Clearing up the mesh about wireless networking topologies: Part 1
Over the past few years, Mesh networks have become more popular, following the trend to create more wireless things. As with other technology trends, there have been a plethora of different mesh networking technologies and architectures.
This series of articles is intended to bring order to the mess of mesh networks. Here in Part 1, network basics will be discussed, focusing on the specifics of wireless, as well as the criteria for evaluating different wireless mesh networking technologies.
In Part 2, I will provide an overview of five different mesh related technologies, including key characteristics, network architecture, strengths and limitations. This information will be aggregated to create an evaluation of these different approaches, including when they should be applied.
To begin we start with the basics of networking and different topologies. It is important to note that network topologies describe the interaction and interconnection of the participants. This means how they communicate with each other and how they establish paths between each other.
Network topologies are not always what they seem. In the wired days, they generally followed the path of the wires " very simple. If devices were wired in a ring, then the network topology is a ring. The journey to wireless complicates everything because we all share the same air space so the path and access method is not always obvious. For example, is a WiFi access point a star topology or a bus?
Some common terminology
Before we go further in looking at these questions, it is important to
first understand some common terminology which will be used throughout
this article.
DSSS - Direct sequence spread spectrum. This is a method of encoding a signal which distributes information over a wide path of spectrum using a pseudo random code. Because of the wide spreading, the signal appears to be noise for those without the spreading code.
FHSS - Frequency hopping spread spectrum. Similar to DSSS, the big difference is that it uses a more constrained spreading algorithm and changes channels as a function of time, theoretically making the transmission more immune to interference.
TSMP - Time synchronized mesh protocol. This is a mesh protocol that uses time slots to allocate spectrum for communication between two nodes. Because time slots differ over pairs, interference is minimized because access to the channel is controlled by timeslot.
AODV - Ad-hoc on-demand distance vector routing algorithm. AODV is a pure on-demand route acquisition algorithm - nodes that do not lie on active paths do not maintain any routing information nor participate in any periodic routing table exchanges. Furthermore, a node does not have to discover and maintain a route to another node until the two need to communicate.
Cluster-Tree - Region based mesh network routing algorithm. In this algorithm, routes are formed and maintained between clusters of nodes. Route discovery is completed and maintained between the clusters " providing access to the children of each cluster.
ISM - Industrial Scientific and Medical band. This describes the frequency bands that can be used license free. Generally we refer to the 2.4 GHz band, but it also covers spectrum in 900 MHz, 5.8 GHz, 433 MHz in North America. 2.4 GHz is used worldwide.
IPv6 - Internet Protocol Version 6. This is the latest version of the popular IP or Internet Protocol. With Version 6, the IP address structure, routing and class of service changes. It is part of the TCP/IP suite of protocols sponsored by the IETF.
PAN ID - Personal Area Network Identifier. This is the term for the network name assigned to particular personal area network.
CSMA - Carrier sense multiple access. This protocol defines the channel access technique deployed by Ethernet, WiFi and bus oriented networks. It provides a method for detecting collisions and retransmitting as a method to acquire a communications channel.
TDMA - Time division multiple access. The protocol defines the channel access technique used by TSMP and GSM networks in which a communications channel is divided into time slots. Each node is allocated a specific time slot for communication.
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