Single Fiber Modem Now Supports SLIP/PPP Protocols

Patton has just enhanced the Model 1180 single fiber modem to support two (out-of-band) flow control signals in each direction. Until now, the 1180 supported only one signal in each direction in addition to the data. This feature is needed in applications that require independent indications of flow control and disconnection of equipment. This can be critical in secure UNIX applications as well as "remote access" requirements running SLIP or PPP.

The need for flow control is well known, especially to printer users. Security requirements may not be as familiar. When a user sits down at a workstation to connect to a host, the first operation is to turn the workstation on. When the workstation is turned on, DTR on the RS-232 interface goes high. The host on the far end will now see DSR go high and will then send a logon message to the workstation. When the user completes his day, he may forget to logout and simply shut off the workstation. When the workstation is shut off, DTR goes low which in turn causes DSR to go low on the far end. The host is now aware the user is no longer working and shuts down the session, preventing someone from gaining access to an active session by simply restarting the workstation. These security applications were solvable by rewiring cables to connect the appropriate control line to the signals required by the host. To support both flow control and power on indication in the same circuit has been relatively straightforward. Simply configure workstation and host to used X-On/X-Off flow control and RTS/CTS for power on indications. However, the newly accepted remote access protocols (SLIP and PPP) do not support X-On/X-Off or any other in-band flow control means. An additional out-of-band flow control must be passed. Thus the change to 1180. Stay tuned for additional products which support SLIP and PPP as well as additional tutorial on these increasingly popular protocols.