ccna 1 capitulo 8 pdf

ccna 1 capitulo 8 pdf.12.2.1 Leased Line LAN with HDLCThe physical leased line WAN works in a similar manner to the Ethernet crossover cable connecting two routers, but the WAN has no distance limitation. In Figure 12-1, each router can send data at any time (full duplex). The rate is also symmetrical, meaning that both routers send data at the same rate.12.2 Basics 251Xbits/secondX bits/secondAll Time Figure 12-1 Leased Lines: Same Rate, Bidirectional, All the TimeAlthough leased lines provide physical layer data transfer facilities, the routers also need to send data using the data link layer protocol on the WAN link. The above diagram works as follows: one of the routers receives a frame from the LAN interface and then unblocks the frame. When that router forwards the frame, it then encapsulates the packet via the WAN Data Link Control (HDLC) protocol, as shown in Step 2 of Figure 12-2. (Note that this diagram does not show the data link header in each frame, but each frame includes both a data link header and a header.)Figure 12-2 Router Encapsulating Data with HDLC The first two figures review some of the details of Layer 1 and Layer 2 of the leased line WAN, respectively. These links are discussed again at the beginning of the first part of this chapter, starting with the Layer 1 details, followed by the Layer 2 details. This section concludes with the configuration details for HDLC. Tip: From now until the "HDLC Configuration" section you are reviewing some of the concepts from ICND1 and the ICND1 exam. If you remember the details of leased lines well (discussed in Chapter 3 of ICND1), you can skip that section of the chapter to the HDLC Configuration.Layer 1 Leased LinesLeased lines have been around for a long time, predating the LAN by more than 20 years. However, they still exist today as a WAN service.