Most enterprises today support at least three separate networks (LAN, WLAN, and voice) to support static and mobile data and voice (Figure 1). Each network was optimally designed to meet different requirements but with the convergence of services the cost and support burden associated with upholding three separate networks are becoming prohibitive. The unification of voice, video, and data service infrastructures for both stationary and mobile devices is inevitable and already termed "quadruple play" by the industry. Specifically the equipment to provide voice services is going to migrate from today's vertically oriented PBXs to IP-based telephony servers supporting call, registration, and enhanced calling services. It is anticipated that core telephony services will integrate and blend with video and text-oriented layered services where network service infrastructure convergence is feasible from an operational and cost perspective. Since voice infrastructure will ride over IP, its quality will depend on QoS-enabled IP core network services for delivery of real-time transport. User and operational advantages are anticipated through a more flexible system based on a PC or server-based model for rapid evolution via voice and data service integration.

The development and integration of rich and integrated applications over a common set of layered services will also enable the unification of electronic mail, voice and text messaging (e.g., IM) over common users' devices and a converged network infrastructure. Nevertheless, matching the scalability, cost, and reliability advantages which the enterprise maintains with its current environment, will be the single biggest challenge in realizing a voice and data convergent communication vision.

Figure 1: Existing separate LAN, Voice, and WLAN
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In order to support voice and video, which are delay sensitive services, data services networks have to address and support basic scheduling capabilities. Since voice is considered by most users and the regulatory domains to be a more critical service than data, securing voice is an important factor. One of the biggest security problems in the enterprise network is the standard "permit all" paradigm of the LAN. While this openness was a catalyst to the growth of computer networks, it also allows devices with security issues to freely connect to the network and potentially compromise other devices. Traditionally LANs have also paid no attention to admission control and cannot separate users with different access rights such as company employees and visitors. As more and more mission-critical services are added to the LAN, steps must be taken to enforce those rights through comprehensive security and QoS mechanisms.