Wi-Fi mobility in hospitals

RSS

GUEST BLOG BY CHRIS BOLINGER, DIRECTOR OF PRODUCT MARKETING FOR LAIRD TECHNOLOGIES' CONNECTIVITY PRODUCTS BUSINESS UNIT

Most client devices that use Wi-Fi in a hospital are computing devices such as computers on wheels, laptops, tablets, and smartphones. With very few exceptions, the applications that run on these devices do not rely on a persistent network connection. In fact, temporary disruptions in network connectivity usually go unnoticed by users because the applications handle those disruptions gracefully.

In contrast, most applications on medical devices cannot handle disruptions in network connectivity. A disruption of even a tenth of a second (100 milliseconds) can cause a failure in transmission of data from a medical device to the network. Loss of even one data packet can wreak havoc with an application that expects a continuous stream of data.

In a typical hospital, providing a persistent Wi-Fi network connection for a stationary medical device can be difficult. Wi-Fi radio frequency (RF) transmissions between the device and an infrastructure endpoint, called an access point (AP), may be absorbed by lead walls or human bodies, redirected by metal objects and surfaces, or disrupted by sources of RF interference.

When a medical device is mobile, providing a persistent Wi-Fi network connection for that device is even more challenging. The device may move from a location where it has an unobstructed RF connection with an AP to a second location where the connection with the AP is more tenuous to a third location where the connection is lost. As soon as a connection becomes suboptimal or tenuous, the device must switch, or roam, from its current AP to another AP.

Done quickly and effectively, roaming can ensure a persistent network connection and protect the applications that rely on such a connection.

Figure 1: A typical Wi-Fi deployment is a set of overlapping “cells” of coverage.

 

When Roaming Occurs

In a typical Wi-Fi deployment in a hospital, a large area is covered by the radio signals of many APs, with each AP offering a “cell” of coverage. As shown in Figure 1, the coverage areas or cells of many APs overlap. Overlapping coverage cells are a prerequisite for roaming.

A Wi-Fi client device typically associates, or establishes a connection, with the AP that provides the strongest RF signal. Because the signal is strong, the client and AP can negotiate a high data rate for transmissions. As the client moves away from the AP, the strength of the signal decreases and the relative impact of interference sources in the area increases. Some transmitted data packets are not received, forcing the sender to retry the transmission. To maintain the reliability of data transfer over the connection, the client and AP negotiate a lower data rate.

If the client continues to move away from the AP, then it eventually reaches the edge of the cell of coverage for that AP. Beyond the edge, the client is out of range and the connection with the AP is lost. The edge of coverage for one AP may be well within the coverage area of another AP. Before losing its connection with the first AP, the client must roam to the second AP and thereby preserve its connection to the network.

While the most common trigger for roaming is the movement of a client, it is possible for a stationary client to roam. Suppose that a stationary medical device is within range of two APs and connected to one of them. If a nurse positions his or her body between the device and the connected AP, the body may block enough of the Wi-Fi signal to disrupt the connection, thereby forcing the device to switch, or roam, to the other AP.  

How Roaming Works

The roaming process has four steps: Evaluate, Scan, Select, and Roam.

Evaluate:In the Evaluate step, the client determines if its connection with the current AP is suboptimal. The most common way to evaluate the current connection is to examine the strength of the RF signal from the current AP. This signal strength is represented by a received signal strength indication (RSSI) which is typically measured in dBm, or decibels (dB) referenced to one milliwatt (mW or m). If the RSSI for the current AP is stronger than threshold value, then the current signal is considered strong enough, and the client will stay connected to the current AP.

Scan:If the connection is less than optimal, then the client will proceed to the Scan step, where it scans the vicinity for other APs. The client radio checks some or, more commonly, all of the frequency channels on which APs may be operating. For each AP that the client finds, the client records information about the AP, including the RSSI for that AP.

There are two types of scans: active and passive. With an active scan, the client radio issues a probe request on a channel and listens for probe responses from APs operating on that channel. With a passive scan, the client radio does not probe but simply listens for beacons from APs on the channel. Active scans are faster and more reliable than passive scans, but active scans are not allowed on some channels, notably Dynamic Frequency Selection (DFS) channels in the 5 GHz band.

Figure 2: As its connection becomes suboptimal, a client evaluates other APs within range.

 

Select:After obtaining information from all APs that are in range, the client evaluates the APs and selects the one that is likely to offer the best connection, as shown in Figure 2. With rare exceptions, the client will compare APs based on RSSI. Because roaming is a disruptive operation, the client will not switch from its current AP to a second AP unless the second AP offers a significantly stronger signal.

Roam:If the client selects an AP other than the one to which it is connected, then the client must roam from the current AP to the new AP. Because a Wi-Fi client cannot be connected to two APs at the same time, the client cannot associate to the new AP until it first disconnects from the current AP.  Once the client associates with the new AP, the two APs must interact to ensure that the infrastructure is aware that the client has moved from one AP to another.

After associating to the new AP, the client must reauthenticate to the network on which the APs reside. While the process of disconnecting and  reconnecting typically takes only a few milliseconds, the reauthentication process can take much longer – so long, in fact, that it can disrupt applications that require a persistent connection.

Optimized Roaming

The most straightforward way to optimize roaming is to accelerate the reauthentication process. Most hospitals require the Enterprise version of Wi-Fi Protected Access 2® (WPA2®), which is the industry standard for strong Wi-Fi security at Layer 2. With WPA2-Enterprise, when a client associates to an AP, the client and AP conduct a mutual authentication using IEEE 802.1X using an Extensible Authentication Protocol (EAP) type such as PEAP or EAP-TLS. EAP authentication requires several interactions with an authentication server on the network. If there is network congestion or if the authentication server is on a network that is remote from the AP, then EAP authentication may take hundreds or even thousands of milliseconds.

The first time a client associates to an AP on a hospital network, a complete EAP authentication must be performed. When a client roams, however, the EAP reauthentication process can be streamlined so that no interaction with an authentication server is required. There are three methods for accelerating EAP reauthentications:

1.    Cisco Centralized Key Management (CCKM), which is supported by Wi-Fi infrastructure products from Cisco and by clients that are certified for CCX

2.    Opportunistic Pairwise Master Key (OPMK) caching, which is supported with WPA2 by some controller-based Wi-Fi infrastructures

3.    IEEE 802.11r pre-authentication, which does not enjoy broad support today

 

Another way to optimize roaming is to optimize scanning. Two ways to optimize scanning are:

1.    Reduce the number of channels that are scanned

2.    Use active, not passive, scanning

Even though the 2.4 GHz band supports 11-14 channels, depending on the regulatory domain for your part of the world, APs in a hospital will operate on only three of those channels. Rather than scanning all 11-14 channels, a client should scan only three. The 5 GHz band supports even more channels than the 2.4 GHz band, and APs may operate on any or all 5 GHz channels. It still may be possible, however, to limit the channels that a client scans when making a roaming decision.

A mobile medical device may not want to scan DFS channels. That’s because active scans are not allowed on DFS channels. A client must do passive scans, and passive scans take much longer than active scans. Mobile medical devices cannot skip DFS channels, however, if any APs to which those devices can connect are operating on those channels. Network administrators must weigh the pros and cons of using DFS channels for mobile medical devices.

Conclusion

Many applications that operate on medical devices require persistent network connections. As the use of Wi-Fi on medical devices increases, so will the need for seamless roaming of those devices. Seamless roaming requires several sophisticated processes that, unfortunately, are not supported by all Wi-Fi client radios. Medical device makers must choose their Wi-Fi radios carefully, and network administrators in hospitals should include roaming tests in the criteria for selecting medical devices.

For more details on Wi-Fi roaming in hospitals, read the Laird Technologies white paper, Wi-Fi: The Importance of Mobility in Hospitals.

About the author. . .  Before becoming Director of Product Marketing for Laird’s Connectivity Products Business Unit,  Chris Bolinger was the Vice President of Engineering for Summit Data Communications, Inc., a company that he helped found in early 2006 when he left the Wireless Networking Business Unit of Cisco Systems.  Prior to joining Cisco in 2000, Bolinger worked as a software engineer for five years and a Product Manager for nine years at software companies such as Sterling Software and PLATINUM technology. Bolinger earned a B.S. in Computer Science at the University of Akron and an MBA at George Mason University.

 

Discuss this Blog Entry 57

on Apr 3, 2014

Glad found these mapping. It can be useful to patients as well.
www.spectra.com

on Apr 27, 2014

The source work with peace working under guidelines to form with more active sensible ideas and it runs through max terminal.
buy followers instagram

on May 5, 2014

I high appreciate this post. It’s hard to find the good from the bad sometimes, but I think you’ve nailed it! would you mind updating your blog with more information?
https://www.rebelmouse.com/bobbyriomagneticmessaging/

on Jun 7, 2014

This is a great inspiring article.I am pretty much pleased with your good work.You put really very helpful information...
how can i control my anxiety naturally

on May 10, 2014

This is such a great resource that you are providing and you give it away for free.
winning the one reviews

on May 22, 2014

I can set up my new idea from this post. It gives in depth information. Thanks for this valuable information for all,..
orange bail bonds

on Jun 2, 2014

One essential thing that you need to take into account prior to you create your speech is to get a particular theme. There are a lot of theme samples you can see around especially on the internet that's relevant to the groom’s mother wedding speech. It is extremely easy to combine concepts or tales in your speech in an arranged approach after you already have a particular theme. Find out more on this blogspot blog

on Jun 25, 2014

Gabriel Jenkins
I must say, I thought this was a pretty interesting read when it comes to this topic. Liked the material. . .

on Jul 8, 2014

Nice info! I was able to help a colleague of mine to get through a problem he was stuck in regarding this topic. Thank you for providing this info. My colleague thanks you as well! kontorimööbel

on Jun 17, 2014

This is very educational content and written well for a change. It's nice to see that some people still understand how to write a quality post.!
ways to improve vision without glasses

on Jun 17, 2014

Interesting post. I Have Been wondering about this issue, so thanks for posting. Pretty cool post.It 's really very nice and Useful post.Thanks
weiterbildung

on May 29, 2014

What? Is it time for recess yet? He must convince Lalita and her outrageous family, however, that his veneer of snobbery is not who he truly is in order to win her heart. This work has a lot of interesting information, and is a very resourceful piece. Braun Replacement Pulsonic 9000 Series Foil I recently purchased this new shaver head through Amazon. Diabetes Meal Plan Type 2 Diabetes In Older Cats Symptoms Worked just like I wanted it too. For the one that comes with it is for close up pictures. Though there are several cartridges they really seem to last a long time and each cartridge is around $14.00, better than $30 - $40 a cartridge! Type 1 Diabetes Ribbon Pin

on Jun 22, 2014

Wonderful illustrated information. I thank you about that. No doubt it will be very useful for my future projects. Would like to see some other posts on the same subject!
seo uk

on Jun 8, 2014

The starter point and active plea to cover on the topic parameter to sum big values to charge meet on the level up garden with the point to buy youtube views cheap

on Jun 18, 2014

I am hoping the same best effort from you in the future as well. In fact your creative writing skills has inspired me.
how to get fake instagram followers

on Jun 11, 2014

The better new connection with more plenty arrangement will compare big portions to connect on the major clicks to submit more value ideas and facebook votes

on Jun 23, 2014

The slight conversions and more power locations will decide big opportunities for the aiming process after big ride saving portions to buy facebook photo likes

on Jul 2, 2014

thanks for sharing....

on Jul 2, 2014

The complete system points after click notes with sensational acts to the big pattern rides with simple teach portion on the click source. how to treat diabetes

on Jul 4, 2014

I wanted to thank you for this great read!! I definitely enjoying every little bit of it I have you bookmarked to check out new stuff you post. Company Spot

on Jul 7, 2014

I wanted to thank you for this great read!! I definitely enjoying every little bit of it I have you bookmarked to check out new stuff you post.
free credit score

on Jul 7, 2014

thanks for this usefull article, waiting for this article like this again.
3 credit scores

on Apr 19, 2014

Part of a class I am taking involves this particular subject and I am researching for information to use in an upcoming report. Your post is really helpful; do you have any others on this topic?
free vpn

on May 14, 2014

Thanks for your post. I’ve been thinking about writing a very comparable post over the last couple of weeks, I’ll probably keep it short and sweet and link to this instead if thats cool. Thanks.
conversation chemistry pdf

on May 18, 2014

I read a article under the same title some time ago, but this articles quality is much, much better. How you do this..
potty training in 3 days

on Jun 8, 2014

Thanks so much for sharing this awesome info! I am looking forward to see more postsby you!
60 second panic solution review

on Jun 10, 2014

I admit, I have not been on this web page in a long time... however it was another joy to see It is such an important topic and ignored by so many, even professionals. professionals. I thank you to help making people more aware of possible issues.
how to cure acne fast at home

on Jun 23, 2014

This content is written very well. Your use of formatting when making your points makes your observations very clear and easy to understand. Thank you.
bail bonds culver city

on Jun 24, 2014

I admit, I have not been on this web page in a long time... however it was another joy to see It is such an important topic and ignored by so many, even professionals. professionals. I thank you to help making people more aware of possible issues.
free music online

on Jul 12, 2014

There is so much in this article that I would never have thought of on my own. Your content gives readers things to think about in an interesting way. Thank you for your clear information. metal garden trellis

on Apr 20, 2014

I have found this article very exciting. Do you have any others on this topic? I am also sending it to my friend to enjoy your writing style. Thanks
buy instagram likes

on Jul 9, 2014

Nice blog and absolutely outstanding. You can do something much better but i still say this perfect.Keep trying for the best.
watch movies online

on May 5, 2014

I would like to say that this blog really convinced me to do it! Thanks, very good post. enjoytoday.be

on May 9, 2014

This conent is simply exciting and creative. I have been deciding on a institutional move and this has helped me with one aspect. Cheers!
animal onesies

on May 23, 2014

This embroidery machine is awesome! Several owners had negative issues...I suggest if you purchase this particular embroidery machine that you remember to thread it correctly, push the bobbin down slightly after you insert it, make sure you use 90# wgt bobbin thread, and go to Brother's website for instructions on making adjustments to bobbin tension. We tried to get some more life out of the litter by adding some baking soda, this was a terrible idea! Cleaning the feces out every 7-10 days and stirring the litter does seem to help and is much better than the 2-3 times a day we were messing with the clumping litter, and I don't mind doing it myself. I bought a regular old percolator. I'm a convert! Two thumbs up! Can Tomato Plants Grow Year Round Alabama fertilizer
Back to dryer sheets for me. The last section is dedicated to persuading you to embrace Christ as your savior. This is a must have app, works fantastic! Convert your paper docs to pdf with very good quality! Who needs a scanner when you have this app! Tomato Plant Dying Top Down Indiana Tomato Plant Sprouting Time Arkansas www.joblink-inc.org. Learn more

on May 23, 2014

Your article has helped me to understand this subject on a different level. I would like to appreciate your efforts for exploring this issue. Thank you for your information.
marble restoration

on Jul 5, 2014

Thank you very much for the sharing! COOL..
photobooth

on May 24, 2014
on Jun 11, 2014

Keep up the fantastic piece of work, I read few blog posts on this web site and I believe that your site is real interesting and has lots of great information.
baby2000

on May 27, 2014

Cold calling hundreds of people and putting them to my web presentation and replicated website. This 2011, they have created a handset that is all about sheer power. This will get you excited about trying something new without the pressure. http://www.helpwyz.com/buy-twitter-followers/

on Jun 1, 2014

I have been studying this topic for a long time. You have provided great information in your post and some things I have not seen in other content I have read by others.
DUI Attorney

on Jun 3, 2014

Thank you for helping people get the information they need. Great stuff as usual. Keep up the great work!!! Boxsäcke

on Jun 6, 2014

This post has helped me for an article which I am writing. Thank you for giving me another point of view on this topic. Now I can easily complete my article. Cheers
http://www.bestproteinpowderguide.co.uk/

on Jun 21, 2014

For most of the people who are overweight, it becomes very difficult to reduce the extra kilos of the body. Rigorous workouts, crash diets etc. almost seem like an impossible thing to be done. Extra kilos in the body also mean reduced stamina which ultimately makes it very difficult to reduce weight. Margarita Shelton

on Jun 22, 2014

Isn’t it really tough to pretend like you don’t care when you really do care? If you are overweight, then you may have to put the act of you don’t care almost every day. Be it in grocery store, your work place or during a get together, it’s always like people have their eyes on you. Arlene Barnett

on Jun 23, 2014

Thank you for taking the time to publish this information very useful!
bowwowinsured.com

on Jun 25, 2014

Thanks you very much for sharing these links. Will definitely check this out..
how to text your ex to get her back

on Jun 25, 2014

Pretty good post. I just stumbled upon your blog and wanted to say that I have really enjoyed reading your blog posts. Any way I'll be subscribing to your feed and I hope you post again soon. Big thanks for the useful info.
buy trick photography and special effects

on Jun 27, 2014

Since the popularity and attention that Garcinia Cambogia has receive since it was shown on television, many researchers, investigators, and costumer have been working to discover the effectiveness that this diet product has. Mattie Clarke

on Jul 1, 2014

Your work is very good and i appreciate you and hoping for some more informative posts.keep writing

jack walker

Please or Register to post comments.

Blog Archive
Newsletter Signup
Connect With Us

Sponsored Introduction Continue on to (or wait seconds) ×