**NATIONAL COMMUNICATIONS SYSTEM**

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height="1.4069444444444446in"}

Route Diversity Project

Wireless Communications Capabilities

White Paper

> Evaluation of Wireless Mesh Networking
>
> in Support of ESF #2 Disaster Response Role

February 2007

Contract Number: DCA100-01-D-4001

CDRL: A037 DI-MISC-80711A

Prepared for: Technology and Programs Division (N2)

P.O. Box 4502

Arlington, VA 22204-4502

Prepared by

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height="0.25833333333333336in"}

TABLE OF CONTENTS

[Executive Summary ES-1](#executive-summary)

[1.0 Introduction 1](#introduction)

[2.0 Purpose 1](#purpose)

[3.0 Wireless Mesh Networking 1](#wireless-mesh-networking)

[3.1 Introduction to Wireless Mesh Networking
2](#introduction-to-wireless-mesh-networking)

[3.2 Functionality 3](#functionality)

[3.2.1 Access 3](#access)

[3.2.2 Media Access Control and Physical Layers
4](#media-access-control-and-physical-layers)

[3.2.3 Routing Layer 5](#routing-layer)

[3.3 Wireless Mesh Network Applications
5](#wireless-mesh-network-applications)

[3.3.1 Voice Communications 5](#voice-communications)

[3.3.2 Video Communications 6](#video-communications)

[3.3.3 Data Services 6](#data-services)

[3.4 Wireless Mesh Technical Features
6](#wireless-mesh-technical-features)

[3.5 Wireless Mesh Networking Advantages and Disadvantages
8](#wireless-mesh-networking-advantages-and-disadvantages)

[3.5.1 Advantages of Wireless Mesh Networks
8](#advantages-of-wireless-mesh-networks)

[3.5.2 Disadvantages of Wireless Mesh Networks
9](#disadvantages-of-wireless-mesh-networks)

[3.6 Trends 10](#trends)

[3.6.1 IEEE 802.11s Standard Development
10](#ieee-802.11s-standard-development)

[3.6.2 Vendor Offerings 10](#vendor-offerings)

[3.6.3 Ongoing Wireless Mesh Implementations
11](#ongoing-wireless-mesh-implementations)

[4.0 Possible Scenarios and Deployment Approaches
11](#possible-scenarios-and-deployment-approaches)

[4.1 Scenario and Deployment Approach #1
12](#scenario-and-deployment-approach-1)

[4.1.1 Scenario #1 12](#scenario-1)

[4.1.2 Deployment Approach to Scenario #1
12](#deployment-approach-to-scenario-1)

[4.2 Scenario and Deployment Approach #2
14](#scenario-and-deployment-approach-2)

[4.2.1 Scenario #2 14](#scenario-2)

[4.2.2 Deployment Approach to Scenario #2
14](#deployment-approach-to-scenario-2)

[5.0 Recommendations 16](#recommendations)

[6.0 Next Steps 16](#next-steps)

[Appendix A: Functionality A-1](#__RefHeading___Toc156205686)

[Appendix B: Technical Features B-1](#appendix-b-technical-features)

[Appendix C: Acronyms C-1](#appendix-c-acronyms)

[Appendix D: References D-1](#appendix-d-references)

# Executive Summary

This document evaluates wireless mesh networking. It will support
Emergency Support Function (ESF) #2 Communications by helping the
National Communications System (NCS) accomplish its disaster response
role in coordinating the establishment of required temporary National
Security/Emergency Preparedness (NS/EP) telecommunications and the
restoration of permanent telecommunications services. In addition, as
part of the Route Diversity Project (RDP), the information in this paper
can help NCS member agencies to make educated decisions on appropriate
alternative communications infrastructures whenever typical methods of
transmission malfunction or experience failure. Managed by the NCS, the
RDP aids NCS member agencies by providing technical and regulatory
information to help them increase the resiliency of their
telecommunications networks \[1\].

Wireless mesh technology allows wireless broadband solutions to quickly
establish network connections over a metropolitan area network (MAN). A
wireless mesh network is a configuration of wireless access nodes that
allows for continuous connections to a network infrastructure by routing
data packets via intermediate nodes until a destination is reached.
Wireless mesh networks offer redundancy and reliability because the
network is easily extended with the addition of self-organizing nodes
requiring minimal setup, and alternate routes are automatically
calculated in the event a path becomes blocked. In addition, the
majority of wireless mesh networks and the standard currently in
development are based on 802.11 (Wireless Fidelity \[Wi-Fi\])
technology. As a result, wireless mesh networks can support numerous
communication applications (e.g., voice, video, text, and data
services), thereby offering mobility and greater flexibility in
communication capabilities.

Wireless mesh networks incorporate a wide range of radio technologies
and routing protocols because manufacturers are currently providing
proprietary solutions due to the lack of a formal wireless mesh
networking standard. In addition, issues with scalability and security
still remain unresolved; throughput continues to degrade significantly
with each additional hop, and security schemes are not designed for
multi-hop communication links. However, an Institute of Electrical and
Electronic Engineers (IEEE) task group is currently developing the
802.11s wireless mesh network standard to solve existing problems, and
interoperability will become less of an issue once the standard is
approved.

Government departments and agencies responding to a disaster can use
wireless mesh technology whenever a rapidly deployable network is
necessary to provide temporary backup communications. A properly
installed wireless mesh network will allow local, state, and federal
agencies to stay connected at all times, supporting their efforts to
successfully coordinate emergency operations and route diversity
missions.

Incident commanders can apply their wireless mesh networking experience
when assessing an emergency situation and selecting a solution to
coordinate emergency response missions. This document is intended to
promote understanding of how wireless mesh technology and the deployment
of such solutions will fulfill disaster communication needs.

# 1.0 Introduction 

Following the attacks of September 11, 2001, initial reports indicated
that telecommunications assets near the impacted areas were either
congested or incapacitated, causing users to experience a lack of voice
service or intermittent service at best. This situation generated
concern that key federal agencies in Washington, DC, were at risk of
losing critical wireline telecommunications services if the
infrastructure was damaged or destroyed. The National Communications
System (NCS), tasked by the National Security Council (NSC), addressed
this concern by initiating the Backup Dial Tone Project, now known as
the Route Diversity Project (RDP). As a part of this project, the NCS
has pursued demonstrations and performance evaluations of several
technologies to test and analyze the ability of each to mitigate
vulnerabilities found in agency wireline networks and to provide backup
communications during emergency situations.

In the wake of Hurricane Katrina, the NCS, in its role as Emergency
Support Function (ESF) #2 lead, was responsible for coordinating the
restoration of National Security/Emergency Preparedness (NS/EP)
telecommunications services and facilities. Outages in the public
switched telephone network (PSTN) pointed out the need for further
evaluation of wireless technologies to support alternate means of
communications across the impacted geographic areas, not just for a
single facility or agency campus. The RDP, in support of ESF #2, is
currently preparing white papers on the following wireless technologies:
Wireless Fidelity (Wi-Fi), Worldwide Interoperability for Microwave
Access (WiMAX), and Wireless Mesh Networking. These white papers will
support network planners in designing and implementing communications
for public and private networks, both in support of day-to-day
operations and as a backup during emergency situations.

This paper focuses on wireless mesh networking, which is a method to
route data, voice, and video transmissions between nodes or wireless
routers before the signal reaches its destination. Wireless mesh
networks are capable of providing high-speed connectivity to computers,
telephones, and personal devices (e.g., personal digital assistant
\[PDA\]). This capability may provide localized and regional network
coverage in the event of a wireline network failure.

# 2.0 Purpose

This technology evaluation White Paper documents and analyzes the
functionality, applications, and features of wireless mesh networks. The
specific features selected for analysis are common to most wireless
technologies and allow a common platform for comparison. The paper
addresses current trends, as well as how progress with wireless mesh
technology is leading to the development of a formal standard. It also
assesses operational issues, potential deployment scenarios, and success
stories and provides recommendations for the use of wireless mesh
networks for backup communications.

# 3.0 Wireless Mesh Networking

This section provides an overview of wireless mesh networking and
discusses various aspects, including functionality, wireless mesh
network applications, technical features, advantages and disadvantages
of wireless mesh networks, and current trends in the technology.

## 3.1 Introduction to Wireless Mesh Networking

Wireless mesh networking defines a technology in which nodes within a
network act as repeaters to relay packets of wireless data through
intermediate nodes until the data reaches its destination. The result is
a wireless network that can span large distances. Wireless mesh networks
comprise two types of nodes: mesh routers and mesh clients. In addition
to providing the routing capability for gateway/bridge functions as in a
conventional wireless router, mesh routers contain additional routing
protocols to support multiple hops in a wireless mesh network. Thus,
mesh routers can achieve the same coverage with much lower transmission
power. Mesh clients are capable of sending and receiving messages, but
can also function as a router to relay data to neighboring nodes. The
hardware and software platforms for mesh clients are much simpler than
those for mesh routers in order to accommodate mobility. This type of
infrastructure is decentralized, reliable, resilient, and relatively
inexpensive because each node needs to transmit only as far as the next
node \[2\].

Wireless mesh networks can be employed in one of two arrangements: a
full mesh topology or a partial mesh topology. In a full mesh topology,
each node is directly connected to all of the other nodes in the
network, whereas in a partial mesh topology, nodes are only connected to
some of the other nodes. As a result, wireless mesh networks are
considered very reliable. If one node drops out of the network because
of hardware failure or for any other reason, neighboring nodes simply
find another route. Thus, wireless mesh networks are considered
dynamically self-organized and self-configured, whereby nodes
automatically establish an ad hoc network to maintain connectivity
\[3\]. A typical wireless mesh infrastructure is illustrated in Figure
1.

![](media/image3.jpeg){width="6.238194444444445in"
height="3.022222222222222in"}

Figure 1. A typical wireless mesh network \[4\]

Wireless mesh technology can incorporate various radio technologies;
however, current mesh networks typically use the Wi-Fi technology
platform to establish a wireless network. Because a formal wireless mesh
networking standard is lacking, the majority of mesh networking
solutions on the market are proprietary and employ various routing
protocols, and therefore will not interoperate with solutions
manufactured by different vendors. As a result, an Institute of
Electrical and Electronics Engineers (IEEE) task group is currently
developing the 802.11s standard for Extended Service Set (ESS) Mesh
Networking to solve the interoperability problem by defining an
architecture and protocol that support both broadcast/multicast and
unicast delivery \[5, 6, 7\].

Wireless mesh networks are designed for wireless metropolitan area
networks (WMAN) and are capable of extending service coverage simply
through the installation of additional nodes. This feature enables
wireless mesh networks to support voice, video, and data services over
longer distances. However, current routing protocols have scalability
issues, because throughput drops significantly as the number of nodes or
hops increases. Overall, wireless mesh networking could allow people
living in remote areas and small businesses operating in rural
neighborhoods to connect their networks for affordable Internet
connections \[8\].

Finally, wireless mesh networking can be used in conjunction with other
emerging wireless technologies, such as WiMAX, to extend the coverage
area of the network and to provide high-speed mobile data and
telecommunications services. For example, WiMAX can be used as a
backhaul technology to connect multiple mesh networks with each other
and to external servers. WiMAX networks are based on the IEEE 802.16
standards \[9\]. Table 1 provides a high-level comparison between Wi-Fi,
WiMAX, and wireless mesh networking technologies.

Table 1. High-Level Comparison of Emerging Wireless Broadband
Technologies \[9, 10, 11\]

+---------+-------------------+-------------------+-------------------+
| **Techn | **Wi-Fi**         | **WiMAX**         | **Wireless Mesh** |
| ology** |                   |                   |                   |
+---------+-------------------+-------------------+-------------------+
| **Fea   | -   WLANs (e.g.,  | -   Metropolitan  | -   Peer-to-peer  |
| tures** |     indoor,       |     area networks |                   |
|         |     office,       |     (MAN)         |   communications, |
|         |     campus        |                   |     with each     |
|         |     environment)  | -   PMP and P2P   |     mobile user   |
|         |                   |     capabilities  |     acting as a   |
|         | -   PMP mode,     |                   |     client and    |
|         |     with each     | -   Can operate   |     router        |
|         |     client        |     in            |                   |
|         |     connected to  |     line-of-sight | -                 |
|         |     an AP; P2P    |     and non       |  Self-organizing, |
|         |     mode, with    |     line-of-sight |     self-healing, |
|         |     each mobile   |     situations    |     and           |
|         |     user          |                   |                   |
|         |     connected     | -   Supports      |  auto-configuring |
|         |     directly to   |     fixed,        |                   |
|         |     the others    |     portable, and | -   Typically     |
|         |                   |     mobile        |     uses wireless |
|         | -   Can operate   |                   |     technologies  |
|         |     in            |    communications |     in the        |
|         |     line-of-sight |                   |     unlicensed    |
|         |     and non       | -   Typically     |     band,         |
|         |     line-of-sight |     used as a     |     including     |
|         |     situations    |     backhaul to   |     Wi-Fi         |
|         |                   |     connect       |                   |
|         | -   Supports      |     multiple      |                   |
|         |     fixed,        |     Wi-Fi         |                   |
|         |     portable and  |     hotspots to   |                   |
|         |     mobile        |     external      |                   |
|         |                   |     networks      |                   |
|         |    communications |                   |                   |
+---------+-------------------+-------------------+-------------------+

## 3.2 Functionality

### 3.2.1 Access

Wireless mesh network architectures can be configured in one of three
ways: infrastructure/backbone wireless mesh networks, client wireless
mesh networks, or hybrid wireless mesh networks. In the
infrastructure/backbone wireless mesh network, mesh routers can connect
to the Internet and provide a backbone for conventional clients through
gateway/bridge functionalities. In contrast, client wireless mesh
networks provide peer-to-peer networks among client devices, in which
mesh client nodes perform routing and configuration functionalities, as
well as provide end-user applications to customers. The hybrid wireless
mesh network architecture is a combination of infrastructure and client
meshing, in which mesh clients can access the network through mesh
routers as well as directly mesh with other mesh clients. With this type
of network topology, wireless mesh networks can organize themselves,
select the best path for user traffic, route around failures or
congestions, and provide secure connections \[2\].

Mesh clients within a wireless mesh network typically associate and
authenticate with other nodes on the network in the same way as a client
connects to an access point (AP) in a Wi-Fi network. When a new mesh
client joins a wireless mesh network, it broadcasts its presence to
listeners on the network with a simple discovery protocol. Existing
nodes recognize the new node and reconfigure and retune the network
transparently to incorporate it \[12\].

The routing functionality is performed differently because each node
frequently recalculates the best path based on received signal strength,
throughput, error rate, and latency. Using ad hoc routing protocols,
nodes plan the route that will make the fewest hops before reaching a
wired connection or a backhaul node. As previously mentioned, a formal
standard is lacking, and therefore, vendors use various routing
protocols to establish communication links between routers in a wireless
mesh network \[12\]. As a result, different vendor solutions will not
currently interoperate with each other.

### 3.2.2 Media Access Control and Physical Layers

In a wireless mesh network, the physical (PHY) layer determines the
capacity of a link and the quality of the communication, while the media
access control (MAC) layer coordinates access among the distributed
nodes. A key challenge in mesh networks is the need for sufficient
network capacity to meet the requirements of applications, especially
when network density increases over time and newer applications require
higher throughputs. To further increase capacity, multi-antenna systems
such as antenna diversity, smart antenna, and multiple-input
multiple-output (MIMO) systems have been proposed for wireless
communications. In addition, wireless radios in mesh networks use
schemes such as orthogonal frequency division multiplexing (OFDM) and
ultra-wide band (UWB) techniques to support high-speed transmissions
\[2\].

Differences exist in the MAC layer of wireless mesh networks compared to
traditional wireless networks (e.g., Wi-Fi, WiMAX). The MAC layer for
wireless mesh networks is concerned with multiple hop communications,
whereas other technologies are only concerned with single hop
communication links. In addition, the MAC presents distributed control,
rather than centralized control, to better enable
multipoint-to-multipoint communications across various client nodes.
Network self-organization is also needed for better collaboration
between neighboring nodes. Finally, the MAC protocol for wireless mesh
networks can be designed to work on a single channel or multiple
channels simultaneously \[2\]. Appendix A provides additional detailed
information about the MAC and PHY layers of wireless mesh networks.

### 3.2.3 Routing Layer

Currently, many routing protocols for ad hoc networks exist, but this
area is still considered one that requires additional research. One
reason for the variety of routing protocols for wireless mesh networks
is the lack of a standard, which would define its operation. Another
reason for the abundance of routing protocols includes the range of
applications for wireless mesh networks, which can have diverse
operational requirements. An optimal routing protocol for wireless mesh
networks will capture the following performance metrics, including
scalability, reliability to avoid link failures or congestion, and
efficient routing within the mesh infrastructure \[13\]. Appendix A
provides additional detailed information about the routing layer of
wireless mesh networks.

## 3.3 Wireless Mesh Network Applications

Wireless mesh networking can be used for various applications, including
voice communications, video communications, and various data services.
This section describes how wireless mesh networks support these
applications.

### 3.3.1 Voice Communications

Internet telephony, better known as Voice over Internet Protocol (VoIP),
is a technology that allows for transport of voice traffic using an
Internet Protocol (IP) network infrastructure. The maturity of IEEE
802.11 Wi-Fi technologies has allowed for improved support of VoIP and
wireless Internet telephony. Common VoIP consists of
[hardware](http://www.webopedia.com/TERM/V/hardware.html) (e.g., call
servers and routers) and
[software](http://www.webopedia.com/TERM/V/software.html) (e.g., voice
codecs) components that enable users to use the
[Internet](http://www.webopedia.com/TERM/V/Internet.html) as the
transmission medium for telephone calls; IEEE 802.11 Voice over Wi-Fi
(VoWi-Fi) is the wireless version of this technology designed to work
with wireless devices (e.g.,
[laptop](http://www.webopedia.com/TERM/V/laptop_computer.html)s,
personal digital assistants
\[[PDA](http://www.webopedia.com/TERM/V/PDA.html)\], and wireless IP
phones). Based on IEEE 802.11 Wi-Fi technology, as described in Section
3.2.1, VoWi-Fi via wireless mesh networks provides mobile users (e.g.,
agency, law enforcement, emergency response, command and control \[C2\],
and incident personnel) reliable voice communications during critical
missions with the ability to roam flexibly in a wireless environment.

Typically, a VoWi-Fi user device connects to an AP in a wireless mesh
network to authenticate to a designated backbone VoIP network. Once
associated to an AP and authenticated to the appropriate VoIP network, a
user has the capability of mobile voice communications across a
wide-area footprint. The self-routing mechanisms between neighboring
nodes in wireless mesh networks allow for more reliable communications
even when typical communication paths may be hindered or unavailable,
allowing for improved and flexible support of various challenging
short-and long-term voice service needs, such as in commercial,
healthcare, private, C2, and incident site environments.

### 3.3.2 Video Communications

Maturity among IP networks and VoIP technology has generated popular use
of multimedia communications. Multimedia communications (e.g., video
conferencing) allow users at distant locations using a packetized
network to interact in real time with full-motion video and audio. Two
video conferencing sites can interact "face-to-face" or join a call with
several other sites in a virtual meeting room. This capability has led
many commercial, private, and government organizations to adopt VoIP
video (video and audio) as an alternative medium for conducting
important conferences, surveillance, and situational awareness. In turn,
the ability to view unfolding events in real time allows a dispatcher or
commanding personnel to coordinate with appropriate support (e.g., law
enforcement, emergency medical service \[EMS\], and firefighters) to
provide even more improved onsite response.

Video applications over wireless mesh networks operate similarly to
VoWi-Fi, because support of both applications is based on Wi-Fi
technologies. Video IP-enabling software is initially installed on a
wireless-enabled user device. A wireless user, associated to an AP or
node in a wireless mesh network, initiates a conference session via the
Session Initiation Protocol (SIP) with a wired or wireless video
IP-enabled user, using the transmission control protocol (TCP)/IP
transport layer protocol. Once a session has been initiated and
appropriate packet acknowledgements have been received, the initiating
user is capable of sending real-time video traffic and audio (usually
compressed) to the destination user over a flexible and scalable
packetized network.

### 3.3.3 Data Services

Wi-Fi-based wireless mesh networks are capable of supporting data
applications used by a majority of the information technology (IT) user
community. Foremost is unified communications, an application set that
aims to tie together voice-mail, e-mail, fax, video, and instant
messaging. These applications are more critical today because of the
increase in the number of mobile workers and the availability of devices
with such capabilities.

For example, law enforcement officers deployed in different locations
can send critical text messages, such as strategic guidance, to one
another by using Wi-Fi-based wireless mesh networks. A mobile office
user can exchange e-mails with other users while walking between
buildings in a multi-building campus environment. In a wireless mesh,
EMS can access hospital databases to receive and view streaming
multimedia documentation for assistance in providing immediate patient
care, because one node can automatically discover and use a neighboring
node as a relay. Mobile warfighters located anywhere within a wireless
mesh network can query a base's information system to download critical
maps describing an area's geography.

## 3.4 Wireless Mesh Technical Features

As described previously, wireless mesh networks are essentially composed
of IEEE 802.11 Wi-Fi nodes in a mesh configuration. In the mesh
configuration, each node not only communicates to client users, but can
also communicate directly to neighboring nodes. The Wi-Fi standards that
have been typically used in wireless mesh networks include IEEE 802.11a,
b, and g.

Although nodes in wireless mesh networks operate similarly to typical
non-mesh Wi-Fi APs, there are several additional technical attributes
that are distinct to wireless mesh operations. Typical 802.11 a, b, and
g standards support some measure of security using mechanisms such as
Wired Equivalent Privacy (WEP) and Wi-Fi Protected Access (WPA)
developed by the Wi-Fi Alliance. Security between wireless mesh nodes is
currently supported by WPA, WPA2, and the development of the IEEE
802.11i security standard, which incorporates mechanisms such as
Temporal Key Integrity Protocol (TKIP) and Advanced Encryption Standard
(AES) \[14\].

The 802.11a standard supports wireless access in the 5 Gigahertz (GHz)
frequency range, whereas the 802.11b and g standards support the
unlicensed band 2.4 GHz. While the 802.11b and g standards can support
wireless access up to about 300 feet indoors and 1,000 feet outdoors,
the 802.11a standard supports wireless access at a lesser range of up to
approximately 225 feet. Additionally, both the 802.11a and g standards
can support high-speed data rates up to approximately 54 megabits per
second (Mbps), while the 802.11b standard supports data speeds up to 11
Mbps \[10, 11\].

Wi-Fi was originally designed for best-effort services. To enable
Quality of Service (QoS) techniques in Wi-Fi networks, the IEEE 802.11
committee passed the 802.11e specification in September 2005 to define
changes to the operation of the 802.11 MAC layer that enables
prioritization and classes of service \[15\]. To support faster roaming
between nodes, wireless mesh network nodes incorporate the IEEE 802.11r
working standard, which lowers hand-off delays \[16\].

The IEEE 802.11s standard, expected to be finalized by 2008, aims to
integrate routing at the MAC layer to increase routing and hand-off
efficiency by providing a protocol for auto-configuring paths between
nodes over self-configuring multi-hop topologies \[17\]. Table 2
summarizes those technical features for the various Wi-Fi technologies
used in wireless mesh networks.

Table 2. High-Level Comparison of Wireless Mesh Network Technologies
\[10, 11, 13, 18\]

+---------+------------+------------+-------------+------------------+
| **Te    | **Wireless |            |             |                  |
| chnical | Mesh       |            |             |                  |
| Fe      | Tech       |            |             |                  |
| ature** | nologies** |            |             |                  |
+=========+============+============+=============+==================+
|         | *          | *          | **802.11g** | **Wireless Mesh\ |
|         | *802.11a** | *802.11b** |             | Configuration**  |
+---------+------------+------------+-------------+------------------+
| **Sec   | [[WEP      | [[WEP      | [[WEP]{.un  | WPA, WPA2,       |
| urity** | ]{.underli | ]{.underli | derline}](h | 802.11i          |
|         | ne}](http: | ne}](http: | ttp://www.w |                  |
|         | //www.webo | //www.webo | ebopedia.co |                  |
|         | pedia.com/ | pedia.com/ | m/quick_ref |                  |
|         | quick_ref/ | quick_ref/ | /WEP.html), |                  |
|         | WEP.html), | WEP.html), | [[WPA]{.u   |                  |
|         | [[WP       | [[WP       | nderline}]( |                  |
|         | A]{.underl | A]{.underl | http://www. |                  |
|         | ine}](http | ine}](http | webopedia.c |                  |
|         | ://www.web | ://www.web | om/quick_re |                  |
|         | opedia.com | opedia.com | f/WPA.html) |                  |
|         | /quick_ref | /quick_ref |             |                  |
|         | /WPA.html) | /WPA.html) |             |                  |
+---------+------------+------------+-------------+------------------+
| **Fr    | 5 GHz/     | 2.4 GHz/   | 2.4 GHz/    | 5GHz (802.11a)   |
| equency |            |            |             | 2.4GHz           |
| Band/** | OFDM       | 11         | [[OFDM]{.un | (802.11b/g) with |
|         |            | Channels,  | derline}](h | self-channel and |
| **      |            | [[DSSS     | ttp://www.w | frequency        |
| Channel |            | ]{.underli | ebopedia.co | selection        |
| Modul   |            | ne}](http: | m/quick_ref |                  |
| ation** |            | //www.webo | /OFDM.html) |                  |
|         |            | pedia.com/ | above 20    |                  |
|         |            | quick_ref/ | Mbps,       |                  |
|         |            | DSSS.html) | [[DSSS]{.un |                  |
|         |            | with       | derline}](h |                  |
|         |            | [[CC       | ttp://www.w |                  |
|         |            | K]{.underl | ebopedia.co |                  |
|         |            | ine}](http | m/quick_ref |                  |
|         |            | ://www.web | /DSSS.html) |                  |
|         |            | opedia.com | with        |                  |
|         |            | /quick_ref | [[CCK]{.u   |                  |
|         |            | /CCK.html) | nderline}]( |                  |
|         |            |            | http://www. |                  |
|         |            |            | webopedia.c |                  |
|         |            |            | om/quick_re |                  |
|         |            |            | f/CCK.html) |                  |
|         |            |            | below 20    |                  |
|         |            |            | Mbps        |                  |
+---------+------------+------------+-------------+------------------+
| **Range | Shorter    | 300 feet   | 300 feet    | Minimum range    |
| and     | range than | (indoors)  | (indoors)   | based on 802.11a |
| Cov     | 802.11b    |            |             | or b/g.          |
| erage** | (\~225     | 1,000 feet | 1,000 feet  |                  |
|         | feet)      | (outdoors) | (outdoors)  | Maximum range    |
| *(c     |            |            |             | based on the     |
| ommonly |            |            |             | number of nodes  |
| adver   |            |            |             | in configuration |
| tised)* |            |            |             |                  |
+---------+------------+------------+-------------+------------------+
| **Data  | Up to 54   | Up to 11   | Up to 54    | Minimum rate     |
| Rate**  | Mbps       | Mbps       | Mbps        | based on 802.11a |
|         |            |            |             | or b/g.          |
|         |            |            |             |                  |
|         |            |            |             | Maximum rate     |
|         |            |            |             | based on the     |
|         |            |            |             | number of node/  |
|         |            |            |             | hops             |
+---------+------------+------------+-------------+------------------+
| **      | 802.11e    | 802.11e    | 802.11e     | 802.11e          |
| Quality |            |            |             |                  |
| of      |            |            |             |                  |
| Service |            |            |             |                  |
| (QoS)** |            |            |             |                  |
+---------+------------+------------+-------------+------------------+
| **Sca   | Yes        | Yes        | Yes         | Yes              |
| lable** |            |            |             |                  |
+---------+------------+------------+-------------+------------------+
| **C     | Not        | Int        | In          | Uses 802.11      |
| ompatib | int        | eroperable | teroperable | a/b/g            |
| ility** | eroperable | with       | with        |                  |
|         | with       | 802.11g.   | 802.11b.    |                  |
|         | 802.11b/g  | Not        | Not         |                  |
|         |            | int        | in          |                  |
|         |            | eroperable | teroperable |                  |
|         |            | with       | with        |                  |
|         |            | 802.11a    | 802.11a     |                  |
+---------+------------+------------+-------------+------------------+
| **Ro    | Pa         | Pa         | P           | 802.11r          |
| aming** | ss-through | ss-through | ass-through |                  |
|         | support of | support of | support of  |                  |
|         | 802.11r    | 802.11r    | 802.11r     |                  |
+---------+------------+------------+-------------+------------------+
| **R     | Pa         | Pa         | P           | 802.11s          |
| outing/ | ss-through | ss-through | ass-through |                  |
| Han     | support of | support of | support of  |                  |
| d-off** | 802.11s    | 802.11s    | 802.11s     |                  |
+---------+------------+------------+-------------+------------------+

Appendix B provides additional detailed information about each 802.11
attribute mentioned above, along with additional focus on security and
QoS.

## 3.5 Wireless Mesh Networking Advantages and Disadvantages

This section discusses the primary advantages and disadvantages
associated with wireless mesh networking.

### 3.5.1 Advantages of Wireless Mesh Networks

Network connections based on wireless mesh technology present many
benefits to users, especially in the areas of reliability, ease of
deployment, and cost. Wireless mesh networks are inherently redundant
and reliable because each node is connected to several other nodes
within the network. If one node falls out of the network, neighboring
nodes are able to dynamically configure an alternate route, because each
node maintains an up-to-date list of nearby nodes and frequently
recalculates the optimal path between adjacent nodes. In addition, if
the network changes in any way, nodes quickly reconfigure their routing
tables to manage traffic flow \[12\]. Wireless mesh networks, therefore,
are self-healing and self-organizing. Wireless mesh networks also
present an alternative to wireless switching, which eliminates
centralized failure because nodes are able to communicate with other
nodes without being routed through a central switch point.

Wireless mesh networks also greatly simplify the deployment process of
wireless metropolitan area networks because extensive amounts of wiring
are no longer necessary. Mesh networks do not require elaborate planning
or site mapping because a mesh node is simply thrown into a network
(e.g., installed on a post or building) and will automatically configure
itself to connect to the network. In addition, the mesh network can be
easily extended by installing additional nodes, thereby improving
wireless range and bandwidth to support other services (e.g., public
utility meters, bus stops and train stations, and government services)
\[12\]. User acceptance is also expedited because most applications are
based on the IEEE 802.11 (Wi-Fi) technology. Wireless mesh networking
offers users situated in locations not accessible by wires with an
alternative method for easily connecting to a nearby network in order to
perform high-speed voice, video, and data services.

Wireless mesh networking also significantly reduces the number of
backhaul nodes, as well as deployment and operational expenses. In a
mesh network, APs act as intermediate data transmission nodes or
routers, and connect to each other wirelessly. Thus, the need for
Internet gateways is decreased because only a small fraction of APs are
directly connected to the network. Operating costs are lowered because
the lower power requirements of wireless mesh networks can be satisfied
with low-cost or renewable energy sources. In addition, excessive costs
due to labor are eliminated because wireless mesh networks are
self-organizing and require minimal set up \[12\]. The auto-recovery
feature also helps reduce labor costs since a technician is not required
to reestablish transmission paths. All of these benefits make wireless
mesh networking a leading technology to support backup wireless
communications.

### 3.5.2 Disadvantages of Wireless Mesh Networks

Although wireless mesh networking is growing in popularity, a few
limitations must be taken into account before initiating deployment.
There are several challenges in deploying mesh networks, mainly because
there are currently no official standards for them. The development of
the IEEE 802.11s standard, which addresses mesh networks, is in
progress, with a targeted draft release date in 2007. As a result, mesh
equipment (e.g., mesh routers, mesh clients) on the market today uses
various routing protocols and will likely be obsolete after ratification
of the 802.11s standard. Current solutions are not interoperable because
of the proprietary nature of vendor solutions and use of various 802.11x
Wi-Fi technologies.

Some of the major challenges with wireless mesh networking include
scalability and security. In networks that use link state or distance
vector routing protocols, the amount of routing overhead increases as
the number of nodes in the network grows. In addition, network
performance degrades significantly as the number of nodes or hops in a
wireless mesh network increases. For example, routing protocols may not
be able to find a reliable routing path, transport protocols may lose
connections, and MAC protocols may experience substantial throughput
reduction. Wireless mesh networks also lack efficient and scalable
security solutions due to the nature of being a distributed network
architecture, having a shared wireless medium, and the ability for the
network topology to change. There is no centralized trusted authority to
distribute a public key in a wireless mesh network. In addition,
existing security schemes are not designed to support multiple hop
communication links found in wireless mesh networks \[2\].

Wireless mesh networks also face general wireless issues such as
bandwidth constraints and radio frequency (RF) connectivity because
wireless links provide limited bandwidth, which is affected by the
surrounding environment and may not be available at all times because of
interference and propagation problems. In addition, there are energy
constraints in which devices that operate on a battery will experience a
shorter operating lifetime due to the added routing capability in each
node. Lastly, there are no schemes currently available to allow wireless
mesh networks to fully support real-time delivery of multimedia traffic.

## 3.6 Trends

This section explains the 802.11s standard development in progress,
market vendor solutions, and ongoing wireless mesh networking
implementations.

### 3.6.1 IEEE 802.11s Standard Development

As mentioned in previous sections, there is no formal standard for
wireless mesh networks at this time. However, an IEEE task group is
currently working to develop the 802.11s standard for ESS wireless mesh
networks, which specifies enhancements to the 802.11 MAC to define
capabilities in several areas, including topology discovery, path
selection and forwarding, channel allocation, security, traffic
management, and network management. The task group is working on a path
selection protocol called Hybrid Wireless Mesh, which allows vendors to
use their own protocols for path selection that will be interoperable
with each other. In addition, the task group intends to extend the
security mechanisms specified in 802.11i to support multiple hop
security. Distributed and centralized authentication schemes will also
need to be supported, and re-authentication must occur rapidly for
roaming nodes to preserve session persistence or continuous connectivity
within the network. Finally, extensions to the QoS mechanisms defined in
802.11e are being considered to support hop-by-hop congestion control,
and the task group is looking at ways to implement rate control to
reduce congestion \[6, 7, 11\].

The IEEE task group issued a call for proposals, received 15 of them in
response, and selected 2 for further development. The Wi-Mesh proposal
intends to provide seamless communications for wireless users regardless
of vendor and is designed to work for consumer and small business,
metropolitan, and military applications. On the other hand, the SEEMesh
proposal introduces mesh portals, which offer interoperability to mesh
networks by allowing older and newer wireless standard technology to be
recognized and incorporated into the network. The two proposals were
merged in January 2006 and the standard is targeted to be ratified by
2008 \[19, 20\].

Because a formal wireless mesh networking standard is lacking, the
majority of mesh networking solutions on the market are proprietary and
employ various routing protocols, and therefore will not interoperate
with solutions manufactured by different vendors.

### 3.6.2 Vendor Offerings

Wireless mesh networking has given rise to numerous manufacturers
dedicated to developing integrated solutions to deliver broadband
services to homes, businesses, and communities. Many manufacturers
provide proprietary wireless mesh solutions to support high-speed voice,
video, and data applications. However, the wireless mesh equipment that
is provided will not interoperate with other vendor solutions, since
different radio technologies are employed because a formal wireless mesh
standard is lacking. Currently, vendors offer a wide range of indoor and
outdoor wireless mesh hardware and software, including APs, routers, and
client devices (e.g., laptops, PDAs), that are typically based on Wi-Fi
technology, with the incorporation of additional routing capabilities.
With the approval of a wireless mesh standard, vendor solutions
currently on the market will most likely become obsolete \[13\].

### 3.6.3 Ongoing Wireless Mesh Implementations

Full-scale, standard wireless mesh network deployments have not been
carried out in the United States because wireless mesh networking is a
fairly new technology and a formal standard has not yet been ratified.
However, the potential for wireless mesh networks in the U.S. broadband
market is growing due to service gaps that exist in many current
terrestrial networks (e.g., remote and rural areas); thus, vendors have
begun testing proprietary wireless mesh technology by implementing
networks in various cities across the United States.

In December 2006, the City of Southaven, Mississippi announced that it
will "unwire" the entire 36 square miles of the city with a metro-scale,
Wi-Fi mesh network to provide its residents with high-quality, wireless
broadband Internet access. This follows a growing trend among cities
across the United States, including Philadelphia, San Diego, San
Francisco, Chicago, and Minneapolis, that are implementing municipal
wireless mesh networks to provide low-cost Internet access to users
\[15\].

Also in December 2006, Hopling Technologies announced the development of
fourth-generation mesh equipment, including quad-radio Wi-Fi APs that
segment large wireless mesh networks into priority networks for public
safety and general public Internet access. Similarly, in August 2006,
Firetide Inc. announced a partnership with AgileMesh to produce wireless
video surveillance networks that public safety forces can deploy to give
them more eyes at crime and emergency scenes. In June 2006, ClearMesh
Networks announced the launch of its next generation wireless optical
mesh solution, which enables service providers to roll out
business-class services at 5 to100 Mbps to small and medium business
markets \[15\].

Although there have been significant advancements in wireless mesh
technology over the past couple of years, the main issue of
standardization still remains. Wireless mesh networks provide users the
transmission speeds and service range to support high-quality voice,
video, and data applications, but until a formal standard is approved,
wireless mesh equipment from different manufacturers will not be
interoperable, thereby limiting user acceptance.

# 4.0 Possible Scenarios and Deployment Approaches

Section 4.0 examines two WMAN deployment approaches developed, based on
the given scenarios, to mitigate possible communication vulnerabilities
or failures and improve coordination efforts by offering better
communication resources.

## 4.1 Scenario and Deployment Approach #1

This section describes a possible communications solution that leverages
an existing WMAN system to assist coordination and support of a
presidential campaign conference in a metropolitan city.

### 4.1.1 Scenario #1

An independent political party is hosting a conference in Chicago,
Illinois to increase voter support for its presidential candidate in the
upcoming election. Thousands of people are expected to attend to gain a
better understanding of the candidate's plans for the future. Because of
the anticipated large crowd, city officials decide to conduct the rally
outdoors. They will close off several city blocks along a major street
and set up a platform at the end of the route from which the candidate
will give his speech.

The City of Chicago decides that extra precautionary measures must be
taken to ensure a safe environment for all participants, including the
visiting presidential candidate. Secret Service personnel, law
enforcement officials, and emergency personnel must coordinate
effectively to prevent and mitigate any violent uprisings and
activities.

In order to avoid potential threatening situations, government officers
realize that security and emergency personnel must be provided with
technology capable of delivering critical information in a timely
manner. Because of the large crowds, many officials will be monitoring
the conference on foot or on bicycles; thus, the speed with which they
receive information is a very important factor. Security personnel and
first responders must be equipped with a solution that will provide
quick, flexible, and effective means of voice and video communications
and information access to mitigate any escalating circumstances and
ensure the safety of the presidential candidate and other participants.

### 4.1.2 Deployment Approach to Scenario #1

As a result of the situation described in Scenario #1, a solution is
needed that will provide quick and effective support to help security
personnel supervise the political conference efficiently and prevent any
potential problems, as well as protect the visiting presidential
candidate. The issues described previously require various
communications capabilities, including voice, video, text messaging, and
data access. This section describes how wireless mesh technology can be
used to perform fast, high-quality wireless communications to ensure
safety for all individuals during a planned large event.

In preparation for the political conference, the Federal Emergency
Communications Coordinator (FECC) learns that the city of Chicago
recently implemented a wireless mesh network based on IEEE 802.11
(Wi-Fi) technology. The FECC decides to use this network infrastructure
to provide security personnel with critical, high-speed, wireless
communications for the upcoming rally. The FECC immediately instructs
technicians to install Wi-Fi enabled surveillance cameras on top of
streetlamps to continuously monitor the street on which the rally will
take place. In addition, all Secret Service personnel are equipped with
an all-in-one, Wi-Fi certified portable device capable of conducting
voice, video, and data services. Because of the self-organizing feature
of wireless mesh networks, the surveillance cameras and portable devices
do not require any additional configuration to establish a connection
with the existing network. The FECC also decides to set up a command
center in a nearby office building that is capable of connecting to the
wireless mesh network to further provide effective monitoring and
coordination of incident response activities.

During the rally, a surveillance camera caught two protesters in a
nearby alley plotting to sabotage the events. The video transmissions
were forwarded to the command center where party officials were
notified. Coordinators, using a custom-defined private user group via
designated wireless mesh nodes, immediately performed video
teleconferences (VTC) with Secret Service agents in the vicinity,
providing physical descriptions of the potential perpetrators. All other
security personnel were notified via voice or text communications on a
different user group to standby in case the situation escalated. Within
a couple minutes, the two individuals were confronted and apprehended to
ensure the safety of all participants, including the presidential
candidate.

By using the existing wireless mesh infrastructure and quickly deploying
additional Wi-Fi capabilities, Secret Service personnel were able to
conduct reliable, high-quality voice and video communications and text
messaging across the city block and stay connected to security
coordinators at all times. Wireless mesh technology assisted the City of
Chicago to provide critical safety to the visiting presidential
candidate and thousands of political supporters through a seamless
process. Figure 2 illustrates the high-level deployment approach to a
solution that uses an existing wireless mesh network to support voice
and video communications, as well as surveillance and monitoring
applications.

![](media/image4.jpeg){width="5.7in" height="3.357638888888889in"}

Figure 2. Existing Wireless Mesh Scenario \[4\]

## 

## 4.2 Scenario and Deployment Approach #2

This section describes a possible WMAN solution that can be quickly
deployed in response to a large hurricane that destroys typical methods
of communications.

### 4.2.1 Scenario #2

A large hurricane strikes Miami, Florida with great force, cutting off
power to the entire city and knocking down many cellular and radio
towers, various antennas located on tall buildings, and telephone lines.
The storm also floods the switch offices that route calls, which
overwhelms phone lines and results in a defunct phone system. Residents
are unable to acquire further information about the storm because
typical communication services have been rendered inoperative. Thousands
of city residents have become trapped as a result of coastal flooding
and are in critical need of aid.

The storm begins to calm, but it is uncertain for how long. During this
window of opportunity, coordinating federal, regional, state, and local
relief agencies attempt to respond in a timely manner; however, typical
methods of communications between command and control officers and with
first responders fail due to damaged landline communications
infrastructures. Consequently, emergency workers are unable to
effectively receive critical instructions, leading to extreme confusion
and loss of valuable time. A rapidly deployable backup communications
system is necessary to coordinate emergency response to save the lives
of many trapped individuals.

### 4.2.2 Deployment Approach to Scenario #2

As multiple federal, state, and local agencies move into the area, an
FECC quickly sets up several command centers and field offices across
the city, but because of the malfunctioning of typical communication
methods, communications support for rescue efforts is drastically
hindered. Emergency relief workers are in desperate need of
interoperable voice communication capabilities with commanding officers
and other responders in order to receive instructions and to locate
victims.

The FECC decides to quickly deploy a citywide wireless mesh of Wi-Fi APs
that work together to provide communications backup during the disaster.
The Wi-Fi mesh is a self-correcting, decentralized, inexpensive, and
low-power network of Wi-Fi antennas. During deployment, technicians
place Wi-Fi nodes onto the rooftops of houses and buildings and allow
each node to automatically configure itself to connect to the network.
Each node is tactically spaced to ensure enough redundancy for adequate
coverage to not only share a connection to the Internet, but also
accommodate VoIP phone calls and text messaging.

The nodes are small, durable, and less vulnerable to damage from high
winds than cell phone towers. Once the nodes are deployed, using
standard off-the-shelf technology, emergency support coordinators are
issued portable Wi-Fi enabled emergency transponders to receive pages,
talk to one another, perform simple text messaging, transmit photographs
and video, and retrieve city road maps.

However, coverage gaps exist because the network was implemented in such
a short time period, resulting in communication breaks whenever
responders wander out of range. It is decided that the wireless mesh
architecture will be more effective if additional mesh routers are
placed in tactical vans to further support mobility. Now, as various
responders move around the city, the FECC and other coordinating agency
officials are able to maintain voice and video communications without
any service interruptions.

The wireless mesh network also integrates WiMAX technology to provide a
backhaul, creating high-speed links to external data systems and other
state agencies. Video over IP via a WiMAX backhaul is used to assess the
damaged area and to relay the information to the FECC, who then provides
the necessary instructions to other support agencies working to save the
citizens of Miami. In addition, the wireless mesh network based on Wi-Fi
technology is used to access news information (e.g., CNN), because
satellite connectivity is too difficult to establish under such adverse
weather conditions. Though still vulnerable to loss of power (although a
backup battery could keep each node running for days), these meshes
offer a viable alternative to a more vulnerable phone system and present
a realistic way to maintain communications with various disaster
response agencies and the outside world. Figure 3 illustrates the
Scenario #2 deployment.

![](media/image5.png){width="5.199305555555555in"
height="3.265972222222222in"}

Figure 3. Deployable Wireless Mesh Network Disaster Backup Scenario
\[4\]

As a result of implementing a wireless mesh network based on Wi-Fi
technology, emergency workers coordinated efforts to locate survivors
and provide quick assistance in cases where multiple responders were
needed to free a trapped individual. The ability to stay connected and
communicate with various relief agencies was key in preventing a rise in
the number of casualties.

# 5.0 Recommendations

The Federal Response Plan anticipates a variety of different emergency
situations, requiring a wide range of communication capabilities. Common
applications helpful during crisis situations include voice, video,
text, and data services. Whatever the need, NCS and other response
elements can leverage wireless mesh networking to provide temporary or
backup communications in support of these applications while in the
field to successfully complete critical missions and operations.
[]{.mark}

[]{.mark}

In certain emergency situations, wireless mesh technology should be
selected if high-speed communication applications are required over long
ranges. Wireless mesh networking is designed for metropolitan area
networks by incorporating additional routing nodes to increase
redundancy and extend common Wi-Fi network coverage areas and is a great
alternative to DSL and cable to fill service gaps in remote and rural
areas. Wireless mesh networks also provide high data rates to support
low latency applications such as VoIP and video teleconferencing.

A wireless mesh network should also be implemented when a broadband
wireless communication network must be established in a short period of
time. Compared to traditional broadband networks that require the
installation of extensive wiring, large amounts of time and money can be
saved by deploying a wireless mesh network. Wireless mesh networks can
be set up in a matter of hours by simply installing nodes in strategic
locations. The self-organizing feature of wireless mesh technology
enables nodes to configure themselves to connect to a network---a
technician is not needed to lay down wires.

Reliability is another major benefit of wireless mesh networks. If the
performance of high-speed voice, video, and data applications without
the threat of many service interruptions is desired, then a wireless
mesh network should be implemented rather than other wireless
technologies. The fact that each node within the network is connected to
several other nodes ensures that transmissions will reach their
destination even if a node temporarily falls out of the network. These
capabilities make wireless mesh technology an optimal solution for
communication needs during large-scale disaster events requiring the
coordination of several agencies and numerous personnel.

Finally, many vendors currently provide proprietary wireless mesh
network solutions, and the interoperability among these different
technologies is limited. Users should wait until the technology matures
and a single standard emerges before deploying a wireless mesh network;
however, if it is necessary to implement a wireless mesh network right
away, it is recommended that a single manufacturer's equipment be used
to ensure proper operation.

# 6.0 Next Steps

Wireless mesh technology can be incorporated into numerous equipment
items (e.g., routers, laptops, VoIP phones, etc.), with each capable of
supporting various applications depending on the level of technology
installed. Before deploying a wireless mesh network, disaster response
coordinators must perform specific assessments to determine if a
wireless mesh solution will best meet mission and operation needs in
times of crisis or emergency.

Initially, emergency communications coordinators must analyze and assess
the operating environment to understand mission requirements. For
example, requirements may vary depending on the size and location of an
emergency or other event. Based on the needs, relief agencies must
determine where traditional communication systems create gaps and work
toward determining enhanced solutions necessary to manage rescue efforts
and missions more efficiently and effectively. Vendor products need to
be evaluated and compared because many wireless mesh hardware solutions
are proprietary and tailored to support specific capabilities (e.g.,
residential use, enterprise use, internal versus external antennas).
Once all requirements and essential capabilities are defined, government
coordinators and command centers will be able to better select and
implement an appropriate wireless mesh network solution that will
simplify the coordination of emergency, incident, and tactical response
situations, leading to improved safety for all citizens.

The benefits of wireless mesh networks, including reliability and
greater flexibility in communications, make it an attractive alternative
to serve as a dependable backup communications system to current
networks, as well as an easily deployable communications solution in
disaster response scenarios. With proper research and engineering, the
deployment of wireless mesh networks will help federal departments and
agencies to be fully prepared to handle any emergency.

# Appendix A: Functionality

**A.1 Media Access Control and Physical Layers**

While the media access control (MAC) layer of most wireless technologies
covers single hop communications links, the MAC layer of wireless mesh
networks has been enhanced to enable multiple hop communications. In
addition, the MAC offers distributed control and works for
multipoint-to-multipoint communications. Network self-organization is
also needed for better collaboration between neighboring nodes. Finally,
the MAC protocol for wireless mesh networks can be designed to work on a
single channel or multiple channels simultaneously.

The majority of wireless mesh networks and the current mesh networking
standard under development are based on IEEE 802.11 technology and use
the Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) protocol
to access the medium. CSMA/CA is a method used to avoid two signals
colliding and canceling out each other. The process starts with the
sending station sensing the air for activity. If the channel is busy,
the transmission is scheduled for later, at which point the channel is
sensed again. If no activity is detected, the station waits an
additional random period of time and then transmits information if the
medium is still free. The receiving station sends a packet
acknowledgement (ACK) frame back to the sending station after it obtains
the data packet intact. The process is complete when the sending station
receives the ACK frame. If the ACK frame is not detected by the sending
station, either because the ACK was not received intact or the original
data packet was not received intact, a collision is assumed to have
occurred and the transmission process is restarted \[21\].

However, CSMA/CA is an inefficient random access protocol in multi-hop
networks because of poor scalability. In multi-hop mesh networks,
packets need to compete for medium access at each hop, resulting in the
reduction of throughput at each hop. Thus, it has been proposed to
revisit MAC protocol designs based on Time Division Multiple Access
(TDMA) or Code Division Multiple Access (CDMA). Nevertheless, this
solution would raise issues regarding the complexity and cost of
developing a distributed MAC with TDMA or CDMA, as well as the
compatibility of TDMA or CDMA MAC protocols with existing protocols
\[2\].

A request to send/clear to send (RTS/CTS) protocol is also available at
the 802.11 MAC layer. The RTS/CTS feature significantly reduces the
chances for collision and is used for larger size packets, where
retransmission would be expensive from a bandwidth standpoint. A sending
station requests authorization to transmit for a specific amount of time
by broadcasting an RTS frame before sending any information. If
approved, the receiving device broadcasts a CTS frame, at which point
the sending machine can transmit its information without any chance of
collision \[10, 11, 21\].

In the physical (PHY) layer, wireless mesh networks have employed
modulation techniques such as orthogonal frequency division multiplexing
(OFDM) to further increase capacity and support higher data rates. OFDM
is based on frequency division multiplexing (FDM), which uses multiple
frequencies to simultaneously transmit multiple signals in parallel
across a wired or wireless medium. The frequency spectrum is divided
into several subcarriers (also referred to as sub-channels), in which
each signal is transmitted over one subcarrier by modulating the
subcarrier with a standard modulation technique (e.g., phase-shift
keying \[PSK\], quadrature amplitude modulation \[QAM\]). The signal is
then demodulated at the receiver, using filters to separate the
individual carriers \[21\].

OFDM is more spectrally efficient than FDM by using frequencies that are
orthogonal, thereby allowing the spectrum of each sub-channel to overlap
one another without interference, thereby greatly improving the use of
available bandwidth. OFDM is also designed to accommodate either time
division duplexing (TDD) or frequency division duplexing (FDD)
deployments, allowing for both full- and half-duplex terminals in the
FDD case. TDD is a technique in which the system transmits and receives
within the same channel, assigning time slots for both transmit and
receive modes. Conversely, FDD requires two separate channels in order
to transmit and receive data \[21\].

Currently, wireless mesh networks incorporate a wide range of
proprietary technologies and protocols because a formal wireless mesh
networking standard does not exist. As a result, there are many MAC and
PHY layer issues for wireless mesh networks that have yet to be solved.
For instance, to make the MAC protocol scalable, new distributed and
collaborative schemes must be proposed to ensure that network
performance (e.g., throughput and Quality of Service \[QoS\] parameters
such as delay and delay jitter) will not degrade as the network size
increases. In addition, it is necessary to identify new wideband
transmission schemes for the PHY layer to achieve higher transmission
rates in a larger area network. The IEEE 802.11s standard for extended
service set (ESS) wireless mesh networks intends to enhance the existing
802.11 (Wi-Fi) MAC and PHY specifications in order to support multi-hop
transmissions.

**A.2 Routing Layer**

A routing algorithm is a convention or standard that controls the way in
which nodes agree to route data packets between computing devices until
the information reaches its destination. Many routing protocols
currently exist for wireless mesh networks, but the optimal routing
protocol must consider multiple performance metrics, scalability,
robustness, and efficient routing with a mesh infrastructure. Routing
algorithms must also keep routing tables reasonably small, choose the
best route for a given destination (e.g., fastest, most reliable,
highest throughput, or cheapest route), and keep routing tables
up-to-date to account for network topology changes. Routing tables
maintain a record of the best routes to various network destinations
\[13\].

Initially, all nodes in a wireless mesh network need to gather
information about the underlying network topology to know how to
communicate with other nodes. This process of gathering such information
can be done proactively, which disseminates routing information to other
nodes within the network even before it is needed, or reactively, which
gathers routing information on demand only when it is required.
Proactive methods have been determined to scale poorly in mobile
wireless mesh networks; however, there are methods which limit the scope
and frequency of dissemination of such routing information, resulting in
more robust and scalable proactive routing protocols. The reactive
method works well in wireless networks that continuously change in
topology and has been widely accepted for wireless mesh networks \[2,
13\].

Once all of the nodes gather information about the network, they must be
able to determine alternate routes to forward data to its destination if
a designated path becomes unavailable. The two most commonly used types
of routing algorithms are distance vector algorithms and link-state
algorithms. Distance vector algorithms assign a cost to each of the
links between each node in the network. Nodes will then route data from
its source to its destination via the path that results in the lowest
total cost. The basic concept of link-state routing is that every node
receives a map of the connectivity of the network in the form of a graph
showing which nodes are connected to which other nodes. Each node then
independently calculates the best next hop for every possible
destination in the network.

Distance vector algorithms and link-state algorithms both compute
least-cost paths using link cost as a performance metric. The most
common performance metrics in wireless mesh networks include expected
transmission count (ETX), round-trip time (RTT), and hop count. ETX is
the loss rate of broadcast packets between a pair of nodes, while RTT is
the round trip delay between a pair of nodes. Hop count is simply the
number of links between a pair of nodes \[13\].

Although numerous routing protocols have been designed for wireless mesh
networks, the more commonly used protocols include Dynamic Source
Routing (DSR), Hazy Sighted Link State (HSLS), Ad hoc On-Demand Distance
Vector (AODV), and Optimized Link State Routing (OLSR) \[13\]. The IEEE
802.11s wireless mesh network standard currently in development will
attempt to define a routing protocol that integrates multiple
performance metrics and solve the scalability issue (e.g., reduced
throughput as number of hops increase).

# Appendix B: Technical Features

**B.1 Security**

Wireless mesh networks are self-organized and rapidly deployed, offering
mobility and connectivity with minimal constraints anywhere and anytime.
However, wireless mesh networks are more vulnerable to attacks than
traditional networks because security can be more easily compromised.
Moreover, the distributed network architecture complicates the
deployment of trusted authorities.

The weak range of wireless transmission media requires the forwarding of
messages through intermediate nodes to guarantee the routing function.
Consequently, network nodes operate as routers because no centralized
infrastructure and services exist. The existence of anonymous and
temporary nodes in the routing function can represent a serious
weakness; therefore, several mechanism have been proposed to better
support wireless local area network (LAN) security in wireless mesh
networks.

Security in wireless mesh networks can be divided into two categories:
(1) solutions that are built into the wireless mesh components and (2)
solutions that are independent of actual components, but are
incorporated to support the standards used. Wireless mesh solutions with
incorporated security include techniques such as Wi-Fi Protected Access
(WPA/WPA2), Institute of Electrical and Electronic Engineers (IEEE)
802.11i, Temporal Key Integrity Protocol (TKIP), and 802.1X/Extensible
Authentication Protocol (EAP). Solutions that use additional security
not built into the Wi-Fi standard include techniques such as Internet
Protocol Security (IPSec), Secure Sockets Layer (SSL), or Point-to-Point
Tunneling Protocol (PPTP) encryption.

**B.1.1 IEEE 802.11i**

IEEE 802.11i is an amendment to the
[802.11](http://en.wikipedia.org/wiki/IEEE_802.11) standard specifying
security mechanisms for [wireless
networks](http://en.wikipedia.org/wiki/Wireless_LAN). The draft
standard, ratified in [June](http://en.wikipedia.org/wiki/June_24)
[2004](http://en.wikipedia.org/wiki/2004), supersedes the previous
security specification, [Wired Equivalent
Privacy](http://en.wikipedia.org/wiki/Wired_Equivalent_Privacy) (WEP),
which was shown to have severe security weaknesses. [Wi-Fi Protected
Access](http://en.wikipedia.org/wiki/Wi-Fi_Protected_Access) (WPA) had
previously been introduced by the [Wi-Fi
Alliance](http://en.wikipedia.org/wiki/Wi-Fi_Alliance) as an
intermediate solution to WEP insecurities. WPA implemented a subset of
802.11i. The Wi-Fi Alliance refers to its approved, interoperable
implementation of the full 802.11i as WPA2. 802.11i makes use of the
[Advanced Encryption
Standard](http://en.wikipedia.org/wiki/Advanced_Encryption_Standard)
(AES) [block cipher](http://en.wikipedia.org/wiki/Block_cipher); WEP and
WPA use the Ron's Code 4
([RC4](http://en.wikipedia.org/wiki/RC4_(cipher))) [stream
cipher](http://en.wikipedia.org/wiki/Stream_cipher) \[22\].

The 802.11i architecture contains the following components:
[802.1X](http://en.wikipedia.org/wiki/802.1X) for authentication
(entailing the use of
[EAP](http://en.wikipedia.org/wiki/Extensible_Authentication_Protocol)
and an [authentication
server](http://en.wikipedia.org/wiki/Authentication_server)); Robust
Secure Network
([RSN](http://en.wikipedia.org/wiki/Robust_Security_Network)) for
keeping track of wireless link associations; and AES-based Counter Mode
CBC-MAC Protocol ([CCMP](http://en.wikipedia.org/wiki/CCMP)) to provide
[confidentiality](http://en.wikipedia.org/wiki/Confidentiality),
[integrity](http://en.wikipedia.org/wiki/Data_integrity) and origin
[authentication](http://en.wikipedia.org/wiki/Authentication).

802.1X is incorporated in many network switches and can be configured to
authenticate hosts that are equipped with client software, denying
unauthorized access to the network at the data link layer. The
authentication is usually performed by a third-party component such as a
Remote Authentication Dial-In User Server/Service (RADIUS) server and
provides for client-only authentication. For example, upon detection of
a new client (supplicant), the port on the switch (authenticator) will
be enabled and set to the \"unauthorized\" state. In this state, only
802.1X traffic will be allowed; other traffic (e.g., DHCP and HTTP) will
be blocked at the data link layer. The authenticator will send out the
EAP-Request identity to the supplicant, and the supplicant will then
send out the EAP-response packet that the authenticator will forward to
the authenticating server. The authenticating server can accept or
reject the EAP-Request; if it accepts the request, the authenticator
will set the port to the \"authorized\" mode and normal traffic will be
allowed. When logging off, the supplicant will send an EAP-logoff
message to the authenticator. The authenticator will then set the port
to the \"unauthorized\" state, once again blocking all non-EAP traffic
\[22\].

**B.1.2 Wi-Fi Protected Access**

WPA, produced by the Wi-Fi Alliance, has two modes. The more complicated
mode is commonly used by large organizations and requires RADIUS servers
to distribute keying. The simpler of the two is based on distributing a
preshared key to all wireless clients: WPA-PSK. Key derivation for the
wireless link is based on random numbers exchanged along with the
preshared key. As with any protocol that uses a preshared key, WPA is
vulnerable to dictionary attacks. With the preshared key, an attacker
can monitor the four-way handshake and derive the unique key for any
other device \[22\].

**B.1.3 Temporal Key Integrity Protocol**

Part of the 802.11i standard, TKIP is designed to offer increased
security on wireless interfaces with hardware assistance for RC4. RC4 is
a stream cipher designed by Ron Rivest for RSA Data Security (now RSA
Security). It is a variable key-size stream cipher with byte-oriented
operations. The algorithm is based on the use of a random permutation.
To ensure frame integrity, TKIP is used with the Michael Integrity Check
to detect frame tampering during transport. TKIP was the first attempt
to mitigate the security gaps in WEP. As with WEP, TKIP designers
realized that it was not a perfect solution to 802.11 security, but that
it would provide better security than WEP. TKIP addresses WEP's security
weaknesses through per-packet key mixing and automatic rekeying \[9\].

**B.1.4 802.1x-Based EAP Authentication**

Where TKIP addressed the weaknesses of 802.11 encryption, 802.1x/EAP
addresses weaknesses in 802.11's authentication process. 802.1x is an
extensible framework, not a true protocol in and of itself. Three widely
considered standards-based protocols are EAP-Transport Layer Security
(EAP-TLS), Protected EAP (PEAP), and Tunneled Transport Layer Security
(TTLS). All three use TLS to provide strong cryptographic protection of
user credentials and use the TLS key exchange to provide the foundation
for link-layer keys \[9\].

**B.2 Frequencies and Channels**

In wireless mesh networks, access point (AP) nodes can automatically
select their channel scheme based on the frequencies used by neighboring
nodes. Based on 802.11a, b, and g standards, the two major frequencies
used in a wireless mesh network include 2.4 Gigahertz (GHz) Industrial,
Scientific, Medical (ISM) band and 5 GHz Unlicensed National Information
Infrastructure (UNII) band.

The 2.4 GHz band is used by 802.11, 802.11b, and 802.11g wireless
devices. Operating in the unlicensed 2.4 GHz band can allow 802.11b and
g signals to become susceptible to interference from other devices
operating on the same frequency, such as microwaves, cordless
telephones, and Bluetooth.

The 5 GHz band, which is used for 802.11a wireless devices, is further
divided into three bands: lower, middle, and upper. These bands use 100
megahertz (MHz) of spectrum, with each band providing four
non-overlapping channels and subject to less interference than 802.11b
and 802.11g devices. Devices operating in the 2.4 GHz range use
frequency hopping spread spectrum (FHSS) or direct sequence spread
spectrum (DSSS) signal coding techniques and those operating in the 5
GHz range use orthogonal frequency division multiplexing (OFDM) signal
coding. Using a higher carrier frequency results in 802.11a signals
being absorbed more readily by their surroundings, possibly limiting the
range of the network footprint compared with 802.11b and 802.11g
networks.

The IEEE 802.11n group recently standardized six multipath channel
models (models A-F) corresponding to different environments ranging from
small indoor spaces to a metropolitan block \[10, 11\]. Table B-1 lists
the range of frequencies for each Wi-Fi standard that can be used in
wireless mesh networks.

Table B-1. Wi-Fi Standards---Frequency Channels \[10, 11\]

  -------------- ------------------- ------------------ ------------------
  **Wi-Fi        **802.11a**         **802.11b**        **802.11g**
  Standard**                                            

  **Transmit     5.18, 5.20, 5.22,   2.412, 2.417,      2.412, 2.417,
  Frequency**    5.24, 5.26, 5.28,   2.422, 2.427,      2.422, 2.427,
                 5.30, 5.32, 5.745,  2.432, 2.437,      2.432, 2.437,
                 5.765, 5.785, 5.805 2.442, 2.447,      2.442, 2.447,
                 GHz                 2.452, 2.457,      2.452, 2.457,
                                     2.462 GHz          2.462 GHz
  -------------- ------------------- ------------------ ------------------

**B.3 Range and Coverage**

Just as Ethernet cabling is typically limited by the various length of
cable types, wireless networks cannot emit radio signals to infinite
ranges. Many factors affect the true distance at which radio frequency
(RF) signals can be transmitted and actual speeds for data on that
signal. Products often list a wireless range that cannot be realized in
true environments because the estimated range assumes ideal conditions
(e.g., no weather interference, no multipath). Depending on
environmental conditions, the range of wireless service can fluctuate
with obstructions from various objects, such as buildings, walls, and
cluttered metal infrastructures.

Range and coverage is an important consideration to a wireless
implementation. Note that the intent of Wi-Fi technology is to extend
wired-network access wirelessly within smaller footprints that surround
each Wi-Fi enabled AP. However, in a wireless mesh, the network can be
configured to include many cascaded AP nodes to extend service beyond
the range that is typically local to an AP. Thus, the range and coverage
of a wireless network can depend on the number of APs used in the
network configuration. In addition, the range of a wireless network
depends on the operating frequency that is determined by the Wi-Fi
standard used.

By using the frequencies and channels described previously, Wi-Fi
solutions can provide adequate ranges of coverage in most
implementations. Table B-2 lists the typical maximum coverage ranges for
each Wi-Fi standard that can be used in wireless mesh networks.

Table B-2. Wireless Mesh---Coverage Range \[10, 11\]

+------------+-------------+--------------+------------+--------------+
| **Wi-Fi    | **802.11a** | **802.11b**  | *          | **Wireless   |
| Standard** |             |              | *802.11g** | Mesh**       |
+------------+-------------+--------------+------------+--------------+
| **Range of | Shorter     | 300 feet     | 300 feet   | Range based  |
| Service**  | range than  | (indoors)    | (indoors)  | on number of |
|            | 802.11b     |              |            | APs          |
|            | (\~225      | 1,000 feet   | 1,000 feet |              |
|            | feet)       | (outdoors)   | (outdoors) |              |
+------------+-------------+--------------+------------+--------------+

**B.4 Data Rate**

Data rate speeds in wireless mesh networks depend on various factors
such as the coverage footprint, the technology used (e.g., 802.11a, b,
or g), and the number of cascaded AP nodes. Typically, the data
throughput performance of wireless systems will depend on the range of
coverage and utilization of wireless network resources. Wireless devices
can provide expected throughput rates when operating within the
designated coverage ranges of an associated AP (e.g., several feet).
Data throughput will decrease as a wireless device deviates farther from
an AP, as more wireless users occupy an AP, or when high-use bandwidth
applications are being performed. Additionally, when data is transmitted
across multiple cascaded nodes, the data rate can decrease with hops at
each additional node. Table B-3 lists typical data rates supported by
the various Wi-Fi standards used in wireless mesh networks \[1\].

Table B-3. Wi-Fi Standards---Data Rates \[10, 11\]

  -------------- ------------- ------------- ------------- --------------
  **Wi-Fi        **802.11**    **802.11a**   **802.11b**   **802.11g**
  Standard**                                               

  **Data Rates** 1, 2 Mbps     5, 9, 12, 18, 1,2,5.5, 11   6, 9, 12, 15,
                               24, 36, 48,   Mbps          24, 36, 48, 54
                               54 Mbps                     Mps.
  -------------- ------------- ------------- ------------- --------------

Data rate selection (DRS) is a feature that Wi-Fi provides to
dynamically adjust the data rate at which a wireless device can operate.
DRS works by automatically adjusting the data rates of a connection as a
wireless device operates farther from an AP. It will also dynamically
adjust the speed if increased signal interference is detected.

**B.5 Quality of Service**

Quality of Service (QoS) is the ability of a network element (e.g., an
application, a host, or a router) to provide some levels of assurance
for consistent network data delivery. QoS issues in wired LANs are
typically neglected because the physical layer bandwidth of wired LANs
can be very high.[^1] However, Wi-Fi technology in wireless mesh
networks incur some distinct features compared to wired LANs, including
higher bit error rate, higher delay, and lower bandwidth. The
characteristics of the wireless channel can make high data rate very
difficult to achieve.

Wi-Fi was originally designed for best-effort services. The Carrier
Sense Multiple Access (CSMA) technique used in the Wi-Fi 802.11 standard
provides fair and equal access to all devices. It is essentially a
"listen-before-talk" mechanism. This is not an issue with typical data
applications, such as exchanging e-mail, transferring data files, and
browsing the Internet, but applications such as video and multimedia
streaming create unique and challenging QoS requirements. Many users
require multimedia distribution to work perfectly without dropouts or
glitches, pushing more demand for higher bandwidth capability. Network
administrators need mechanisms to ensure that applications with
stringent QoS requirements will function properly over a congested
network. These developments have triggered the development of a QoS
enhancement for the 802.11-based wireless LAN (WLAN) \[10, 11\].

QoS mechanisms allow for access rule modifications so that high priority
data is given preferential access to the medium. It will therefore gain
access at the expense of the lower priority traffic. To enable QoS
techniques in Wi-Fi networks, the IEEE 802.11 committee passed the
802.11e specification in September 2005 to define changes to the
operation of the 802.11 MAC layer that enable prioritization and classes
of service \[10, 11\].

The IEEE 802.11e specification allows packets to gain priority by
defining four traffic classes, each with its own queue. By default,
priorities are assigned based on application type, such as for voice,
video, best-effort, and background. The definitions of the four classes
provide flexibility to be changed from the default. To identify the
class of each packet, the specification uses markers similar to the ones
used in wired Ethernet. Acknowledging those markers, a Wi-Fi AP is
capable of providing voice packets top priority for transmission,
followed by video, and so forth. This method is combined with other
mechanisms (e.g., random back-off periods) to prevent packet collisions
from different sources \[10, 11\].

Another key feature of the specification is a way of scheduling
communications between nodes and user devices to minimize unnecessary
power usage in handheld devices. The performance of this feature can
also be modified based on configured user priority.

**B.6 Scalability**

Wireless mesh networks provide convenience for organizations and users
to network computers where mobility is most needed or where wireline
infrastructure is not readily available. In a wireless mesh network,
Wi-Fi technology (802.11a, b, and g) can allow for flexible
configuration of data speeds and coverage ranges by using different
modulation techniques and frequency bands to provide wireless data
access to various deployed environments, ranging from the wireless needs
of a small office to a large-scale city block environment. To
accommodate a large footprint, multiple nodes can be rapidly integrated
and self-configured, creating a larger network.

**B.7 Compatibility and IEEE 802.11s**

A factor that affects scalability is compatibility, which is a
two-pronged consideration: compatibility of wireless devices with one
another and compatibility with wireless technologies.

Because Wi-Fi technology is a standard created by the IEEE and marketed
by the Wi-Fi Alliance, most product manufacturers have developed
solutions that are commonly interoperable. Generally, a wireless mesh
network incorporating nodes that use the 802.11b standard will
interoperate with other 802.11b-based nodes as a result of using the
same frequency at the 2.4 GHz range. Note, however, that wireless
devices operating based on the 802.11a standard will not be
interoperable with other 802.11b-based devices because the 802.11a
standard is designed for devices operating in the 5 GHz range. Devices
based on the 802.11g standard are typically compatible and interoperable
with other 802.11b-based devices because 802.11g uses the same frequency
range as 802.11b. In addition to typical Wi-Fi operation, wireless mesh
configurations require the use of other signaling protocols and routing
mechanisms that many existing Wi-Fi product vendors do not support.
Currently, many wireless mesh implementations are proprietary and
require the use of mesh nodes from the same vendor throughout the
network \[10, 11\].

The IEEE 802.11s proposal is an unapproved and developing IEEE 802.11
standard for [extended service set
(ESS)](http://en.wikipedia.org/wiki/Extended_Service_Set) [mesh
networking](http://en.wikipedia.org/wiki/Mesh_networking). 802.11s
specifies an extension to the IEEE 802.11
[MAC](http://en.wikipedia.org/wiki/MAC) to solve the interoperability
problem by defining an architecture and protocol that support both
[broadcast](http://en.wikipedia.org/wiki/Broadcasting)/[multicast](http://en.wikipedia.org/wiki/Multicast)
and unicast delivery using "radio-aware metrics over self-configuring
multi-hop topologies." The 802.11s proposal, which introduces "[Mesh
Portals](http://en.wikipedia.org/w/index.php?title=Mesh_Portals&action=edit)"
will enhance interoperability in mesh networks by allowing older and
newer 802.11 Wi-Fi technologies to be recognized and incorporated into a
coexisting network \[19, 20\].

**B.8 Roaming**

Mobility forces clients to roam from one mesh node to another and it
also causes meshes to reconfigure themselves at high vehicular
velocities. An example of a mobile mesh node is one in a bus or a train
moving through a fixed municipal mesh. As roaming occurs, the clients or
mesh nodes must disassociate from one node and associate with another
causing an interruption of service. Such interruptions create latency
that impacts voice services dramatically and can also cause a loss of
data connections. The roaming process must be fast to minimize
interruptions in traffic. Roaming times must be measured under different
conditions, including velocity, traffic load, traffic type, and amount
of cell overlap \[2\].

The IEEE 802.11r standard, currently in development, refines the
transition process of a mobile client as it moves between candidate
access points. Under 802.11r, clients can use the current access point
as a conduit to other access points, allowing clients to minimize
disruptions caused by changing channels \[2, 10, 11\].

**B.9 Cost**

As a result of the maturity of Wi-Fi technologies and increased
development from many Wi-Fi product vendors, Wi-Fi solutions have become
more affordable than in previous years. Thus, wireless mesh networks
using Wi-Fi solutions also can be more cost-effective when compared with
traditional wireless voice communications technologies (e.g., cellular,
land mobile radio \[LMR\], satellite). Wi-Fi solutions and their costs
are differentiated depending on type of use such as residential (e.g.,
homes, small business) or enterprise level (e.g., corporate use,
military, and law enforcement deployments). Full wireless mesh solution
offerings at the enterprise level may cost more than those for partial
wireless mesh or Wi-Fi residential use because of the need to support
extensive capabilities (e.g., security, QoS, scalability, ruggedness)
and increased numbers of users and nodes.

As wireless mesh networking standards become more developed and vendor
solutions become more available, wireless mesh networks will provide the
capability to deliver high-performance, while reducing cost attributed
to the ease of implementation, decreased need for cabling, scalability
to accommodate an increased user population, and flexibility to support
various applications without the complexities (e.g., reconfiguration,
tower licensing, limit vendor product offerings) typically experienced
with wired networks and traditional wireless voice communications.

# Appendix C: Acronyms 

  -------------- --------------------------------------------------------
  **ACK**        Acknowledgement

  **AES**        Advanced Encryption Standard

  **AODV**       Ad hoc On-Demand Distance Vector

  **AP**         Access Point

  **C2**         Command and Control

  **CCK**        Complementary Code Keying

  **CCMP**       Counter Mode CBC-MAC Protocol

  **CDMA**       Code Division Multiple Access

  **CSMA/CA**    Carrier Sense Multiple Access with Collision Avoidance

  **CTS**        Clear to Send

  **DRS**        Data Rate Selection

  **DSR**        Dynamic Source Routing

  **DSSS**       Direct-Sequence Spread Spectrum

  **EAP**        Extensible Authentication Protocol

  **EMS**        Emergency Medical Service

  **ESF**        Emergency Support Function

  **ESS**        Extended Service Set

  **ETX**        Expected Transmission Count

  **FDD**        Frequency Division Duplexing

  **FDM**        Frequency Division Multiplexing

  **FECC**       Federal Emergency Communications Coordinator

  **FHSS**       Frequency-Hopping Spread Spectrum

  **GHz**        Gigahertz

  **HSLS**       Hazy Sighted Link State

  **IEEE**       Institute of Electrical and Electronic Engineers

  **IP**         Internet Protocol

  **IPSec**      IP Security

  **ISM**        Industrial, Scientific, Medical

  **IT**         Information Technology

  **LAN**        Local Area Network

  **LMR**        Land Mobile Radio

  **MAC**        Media Access Control

  **MAN**        Metropolitan Area Network

  **Mbps**       Megabits per second

  **MHz**        Megahertz

  **MIMO**       Multiple-Input, Multiple-Output

  **ms**         millisecond

  **NCS**        National Communications System

  **NSC**        National Security Council

  **NS/EP**      National Security and Emergency Preparedness

  **OFDM**       Orthogonal Frequency Division Multiplexing

  **OLSR**       Optimized Link State Routing

  **P2P**        Point-to-Point

  **PDA**        Personal Digital Assistant

  **PHY**        Physical

  **PMP**        Point-to-Multipoint

  **PPTP**       Point-to-Point Tunneling Protocol

  **PSK**        Preshared Key

  **PSK**        Phase-Shift Keying

  **PSTN**       Public Switched Telephone Network

  **QAM**        Quadrature Amplitude Modulation

  **QoS**        Quality of Service

  **RADIUS**     Remote Authentication Dial-In User Server/Service

  **RC4**        Ron's Code 4

  **RDP**        Route Diversity Project

  **RF**         Radio Frequency

  **RSA**        RSA Security Company

  **RTS**        Request to Send

  **RTT**        Round-Trip Time

  **SIP**        Session Initiation Protocol

  **SSID**       Service Set Identifier

  **SSL**        Secure Sockets Layer

  **TCP**        Transmission Control Protocol

  **TDD**        Time Division Duplexing

  **TDMA**       Time Division Multiple Access

  **TKIP**       Temporal Key Integrity Protocol

  **TLS**        Transport Layer Security

  **TTLS**       Tunneled Transport Layer Security

  **UNII**       Unlicensed National Information Infrastructure

  **UWB**        Ultra-Wide Band

  **VoIP**       Voice over Internet Protocol

  **VoWi-Fi**    Voice over Wi-Fi

  **VPN**        Virtual Private Network

  **VTC**        Video Teleconference

  **WEP**        Wired Equivalent Privacy

  **Wi-Fi**      Wireless Fidelity

  **WiMAX**      Worldwide Interoperability for Microwave Access

  **WLAN**       Wireless Local Area Network

  **WMAN**       Wireless Metropolitan Area Network

  **WPA**        Wi-Fi Protected Access
  -------------- --------------------------------------------------------

# Appendix D: References

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3.  Poor, Robert. (2003). *Wireless Mesh Networks*. Retrieved February
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6.  Murphy, J., Saraf, A., & Network World. (2006). *802.11s Extends
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9.  Ohrtman, Frank, & WMX Systems, LLC. (2006). *WIMAX: A SIMPLE
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10. Carpenter, Tom, & Planet3 Wireless. (2006). *Wireless# Certification
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11. Northern Sky Research. (2005). *Broadband Wireless Markets*.
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12. Booz Allen Hamilton. Systems Resource Center. (2006). *Wireless Mesh
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13. Kowalik, K., Davis, M., & Dublin Institute of Technology. (2006).
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16. Calhoun, Pat, & O'Hara, Bob. (2005). *802.11r Strengthens Wireless
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17. Kaka, Yusuf. (2006). *Future of VoIP and the Race for Wireless VoIP
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18. Krag, T., Buettrich, S., & O'Reilly Network. (2004). *Wireless Mesh
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19. Hachman, Mark. (2006). *Rivals Agree On 802.11s Wireless Mesh
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    Plattner Institute, Retrieved February 6, 2007, from
    http://www.hpi.uni-potsdam.de/\~meinel/projects/security_in_mesh_and_ad-hoc_networks.html.

[^1]: 1 gigabit per second (Gbps) is now a common link speed between
    switches in enterprise LANs, whereas10 Gbps 802.3ae Ethernet will
    appear soon.