Cisco Systems OL-6426-02 manual Dial Backup, Dialer Interface, Backup Interface

Appendix B Concepts

Dial Backup

PVC

A PVC is a connection between remote hosts and routers. A PVC is established for each ATM end node with which the router communicates. The characteristics of the PVC that are established when it is created are set by the ATM adaptation layer (AAL) and the encapsulation type. An AAL defines the conversion of user information into cells. An AAL segments upper-layer information into cells at the transmitter and reassembles the cells at the receiver.

Cisco routers support the AAL5 format, which provides a streamlined data transport service that functions with less overhead and affords better error detection and correction capabilities than AAL3/4. AAL5 is typically associated with variable bit rate (VBR) traffic and unspecified bit rate (UBR) traffic. Cisco 1800 series routers also support AAL1 and 2 formats.

ATM encapsulation is the wrapping of data in a particular protocol header. The type of router to which you are connecting determines the type of ATM PVC encapsulation types.

The routers support the following encapsulation types for ATM PVCs:

•LLC/SNAP (RFC 1483)

•VC-MUX (RFC 1483)

•PPP (RFC 2364)

Each PVC is considered a complete and separate link to a destination node. Users can encapsulate data as needed across the connection. The ATM network disregards the contents of the data. The only requirement is that data be sent to the ATM subsystem of the router in a manner that follows the specific AAL format.

Dialer Interface

A dialer interface assigns PPP features (such as authentication and IP address assignment method) to a PVC. Dialer interfaces are used when configuring PPP over ATM.

Dialer interfaces can be configured independently of any physical interface and applied dynamically as needed.

Dial Backup

Dial backup provides protection against WAN downtime by allowing a user to configure a backup modem line connection. The following can be used to bring up the dial backup feature in Cisco IOS software:

•Backup Interface

•Floating Static Routes

•Dialer Watch

Backup Interface

A backup interface is an interface that stays idle until certain circumstances occur, such as WAN downtime, at which point it is activated. The backup interface can be a physical interface such as a Basic Rate Interface (BRI), or an assigned backup dialer interface to be used in a dialer pool. While the primary

Cisco 1800 Series Integrated Services Routers (Fixed) Software Configuration Guide

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