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EXNET® Fault Recovery and Redundancy

Overview

An EXNET® system is self-healing with hardware failures involving a segment of the EXNET® ring and an EXNET-ONE card. If a failure occurs, a node or ring segment is automatically bypassed as the EXNET® port on the EXNET-ONE card is looped back.

Hardware Requirements

There are no special hardware requirements to enable EXNET® Fault Recovery. Configure the hardware as previously described in this document.

Operation

The EXNET® cable is a fiber optic cable with separate cables for transmitting and receiving. During normal operation, the EXNET-ONE card receives packets from the ring through its EXNET Port A and transmits packets onto the ring through its EXNETPort B. In loopback mode, ring traffic is both received and transmitted through the same EXNET® port. The two modes of operation are shown in EXNET-ONE Port Status.

Figure 5-10 EXNET-ONE Port Status

Loopback Mode Information

When an EXNET® port is placed in loopback mode, the Fault Detect LEDs turn red and the host receives a Ring Status Report message indicating the status (normal or loopback) of both EXNET® ports on the card.

An EXNET® port cannot be placed in loopback mode by the host. To isolate a node from an CSP system, do one of the following:

1 Take the EXNET-ONE card out of service.

2 Power-down the node.

Normal Operation

Normal Ring Operation shows the connection between nodes during normal operation. All nodes are receiving ring traffic on their EXNET A port and transmitting traffic on their EXNET B port.

During normal operation, the Signal Detect and Fault Detect LEDs are green.

Figure 5-11 Normal Ring Operation

Loopback Mode

Loopback Mode shows how EXNET® ports on the EXNET-ONE card are put in loopback mode because of a failure in an EXNET® ring segment.

• The EXNET® ports connected to the failed ring segment (Node 1/EXNET A, Node 4/EXNET B) are placed in loopback mode.

• The traffic on the EXNET-ONE cards is both transmitted and received through one EXNET® port.

• A ring connection is maintained between all nodes, and no calls are dropped.

Figure 5-12 Loopback Mode

Ring Segment Failure

This section describes what happens when a your system experiences a ring segment failure.

Single Ring

Ring Segment Failure illustrates the ring connection between nodes after the failure of a ring segment in a single ring configuration.

• The node that was connected to the failed segment at its EXNET A port loops back its EXNET A port.

• The node connected to the failed segment at its EXNET B port loops back its EXNET B port.

• A complete ring is maintained between all nodes.The host receives a Ring Status Report message from the affected nodes indicating that the affected EXNET® ports are in loopback mode.

Redundant Ring

A redundant EXNET® ring configuration has no effect if an EXNET® ring segment fails on one of the rings. The affected ring self-heals and a complete loop is maintained on both rings.

Figure 5-13 Ring Segment Failure

EXNET-ONE Card Failure

This section describes what happens when your system experiences an EXNET-ONE card failure.

Single Ring

EXNET-ONE Card Failure – Single Ring shows the ring connection between nodes after the failure of an EXNET-ONE card in a single ring configuration.

• The node that was connected to the failed node’s EXNET A port loops back its EXNET B port.

• The node connected to the failed node’s EXNET B port loops back its EXNET A port.

• All calls on the failed node connected across the ring are purged.

• A ring connection is maintained between all remaining nodes. The host receives a Ring Status Report message from the adjacent nodes indicating that the affected EXNET® ports are in loopback mode.

Figure 5-14 EXNET-ONE Card Failure – Single Ring

Important! If the EXNET-ONE card is reset, the EXNET® ring resets when the node rejoins the ring.
If the Master Node fails in a non-redundant system, the EXNET® ring resets and all inter-nodal connections are purged. To determine the Master Node, send a Ring Status Query to each node.

Redundant Ring

EXNET® Card Failure – Redundant Ring shows the ring connection between nodes after the failure of an EXNET-ONE card in a redundant ring configuration.

Figure 5-15 EXNET® Card Failure – Redundant Ring

• The node that was connected to the failed node’s EXNET A port (Node 2) loops back its EXNET B port on the affected ring
(Ring 1).

• The node that was connected to the failed node’s EXNET B port (Node 4) loops back its EXNET A port on the affected ring
(Ring 1).

• Traffic to and from Node 3 is routed through Ring 2. Traffic on other nodes is still carried on both rings. The host receives a Ring Status Report message from the adjacent nodes indicating that the affected EXNET® ports are in loopback mode.

Important! In this scenario, there is no longer EXNET® Redundancy for Node 3. If the EXNET-ONE card for Ring 2 fails, Node 3 is isolated from the CSP system and all inter-nodal connections involving Node 3 are dropped.

Excel's open architecture, proprietary, 1.3 Gbps fiber optic network using a packet-based protocol.
The point in the Excel platform where a DS0 connects to a network. Also known as a "socket."
A type of diagnostic test in which the transmitted signal is returned to the sending device after passing through a data communications link or network.