SIP PBXes stake a claim

About the only thing that didn't go smoothly was using phones with NAT-based IP addresses on the other side of a SIP firewall. This may have been a configuration issue with the Ingate Firewall 1600 we used in this test (see "SIP-Capable Ingate Firewall Protects Phone, Data Networks," below). Despite the straightforward, Web-based management interfaces on CM and CCS, we couldn't resolve the issue in the time available.

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We did manage to sneak a peek at a significant update to CM that will add some important features when it becomes available in midsummer. For example, one potentially useful new feature (which we were unfortunately unable to test) is CM's ability to automatically bridge calls to a cell phone as well as to a desk phone, allowing single-number access to users.

Overall, Avaya shows an excellent grasp of larger organizations' needs when it comes to moving to IP telephony in general or SIP specifically. The media gateway will work with virtually any legacy PBX, for example, so it's perfectly reasonable to start building your SIP phone system while continuing to use your current phone system.

Siemens HiPath 8000 Real-Time IP System

Unlike Avaya's offering, the Siemens HiPath 8000 is built from the ground up to be a SIP solution for the large enterprise. Following a practice we're seeing more and more often, the Siemens product lives in an IBM xSeries server running Suse Linux.

Siemens itself doesn't offer advanced services such as voice mail and large conferences; instead, the company tapped IP Unity to provide these functions. The IP Unity server is included in the HiPath 8000 package, and the products are seamlessly integrated -- but as with Avaya's PBX, the two devices will use up more rack space.

The HiPath 8000 clearly set the standard for SIP support in this test. Because the product was released just a few weeks before our tests, Siemens used the latest technology and most current practices in developing this system, and the results showed. The HiPath 8000 steamed through everything we threw in its path. We tried it with the Versatel 1500L media gateway, and the HiPath worked on the first try -- with the whole setup, configuration, and connection process took only a few minutes. We hooked up the HiPath to the Ingate Firewall 1600, and that worked perfectly as well. The HiPath 8000 also sailed through the NAT traversal that had stumped the Avaya PBX.

The HiPath 8000 worked nicely with every SIP phone and softphone we tried. Siemens sells its own softphone product, but any softphones, including freeware versions, work fine as long as they're completely SIP-compliant.

However, the HiPath's recent release date also means there are some features Siemens has yet to deliver. For example, you can't currently have a hot backup running for real-time redundancy, and there's no means to provide such a backup for the IP Unity server. Likewise, the Siemens media gateway we used in our tests provided only basic services such as T1/E1 and POTS connections. But because it worked perfectly with advanced media gateways such as the Versatel 1500L, this isn't a significant disadvantage -- you can boost the gateway services with a third-party product.

Siemens does scale very well. The HiPath 8000 supports, in one way or another, offices as small as five users and as large as, well, whatever you like. Siemens says there's no upper limit to the number of users the HiPath 8000 supports if you network enough of the systems. Unfortunately, we didn't have access to an infinite number of phones to test that statement, but we did push the HiPath 8000 to 4,782 channels in a SIP-to-SIP test through the Versatel media gateway. This was well above the 4,000-channel limit of the single platform we tested.

Advanced calling features, including voice mail, unified messaging, system announcements, and even lawful intercept, are handled by the IP Unity server. Although you can set up small conference calls without it, the IP Unity server is the only way to set up larger conferences.

One interesting advanced feature Siemens does provide is "VoIP survivability" for remote offices. It acts as a backup system. If remote offices are connecting to the central PBX through the media gateway and the connection goes down, outside calls will be automatically routed to the PSTN and internal calls will continue as usual through the media gateway at the remote end. Some third-party media gateways and VoIP firewalls also do this, but Siemens was the only company in this test that provided this capability.