40. What is wireless quality of service (QoS) and how is QoS quantified?

Quality of service refers to providing preferential treatment to high-priority data. QoS can be applied to wired and wireless protocols.

Typically, throughput (bits/second), latency (ms), jitter (ms), and dropped packet rate are the parameters used to quantify QoS, although a particular medical device might specify other parameters.

802.11 provides four access categories (QoS levels): voice, video, best effort, and background (listed in descending order of priority). Devices with voice settings have the best opportunity to connect to the network and so, statistically, should have the lowest jitter, dropped packet rate, and latency. The article “Medical-Grade, Mission-Critical Wireless Networks” provides a good discussion of QoS.34 See section 5.5 of ANSI/AAMI/IEC TIR80001-2-3:2012 for information on QoS mechanisms.35

Wired Ethernet (802.3) has QoS mechanisms including ToS (type of service) and 802.1p.

41. What QoS level is required for a Wi-Fi wireless network with medical devices?

There is no one QoS level for every medical device—QoS requirements depend on specific medical devices, manufacturer recommendations, and the HDO’s existing QoS policy.

It is important to remember that QoS settings must be applied in both directions. That is, a device that requests a high QoS setting for data it transmits does not automatically cause the data transmitted to that device to have the same QoS settings. Also, the wired and wireless network segments handle QoS differently: organizations should plan a combined wireless and wired QoS mapping and classification scheme for all critical traffic.

Generally speaking, most organizations do not need to modify the wireless QoS settings from defaults. Usually enabling QoS in WLAN infrastructure hardware enables the Wi-Fi Alliance–recommended settings that work for voice, video, background, and best effort traffic. When the wireless traffic enters the wired segment of the network, wired QoS tags may be applied.

Determining the QoS required for devices in your organization should include these steps:
a. Obtain the specifications for each type of wireless device supported on the WLAN. NOTE: As long as someone is putting the list together, consider keeping it up to date as a tool for the future as new devices are brought online and old devices are removed.
b. Refer to your WLAN infrastructure and wired LAN infrastructure best practice guides for healthcare or enterprise deployments.
c. Quantify medical device or application-level thresholds that exceed acceptable levels. These metrics include maximum allowed jitter, latency, and packet loss rate in addition to any other parameters a device manufacturer may include. These parameters will guide decisions for marking the traffic: those that require the lowest jitter, latency, and packet loss rate will generally receive the highest QoS settings.
d. Since the wireless network is connected to a wired LAN, the wired LAN must also be configured in parity with the wireless network settings. For example, if medical telemetry needs to be marked as high priority, the wired LAN must either trust those markings (recommended) or—if configured to inspect and police the traffic—it must apply a level of priority consistent with the wired LAN QoS policy. Wired QoS policies have many more options than wireless networks do.
e. See section 5.4 of ANSI/AAMI/IEC TIR80001-2-3 for more information on network performance requirements.35