Guidelines for Implementation

The following set of guidelines is useful for the successful implementation and management of in-house LANs that support voice communications:

- Prior to implementing IP-Centrex, the personnel who are responsible for telephony should acquire reasonable knowledge of the technology embodied in the first three layers of the OSI model—namely the physical data link and network layers. This would cover aspects of cabling, Ethernet, and IP as general technologies that are critical to the function of enterprise IP telephony and hence IP-Centrex. This knowledge might be obtained by communicating with other existing IP telephony installations (whether IP-PBX or IP-Centrex) and from vendors' literature.

- Membership in a Centrex users' group is an invaluable way to share information with other analysts and managers, and to provide feedback to suppliers.

- The cabling system is the key to a "clean" network installation. A well-designed, installed, and certified cabling system will form the foundation of an enterprise-grade LAN capable of supporting the demands IP telephony.

- The physical installation of an IP-Centrex service has to be well coordinated with a number of crucial departments, in addition to the users. These include the premises management, information technology/services operations, and senior management. In many situations any installation work (such as the pulling of new cable runs or the placing of phone sets) has to be done outside regular working hours.

- Every detail of an IP-Centrex installation, as part of the overall

- LAN infrastructure, must be fully documented. This documentation starts with the user's name, and continues through the identification of the voice terminal (IP phone or a computer with softphone), the jack identification, and various cross-connect positions to the port on an Ethernet switch. The identity of other users in a calling group, with interdependent call forwarding, must also be recorded to help with fault diagnosis.

- Feature validation and configuration of Ethernet switches and routers on a LAN will be necessary as part of the upgrade to carry voice and video over an IP network. Software and firmware upgrades may be required on such equipment to enable QoS and high-reliability capabilities, along with the planned configuration of these features to provide for end-to-end QoS capabilities. We recommend that some testing be undertaken to ensure that the characteristics of the LAN will support IP telephony under a range of call loads during peak data traffic. This can be done using specialized simulation software and "virtual" call endpoints that simulate call loads on the network while capturing statistical information on the ability of the network to carry the voice traffic. The overall architecture of the network must be in keeping with current design rules that stipulate a hierarchy of connectivity, such as the core, distribution, and edge approach, along with using both layer 2 and layer 3 switching with VLANs. Network reliability is paramount; all financial and technically practical approaches should be considered to ensure high uptime (over 99.9%) of the network infrastructure, including the processes and procedures used for troubleshooting, upgrade, and general maintenance.

- Data-oriented operations personnel have lower expectations of the availability, or uptime, of their network than do telephony support staff. Planned maintenance of networking equipment may include scheduled downtime, which may well be unacceptable to the phone users. There is more likelihood of problems with IP networks than with voice-only service.

- Understand and deal with issues surrounding the powering of IP phone sets, which is a significant factor in the overall reliability of an IP telephony system.

- IP-Centrex service, partly because of the physical separation between control and switching functions, will always involve multiple vendors, with the risk of finger-pointing. For the LAN equipment we are free to pick and choose, if the vendors support industry standards. With telephones, we will probably want to stay with one vendor; otherwise users will encounter a reduced feature set.

- The line of demarcation between carrier and customer must be clearly identified, as the sets and switches on the users' side of the demarcation line will be totally the customer's responsibility.

- There will always be tension between the needs for security and the desire for accessibility and mobility. The security arrangements must be monitored and tested frequently, as they will need updating to meet new threats or to handle increased traffic loads.

- Any organization that has a number of IP-Centrex installations in different locations must have the ability to manage these networks from a central site over a WAN, typically a corporate intranet. For this purpose there should be as much conformity in access technologies, protocols, and bit rate as possible.

- Both end-user and support personnel training are critical components to any voice technology implementation, and they are especially important with IP-Centrex. The ability to provide end users with an interface to the system, allowing them to make changes to their IP telephone, is a powerful feature that could either reduce or increase management overhead, depending on the nature of education provided.

- Finally, a wise project manager knows that an unexpected technicians' strike, or a sudden shortage of a specific type of network interface card, can hold up installation for several weeks without warning. Since so many players are involved in the implementation of IP-Centrex at any site, it is sensible to allow at least one month's leeway for the completion date of a new or significantly enhanced service.