[Wireless Considerations in Healthcare Environments]

첨부 wireless_hc_environ061208.pdf

Wireless Considerations in Healthcare Environments
Version 1.0
May 14, 2008

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Wireless Considerations in Healthcare Environments
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RF Design Considerations
Overview
The purpose of WLANs is to provide mobility for current and future applications. Often applications can be moved from the wired media to WLANs with little effort and few problems. But often the applications that were developed on the wired media do not have the connection logic or sufficiently flexible timing values to move gracefully to a WLAN, which becomes a WLAN design issue since applications have different bandwidth requirements.
The 802.11 standards are 10 years old and differ greatly from the latest 802.11 specifications. The latest 802.11n specification has protocol and hardware differences that are far different than the 1997 specification. Because the protocols and hardware of 10 years ago must interoperate with protocols and hardware simultaneously on the same RF media (air), the interoperation of the old and new becomes a design consideration. With wired networks those differences are separated and segregated by an Ethernet cable to the point of the switch port. Once the signals are in the switch, all signals becomes equal. Therefore, the WLAN design must consider the performance of each client device type and the application(s) that run on the client.
The Wi-Fi Alliance has a certification process for clients and access points (see the link in Appendix B, “References”). The Wi-Fi Alliance is an organization that is supported by the majority of large companies selling Wi-Fi products. The Wi-Fi Alliance’s certification processes are optional and there is no requirement for a client device or an access point to obtain Wi-Fi certifications. The vendors of Wi-Fi products pay fees to the Wi-Fi Alliance to have their devices tested for interoperability. The devices are tested to adherence to 802.11 specifications, but only to the level and to the parts of any specification that the Wi-Fi Alliance deems necessary.
It is important to consider the fact that a product that carries a Wi-Fi certification may not be of sufficient product quality to be considered enterprise class. The devices are not tested for radio signal strength and, to date, there is no certification testing for secure fast roaming, although there is an 802.11 Task Group (802.11r) working on a secure fast roaming specification. The 802.11r specification takes into account the 802.11e QoS and traffic stream specifications. Excluding 802.11r, almost all roaming decisions are made by the client and not the access point. The access points and the wireless controller have little if anything to do with client roaming. The quality of roams depends in a large part to how well a client’s firmware, radio, and the operating system work together. A client with a good integration of these attributes will have better roam times and more consistent roams.
The Wi-Fi Alliance’s Web site maintains a searchable, up-to-date list of devices that have passed their certification tests. Part of the process of evaluating the performance of clients to be added to your WLAN should include checking the Wi-Fi Web site to determine if the client is 802.11 certified and if it supports EAP and other items that may be required. The site provides information on what each certification involves. The CTIA Certification Program for cellular phones now requires that dual-mode WLAN phones go through the Wi-Fi certification for dual-mode phones.