GateWay Fax Systems, inc. | Model 90si Secure Fax Gateway User's Guide |
wall, wait a moment, and plug it back in.
3.7Selecting a Transmit Protocol
As always, the 90si automatically determines and switches to the correct protocol as a receiver. So, as usual, you must select the transmit protocol that you wish to use. There are two ways to do this; using the Default Protocol Setting (Send via HOOK, 1, START) or by manually dialing the appropriate transmit protocol's One-Time Code as you are sending the fax (Send via HOOK, "One-Time Code", START). When using the One-Time Codes, in- sure that your Secure Phone / Crypto's Secure Data mode is set correctly for the mode you choose (Sync or Async & Baud Rate).
The 90si supports four different secure fax protocols plus a few subset of these first two; Async, Mil-Std-188-161, Ricoh (AKA: Modified Group 3 or 3312) and Compat (AKA: Compatible or Valutec) mode. With the Async pro- tocol the user must select a baud rate or speed of which the 90si supports four; 2400, 4800, 9600 and 19200 bps.
The Mil-Std protocol has four subsets; Handshake with FEC, Handshake w/o FEC (recommended), Broadcast with FEC and Broadcast w/o FEC. As the Mil-Std, Ricoh and Compat modes are synchronous, baud rate selection is automatic.
The 90si's factory default protocols is Asynchronous 9600bps.
3.7.1SCIP Async Protocol
The Async protocol has been around since the late 1980's, however it has never been widely used until the pro- duction release of the KSV-21 Crypto Card for the STE. The KSV-21 does not support synchronous secure data modes when the STE is connected to a PSTN line. While it does support synchronous when connected to an ISDN line, the overwealmingly large number of STE's connected to PSTN lines will drive most secure fax users to this mode. As a result, the 90si comes with the Async Protocol (with a baud rate of 9600 bps) set as the factory default. The 90si supports Async baud rates of 2400, 4800, 9600 and 19,200 bps (bits per second).
3.7.2MIL-STD-161 Protocols (Synchronous)
As mentioned earlier, the 90si impliments four flavors of the synchronous Mil-Std protocol:
HANDSHAKE with FEC Off
This is the only Mil-Std protocol we recemmend for use with desktop (non Tactical) cryptographic devices such as the STE, OMNI and SECTERA. The handshaking that it gets its' name from come in the form of "acknowl- edgements" from the receiving fax machine which occur at the beginning of the transmission and between each page. Forward Error Correction (FEC) is not necessary with these cryto devices because they provide their own, quite effective, error correction.
HANDSHAKE with FEC On
As described above but with FEC turned on. This error correction technique adds about 20% more data to the im- age data but allows operation on noisy communications links with a Bit Error Rate of up to 10-2.
BROADCAST with FEC Off
The broadcast mode was designed for point-to-multipoint battlefield radio networks and is a poor choice for mod- ern secure telephone networks. Requiring no response from the receiving secure fax, the sending secure fax has no way of knowing if the transmission was received.
BROADCAST with FEC On
As described above but with FEC turned on.
