The HP/Agilent 4957A Protocol Analyzer is a portable field instrument for monitoring, decoding, and simulating data communication protocols across serial data networks. It performs multi-layer analysis from physical layer (Level 1) through data link (Level 2) and packet (Level 3), supporting both packet-oriented protocols (SDLC, HDLC, BiSync) and character-oriented protocols (ASCII, Baudot, IBM EBCDIC). The analyzer handles asynchronous and synchronous transmission modes with data rates up to 64 Kb/s in standard configuration and 256 Kb/s with Option 001, extending to 1.544 Mb/s with the HP 18282A ISDN/T1 interface pod.
## Technical Specifications
**Protocol Support**
• Packet-oriented: SDLC, HDLC, BiSync
• Character-oriented: ASCII, Baudot, IBM EBCDIC
• Asynchronous and synchronous modes
• RS-232C (V.24), RS-449, V.35, X.25
• X.21, ISDN BRI/PRI, and T1 via external pods
**Data Rates and Capacity**
• Monitoring, simulation, and BERT: up to 64 Kb/s
• High-speed monitoring with Option 001: up to 256 Kb/s at 115.2 kbaud
• T1 decoding: 1.544 Mb/s with HP 18282A pod
• Capture buffer: up to 3/4 MB
**Measurement and Control**
• 63 programmable triggers for characters, errors, timeouts, and interface transitions
• Five timers with 1 msec resolution, maximum 65535 msec each
• Five counters, maximum count 65535
• Cursor timing: 6 to 66 seconds (rate-dependent)
**Character Framing and Error Detection**
• Information bits: 5, 6, 7, or 8 plus parity
• Stop bits: 1, 1.5, or 2 (asynchronous)
• Error checking: CRC-CCITT, CRC-CCITT preset 0, CRC-16, CRC-12, CRC-6, LRC, parity
• Parity modes: odd, even, none, ignore
**Transmission Control**
• Send strings: up to 251 characters per string, 1743 characters total
## Key Features
• High-resolution 13 cm (5-inch) display with VT100 terminal emulation (80-column)
• Softkey-driven interface with full ASCII keyboard and cursor control
• Five onboard microprocessors
• 128 KB nonvolatile RAM and 613 KB floppy drive
• Integrated patch panel for flexible line connections
• Multiple display formats: DTE/DCE overlay, lead status, frame decode, partial packet decode
• Bit error rate testing capability up to 64 Kb/s
## Typical Applications
• Field troubleshooting and maintenance of serial data networks
• Protocol compliance and interoperability testing
• Network simulation and emulation
• Transmission quality assessment via BERT
## Compatibility & Integration
The 4957A accepts external interface pods designed for HP 4951C and HP 4952A analyzers, enabling expansion to ISDN, T1, X.21, and MIL-188C protocols. Weight approximately 13 pounds.
