Thursday, December 12, 2019
Tuesday, January 2, 2018
The Importance of System Engineers (SEs)
The Importance of Customer Support
Friday, November 24, 2017
What are Antennas
|Examples of increasing antenna gain. Top: Low gain dipole. Middle: High gain dipole. Bottom: High gain directional.|
- Just as antenna designers cannot build a perfect sphere, they cannot build a perfect cone. As a result, there is some amount of RF energy that is projected and received in the other directions. These are known as backlobes and sidelobes, as seen in the figure above. If two neighboring antennas are placed very close together, they can interfere with each other, thus a certain amount of separation distance (at least a few feet) is generally recommended when placing directional antennas next to each other.
- The beamwidth is defined by where the energy of the antenna drops by 3 dBi (i.e. half) of the peak. Thus, while the gain of the antenna is less beyond this beamwidth, it is also generally not zero, which needs to be accounted for in Wi-Fi design.
|Examples of different antenna types, with their typical potential for beamwidth and gain.|
APs with Internal Antennas
APs with External Antennas
Monday, October 16, 2017
What Has Happened
A Summary of How WPA2 Security Works
A Summary of the Vulnerability
How this Vulnerability Impacts Access Point Products and Networks
For More Information
Friday, September 8, 2017
Generally, three are two types of bandwidth throttling available on network equipment:
- Per-User Bandwidth Throttling: This limits the maximum amount of Internet bandwidth that each client device can consume
- Per-Subnet/VLAN Bandwidth Throttling: This limits the aggregate maximum amount of internet bandwidth that all client devices on the subnet / VLAN can consume at one time.
Unfortunately, setting the oversubscription ratio is an empirical exercise, and over time, the oversubscription ratio tends to decrease as more devices, each consuming more bandwidth, are connecting to your networks. In the pre-smartphone days, a 30:1 or even 40:1 was common for most wired / wireless networks.
Determining Appropriate Bandwidth Throttling Values
Of course, in reality complex networks are an Animal Farm (i.e. while all client devices are equal, some client devices are “more equal” than others). Thus, different classes of users will require different levels of service.
Tuesday, August 15, 2017
What is Tri-Band?
Why is Tri-Band Better than MU-MIMO?
|Multi-User Multi-In Multi-Out (MU-MIMO)|
- Increased overhead: The sounding frames and their responses consume airtime. While this is less than the presumptive gains of talking to multiple client devices simultaneously, it does indicate a loss. Most MU-MIMO access points only get a 1.7x - 2.2x increase in speed when talking downstream to three compatible client devices.
- Client device compatibility: The client devices need to be compatible with MU-MIMO in order to understand the sounding frames and to send the appropriate response. As of August 2017, there are still surprisingly few MU-MIMO compatible client devices on the market. There are some USB dongles available for PCs. The flagship mobile client device for MU-MIMO had been the Samsung Galaxy Note 7, which failed in the market for unrelated incendiary reasons. The Apple iPhone 7, while originally rumored to support it before its launch, quietly did not support MU-MIMO. Given Apple's notorious secrecy, we still don't know whether or not the upcoming Apple iPhone 8 will or will not support MU-MIMO.
- Client separation: MU-MIMO requires that the client devices it talks to simultaneously must be physically separated from each other. If the client devices are in too-close proximity, the beam forming won’t be able to successfully maximize the signal at one client and minimize the signal of the other (neighboring) clients.
- Downstream only: MU-MIMO only works for downstream traffic, from the AP to the client device(s). Upstream traffic from each client device to the AP must still happen one at a time, otherwise the AP will hear multiple client devices at once and won’t be able to distinguish between them.
The Takeaway Message
Monday, July 31, 2017
A Simplified Explanation of the Physics
A Simplified Explanation of the Math
- RSSI = Received signal strength indicator [dBm]
- d = distance of wireless link [m]
- f = operating frequency of wireless link [Hz]
- c = speed of light (i.e. 300 billion m/s) [m/s]
- PTx = transmit power of transmit radio [dBm]
- GTx = gain of transmit antenna, less cable losses [dBi]
- GRx = gain of receive antenna, less cable losses [dBi]