Wireless network troubleshooting requirements from the perspective of network development

Source: Internet
Author: User
Tags network troubleshooting

First, when the last 100 meters of wireless

Anyone with a longer experience of network failure maintenance is aware that about 75% of the early network failures come from physical connectivity failures, from cable or physical interfaces. With the implementation and execution of the integrated cabling concept, the improvement of manufacturing process, the improvement of cable and interface quality, the ratio of this fault has been greatly reduced. So what happens to the cable and the physical interface when our last 100 meters are wireless?

1.1 The Great Leap forward of flexibility and the retrogression of technology itself

First of all, we should have a clear understanding that wireless WLAN network is in fact the promotion of network flexibility and network technology regression. Technically speaking, the WLAN itself has regressed network technology for at least 5-10 years, from switching Ethernet to a shared Ethernet age. This retrogression is particularly so in the case of physical media, because in the current switching Ethernet technology, each user is exclusive transmission media, but in wireless technology, all users share the physical channel, as long as the user is visible to each other, no matter how many AP, all work at the same frequency point users share the same physical media. This is the characteristic of a typical coaxial shared Ethernet or hub based shared Ethernet.

Then the problems of physical data collision, network users and the scale of data volume cannot be extended in shared Ethernet, so the factors that need to be considered in the network scheduling are increased.

1.2 The dual promotion of convenience and management complexity

Compared to Ethernet, WLAN in the promotion of convenience, while its transmission medium has changed markedly, from now almost absolutely credible copper and fiber into an absolute untrusted spectrum resources, therefore, management of wireless network administrators must have the necessary to manage Ethernet network of sufficient TCP/IP knowledge, You must also understand the RF knowledge in wireless networks, such as a true understanding of the concepts of signal-to-noise ratio, signal strength, transmit power, antenna gain, interference, and the unique characteristics of the 802.11 protocol, such as the concept of retransmission. The management of wireless networks presents a new challenge to the knowledge system of network administrators, and the complexity of the management of access media is improved geometrically.

1.3 From the administration "have" to the management "none"

Traditional Ethernet is a wired network, all the connections are visible, a terminal connected to the specific which device is clear. The wireless network connection is not visible, a terminal in the entire access process will continue to switch from one access device to another access device. In some extreme cases, the device will switch between two different access AP dozens of or even hundreds of times, and this switch is entirely determined by the client, the traditional network management software refresh rate has been completely unable to grasp this situation, this is undoubtedly how to carry out wireless network management needs to solve another key problem.

Second, the Motorola system will be wireless troubleshooting visualization

2.1 The visualization of wireless network topology

A different wireless network topology. When we discuss the wired network topology map, we simply connect the client to the physical interface of the access switch. But in wireless the same AP also needs to discuss its ESS/BSS problem, so the topology map should be the client access to which BSS, and then this BSS access to which ESS. Therefore, the topology map of the wireless network is completely different from that of the wired network.

2.2 Different physical states

In the wireless domain, there is no clear cable connection, only the coverage of the wireless area is good or bad, and the dynamic characteristics of wireless network caused this coverage is changed. Therefore, we need real-time thermal maps to monitor the entire wireless network to make it truly visible.

2.3 Physical layer Row wrong

At the physical level, it is generally accepted that wireless interference is the culprit of network quality. But in fact, the combination of resource utilization and interference intensity in wireless networks is the real problem, and interference is not only WLAN interference, but also other common frequency interference, such as microwave, 2.4GHZ radio remote control radio frequency signal or Bluetooth signal. Therefore, in the physical layer, we must analyze all the interference sources and monitor their resource utilization. It is not possible to really locate the problem by simply using some free tools online.

To give a simple example, you can randomly find two AP, set it on the same channel, and then transfer their power to the maximum, physical interval of only 10 centimeters. With the traditional software, this kind of interference is very strong. But if there is a user on the AP, another AP does not have a user, or even if the two AP have users, in the AP's competitive strategy set reasonable, the user traffic is not large, we will still be very good online perception.

Conversely, if we pull the distance between two AP to 30 meters, each AP access users, and the use of large traffic, at this time, with the traditional software to see less interference, but the actual use of the perception is very poor.

In another case, if we use only one AP and have several users simultaneously, all users will feel bad when they are in a position where they are not visible to each other and watch high-quality video. But in this case, the traditional software will think that this is not interference.

The Motorola system chooses the entire physical layer of the entire wireless network to complete the presentation, including the interference intensity of each channel, channel utilization rate and whether there is non-WLAN interference. In the example below, Channel 11 interferes with -25DBM, but utilization is only 5%, and Channel 1 interferes between 40 and -50dbm, interface utilization is up to 100%, and persistent microwave interference. In this case, the Channel 1 interference is small, but the basic is not available. Channel 11 interference is very strong, but must be the best customer experience. Therefore, physical layer visualization is very important in wireless networks.

2.3 Do you really know the situation of the network?

In traditional Ethernet, if the user appears to play the game frequently "card" situation, then, look at the Internet export congestion level and user ping DHCP server response time, can basically locate the problem. But for wireless networks, frequent "cards" are likely to be caused by both wireless and wired factors.

If the response is slow, you need to locate whether it is wireless slow or cable slow, and if wireless is slow, be sure what kind of wireless factor is causing the slow. So, in the end is due to interference, conflict, the overall performance of the wireless network or cover unreasonable frequent roaming handoff caused this problem?

Sometimes, because the wireless network is shared, we in the wireless as long as one or several users are low speed users, overall network performance will be greatly reduced. In 20 terminals, which are partially 802.11n AP networks (such as 18 802.11n plus 2 802.11b), their overall network performance may be much lower than the 20 NICs that are 802.11g. Therefore, if a user plays a game card, it is likely that another user's network card speed caused by low.

In addition, how to troubleshoot users frequently switch between two AP? How to troubleshoot the user's performance is due to interference? For wireless network troubleshooting, you need to look at the whole situation of a channel, a user, a BSS, not just a user.

Motorola system through an interface can remotely understand the data signal noise ratio (interference), user retransmission (empty load), data transfer rate (whether there is a low rate of user impact on the entire network performance), the user's transmission channel allocation (whether the user in a short time within two different channels to launch, that is, frequent roaming) , fully visually monitor all possible failures.

If the network management personnel is insufficient, can not real-time monitor, the Motorola system may define the two important indexes--the transmission rate and the retransmission rate threshold, to the network real-time monitoring, once the index surpasses the threshold to be possible to know this situation through the alarm, And through a detailed analysis of historical data to identify the specific reasons for the network failure.

For example, from the figure of the network administrator to understand the past 24 hours of different types of message ratios, if this trend analysis to enlarge to the quarter or year, we can analyze the network trends, timely adjustment of the network to avoid large-scale outbreak of problems.

Third, through the troubleshooting visualization to ensure the true availability of the network

Network last 100 meters by the WLAN takeover is the general trend, the application of the multi-terminal synergy is the general trend, the key application efficiency promotion through mobile application mode is also the trend. Wireless network Technology Backward is the actual situation, wireless network physical Media vulnerability is the actual situation, wireless network is not visible is the actual situation.

It is unrealistic to require that wireless networks be completely free of faults, and that the high efficiency of wireless network troubleshooting is something we must provide, especially when deploying key applications on a wireless basis.

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