Condition: New (Never Used / New Old Stock)Interface: EIA-232 Serial / RJ48S Network JackFCC Registration Number: 1DZUSA-21951-DE-NCountry/Region of Manufacture: United States (Simi Valley, California)Item Description: Up for sale is a vintage, New Old Stock (NOS) / Brand New in Box HT Communications Pro 4000 Data Series DDS DSU Modem, Model P4501.This unit is brand new, completely pristine, and has never been deployed. It features a modular configuration panel with toggle switches for interface handling (EIA-EIA232 interface, CNST-Constant RTS, LL Local Loopback, RL Remote Loopback, and TP Test Pattern setups).Perfect for vintage enterprise networking setups, industrial systems requiring exact legacy telecom replacements, or telecommunications collectors.Model Number: P4501Revision: HPower/Fuse Specs: 250 VAC, Slo-Blo, 0.5 AMPCondition Notes: Brand new item in its original box. The box may show minor shelf wear from long-term storage, but the hardware inside is immaculate.Shipping & Handling Suggestions:Shipping Carrier: USPS Ground Advantage or UPS Ground (safe, economical options).Package Weight: Approx. 2–3 lbs. Device is an HT Communications P4501 Data Service Unit (DSU) / Synchronous Modem.Manufactured by HT Communications, Inc. out of Simi Valley, California, this type of vintage enterprise networking hardware was commonly deployed during the 1980s and 1990s. Its primary function was to connect a local computer networking interface (like an EIA-232 or V.35 serial link) to a dedicated Digital Data Service (DDS) leased telephone line via an RJ48S jack connection. Essentially, it acted as a bridge allowing early corporate computer systems to communicate over high-speed, point-to-point telecom infrastructure. Brand New in Box