Mesh Wi-Fi Networks: Architectures and Experimental Results

Mesh Wi-Fi Networks: Architectures and Experimental Results

E. Patiniotakis (Hellenic Telecommunications Organization S.A. (OTE), Greece), St. Perdikouris (Hellenic Telecommunications Organization S.A. (OTE), Greece), G. Agapiou (Hellenic Telecommunications Organization S.A. (OTE), Greece), I. Chochliouros (Hellenic Telecommunications Organization S.A. (OTE), Greece), K. Voudouris (Hellenic Telecommunications Organization S.A. (OTE), Greece), E. Dimitriadou (Technological Educational Institute of Athens, TEI-A, Greece), I. Fraimis (Hellenic Telecommunications Organization S.A. (OTE), Greece) and A. Ioannou (Wireless Telecommunications Laboratory, University of Patras, Greece)
DOI: 10.4018/978-1-61520-805-0.ch005
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Abstract

Wi-Fi mesh is a fast growing and mature technology which is widely used and has been proven very useful for healthcare including applications for ambient people. In this chapter, we attempt a quick introduction of the principles of 802.11s protocol that refers to mesh topology Wi-Fi networks. Specifically, we describe the main operations and functions performed in a Wi-Fi mesh network such as routing procedures, synchronization as well as QoS capabilities and security mechanisms that are crucial for carrying sensitive information like medical data. Finally, in the second part of this chapter, actual measurements are presented from an experimental network that consisted of four dual radio (2.4 GHz and 5 GHz) mesh access points. Key parameters are evaluated, such as maximum throughput for different distances, jitter, delay and data loss which affect the transmission of sensitive data. Moreover, the handover capability of the system is presented in terms of data throughput and voice quality degradation during the transition.
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Technology Overview

WLAN mesh networks are targeted primarily for home, commercial, neighborhood, community, municipality, rural broadband, emergency and first responder, and public safety. Also for small to medium business, large enterprise and military networks.

The 802.11 mesh network is created from a collection of access points (APs) interconnected via wireless transmission that enables automatic topology learning and dynamic path configuration to occur. The network is decentralized and simplified because each node needs to transmit only as far as the next node. The frequency used for the communication between access points is either 2.4 GHZ (802.11g) or 5 GHz (802.11a). The maximum throughput in all cases is 54 Mbps. At this point it is important to mention that the upcoming 802.11n standard which uses Multiple Input- Multiple Output (MIMO) techniques promises rates up to 300 Mbps. The mesh access points (MAPs) are typical 802.11 access points that have routing and/or forwarding capabilities so that they can connect to each other and identify all the possible hops from source to destination. If one mesh point has also the capability to serve client stations or non-mesh nodes, it is called mesh point (MP). In most mesh Wi-Fi networks; there exists an access point (often called as “root MP”) that has two interfaces. The one is a wireless interface so that it establishes connections with all neighboring MPs, while it has also a contact to the wired network. This MP is referred as Mesh Portal (MPP).

WLAN mesh networks are defined as:

WLAN mesh is an IEEE 802.11-based wireless distribution system (WDS), which is a part of a distribution system (DS), consisting of a set of two or more MPs interconnected by IEEE 802.11 links and communicating through the WLAN mesh services. A WLAN mesh may support zero or more entry points (mesh portals [MPPs]), automatic topology learning, and dynamic path selection (including across multiple hops) [1].

Figure 1.

Typical mesh network

A set of MP radio interfaces that are interconnected to each other using the same channel are referred to as a unified channel graph (UCG).

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