cisco ccna definition

cisco ccna definition.While leased lines can provide guaranteed bandwidth and short latency for connections, other solutions such as ATM have similar characteristics. The main disadvantage of leased lines is that they are too expensive - they are usually the most expensive WAN solution. Another disadvantage is that each connection requires a separate router interface. For example, if you have a headquarters router that needs to access 4 remote sites, that router must have 4 WAN interfaces for the 4 leased lines. If you use Frame Relay or ATM, only one WAN interface is needed to provide the same connectivity.The leased lines use synchronous serial connections with data rates ranging from 2400bit/s to 45Mbit/s (DS3 connections). Synchronous serial connections allow you to send and receive messages simultaneously without having to wait for a signal from the remote end; synchronous connections also do not need to indicate this at the start of a transmission or at the end of a transmission. These two aspects and the way in which the clock frequency is provided are the three main differences between synchronous and asynchronous connections - asynchronous connections are typically used for dial-up connections (such as modems) oWhen using leased lines, the following equipment is required..DTE: a router with a synchronous serial interface that provides data link layer framing as well as terminating WAN connections - .DTE: a router with a synchronous serial interface that provides data link layer framing as well as terminating WAN connections.DCE: CSU/DSU terminating the operator leased line, providing clocking and synchronization for the connection. Exam Essentials Serial interfaces are used for WAN services such as private circuits (leased lines) and Frame Relay. Figure 24.2 illustrates the equipment required to connect using leased lines. The CSU/DSU is responsible for handling physical layer framing, clocking, and connection synchronization. It can beCommon data link layer protocols used for private connections include PPP and HDLCo CSU/DSURouter CSU/DSUFigure 24.2 Example of a leased lineCircuit-switched connections Circuit-switched connections are dial-up connections, similar to those used by PCs that dial up to an ISP through a modem. Circuit-switched connections include the following. . Asynchronous serial connections: this includes analog modem dial-up connections and standard telephone systems. Telephone carriers often refer to the standard telephone system as plain old telephone service (POTS) o. Synchronous serial connections: this includes ISDN Basic Rate Interface (BRI) and Base Group Rate Interface (PR1) dial-up connections; it