh routers or gateways. Due to the client devices forming the network, they perform the functions of routing and self configuration. The clients relay packets on behalf of other nodes and essentially take on the roles of mesh routers. A client mesh is essentially the same as a traditional mobile ad hoc network, even using the same communication standards.
The Hybrid-mesh architecture (Figure 3) is a combination of infrastructure and client-mesh architecture and consists of mesh routers and mobile clients. The routers forming the networks backbone and the clients actively participate in the mesh by providing network tasks such as routing and forwarding packets. Clients providing these functionalities are therefore able to be a dynamic extension of the more static infrastructure part of the mesh. The hybrid-mesh architecture is flexible and allows for the combination of benefits from infrastructure and client mesh networks. In emergency/disaster scenarios, it allows mobile devices to extend the restricted range of coverage of the mesh routers.
One of the primary features of WMNs is their ability to dynamically self-organize and self-configure. The nodes of a WMN can automatically detect nearby nodes, then establish and maintain network connections, in a sort of ad hoc fashion. This is typically implemented at the network layer through the use of ad hoc routing protocols. WMNs’ self-configuring nature in turn allows for easy and rapid deployment. WMNs are also dynamically allowing them to adapt to changing environments and essentially self-heal in case of node or connection failures. This self-healing capability combined with the mesh topology’s inherent redundancy provides wireless mesh networks with a high level of robustness and fault tolerance. (Portmann & Pirzada 2008)
Mobility is dependent on the type of node in question. The mesh routers can be mobile, unlike traditional infrastructure network backbones and moved according to specific demands arising in the network, while mesh clients can be stationary or mobile nodes.
WMNs support multiple types of network access, backhaul access to the Internet and peer-to-peer (P2P) communications. They are also capable of integrating with other wireless networks and providing services to the end-users of these networks. (Wang 2011)
Within WMNs’ there is the issue of power-consumption and this in turn creates constraints depending on the on the type of mesh nodes. Mesh routers usually do not have strict constraints on power consumption (unless they are highly mobile and rely on battery or solar power). However, mesh clients may require power efficient protocols. As an example, a mesh-capable sensor requires its communication protocols to be power efficient. The MAC or routing protocols optimized for mesh routers may not be appropriate for mesh clients such as sensors, because power efficiency is the primary concern for wireless sensor networks.
The interconnections by wireless mesh links are typically:
-Single radio mesh
-Dual radio mesh
-Multi radio mesh
Single radio mesh
A single radio mesh node has a single radio that is used for local access and mesh backhaul. All nodes tune to same frequency and backhaul is a shared network. Mesh-network is formed using omni-directional antennas to send and to receive to all the other nodes within range. Mesh nodes and clients share the available bandwidth, system capacity is therefore very low and latency is high and unpredictable. Most mesh products today are single radio technology. These products are simple, but won’t scale to a large system and have very limited capacity
Dual radio mesh
Dual-radio mesh nodes have two radios, access and backhaul radios are separate. Mesh network is formed using omni-directional antennas and backhaul is a shared network on a single channel. Dual radio mesh is an improvement and solves the mesh forwarding problem, but still limited capacity and scalability.
Multi radio mesh
Multi-radio mesh nodes have multiple radios, client access and mesh backhaul are each independent. The backhaul mesh is multiple point-to-point links and not a shared network. Dedicated radios with directional antennas allow independent operation of backhaul links for greater capacity and point-to-point links enable greater separation of mesh nodes. This gives the Backhaul mesh the performance of wired network.
Implications For Wireless Network
Increasing use of video for communication at both command points and in the field
Network must deliver adequate bandwidth to support any-endpoint-to-any-endpoint delivery of real-time video streams
Network capable of collecting and delivering adequate bandwidth (potentially 1 to 2 Mbps per camera and viewer), plus aggregate backbone capacity to support all endpoints
Constant movement of nodes, in vehicles and on foot
Network must support roaming with seamless mobility to maintain persistent connections with mobile workers
Handoff between wireless network nodes of under 50 ms
Broad geographic footprint of the required service area
Network must cost-effectively scale to metropolitan-area geographies; equipment must be installable in a range settings
Mesh wireless to reduce requirement for wired backhaul; equipment installable on utility poles, rooftops, exterior building walls, trees, cable infrastructure, etc.
Steep growth in use of high-bandwidth, delay-sensitive video,
data and voice applications
Network must deliver huge amounts of bandwidth with low, predictable latency and jitter
Mix of single- and multi-radio nodes and switched mesh for capacity; traffic classification for QoS
Life-critical nature of public safety applications
Network must exhibit extremely high, carrier-grade network reliability and resilience
High hardware MTBF, automatic routing around failures, battery backup
Value of ad hoc networks for emergency/disaster recovery, establishment of on-scene networks, etc.
Wireless equipment must facilitate simple, rapid deployment of ad hoc wireless networks
Flexible power sourcing; auto-configuration features; portable, rugged, weather-resistant hardware
Budgetary constraints and operating expenses
Network must deliver cost-effective bandwidth and low cost of operation
Mesh to minimize backhaul costs; ease of installation and maintenance features
Sensitivity of public safety communications
Network must be secure from outside tampering and eavesdropping
Security features for authentication, encryption, and network virtualization: 802.1x, Web authentication, WEP, WPA and WPA2, etc.
Need for complete solution
Proven interoperability with network cameras, laptop wireless cards, mobile routers, and other end-user equipment
Documented performance testing of network’s interoperability with relevant third-party equipment
In terms of transmitting video, if a first responder sends video from an incident scene to a central command or to other responders to view on in-vehicle laptops or handhelds, it may be more desirable to use lower-quality images transmitted at higher frame rates. An example would be a 1:60 compressions on the video stream from the scene, for a frame size of 8 KB. This stream, with lower resolution but a higher frame rate for better continuous motion, would require approximately 1 Mbps network bandwidth.
The below table shows how the combination of image quality (determined by compression level) and frame rate determines the amount of network bandwidth required for a particular video stream.
BANDWIDTH REQUIREMENTS (Mbps)
1:60 (lowest quality)
1:30 (most common)
1:5 (highest quality)
(BelAir Networks 2007)
These figures are conservatively based on the M-JPEG compression format widely available in IP network cameras. Many network cameras also support more efficient compression standards such as MPEG-4 and H.264, which may reduce bandwidth consumption by another 50-70%, depending on how much images change from frame to frame.
A typical network planning guideline for fixed-position surveillance cameras with M-JPEG compression is to allocate 1 Mbps per camera. This enables 4 FPS of video with an image quality good enough for recording (1:30 compression at VGA resolution) while keeping storage requirements reasonable. Cameras equipped with MPEG-4 codecs could deliver twice the frame rate (8 FPS) with the same image quality for the same 1 Mbps of bandwidth per camera.
The below table provides an outline of the number of video endpoints (cameras and viewers) that can be supported in a given square mile based on the density of wireless network coverage.
Aggregate Capacity Per Sq Mi
(BelAir Networks 2007)
Comparison with other potential networking technologies
Reliability, adaptability, and scalability are the most important attributes of a wireless network. (Poor 2003)
Point-to-point networks can provide reliability, but 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 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
Suitability in Applications
None (two end points)
Moderate (7-30 end points)
Yes (thousands of end points)
There are however some issues concerning Wireless Mesh Networks
In WMNs, due to its ad hoc architecture, the centralized multiple access schemes such as TDMA and CDMA are difficult to implement due to their complexities and a general requirement on timing synchronization for TDMA (and code management for CDMA).
Distributed multiple access schemes such as CSMA/CA are more favourable. However, CSMA/CA has very low frequency spatial-reuse efficiency, which significantly limits the scalability of CSMA/CA-based multi-hop networks.
During the deployment of a network it is important to plan and design the infrastructure before physically implanting it. This can often be a time consuming task and can take days or weeks However, during emergency situations a rapid response is an important aspect.
WMN Pre-deployment considerations
WMNs can be deployed incrementally; one node at a time, as needed with no existing communication backbone required. As more nodes are added, the reliability and connectivity of the network increases.
One of the first steps in the deployment of a WMN is finding appropriate locations for the mesh routers. Ideal locations are away from possible danger, the higher the better, with little or no surrounding objects to cause interference.
There are other considerations when deploying an emergency WMN. The evaluation of existing communication systems, such as police and ambulance services should be conducted to determine if the mesh routers can be connected to the existing emergency service networks.
The primary purpose of a communication network in a major emergency/disaster is to support the typically hierarchical command and control structure and to allow for the flow of information among all those involved in rescue operations.
From this Portman and Prizada (2008) identified four types of communication networks for public safety and disaster/emergency recovery applications:
Personal Area Networks (PANs) are made up of devices carried by individual first responders, PDAs, mobile phones or their rescue equipment. An example is fire-fighters with devices connected by a PAN that allow for the detection of hazardous gases or the monitoring of their vitals, location, and oxygen status.
An Incident Area Network (IAN) is a temporary network that is created for the duration of the rescue/recovery effort. IANs are necessary when the current fixed network infrastructure is unavailable at the incident scene, either due to their being destroyed, disabled or never existing. IANs allow first responders to share important information and coordinate their rescue efforts.
A Jurisdiction Area Network (JAN) is the primary communications network for the first responders and handles all non-IAN voice and data traffic.
JANs networks are normally installed by local emergency services or public safety agencies to provide a wide area (such as a city) communications infrastructure for use in emergency and disaster situations. First-responder client devices typically connect to JANs via an IAN but can also communicate directly via one or more JANs should a connection with the local IAN fail or be otherwise unavailable.
Extended Area Networks (EANs) provide wide area connectivity between various areas such as regional and national public safety networks.
(Portmann & Pirzada 2008)
The above figure gives a network diagram of these four types of networks and their interrelationships.
Due to their rapid deployment and self-configuration capabilities, WMNs are a promising technology for IANs and also great potential to serve as the basis for JANs. The key features of WMNs which are relevant to this context are their inherent fault tolerance, self-healing capability, and the low cost of wide area deployments.
Standardisation status of the involved techniques
“The availability of high-performance and low-cost hardware based on 802.11 standards has been one of the key drivers behind the recent surge of interest in WMN technology, in terms of both research and development.” (Portmann & Pirzada 2008)
Currently several companies provide mesh networking products for a range of applications, such as public safety and emergency/disaster recovery communications. Most of these products are based on IEEE 802.11 hardware, but unfortunately the majority implement their own proprietary mesh protocols for routing and network configuration, making integrating mesh routers from different vendors into a single WMN difficult, if not impossible. Currently several IEEE working groups are in the process of defining mesh networking standards.
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IEEE 802.11s may be the most important emerging standard for WMN technology, within the context of public safety and disaster recovery communications. 802.11s defines a default mandatory routing protocol (Hybrid Wireless Mesh Protocol, or HWMP), yet allows vendors to operate using alternate protocols. It endeavours to further develop the media access control (MAC) protocol of 802.11 networks to support mesh functionality. This is different to current WMNs, because they implement mesh functionality at the network layer.
Case study from real-world examples, successful stories, industry projects, academic/university testbeds etc.
Bind the sections together in a good overview.
Draw conclusions based on your investigation.
Any further reflection and discussion.
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