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DAS continues to be used in several venues, especially large healthcare facilities.  This despite the reluctance, or even denial of responsibility, by WLAN AP manufacturers to support wireless networks that use DAS.   This makes for difficult decisions by hospital designers and administrators.

I have spoken with several WLAN instructors regarding this, and they have all simply said "Don't use DAS". 

Outstanding companies, such as InnerWireless, provide excellent design services and remediation for their customers, but they too have difficulties convincing potential customers to use the technology.

The arguments in favor of using DAS, especially to industries already invested in or familiar with the technology are strong.   On the other hand, trying to diagnose networking problems without the assistance of the wireless Infrastructure manufacturer can be very trying.

What suggestions can you make regarding the likelyhood of succesfully installing and maintaining a WLAN network over DAS ?

Suggestions for particular equipment to merge together, or stay away from, would be especially appreciated.

Thanks.

Hi Howard,

As you probably know already - Re: "Don't use DAS" - is correct as it is mentioned in the CWNA / CWDP training material.

(I hope the WLAN instructors / CWNTs you talked to have explained in detail what the issues are). It is not only about providing

services, but also issues doing the analysis and wireless security (WIPS) also has it challenges using DAS.

The main reason is how the WiFi protocol works and it creates issues "hidden nodes".  We have seen this in countries in Asia were

they want to go "cheap" by using 1x WiFi AP and connect a very large DAS system to it (or splitters and amplifiers/antennuaters

where needed).  From a signal strength measurement perspective "measuring the bars" everything looks okay, until more and

more devices come on the network then the DCF (Distributed Coordination Function) will have challenges, frame coordinations,

RTS/CTS can be enabled, but still have challenges, CCI/CCA, basically what you are doing is creating a very large cell with many

WiFi devices in it. 

In most cases (e.g. airports) these networks (DAS and WiFi) will be separately deployed, however in 2013 I spoke to a company

called Axelwireless (now Cobham) that they connect WiFi APs to the backbone (and provision PoE, PoE+ and DAS is used as

a Distribution System only for the cabling back to the core switches/routers).  I do not have the capacity details, but now with

802.11n, 802.11ac, 802.11ac there is more demand on the capacity of bandwidth of the backbone. You can check with them as

with other DAS-vendors. 

Another discussion I had last Saturday at the ITU (International Telecom Union) event about Smart Cities is that 2x vendors discussed

to move away from DAS, but more go for the small cell solutions (but these are cellular/mobile vendors and not WiFi vendors). Another

vendor has an integrated solution with 16x radios built-in (for all type of services, including WiFi, but mainly for Smart City designs and

outdoor environments).

Search on BICSI and DAS:

Recently BICSI released a standard - Distributed Antenna Systems   

DAS is more of the integration of business/mission critical services (e.g. First responders, like Firebrigade, Emergency service, Police, etc.)

https://www.bicsi.org/book_details.aspx?Book=BICSI-006-CM-15-v5&d=0

I work closely with the team, but WiFi is not part of this. Next month I have a further discussion with the BICSI Wireless committee

about the WiFi aspects as well.

Presentations - BICSI Las Vegas conference 20th-23rd September:

• Designing wireless (WiFi) networks for buildings 3-hour hands-on Workshop
• https://www.bicsi.org/fall/2015/Schedule.aspx?d=0  
• [EDIT]  the reason BICSI removed it from the site as this session is fully booked already

• The Need for Wireless Standardization, Certification, Accreditation & Wireless Service, Security Management and Auditing
• https://www.bicsi.org/fall/2015/Schedule.aspx?d=3

WiFiTrek

If you happen to be at the BICSI conference let me know (as you can find more about DAS in detail at this conference)

it is more "Cabling" and "DataCentre" focused, but wireless is coming up.

Otherwise if you are at the (Certitrek/CWNP) WiFitrek conference in San Francisco we can discuss in further detail.

Best regards,

Ronald

CWNE/CWNT

Board of Advisors of CWNE certification

Ronald,

Thank you so much for all of the information.  I had not heard the details previously.

Several years ago my company had experienced large problems at an Asian airport.   Although our 2.4 GHz Wi-Fi performance was very poor, our Bluetooth devices worked perfectly.

At the time, I had surmised other problems in the RF environment.   Now I have a different perspective, and want to research the problem a little further.   

I know that DAS providers consider MIMO-DAS to be especially troublesome to design, and except for the potentially reduced airtime, I would expect 802.11ac to complicate the issue even more.