Zultys Technologies this week is set to announce a clustering technology for its IP PBXs aimed at letting users create resilient, high-scale VoIP systems using groups of small call servers.Zultys Technologies\u00a0this week is set to announce a clustering technology for its IP PBXs aimed at letting users create resilient, high-scale VoIP systems using groups of small call servers.MXCluster could help Zultys users with MX250 IP PBXs increase their system capacity by linking multiple low-cost boxes, instead of upgrading to a high-end IP PBX from Zultys or other vendors, the company says. Tying together MX250s in a cluster also increases the failover capabilities of the device and public switched telephone network (PSTN) links.Announced last year, the MX250 is a Linux-based IP PBX appliance that uses Session Initiation Protocol (SIP) for call setup and signaling. SIP is a VoIP call control and application protocol technology.The box includes up to 200 hours of voice mail storage and can handle up to 250 attached SIP phone users. (Zultys makes a SIP phone, but the MX250 can work with any standards-based SIP endpoint, such as a Cisco or Pingtel SIP IP phone or Windows PC with the SIP-based Windows Messenger client.)Version 2.2 of the MX250 operating system software allows two to four MX250s to link together to provide IP phone connectivity for up to 1,000 users. The cluster also combines the voice mail storage of the separate systems into a virtual store of 800 hours of voice mail across the clustered systems' hard disks. The clustered systems have one IP address and share one user directory database.Current MX250 customers now can add a few hundred users, without having to upgrade to a larger system such as Zultys' MX1200, a single system that supports 1,200 IP phones, says Iain Milnes, CEO and founder of Zultys.MXCluster requires one standby MX250 server for clusters of two, three and four live IP PBXs. A single master node in the cluster distributes call processing and voice mail processing and storage across the cluster. Zultys says a cluster can be set up in less than an hour, and IP phones and PCs do not need reconfiguring when clustering more MX250s with an existing system (provided a MX250 acts as the master node in the cluster).In addition to MXCluster, the company is introducing its XRS12 appliance for pooling voice T-1 lines and sharing bandwidth among MX250 boxes in a cluster. The XRS12 can consolidate 12 PSTN T-1 connections into one box and then share the lines among four MX250s in an MXCluster configuration. This lets PSTN lines remain live in case one of the nodes in the cluster fails.Healthcare Billing, a Boca Raton, Fla., company, uses several MX250s in its central site and at remote sites around the state. The MX devices' quick setup proved useful, says Corey Wilson, director of IT for the firm, which outsources hospital billing jobs.During a recent office move, new MX250s were installed and brought up in a day, replacing a Lucent\/Avaya Merlin key system used in the old office, he says. Wilson says he figures it would have taken at least three days to move and set up the older key system.The MX250 competes with small-office IP PBXs such as 3Com's NBX, Alcatel's OmniPCX, Avaya's IP Office, Cisco's CallManager Express and Nortel's BCM.These vendors also offer clustering configurations for linking multiple small-office boxes.An MXCluster configuration requires a spare MX250 and license, which costs $6,000, and a XRS12 appliance, which costs $1,800. Zultys' MXCluster software is available as a free upgrade to MX250 customers.