Asterisk T1/E1 Bridges

High-Availability/Failover Asterisk clusters

Introduction: Obtaining a reliable, fault tolerant, highly available system with ASTERISK® has been difficult and nearly impossible especially from the PRI/TDM standpoint. IP based toolsets have been around for a number of years to allow integrators the ability to provide fault-tolerance on the VoIP side of their implementation. Until today however, providing quick, reliable and robust T1/E1 fail-over has been nearly non-existent. The foneBRIDGE fills this void allowing IT Managers and Systems Integrators to implement Asterisk in the most demanding of environments where downtime is a luxury a business simply can not afford.

High Availability

The general objective of deploying HA (High-Availability) in a server environment is to provide reliability, availability, and serviceability (RAS). In the traditional Asterisk implementation model, T1/E1 connectivity is provided by PCI based interface cards on a single server. In this scenario the systems overall integrity and availability is limited by the reliability of that single server. For many businesses, taking this gamble on a mission critical function such as voice is unacceptable.

As an externalized point of T1/E1 termination, the foneBRIDGE is decoupled from the single server limitation and when combined with the proper tool set can be implemented to provide rapid and automatic failover amongst a cluster of servers.

The most common tool set used to provide this functionality when paired with the foneBRIDGE and Asterisk is the 'heartbeat' tool from the Linux-HA project As the name employs, 'heartbeat' monitors the state of 2 or more nodes (servers) in an Asterisk cluster. If it detects a fault, for example when a primary node stops responding to the heartbeat messages it executes scripts that allow it to quickly failover to a secondary server. All of this is done transparently and without user intervention.

Rapid Recovery

With the foneBRIDGE, rapid failover and system recovery can occur in seconds, not minutes or hours. Through the foneBRIDGEs’ rapid re-configuration options, we can program it on the fly through high availability tools to begin routing the TDM stream and calls to a secondary standby server in under one second. Add to that the short amount of time it takes the server to start Asterisk and clear circuit alarms and your stand-by server can be operational and handling calls in under 3 seconds, all transparently and without admin intervention.

Uptime During Maintenance and Upgrades

Over are the days when it was necessary to bring down a server for patching or software upgrades. With fone-
BRIDGE, the server admin can manually failover to a back-up server and maintain the voice system operational while
performing upgrades or patching on the primary server. This unique feature also lends itself nicely to the ability to
failover to a server where production testing can be done on new code releases or features and in the event of a bug
discovery or issue that may jeopardize the integrity of operations the system admin can easily fail back to a primary
server with only seconds of downtime.


With connectivity externalized, and placed on the Ethernet not tied to any PCI card or single server, adding additional
T1/E1 capacity to an Asterisk implementation is simplified and can be realized with little or no downtime to operations.

foneBridge2 Network Diagram

Products Documentation:

Asterisk/Trixbox-High Availability Guide
TDMoE Protocol Specifications


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