The Case for Converged IP-PBX Systems

There are several advantages for implementing a converged IP-PBX system or a client/server IP-PBX. First let’s review the case for the converged IP-PBX system.

A converged IP-PBX system occupies the gray zone between the traditional PBX system and the evolving client/server design because it can offer customers the best of both worlds: the reliability, redundancy, and feature/function performance benefits of legacy circuit switched PBXs and the unique capabilities of ToIP technology to leverage LAN/WAN infrastructure in support of dispersed common carrier equipment and desktop terminals. A converged PBX system is best viewed as a bridge between the existing circuit switched world of voice communications and the emerging packet switched world. Instead of attempting to leap from the old world to the new world in one jump, it makes more sense to travel a longer, but less risky, road.

A converged IP-PBX system and an IP packet switched client/server platform can provide each of these customer benefits. The latter solution is usually optimized in a green field situation—a new customer location without a previously installed system, although a customer may still elect to install a converged system for incremental migration from a circuit to a packet switched solution. Many customers with an existing circuit switched system installation are likely to upgrade to a converged system with a minimal investment in new hardware and/or software. In contrast, a client/server design represents a major design break from previously installed circuit switched PBX systems and entails replacement of most existing common equipment and desktop terminal instruments.

The following are probable reasons a customer requiring ToIP capabilities might choose a converged IP-PBX system solution instead of an IP packet switched client/server design:

1. ToIP requirements

2. Investment protection

3. Critical reliability

4. Private network compatibility

5. Feature requirements

6. Pricing

ToIP Requirements

A large number of PBX system customers may not currently require ToIP capabilities for their enterprise communications system, although future plans are very likely to require support of ToIP options. A converged IP-PBX system is fully capable of being configured without any IP-based elements at initial installation but can support such a requirement when needed. The group of customers who are risk-averse may also choose to delay installation of ToIP options at the present time because they are taking a wait-and-see attitude toward the emerging technology. Early versions of products incorporating new technology may not satisfy accepted benchmark reliability standards for telephony applications. In addition, ToIP standards are still in a state of flux, and customers may wish to wait until control signaling protocol and voice codec standards have stabilized. Some first-wave customers who installed IP-PBX systems shortly after product introduction have watched as evolving standards and system upgrades obsoleted their installed terminal equipment, voice codecs, and/or telephony servers. A converged IP-PBX reduces this risk by allowing customers to upgrade and enhance their system for active ToIP capabilities when the time is acceptable.

A converged IP-PBX system is also ideal for customers who wish only to test ToIP technology without installing a 100 percent IP peripheral solution. For trial purposes it is less costly to use a converged IP-PBX system that is also functioning as the full-time circuit switched communications system than to purchase and install a dedicated IP packet switched client/server design. For trial purposes, a select number of IP peripherals can be installed on a converged IP-PBX system. If the trial is successful, additional IP ports can be equipped and activated when needed. A very important factor in the successful implementation of an IP-PBX system is the LAN/WAN infrastructure, because the network must be properly designed and programmed to provide an acceptable Quality of Service (QoS) level for real-time voice communications applications. A small-scale IP-PBX trial is usually necessary to discover in advance whether or not a major LAN/WAN overhaul is needed. What works on paper does not always work in real life. Using a converged IP-PBX system is the most efficient solution for trial testing ToIP QoS levels for station and/or trunk traffic communications.

Investment Protection

All customers make substantial financial and organizational investments in their installed premises communications system and usually seek to maximize their return on investment (ROI). Replacing an installed circuit switched PBX system with a new IP packet switched client/server design solution at the present time may be counter to this customer objective. For example, a customer may not have fully depreciated the installed system’s common equipment and desktop terminals. Replacing cabinet and port interface hardware with a telephony call server and gateways and digital telephones with new IP telephones is an expensive proposition, as are major upgrades to the LAN/WAN infrastructure to support real-time voice-grade QoS levels. Training expenses for station users, system managers, and maintenance personnel also add to upfront cost outlays. Additional costs are associated with a disruption of communications operations and procedures when migrating from an installed system to an entirely new platform. Although the data communications world has grown accustomed to constant change, one of the most fundamental characterizations of the voice communications world is reluctance to change.

Upgrading an installed circuit switched PBX system to a converged IP-PBX system is less costly than overhauling the entire communications system and network and is typically a far less disruptive experience because most station users are likely to retain their legacy desktop terminal equipment over the short term. The few station users who migrate to a ToIP desktop are more easily trained and supported in this environment. All of the features and functions available to station users before the system upgrade will remain available afterward, which is not usually the case if the legacy common control design is replaced with a new telephony call server loaded with a different software package.

PBX life cycles have fluctuated during the past several decades. Before the introduction of the computer-controlled digital PBX in the 1970s, the typical installed life of a PBX system was greater than 10 years. PBX systems did not change significantly over short periods. During the 1980s, the typical PBX life expectancy shrunk to between 6 and 8 years because of continual major design changes and dramatic software program upgrades. Since the early 1990s, the life cycle of an installed PBX system has slowly been increasing because system designers have become more cognizant of product migration strategy and its effect on market positioning and sales. Another reason for increased system life is that an increasing number of recent system performance enhancements and upgrades had minimal effect on the core processing and switching system design, because they were focused on peripheral server applications. The concept of upgrading an older PBX system to the current platform instead of the earlier system forklift approach makes possible a cost effective and operationally efficient migration from a circuit switched design platform to a converged circuit/packet switched system.

Upgrading a circuit switched PBX system to a converged IP-PBX system may be as simple as adding a few new port interface cards that provide ToIP gateway and gatekeeper functions for IP peripherals (stations, trunk). A gateway used for ToIP applications is defined as a device that provides a translation, or conversion, between IP and TDM/PCM signaling protocol and communications signals. There must be a physical and logical interface between circuit and packet switched communications networks. A gatekeeper performs or facilitates several basic call control functions within an IP communications network: peripheral equipment registration with the network; address translation of LAN aliases (i.e., telephone directory numbers into IP addresses); and bandwidth management of LAN/WAN network resources. The gatekeeper function in a pure IP communications design is similar to the call control processor in a traditional PBX system. Additional interface cards may be required for support of remote cabinets and port carriers when using the LAN/WAN to transport intercabinet signaling for call control and voice communications traffic. In some cases there may be a requirement for a call processing and/or system memory upgrade. It is most likely that a generic software release upgrade would be required unless a very recent software release is already installed.

A sizable percentage of the current installed base of circuit switched PBX systems can be upgraded to a converged IP-PBX system platform with the hardware/software additions just described. It is estimated that more than 65 percent of the current installed PBX base can be upgraded to a converged IP-PBX system without a major system overhaul. As the oldest installed PBXs are replaced or upgraded, the percentage of upgradeable systems will continue to increase. More than two-thirds of currently installed circuit switched PBXs can be upgraded in place to a converged IP- PBX system platform while protecting up to 90 percent of a customer’s original hardware/software investment. Examples of circuit switched PBXs installed during the past decade that are easily upgraded to a converged system include Avaya Definity ProLogix and ECS models, Nortel Networks Meridian models (Option 11C/51C/61C/81C), Siemens Hicom 300 models, and NEC NEAX 1000/2000/2400 models. These systems alone represent almost two-thirds of the North American installed PBX system base.

Critical Reliability

Traditional circuit switched PBX systems are known for their high reliability standards. The frequently quoted 99.999 percent system reliability benchmark is not a marketing gimmick but the reality. Five “9s” does not apply to every system PBX system component, such as a port circuit card, but to overall system availability. Individual port circuit cards or telephone instruments occasionally may fail, and software glitches may cause a feature failure or call disconnect, but total system failure is a rarity in the world of telephony. The reason for high system reliability, as a result of very low PBX system component failure rates, commonly expressed as Mean Time Between Failures (MTBF) or Mean Time Between Outages (MTBO), is that many system operations are supported by redundant hardware and/or software elements and great care in the electronic design and manufacture of hardware components. During the past decade, most PBX customers have installed and operated their communications systems without ever experiencing a catastrophic failure. Traditional circuit switched PBX technology has reached the bottom plateau of the failure rate curve. In case of failure, redundant system elements, such as main processor boards, system memory storage, switch network and transmission paths, and power supplies, are usually duplicated in a hot standby mode for intermediate and large PBX system models from many, but not all, system suppliers. For example, the Siemens HiPath 4000 and NEC NEAX 2400 IPX systems offer optional duplication of the listed critical system elements.

Although a converged IP-PBX is designed and equipped with several new hardware components and its software generic program includes new features and functions, the system, for the most part, is based on tried and true technology. The most important architecture element of any PBX system design is its common control complex, whether it is based on a proprietary cabinet carrier equipped with several printed circuit board modules or a third-party processing server. All PBX functions begin and end under the control and supervision of the common control complex. Traditional circuit switched PBXs and the upgraded converged IP-PBX version are based on the same common control complex, with perhaps a few modifications, such as an upgraded processor board. The hardware and software components and the core internal diagnostics, maintenance, and management functions remain basically unchanged when the system is upgraded to support ToIP capabilities and applications. The catastrophic failure rate should remain at (or be very close to) the expected 99.999 percent level. Unless an expensive fault tolerant server is used in the client/server IP-PBX system design or a dedicated back-up server is available, the common control reliability level will be less than that offered by a converged IP-PBX system. It should be noted that no client/server IP-PBX system currently uses a fault tolerant server, and very few are currently available with a backup server option.

The reliability of the PBX center stage switch complex is also a very important system factor for minimizing occurrences of catastrophic failure and supporting communications connections. In a converged IP-PBX, the center stage switch function is necessary for all calls among circuit switched peripherals and calls between circuit switched and packet switched peripherals. A client/server IP-PBX design makes use of LAN/WAN switches and routers for all call connections, even calls originating or terminating at non-IP ports. Although some converged IP-PBXs are based on a redundant internal switch network design with numerous duplicated hardware elements, a redundant LAN/WAN design requires multiple switches and routers at the Layer 2 and Layer 3 network levels for redundant connections and transmission paths for calls. More equipment is needed, more communications links must be supported, and more overhead costs are incurred. A configuration with a sizable number of non-IP peripherals in the IP-PBX configuration favors a design with traditional circuit switching capabilities in addition to ToIP capabilities. Except in a few isolated situations, there are very few intermediate/large customer installations that have mandatory requirements for 100 percent IP station users. Until the percentage of IP desktops outnumbers traditional analog and digital desktops, the converged IP-PBX system solution may be the preferable solution for customers with ToIP requirements.

Private Network Compatibility

There has been significant growth in the number of PBX private networks during the past 20 years. Private networks initially were limited to Fortune 500–type customers who had sufficient traffic volume to justify expensive private line facilities. The boom in private networks can be traced to the introduction of virtual private networking (VPN) services in the 1980s, such as the AT&T’s Software-Defined Network (SDN), and the continuing decline in private line lease rates that coincided with the increased availability of wideband and broadband digital carrier facilities. Many present-day private networks are based on a mix of private lines and virtual network facilities and provide a high degree of feature-transparent operation across PBX system locations.

Intelligent feature transparent networking requires a common PBX system platform for optimal transparency of feature/function operation. The evolving Qsig.931 standard for interoperability between dissimilar PBX systems currently provides a limited level of transparency among most of the leading PBX systems. Although a Qsig-based private network implementation may be adequate for some customers, it is not an acceptable solution for most customers. A multisystem network, including PBXs from a variety of suppliers, does not lend itself to a unified systems management solution. The option to centralize network and systems management functions at one location is not currently available in a mixed system platform network. There are other network issues to consider, such as feature/function and desktop terminal uniformity. Unique features on one system cannot be supported transparently across the network to be enjoyed by all stations users. If station user interfaces and telephone instruments are not standardized across the network, training costs increase and station user productivity is affected when an individual moves between network locations.

Taking into account these private networking issues, a customer wishing to migrate from a circuit switched PBX to an IP-PBX is best served by upgrading the installed system to a converged system platform. The upgraded and converged IP-PBX system will retain existing networking capabilities, and station users will have continued access to their accustomed feature sets. A few converged IP-PBX offerings, such as the Siemens HiPath 3000/4000 families and NEC NEAX 1000/2000/2400 families, provide IP station users the option of simply adding an IP adapter to the installed digital telephone or installing a replacement IP telephone with the same look and feel as the older digital telephone model. Replacing a circuit switched PBX system with a client/server IP-PBX system from another supplier will reduce networking performance and force station users to learn how to use a new telephone to access and implement a different feature set.

Feature Requirements

Each customer has unique feature requirements, although there is a common core of features on most everyone’s shopping list that is available with most every PBX system, regardless of switching technology or architecture design. A survey of the leading circuit switched PBX systems indicates that there are at least 500 software features that support a wide range of customer applications, ranging from basic station user desktop features, such as Call Forward, to advanced contact center ACD features, such as ACD agent skill profiling. Most station users, when surveyed, will come up with a list of fewer than a dozen PBX features that they commonly use in their everyday workplace. This does not mean that PBX systems should have a much smaller set of features because the typical station user uses a small percentage of currently available features.

Different station users use different features, and it is likely that in a large system environment a very high percentage of the available PBX features are used by at least one of the system’s station users or administrators. Unique user populations within the PBX system make use of different features groups, such as attendant features, message center features, or ACD features. There are also many PBX features that station users are not aware of that support high-level system operations that are activated concurrently with many station users operations, such as CDR for off-premises calls, or Automatic Route Selection (ARS) when placing long distance calls.

Most of the currently marketed circuit switched PBX systems have software feature packages based on more than 20 years of additions, upgrades, and enhancements. A converged IP-PBX based on its antecedent circuit switched system platform would share the same highly developed and refined feature package, with no sacrifice in performance potential. Very few client/server IP-PBXs are based on previously available circuit switched PBX software feature packages. Most of the first-generation client/server designs are from system suppliers relatively new to the communications system market, with less than 5 years of software feature development. In addition, a few experienced PBX system manufacturers currently offer client/server IP-PBXs with far fewer features and functions than are available with their traditional circuit switched systems.

An analysis of the currently available client/server IP-PBX systems reveals that there are several functional areas where these new system designs are likely to be feature deficient when compared with circuit switched or converged system designs. Feature/function gaps are most common in attendant position, ACD, and private networking. There is also the occasional missing desktop station user feature that has been a longtime standard offering on circuit switched that customers cannot do without.

It has been the standard practice for customers to always ask for more features and functions in their new communications systems in addition to the features they have in their currently installed PBXs. Upgrading to a converged IP-PBX would satisfy this requirement. Replacing a circuit switched PBX system with a client/server IP-PBX that lacks more than a few traditional features and functions should not be acceptable because a smart customer does not trade a few new ToIP features for longtime available features.

Pricing

Price is a concern for all customers across all market segments. Very few customers have unlimited funds for their next communications system purchase. Among all the customer purchase criteria, pricing is the most prevalent. Every PBX system configuration has its own price point, and few customer configurations are identical. One cannot say that a converged IP-PBX is always priced higher or lower than a client/server IP-PBX because it is configuration dependent. Based on current pricing schedules, however, comparisons between the two IP-PBX design types can be made for specific defined configurations, and there are several pricing model assumptions that are usually valid regardless of system model:

1. An IP telephone is priced higher than a digital telephone with comparable capabilities, such as line appearances, programmable feature buttons, display field, speakerphone option.

2. Analog station (telephones, fax terminals) and PSTN trunk circuit connections are more expensive with a client/server design because gateways are more expensive than the traditional port circuit cards used in converged IP-PBXs.

3. Emergency power costs are greater for a client/server design because there is more distributed hardware equipment, such as telephony call servers, database servers, Ethernet switches, routers, and desktop terminals.

4. The cost to add an incremental IP port to a converged IP-PBX is greater than a client/server design because the converged system requires a port circuit card housed in a port carrier to support the added port.

5. Cabling costs for a green field installation are less for a client/server design than for a converged design.

Adding a few IP ports to a circuit switched PBX upgraded to a converged system will naturally be far more cost effective than replacing the entire system with a client/server design. If a significant number of IP ports are required, however, the cost of a client/server design is likely to be less expensive because the only significant variable cost is the price of a telephone. Converged systems require gateway/gatekeeper function port circuit cards to support IP telephones and/or IP trunk circuit connections for non-IP stations.

Figure 1 and 2 shows the two types of IP-PBX designs at a fixed port capacity. The customer configuration assumes a mix of single-line analog telephones, multiple-line telephones (digital or IP), PSTN local trunk circuits, and private network trunk circuits (PSTN or IP WAN). Design requirements such as redundancy (call processing, memory storage, power, switching) can significantly influence the shape of the two curves, as can advanced application requirements, such as contact centers, but the general trend lines would remain the same.

Figure 1: IP-enabled circuit switched PBX.

Figure 2: TDM/LAN IP-PBX.

Major differences in the design types are best exemplified at the two extremes of the price plots, 0 percent and 100 percent IP ports. At minimal mandatory IP port requirements, a converged system is priced significantly less than a client/server design that is ill-suited to support non-IP ports, despite a lower cost for common control and reuse of LAN switches and IP routers, because IP telephones are more expensive and support of analog devices is very expensive. At maximum IP port requirements, a converged system is priced significantly more than a client/server design because of the requirement for gateway/gatekeeper port circuit cards. As mandatory IP port requirements increase, a client/server design is the favored solution because higher priced IP telephones are offset by reduced common equipment and wiring costs as compared with a converged solution.

A few closing comments regarding IP-PBX system pricing:

1. Client/server designs are priced lower than converged solutions as mandatory IP port requirements increase and/or traditional circuit switched port requirements decrease.

2. Green field environments are optimal for client/server designs because the newly installed LAN/WAN infrastructure can be initially designed and voice-grade QoS, and a single cabling system can be installed for all media communications needs.

3. Upgrading a circuit switched PBX to a converged IP-PBX system is more cost effective than replacement with a client/server system, regardless of IP port requirements, because the common control complex and cabinet equipment is already in place and paid for.