Cisco PA-4E1G/120
4-Port E1 G.703 Serial Port Adapter (120ohm/Balanced)
Product Highlights
Organizations maintaining legacy TDM and leased-line WAN infrastructure need reliable, standards-compliant E1 interfaces that integrate seamlessly with their existing Cisco routing platforms. The Cisco PA-4E1G/120 is a 4-Port E1 G.703 Serial Port Adapter designed for balanced 120-ohm environments, delivering up to four synchronous serial interfaces fully compatible with the G.703 and G.704 standards.
Each port operates in full-duplex mode at E1 speed (2.048 Mbps), providing dependable connectivity to telephone lines, PTT networks, and leased-line services. The adapter supports both framed and unframed service access modes, giving network engineers the flexibility to match their circuit provider's configuration. Clocking can be derived from the received data stream (line-recovered) or generated internally by the port adapter itself.
The PA-4E1G/120 uses standard 15-pin D-shell (DB-15) receptacles, with balanced adapter cables available in RJ-45, twinaxial, or DB-15 terminations at the network end to accommodate regional cabling standards. It is supported across a wide range of Cisco platforms — including the 7200, 7200 VXR, 7500 (via VIP), 7100, 7301, 7304, 7401ASR, and 7600 series routers — and supports online insertion and removal (OIR) on several of those platforms for non-disruptive maintenance. For organizations sustaining E1 WAN connectivity on proven Cisco infrastructure, the PA-4E1G/120 remains a cost-effective, field-proven solution.
Features & Benefits
G.703/G.704 Standards Compliance
The PA-4E1G/120 is fully compatible with the ITU-T G.703 and G.704 standards, ensuring interoperability with carrier E1 circuits worldwide. G.703 defines the physical and electrical characteristics for E1 transmission, while G.704 provides the framing specification. This standards-based design guarantees seamless integration with telecom provider infrastructure and PTT networks.
Flexible Clocking Options
The adapter supports both line-recovered and internal clock modes. By default, the interface recovers its clock signal from the received data stream. Alternatively, the port adapter can generate its own internal clock signal independently of the motherboard or system clock, providing flexibility in diverse network timing architectures.
Balanced 120-Ohm Cabling
Purpose-built for balanced (120-ohm) twisted-pair environments, the PA-4E1G/120 uses DB-15 receptacles that support adapter cables with RJ-45, twinaxial, or DB-15 connectors at the network end. This accommodates varying regional cabling standards and simplifies deployment across international sites.
Hot-Swappable on Supported Platforms
Online Insertion and Removal (OIR) is supported on the Cisco 7100, 7200, 7200 VXR, uBR7200, 7201, 7301, and 7401ASR platforms. This allows network administrators to replace or install the port adapter without powering down the router, minimizing service disruption during maintenance windows.
Per-Port Status LEDs
The PA-4E1G/120 features a row of three status LEDs per port plus an ENABLED LED. After system initialization, the ENABLED LED confirms the adapter is operational. The per-port LEDs provide at-a-glance status monitoring, simplifying troubleshooting in dense chassis environments.
Deployment Scenarios
Legacy TDM WAN Connectivity
Organizations with existing E1 leased-line circuits can use the PA-4E1G/120 to maintain reliable WAN connectivity on their Cisco routing infrastructure. The adapter bridges traditional TDM networks with IP-based routing, supporting both framed and unframed E1 service modes.
Telecom & PTT Network Interconnection
Service providers and enterprises connecting to post, telephone, and telegraph (PTT) networks benefit from the PA-4E1G/120's G.703/G.704 compliance. The four-port density allows multiple circuit terminations in a single port adapter slot, conserving valuable chassis real estate.
International Branch Office WAN
The balanced 120-ohm design with support for RJ-45, twinaxial, and DB-15 network-end connectors makes the PA-4E1G/120 well-suited for international deployments where regional cabling standards vary. It provides a consistent interface across geographically distributed sites.
General
Interfaces
Physical
Indicators
Compliance
Compatibility
Lifecycle
Compatibility Notes
Supported Platforms
- Cisco 7200 Series — NPE-225, NPE-400, NPE-G1
- Cisco 7200 VXR Series
- Cisco 7100 Series (e.g., 7120, 7140)
- Cisco 7000 Series — Requires RSP7000/RSP7000CI with VIP2, VIP4, or VIP6-80
- Cisco 7500 Series — Via Versatile Interface Processor (VIP)
- Cisco uBR7200 Series
- Cisco 7201 Router
- Cisco 7301 Router — NPE-G1
- Cisco 7304 Router — Via PCI Port Adapter Carrier Card; NSE-100, NPE-G100
- Cisco 7401ASR Router
- Cisco 7600 Series — Via FlexWAN and Enhanced FlexWAN modules
Cabling
The PA-4E1G/120 uses DB-15 receptacles. Compatible balanced (120-ohm) adapter cables terminate at the network end with RJ-45, twinaxial, or DB-15 connectors. Balanced and unbalanced cables are not interchangeable — do not use 75-ohm cables with this adapter.
Compliance
The E1-G.703/G.704 interface on the PA-4E1G is compliant with BABT 221.
Downloads & Resources
Frequently Asked Questions
| Part Number | Product | Key Difference |
|---|---|---|
| PA-4E1G/75 | 4-Port E1 G.703 Serial Port Adapter (75ohm/Unbalanced) | Unbalanced 75-ohm version using BNC connectors at the network end — choose based on your cabling infrastructure |
| PA-8E1G/120 | 8-Port E1 G.703 Serial Port Adapter (120ohm) | Doubles port density to 8 E1 interfaces per slot for higher-density deployments |
| PA-4T+ | 4-Port Serial Port Adapter (Enhanced) | General-purpose synchronous serial adapter supporting V.35, X.21, RS-232, and other serial standards — not E1-specific |
| PA-MC-4E1/120 | 4-Port Multichannel E1 Port Adapter (120ohm) | Adds multichannel (channelized) E1 capability for granular timeslot-level bandwidth allocation |