The Case for the Client/Server IP-PBX

A client/server IP-PBX is likely to be the standard design platform of the future for enterprise communications systems. Although there are several drawbacks to current client/server IP-PBXs, there may be several benefits to customers who select it as their enterprise communications solution. Recalling the pricing discussion in the preceding paragraphs, the upfront capital investment for a client/server design is favorable for customer solutions with the following characteristics:

• Green field location

• Large percentage of IP peripherals, such as telephone instruments

• Remote location requirements with small port capacities

• Small port capacity requirements with PBX performance requirements

Green field locations without existing PBX equipment and with the newest generation of LAN switches and IP routers that can be programmed to support voice-grade QoS levels are best suited to cost effectively support a client/server design. A client/server design that supports a significant number of IP stations and minimal analog communications equipment will be more optimally priced, and support of remote IP stations likely will be less expensive than circuit switched alternatives. Customers with KTS/Hybrid port capacity requirements, but who require the performance capabilities of a larger, more complex PBX system, are likely to discover that the price of a client/server design is a more attractive alternative to a full-featured circuit switched or converged system solution.

The most common reasons given by system suppliers to promote the performance value of a client/server IP-PBX are:

1. Using a converged network for a variety of communications media: voice, data, video, text, graphics

2. Universality of IP transport

Figure 1: Basic client/server IP/PBX design.

1. Lowered communications bandwidth requirements and more efficient use of existing bandwidth

2. Simplified centralized management and administration

3. Rapid deployment of new technology and applications

4. Fully distributed network design

5. Scalability

Converged Network

The concept of the integrated voice/data PBX system in the early 1980s was driven by the increasing amount of data traffic generated by geographically dispersed desktop CRT terminals linked to a centralized host processing system. It was thought that the circuit switched telephony network could be used to carry voice and data enterprise communications traffic. The advent of Ethernet LAN hubs and switches in the mid-1980s effectively ended the dream of the PBX system as an all-media office systems controller. Today the pendulum has swung the other way; packet switched LANs carry telephone-generated voice communications in addition to PC client data traffic. To data communications network designers and managers, the telephone is viewed as just another client, and voice features and functions are just other applications supported by a LAN-based server. If a customer is seriously thinking about migrating to an IP-PBX system, then a client/server design using the existing LAN/WAN infrastructure is the optimal solution. As LAN bandwidth capacity continues to increase, more video communications traffic will be carried between desktops with decreasing dependence on larger, more expensive, room-based videoconferencing systems.

Figure 2: IP-PBX pricing: converged versus client/server.

Universality of IP Transport

Ten years ago the Internet was used almost exclusively by government and higher education institutions. Today the Internet is everywhere, and IP control and transmission signaling have become the standard for data communications networks. There is universal access to LANs and WANS in all medium and large enterprises across all industry sectors. The client/server enterprise data communications network design has replaced the host mainframe design that was dominant in the 1970s and most of the 1980s, and IP networking has replaced IBM’s Systems Network Architecture (SNA) as the standard. If a customer is looking at an IP-PBX system solution, the current data networking infrastructure is favorable to a client/server design.

Network Bandwidth

Using the same communications network for voice and data traffic reduces overall bandwidth requirements because the two traffic streams can be interleaved and QoS levels can be engineered and programmed to satisfy real-time voice communications requirements. There will be cost savings and increased network efficiency due to economies of scale as a customer migrates an increasing percentage of traditional circuit switched PBX traffic to the packet switched LAN/WAN. The major bandwidth cost savings and optimization will be attributed to off-prem- ises communications because circuit switched PSTN trunk carrier facility requirements can be reduced.

Simplified Centralized Management and Administration

A single communications management system is less costly to operate and more easily administered than separate systems for voice and data communications. The primary elements of an IP-PBX client/server design—desktop IP telephones and telephony call server(s)—are indistinguishable to a data network management system when compared to with PC clients and a data processing server or database manager. All voice system moves, adds, and changes are performed from the data network management workstation, as are maintenance and service operations.

Rapid Deployment of New Technology and Applications

A client/server design lends itself more to rapid deployment of new technology and applications because there are fewer hardware elements in the system architecture than in a converged IP-PBX that retains the traditional proprietary common equipment components of a circuit switched PBX. It is far easier to implement a technology upgrade for a client/server IP-PBX because there are fewer if any, proprietary switching network elements, and new advanced applications can be implemented through a software upgrade or an optional applications server. Client/server designs based on third-party servers are easily upgraded and enhanced by replacing the existing server with a newer, more powerful server. Migration between client/server IP-PBX generations will be smoother and less disruptive than between converged system generations that are based on more proprietary and costly common equipment hardware.

Fully Distributed Network Design

A client/server IP-PBX is by definition a distributed network design. A single telephony call server can support premises and off-premises IP stations. Premises stations can be distributed in a single building or across a campus. Multiple server designs can be programmed to support redundant emergency call processing in case of individual server failure. The servers can be colocated or distributed for disaster recovery situations. Customers have multiple layers of LAN/WAN switching and routing that preclude single points of failure.

Scalability

A client/server design has the potential to be highly scalable because IP telephones are easily added to the system without the need for specialized port interface circuit cards, and port capacity can be expanded through the addition of another server. Converged IP-PBXs require port interface cards, if only for control signaling, and, except for the rare system model based on a distributed processing design, there are call processing and port capacity limitations when using a single common control complex. The switching and transport limits of a client/server design are virtually boundless because a customer can continually install switches and routers to the LAN/WAN infrastructure to support increased traffic or more stringent QoS levels.

There are many customers for whom a converged or client/server IP-PBX system design will satisfy financial, feature performance, and applications requirements. Many enterprise communications system customers may also decide that their circuit switched PBX system will continue to be a satisfactory solution for current and near-term needs. A customer may not be ready to immediately replace his legacy PBX system with an IP-PBX system, but should seriously consider testing ToIP technology very soon.