Amazon.com: U.S. Robotics USR5686D 56 Kbps Fax / Modem - Serial Rs-232 : Electronics
HAWKING PN580U Data/Fax Modem 56Kbps USB V.90 (down-stream up to 56,000 bps). V.34bis, V.32bis, V.32, V.22bis, V.23, V.22, V.21 Error Correction Protocol V.42 and MNP Class 2 to 4 Data Compression Protocol