Cisco Certifications Tutorials

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14 http:\\ciscocertifications.info You must run through the entire System Configuration Dialog until you come to the item that you in- tend to change. To accept default settings for items that you do not want to change, press the Return key. To return to the privileged EXEC prompt without making changes and without running through the en- tire System Configuration Dialog, press Ctrl-C. WAN Protocols Connection Terms Customer Premises Equipment (CPE) Devices physically located at the WAN subscribers premises. Includes both owned and leased devices. Central Office (CO) A switching facility that provides the nearest point of presence for a providers WAN service. Demarcation (Demarc) The point at which the CPE ends and the local loop portion of the service begins. Usually the tele- communications closet at the subscriber's location. Local Loop Cabling that extends from the Demarc to the CO. Data Terminal Equipment (DTE) Usually the router where the packet switching application resides. Date Circuit-terminating Equipment (DCE) The device used to convert the user data from the DTE into an acceptable WAN protocol. This usually consists of a DSU/CSU device, modem, or NT1 device. *Keypoints: Know the definitions of the connection terms listed above. Frame Relay Frame relay is a fast WAN protocol that operates at the Physical and Data Link layers (mostly Data Link layer) of the OSI model. Works between DTE and DCE devices. Uses Packet Switching. DTE consists of terminals, PC's, routers and bridges, all of which are customer owned end node devices. DCE devices such as packet switchers are owned by the service provider. Frame Relay uses Permanent Virtual Circuits (PVCs). The connection is identified by a Data Link Connection Identifier (DLCI). Frame Relay offers a speeds between 56 Kbps and 2,078 Mbps. However, the default setting for a se- rial DCE interface is T1. Frame Relay uses a CRC, bad packets are discarded and the receiving station requests re-transmission of any missing frames. Data Link Connection Identifiers (DLCI) Used to identify the virtual circuits. DLCIs can be set to a number between 16 and 1007. Local Management Interfaces (LMI) Provide information about the DLCI values and the status of virtual circuits. The default is Cisco but there are 3 possible settings: