Performance testing of VOIP applications carried by wireless Mesh Networks

With the rapid development of various wireless data networks, the market has already put forward demanding requirements for various technologies. Only technologies that meet user needs can survive well. The Mobile Self-Organizing Network (MANET) originating in the military field has received crazy attention from various research organizations since the end of the last century, because it is easy to deploy, self-managed, and does not rely on infrastructure and other features to meet the needs of disaster and field scenarios, however, due to its performance and cost disadvantages, it has not been widely used in civil facilities.

To improve MANET's applicability to civil networks, Wireless Mesh networks have been proposed in recent years, the core idea is to physically separate the peer nodes that act as routers and hosts in the traditional MANET into a wireless mesh router node and a wireless mesh client) and connect the wireless mesh router to the Internet through the border gateway.

The Wireless Mesh Network inherits the advantages of MANET self-organization and has the advantages of high bandwidth, low cost, reliability, and scalability. Because a wireless mesh router is a fixed device and cannot be moved easily after deployment, the cost of the network adapter that supports mobile MANET is relatively low. As we all know, the bandwidth and distance of wireless transmission are inversely proportional, therefore, a low-cost wireless mesh router can effectively increase the transmission bandwidth. Second, because the wireless mesh router is a network connection, failure of a link does not affect transmission. Such a network has a high degree of reliability. Thirdly, because the wireless mesh network inherits the self-management features of the Mobile Self-Organizing Network, the expanded wireless router can be configured automatically, so it is highly scalable. Finally, the wireless mesh network meets the Internet access requirements that are indispensable for any civil facilities and is more practical than MANET.

Due to this advantage, wireless mesh networks have become the focus of research institutions, and their support for upper-layer applications is focused on mobile voice services, however, the performance evaluation results of traditional MANET for VOIP services are always unsatisfactory. Here, people are very concerned about whether the wireless mesh network can meet the quality requirements of users for real-time voice services.

Iometrix, a professional testing company, conducted the first performance evaluation and testing of Wireless Mesh Networks Based on the draft study by the IEEE 802.11 Working Group. This test compares the two most popular wireless Mesh Network Solutions: single-radio wireless backhaul) solution and multi-radio outdoor mesh solution.

This test evaluates the average Opinion score (Mean Opinion Socore, MOS, it is an evaluation indicator for the user's subjective voice quality experience stipulated by the telecommunications industry standards ). This test also evaluates the performance of switching latency in user roaming scenarios. The final test data is effectively analyzed and extracted to characterize the system features related to wireless mesh VOIP applications. In the following chapter, we analyze the performance characteristics of the VOIP Application carried by the Wireless Mesh Network Based on the test results.

Challenges of voice quality to Network

With the increasing popularity of wireless mesh network applications, the demand for voice application support has increased dramatically. Users are happy to replace cellular phones with low-cost wireless network-based VOIP services, because the cost of wireless VOIP applications is basically equivalent to the cost of wireless broadband infrastructure access. New Dual-mode mobile phones combined with 802.11 access and cellular network access have intensified this trend.

However, for wireless VOIP to meet users' needs for voice quality, the underlying wireless access network must have features such as high throughput, low latency, and end-to-end queuing of voice packets, currently, not all wireless mesh networks meet this requirement.

It is particularly worth noting that Multi-hop (Multi-hop) means that wireless transmission in the access network must pass through multiple wireless routers to reach the AP. In traditional wireless networks, wireless transmission is only a one-hop access from a mobile terminal to an AP. After a mobile self-organizing network is introduced, wireless transmission is allowed to reach the Access Point through multiple wireless devices, the router of the Wireless Mesh Network inherits the features of the Mobile Self-Organizing Network .) Features are retained in the wireless mesh network, which may cause performance problems such as bandwidth attenuation and network latency. Such performance problems may be magnified more significantly when the scale of wireless mesh network deployment expands.

To support VOIP applications, vro nodes of the Wireless Mesh Network also need to manage other business flows of clients of the Wireless Mesh Network reasonably so that they do not affect the transmission priority of VOIP packets that require high real-time performance. At present, the biggest problem is that the priority of voice business grouping packages defined in the standardization work is not effectively adopted by the wireless mesh network router nodes in actual deployment, because these nodes cannot well identify the VOIP packets initiated by the client.

Iometrix tests and compares the performance of indoor single-channel wireless return and outdoor multi-channel wireless Mesh Network Solutions to assess whether they can meet the aforementioned voice quality requirements.

The first test system was designed based on the indoor single-path wireless return solution for hotels, clubs, hospitals, office buildings and schools. This system can be seen as the most basic wireless mesh access solution, which is a benchmark for the wireless mesh system.

The second test system was designed based on a wireless mesh network and provided by Strix Systems to support high-bandwidth wireless data services. This solution uses six reusable wireless channels.

The two systems that participated in the evaluation share some unified performance configurations: they all use dedicated 802.11a wireless network card for back-trip connection, which is more efficient than using a single band for uplink and downlink connections at the same time, and higher bandwidth than 802.11b access.

Iometrix performs the above two sets of Wireless Mesh Network System VOIP voice quality tests in the Azimuth System 800 Watt RF shielding environment, results The early random disturbance caused by various wireless environments such as noise and interference is separated. Through strictly controlled RF attenuation, this experimental system also simulates factors such as distance, movement, and obstacle in real conditions, including 600 wireless mesh clients.

To test the voice quality, Azimuth System has established 30 two-way end-to-end wireless calls. Each call spans one to four hops of the relay wireless router, and monitors the VOIP business flow at both ends. Iometirx measures one-way latency, jitter, packet loss rate, and other indicators to calculate the MOS value. Network jitter is measured in accordance with RFC 1889.

Finally, this test is performed simultaneously in the absence of other business flows and in the addition of 50% Other business flows (when other business flows are involved in interference, technologies are used to protect the priority of the voice service.) observe the influence of other business flows on the VOIP service flow, and compare whether the priority of the VOIP service is effective in the actual product.

Test Result Analysis

Iometrix draws the following conclusions:

First, compare two indoor single-channel wireless return and outdoor multi-channel wireless mesh network solutions without loading Other business flows. The results show that most of the calls that meet the quality requirements are completed by a one-hop Wireless route. Once the call passes through two or more hops, the quality begins to drop sharply; while the latter's quality-compliant calls are evenly distributed through 1-4 hop routes, that is, when multiple wireless mesh networks are connected, the increase in the number of hops will not affect the call quality.

Secondly, when 50% of other traffic interference is added, the voice quality of the One-hop route in the indoor single-path wireless return solution is reduced by 10%-45%, in the outdoor multi-channel wireless mesh network solution, the number of calls meeting the quality requirements is reduced from 36 to 23 before other business flows are loaded.

Finally, in order to test the roaming switching performance, Iometrix constructs a wireless mesh network client node (as a mobile terminal) to move between two wireless mesh network router nodes. The entire switching latency starts when the node receives the frame sent by the mobile terminal for the last time before the switchover, and stops when the node receives the frame sent by the mobile terminal for the first time after the switchover. The test results show that both systems have good performance in terms of switching performance, which is applicable to the mesh network structure. Among them, the frame drop rate of the indoor single-path wireless return solution is zero, because the system has established a nearby link before the one-hop wireless link is destroyed; the switching latency of the outdoor multi-channel wireless mesh network solution is less than 50 milliseconds, which can fully meet the voice quality requirements of the VOIP service.

As the evolution of mobile self-organizing networks in the civil equipment market, the wireless mesh network inherits the advantages of MANET self-organizing and has advantages such as high bandwidth, low cost, reliability, and scalability, therefore, this year, we have received extremely important attention from various research fields. Its support for upper-layer applications, especially VOIP applications, is the key to its success in the market. Iometrix started the first performance evaluation of the VOIP Application carried by the wireless mesh network. The test targets two solutions: indoor single-channel wireless return and outdoor multi-channel wireless mesh network, the results show that the increase in the number of wireless route Hops has a great impact on the former, but has little impact on the latter. Because of the mesh network structure, the switching latency of the two solutions can meet the needs of VOIP voice services.

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• Topic: Wireless Mesh Network