What is TN5250?
TN5250 (Telnet 5250) is the TCP/IP protocol that connects terminal emulators to IBM i (formerly AS/400, iSeries) systems. It's the same protocol used by IBM iAccess, Mochasoft, and other terminal emulators for decades.
Unlike screen-scraping approaches that work with pixel coordinates, TN5250 provides structured access to screen content - field positions, attributes, input areas, and function keys. This makes automation reliable and resilient to display changes.
How legacy bridge automates TN5250
Session management
Opens and maintains persistent TN5250 sessions to your AS/400 (IBM i). Handles reconnection, session timeouts, and concurrent connections for high-throughput processing.
Screen recognition
AI vision reads the current screen state, identifying which program or menu is displayed. Adapts to screen variations, custom menus, and non-standard layouts.
Intelligent navigation
Navigates multi-level menus to reach the target screen. Handles function keys (F3, F6, F12, etc.), page up/down, and command-line entry.
Field-level data entry
Enters data into specific fields by position. Respects field attributes - numeric-only, date formats, required fields - and validates before submission.
Error recovery
Detects error messages on Row 24, interprets the error, and takes corrective action - adjusting data format, clearing fields, or routing to human review.
Technical architecture
- Protocol
- Standard TN5250 over TCP/IP (port 23 or custom)
- Connection
- Cloud-to-VPN or direct network access via secure tunnel
- Authentication
- Uses your existing AS/400 (IBM i) user profiles - no service accounts required
- Concurrency
- Multiple simultaneous sessions for parallel processing
- Latency
- Fast automated field entry, optimized for high-volume data entry
- Monitoring
- Real-time dashboard showing active sessions, screens, and entry progress
Zero changes to your AS/400 (IBM i)
Because legacy bridge connects via standard TN5250, your AS/400 (IBM i) system requires no modifications. No RPG program changes, no new APIs, no additional software installed on the server. If your system accepts terminal connections today, it works with legacy bridge today.
