New to Fixed Wireless? A MAC Protocol Primer for Outdoor Environments 

A MAC Protocol Primer for Outdoor Environments - Visp App

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Network communication is critical to keep subscribers happy and your WISP profitable

Communication is important in thousands of scenarios. In the ISP space,  constant network communication ensures devices remain connected and responsive.

This simplistic description doesn’t take into account the complexity of an ISP network. In addition to customer WiFi routers, communication towers,  and the WISP network core, there are numerous access points, backhauls, and routers in between that receive and send signals to keep packets flowing. Network communication includes both transmission and reception.

Seven communication layers make up the network and the MAC Access Control sublayer resides in Layer 2, called the Data Layer. This layer is responsible for keeping the data moving between nodes. The MAC address is a unique identifier for each piece of hardware in the network that makes up a node in the MAC layer.

Outdoor environments complicate communication. A network administrator building a network must plan for disruptions from weather, interference and other factors to keep subscribers connected.

This brief primer on wireless MAC protocols for outdoor environments is designed for individuals who are new to the fixed wireless broadband industry.

Network Communication Annoyances

A helpful way to visualize access control is as if you are creating an environment for a public speaker. Your access point is the speaker, and subscribers are the audience. Little or no echo and low noise means communication can be natural and efficient.

If your access points are victims of bad engineering and riddled with echoes or noise, one or more of your subscribers become the annoying guy in the back row who repeats, “I can’t hear you!” You’re frustrated and the affected audience members feel let down.

A network must take into consideration transmission and reception. It’s configured as either a full-duplex system that sends while it receives or a half-duplex system that performs one of those actions at a time. 

Many fixed wireless solutions are half-duplex systems, which means they do not talk and listen at the same time. This is also true of Wi-Fi.

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Full-duplex systems separate wireless channels

. Many fixed wireless half-duplex PtMP systems use a single frequency space to separate reception (Rx) and transmission (Tx). They use timing, similar to how respectful people wait for one another to finish speaking before they speak. 

Outdoor Fixed Wireless 

There are some quirks that you should consider for outdoor fixed wireless, including the hidden node problem. This occurs when a node can communicate with an AP, yet interrupts other nodes due to insufficient schedule technology for fixed wireless.

The Carrier-Sense Multiple Access (CSMA) MAC protocol detects the absence of another signal in a shared transmission channel before sending a message to a node. If there is a transmission in progress, it waits until the transmission is completed before “talking”.

Although it works well for WiFi where clients can hear one another, the use of directional antennas, frequency of obstacles, and distance in outdoor fixed wireless environments will influence the viability of the CSMA protocol. 

Different vendors have different MAC protocols and could have a substantial impact on the scalability of your outdoor fixed wireless deployment. With the wrong configuration, you’ll experience a decline in performance and angrier customers as a result. 

Timing Solutions

To address this issue, manufacturers have stepped in to provide solutions to outdoor fixed wireless modulation and timing issues.

Cambium, Radwin, MikroTik, Mimosa and Ubiquiti are among the leading vendors that have developed solutions for time-slot protocols for the fixed wireless broadband market. They schedule transmissions and receptions and each action waits until it’s their time to talk or listen. 

4G and 5G LTE address mobile broadband issues with components that help a device move between sectors. Pioneers like BaiCells, Telrad, Cambium and Airspan are making great strides in adopting LTE throughout the industry. But some prefer the cost and data delivery of traditional fixed wireless PtMP solutions over LTE. 

PtMP Solutions

As you investigate PtMP solutions, keep in mind that each vendor has their own scheduling algorithms. When you use Time-Division Multiple Access (TDMA) with GPS synchronization, your APs don’t hear each other due to the synchronized listening times and clients are directional so GPS synchronization can greatly improve your network’s efficiency. 

When you have vendors that support frequency reuse, it allows you to use your spectrum efficiently, which is the most priceless resource a WISP has. 


There are answers out there for those who search for them — you just have to know where to look. A big advantage in the internet service providers’ space is the willingness of experienced WISP owners and operators to help those who are just coming up. 

To get answers to your network communication questions, visit these free resources: 

WISP Talk – Private Facebook Group

Everything WISP – Private Facebook Group

WISPA – Wireless Internet Service Providers Association Blog

Start Your Own ISP

If you’d like to hire a consultant, contact – we work with many experienced consultants and are happy to refer them. 

To learn more about protocols for the Node Problem, visit the Wikipedia Hidden Node Problem article. (

Find out more about Carrier-sense Multiple Access transmissions and Time-Division Multiple Access at Wikipedia. 

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