cisco ccna in 60 days 3rd edition pdf

cisco ccna in 60 days 3rd edition pdf.the same way of assigning addresses to VCs. In ATM, two identifiers are assigned to VCs: the Virtual Path Identifier (VPI) and the Virtual Channel Identifier (VCI), which serve the same purpose as the Frame Relay DLCI. Like DLCI, VPI/VCI is only locally meaningful.There are two standards (FRF.5 and FRF.8) that define how to convert frames and addresses between Frame Relay and ATM.. FRF.5 (Network Interconnection): both DTEs are Frame Relay DTEs, and operators use ATMO. FRF.8 (Service Interconnection): one DTE is a Frame Relay device, the other is an ATM device, and the operator uses ATMoFigure 25.6 provides an example of these two standards. FRF.5 defines how two Frame Relay devices (Router A and Router B in Figure 25.6) send frames over the ATM backbone. In FRF.5, the switch receives a Frame Relay frame, determines which ATMVC should be used to send the information to the destination, encapsulates the Frame Relay frame into an ATM frame, and splits the ATM frame into multiple ATM letter elements. After the destination operator switch receives the ATM elements, it assembles them into ATM frames, extracts the encapsulated Frame Relay frames from them, and then looks up the DLCI in the switching table. o When switching the frames to the next segment, if the local DLCI is different, the switch modifies the DLCI in the frame header and recalculates the cyclic redundancy checksum (CRC). oThe connection between Router A and Router C is an FRF.8 connection. In FRF.8, the two DTEs use Frame Relay and ATM, respectively, and the operator uses ATM to transmit information between the two DTEs. For example, in Figure 25.6, Router A sends Frame Relay frames to Router C. Unlike in FRF.5, the operator switch converts the Frame Relay frames into ATM frames, divides the ATM frames into multiple elements, and assigns the correct VPI/VCI addresses to the elements so that they can be transmitted to the remote ATM switch. In this example, Router A thinks it is communicating with another Frame Relay device (Router C), and Router C thinks it is communicating with another ATM device (Router A).Figure 25.6 Example of Network Interconnection and Service Interconnection2523 Data Rate of VCsEach data VC has a number of parameters that affect its data rate and throughput; these parameters include CIR (Committed Data Rate), Be (Committed Burst Rate), BE (Excess Burst Rate), and Access Rate. This section describes these four parameters and how the Frame Relay switch performs VC traffic contracts based on them.The CIR is the VC contracted average rate over a period of time. The carrier guarantees that the VC rate will not fall below this value regardless of any major outages in the carrier's network.