High availability telephony is the practice of making IP telephone services available during various types of service outages.  High availability services can handle problems like hardware failures, power outages, telephone lines down and, especially with IP telephony, WAN outages. Because of the importance of constant availability of communications, high availability solutions will provide for a 99.99% availability of communications services.

BNICG helps companies implement High Availability Telephony solutions to ensure that a company’s communications are uninterrupted.

The most typical High Availability solutions include:

• Redundant PBX Servers
• Redundant PSTN Connections

Redundant PBX Servers

In the case of IP PBX servers, a hardware failure, such as a bad power supply, failed hard disk, motherboard malfunction, and so on, will cause immediate failure of all calls.  In many cases, these failures can cause interruption of services for hours, possibly days, while replacement hardware is found, installed, and in the case of a failed hard disk, restoration of data.

It is imperative that PBX servers have all hardware components redundant.  Items such as hard disks and power supplies can all be made redundant so that if one fails, another is already on standby without administrator intervention.

In addition, PBX servers themselves can be made redundant.  If an entire server fails, the spare can be ready to take over operation immediately, also without administrator intervention. An example of this configuration is shown below.

Redundant PSTN Connections

Most IP Telephony systems will connect multiple remote sites to a corporate office using a private WAN or an Internet connection. However, if this connection fails, critical communication services will be interrupted.

It is crucial, therefore, that remote systems have the ability to make calls (especially emergency calls) when a WAN outage occurs. It is even possible, through special phone translations, that backup internal station to station calls can be preserved.

This process is handled by devices known as Local Survivable Gateways (LSGs). These devices connect a remote site directly to a local phone carrier as well as monitor connections between the remote office and the corporate office via the WAN connection. During normal operation, remote office calls (except for emergency calls, like 911) are passed through the WAN to the corporate office and ultimately to the PSTN. If the WAN connection fails, the LSG will automatically reroute calls directly through the PSTN until the WAN connection comes back up.

The images below show an example of how this works.