Cisco Systems DC-157 User's Manual
Contents
1. CTS signal be high for the entire session If CTS is not high the user input is ignored and incoming connections are refused or sent to the next line in a rotary group Figure 28 EXEC and Daemon Creation on a Line Configured for Continuous CTS Hang up Idle state DTR high watching CTS Close connection DTR low for 5 seconds DTR going low CTS lowered o DTR high watching Ready DTR high watching Incoming network connection Create daemon DTR high Ready watching and active fs CTS lowered or network connection closed 1004a mi Cisco 10S Dial Technologies Configuration Guide Modem Signal and Line States Signal and Line State Diagrams il Configuring a Line to Disconnect Automatically Command To configure automatic line disconnect use the following command in line configuration mode Purpose Router config line autohangup Configures automatic line disconnect The autohangup command causes the EXEC facility to issue the exit command when the last connection closes This feature is useful for UNIX to UNIX copy program UUCP applications because UUCP scripts cannot issue a command to hang up the telephone This feature is not used often Supporting Reverse M odem Connections and Preventing Incoming Calls In addition to initiating connections th2. Signal and M odem Signal and Line States This chapter describes modem states in the following section Signal and Line State Diagrams To identify the hardware platform or software image information associated with a feature use the Feature Navigator on Cisco com to search for information about the feature or refer to the software release notes for a specific release 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 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 gy Modem Signal and Line States W Signal and Line State Diagrams The diagrams show two processes The create daemon process creates a tty daemon that handles the incoming ne
3. e Cisco IOS software can receive incoming connections This capability allows you to attach serial and parallel printers modems and other shared peripherals to the router or access server and drive them remotely from other modem connected systems The Cisco IOS software supports reverse TCP XRemote and local area transport LAT connections The specific TCP port or socket to which you attach the device determines the type of service that the Cisco IOS software provides on a line When you attach the serial lines of a computer system or a data terminal switch to the serial lines of the access server the access server can act as a network front end device for a host that does not support the TCP IP protocols This arrangement is sometimes called front ending or reverse connection mode The Cisco IOS software supports ports connected to computers that are connected to modems To configure the Cisco IOS software to function somewhat like a modem use the following command in line configuration mode This command also prevents incoming calls Command Purpose Router config line modem callout Configures a line for reverse connections and prevents incoming calls Figure 29 illustrates the modem callout process When the Cisco IOS software receives an incoming connection it raises the DTR signal and waits to see if the CTS signal is raised to indicate that the host has noticed the router DTR signal If the host does not respond within the in
4. eate EXEC or exit N 7 DTR high a 4 S 1001a f Ready and active Supporting Dial In and Dial Out Connections To configure a line for both incoming and outgoing calls use the following command in line configuration mode Command Purpose Router config line modem inout Configures a line for both incoming and outgoing calls Figure 27 illustrates the modem inout command If the line is activated by raising the data set ready DSR signal it functions exactly as a line configured with the modem dialin line configuration command described in the section Automatically Answering a Modem earlier in this chapter If the line is activated by an incoming TCP connection the line functions similarly to lines not used with modems mi Cisco 10S Dial Technologies Configuration Guide Modem Signal and Line States Signal and Line State Diagrams il Figure 27 EXEC and Daemon Creation for Incoming and Outgoing Calls Idle state DTR high watching CTS Close connection DTR low for 5 seconds eee eee eee KK L CTS lowered DTR high Sal roe ati iti z7 watching Ready DTR going Hang up low activation f Incoming network connection daemon Ready DTR high and watching DTR high Ready active CTS watching and CTS active gt CTS lowered or exit
5. ever 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 gy Modem Signal and Line States W Signal and Line State Diagrams Figure 26 EXEC Creation on a Line Configured for a High Speed Modem Idle state DTR low watching ti CTS 74 S Ring transition 7 4 N 4 I 1 I I Raise DTR 1 f aise I I 1 i i I i Lower DTR l I I I i i I l I l i i l Answer A timeout NN S DTR high Hang up DTR low z watching Ringing CTS I I I I L I i Lower DTR i close connection CTS raised L I I I I I 1 I I I CTS lowered 1 Cr
6. f CTS lowered or network connection closed 1004a _ 7 amp Note If your system incorporates dial out modems consider using access lists to prevent unauthorized use Configuring a Line Timeout Interval To change the interval that the Cisco IOS software waits for the CTS signal after raising the DTR signal in response to the DSR the default is 15 seconds use the following command in line configuration mode The timeout applies to the modem callin command only Command Purpose Router config line modem answer timeout seconds Configures modem line timing amp Note The DSR signal is called RING on older ASM style chassis Cisco 10S Dial Technologies Configuration Guide B 0c 161 Modem Signal and Line States W Signal and Line State Diagrams Closing Modem Connections Command amp Note The modem cts required command was replaced by the modem printer command in Cisco IOS Release 12 2 To configure a line to close connections from a user s terminal when the terminal is turned off and to prevent inbound connections to devices that are out of service use the following command in line configuration mode Purpose Router config line modem cts required Configures a line to close connections Figure 28 illustrates the modem cts required command operating in the context of a continuous CTS signal This form of modem control requires that the
7. terval set by the modem answer timeout line configuration command the software lowers the DTR signal and drops the connection Cisco IOS Dial Technologies Configuration Guide gy Modem Signal and Line States W Signal and Line State Diagrams Figure 29 Daemon Creation on a Line Configured for Modem Dial Out Idle state DTR low SA Incoming network 7 4 connection 7 I N 1 I 1 I 1 I i Raise DTR I 1 l i I i 1 Lower DTR i l i l l i l l 1 l l i l l i l l l l Answer y l timeout NN l N DTR high i me watching Ringing l CTS l Close i connection i I l l l l l i i CTS raised l l I l 1 I Network A Fy connection y 1 closed or 1 CTS lowered A Create daemon 7 SS 4 N 1 SS DTR high eZ watching CTS 1930 Ready and active mi Cisco 10S Dial Technologies Configuration Guide
8. twork 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 DTR high Network connection closed User typed activation character Incoming network connection DTR high DTR high Ringing Create ip Create daemon EXEC S1201a Ready and active Ready and active mi Cisco 10S Dial Technologies Configuration Guide Modem Signal and Line States Signal and Line State Diagrams il Configuring Automatic Dialing Command With the dialup capability you can set a modem to dial the phone number of a remote ro
9. uter 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 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 Command 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 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 what
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