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7 Metrics to Measure for Improved Wireless Network Performance

By Jay Botelho, Director of Engineering at LiveAction

Over the past decade, wireless networks have played an increasingly critical role in business operations. As such, upholding wireless network performance has never been more crucial. However, this can be difficult due to wireless networks being shared environments, the ever-increasing demand on top of fixed capacities, and the fact that Wi-Fi deployments require specialized training to troubleshoot.

The good news is that wireless performance KPIs can serve to help establish a baseline for stability and efficiency of the various components and activities of a wireless network. Understanding the various wireless network performance metrics can help you more quickly detect and resolve wireless issues that will inevitably arise. And, faster troubleshooting ultimately reduces the frequency and duration of downtime incidents, which improves end-user productivity and helps your business' bottom line.

The first step to tapping into these valuable wireless performance metrics is to decide whether WLAN traffic should be captured over the air or on the wire, and under what circumstances. This depends on the KPIs you are focusing on, and what you are trying to accomplish. When capturing WLAN traffic, is it necessary to see the payload of the packets, encrypted or otherwise? As technologists, our answer is typically "more data is better," but oftentimes the answer to that question is "no," as wireless payloads add very little when troubleshooting wireless problems. The issue is typically embedded in the protocol decode, not the packet payload.

If the WLAN has performance or quality issues, then you are generally interested in just the WLAN packets and headers, not the data payload. If the issue you're looking into is an application issue, then remove all the WLAN variables like signal strength, interference, and encryption, and do your captures on the wired side of the AP. Following this process of elimination will result in quicker determination of the fault.

Let's take a closer look at seven of the most common wireless network performance metrics or KPIs and why they matter: 

1.     Packet Loss - Packet loss is an indicator of interference, congestion, low bandwidth, etc., in both wired and wireless environments. The term refers to a packet or packets of data being transferred from one computer to another that are unable to reach their destination. Represented as a ratio of packets received at the destination over those sent by the source, packet loss metrics can be used to measure the overall health of your wireless network, but are even more valuable when focusing on the interaction between a specific AP and client. Acceptable packet loss differs by data type; in the case of general data transfer, a packet loss up to 3% can be considered acceptable, but in the case of VoWLAN, a packet loss rate of 1 to 2% is almost intolerable for a clear and understandable audio conversation.

2.     Latency - Also referred to as delay, latency is a measure of the time consumed in the transfer of data from one point to another in a network. Latency as a wireless network metric is very useful, but can be caused by a number of factors. The first is transmission delay, which refers to the overall time it takes the data to travel from the sending to the receiving device over the air. Although this time should typically be extremely short (think speed of light over just a few hundred feet), keep in mind that interference, or other wireless factors, may prevent the data from being received at the destination. This requires a retransmission, and depending on network utilization, this can make the perceived transmission delay seem quite long. Next is routing, or processing delay. Every time data is processed by a computer or an AP, router, or switch, some amount of delay is introduced, and this delay is proportional to how busy the device is when the data is received. And depending on where the source and destination are located, there could be several "hops" along the way that each introduce routing delay.

Latency is a KPI which is mostly used in monitoring TCP and UDP. High latency is a key indicator of slow network connections. While a high latency up to 100 milliseconds might be acceptable for general data, a tolerable threshold for real-time applications is often less than 50 milliseconds.

But, let's not forget about roaming latency, something that is unique to wireless networks. This metric represents the amount of time it takes for a mobile wireless client to transition from one access point to another. Roaming latency can be calculated by measuring the amount of time between the last known data packet for a device on one access point, and the first data packet seen for that device on another access point. This calculation represents the actual user experience. Over time, 802.11 specifications have significantly reduced the overhead in performing roaming operations, but roaming remains one of the most troublesome operations on wireless networks, and can adversely affect VoWLAN and wireless connections operating over VPNs. In modern 802.11 networks look for roaming latency to be well under 100 msec. 

3.     Network Jitter - This is a measure of a network's transfer rate consistency, and it serves as an indicator of the variability in a network's delay time. TCP connections are very tolerant of jitter, and since that represents most network traffic, jitter is often ignored. But real-time applications like voice and video expect very low jitter, and are significantly degraded when jitter is present. And wireless networks are much more susceptible to jitter than wired networks due to interference and other radio frequency issues. For general data, jitter up to 100 msec might be considered acceptable, but for real-time data, jitter above 20 msec can be problematic.

4.     Packet Re-transmissions - When a data packet is sent out successfully, and doesn't reach its destination, it has to be transmitted again, or retransmitted. This has a ripple effect on the wireless network, delaying not only the transmission in question, but also reducing the overall throughput of the network. Retransmissions exist in all networks but are much more common in wireless networks due to interference from other technologies, hidden nodes, adjacent channel interference, and poor signal strength.

5.     Uptime - Uptime or availability is a wireless network performance metric that indicates the amount of time that a wireless network is available for effective use. This is perhaps the most straightforward and easily understood KPI. 

6.     Bandwidth and Throughput - As wireless network efficiency KPIs, bandwidth and throughput sound similar, but there is a subtle difference. Bandwidth is a measure of the amount of data that a network path is expected to bear, or that can be expected to transfer successfully from one point to another in a network, within a given time. Throughput refers to the amount of data that actually gets transferred from one point to another within a network path. These metrics can be viewed in terms of Kbps, Mbps or Gbps and the differences between the two can be used to determine how well a wireless network is performing.

7.     Signal Strength - Ideal Wi-Fi signal strength varies based on many factors, such as background noise, number of clients on the network, desired data rates and what applications will be used. For example, a VoIP or VoWiFi system may require higher signal strength than a barcode scanner system in a warehouse. Signal strength is measured in decibel-milliwatts or dBm, and is always a negative number (at least for Wi-Fi due to the imposed max power limit). For example, -20dBm is a higher signal than -50dBm. In general the greater the signal strength the better the wireless network throughput, and wireless networks are often engineered such that the desired coverage area will always offer a signal strength above a minimum value, typically around -65 to -70dBm depending on the desired minimum data rate for the network. 

Managing and troubleshooting wireless network performance is a major challenge for IT teams today, and as Wi-Fi continues to evolve, this task won't get any easier. By understanding, correctly measuring and frequently analyzing the above seven wireless KPIs, you'll improve the performance of your organization's wireless network, and user experiences for the employees, departments and customers that rely on it day in and day out.


About the Author

Jay Botelho is the Director of Engineering at LiveAction.

Published Tuesday, August 06, 2019 7:34 AM by David Marshall
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