American Technology Labs VRT-2 CSU/DSU 56Kbps Dedicated Digital Leased Line

American Technology Labs VRT-2 CSU/DSU 56Kbps Dedicated Digital Leased Line

The American Technology Labs VRT-2 is a desktop CSU/DSU (Channel Service Unit / Data Service Unit) designed for 56 Kbps dedicated digital service (DDS) leased-line circuits. It provides the interface between customer DTE equipment and the telephone company's digital leased line, handling line conditioning, signal regeneration, and loopback functions required for DDS operation. The VRT-2 supports two DTE channels, making it suitable for point-to-point or frame relay applications where dual data ports are needed.

Specifications & What's Included

• Manufacturer: American Technology Labs
• Model: VRT-2
• Device Type: CSU/DSU (Channel Service Unit / Data Service Unit)
• Data Rate: 56 Kbps (DDS — Dedicated Digital Service)
• Circuit Type: Dedicated point-to-point leased line; frame relay
• DTE Channels: 2 (Channel 1 and Channel 2, labeled on rear panel)
• DTE Connectors: DB-25 (RS-232 / V.35 compatible) — two ports on rear panel
• Line Interface: Single line port (RJ-style) on rear panel
• Front Panel: Row of LED status indicators (Tx, Rx, timing, loop, and link status); rotary control knob
• Form Factor: Desktop enclosure, beige/tan metal chassis
• FCC Registered: Yes (FCC Registration No. IKGUSA-61… per bottom label)
• Unit only — no power supply, cables, or accessories included unless pictured

Applications

CSU/DSU units like the VRT-2 were a standard building block of enterprise WAN connectivity through the 1980s and 1990s. A CSU (Channel Service Unit) terminates the telco's DDS leased line and provides loopback test capability required by the carrier, while a DSU (Data Service Unit) converts the customer's DTE serial interface into the bipolar line signal the network expects — the VRT-2 integrates both functions in one desktop box. At 56 Kbps, these circuits were the primary dedicated WAN link for inter-office connectivity, frame relay access, and remote site connections before broadband became widespread. The dual-channel design of the VRT-2 allowed a single unit to serve two DTE devices or split a circuit between two endpoints, useful in small branch office or multipoint configurations. Today, legacy 56K DDS circuits are largely replaced by DSL, T1, and broadband alternatives, but VRT-2 units remain in demand for maintaining older private-line infrastructure, test lab environments, and facilities that still operate DDS circuits.