Posts Tagged ‘802.11a’
Cisco band select and client RSSI.
I wanted to quickly touch on one more parameter pertaining to Cisco band select and that would be the acceptable RSSI level that client can register for it to be able to participate with band select.
The key thing is understand what the RSSI signifies to a WLAN device, it’s a received signal strength indicator it shows you in a numerical reading (usually dBm) of what the signal strength is of a wireless client.
The closer to 0 (zero) the value is the better the signal is and the better the link speed (of course the speed is also dependant on many other factors). The key to tweaking this is to know what client devices you have in your network, then you want to know the specifications of those client devices and see what RSSI values correlate with what link speed (You should be able to find that somewhere in the manufacturer’s website or in their documentation). Then you will need to decide what link speed is acceptable for your environment.
Here are the details from the Cisco Aironet a/b/g PCI Desktop Adapter
So judging from you could probably change the acceptable RSSI value to 81 dBM, this way any dual band clients will connect at 36 Mbps and above. (Just keep in mind different WLAN client devices register RSSI values on different scales so the above example is not going to fit well for everyone out there.) This setting may also take a bit of trial and error as well, because if set the acceptable RSSI too high not many dual band clients will connect to the 5 GHz range, set it too low and clients may just roam to the 2.4 GHz range very quickly because they may quickly be out of range of any 802.11a signal.
Wireless Networking and the 5 GHz RF Range.
As I speak with other IT professionals concerning wireless networking, one thing that seems to shock people is when I start talking about the 5 GHz RF range. Usually the first thing they say is along the lines of “You are still using that?”, most people still see the 5 GHz range associated with the 802.11a standard and nothing more, while it’s true potential is finally coming to light (and people are now seeing the limitations of the 2.4 GHz frequency).
Since this topic can get in depth, and I prefer to keep my posts to a decent length, and to the point, we will jump into the advantages of utilizing the 5 GHz range:
- Less congestion, anyone who has been administrating or implemented a wireless knows how many other devices are using the 2.4 GHz range everything from BlueTooth devices (which is found in almost every phone), microwaves (found in office lunch/break rooms), to cordless phones. More particularly microwaves and cordless phones they will congest the 2.4 GHz spectrum without regard for any other device using the RF band. The 5 GHz does not suffer from as much interference as the 2.4 GHz range does, of course proper survey’s should be done prior to rolling out a Wi-Fi network just to be sure.
- More non-overlapping channel, the 5 GHz range consists of 3 bands. These bands provide us with 21 non-overlapping channels this gives us the ability to more densely pack an area with 802.11a/n access points. Decreasing the amount of clients per AP (With proper load balancing) providing increased throughput, and making roaming a seamless process. Where as the 2.4 GHz range only gives us 3 non-overlapping channels (1, 6, 11). Detailed information on each UNII band can be found below.
- Channel Bonding. While you can perform channel bonding in the 2.4 GHz it is better suited for the 5 GHz range. Channel bonding is how you achieve speeds up to 600 Mbps in 802.11n it does this by making the channels 40 MHz wide compared to 20 MHz wide. Channel bonding at the 5 GHz range still leaves you with 12 non-overlapping channel, while channel bonding in the 2.4 GHz range gives you 1 (possibly 2) channel.
- Future use. The next wireless standard after 802.11n, is most likely going to be 802.11ac which is promising us Wi-Fi speeds in the Gbps’s it plans to accomplish this by using 40, 80, or 160 MHz wide channels this is going to rule out the 2.4 GHz range completely. (Unless it’s changed.)
- UNII-1/Lower Band (5.150 to 5.250 GHz) Non-overlapping channels 36, 40, 44, 48
- UNII-2/Middle Band (5.250 to 5.350 GHz) Non-overlapping channels 52, 56, 60, 64
- UNII-2 Extended (5.470 to 5.725 GHz) Non-overlapping channels 100, 104, 108, 112, 120, 124, 128, 136, 140
- UNII-3/Upper Band (5.725 to 5.825 GHz) on-overlapping channels 149, 153, 157, 161, 165
CCIE or Null! 