ccna 1 capitulo 9 pdf

ccna 1 capitulo 9 pdf.252 Chapter 12 Point-to-Point WAN requires that the line be laid in the building where each router is located. The telephone company then establishes an end-to-end pair of line devices, with one pair used to send data in the direction of each other (full duplex). Figure 12-3 gives an example of such a line, where the telephone company uses two traditional central office (CO) switches to establish a short-lease line between the two routers.ICND1 -3-3 Figure 12-3 One of the cabling options for building a short leased line within a telephone company Figure 12-3 probably contains more detail than you would like to know about this leased line WAN, at least from an enterprise customer's perspective. More commonly, most network administrators think of leased lines in terms of Figure 12-4, which gives several key components and terms for the equipment on both ends of the leased line, as follows. Customer premise equipment (CPE): This term refers to the equipment at the other end of the link that is located on the client side. Channel Service Unit/Data Service Unit (CSU/DSU): It normally provides a function called clocking, which tells the router exactly when to send and receive each digit via the signal over the serial cable. Serial Cable: This is a short cable used to connect the CSU to the router's serial interface.Figure 12-4 Point-to-Point Leased Lines: Components and Terminology CPE consists of several separate orderable sections. For an external CSU/DSU, the serial cable must be used to connect to the serial interface between the CSU and the router. Many of today's routers use serial interfaces. These serial interfaces are usually detachable on the router (called WAN Interface Cards, WICs). WICs have one style (size/shape) of physical connector, while CSUs have several types of connectors. So when installing a leased line, the administrator must select the correct type of cable with a connector that matches the connector on one end of the WIC and the other end matches the CSU/DSU. Three types of serial cables are shown in Figure 12-5. All three cables have the Smart Serial connector at the top, which has been widely used on Cisco serial interface cards. The other end of each cable uses one of the physical serial connector standards common to CSU/DSU products.11.2 Basic Content 253V-front viewEIA/TIA-232 V.35 X.21 Figure 12.5 Serial cable for connecting CSU to router Today, many leased lines inherit the Cisco WICO from the CSU/DSU That is, the WIC hardware includes the CSU/DSU functionality, so the external CSU/DSU is no longer needed. A comparison with Figure 12.4 shows that the external CSU/DSU and the serial cable at each end are no longer useful because the phone company's cable can be connected directly to the WIC. Figure 12.6 shows a router with four WIC card slots. You can see the panel for each slot without a WIC card installed. The front of the figure shows one of the WIC-4T1/E1 cards, which supports 4 serial links with CSU/DSU sets. There are 4 RJ-48 ports on the front of the WIC and these connectors have the same size and shape as the RJ-45 family. Leased lines and 7... Carrier Systems The telephone company can provide leased lines at various rates. However, the telephone company's tenants cannot select the rate. The rate follows an oldThe standard for technology, the "eight-carrier system".Quad Module 2GigabitFigure 12.6 Serial WIC Router with CSU/DSU and RJ-48 PortsWAN Interface Card (WIC) Slot Aux Ethernet Interface Back in the 1950s and 1960s, Bell, based in the United States, developed and deployed digital voice and T-carrier systems. As part of these efforts, they standardized on different transmission rates, including 64 kbit/s, 1.544 Mbit/s, and 44.736 Mbit/s. Bell also developed Time Division Multiplexing (TDM) technology, which allowed multiple basic rates to be combined on a single line. For example, a common standard called Digital Signal Class 1 (DS1), or T1, combines 24DS0 (at 64kbit/s) and 8kbit/s overhead into a single physical line carried at l.544Mbit/s USB RJ-45.