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).

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.
• 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