ccna 1 certificate and letter

ccna 1 certificate and letter.DS3 (T3) 44.736 Mbit/s (28 DS1, plus management overhead)The Role of the CSU/DSUThe final part of the discussion of WAN links in the enterprise work network interconnection is the CSU/DSU (CSU for short). For ease of understanding, the following paragraphs up to Figure 12-7 assume that the leased line has an external CSU/DSU, as in the preceding Figure 12-4. hint: Many people refer to the CSU/DSUM simply as the CSU.The CSU sits between the telephone company's leased line and the router, and it is able to read the text and their protocols on both ends at Layer 1. On the telephone company side, this means that the CSU is connected to the line from the telephone company, so it must know all the details about the T-carrier system (TDM) and the rates used by the telephone company. This CSU must be configured to match the telephone company's settings in order to work at the same rate. For example, a CSU connected to 256 kbit/s partial Tl must be a completely different configuration than a CSU connected to full Tl (1.544Mbit/s).On the router side, this CSU is connected to a router whose roles are called DCE and DTE respectively. the CSU as a DCE (data terminal equipment) is controlled by the clocking signal (clocking signal) of the CSU (DCE). That is, the CSU tells the router when to send and receive data; the router will only attempt to send and receive data when the DCE has sent the correct electrical pulses in that cable.The DCE and DTE work a bit like an overly anxious child ready to throw the ball to his parents as fast as possible. But this child must wait until the parent yells "Go!" before throwing the ball. The parent sits there and shouts "Go! Go! Go! Go! Go! Go!" and they are willing to catch the ball at that rate. Similarly, the CSU/DSU is configured to tell it to clock the router at this rate, and the CSU yells "Go!" by changing the current (clock signal) of certain wires in the serial cable. .Figure 12-7 illustrates the main concepts of the CSU/DSU role.Figure 12-7 Roles of DCE and DTE in CSU/DSU and Router Serial Interface Building a WAN link in the lab actually shows that to prepare for CCENT and CCNA, you can pick up some used router and switch hardware for manual practice. This way, you don't have to actually draw a leased line and CSU/DSU from the phone company, you can build a leased line with a little cabling skill. This short topic has provided enough information for you to build a WAN link in your lab. First, when establishing a true WAN link between two sites using the telephone company's facilities, the serial cable that is typically used to connect the router to the external CSU/DSU is the DTE cable. For example, the conceptual diagram in Figure 12-4 earlier shows a DTE serial cable connecting each router to a CSU.12.2 Basics 255 Instead of a CSU and pulling a leased line from the phone company, you can model a WAN link by connecting the serial interfaces of the two routers together with a DTE cable and a slightly different DCE cable, with a female connector for the DCE cable and a plug-type connector for the DTE. The DCE cable has a female connector and the DTE has a plug type connector (maleconnector), which allows the two cables to be connected directly together. This completes the physical connection of the data transmission path. The DCE cable serves the same purpose as an Ethernet crossover cable by swapping the transmit and receive wires. As shown in Figure 12-8.Enter the clock rate command here