Wireless networks play a critical role in most organizations today. When the network is down, users are affected and can become frustrated.
This is why maintaining wireless network performance is crucial and should be a top priority for IT teams. However, this can be difficult for a number of reasons, such as the increasing demand on top of fixed capacities that wireless networks experience, the fact that Wi-Fi deployments require specialized training to troubleshoot, and that wireless networks are shared environments.
Fortunately, there are wireless key performance indicators (KPIs) that establish a baseline for efficiency and stability of the various activities and components of your wireless network. It’s important to understand these metrics to be able to detect and resolve issues faster, which can reduce the frequency and duration of downtime incidents. As a result, you can help improve end-user productivity and ultimately the bottom line.
Before we begin, it’s important to determine if WLAN traffic should be captured over the air or on the wire, and under what circumstances. This decision will depend on your business objectives and KPIs. You need to be thinking about your needs and ask yourself is it necessary to see the payload of the packets, encrypted or otherwise? As technologists, we tend to default to the idea that “more data is better,” but it’s common for many organizations to answer “no” to that question, since wireless payloads add very little when troubleshooting wireless problems. The issue is usually embedded in the protocol decode, instead of the packet payload.
If your WLAN is experiencing quality or performance issues, then you should be looking at just the WLAN packets and headers, and not the data payload. If you’re dealing with an application issue, then eliminate any WLAN variables like interference, encryption and signal strength, and do your captures on the wired side of the AP. Following this process of elimination will help you isolate the root cause of the issue quicker.
Here are some of the most common wireless network performance KPIs that your team should be monitoring:
Uptime, also known as availability, is a wireless network KPI that indicates the amount of time a wireless network is available for effective use. This is perhaps the most easily understood and straightforward KPI.
2. Network Jitter
Jitter measures a network’s transfer rate consistency, and indicates the variability in a delay time. While TCP connections are very tolerant of jitter, and since it represents the majority of network traffic, jitter is usually ignored. However, real-time applications like video and voice expect very low jitter. These applications’ performances are significantly impacted when jitter is present. Additionally, wireless networks are much more prone to jitter than wired networks because of radio frequency and interference issues. For general data, jitter up to 100 msec might be alright, but for real-time data, jitter above 20 msec can cause major issues.
3. Bandwidth and Throughput
Although bandwidth and throughput sound similar as wireless network efficiency KPIs, there is a subtle difference. Throughput measures the amount of data that actually gets transferred from one point to another within a network path. Bandwidth is the amount of data that a network path is expected to bear, or that is expected to successfully transfer from one point to another in a network, within a set amount of time. Both bandwidth and throughput can be viewed in terms of Kbps, Mbps or Gbps and the differences between the two can be used to determine the performance of a wireless network.
4. Signal Strength
There are many factors that determine the ideal Wi-Fi signal strength, such as desired data rates, number of clients on the network, background noise, and what applications will be used. For instance, a VoWiFi or VoIP system may require higher signal strength than a barcode scanner system in a warehouse. You can measure signal strength in decibel-milliwatts or dBm. It is always a negative number (at least for Wi-Fi due to the imposed max power limit). So, this would mean -20dBm is a higher signal than -50dBm. Typically, the greater the signal strength is, the better the wireless network throughput will be. Also keep in mind that 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.
5. Packet Loss
Packet loss is an indicator of congestion, low bandwidth, interference, etc., in both wireless and wired environments. It refers to a packet or packets of data that are transferred from one computer to another, but unable to reach their destination. Packet loss is represented as a ratio of packets received at the destination over those sent by the source. This KPI can help you measure the overall health of your wireless network, especially when focusing on the interaction between a specific AP and client. Acceptable packet loss benchmarks differ depending on the data type. For example, if it is general data transfer, a packet loss up to 3% can be considered acceptable, but with VoWLAN, a packet loss rate of 1 to 2% is almost intolerable for a clear and understandable audio conversation.
6. Packet Re-transmissions
When a data packet is sent out successfully, but doesn’t reach its destination, it needs to be transmitted again, or retransmitted. Consequently, the wireless network experiences delays for the transmission in question, as well as a degradation to the overall throughput of the network. While retransmissions exist in all networks, they are much more common in wireless networks due to poor signal strength, hidden nodes, interference from other technologies, and adjacent channel interference.
Latency, also referred to as delay, is a measure of the time consumed in the transfer of data from one point to another in a network. Latency is generally used to monitor TCP and UDP. High latency is a key indicator of slow network connection and poor performance. The threshold varies based on the situation. For instance, a high latency up to 100 milliseconds may be acceptable for general data, but a tolerable threshold for real-time applications is typically no more than 50 milliseconds.
Latency can be caused by a variety of factors. The first refers to the overall time it takes the data to travel from the sending to the receiving device over the air and is known as transmission delay. Although this time is usually very short (think speed of light over just a few hundred feet), interference or other wireless factors can prevent the data from reaching the destination. When this occurs, you must retransmit the data, and depending on network utilization, this can make the perceived transmission delay seem quite long. Another factor that can cause latency is routing, or processing delay. Whenever data is processed by a switch AP, a computer, or router, some amount of delay is introduced. The length of the delay is proportional to how busy the device is when the data is received. And there could be several “hops” along the way that each introduce routing delay, depending on where the source and destination are located.
Additionally, roaming latency, which is unique to wireless networks, represents how much time it takes for a mobile wireless client to transition from one access point to another. One can calculate roaming latency 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 length of time represents the actual user experience. While 802.11 specifications have greatly reduced the overhead with roaming operations, it still remains one of the most problematic operations on wireless networks, and can adversely affect wireless connections and VoWLAN operating over VPNs. As a general rule of thumb, look for roaming latency in modern 802.11 networks to be well under 100 msec.
As organizations continue to become increasingly dependent on their wireless networks, maintaining performance is crucial for the business.
On top of that, as Wi-Fi continues to evolve, this task will only continue to become more difficult and complex.
However, by understanding, correctly measuring and frequently analyzing the above KPIs, you can improve your organization’s wireless network performance, and ultimately the user experiences for the employees, departments and customers.
This is a guest post from Jay Bothelo
Jay Director of Engineering at LiveAction holds a Master’s Degree in electrical engineering and has been working in networking as an engineer and product manager for over 25 years.