EPABX: To Select, Zero in…

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With many options available in the market to day, choosing the EPABX that meets the organizational requirements is indeed a daunting task. The price of a PBX for small and medium (SME) organizations or an educational institute may go up to Rs 5,000,000 and hence the need to formulate metrics and a process by which offerings from different vendors can be analyzed. 


Types of Systems

The traditional PBX is based on time division multiplexing (TDM) platform, handling calls from either analog or digital phones.

These are provided by vendors like Alcatel, Avaya, Nortel, Ericsson, Siemens, and Tadiron. The IP PBXs, based on packet-switched platform are of the second category, being provided by companies with data communication background such as 3Com, and Cisco, allowing the transport of packetized voice across IP phones, PCs, and PSTN. The traditional PBX manufacturers have also noticed the inroads of Internet into corporate communication and have come with PBXs that are IP-enabled. These, while continuing to support circuit-switched voice calls, also allow integration with the organizational intranet/Internet. Since most of the small and medium-sized organizations still use traditional analog phones, but also have a high-speed intranet/LAN, IP-enabled PBX will provide the necessary flexibility for integrating organizational voice and data networks. 

After narrowing down on one of the above types of PBX systems, the next task most of the organizations face is to select the set that will take care of their future needs too. Here, the telecom manager has to decide which are must-have features and which can be made available as and when there is a demand in the future. Normally the life of a medium scale PBX is up to 10 years. Hence the feature set has to be carefully crafted so that the PBX can provide the needed functionality to meet the organizational requirements within this life period. While it may be economical for SMEs to buy the PBX outright and outsource the maintenance and operation, for large organizations that have mission-critical applications build operate and transfer (BOT) would be a viable option to hedge against technology obsolescence. 


PBX Features

 The basic or must-have features and add-on features will depend on individual organization’s requirements. Obviously, one of the must-have features is the number of analog, digital and trunk extensions that can be supported by the EPABX. Most of the vendors offer modularized ports so that the number of modules can be chosen depending on the current and future requirements of the organization. The average price per port varies between Rs 3,000 and Rs 6,000. The organization should keep in mind the scalability of the PBX over a life period of about 10 years or so before deciding on the product. Most of the EPABX systems are expandable. However, the additional cost per extension over the base/fixed ports should be taken into account while deciding on the port configuration. 

If the different units of the organization are spread out in different campus areas, the EPABX should support a distributed architecture where regional modules support extensions in different geographical areas, coordinated and controlled independently or by a centrally located control unit. The distributed architecture provides redundancy through a survival module, in case there is a failure of any other module or link. It also provides flexibility in billing and call accounting at different locations of the organization. Though most of the EPABX systems provide distributed architecture, the functionality, reliability and call control differ from product to product. 

The Typical Feature Set to Look for

The other important things to consider are reliability and availability. These are provided through features referred to as ‘hot standby’ and ‘hot swappability’. Hot standby means that even in the case of error or failure an alternative resource to resume the service of the failing unit without disrupting an established call or a call in progress is always available. Hot standby can be in terms of processors, line cards, and control units. Associated with hot standby is hot swappability, which keeps the system working normally without the need for powering down, when a failed component such as line card or processor is removed for repair, thus providing maximum uptime. 


It has become almost mandatory for organizations to have voice mail facility. While some vendors provide voice mail support built into the EPABX using additional cards, some offer PC-based voice mail support. While PC-based voice mail systems are scalable easily, the maintainability is better with card-based voice mail systems. Typically, the licensing is based on the number of mail boxes configured. Unified messaging is also being provided by some vendors. 

Different access authorizations can be assigned to each PBX user for each class of service. For example, users can be configured for no-toll access, outward restricted toll access, and unrestricted toll access. PBX systems vary in providing support to classes of service.

While caller line identification (CLI) on digital extensions is common in most of the PBX systems, only a select few offer it on analog extension. Call forwarding, simultaneous ringing, and call back are offered by almost all vendors on extensions, but only in selected products over PSTN/cellular networks. Although most products offer group conferencing, the flexibility offered by the system in terms of maximum number of parties that are supported in each group and dynamic formation of groups vary across products. Some PBX systems support sending either pre-defined or user defined text messages across extensions. With most of the basic telecom operators providing short messaging service (SMS) over even fixed wire-line telephones, PBX support for short messaging may be required. 


The malicious-calls-tracking feature enables screening of unwanted calls and spamming. Screening can be done using a static table of numbers or can be dynamically detected by the malicious-call-tracking software on the PBX. Support for remote maintenance is very much required if the system is purchased using BOT so that the service provider can monitor if there are by problems and take corrective action from outside the campus. 

Most of the products provide an Ethernet interface so that the PBX can be connected to the local area network. Once on the local area network, using protocols like Simple Network Management Protocol (SNMP), the switches can be monitored from the central manager software running on a workstation. Some vendors also offer proprietary administration software that provides multi-site administration, including backup/restore, configuration and reporting. This transforms the PBX into an Internet network element. VoIP goes a step further, providing connectivity between the telephone extensions and the computers installed in the local data network. Using a VoIP gateway, computer users will be able to make calls to PBX phone extensions or to phones on the PSTN. This feature is normally available as an add-on feature and the VoIP cards do the translation between computer calls to voice calls and vice versa. This is an ideal solution for educational institutes where each of the hostel rooms is provided with Internet connectivity. The same wiring infrastructure can be used to provide telephone facility too. 

Computer telephony integration (CTI) provides the integration of voice and data services. Using CTI, telephony is integrated with applications such as customer relationship management (CRM) to provide unified window to users, so that they can perform all their telephony and application-related tasks seamlessly. Interactive voice response system (IVR) is one of the popular CTI applications where a computerized operator provides the front end for navigating various information services of the organization. Another application is ‘universal in-box’ that supports services such as e-mail, voice mail and fax on a single platform. Using text-to-speech and speech recognition technologies, the unified messaging solutions are able to deliver the message on multiple platforms. Through telephony application program interface (TAPI), applications can 

be developed that integrate the voice and data services of an organization. Basic CTI interface is built into most of the products, although specific applications such as IVR or universal in-box are available as add-ons. CTI is extensively used by call centres and business process outsourcing companies. 


A feature that has gained importance recently is mobility, offered through digital enhanced cordless telephony (DECT) technology. DECT, operating in the 1.80—2 GHz frequency spectrum, developed by European Telecommunications Standards Institute (ETSI), provides digital cordless telephony coverage within a geographically limited area. DECT support is available in most of the products as an add-on feature. If the campus covered is large, organizations may go in for DECT support and provide DECT phone to selected employees for access while they are on the move in the campus. 

QSIG is the signaling and control standard for inter-Private Integrated services Network eXchange (PINX). QSIG offers user benefits including vendor independence, guaranteed PBX interoperability, free-form network topology, support for unlimited number of nodes, flexible numbering plan, and flexibility of interconnecting transmission technologies. Supplementary services offered by QSIG include name identification, call intrusion, do not disturb, path replacement, operator services, mobility services, and call completion on no reply. QSIG compliance ensures that heterogeneous PBX systems in the organization can be internetworked seamlessly. 

Though most PBXs offer call charge management, the details and the flexibility of the charge management system is a consideration. Evaluation of charges by extensions, trunks and departments provides a comprehensive accounting mechanism for organization. Some products are even capable of providing e-mail-based billing or

sending the charges in a predefined format through the LAN to the organization’s accounting server for billing and consolidation. 


Apart from the features offered by PBX systems, Telecommunications Engineering Center (TEC) certification and letter of support from original equipment manufacturer are also essential if the organization is doing an outright purchase of the PBX. It is also recommended that the vendor has support facility near the organization’s premise so that the contractual obligation regarding resolution and repair can be honored by the vendor within the time frame. Finally, the organization should depute a team to go and visit the facility of the vendor as well as one of the sites where the PBX system is deployed so that the features and capabilities of the PBX system can be checked and verified. 

Dr V Sridhar, associate professor; Dilip Mohapatra, manager (computer services); and

AK Srivastava, officer in-charge (telephone systems), Indian Institute of Management, Lucknow



With numerous choices available in terms of features, choosing the PBX system that meets the current organizational requirements as well as that can meet the future demands at an optimal price is not easy. Though companies such as Infotech Market Intelligent Services

( provide evaluation of different products you are considering for a fee, doing the evaluation in-house is always preferable. Following are the steps one can adopt in arriving at the final purchase decision:

A methodology to select products based on features: 

Allocate weight (and hence maximum points) for each feature; using a point-based scheme; allocate points for each product you are considering depending on how the feature is implemented in the product. For example, if we allocate five percentage points to the call forwarding feature, and if a product allows call forwarding only to extensions, then it may be allocated 1 percent as compared to a product that gets 5 percent for call forwarding to PSTN and cellular phones apart from the extensions. 

Prescribe a benchmark that has been agreed across the organization, in terms of percentage points for both the must-have and add-on features. Calculate the deviation between the points awarded to each product from the benchmark percentage points and mark them on the graph as shown in the figure given below:

For illustrational purposes, we have positioned four comparable products: A, B, C, and D in the above figure. D exceeds the benchmark specifications in both types of features and hence is clearly the best product. C is in the positive quadrant and hence is definitely suitable but in certain features it may not be as good as D. Both A and B lie in negative quadrants; the former short on must-have features and the later on add-on features. However, if the deviations are not major (such as simultaneous ringing is supported only on extensions and not on

PSTN/cellular phones), then they could be considered for financial analysis. The circle around the origin gives the acceptable tolerance level of deviations from the benchmark specifications. Any product falling outside the circle in the negative quadrants can be rejected. 

This methodology provides an objective assessment of the technical merits of a PBX system based on the combination of features and organizational requirements.

  • After allocating the points based on technical merit, these points can be taken forward to the financial evaluation stage and given appropriate

    weightage. The reason for carrying out this exercise is that if a product offers add-on features at relatively marginal prices, then it should be selected since it will provide flexibility to meet the future organizational requirements. This process will ensure coverage of the cost of technology obsolescence. 

  • For outright purchase, take into account the annual maintenance charges over the considered lifetime for cost calculations. Also add the cost of operators provided by the vendor who apart from handling calls also take care of day-to-day operational problems. 

  • Do not buy features or applications that you don’t need. For example, mobility support, which is often available as an add-on feature is not needed if the customer premise is not geographically large and dispersed. However, do not just buy the basic module that blocks any future plans.

  • Ensure interoperability so that the system can inter-work in a heterogeneous environment.

  • After the product is bought, invest in training your telecom department professionals so that they can take care of the maintenance of the PBX system without much of vendor support.