Figure 17–1 Central offices located strategically throughout a local telephone network are designed to service an area referred to as a CSA. All locations residing within the CSA are served by the central office. The services connecting to the locations within the CSA are referred to as access services.
Figure 17–2 Connecting the telephone set to the central office requires a protector or NID—network interface device—where the inside and outside wires are tied together.
Figure 17–3 Protectors placed on the side of buildings or inside a basement or other termination room consist of tip, ring, and ground lugs.
Figure 17–4 The two wire pair from the drop wire is terminated at the terminal. The terminal ties the drop line to the distribution cable.
Figure 17–5 Digital loop carriers are placed strategically throughout the access network. Two common architectures found in the network are the universal and the integrated.
Figure 17–6 Digital loop carrier architectures have evolved over the past twenty years. Today, many carriers tie DLCs together in a region using SONET ring architectures.
Figure 17–7 The telephone access circuit travels from the switch across the MDF where it is connected to the outside plant cable. The outside plant cable terminates at the customer premises on a network interface device. Inside wire is the final leg of the circuit.
Figure 17–8 Standard ISDN BRI interface includes a two-wire connection between the switch and the customer premises and a four-wire connection between the NT and the end terminating device.
Figure 17–10 Special services circuits travel through the serving central office where they are fed into devices called channel banks. The circuits do not interface into the class 5 switch.
Figure 17–11 Often banks purchase special services circuits for each branch. In our example, the 56 kbps circuits feed back to a central hub creating a hub and spoke architecture.
Figure 17–13 An OPX line is fed out of an OPX or station side port and fed back to the OSP—outside plant—cable feeding a location down the street or in the next lot or so forth. If the distance between the PBX and the remote location is too great, the OPX line will ride back to the CO where it is amplified and tied to the end station.
Figure 17–14 Special services circuits terminate on the vertical side of the MDF and are cross connected via frame wire to a channel bank or other transmission equipment.
Figure 17–15 A DSL circuit connects to the serving central office by a two-wire connection in the same way as standard telephone service. The circuit is aggregated with other DSL circuits and connected to the central switching/routing center where the traffic is groomed according to type.
Figure 17–16 ADSL circuits can carry both the high-speed broadband DSL signal and the traditional POTS signal. A splitter is used at each end of the circuit to filter out the voice frequency (VF) signal directing it to the switch. The DSL signal is fed into the DSLAM.
Figure 17–17 The DSL modem connects to the terminating device, in our example a laptop computer, via an Ethernet RJ-45 connection. The DSL circuit connects into the DSL modem by terminating on a standard RJ-11 jack.
Figure 17–18 An RJ-48 termination is made between the NIU and the DCE. Four wires coming from the CO are terminated onto the Smart Jack.
Figure 17–21 A SONET MUX has the ability to accept copper T1 circuits and groom them into VT-1.5. Typically, multiplexers deployed in the access network contain DS-1 interface cards.
Figure 17–22 A loop-back is used to loop the circuit in one direction. The diagram shows a loop-back plug being placed in the DSX port tied to the class 5 switch. The signal will travel from the switch to the DSX panel and back to the switch. A test box can be connected to monitor the port on the DSX panel to determine if the signal traveling out of the switch is good or bad. Placing a loop toward the switch should make the switch port look up and good.
Figure 17–24 A circuit connection made between two ports on a DSX panel requires the transmit and receive to be reversed in order to line up transmit to transmit and receive to receive.
Figure 17–25 IOF—interoffice facilities—are sold by ILECs to other service providers. DS-1, DS-3, and SONET circuits are sold at a reduced cost to the provider. The access network circuits are groomed onto IOF circuits that tie to a regional switching center.