Longitudinal shrinkage of a cable sheath can have major impact on cable attenuation, with polymer relaxation rather than melt temperature as the dominant factor. There are three distinct segments in the external fiber optic network-the well established trunk network, the access network from the point of presence (POP) to the passive node (PN) curb side cabinet or underground closure and the drop network between the PN and the subscriber. System architecture will influence the cable selection, but typically the trunk network is built from traditional cable types-loose tube or slotted core-established for many years. Signals are multiplexed and as a result the overall fiber count need not be excessive. For the access network, signals are typically not multiplexed and so the number of fibers is more directly linked to the number of subscribers. The link from the PN to the subscriber is satisfied by a range of diverse low fiber count products, which are outside the scope of this article.
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