Centrex is a set of specialized business solutions (primarily, but not exclusively, for voice service) where the equipment providing the call control and service logic functions is owned and operated by the service provider and hence is located on the service provider's premises. Since Centrex frees the customer from the costs and responsibilities of major equipment ownership, Centrex can be thought of as an outsourcing solution.
Call control and service logic refer collectively to the functions needed to process a telephone call and offer telephone features. The following are examples of call control and service logic functions:
- recognizing that a party has gone off hook and that dial tone should be provided
- interpreting the dialed digits to determine where the call is to terminated
- determining whether the called party is available, busy, or has call forwarding, and then applying the appropriate treatment (e.g., ringing the phone, applying busy signal, applying a call waiting tone, delivering the call to voicemail, or forwarding the call to another party)
- recognizing when the called party answers the phone and when either party subsequently hangs up, and recording the appropriate information for billing
In traditional Centrex service (i.e., analog Centrex and ISDN Centrex), call control and service logic reside in a Class 5 switch located in the Central Office. The Class 5 switch is also responsibility for transporting and switching the electrical signals that carry the callers' speech or other information (e.g., faxes). Traditional Centrex service has a number of benefits that are discussed elsewhere on this site.
Packet + Centrex = IP Centrex
In IP telephony, voice conversations can be digitized and packetized for transmission across the network. IP Centrex refers to a number of IP telephony solutions where Centrex service is offered to a customer who transmits its voice calls to the network as packetized streams across a broadband access facility. IP Centrex builds on the traditional benefits of Centrex by combining them with the benefits of IP telephony. One of these IP telephony benefits is increased utilization of access capacity. In IP Centrex, a single broadband access facility is used to carry the packetized voice streams for many simultaneous calls. When calls are not active, more bandwidth is available for high speed data sessions over the LAN, like Internet access. This is a much more efficient use of capacity than traditional Centrex. In analog Centrex, one pair of copper wires is need to serve each analog telephone station, regardless of whether the phone has an active call; one the phone is not engaged in a call, the bandwidth capacity of those wires is unused. An ISDN BRI can support two simultaneous calls (i.e., 128 kbps), but similar to analog lines, an idle BRI's bandwidth capacity cannot be used to increase the corporate LAN's interconnection speed.
See the network architecture page for more details on how IP Centrex works.
Network ArchitecturesIP Centrex solutions are being developed on a number of platforms, including Class 5 switches and softswitches.
Class 5 Switch Architecture
In this platform, existing Class 5 switches (without any special upgrades!) support IP Centrex service in addition to traditional Plain Old Telephone Service (POTS) and ISDN lines. This is accomplished through the introduction of a new network element--the Network Gateway--and a new type of CPE--the Customer Gateway. (As an alternative to using a Customer Gateway, a customer may use new IP Phones, which are described on the IP Centrex CPE page of this site.) The Network Gateway and Customer Gateway signal each other over a packet network using an IP telephony protocol, such as H.323 or SIP. They also each support traditional interfaces to communicate with existing equipment. The Network Gateway connects to the switch as if it were a digital loop carrier system. (Digital loop carriers use protocols like GR-303 to deliver POTS and ISDN signaling information to switches for longer-than-average loops.) The Network Gateway translates any signaling information it receives from the Customer Gateway into a protocol that the switch understands; it also depacketizes the voice stream for delivery to the switch. Similarly, it translates signaling messages from the switch into the IP telephony protocol and packetizes the voice stream for transmission to the Customer Gateway. The Customer Gateway performs comparable functions for the standard telephone sets that it supports. As a result, the Network Gateway, Customer Gateway, and packet network connecting them appear to the Class 5 switch as an ordinary digital loop carrier (DLC) system, and the telephone sets connected to the Customer Gateway appear to the switch as ordinary phone lines. Because the IP Centrex solution is treated as a DLC system by the Class 5 switch, the switch is able to deliver the same features to IP Centrex users that it delivers to analog and ISDN Centrex users. Consequently, an extensive set of features is immediately available to IP Centrex users without needing to upgrade the Class 5 switch.
In a different approach to IP Centrex, the Class 5 switch is replaced by a softswitch. A softswitch is a telephony application running on an industrial grade server in the network. Like the Class 5 switch, the softswitch provides call control and service logic. Unlike the Class 5 switch, the softswitch is not involved in transport or switching of the packetized voice stream. The softswitch and the IP Centrex CPE (Customer Gateways and IP Phones) signal one another over a packet network using an IP telephony protocol, such as H.323 or SIP. After it receives call setup information, the softswitch determines where the called party resides. If the called party is a member of the Centrex group, then the softswitch instructs the originating Customer Gateway (or IP Phone) and terminating Customer Gateway (or IP Phone) to route the packetized voice streams directly to one another; consequently the voice stream never leaves the LAN/WAN. If the called party is served by the Public Switched Telephony Network, then the softswitch instructs the originating Customer Gateway (or IP Phone) to route the packetized voice stream to a trunk gateway. The trunk gateway has traditional interoffice facilities to Class 4 or Class 5 switches in the PSTN. The trunk gateway packetizes/depacketizes the voice stream so that it can be transmitted over these circuit-switched facilities. The trunk gateway works in conjunction with a signaling gateway. The signaling gateway is used to exchange SS7 messages with the PSTN. Both the trunk and signaling gateways receive their instructions from the softswitch.
Softswitches have only recently become available, and though feature development is proceeding rapidly, today's softswitches do not yet support a rich set of features. Consequently, the trials currently being planned are largely aimed at user's with more modest feature requirements.
The softswitch architecture for IP Centrex is illustrated the network diagram below. The diagram also explains the function of each component.
IP Centrex CPECustomer Gateways, Terminal Adapters, and Integrated Access Devices (IADs)
IP Phones and LAN Phones
Softphones and Firmphones
Ethernet Switches for LAN
Customer Gateways, Terminal Adapters, and Integrated Access Devices (IADs)
A Customer Gateway allows existing analog and/or ISDN station equipment to be used on IP Centrex lines. The Customer Gateway has an Ethernet interface for connecting to the LAN. It also provides jacks to connect analog devices (telephones, fax machines) and/or ISDN telephone sets. On behalf of the analog devices it serves, the customer gateway performs voice digitization & packetization and converts analog signaling into IP telephony messages. On behalf of the ISDN telephones it serves, the Customer Gateway performs voice packetization and converts Q.931 messages into IP telephony messages. The customer gateway sends the IP telephony messages across the LAN, over the broadband access facility, and through the managed backbone network to the Network Gateway (for Class 5 switch architectures) or to the Softswitch (for Softswitch architectures.)
A Customer Gateway serves a number of stations and would typically be located in a telephone closet where it connects to the building's telephone wiring. A Terminal Adapter is similar to a Customer Gateway in its function. However, the Terminal Adapter can only support one or several stations and would typically be located near a user's desk. A common use a Terminal Adapter is to allow a conventional fax machine to be part of an IP Centrex group.
The term Integrated Access Device (IAD) is used when a Customer Gateway or Terminal Adapter is combined with an IP Router, Ethernet hub/switch, and broadband service device (e.g., DSL modem, cable modem) into a single piece of CPE.
IP Phones and LAN Phones
The IP Phone (also known as a LAN Phone or Ethernet Phone) combines the Customer Gateway functionality and telephone set functionality into one device. The IP Phone has an Ethernet interface to the LAN. It digitizes and packetizes the user's speech and also generates the appropriate IP Telephony signaling messages. An IP Phone is typically a multi-button device with an LCD screen; it often can support advanced call control capabilities. Some IP Phones contain an integrated passive hub or Ethernet switch. The passive hub allows the Ethernet connection from the user's PC to be plugged into the IP Phone, and the IP Phone is subsequently plugged into the LAN. This passive hub allows the two devices to use the same LAN connection and avoids the need for additional wiring to the desktop for the IP Phone. An integrated Ethernet switch also minimizes the wiring requirements to the desktop but it also can support QoS mechanisms to prevent the PC's data traffic from impairing voice quality during calls.
Softphones and Firmphones
When a PC is equipped with microphones and speakers (or a headset), the PC can be used as a telephone. In this configuration, known as a softphone, the PC is loaded with a software application that performs the functions of an IP Phone. Because the same processors are used to support the softphone application as well as other applications, a call's quality can degrade when the Operating System seizes the PC's resources. This problem is resolved by the firmphone. A firmphone is a softphone where a new hardware card is added to the PC. This card provides dedicated hardware resources for Voice over Packet, so call quality does not degrade when the OS is busy.
Ethernet Switches for LAN
Ethernet LANs for data applications can be built using Ethernet hubs or switches. Depending on a number of factors, including the number of PCs, the number of Centrex stations, the pre-existing data traffic, and the LAN's pre-existing capacity, it may be necessary to upgrade a hub-based LAN to Ethernet switches before adding IP Centrex service. In some instances, it may be desirable to build a separate LAN (or portion of a LAN) just for IP Centrex service; in this approach, it is easier to address reliability and quality of service concerns.
IP Centrex FeaturesWhen offered in a Class 5 switch architecture, IP Centrex provides all the calling features and call control capabilities available today for Analog Centrex and ISDN Centrex services. (It is expected that softswitches will also offer similar features as softswitch products mature.) In addition to this rich set of features, IP Centrex offers other benefits and applications.
Examples of some of the most popular Centrex features are listed below.
ISDN and IP Centrex Features
Account Codes - track and manage telecom expenses.
Anonymous Call Rejection - automatically reject incoming calls from parties who do not deliver their name or telephone number with the call.
Automatic Callback/Ring Again - when encountering a busy signal, a caller can dial an activation code and be automatically called back when the called station becomes idle.
Automatic Line/Direct Connect ("Hotline") - automatically dials a pre-assigned Centrex station's extension number or external telephone number whenever a user goes off-hook or lifts the handset.
Barge In - allows a user to bridge himself or herself on to a existing call (at another Centrex station) to form a three-way conference call. Barge-In is often used in conjunction with Directed Call Pickup.
Call Block - automatically reject incoming calls placed from specific telephone numbers.
Call Forwarding (Busy, Don't Answer, Multiple Simultaneous, Variable, Selective) - automatically routes incoming calls to a given extension to another preselected number under a variety of circumstances. Call Forwarding Busy forwards calls when the called extension is busy. Call Forwarding Don't Answer forwards calls when there is no answer after a specified number of rings. Call Forwarding Multiple Simultaneous indicates the number of forwarded calls (originally dialed to the same Centrex extension) that can occur simultaneously. Call Forwarding Variable allows users to forward all calls to their extensions to another number (that they select). There are various call forwarding options that allow differential call forwarding to be applied depending on whether the caller and/or the forwarded number are members of the Centrex group or external lines. In addition, Selective Call Forwarding allows the user to pre-select which calls will forward to a different telephone number, based on the based on the calling party's telephone number.
Call Hold (Hard Hold) - calls can be put on hold by dialing a feature activation code (phone does not need a Hold button). After a call is put on hold, the user may perform some task related to the call (e.g., look up customer information), originate another call, answer another call by using a Call Pickup feature, answer an incoming call with the Call Waiting feature, or return to a previously held call.
Call Park - allows user to place call on hold, move to a different location, and then resume the call from any other station in the Call Park group.
Call Pickup - The lines (or a portion of the lines) in a Centrex group can be made members of a pickup group. A call ringing on any station in the pickup group can be answered from any other station in the pickup group.
Call Restrictions/Station Restrictions - prevents certain types of calls from being made or received by particular stations. For example, phones in public areas can be blocked from originating calls to external numbers to prevent unauthorized users from incurring toll charges. Phones in certain areas may be blocked from receiving external calls to limit employees abilities to receive personal calls. A wide variety of restrictions is available which can address incoming calls, outgoing calls, toll restrictions, code restrictions, and differential treatment for internal and external calls.
Call Return - allows user to originate a call to the last party or number that called the user, regardless of whether the user answered the original call or knows the caller's identity.
Call Selector - uses a special ringing pattern to alert called user of incoming calls from pre-selected telephone numbers.
Call Transfer - transfers an existing call to another party (inside or outside the Centrex group)
Call Waiting Originating - When a Centrex user (who is assigned the Call Waiting Originating feature) places a call to another Centrex user whose line is engaged, the calling party will hear ringing (instead of a busy signal) and the called party will hear the Call Waiting tone. If the calling user's line has Call Waiting Originating, the called user's line does not need Call Waiting Terminating in order for that user to receive the Call Waiting tone. Upon hearing the Call Waiting tone, the called party can put the current conversation on hold to answer the incoming call.
Call Waiting Terminating - alerts the user to incoming calls when the user's line is engaged on an established call. Upon hearing the Call Waiting tone, the called party can put the current conversation on hold to answer the incoming call. Different Call Waiting tones are available to indicate whether the caller is on an outside line or is part of the Centrex group. Tone Block/Cancel Call Waiting is a related feature that allows a user to disable Call Waiting tones for the duration of call so that they are not interrupted.
Caller ID - allows the user to identify the name and telephone number of a calling party before answering an incoming call. Another version of this feature--Caller ID on Call Waiting--allows for the calling name and number to be delivered when the called party is on another call.
Calling Number Delivery Blocking - prevents a caller's telephone number and/or name from being divulged to the called party (who might otherwise receive that information if they subscribe to Caller ID).
Consultation Hold - calls can be put on hold by depressing the switch-hook or pressing the flash button. After completing a second call, the user is automatically reconnected to the originally held call.
Code Restriction - prevents a user from dialing one or more three-digit codes. Code Restriction can be used to reduce per call charges for certain services or restrict access to long distance carriers (other than the company's pre-selected long distance carrier).
Dial Call Waiting - allows the user to automatically send a Call Waiting tone to another Centrex user when the called party's line is engaged. If the calling user invokes Dial Call Waiting, the called user's line does not need Call Waiting Terminating in order for that user to receive the Call Waiting tone. Upon hearing the Call Waiting tone, the called party can put the current conversation on hold to answer the incoming call. Dial Call Waiting is activated on a per call basis, so the caller can decide to use it only when the call is important enough to interrupt an ongoing conversation.
Directed Call Park - allows user to place call on hold, specify the extension number from which the call will be resume, and subsequently move to that location and resume the call.
Directed Call Pickup - allows a call ringing at a Centrex station to be answered at a different station. At the station where the call is to be answered, the user dials a feature code and extension number of the ringing telephone. If the user does not finish dialing prior to someone else answering the call, then the user hears a busy signal (if the Barge-In feature is not assigned) or is bridged onto to the call to form a three-way conference call (if the Barge-In feature is assigned).
Distinctive Ringing - uses a special ringing pattern to indicate to the called user whether an incoming call is from outside or from within the Centrex group. If the user also has Call Waiting Terminating, then the Call Waiting tones will also be distinctive based on the origin of the call.
Executive Busy Override - allows user to bridge onto a busy line and establish a three-way call. This is similar to Directed Call Pickup with Barge-In, except that Executive Busy Override provides a warning tone prior to bridging the call.
Intercom Dialing - allows user to call Centrex extensions by dialing a standard 4-digit code instead of the entire 7-digit telephone number.
Hunt Groups - allows calls to be redirected to other predetermined lines when the called line is busy. Hunting allows a number of lines to be grouped into a "pool" so that an incoming call is directed to whichever of the lines is available. There are a number of different hunting options which determine how an available line is selected.
Last Number Redial - allows user redial the last number called by dialing an access code or by pressing a single button.
Message Waiting Audible - provides the user with an audible notification--a "stutter" dial tone--when messages have been left in the company's voice mail system. Centrex service provides a Simplified Message Desk Interface (SMDI) interface so that the company's (or a third party's) messaging system can activate stutter dial tone on specific lines (and deactivate it after the messages have been retrieved).
Message Waiting Lamp - provides the user with a visual indication when messages have been left in the company's voice mail system. The indication may be a flashing lamp on a compatible telephone or on an adjacent visual message waiting device.
Music-On-Hold - provides a musical interlude for callers who are waiting on hold.
Repeat Dialing - automatically dials the last telephone number the user called, and, if that number is busy, continues to monitor the busy line and establishes the call when the line becomes idle.
Speed Dialing - allows the user to call frequently called telephone numbers by dialing an abbreviated speed calling code instead of the entire number.
Station Message Detail Recording (SMDR) - allows the corporate telecom manager to receive call detail records on a per-station basis before the monthly telephone bill is even issued. SMDR helps the customer control telephone fraud and abuse, perform accurate cost accounting, and analyze call patterns to identify opportunities for cost reductions.
Three-Way Conferencing - allows user to add a third party to an existing conversation forming a three-way conference call.
Toll Restriction - blocks a station from placing calls to telephone numbers that would incur toll charges.
700/900 Blocking - blocks a station from placing calls to 700 and 900 numbers.
For more information on these features, including examples of how companies are using these features as part of their office operations, consider visiting:
All the capabilities available to Analog Centrex users are also available to ISDN Centrex. In some cases, the same features are available on both platforms. In other cases, ISDN Centrex offers equivalent functionality by using different features. Naturally, ISDN Centrex offers additional features not available on Analog Centrex. Such ISDN features are available to IP Centrex users, and a few high runners are described below.
Multiple Call Appearances - Multiple Call Appearances allow each station to have three or more appearances of the user's primary phone number. Each appearance gives the user the ability to handle one call. Consequently, Multiple Call Appearances allow the user to originate and/or terminate multiple calls simultaneously. Unlike an analog multi-line phone, the station needs only one line (and one phone number) for Multiple Call Appearances. Each call appearance is controlled by a separate button on the telephone set, so it is easy for the user to switch between call appearances. When the user is involved in a call on one call appearance and another call is offered on a different call appearance, the user may use the Caller ID information to decide whether to answer the ringing call appearance or let the call be forwarded to voicemail. To answer the ringing call appearance (or originate a second simultaneous call), the user simple puts the first call appearance on hold. Calls on different appearances can be combined together to form a three-way or six-way conference call.
Shared Call Appearances - Shared Call Appearances allow a station to have one or more call appearances for a different user's telephone numbers. This capability can support a wide variety of call coverage configurations. A group of stations can be set up such that a call to any station can be answered from any other station. A secretary may monitor the lines for a group of executives. Since each executive's phone number has a separate appearance on the secretary's phone, the secretary can answer calls to different executives with the appropriate greeting. Some secretaries may answer calls for an executive on the first ring. Alternatively, the secretary can monitor when the executive's line is busy and answer calls only when the line is in use. It is even possible to first ring the executive's phone (so the executive has the option to answer first) and then ring the shared appearance on the secretary's phone.
Secondary Telephone Numbers - Secondary Telephone Numbers allow one or more additional telephone numbers to be assigned to a station. Each secondary telephone number has one or more call appearances on the station, and, like the primary telephone number, can be accessed from other stations via Shared Call Appearances. Because the Secondary Telephone Number has separate call appearances from the primary telephone number, it is easy for the user to determine which telephone number the caller dialed. This allows the user to have different telephone numbers for various purposes (marketing campaigns, important customers, private numbers) and answer each call with an appropriate greeting.
Customer BenefitsIP Centrex offers a wide range of benefits and advantages to the customer. Some benefits are an inherent part of the Centrex concept, and apply equally to IP Centrex and previous technologies. Other, newer benefits are unique to IP Centrex and are not available on analog or ISDN Centrex lines. The benefits of IP Centrex are divided into the two groups below.
- New Centrex benefits available to only IP Centrex lines
- General Centrex benefits available to all Centrex lines, including IP Centrex
Convergence: IP Centrex allows the customer to combine its existing solutions for data connectivity and telephone service into a consolidated network--both within the enterprise and on the access connection to the network.
Mutlilocation Centrex: Multilocation Centrex is the ability to make two or more locations part of the same Centrex group. With IP Centrex, geographic location is not a factor when defining a Centrex group. Branch offices, telecommuters, and even business travelers can be combined into a single Centrex group with the main office, even if they are all served by different wire centers. This is possible because packet transport is so inexpensive and is not mileage sensitive. Multilocation Centrex provides the following advantages to the customer:
- Easier for the corporate telecom manager to administer one large Centrex group rather than several separate Centrex groups.
- Uniform services and features for all users, regardless of where their office is.
- Extend advanced business features to telecommuters' homes without any Foreign Exchange costs.
- Uniform dialing plan across company. Abbreviated dialing can be used to call the office next door or the office across the state.
- No toll charges for calls between locations.
- Better utilization of adjunct CPE solutions, such as voicemail systems or IVR equipment.
Reduction of MAC Activity: With IP Centrex, certain Move, Add, and Change (MAC) activities can be eliminated when a user (of an IP Phone) changes offices. The phone number and features follow the IP Phone throughout the LAN, without needing any change orders.
Mixed Technology Groups: IP Centrex is fully compatible with previous Centrex services. Analog lines, ISDN lines, and IP Centrex lines can all be made part of the same Centrex group. This makes it simple for existing Centrex customers to introduce IP Centrex. They don't have to convert their entire group at once. Instead, they can add or convert lines to IP Centrex on a line-by-line basis.
Use of Existing Centrex Management Tools: Current analog or ISDN Centrex customer can continue to use existing Centrex management tools for many administrative functions on IP Centrex lines. For example, Macstar(SM) or Centrex Customer Rearrangement System/CCRS(TM) can be used for IP Centrex. In addition, Station Message Detailed Recording (SMDR) can be used to get the calling records for an IP Centrex station.
The following benefits apply to IP Centrex as well as to earlier Centrex technologies:
Lower capital investment cost: Since the service provider owns the infrastructure, the start-up costs for Centrex service are much lower than purchasing a CPE-based solution, like key systems, traditional PBXs or IP PBXs.
Scalability: With Centrex service, the customer can buy the exact number of lines that are needed, and readily add or remove lines. In contrast, when you remove a station from a PBX, there is no cost savings, since the equipment was already purchased. Also, when adding stations to a PBX, there are costs not only for the line cards, but periodically for new common equipment, like shelves to accommodate the line cards.
Simplicity: With Centrex service, the service provider is responsible for installing and configuring the service. With a PBX, the customer, or the customer's consultant, takes on this responsibility.
Operations and Maintenance: The service provider is responsible for the day-to-day operations and maintenance of Centrex. This includes adding new lines and changing faulty components. With a PBX, the customer is responsible for these functions, as well as for keeping an inventory of spare parts.
Upgrades: One of the principles of Centrex is that the service provider continues to upgrade the service. This includes not only the major evolutionary upgrades, like from analog to IP, but also more mundane upgrades, like installing a new switch generic which offers more features.
Reliability: The Centrex service provider monitors the network 24 x 7 and has staff to immediately respond to alarms and equipment failures.
Standardized CPE: Centrex station equipment uses standardized protocols and conforms to an open interface. This allows multiple equipment suppliers to manufacture Centrex CPE, and the customer can purchase any suppliers' brand of CPE. This competition drives down station equipment prices. In contrast, many PBXs use proprietary station sets, and the customer can purchase only the station sets designed to work with a particular PBX. Since the customer is locked into a limited selection of CPE, PBX station prices are often higher than comparable Centrex station equipment.
Eliminate floor space and environmental requirements: With Centrex service, the infrastructure is located on service provider premises. In contrast, PBX and key system solutions are located on the customer premises. The customer must provide floor space for the equipment. The customer must ensure that the room the equipment is in meets certain environmental requirements, such as air conditioning, humidity, and fire protection.
Features: Of course, Centrex offers a wide range of business-oriented features that can be configured to meet the customer's needs.
Applications and ConfigurationsIP Centrex can be used in a variety ways. The diagrams below show some examples. Click on each icon to see a larger version of the diagram as well as a description of the implementation. These diagrams are for demonstrative purposes only and do not show the full range of IP Centrex configurations. For example, it is possible to combine elements from different diagrams together to create other configurations. Also, for simplicity, these diagrams show only the Class 5 switch approach to IP Centrex. Comparable configurations are possible for Softswitch-based IP Centrex.
|Centrex Group Completely Converted to IP Centrex Using IP Phones |
|Centrex Group Completely Converted to IP Centrex Using Legacy Station Equipment |
|Multilocation Centrex Combining Main Office and Branch Office into One Centrex Group |
|Multilocation Centrex Combining Main Office and Telecommuters' Homes into One Centrex Group |
White Papers and ArticlesA number of magazines and companies have published information on IP Centrex. You might want to check these out.
- ISDN Centrex White Paper: This PDF file from the Council for Access Technologies describes the overall benefits of Centrex as well as the features and management capabilities that ISDN Centrex introduced. Although this paper does not emphasize IP Centrex, much of the content applies to equally to IP and traditional Centrex. A related PDF file answers Frequently Asked Questions about ISDN Centrex for Telecommuters.
- IP Centrex Creates New Opportunities for Equipment Manufacturers: This PDF file from Telcordia Technologies describes how IP Centrex works on a Class 5 switch platform and discusses the new business opportunities that are created by IP Centrex.
- The New Centrex: This article, by Bill Michael, is from the Feb.5, 2001 issue of Computer Telephony magazine.
- Centrex Revisited: This article, by Warren S. Hersch and Rick Laezman, is from the March 5, 2001 issue of Teleconnect magazine.
- Centrex Versus PBX: A New Look at an Old Debate: This article, by Ian Angus, was published by Telemanagement and is available from the One Unified web site.
- Making The Case For IP Centrex: This article, by William Flanagan, was published in the March 2003 issue of Internet Telephony. In addition, a sidebar by Bob Massad discusses How To Manage An IP Centrex Service.
- There are many more articles available on the web. Click here to use Google to search for "ip centrex".
Are you a telecom equipment supplier or service provider?The IP-Centrex.org members are interested in creating industry initiatives to address issues related to the development and deployment of IP Centrex services. Topics we are studying include:
We'd like to work with you!
- Service uniformity across various suppliers' platforms
- Open standards and interoperability for IP Centrex Customer Gateways and IP Phones
- Impact assessment to help service providers and end-users prepare for IP Centrex deployment
- Simplification of service order negotiation & flowthrough for provisioning
- Maintenance and testing procedures and solutions
Industry LinksThe following companies participated in IP-Centrex.org's initiatives:
- Appia Services
- IP Centrex Limited UK
- MERA Systems
- National Centrex Users Group
- Nortel Networks
- One Unified
- Sonus Networks
- Sylantro Systems
Anderson Jose Mariño Ortega