The article discusses the data transmission quality in wireless telecommunication networks developed according to IEEE 802.11 standard, which are important for design, installation and further operation of the networks. In particular, attention is paid to determining the range of guaranteed radio communication and the probability of packet loss. It is proposed to use the ping program as a method of determining the range of guaranteed radio communication and the probability of packet loss for IEEE 802.11 standard routers. The program allows to approximate the conditions of data transmission to real conditions, and, working for a long period of time, allows to determine the probability of packet loss. One of the advantages of the method proposed in the article is its availability in use, as no special equipment is required. In addition, the article presents the results of comparison of the quality of data transmission evaluation obtained by the proposed method with the data of technical documentation for equipment. This fact confirms the adequacy and accuracy of the proposed method. During the testing of the equipment, information about the number of sent, received and lost packets in the radio channel under study will be obtained, in addition, the average value of the delay in the transmission of data over the channel will be determined. The scope of application of the considered method for determining the range of guaranteed radio communication in wireless telecommunication networks of IEEE 802.11 standard is also proposed. An example of using the method is building a network coverage map or creating a database with the technical characteristics necessary for the design of local telecommunication networks with wireless access.
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In: K. E. Samouylov, L. A. Sevastianov, D. S. Kulyabov (eds.): Selected Papers of the VIII Conference “Information and Telecommunication Technologies and Mathematical Modeling of High-Tech Systems”, Moscow, Russia, 20-Apr-2018, published at http://ceur-ws.org
It is often necessary to test the technique to determine the quality of network access
services at a distance from the access point at the process of designing and operating
IEEE 802.11 wireless LAN networks [
In the process of designing a new local telecommunication network with wireless
access, an important issue is the exact location of wireless access points, since the quality
of services provided by the network and the speed of the handler process depends on
the fact whether the location of the wi-fi point is chosen correctly. This question is
particularly relevant in the case of building a local wireless telecommunications network
with a given speech transmission quality [
First of all, it is necessary to introduce the concept of guaranteed radio communication for IEEE 802.11 standard modern telecommunications networks with wireless access. It is well known, that multitrafic is passed in modern IP networks, which is usually "split" for video trafic, voice trafic and data transmission. Therefore, the area of guaranteed radio communication is limited to a line, each point of which is far away from the base station, and at the same time it meets the minimum required transmission quality requirements for all types of trafic. The requirements for the quality of transmission over communication channels for each type of trafic have their own characteristics. Accordingly, the area of guaranteed radio communication is limited to the most stringent requirements applicable to one of the three types of trafic. The most sensitive of these types of trafic is voice trafic, so we use the requirements for speech transmission over IP networks as a requirement to limit the area of guaranteed radio communication.
There are two methods, most common for assessing the quality of speech transmission
in modern packet telecommunication networks: the method of subjective assessment
of the quality of speech transmission MOS (Mean Opinion Score) and E-model. We
would like to draw attention to the method of objective assessment of speech quality –
E-model. This method is governed by ITU-t G. 107 recommendation. The E-model is a
common model for assessing the quality of speech transmission in networks. The main
task of the method is to find the values of the parameter called R-factor. R-factor is
an integral index of speech transmission, calculated by the specified parameters of the
speech path, taking into account its configuration [
The method of calculation of the R-factor takes into account the following features
of speech:
1. the appearance of speech packets loss in the transmission of speech in the network
with packet switching, due to the increase in the transmission delay time;
2. use of codecs of diferent types in the network. The use of low-speed codecs, such
as G723, G729, etc., can result in packet loss and transmission delays. The use
of low-speed codecs allows you to increase the bandwidth of the network, but
it significantly reduces the quality of the voice signal compared to the case of
high-speed codecs, such as G. 711, G. 726-32, etc.
3. speech transmission between two subscribers or group call support;
4. the use of voice activity detectors VAD (Voice Activity Detection) in the network,
which allows to detect voice activity when a signal occurs and separate speech from
noise [
These features have a diferent efect on the signal delay time, which creates
inconvenience due to overlapping conversations and the occurrence of echo. The efect of delay
becomes critical when its value in one transmission direction exceeds 250 ms [
When calculating the R-factor, it is possible to localize the following causes and
places of delays in the formation, transmission and processing of speech packets in the
conversation: in the codec (encoder or decoder), in the receive or transmit bufer, in the
summator, in the adaptation module, in the IP network, in the switch [
It is proposed to use the following scheme of testing equipment to determine the range of the guaranteed radiocommunication using the ping program (see Fig. 1). You need to take two laptops (one used as a server, the other as a client) and a router supporting one of the IEEE 802.11 b/g/n wireless transmission standards.
The router configuring and a wireless LAN creating are done through the web interface of the router. In order to do this, you need to connect the router to the first laptop using a cable with a connector of standard RJ 45, called “twisted pair”, and then connect to the IP address of the router by default using a browser. In our case, Wi-Fi router Asus Rt-N12 with a standard IP address by default-192.168.1.1 is used. Then it is necessary to connect the second laptop to the created local network. In order to do this, it is required to check the operation of the PC2 wi-fi adapter, select the local wireless network created by the router, enter the appropriate username and password. The exchange of packages is checked after connecting the laptop to the network.
Afterwards, it is necessary to customize your ping on the first laptop: you should open the Execute task window using the win+r shortcut, enter the cmd command, and then open the command window. It is necessary to enter a command on the opened command window to start the ping utility. Ping program has several diferent parameters that afect the principle of its operation. In order to test wireless routers, you need to bring the transmission conditions closer to the real ones. Therefore, Ethernet packets with data must be sent to the router. Accordingly, the ping utility must constantly form a packet size of 1 kb. In our case, this command is as follows: ping [router ip address] –l 1000 –t. With this command we create a packet size of 1000 bytes that will be transmitted from PC1 to PC2 and back again until we enter the command Ctrl+C.
The program runs for a long period of time, suficient to fully estimate the probability of losing packets. After that, the program is stopped by a certain combination of keys. In our case, the program has a suficient duration of 20 minutes. In other words, the program must transfer 1000+ packets. At the end of the program work we will see information about the number of the packets sent, received and lost, in addition, we will know the average value of the delay in the transmission of data through the channel. After the end of the program and the probability of loss of packets for this point, the distance between the router and the receiving laptop increases. Testing is repeated for multiple points to obtain the average probability of packet loss. It is assumed to start with a distance of 5 m between PC1 and PC2 and increase by 5 m for a more accurate result. In addition, a fundamental condition for this type of testing is to perform measurements in conditions of direct radio visibility, since various obstacles between PC1 and PC2 can lead to less accurate values.
4.
The following results were obtained during the testing of the section of the experimental telecommunications network with wireless access of IEEE 802.11 standard (see Tab. 1).
The results of a wireless LAN standard IEEE 802.11 testing
Measurements were carried out at 6 diferent points at a distance between PC1 and PC2 – 5 m, 10 m, 15 m, 20 m, 25 m and 30 m. In the following, as an example, we present the result of one point processing using the ping program (see Fig. 2). Figure 2 shows the statistics that are generated after the test packets are transmitted. You can see the number of packets sent, the number of packets received, the number of packets lost, the minimum time for receiving and transmitting one test packet, the maximum time for receiving and transmitting one test packet, and, accordingly, the average time for one test packet receiving and transmitting.
In order to generate the guaranteed radiocommunication segment parameter value let’s carry out the averages calculation: the average latency of transfer and acceptance transmission for 6 experiments — 332,33 ms; the average number of packets sent – 1207 PCs; the average number of packets lost for 6 experiments — 11; the percentage of losses for 6 experiments is 0.91%.You should pay attention to the fact that the average value of the transmission delay in one direction is 165 ms. Estimation the probability of packet loss in the range of 1-3% and the average value of the transmission delay in one direction within 250 ms, indicates a good quality of speech transmission over the channel.
5.
Considering the fact that the proposed method is simple and requires no special equipment, there are other areas of potential use.
1. The use of the proposed method makes it possible to obtain not only a zone of
guaranteed radio communication for a particular equipment, but also the correspondence
of the probability of packet loss on distance.
2. Testing a large amount of equipment for wireless access will allow you to create
a database with the technical characteristics required for the design of local
telecommunications networks with Wi-Fi access and a given speech transmission
quality [
In addition, the use of laptops as a server and client brings test conditions closer to the real conditions in which computers or smartphones usually act as network subscribers. 6.
Summing it all up, it is necessary to mention that the method proposed in the article is efective and adequate. The comparison of technical parameters of the router given in technical documentation with the parameters received in the conditions of testing can serve as the certificate of its adequacy. According to the data stated in the router technical documentation, under the conditions of direct radio visibility, wi-fi router Asus Rt-N12 provides data transmission to a distance of 30 m with a probability of packet loss of 1-3%. As shown earlier at a distance of 30 m between PC1 and PC2, the probability of packet loss does not exceed 1%. In turn, the efectiveness of the method is confirmed by its simplicity, reliability and a wide range of possible applications.