Integrating a wireless LAN into an existing wired LAN
In determining a basic framework for the replacement of low-voltage signal wiring with wireless systems there are common elements that, once identified, will simplify the network design. This is true of most design, as is evidenced by the unfortunate proliferation of such techniques as "cut and paste," "cookie-cutter," and simple plagiarism, whether through expediency or laziness. Every sophisticated network is segmented according to function; this could be by department, process area, access rights, or any other parameter the network administrator needs in order to properly administer and secure the network. As wireless local area networks (WLANs) become more ubiquitous, it is becoming almost a fait accompli that necessary expansions of existing wired networks will be either extended-or replaced-by WLANs.
The cost difference in implementing a WLAN to that of maintaining an existing wired network is enormous in favor of the WLAN. We are not talking about the initial capital expense, even though the savings are considerable; we are also talking about long-term operating and maintenance (O&M) costs and return on investment. As I demonstrated in a proof of concept (POC) project, which was described in the February 2015 issue of Control Engineering, the initial expense for installation of an operational WLAN was 78% less than a comparable wired link. Consider also that the wired link provides a simple point-to-point connection versus a WLAN providing coverage over a wide area; the benefits of a WLAN add up quickly.
Within these cost savings an almost immediate return on investment (ROI) from the elimination of the physical medium and the labor required to install it can be realized. For the cost of the single-wired link in the POC, six WLANs could have been installed with more capacity and coverage. Add to this the cost of maintenance and replacement of wired systems, which can be considerable, versus the minimal cost of simply replacing an access point (AP), and you can see the distinct cost advantage of a WLAN. An additional benefit is time: for the POC the installation time was a two days; the wired system would have required two weeks to provide a working system.
These factors alone speak to the utility and benefits of WLANs. However, there are still many wire-line aficionados who are very attached to their cables, routers, and switches. I am not stating that these systems will go away any time soon. There is and will always be a place for physical, wired networks, particularly those based upon optical fibers. Copper networks will always be with us, but they serve a very specific and useful purpose, and the returns would not justify their replacement.
This is not to say that performance, availability, and utility of segments of some existing wired networks cannot be vastly improved by replacing them with WLANs. Traditionally, this approach was taken when a new network segment or device was out of the physical range of an economical wired network extension. Another situation in which WLAN use was favorable was when the addition of cable and conduit underground or overhead was impossible or prohibited; we have done several point-to-point bridged wireless connections under these conditions. These wireless links, though very limited in function, work very well while wired connections are failing or have failed on a regular basis.
In considering the move to integrate a WLAN into an existing wired network, it is advisable to start small. This is not a reflection on the technology, as WLANs can theoretically be as large as desired (the theoretical limit is 2,007 clients to a single AP). Starting with a small WLAN segment will allow network administrators and users to become accustomed to the technology and will "soften the blow" to the wire-line diehards. This approach will provide a "learning curve" and educate users on the network’s capabilities.
While there will be pitched resistance in some quarters to the implementation of WLANs, users will expect—if not demand—the implementation of a wireless network given the ubiquity of portable wireless devices. In the workplace, particularly in the industries this magazine serves, the use of wireless technology will greatly enhance monitoring capabilities, allowing flexibility and mobility along with enormous cost savings. The ability of a mobile worker to access data or view process operations from a mobile device such as a tablet or smartphone will translate into incremental increases in worker efficiency and productivity. These capabilities, along with the savings in long- and short-term costs, are making the adoption of WLANs in the process industry hard to ignore.
Small network segments allow an admin to work on a pilot scale. An audit of wired devices should be the first step; this will determine which devices actually do need to remain wired. There are several reasons for allowing a device to remain wired: the device is not suited to wireless communication due to the age of the technology; or the device is "mission critical" and needs to be physically connected for redundancy or fault tolerance. This first audit will give the admin or the designer an idea of where to begin the required surveys.
Once the surveys are completed, is the next step is simply a matter of placing the AP(s) and securing the network. Depending upon the size of the segment being replaced, there are several security options available. It is likely that an authentication server is already in place if this is a large enterprise network; the user database will not have to be rebuilt, greatly expediting commissioning of the WLAN. For smaller networks, it is probable that older equipment will need to be upgraded to become wireless capable; there are many options to make this happen. It is also probable that the budget for replacement of the wired LAN will likely include upgrade funding. It becomes apparent that upgrades are advisable in order to get the fullest benefit from the new WLAN; old technology will simply slow everyone down, and it defeats the purpose of the upgrade and expansion.
Finally, and I bring this up with some trepidation, progress is a double-edged sword. For everyone that benefits from the implementation of new technology, there will be someone who loses. Depending upon where the losers are in the food chain, they can create varying degrees of mayhem. It is advisable that the administrator does his or her homework and has all the facts ready for the eventual (and contentious) meetings that will be convened over the proposed upgrade.
The two largest concerns tend to be cost and security. The bean counters who seem to hold sway over the industry are actually on the right side of this one: It simply costs less to install and operate a wireless network. Concerning security, great pains and Herculean efforts have been taken by some very talented people to ensure that WLAN security is robust and that properly protected WLANs are practically impenetrable. With the possible exception of physically destroying equipment or jamming (analogous to cutting cables or destroying switches and routers, which are NOT federal crimes like jamming is), WLANs are extremely durable. The POC network worked very well throughout a harsh winter, which included a foot of snow at one point. Hacking a WLAN is also extremely difficult; the latest and greatest encryption techniques have been brought to bear on the technology. Most hacking exploits have succeeded by using "human engineering" techniques and are inside jobs—it is estimated that over 80% of all network breaches are an inside job. Suffice it to say that WLANs are more secure and robust than wired networks in many ways.
Integrating WLANs into existing wired networks is not difficult or daunting. It is a natural progression in a very sophisticated technology that has been honed to a fine point by some of the best minds in the business. Upgrading your wired network to a WLAN is more a matter of changing a user’s work habits than any radical lifestyle change.
The most strident criticism and resistance will come from those who have invested time and money into wiring and wired equipment. To reiterate, someone’s pet wire-line protocol will be eliminated or curtailed, along with, possibly, their job function. Having been in the instrumentation and controls business for the last 30 years, I can state that those who had cut their teeth on relays, vacuum tubes, and 3 to 15 PSI vehemently mounted resistance to the adoption of programmable logic controllers (PLCs) and electronic instrumentation, and we all know how that turned out. That said, relays still have a place in the controls industry; wiring will always be needed and have a place in data communication. And don’t be too concerned: If you have been following this blog for any length of time, you will understand that it still takes a considerable amount of wiring to support a WLAN.
One last note, albeit tongue-in-cheek: A time-honored method of deflecting any issues surrounding an upgrade is to offload it to a consultant or specialty contractor. This has the effect of insulating an administrator and his employer from the bad effects, if any, while allowing them to bask in the admiration of their employees.
– Daniel E. Capano, owner and president, Diversified Technical Services Inc. of Stamford, Conn., is a certified wireless network administrator (CWNA); email@example.com. Edited by Chris Vavra, production editor, CFE Media, Control Engineering, firstname.lastname@example.org.
www.controleng.com/blogs has other wireless tutorials from Capano on the following topics:
Choosing between single and multi-channel architecture
Virtual and physical WLAN site surveys
WLAN design preparation and needs analysis
www.controleng.com/webcasts has wireless webcasts, some for PDH credit.
Control Engineering has a wireless page.