 carrier standards and technolo- gies such as GR-303 and optical remotes that use fiber instead of copper for the trunk line between the remote terminal and the central office ter- minal go a long way toward solving this problem by making bandwidth allocation far more flexible. There is still quite a ways to go, however. Typically, as long as a customer is within 12,000 feet from a central office (CO) they will be given a dedicated connection to the network, as shown in Figure 3-18. If they are farther than 12,000 feet from the CO, however, they will normally be connected to a subscriber loop carrier sys- tem of one type or another. 96 customers - Figure 3-16 64 Kbps each Subscriber loop carrier system -Customers share access to the network via a collection 5 T1s (4 active, 1 spare) of multiplexed 20 conductors Switch facilities to reduce outside plant cost. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Chapter 3 Figure 3-17 A remote loop carrier terminal Figure 3-18 Carrier Serving Area (CSA) architecture 12 Kft. Remote Terminal 12 Kft. Either way, the customer's local loop, whether as a standalone pair of wires or as a time slot on a carrier system, makes its way over the phys- ical infrastructure on its way to the network. It may be aerial, as shown in Figure 3-19, or underground, as shown in Figure 3-20. If it has to Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Telephony Telephony Figure 3-19 Aerial plant- Telephony is the lowest set of facilities on the pole. Figure 3-20 Underground plant travel a significant distance, it may encounter a load coil along the way, which is a device that "tunes" the local loop to the range of frequencies required for voice transp