Cell Backhaul: the basics of fiber protection

Copper T1 service to cell tower sites is quickly becoming inadequate.   Wireless cell carriers continue to increase new cell site locations and to upgrade existing 3G sites to 4G/LTE.  The drivers for this increase in bandwidth demand are the millions of ‘multiple screen consumers’ equipped with wireless devices proliferating our social scenes.  The market is demanding that communications consumers be always connected everywhere across multiple devices each often running multiple applications creating a level of Tel

Copper T1 service to cell tower sites is quickly becoming inadequate.   Wireless cell carriers continue to increase new cell site locations and to upgrade existing 3G sites to 4G/LTE.  The drivers for this increase in bandwidth demand are the millions of ‘multiple screen consumers’ equipped with wireless devices proliferating our social scenes.  The market is demanding that communications consumers be always connected everywhere across multiple devices each often running multiple applications creating a level of Teledensity or Broadband density that is unprecented.  The surge in cell backhaul bandwidth threatens to overwhelm cell backhaul facilities. The result of course, is that fiber is now becoming the cell backhaul medium of choice.


However, recent advances in the construction of fiber should not lull service providers into forgetting the basics of fiber protection.  FTTH delivers the ultimate in bandwidth, a single fiber to every home but the point of failure impact is minimized across a single customer in a FTTH customer, 32 in a GPON network.  Like traditional TDM networks of the past, single point of failure impact on a cell backhaul network can affect thousands.  History has repeated itself in fixed wireline backhauling wireless traffic.Proper fiber management is paramount. 


Manufactures of fiber management are mistakenly designing route schemes where a jacketed fiber circuit travel over  a 90 degree edge thinking their fiber can handle it. Over time, as max capacity of the fiber management product begins to be reached, weight and friction can affect the long-term reliability as the 90 degree bend can affect even the latest advancement in fiber. Try placing a patch cord on a light meter and pinch the cordage to a 90 degree bend and you’ll know what I mean.


While the industry moves to an apparent disregard of the standard, it continues to ignore the effect traditional riser-rated jacket material has on performance in harsh environments. These jacket materials are stiff when cold and will relax when temperatures begin to climb. As thermal coefficient of expansion/contraction takes place through several thermal cycles, the fiber is subject to bend radius violations which can create unacceptable light conditions. It’s during these wide temperature fluctuations that the adherence to a manufacturer’s routing recommendations within the industries becomes critical. And this is only true if the scheme is a good one. If a fiber is routed with a properly controlled diameter, one need not worry. However, if the fiber is not bend-radius protected, and is subjected to a hard 90 degree turn, a piece of sheetmetal or a sagging jumper being pushed into a corner, can effect a condition of intermittent light to no light.


Once you have selected the fiber management solution that best serves the needs of longterm reliability in its design, you are halfway there. As strongly as manufacturers may recommend a particular route path, it appears to be only human nature to “take short cuts.” Depending on a variety of factors like cable pileup and environmental conditions, the consequences of these shortcuts may either become immediately apparent or, over time, are hard to trouble-shoot.


A better approach, and the philosophy core to a superior design, is to use fiber jacket materials that respond well in harsh conditions not only in cold environments but on both ends of the thermometer.  Jacketing materials should remain flexible in temperatures down to -55C and, because the rubber material always wants to return to its extruded state, it should resist sagging in extremely hot environments. Even performing best practices and continual training, the recommended routing path might not be maintained. Having a material that will respond and protect your critical and most fragile points of failure will ensure that the ‘multiple screen consumer’ is always connected.


Johnny Hill is the chief operating officer of Clearfield, Inc. Formerly the vice president of engineering and product management, Hill is considered a longstanding leader and a founding member of the company.Hill has approximately 15 years of strategic and hands-on experience in the telecommunications networking industry.