Quality of Service, or QoS, is an important feature of modern networks. The technology allows for different processing of different types of traffic, thereby ensuring that “important” traffic always has priority over less important one. While this simplistic explanation may make it look simple, it’s actually quite complex and, once you put it in place, you’ll want to find ways to see if it is working.
There is, of course, the obvious. If your important traffic works well even at times of high network usage, chances are that the QoS is doing its job. But to get a clear picture of how things are operating, QoS testing and measuring tools are the way to go. And they are also the topic of today’s post.
Today, we’ll first discuss QoS, explain what it is and, more importantly, how it works. We’ll learn about the classification and marking as well as queuing. Next, we’ll discuss the consequences of not using QoS and talk about the limitations of this powerful technology because, like everything else, it is not perfect. This will lead us to the most important part of this post, our reviews of a few of the best tools for QoS testing and measuring. We’ll explore the most interesting features of a handful of tools that we’ve found to be the most interesting.
So, What Is QoS, Exactly?
As typical network usage grew throughout the years to include more and more traffic of different types and as network congestion became more and more frequent and important, engineers soon realized that they needed a way to organize and prioritize traffic. After all, network congestion is not that bad if you can still ensure that important traffic has a chance to go through. This is what Quality of Service (QoS) is all about. QoS is not just one thing but instead a combination of features and technologies that work together to accomplish the goal of correctly prioritizing and routing network traffic. Through a lot of trial and error, what we have today is a relatively universal QoS system that can be used to reliably ensure that important traffic gets the attention it needs.
An important aspect of QoS is that it has to be implemented from end to end to be of any use. QoS is set up on the devices—such as switches and routers—that handle the traffic. Any such device in the data path must have the correct QoS configuration or else things it won’t have the expected effect. Also, each device must have a QoS configuration that is compatible with the others’. QoS uses priority markings to accomplish its magic. You can easily imagine what would happen if one device considered a higher priority number as more important while another did the opposite.
How QoS works
Before we begin, I’d like to state a few things. First, I’m not a networking engineer. Second, the goal of this explanation is not to be absolutely accurate. I’m knowingly oversimplifying things and even perhaps twisting the reality to a certain extent to make this section easier to comprehend. My goal is to give you a general idea of how it works, not to train you on QoS configuration.
QoS works by identifying what traffic is more “important” and by prioritizing that traffic throughout the network. There’s no “golden rule” as to what traffic is more important than others. Obviously, some traffic–such as voice or streaming video–will normally be considered important simply because it won’t work properly when suffering from performance degradation. Some traffic–such as web browsing in many organizations–is considered unimportant and will therefore not be prioritized.
There are two components to QoS. First, the traffic must be classified and marked. Although there are several ways traffic can be marked, Differentiated Services in the most prevalent today. This is the one we will detail in a short while. The second component is the queuing which will ensure that priority data will be transmitted with as little delays as possible. Queueing is done at the network devices according to Differentiated Services markings.
Differentiated Services, or DiffServ, use a six-bit code in the header of each packed to mark is according to several classes of increasing priority. This marking is referred to as the Differentiating Services Code Point, or DSCP. Typical DSCP values range from 0, the least important traffic to 48, the most important one.
Classification And Marking
For network traffic to be correctly handled according to its priority, it must first be classified and marked appropriately. Marking can be done right at the source. For instance, it is not uncommon for IP telephone sets to mark their traffic as DSCP 46, a high-priority value. For traffic that is not marked at the source, things are a tad more complicated.
Unmarked traffic doesn’t actually exist with DiffServ. By default, all traffic is marked DSCP 0, the lowest priority. It is up to the first network device handling the traffic–usually a switch–to mark it. How is it done? Mostly through ACLs.
ACLs, or Access Control Lists, are a feature of most networking equipment that can be used to identify traffic. As their name implies, they were originally used as a mean of controlling access. ACLs identify traffic based on several criteria. Among them, the more common are the source and destination IP address and the source and destination port number. Throughout the years, ACLs have become more and more refined and can now be used to precisely select very specific traffic.
In the case of ACLs used to insert QoS markings, the rules not only specify how to recognize traffic but also what DSCP value to mark it with.
Now that traffic is marked, all that left is to prioritize it according to its marking. This is normally accomplished by using multiple queues with increasing priority. Although DSCP values are 6-bit wide and can, therefore, range from 0 to 63, networking equipment rarely uses that many queues. It is typical for most networking equipment to use from three to seven queues with five being the most common number. With five queues and over 60 markings, you’ve certainly figured that more than one DSCP value goes in each queue.
The lowest priority queue, which is often called the best-effort or BE queue will be the one that gets the least attention from the routing engine. Conversely, the highest priority queue, which we often call real-time or RT will get the most attention. This ensures that “important” traffic will be routed or switched in priority. Of course, this also means that best-effort traffic might be seriously delayed and perhaps even never delivered. This is something to keep in mind when classifying and marking best-effort traffic.
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Is QoS Mandatory?
The consequences of not using QoS vary widely. For instance, if your network carries no highly sensitive traffic such as Voice over IP (VoIP) or streaming video, not using QoS might make no difference. This is especially true when your current traffic levels are low. In fact, in a situation of low traffic, QoS brings almost no benefit.
But in situations where your network suffers from any—or many—issues such as over-utilization and congestion, then the absence of QoS will lead to all sorts of problems. For traffic that requires real-time or near-real-time transmission–such as Voice over IP, it could, for example, be the cause of garbled, chopped, or unintelligible Audio. Video streaming would also be affected, resulting in excessive buffering or pixelation during playback.
But even other services could suffer from the absence of QoS. Imagine that a corporate network user is trying to access an important web-based accounting system while at the same time, hundreds of users are on their lunch break, heavily browsing the Internet. This could render the accounting application unusable unless its traffic is correctly prioritized using QoS.
QoS Has Limitations
But as good as it is, implementing QoS is not the solution to every problem. Network administrators tend to think that implementing QoS will relieve them of the need to add bandwidth. While it is true that implementing QoS will cause an immediate and very apparent improvement in the operation of high-priority traffic. It will also degrade lower priority traffic.
QoS will take care of temporary network congestion and it will ensure that business-critical services continue to operate correctly while there is congestion but it won’t stop it. You still need to monitor network usage and have a capacity planning program in place.
The Best QoS Testing And Measuring Tools
We’ve seen how QoS is particularly beneficial to real-time traffic such as VoIP traffic or streaming view. It will not come as a surprise, then, that many QoS testing and measuring tools are actually VoIP testing tools. The tools we’ve included on our list share one thing in common, they will thoroughly measure the performance of networks when QoS is in use and they can, therefore, be used to validate that your QoS configuration is performing as expected.
Many network administrators are familiar with SolarWinds, the company that has been making some of the best network administration tools for the past 20 years. Its Network Performance Monitor, for instance, is an SNMP monitoring platform that consistently scores among the best ones available. The company is also famous for its free tools that were each designed to address a specific need of network administrators. They include a Free TFTP Server or an Advanced Subnet Calculator, for example.
For QoS testing and measuring, the SolarWinds VoIP and Network Quality Manager is what you need. It is a dedicated VoIP monitoring tool that is packed with great features. This tool can be used to monitor VoIP call quality metrics, including jitter, latency, packet loss, and MOS. It can also be used to troubleshoot VoIP call performance by correlating call issues with WAN performance. The system also offers real-time WAN monitoring is using Cisco IP SLA technology. Its visual VoIP call path trace feature lets you see and pinpoint call problems along the entire network path.
- FREE TRIAL: SolarWinds VoIP and Network Quality Manager
- Official Download Link: https://www.solarwinds.com/voip-network-quality-manager/registration
Setting up the SolarWinds VoIP and Network Quality Manager is easy and can be accomplished with just a few mouse clicks. The system automatically discovers Cisco IP SLA-enabled network devices, and typically deploys in less than an hour. And once it’s up and running, it provides a very deep insight into your VoIP networking environment.
This tool provides real-time monitoring of site-to-site WAN performance and it also has alerting features to notify you of any abnormal situation. It can help ensure that WAN circuits are performing as expected by utilizing Cisco IP SLA metrics, synthetic traffic testing, and custom performance thresholds and alerts. It also has visual VoIP call patch trace, an invaluable troubleshooting tool.
The SolarWinds VoIP and Network Quality Manager won’t only monitor your WAN circuits, it can also display the utilization and performance metrics of your VoIP gateways and PRI trunks. It can help with capacity planning by allowing you to measure voice quality in advance of new VoIP deployments.
Price for the SolarWinds VoIP and Network Quality Manager start $1,615 for up to 5 IP SLA source devices and 300 IP phones. Other licensing levels–including a device-unlimited license–are also available. And like with most SolarWinds tools, a free 30-day trial is available should you want to test the product before committing to purchasing it.
2. PRTG Network Monitor
The PRTG Network Monitor from Paessler AG is a well-known network monitoring system that does much more than just monitor network bandwidth usage. Through the use of sensors, which are like program add-ons, PRTG can be used to monitor various parameters of networks and systems. The tool can monitor any system, device, traffic, and application in your IT infrastructure. Two specific sensors are particularly interesting in the context of today’s post. The QoS sensor measures parameters such as UDP packet loss, jitter, Ethernet latency, etc. And for IP-SLA enabled Cisco devices, there is an IP-SLA sensor, which can be used to read similar metrics from Cisco devices. Both methods show you the quality of your VoIP connection and enable you to define what level of latency, jitter, etc. are acceptable. Whenever the threshold is exceeded, you can be notified and take appropriate measures to address the situation. Notifications can be sent via email or SMS or pushed to a mobile device using the free client app available for Android, iOS and Windows Phone.
Paessler claims that you could start monitoring with PRTG within a couple of minutes of starting the installation. The tool’s auto-discovery system will scan network segments and automatically recognize a wide range of devices and systems. It will then create sensors from predefined device templates. Specific QoS-related sensors will then need to be set up, making the installation a bit longer but this is still one of the fastest tools to set up.
The PRTG Network Monitor is available in a free, full-featured version which is limited to 100 sensors, where any monitored parameter counts as one sensor. For example, monitoring the bandwidth on each port of a 48-port switch will count as 48 sensors. To monitor more than 100 sensors, you’ll need to purchase a license. You’ll also use up a sensor for each instance of QoS that you want to monitor. Price increases with the number of sensors and starts at $1 600 for 500 sensors up to $14 500 for unlimited sensors. A free device-unlimited 30-day trial version is available.
3. ManageEngine OpManager
The ManageEngine OpManager is another one of the best-known network monitoring tools. It will monitor the vital signs of your servers (physical and virtual) as well as your network equipment and alert you as soon as something is out of specs. The tool features an intuitive user interface that will let you easily find the information you need. The product also features an excellent reporting engine along with some pre-built as well as custom reports. To complete the package, this system’s alerting features are also very complete.
And when it comes to QoS monitoring, the ManageEngine OpManager‘s VoIP monitor option seamlessly integrates with OpManager to proactively monitor and report on your infrastructure’s capacity to handle VoIP calls. The tool uses Cisco IP SLA to continuously monitor critical Quality of Service parameters of VoIP networks. The monitored VoIP parameters include packet loss, delay, jitter, the Mean Opinion Score (MOS) and Round Trip Time (RTT).
The ManageEngine OpManager is priced based on the number of monitored devices. Prices range from $715 for 25 devices to $14 995 for 1000 devices. The VoIP monitoring option adds $125 per device that requires it. Like with most full-featured commercial monitoring tools, a free 30-day trial is available.
VoIPmonitor is an open-source network packet sniffer with a commercial front end for monitoring most VoIP protocols. The tool, which runs on Linux, is designed to analyze the quality of VoIP calls based on network parameters such as delay variation (jitter) and packet loss according to the ITU-T G.107 E-model which predicts quality using the MOS scale. Call information, together with relevant statistics, are saved to a MySQL database. Optionally each call can be saved to a pcap file (a file capture format that can be opened with other analysis tools such as Wireshark) with either only SIP protocol or SIP, RTP, RTCP, T.38, and udptl protocols. VoIPmonitor can also decode speech and play it over its WEB GUI as well as save it to disk as a .WAV file. It natively supports the G.711 alaw and ulaw codecs and commercial plugins add support for G.722, G.729a, G.723, iLBC, Speex, GSM, Silk, iSAC, and OPUS. VoIPmonitor is also able to convert T.38 FAX to PDF.
The VoIPmonitor GUI front end is available either as a locally hosted server at prices ranging from $42/month for 10 channels to $917/month for 6000 channels or as a cloud-based service with prices varying from $20/month for 3 channels to $200/month for 200 channels. Both versions are available in a free and unlimited 30-day trial.
VQmon/EP is different from other QoS monitoring tools in that it is integrated into your devices. It claims to be the most widely used technology for monitoring the quality and performance of live VoIP calls. The system is integrated into a range of IP phones sold by Avaya, Mitel, Polycom, Cisco, and several other manufacturers. It provides built-in support for the industry-standard SIP QoE (RFC 6035) and RTCP XR (RFC 3611) reporting protocols, allowing network administrators to monitor call quality everywhere within their network without the use of probes.
VQmon/EP can detect packet loss and jitter buffer discard events. It can also extract key information from DSP software and produce real-time call quality scores and diagnostic data. This tool generates listening and conversational quality MOS scores and R factors as well as a wide range of diagnostic data. Furthermore, VQmon/EP features real-time call quality thresholds, supporting either alert generation or automatic configuration.