over limited conduits such as the commercial maritime communication satellites of the day. The STU-III is no longer in use, having been replaced by the STE (Secure Terminal Equipment) or OMNI, more modern, all digital systems that overcome many of the STU-III's problems, including the 15 second delay. Operational difficulties in using STU-III phones hindered coordination between the Federal Aviation Administration and NORAD during the September 11, 2001 attacks on New York and Washington. See Communication during the September 11 attacks. STE succeeded STU-III in the 1990s. Similar to STU-III, an STE unit physically resembles an ordinary telephone. Besides connecting to a regular wall phone jack (Public Switched Telephone Network), the STE was originally designed to be connected to Integrated Services Digital Network (ISDN) lines. As a result, in addition to having secured voice conversations, users can also use an STE unit for classified data and fax transmissions. Transfer rate of an STE is also considerably higher (STU-III: up to 9 kbit/s; STE: up to 128 kbit/s). Lastly, an STE unit is backward compatible with an STU-III unit when both units are connected to the PSTN. The heart of an STE unit is the Fortezza Plus (KOV-14) Crypto Card, which is a PCMCIA card. It contains both the cryptographic algorithms as well as the key(s) used for encryption. Cryptographic algorithms include BATON, FIREFLY, and SDNS signature algorithm. When the Crypto Card is removed from the STE unit, neither the phone or the card is considered classified. BATON is a block cipher developed by the NSA with a block size of 128 bits and key size of 320 bits. FIREFLY, on the other hand, is a key distribution protocol developed by the NSA. The FIREFLY protocol uses public key cryptography to exchange keys between two participants of a secured call. Both STU-III and STE are built on technologies that are proprietary, and details of the cryptographic algorithms (BATON and FIREFLY) are classified. Although the secrecy of the algorithms does not make the device less secure, it does limit the usage to within the U.S. government and its allies. Within the Department of Defense, Voice over IP (VoIP) has slowly emerged as an alternative solution to STU-III and STE. The high bandwidth of IP networks makes VoIP attractive because it results in voice quality superior to STU-III and STE. To secure VoIP calls, VoIP phones are connected to classified IP networks (e.g.