PBX Sizing and Growth

When planning the purchase of a PBX, growth capability is a major consideration. Although they may be modular in design, in terms of telephones and outside lines that can be connected to the system, PBXs have a maximum capacity. In most systems, one port represents the ability to connect one telephone or one outside line. A 400 port system can accommodate a total combination of 400 outside lines and telephones.

There are no precise ratios in terms of how many outside lines are required for the number of telephones. A conservative ratio would be 25 outside lines (for incoming and outgoing calls) for every 100 telephones. If there are not a lot of calls, 10 lines may be sufficient. If it's very busy, more than 25 may be needed.

There are statistical tables and software programs available to enable you to judge the total number of outside lines needed. Using these statistics to determine the number of outside lines required is called traffic engineering. In order for this to make sense, you need to know how many calls of what duration will be handled during the busiest hour of the day. Most people do not have this information, and therefore use judgment combined with trial and error in estimating the number of outside lines needed.

In the world of telephone traffic engineering you may hear the term CCS which stands for 100 call seconds (C being the Roman numeral for 100) or, more simply put, 100 seconds worth of telephone calls. 36 CCS or 3600 call seconds are equal to one hour's worth of calls known as an Erlang. The statistical tables or software programs express call volume in this manner to determine the number of outside lines needed to handle this volume of calling. Something called grade of service is expressed in terms such as P.01 meaning that, statistically speaking, one percent of all calls will be blocked.

Another consideration in planning for the system size is that Voice Mail, paging systems and other peripheral systems also take up ports in the PBX.

Additional Considerations On PBX Sizing

Each telephone system from each different manufacturer has maximum capacities for both the number of outside lines and desktop telephones it can support. This is determined by the particular design of he manufacturer and has to do with economics as well as technology. Smaller capacity systems with fewer capabilities are sold at lower price points. As an organization grows, they may reach the point where their current system is "maxed out" and needs replacement, enabling the supplier to sell them a new system. The more basic design of these systems also enables them to be sold at a lower cost. In general, the larger systems (over 100 telephones) may be more flexible in terms of expansion, but even so, the cost of expansion can be significant and may involve the change out of both software and circuit boards. If you are considering a system from a particular manufacturer, looking at their entire product line can provide you with insight into their strategy for providing systems to organizations of varying sizes. A few of the larger manufacturers (such as Avaya, formerly Lucent, formerly AT&T and NorTel, formerly called Northern Telecom) provide systems for 5 telephones up to systems with 10,000 telephones or more. While the smaller systems are overall less profitable, there has been a need for the big companies to compete with the manufacturers of smaller systems to keep their customer base intact.

Most very large organizations have small locations as well, so for a manufacturer to provide complete coverage, it must offer the smaller systems.

Many other manufacturers target a more limited range. There are many more manufacturers of smaller telephone systems (either PBXs or more basic systems sometimes known as "Key Systems") than of large systems. Only 4-5 companies go up to the 10,000+ telephone sizes.

Wireless Networks - Market Growth

In 2001, approximately 1 in 8 people in the world were using mobile telephones. The growth of some vertical wireless data markets is over 80% per year.

Mobile Telephone Service
By 2001, there were 781 million mobile telephone subscribers in the world. Figure 1 shows the recent trend in subscribership to mobile telephone services. Some of the key drivers for continual growth include lower monthly cost of service and pre-paid wireless services. Pre-paid wireless service allows customers with bad or damaged credit to forego the normal credit check required with wireless service and pay for their service before they use it. Many of the new wireless subscribers have credit challenges.


Figure 1: Mobile Telephone Wireless Growth.
Source: GSM MOU

Data Networks
With the demand for high data rate communications solutions, paralleling interest in the Internet, (fueled by easy-to-use application software, its wide array of text, graphics, video and audio content), wireless data market growth has increased substantially. The availability of Internet services over wireless radio channels will be a critical factor in determining overall market growth.

To date, most wireless data applications are non-human in nature. These include applications such as monitoring wireless parking meters, vending machines, and environmental concerns among others. Human access includes the ability to access data available on the Internet, private intranets, new services, and e-mail. The Internet, for example, is being used by businesses for building interactive branding via communication with customers, advertising products and services, publishing product specifications; and acting as a source for point-of-sale applications.

Market growth for wide area wireless data communications services is in the early stages, primarily because wireless data is not yet capable of providing high data transfer rates at a cost comparable to fiber optic cable or wired connectivity. However, the overall market growth of the wireless data market is up. In 1997, there was over 21% growth for circuit switched data (primarily cellular data) and over 89% growth for packet data (ARDIS, RAM, CDPD, and Ricochet).

Market Growth

The market for IXC communications is becoming more competitive through the introduction of more efficient technologies and lower barriers to entry for new carriers. Although the total usage of IXC communication is increasing, the average revenue pre minute is decreasing. As a result, the total industry revenue for the IXC market is decreasing.

Figure 1 shows the growth in number of inter-exchange carriers in the United States. This diagram shows that the deregulation of the telecommunications industry and advances in cost effective technology have increased the number of interexchange carriers from less than 80 in 1993 to more than 200 in 2000.


Figure 1: Number of IXC Carriers in the United States.

Figure 2 shows the decline in IXC revenue in the United States starting in 2000. This diagram shows that total IXC revenues in the United States increased over 6% per year from 1985 through 1995. Since 1996, revenue of the IXC market has been decreasing and total revenues for 2000 was only $108 billion, less than revenue in 1999. This decrease in revenue has occurred despite a sharp increase in the amount of IXC network usage from 1996 through 2000.


Figure 2: United States Inter-Exchange Market Growth

Market Growth : Private Branch Exchange Market

Market Growth
The market for key systems has primarily been replaced by PBX systems and the market for PBX systems is decreasing as they are being replaced by computer telephony systems.

Private Branch Exchange Market
The PBX market has been experiencing a decrease in annual sales since the mid 1990s. In 2000, sales of PBX systems declined by 10%. With computer telephony becoming a cost-effective solution for most companies, traditional PBX systems are slowly being phased out. However, there continues to be a growing market for small PBX that are used in small office/home office (SOHO).

Figure 1 shows the trend that has sent PBX manufacturers scurrying to shore up other technological areas. Emphasis has been recently shifted to networks and distributed intelligence via those networks. PBX’s have not become the networking “mother ship” predicted in the 1980’s and early 90’s. The Internet, VPN’s, and ATM functionality are replacing larger PBX systems.


Figure 1: PBX Market Growth

Computer Telephony Market
The computer telephony market is the key growth area in the private networking industry. In the year 2000, 17% of all U.S. businesses with existing PBX systems began a transition to computer telephony systems.

By 2005, CTI systems are expected to penetrate into 80% of all United States businesses. Computer telephony systems are becoming popular because CTI systems only cost $300-$500 per seat compared to PBX systems that cost $800 or more per seat.

Sales of computer telephony equipment in 2000 was $138 million dollars, up from less than $10 million in 1998. CTI equipment sales are expected to exceed to $3.2 billion dollars by 2005. Figure 2 shows a growth of CTI market worldwide.


Figure 2: Computer Telephony Market Growth

Telecom : Market Growth

Market Growth
By 2001, there were just over one billion telephone lines in the world and the growth for new telephone lines is over 7% per year. The market for public telephone networks is changing from delivery of voice service to data services. In 2000, approximately 97% of all residences in the United States had telephone service. Telephone voice traffic (measured in minutes) has been growing at a rate of nearly 8% per year.

Voice Service
Voice service (telephone line) is any service or feature accessible through the LEC/CLEC or IXC that can be accessed via a standard analog or digital telephone. The key reasons for growth in the number of telephone lines include dial-up Internet access, fax telephone lines, and mobile telecommunications. Figure 1 shows the growth of new telephone lines worldwide. This chart shows that telephone service subscribers continues to grow over 7% each year. Growth had been fairly level at about 50 million additional telephone lines per year. However, during 1999 more than 100 million new telephone lines were added. The recent surge in the number of telephone lines can be explained by the fact that more areas of the world are adding infrastructure to support new technologies that use telephone lines.


Figure 1: Worldwide Telephone Market Growth

Data Transfer
Data transfer is the act of moving data through a network from one data source to another. Generally theses sources are computers and they interface with the network via modems or channel service units (CSU’s). Data transfers can occur over a dial voice grade connection or via a dedicated line.

In 2001, the number of customers that use the Internet was increasing at a rate of nearly 40% a year while data traffic on the Internet (amount of data per user) is expanding at a rate of nearly 100% per year. The amount of data that was transferred over the Internet in the United States in 2000 averaged 27,500 terabytes (1,000 billion bytes) per month. The data transmission on private networks grew 500% between 1997 and 2000 with an average of 3,000 terabytes per month transferred in the United States. Figure 2 shows the data transmission growth within the public telephone networks.


Figure 2: Data Transmission Growth.