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Wireless - Wi-Fi Service Level Expectations
This article explains service level expectations for the UChicago wireless connectivity.
The University of Chicago Wi-Fi service provides wireless networking for all staff, students, and faculty. It is also available to eligible guests of the University of Chicago. There are many challenges in delivering this service over such a large campus to such a numerous and diverse population.
University of Chicago wireless users can expect a good experience for low to medium bandwidth activities in areas with low to medium wireless user population density. These activities include web browsing, checking email, chat, or printing. Most wireless locations on campus do not have high user population density, so most locations should yield a good experience. However, as the number of wireless users rises in that area, network speed will decrease for all users. This happens during class sessions or sporting events, for example. High bandwidth activities like streaming video or large network downloads will also decrease the speed and responsiveness of the network for all users in an area.
Factors Affecting Service Quality
There are six factors that determine the quality of your Wi-Fi experience:
- The installed infrastructure in an area, that is, the number of wireless access points
- The number of wireless users and devices in an area
- The types of user activities occurring in an area
- Limitations of the Wi-Fi protocols
- The level of radio interference in an area
- An individual client's wireless hardware and software
IT Services can modify the wireless infrastructure, but cannot easily modify the other factors. The protocol and regulatory limitations are fixed.
There are two basic types of wireless service supported on the University of Chicago's campus: 802.11g (2.4 GHz) and 802.11n / 802.11ac (5 GHz).
A single access point can serve approximately 25 devices on 802.11g (2.4 GHz), and 25 devices on 802.11n / 802.11ac (5 GHz). This limit is primarily a result of Wi-Fi protocol design. These numbers are estimates and will vary depending on users, devices, and user activities.
Increasing the number of users and devices supported in an area is not as simple as adding additional access points. A maximum of three 802.11g (2.4 GHz) radios can be installed close to one another, due to the number of available non-overlapping wireless channels (2.4 GHz band) allocated by the FCC and supported in Wi-Fi products. Adding more than three 802.11g radios near one another will generally decrease network performance.
More bandwidth is available when using the 802.11ac protocol in 5 GHz, so more clients can be reasonably supported per radio. However, many wireless clients on campus are not 802.11ac capable, and many systems that are capable choose to use 802.11n 2.4 GHz due to poor software implementation on the client. Some vendors market their devices as 802.11ac capable but only support 802.11ac in the 2.4 GHz band. IT Services only supports 802.11ac in the 5 GHz band to maximize bandwidth and provide service for high-density applications.
Wireless is a shared medium, meaning users in the same area are sharing bandwidth. The bandwidth resources are finite, so as you increase the number of clients in an area, the network becomes slower for all clients. There is no fairness mechanism built into the Wi-Fi protocols, so it is possible for a single client to consume much of the available bandwidth. This implies that signal strength and connection speed do not necessarily reflect what a user’s Wi-Fi experience will be. A few wireless clients in the vicinity could be consuming most of the available bandwidth in an area, so other clients with a strong signal and high connection rate will experience slow performance. Nearby users can include people and devices on floors above and below. This shared allocation of bandwidth resources is by protocol design.
Interference also plays a major role in user experience. The radio frequencies used in Wi-Fi are also used by many other types of devices. These devices include cordless phones, wireless headsets, wireless microphones, wireless cameras, etc. When these devices operate near a Wi-Fi network, they can cause interference. Interference can also come from sources such as microwaves. The presence of interference can result in a client showing a connection but not being able to perform network operations, slowing down network operations, or completely disconnecting the client from the wireless infrastructure. Interference is often transient, which makes it difficult to find the source.
Wireless client software and hardware also play a significant role in your Wi-Fi experience. Radio characteristics and power vary greatly across client types. It is possible for two different Wi-Fi devices right next to each to have very different Wi-Fi experiences. Client drivers (the software that controls client radios) have historically been a major source of wireless problems.
Over the years, the number of devices on the wireless network has grown significantly. There are now approximately 3,600 access points installed on the University of Chicago campus.
How IT Services Helps
IT Services is working on several strategies to improve the wireless service.
- We have upgraded every Wi-Fi access point to support 802.11n in the 5 GHz band. This will significantly increase the capacity of every Wi-Fi location on campus so we can provide an improved Wi-Fi experience for many users.
- We continue to expand the number of access points in high-density user areas to help alleviate wireless congestion.
- We are deploying access points capable of detecting interference from outside sources. This will help us proactively mitigate interference problems.
- We work closely with Cisco, our wireless vendor, to improve our wireless services.
- We maintain a close relationship with our Academic Technologies Department in order to continue to improve wireless service to faculty and students.
- We will periodically perform thorough capacity and coverage assessment surveys in every building to ensure the appropriate deployment of wireless access points.