Could someone PLEASE verify the correctness of my explanation???
[I am studying for the "Remote Access" exam] and was hoping for validation!!
----------> fsebera@yahoo.com
NOTE:
Pin 7 is ground and is only used as a reference point for the other pins.
Modem Control - signals 6, 8, 20
Start by powering on the DCE device (modem) and the DTE device (PC, Router). The modem sets signal 6 [DSR] high and usually signal 20 [DTR] high.
If signal 6 [DSR] is low, there is a connection problem between the DTE and DCE devices. When signal DSR is low, it means the DCE and DTE devices do not see each other.
If signal 20 [DTR] is not high, as soon as the communication software is loaded on the PC, signal 20 [DTR] should activate to high. If signal 20 does not activate, the modem may require a manual setting via software of hardware switch setting.
The [CD] signal 8 should be low (on hook), if this signal [CD] was high (off hook), the local modem currently has a connection to a remote DCE device. Before a new connection can be made, this signal must be lowered.
Flow Control - Signals 4, 5
Once the software has been loaded, signals 6 and 20 are high, and signal 8 is low, the DTE device can now attempt to make a call. Dial the remote number, once the remote DCE device has accepted the call, the CD signal 8 goes high to indicate the remote end will communicate with your local DCE device. As long as the DTE device allows the signal DTR [20] to remain high and the DCE device allows the signal CD [8] to remain high, the call will remain active.
Now lets pass some data!!
Data Transfer - Signals 2, 3, 7
The DTE device checks the DTE signal RTS [4] and DCE signal CTS [5], if both signals are low, then both parties are ready to receive data. If at any time the DTE device's RTS signal goes low, the DCE device will stop sending data [to the DTE] as the DTE's buffer is about full. If at any time the DCE device's CTS signal goes low, the DTE device will stop sending data [to the DCE] as the DCE's buffer is about full. All data is transferred on signal TD [2].
Once the data transfer has completed, if either DCE or DTE wants to terminate the connection, one of the two will lower the voltage on the correct signal and the communication terminates.
I.E. If the DTE device lowers the voltage [in reference to signal 7, ground], on signal DTR [20] the DCE device concludes the DTE terminated the connection and wants to end the call. In turn the DCE device will lower the voltage on signal 8, which then signals the far remote end to terminate the communications between both DCE devices, which frees up the pots line for other calls. The far remote DCE should also inform its DTE device to end the call.
However, on the other hand, if the DCE device lowers the voltage on signal CD [8], the DTE device acknowledges the DCE signal change on signal CD [8] and also shuts down communications.
2 3 4 5 6 7 8 20
TD RD RTS CTS DSR Ground CD DTR
DTE DCE DTE DCE DCE Ground DCE DTE
PC/router Modem PC/router Modem Modem Ground Modem PC/router
Cheers
Frank
[I am studying for the "Remote Access" exam] and was hoping for validation!!
----------> fsebera@yahoo.com
NOTE:
Pin 7 is ground and is only used as a reference point for the other pins.
Modem Control - signals 6, 8, 20
Start by powering on the DCE device (modem) and the DTE device (PC, Router). The modem sets signal 6 [DSR] high and usually signal 20 [DTR] high.
If signal 6 [DSR] is low, there is a connection problem between the DTE and DCE devices. When signal DSR is low, it means the DCE and DTE devices do not see each other.
If signal 20 [DTR] is not high, as soon as the communication software is loaded on the PC, signal 20 [DTR] should activate to high. If signal 20 does not activate, the modem may require a manual setting via software of hardware switch setting.
The [CD] signal 8 should be low (on hook), if this signal [CD] was high (off hook), the local modem currently has a connection to a remote DCE device. Before a new connection can be made, this signal must be lowered.
Flow Control - Signals 4, 5
Once the software has been loaded, signals 6 and 20 are high, and signal 8 is low, the DTE device can now attempt to make a call. Dial the remote number, once the remote DCE device has accepted the call, the CD signal 8 goes high to indicate the remote end will communicate with your local DCE device. As long as the DTE device allows the signal DTR [20] to remain high and the DCE device allows the signal CD [8] to remain high, the call will remain active.
Now lets pass some data!!
Data Transfer - Signals 2, 3, 7
The DTE device checks the DTE signal RTS [4] and DCE signal CTS [5], if both signals are low, then both parties are ready to receive data. If at any time the DTE device's RTS signal goes low, the DCE device will stop sending data [to the DTE] as the DTE's buffer is about full. If at any time the DCE device's CTS signal goes low, the DTE device will stop sending data [to the DCE] as the DCE's buffer is about full. All data is transferred on signal TD [2].
Once the data transfer has completed, if either DCE or DTE wants to terminate the connection, one of the two will lower the voltage on the correct signal and the communication terminates.
I.E. If the DTE device lowers the voltage [in reference to signal 7, ground], on signal DTR [20] the DCE device concludes the DTE terminated the connection and wants to end the call. In turn the DCE device will lower the voltage on signal 8, which then signals the far remote end to terminate the communications between both DCE devices, which frees up the pots line for other calls. The far remote DCE should also inform its DTE device to end the call.
However, on the other hand, if the DCE device lowers the voltage on signal CD [8], the DTE device acknowledges the DCE signal change on signal CD [8] and also shuts down communications.
2 3 4 5 6 7 8 20
TD RD RTS CTS DSR Ground CD DTR
DTE DCE DTE DCE DCE Ground DCE DTE
PC/router Modem PC/router Modem Modem Ground Modem PC/router
Cheers
Frank
