Would you use a canoe to navigate the Great Lakes? Sure, it
can be done, but a canoe is probably not a good choice for that trip. What
about taking a power boat up a river that requires portages to avoid waterfalls
and rapids? It, too, can be done but switch the watercraft on those two trips
and the outcome will be much better.
Network construction needs should be guided by similar
logic. There are two basic OSP fiber networks; point-to-point and point-to-multipoint.
There are also cable types that simply make better sense in each situation.
Point-to-point networks are intended to essentially deliver
access or service from one location to another. A good example is linking two
substations together. The concept here is that new substations just do not crop
up often and do not occur in clusters. In
contrast, Point-to-multipoint networks are developed with the understanding
that there will be an array of drop-off and pick-up points along the route, and
new points cropping up as areas are developed, often in clusters.
Two different networks, like two different bodies of water.
There are also cabling solutions that best suit each just like the watercraft. Let’s
look at the key differences between ADSS and lashed fiber, and how you might
determine which one is better suited for these two basic OSP fiber networks.
CLICK TO TWEET: A great debate? ADSS vs. lashed fiber.
ADSS, or all-dielectric self-supporting cable, is a cable
that requires no metallic strand in aerial applications and is commonly used in
proximity to high voltage. ADSS can
certainly be deployed in the communications space, but not without a few
challenging consequences. First, pre-planned
splice closure locations must be used with ADSS because the closures must be
pole-mounted. Elimination of a hanging strand with ADSS is positive from a cost
perspective, but it also means no additional cables may be lashed to the ADSS
cable, and all branch cables and drop cables must be attached to the pole
directly as no midspan attachments may be made.
Deploying ADSS in a point-to-multipoint FTTx project can
drive up costs in several ways:
- Every access point requires double dead ends at
- Hardware is required for securing cable to pole
for routing it to splice closures.
- Figure eights require double dead ends and
special hardware for slack that passes the pole to be secured properly.
- Drop cables need to be fixed directly to the
pole, which either requires more access locations or a need to make drop
attachments on the adjacent poles until reaching the one closest to the
subscriber premise. If those pole spans are too long, a drop cable under
wind/ice load will typically reach fiber strain causing an outage.
In cases where connections are point-to-point, and
especially if some routes must be taken in the power space, ADSS cables are appropriate
solutions. This is not to say that lashed fiber would be inappropriate in this
application. Many networks are built with strand and lashed fiber in the power space;
you simply need to bond the
strand at every other pole.
Unlike ADSS, lashed fiber requires strand to be placed, so the
strand bears all the environmental load.
For this reason:
- Additional cables may be added as future network
- Equipment may be placed directly on the strand,
including splice closures and active devices like 5G small cells.
- Drop and branch cables can be brought off
mid-span without affecting the cable lashed to the strand. If a drop or
multiple drop needs to be run down a series of poles to access the subscriber
from an access point further away, those cables can also be lashed up
eliminating concerns of fiber strain due to wind/ice loading on long spans.
- The working space on the poles remains open and
safer. In places where the risk of damage from rifles/shotguns and squirrel
chew are of concern, lashed fiber cables with steel tape armor may be
installed. This provides a layer of protection not available in ADSS cables.
A cost debate that is often thrown around when discussing
lashed fiber cable is the need for make-ready. The reality is both ADSS and
strand construction will require some amount of make ready work. While there is
typically a greater need for make ready with strand, the cost of that make
ready is far outweighed by the benefits of a more flexible network. Every
effort has a cost, but it is often the hidden future costs that surprise us the
most. As networks and network demands
evolve, flexibility is worth the investment.
When either ADSS or lashed fiber cable networks are built
properly maintenance cost differences are neutral. Life expectancy for both
networks will be similar if good construction practices and handling processes are
followed, evidenced by lashed fiber cable networks that have been in operation
for more than 40 years. Those networks were built before ADSS cables were
introduced and are still expected to provide many more years of service.