The 1505 APs can use 802.11g, sharing it with the client access. This is instead of using 802.11a radio as backhaul. In case that severe radar interference is detected, it is still possible to build the network using 1505 APs. Also, in harbors, it is possible that passing or incoming ships might have radar that affects the mesh network, which might not be present during the survey phase. It is advisable that before you plan and install, contact the local authorities in order to obtain information if there is any known radar installation nearby, such as weather, military, or an airport. The main impact is that the full sector will go one minute on silent mode after channel change (mandated by DFS), but it has the advantages that it prevents MAPs to become isolated if they detect radar, but its parent not. The feature of “full sector DFS mode” is available on mesh releases 4.0.217.200 and later. After this time, they resume normal operation. All devices after going into the new channel, go silent for one minute, to detect for possible radio signals on the new channel. If a RAP sees the radar event, it notifies all MAPs for a channel change. The RAP then triggers a full sector channel change (RAP plus all its dependant MAPs). If a MAP sees the radar on the current channel, it notifies RAP of the radar detection. This causes this section of the mesh network to go down, as RAP has to change channel, and all the MAPs have to search for new parent location. If a RAP sees the radar event, it goes silent for one minute, and then selects a new channel from the 802.11a Auto RF channel list (if currently joined to controller). If no other parent is available in another channel (no redundancy), the MAP remains off network for the 30 minutes of the DFS timer. This situation can occur if the detecting MAP is closer or in line of sight of the radar, and the other APs are not. If the parent does not detect the radar, it remains on the channel and is not visible for the MAP that did detect it. The previous channel is marked as not usable for 30 minutes. Then, the MAP starts to scan channels for a suitable new parent to associate again to the mesh network. If a mesh access point (MAP) sees the radar on the current channel, it goes silent for one minute. This depends on where the radar is detected and on the state of “full sector DFS mode” configuration setting (in case it is disabled): The effects of radar signal over a wireless mesh network with 802.11a backhaul can be different. This is dictated by Federal Communications Commission (FCC) and European Telecommunications Standards Institute (ETSI) standards, and is established to allow the sharing of the 5 GHz spectrum between wireless LAN (WLAN) and military or weather radars that use the same frequencies. If during operation, an access point (AP) detects a radar event over the Radio Frequency (RF) channel that the network backhaul uses, it must immediately change to another available RF channel. It is important to validate the presence of radar on any wireless mesh deployment. The objective is to provide a mechanism to check for possible radar signals that can affect a wireless mesh network that uses 802.11a as backhaul links. It covers both 15 mesh access point families. One based on 4.0.217.200 image, the other using newer functionality on the mesh released, in particular 4.1.192.17M. This document offers two methods to scan for radar signals across 802.11a outdoor channels before deployment of mesh networks.
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