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 Wireless Radio Resource Management (RRM) - How Wireless Networks Self Heal

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Join date : 2011-09-04

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PostSubject: Wireless Radio Resource Management (RRM) - How Wireless Networks Self Heal   Wireless Radio Resource Management (RRM) - How Wireless Networks Self Heal EmptyTue Nov 08, 2011 3:43 pm

Radio Resource Management is a feature that many modern lightweight wireless networks offer. It’s one of the reasons that wireless networks can self heal. Access points must be designed with overlap – they will then reduce their power and have smaller cell sizes.
Smaller cell sizes are generally a good thing. Data rates can be visualised as a series of steps radiating out from the access point – with each step out from the access point the data rate is reduced. The smaller the cell size, the less steps down the data rates take. Users get better coverage and better data rates.
The reason that RRM is so useful is that in the event that an access point should fail, there would ordinarily be a coverage hole. RRM allows the access points to be polled and based on this the powers can be automatically altered – the failed access point results in nearby access points having their powers increased to close the coverage hole.
In addition, to just changing the power on the access points, the algorithm can also change the channel. There’s a limited number of channels available to WiFi and if a channel is suffering interference, then the network can instruct access points to change channel to avoid the interference.
Microwave ovens can be a classic source of interference and result in severe degradation of the 2.4GHz (802.11g) spectrum. Microwave Ovens however, may not affect all channels in the 802.11g band, so changing channel can be an effective technique in overcoming interference.
In the past, wireless networks have been designed with a ‘sparse’ layout of access points. The minimum numbers were deployed to achieve the required coverage. This though has two major problems; as pointed out above, the network cannot ramp up power as the APs are already at maximum power and the network can support fewer clients.
There are less APs and each AP can only handle a certain amount of traffic. So, the answer is to overlap APs and design for ‘primary’ and ‘secondary’ coverage. The Primary coverage is the amount of coverage under normal operation and the Secondary coverage is the amount you can expect when an adjacent access point has failed.
In other words, if you’re designing for voice, your Secondary coverage needs to be able to support your WiFi handsets. If you design your network in this way, you can sustain failures of access points and it have no impact on your network.
We term this type of coverage as ‘Fault Tolerant’ coverage. It means that in the event that you have equipment failures, it’s a normal break-fix type job to replace the failed AP and not a coverage hole affecting your users. If you rely on WiFi voice handsets, it’s the only sensible way to build your network.
In summary, the network has some really useful features built in, which are designed to keep it running – however they can only work if the network was originally designed to the right standard.
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