This document is intended to provide information about Wi-Fi and other RF technologies and standards, and to outline recommendations and best practices for deploying wireless technologies on campus.  

Like many organizations, Cornell’s wireless networks use the unlicensed RF bands specified by the FCC for Wi-Fi and RF applications. Transmission in these bands conforms to the IEEE 802.11 specifications. See below for details on standards and frequency definitions.  

The variety of currently available consumer wireless devices has the potential to create interference and security concerns for the campus wireless network. These consumer devices include cordless telephones, wireless video transmitters, wireless audio speakers, printers, Bluetooth-enabled devices, Wi-Fi access points, and other wireless devices that have not been installed and set up by CIT staff. 

Why Have We Assembled This Document? 

The use of wireless devices on campus for a wide range of applications has increased dramatically in recent years. Many of these wireless device uses are crucial to mission-critical tasks at the university:  including AV functions in meetings and presentations, and general resource sharing. 

At the same time as the critical need for wireless devices has ramped up, available frequencies on which those devices can operate have become more strictly defined, if not actually more limited.  

It is our hope that providing a set of guidelines on best practices for setup and use of a wide variety of wireless devices will provide technical staff with the resources they need to do the right thing when configuring their unit’s RF equipment, rather than simply proceeding as if their equipment is their only concern.  

Following the advice in this document will help avoid interference between implementations, reduce RF congestion and conflict on campus, improve the end user AV experience overall at Cornell, and in some cases keep users on the right side of the law. 

I. Overview: Standards, Spectrum Availability, and Common Uses 

The FCC has established several allocations of the radio spectrum for more or less uncontrolled use, where the requirements are basically to stay within the allocated spectrum and keep the emission levels below a certain threshold. These portions of the spectrum are called the Industrial, Scientific, and Medical (ISM) bands. The intent was to create pieces of spectrum where devices that needed low-power license-free radiation, or that emitted unintended RF radiation (such as diathermy machines, heat sealers, microwave ovens) could operate.  

There is no licensing of users in the ISM bands and any communications equipment has to accept the interference from other users. In terms of ISM bands that are used around campus for communications systems, we are primarily talking about the 900 MHz, 2.4 Ghz, 5.8 Ghz, and 61 Ghz bands, which are all in current use. (Future use may include other bands as equipment becomes available for them.)  

Within the ISM spectrum, some developers found that they could implement digital communications, eventually culminating in the 802.11 protocol, or Wi-Fi. This has become the major use of two of the ISM bands, but is still subject to interference from other users of the bands such as microwave ovens and other non-communication devices, as well as alternative protocols such as Zigbee or Bluetooth. 

As of 2018, the FCC provides the following two ISM bands of the RF spectrum for in use for Wi-Fi device applications without licensing: 

2400-2500 MHz (commonly called “2.4 GHz”)  This band is used for a variety of technologies including Bluetooth, Cordless Telephones, and 802.11 (Wi-Fi). 

5725-2875 MHz (commonly called “5 GHz” or “5.8 GHz”)  The 5 GHz band expands available 802.11 Wi-Fi bandwidth.  

* Dynamic Frequency Selection (DFS) allows access points to identify and take action to avoid external radio transmissions that are considered primary-use or mission-critical and to automatically select channels with low interference levels. 

Notes: 

• On 2.4 Ghz, only 3 non-overlapping channels exist because of the filter skirt shape. Channel 1, 6 and 11. Devices located on other channels will interfere with the channels above and below them; i.e., a device on channel 3 will impact communication on both channel 1 AND channel 6.  
• Channel 44 is reserved for non-Cornell controlled devices. Networks that operate on the 5.8 ghz band that are not part of the Cornell Wi-Fi network must be confined to channel 44.  
• Generally DFS channels are available on the Ithaca campus, but because of wind shear radars at the major airports in the NY metro area, some of those frequencies are locked out on the NY controller.  

II. Wi-Fi Interference Considerations 

Because Wi-Fi networks have been developed within the FCC spectrum designated as Industrial, Scientific and Medical (ISM), a large number of users take advantage of the spectrum. While Wi-Fi may now be the largest user of this part of the spectrum, there are significant numbers of other users as well – including other kinds of communications and networking equipment, or crude devices such as microwave ovens. Each of these can cause interference to Wi-Fi communications.  

Wireless microphones, cordless phones, and wireless cameras each tend to have a strong steady carrier, often randomly placed in the spectrum or on a channel map different than Wi-Fi. Audio devices may take up a relatively small amount of spectrum, and only take out one or two Wi-Fi channels. Video systems tend to have very wide spectrums and can take out multiple wireless channels.  

Cordless phones, meanwhile, may come and go as calls are handled, and change channels between calls on some systems, taking out different Wi-Fi channels with each call. Some rapidly switch channels, or “frequency hop,” which causes interference over an even wider number of channels.  

All of these types of interference can cause missed packets and retries when an 802.11 Wi-Fi system is nearby.  

Heating devices, such as microwave ovens, but also sealers and some kinds of diathermy have very broad and uncontrolled spectrums. Microwave ovens, for instance, have their frequency determined by the physical dimensions of the magnetron (which vary with temperature and heating) and are driven by unstabilized, barely filtered high voltage. The resulting signal is very broad and moves about in frequency as the oven heats or the voltage varies. These devices also operate at quite high power, 500-1000 watts, typically, although only a small portion should leak out of the cooking space. Noise from microwaves usually takes out all of the 2.4 GHz Wi-Fi channels nearby when they are operating. It’s also worth noting that older ovens have poor door seals and may therefore leak a more significant amount of signal.  

Rogue access points 

Wi-Fi on campus is a coordinated system with all the access points (APs) controlled and arranged by a central system. This helps arrange the frequencies they use to minimize interference. Unfortunately, rogue access points – often put up by users in their offices -- are not coordinated, so they can interfere with the campus system.  

In areas where there are fewer signals, the Adaptive Radio Management (ARM) system on the campus network will move nearby APs off a channel being interfered with, assuming that another channel is available with less interference. However, this can create a ripple effect across that area of campus: when one AP has to move channels, the adjacent APs may then also have to move to avoid this AP on the new channel, which perturbs the APs further out, and so on.  

On the 2.4 GHz band, there are only 3 channels that don’t overlap: 1, 6, and 11. So the calculation of where to move the adjacent APs is very constrained, which often means that the rogue APs and the campus APs are sharing the same channel space and interfering with each other.  

Fortunately, the 802.11 protocol has provisions for each AP to listen for quiet air before transmitting. This helps avoid disrupting a transmission from another AP, but both APs are impacted by the resulting reduction of “air time” to do their communications, lowering their throughput. And if enough APs are sharing the same airspace and channels, or if one AP can’t hear the replies of the other AP’s users, eventually it becomes impossible to find clear air time to transmit, and collisions begin to occur and rapidly degrade the communications.  

Another problem that can occur with uncoordinated rogue APs is poor channel choice. Often, users believe that if they choose a non-standard channel, it will avoid interference. In practice, because the channels are so wide, this may actually make things worse. An uncoordinated AP on channel 2, 3, 4 or 5 will degrade communications on the non-overlapping channels 1 and 6, interfering with and getting interference from both channels. Similarly, an AP on channels 7, 8, 9, or 10 will get interference from and interfere with channels 6 and 11. This multiplies the interference effects of having another AP in the same area.  

Other data protocols 

Data protocols such as Zigbee, which operate in the same bands, can also interfere. 

These use a different channel numbering system which may place some of the channels inside the passbands of the Wi-Fi channels in use. And because they are different protocol, they don’t do the same listen before transmit coordination that fellow 802.11 APs do. 

III. Wi-Fi Network Best Practices for Specific Uses and Applications at Cornell 

Wireless Microphones (see also: FCC website) 

Most wireless mics use frequencies from unused broadcast TV spectrum bands. Because the FCC has recently been auctioning parts of the TV spectrum to wireless broadband service providers, the available acceptable frequencies for wireless mic use are more limited. Use in bands 617-652 and 663-698 must stop by July 13, 2020 (or sooner) to avoid disrupting wireless broadband communications.  

Additional best practices: 

• Frequencies that continue to be available for wireless mics include: 
  • Bands below 608 MHz 
  • Certain frequencies in the 600 MHz guard band: 614-616 MHz 
  • Certain frequencies in the 600 MHz duplex gap: 653-657 for licensed use and 657-663 for unlicensed use
• Be sure to plan and coordinate the frequencies of multiple mics to reduce interference. 
• Mics should not use 2.4 GHz, 5.8 GHz, or 900 MHz bands (that includes Bluetooth). 
• Unlicensed mics must not operate at a power level above 50 milliwatts in the TV bands, or 20 milliwatts in the 600 MHz guard and duplex gap bands. 
• Antenna placement and handling: antennas must not be placed within 10 feet of a wireless access point, or a wireless lock.  
• FCC Consumer Alert for Wireless Microphone Purchases (right sidebar) 

Wireless Video Transmitters 

• Must not use the 2.4 or 5.8 GHz bands unless they are 802.11 devices operating on the campus wireless networks.  
• Must not be analog AM or FM modulation devices – these cause severe interference and will be removed.  

Projectors and AV Systems 

• Must not use analog or incompatible RF technology on 2.4 or 5.8 GHz.  
• Should be standard 802.11 and use the Cornell network. Private networks are an interference problem.  
• The current enterprise wireless implementation doesn’t allow multicast, so Bonjour and other plug and play protocols will not work.  

Security cams 

• Must not use the 2.4, or 5.8 GHz bands unless they are 802.11 devices operating on the campus wireless networks.  
• Must not be analog AM or FM modulation devices – these cause severe interference and will be removed.  

Crestron Wireless Touch Panels 

• Touch panel access points can interfere with other access points and wireless devices using the 2.4 GHz band. 

Other Wireless Appliances (IoT) 

• Apple Pencil (Bluetooth) 
• Zigbee and other protocols operating in the 2.4 and 5.8 GHz bands cause potential interference issues, especially when they operate at significant signal levels. Their deployment needs to be coordinated and approved.  
• LoRa IoT wireless devices must be registered and coordinated on campus. 900 MHz coordination will be needed.  

Assistive Listening Systems 

• For these systems, don’t use RF – use IR connectivity. 

Cordless / wireless phones 

• Must be DECT 6.0 standard phones.  
• No devices operating in the 900 MHz, 2.4 GHz, or 5.8 GHz bands.  

Drones (Unmanned Aerial Vehicles) 

Before planning or implementing any use of drones on the Cornell campus, be sure to review the UAV Guidelines from the Risk Management & Insurance website, and to complete both an UAV Flight Request Form and an Event Registration Form. 

• Most drones use 2.4 GHz for control and 5.8 GHz analog FM for video – these are not compatible with 802.11 systems and will both cause and receive interference.  
• Drones should be controlled on 433 MHz or 900 MHz or 1.2 GHz, and the video systems should be on similar frequencies, not on 2.4 or 5.8 GHz. If drones are run on 2.4 GHz, and receive interference from the 5000+ APs on campus, control issues might be experienced which might put people at risk of being hit by an uncontrolled drone.  

Robots 

• When setting up robots that use wireless controls, work with Network Engineering to ensure the frequencies are configured properly.  
• If intending to use the campus wireless infrastructure, be aware that static IP addresses are not supported nor is multicast.  

Industrial Control Systems 

• With increased use on campus and control system movement into IP and Wi-Fi space, those configuring these systems should register their gateway with Network Engineering. Generally ICS systems should not operate on the 2.4 or 5.8 Ghz bands, especially with conflicting protocols such as zigbee. They may operate on 900 Mhz with coordination and documenting their installations, frequencies and locations.  

Point to Point Radios 

• Most point-to-point systems currently running on campus use the 900 MHz, 5.8 Ghz, or 61Ghz bands. New installations should be coordinated both in spectral use, and with their locations and orientations/polarization recorded. (method? DNSDB? Coordinator?)  

Cellular installations  

• Cellular installations on campus must not use Wi-Fi on 2.4 or 5.8 Ghz bands or other protocols that can cause interference to Wi-Fi communications on the campus network. Licensing agreements need to be amended to call this out specifically.  

Systems intending to use Cornell Wi-Fi 

• The Cornell wireless network is an enterprise-level, routed network, using Network Address Translation (NAT), which does not support all of the features that are present on a consumer grade, layer 2 connected, single subnet network. Specifically, Multicast is generally not supported, so plug and play systems like Bonjour which depend on multicast broadcasts to find other components may not operate correctly or at all. Static IP addresses are not supported.