SIP PBXes stake a claim

Von Brian Chee

SIP works. Not only does it work, but it is easier to use, implement, and configure than older VOIP standards.

The promise of SIP has always been interoperability, and the three SIP-based phone systems we reviewed demonstrate why real standards are important. The interoperability part of the equation works, too. You can mix and match manufacturers to a much greater extent than you could with earlier VOIP solutions.

This is not to suggest that every feature of every SIP product is totally interoperable, because they"re not. There are several features on these products for which there is no final standard, and this is where the proprietary nature of PBX products shows up. Nevertheless, it"s clear that these companies are embracing SIP, and they"re making an effort to follow the standard.

At the University of Hawaii"s Advanced Network Computing Laboratory we tested three PBX products: Avaya"s Communication Manager 3.0 and Communications Server; Siemens" HiPath 8000 Real-Time IP System; and Zultys" MX250. After putting them through their paces, we found that interoperability generally worked: these PBXes could certainly talk to other SIP devices, but they couldn"t network effectively with other PBX products from different makers, for example.

They could also use nearly every SIP phone ever designed, and we were pleasantly surprised to find that these units had similar results when we tested their performance and operation using the Spirent Communications Abacus 5000. They consistently made calls that went through and sounded good -- exactly what you expect from your phone system.

Avaya Communication Manager 3.0 and Converged Communications Server

Avaya"s PBX is really two products: Avaya CM (Communication Manager) 3.0 provides the basic call controlling, and Avaya CCS (Converged Communications Server) runs on the S8500 Media Server and is the SIP proxy. It provides additional extensions and enhancements including the presence engine and IM. CCS also works with a separate and optional Avaya product called Meeting Exchange, which handles large conferences and runs on a separate server. Together they form a full-featured SIP PBX.

For this test CM was installed at the factory on the Avaya S8300 Media Server, a single-board Linux machine installed as a blade into a slot on the G700 Media Gateway. The media gateway, in turn, lets CM work with a wide variety of legacy telephone systems, including other IP phones, digital phones, and even POTS phones.

CM communicates with CCS using SIP. When CCS gets a SIP call request (someone dialing a number from their SIP phone, for example), it accepts the request and passes it along to the CM. CM routes those calls to other SIP phones on the network, to legacy PBXes, or to the PSTN. It also handles all of the traditional telephony features, including the dial plan and voice mail. It sets up the calls, enables communications between end points, controls the gateways and trunking, and manages resources.

One consequence of handling so many different types of legacy phone systems is that the Avaya products must also support calling features currently unavailable in SIP. Avaya uses a second SIP channel for these features, but the company says that when new features are added to the SIP standard, they may be added to the products" standard SIP feature set.

Both of these applications can be installed on platforms other than the ones on which they were tested; running CM on a larger platform would allow you to support more people, for example. However, CM and CCS cannot currently be run on the same machine. (Avaya says that will change eventually.) The result is a pair of Linux machines in your rack -- a 2U G700 Media Gateway with the S8300 installed internally and the 1U S8500 running CCS -- which means you use more rack space and must buy more than one platform.

The Avaya engineers apparently raided their interoperability lab for spare phones, showing up in Hawaii with one of everything they could find: phones and softphones from Avaya, Cisco, Polycom, Snom, and others, including some dubbed "unknown generic phone." All of them worked seamlessly with the PBX.

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. Despite the straightforward, Web-based management interfaces on CM and CCS, we couldn"t resolve the issue in the time available.

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.

The HiPath 8000 also has a new graphical management utility that"s reasonably intuitive and easy enough to use in most datacenters. Although the dial plan is still pretty well set in the telephone company mindset, most of the management is not: You won"t have to hire a telephone wizard to use the HiPath 8000.

Zulltys MX250

Think of Zultys as the Little PBX Company That Could. The company bravely agreed to jump into the ring on very short notice, bringing its updated MX250 into this test with almost no time for preparation and facing off against a pair of vastly larger competitors.

We set up the Zultys MX250 ourselves -- there wasn"t time for the company to send an engineer to Hawaii -- and discovered that this device sets new standards for ease of implementation. Part of this easy setup is due to SIP, which makes all of these products comparatively easy to set up, but the rest is due to Zultys" intelligent design and well-chosen defaults. It was so easy to set up, we found ourselves, along with the engineers from Ingate and Spirent, wondering if that was really all there was to it. (Happily, it was.)

The MX250 is a significantly smaller PBX than the others in this test. Our test unit, which was based on a dual-processor PowerPC-based system running Linux, came equipped with a dual T1/E1 gateway and a POTS gateway. Recent upgrades have improved performance and added memory, and the test unit included RAID storage.

Each MX250 device can be used by no more than 250 users at one time and will support no more than 1,000 registered users. You can network as many as 32 devices for about 10,000 users total. So although it won"t handle phone calls for the entire planet, the MX250 is plenty big enough for most small to midsize enterprises.

Adding to its SMB attraction is the ease with which the MX250 is set up and managed, all via a Windows-based GUI on a workstation. Zultys designed its PBX to conform to current interface design and GUI standards, so managers used to working in a graphical environment will feel right at home. It was one of the easiest-to-manage products we"ve run across lately. For example, you can create your user list by using Excel or anything else that will create a CSV file, and then simply import the file into the PBX.

The MX250 is designed to be used in enterprises with about 8,000 users or less, assuming you networked 32 of the devices. Most users won"t try that. What they will try is using the MX250 as their company PBX, probably without a lot of other telephony support. Keeping that in mind, the MX250 contains its own router and firewall, and it supports NAT and DHCP.

It also comes with a wealth of services. Voice mail is included, and each user can define as many as eight phones, including desk, cell, and home phones. Like the other PBXes we tested, the MX250 works with any standards-based SIP phone or softphone.

We found the MX250 as easy to administer as it was to install. The management GUI is the standard means of operating the PBX, and it"s easy to use, intuitive, and complete. As befits a PBX aimed at SMBs, the MX250 won"t require you to hire skilled employees or retrain your entire workforce, although you must understand basic telephony concepts to manage it.

The MX250 won"t scale to huge numbers as the others in this test will, but its capacity is just fine for its target market of small and midsize enterprises: It handles the low end better than the other two PBXes in this test. However, this PBX offers the same support, feature for feature, as its larger competitors. It handles SIP perfectly and will fit within the capabilities of smaller IT departments.

Three"s a crowd

Each of these telephony solutions is a solid choice, depending on your company"s needs. For example, Avaya"s PBX may be complex, but it"s competitively priced, and if you have a legacy phone system of nearly any type, the combination of CM and CCS will work with it nicely. Avaya"s solution will also handle the various connection demands (digital, POTS, and so on) rampant in any large company.

Siemens, meanwhile, could apparently provide phone service to the entire planet, if its marketing literature is to be believed. Take that as you may, but we did find that the HiPath 8000 is an example of SIP at its finest. It supports everything we tried that uses SIP, and the HiPath 8000"s flexibility demonstrates what can be done when a company really tries to follow the standard.

Zultys" MX250 is a significant PBX for the smaller enterprise. It does nearly everything, including a few tasks not normally seen in a PBX, such as serving as a firewall and providing DHCP and NAT services. The MX250 was InfoWorld"s 2004 I IP PBX Technology of the Year, and this updated version maintains that tradition with its crisp management interface and an "easy, too easy" installation.

These products will deliver more than you might expect. The fact that they all support SIP means your company is ready for the future, regardless of where you"re coming from. Just because you have a PBX from one vendor does not preclude having phones, media gateways, or application servers from others. It means your phone system will grow in whatever direction your company may go.

Avaya Communication Manager 3.0 and Converged Communications Server


Very good 8.4

Criteria Score Weight

Features 8 30 percent

Management 8 30 percent

Scalability 9 20 percent

Implementation 9 10 percent

Value 9 10 percent

Cost: As tested, US$40,000 for 100 users

Platforms: Linux

Bottom line: Avaya"s two-part SIP solution is aimed at the larger enterprise and consists of a pair of Linux servers. Its legacy support is great: Communication Manager allows you to connect to and between nearly any other form of telephony, from digital to POTS. For companies that want to move into standards-based IP telephony, this product is a good starting point.0

Siemens HiPath 8000 Real-Time IP System

Siemens AG,

Very good 8.6

Criteria Score Weight

Features 9 30 percent

Management 9 30 percent

Scalability 8 20 percent

Implementation 8 10 percent

Value 8 10 percent

Cost: As tested, $750,896

Platforms: Suse Linux

Bottom line: Siemens HiPath 8000 consists of the PBX software and a companion feature server from IP Unity. Together they give you a functional, capable IP telephony server and soft switch that can handle a huge number of users. Nevertheless, we found it relatively easy to use and manage, and very effective as a phone system.

Zultys MX250

Zultys Technologies,

Very good 8.4

Criteria Score Weight

Features 9 30 percent

Management 8 30 percent

Scalability 8 20 percent

Implementation 9 10 percent

Value 8 10 percent

Cost: As tested, $74,000 including licensing for 250 users

Platforms: Linux

Bottom line: Although the new MX250 features minor upgrades to the similar product we tested last year, it"s still a solid solution for small and midsize enterprises. Scalability is adequate, but you don"t need years of telephony experience to set up and manage the MX250. Everything works easily, and everything worked right the first time.