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Anleitung Zusammenfassung
For more information, see the “Identifying Supported Platforms” section in the “Using Cisco IOS Software” chapter. For a complete description of the modem support commands in this chapter, refer to the Cisco IOS Modem Command Reference. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online. Signal and Line State Diagrams The following signal and line state diagrams accompany some of the tasks in the following sections to illustrate how the modem control works: • Configuring Automatic Dialing • Automatically Answering a Modem • Supporting Dial-In and Dial-Out Connections • Configuring a Line Timeout Interval • Closing Modem Connections • Configuring a Line to Disconnect Automatically • Supporting Reverse Modem Connections and Preventing Incoming Calls Cisco IOS Dial Technologies Configuration Guide DC-157 Modem Signal and Line States Signal and Line State Diagrams The diagrams show two processes: • The “create daemon” process creates a tty daemon that handles the incoming network connection. • The “create EXEC” process creates the process that interprets user commands. (See Figure 25 through Figure 29.) In the diagrams, the current signal state and the signal the line is watching are listed inside each box. The state of the line (as displayed by the show line EXEC command) is listed next to the box. Events that change that state appear in italics along the event path, and actions that the software performs are described within ovals. Figure 25 illustrates line states when no modem control is set. The DTR output is always high, and CTS and RING are completely ignored. The Cisco IOS software starts an EXEC session when the user types the activation character. Incoming TCP connections occur instantly if the line is not in use and can be closed only by the remote host. Figure 25 EXEC and Daemon Creation on a Line with No Modem Control Ready Ringing Exit Create daemon Network connection closed Incoming network connection Ready and active DTR high Ready and active User-typed activation character Create EXEC DTR high S1201a DTR high DC-158 Cisco IOS Dial Technologies Configuration Guide Modem Signal and Line States Signal and Line State Diagrams Configuring Automatic Dialing With the dialup capability, you can set a modem to dial the phone number of a remote router automatically. This feature offers cost savings because phone line connections are made only when they are needed—you pay for using the phone line only when there is data to be received or sent. To configure a line for automatic dialing, use the following command in line configuration mode: Command Purpose Router(config-line)# modem dtr-active Configures a line to initiate automatic dialing. Using the modem dtr-active command causes a line to raise DTR signal only when there is an outgoing connection (such as reverse Telnet, NetWare Asynchronous Support Interface (NASI), or DDR), rather than leave DTR raised all the time. When raised, DTR potentially tells the modem that the router is ready to accept a call. Automatically Answering a Modem You can configure a line to answer a modem automatically. You also can configure the modem to answer the telephone on its own (as long as DTR is high), drop connections when DTR is low, and use its Carrier Detect (CD) signal to accurately reflect the presence of carrier. (Configuring the modem is a modem-dependent process.) First, wire the modem CD signal (generally pin-8) to the router RING input (pin-22), then use the following command in line configuration mode: Command Purpose Router(config-line)# modem dialin Configures a line to automatically answer a modem. You can turn on modem hardware flow control independently to respond to the status of router CTS input. Wire CTS to whatever signal the modem uses for hardware flow control. If the modem expects to control hardware flow in both directions, you might also need to wire modem flow control input to some other signal that the router always has high, such as the DTR signal. Figure 26 illustrates the modem dialin process with a high-speed dialup modem. When the Cisco IOS software detects a signal on the RING input of an idle line, it starts an EXEC or autobaud process on that line. If the RING signal disappears on an active line, the Cisco IOS software closes any open network connections and terminates the EXEC facility. If the user exits the EXEC or the software terminates because of no user input, the line makes the modem hang up by lowering the DTR signal for 5 seconds. After 5 seconds, the modem is ready to accept another call. Cisco IOS Dial Technologies Configuration Guide DC-159 Modem Signal and Line States Signal and Line State Diagrams Figure 26 EXEC Creation on a Line Configured for a High-Speed Modem Idle state Hang up Ringing high, watching Lower DTR Ready and active Ring transition CTS raised DTR CTS Create EXEC Raise DTR Lower DTR close connection DTR high CTS lowered or exit Answ...