Topics Map > University of Chicago > IT Services > Phones & Internet Connections > Wireless Data Networking
Topics Map > University of Chicago > IT Services > Phones & Internet Connections > Wireless
Wireless - Wi-Fi Service Level Expectations
This article explains service level expectations for the UChicago wireless connectivity.
The University of Chicago Wi-Fi service is intended to provide wireless networking for all staff, students and faculty. It is also available to all qualified guests of the University of Chicago. There are many challenges in delivering this service over such a large campus to such a great many and diverse set of clients.
University of Chicago wireless clients can expect a good experience for low to medium bandwidth applications in areas with low to medium wireless user populations. These activities include web browsing, checking email, chat, printing, etc. Most wireless locations on campus do not have high user populations, so most locations should yield a good experience. As the number of wireless clients increase in an area, the speed of the network will decrease for all users. This happens during class sessions, sporting events, etc. High bandwidth applications like streaming video or large network downloads will also decrease the speed and responsiveness of the network for all users in an area.
Basic Factors Effecting Service Quality
There are six basic factors that determine the quality of your Wi-Fi experience:
- The installed infrastructure in an area (i.e., the number of wireless access points).
- The number of wireless clients in an area.
- The types of clients 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 twenty five 802.11g (2.4 GHz) clients and twenty five 802.11n / 802.11ac (5 GHz) clients. This limit is primarily a result of Wi-Fi protocol design. These numbers are estimates and depending on the clients and the type of usage these numbers will vary.
Increasing the number of clients 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 in close proximity. The limit of three neighboring 802.11g radios is 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 in close proximity 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. This is done in order to maximize bandwidth and to be able to provide service for high density applications.
Wireless is a "shared medium," which means that the clients in an 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. One implication of this is that signal strength and "connection speed" do not sufficiently reflect what a client's Wi-Fi experience will be like. A few wireless clients in the vicinity could be consuming most of the available bandwidth in an area, so that other clients with a strong signal and high connection rate experience slow performance. Nearby clients can be on floors above and below. This shared allocation of bandwidth resources is by protocol design.
The types of clients (802.11g, 802.11n and 802.11ac) affect the user experience, as well.
Interference also plays a major role in the quality of the 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 are in operation in the same vicinity as 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 (software that control 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.
What is IT Services doing to help?
IT Services is working on several strategies to improve the wireless service.
- IT Services has upgraded every Wi-Fi access point to support 802.11n in the 5 GHz band. This will significantly increase the basic capacity of every Wi-Fi location on campus, providing an improved Wi-Fi experience for many clients.
- IT Services is continuing to expand the number of access points in high user areas to help alleviate wireless congestion.
- IT Services is deploying access points that are capable of detecting interference from outside sources. These access points help IT Services to proactively mitigate interference problems.
- IT Services continues to work with our wireless vendor (Cisco) to improve our wireless services.
- IT Services maintains close a relationship with our Academic Technologies Department in order to continue to improve wireless service to faculty and students.
- IT Services will be performing thorough Wi-Fi capacity and coverage assessment surveys in every building to ensure the appropriate deployment of wireless access points.