USB Modem Interface Overview

You configure two types of interfaces for USB modem connectivity: a physical interface and a logical interface called the dialer interface:

• The USB modem physical interface uses the naming convention umd0. The device creates this interface when a USB modem is connected to the USB port.
• The dialer interface, dln, is a logical interface for configuring dialing properties for USB modem connections. The dialer interface can be configured using Point-to-Point Protocol (PPP) encapsulation. You can also configure the dialer interface to support authentication protocols—PPP Challenge Handshake (CHAP) or Password Authentication Protocol (PAP).

For information about interface names, see Interface Naming Conventions.

The USB modem provides a dial-in remote management interface, and supports dialer interface features by sharing the same dial pool as a dialer interface. The dial pool allows the logical dialer interface and the physical interface to be bound together dynamically on a per-call basis. You can configure the USB modem to operate either as a dial-in console for management or as a dial-in WAN backup interface.

The following rules apply when you configure dialer interfaces for USB modem connections:

• The dialer interface must be configured to use PPP encapsulation. You cannot configure Cisco High-Level Data Link Control (HDLC) or Multilink PPP (MLPPP) encapsulation on dialer interfaces.
• The dialer interface cannot be configured as a constituent link in a multilink bundle. For information about configuring multilink bundles, see Configuring Link Services Interfaces.
• The dialer interface can perform backup, dialer filter, and dialer watch functions, but these operations are mutually exclusive. You can configure a single dialer interface to operate in only one of the following ways:
  • As a backup interface—for one primary interface
  • As a dialer filter
  • As a dialer watch interface

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