Concerns with IP-Centrex

Concerns with IP-Centrex
We must be aware of the potential issues associated with IP-Centrex, which may not be present with legacy Centrex services. As outlined, a number of requirements must be fulfilled for a successful implementation of IP-Centrex. These major issues are summarized as follows.

Operational Costs
The single most significant issue surrounding the use of Centrex services, legacy or IP-based, is the recurring operational cost. This is the monthly charge made by the provider for supplying IP-Centrex services and related applications.

In financial evaluations, this cost is most often compared to the sum of capital and operational costs of an in-house telephony system over a specified period of time.

Stability
PBX and CO switching technologies have been developed over a number of decades. Thousands of person-years have been invested in software and hardware engineering to create an exceptionally reliable and ubiquitous service. Enterprise-scale IP telephony technology is relatively new and has not achieved the installed base and extensive long-term field-testing of existing circuit-switched technologies. A risk associated with IP Centrex services is that they are based on emerging technologies with complex software. Providers will have to be extra vigilant to ensure the reliability of IP-Centrex infrastructure components.

Security
The Internet revolution has seen a new breed of individuals evolve: hackers. While the compromising of traditional telephony services (long distance and DISA) has long since been exercised by inventive and unlawful individuals, the advent of IP telephony opens up an entirely new twist to this old story. It is foreseeable that hackers, who currently practice their trade on both the Internet and corporate data networks, will now have much more access to, and control of, telephony services. This could evolve into a serious issue; most IP telephony systems are based on widely used operating systems and protocols, which are well-known to the hacker community. A considerable number of techniques currently exist to attack or use the resources of existing data network-based services, the realm of which telephony has now entered. A hacker at a distant location could, given the appropriate access and knowledge, attack, control, or cripple elements of IP-Centrex.

Whether IP-Centrex or private IP telephony is used by an organization, security of the internal network must be given increasing priority, in order to guard against service disruptions and the loss or compromise of corporate and personal assets and privacy.

Network Considerations
Since IP telephony, and hence IP-Centrex, are required to run over the LAN of a customer's organization, that network must have the inherent capability of carrying such traffic. Latency, jitter, and bandwidth characteristics of the LAN must be within tolerable limits for packet voice traffic. These parameters, otherwise known as quality of service (QoS), are created and sustained by both the architecture of the network and the capability and configuration of the electronic equipment (switches and routers) used to build the LAN on which packet voice traffic will flow.

A number of other network considerations must be made when deploying IP telephony technology, such as dynamic host configuration protocol (DHCP), a network service that provides each IP phone with a unique IP address at startup. This could be supported by the provider, but because of the potential in-house requirements of directory integration and other needs, may have to be supported in-house.

A consequence of convergence is that the failure of part or all of an organization's LAN also means the failure of telephony services. While users of traditional voice networks have enjoyed exceptional reliability, this has not been the case historically with LAN infrastructures and for PC users. Therefore, appropriate amounts of redundancy must be built into the LAN infrastructure to provide for high availability (upward of 99.9%). This is usually accomplished through numerous hardware and software techniques, including redundant power supplies, duplicated backbone links, and routing redundancy. Organizations should plan to invest around 15% over the base capital cost of implementing a LAN to increase its reliability.

911 Requirements
The service provider will have to create the capability of connecting 911 services into the IP-Centrex environment. Basic 911 requirements dictate that a caller must be routed to a public safety answering point (PSAP), with information on the caller location provided by ANI and other database information. This can usually be accomplished with IP-Centrex. Enhanced 911 has the extended requirement of being able to locate a caller to within a particular area of a building or campus, or within a limited number of logically grouped telephones. Enhanced 9 1 1 therefore requires substantially more intelligence from the telephony and LAN infrastructure. Such capabilities can be accomplished by having intelligence built into the LAN, whereby an IP phone set and the particular port on an active LAN switch can be queried by management software, which in turn provides a database search for a location of that phone set. This information will have to be passed to the provider and ultimately (and in a timely manner) to the PSAP.

Due to the geographic independence of IP telephony, both IP-Centrex providers and in-house IP telephony systems must provide for appropriate routing of 911 calls to the local PSAP, as opposed to traversing an internal LAN / WAN and connecting to the PSTN at some unrelated location.

Phone Power
Like residential telephones, most traditional Centrex sets are powered from the CO. With IP Centrex however, multiple phone sets (connected to an in-building LAN) cannot derive power from the CO and must be locally powered. This local power is derived in one of two ways: a phone-based power adapter or in-line power. In either case, the power located in the building is used, which may be subject to a number of anomalies and often has no backup (UPS or emergency power). CO power however is quite reliable because it is typically supported by both battery and a diesel generator for longer outages.

A phone-based power adapter is a small ac/dc power transformer cube connected to a standard ac power outlet near the IP telephone; it provides the necessary power to the set.

In-line power is delivered on the same cable as signaling. Power is "injected" onto the cable either from a special patch panel or by the network Ethernet switch itself (on a per-port basis). In-line power can also be used to power wireless LAN access points, which would be in support of wireless in-building IP-Centrex.

Broadband Connectivity and Call Processing
Reliance on a single broadband connection from the CO for telephony services creates a potential single point of failure. While this is also true of legacy Centrex services and their multipair copper cables from the CO, IP-Centrex can be additionally protected if the telco provides some element of redundant IP call-processing equipment at the customer location. This could provide very basic call capability until normal services are restored. In addition, redundant broadband connectivity should be established, at an additional cost, ideally through a physically separate connection with another carrier. Such a connection could also be created using a lower-performance (and hence, lower-cost) link until the main link is restored.

Messaging and Directory Integration
It is anticipated that the use of an internal IP-PBX will allow an organization to configure unified messaging and directory services in a more controlled and secure manner than with the use of an IP-Centrex service, which might require significantly more involvement between the customer's and the service provider's management. Since internal e-mail systems and network-based directories are cornerstones of data networking, telephony integration to these elements in larger organizations will be vitally important.