Centrex

Centrex ( Central Office Exchange ) provides the functions of a telephone system for individuals or businesses using elements of a public telecommunications network (eg ISDN) ready. As synonymous terms, the terms virtual PBX, Hosted PBX (Private Branch Exchange) and NetPBX have established.

The technology was developed at the end of the 1950s in the U.S., and offered there at the beginning of the 1960s on the market. In Germany, first offers were elaborated on this technique only with the deregulation of the telephone market in the early 1990s.

2.1 Wide Area Centrex ( WAC)
2.2 Call Center
2.3 Central Attendant
2.4 teleworkstation

3.1 Organisation
3.2 technology
3.3 User Equipment

Principle

Each phone is directly connected to the public telephone network of a network operator. The network operator reserved numbers and breakdown according to user request and grants a special tariff for internal calls. Unlike telephone systems need to be with Centrex user, ideally sourced and do not maintain their own systems.

Services

All services provided by Centrex based first of all on the situation on the market of telephone systems. These include standard telephony services as well as Advanced Services group as well as value-added and supplementary services. Then, for Centrex - because these services are already provided in the public network nodes - even special transport services, which are always considered separately in private networks. In this statement lies also one of the main differences between the private and the managed services. Specifically, these groups of services can be distinguished:

Standard services provide basic functionality for handling telephony and are also available in all public networks. These then include such tasks as the connecting and disconnecting, and phone number management.
Services group extend the existing standard services to special services that take into account the extensive communication behavior of a private group, and so are of limited available in public networks. The majority of these services has also been specifically placed in the history of the telephone systems on the market. These services include services such as then an internal dial plan or call transfers and more circuits.
Value-added services provide a summary of services that are tailored to a specific user group. This particular call center and telecommuting jobs play an important role.
Additional services complement the standard and group services in the form of specially hosted systems that provide centrally, for example Unified Messaging or voice mailboxes. This is mainly comfort services can be easily deployed.
Administration of the respective services and groups is a prerequisite for the establishment of Centrex. In contrast to local applications such as telephone systems a number of special features are the use of centralized systems observed, since various active and passive nodes can be in a group.

Services group

The general membership functions are standard in modern communication and should not be considered further here. Among the centrex - specific properties include not only the services available in phone systems especially the following features:

Internal numbering ( intercom number) - In addition to a number of the public network, each participant receives an internal number, by which it is achieved within the group. This function is of particular interest in the use of Wide Area Centrex and is presented here in more detail by way of example.
Involvement of private telephone systems - In addition to individual terminals, it is also possible to integrate telephone systems in Centrex groups. This phone systems are expandable, virtual network across multiple locations or gradually replace by Centrex connections.
Extension to the public network - While with phone systems only its own local network is achieved, can be personalized with Centrex, many variants of access to the public network design.
Mini group - Each participant in a so-called mini - group remains with his phone connection first as a member of the public network and enters his Centrex group only by entering a combination.
Automatic Call Distribution ACD - With Centrex calls can be distributed within the whole group after an automatic procedure.
Manual call distribution - within a Centrex group can, depending on the authorization, all calls distributed to any location, be adopted or transferred.

Agencies

An important means of communication remain even in the age of speech recognition systems still staffed front switchboards. With this Centrex Attendant Consoles can be distributed over several sites and also operate several private group - the latter refers to a so-called Centrex complex and is equipped with telephone systems currently very limited. With access to the resources of the public network consist of attendant consoles at several sites no restrictions on the transfer of calls within the network. It is expected that in the context of Centrex Attendant Consoles continue to have a great importance and offer new functionalities.

Administration

The administration of his private group for the user is given an important tool in the hand, with which he can make his demands on the communication itself. While in the past at Centrex administration of special devices dependent and limited the possible functions, the transition to new versions of the management is discussed with Centrex. A special role is played here in the future to the web- based solutions.

Technology

Centrex is based on the components of the public network. These are generally:

Public network nodes as carriers of the control functions,
Networks for communication between network nodes and users,
Terminal equipment as a direct interface to the user.

Support each Centrex solution is the switching system, in which the necessary processes are controlled and managed. For this purpose, a Centrex group is formed, which can be identified by its unique Business Group Identification ( BGID ) within the system. This identifier is queried during the mediation process; has a connection to a BGID the system provides him also stored there services and applications of the private group. Importantly, this identification is also build cross-site groups, where multiple nodes are involved.

Interfaces

With Centrex must be available, which is also possible in conventional private groups by definition all interfaces. The crucial difference from private systems, the architecture of the public network, based on publicly available and defined interfaces and protocols. But this also, only the publicly defined features are available. Shall now special services are offered, as are common in private systems, it applies the existing protocols to expand accordingly and that sense they are not without limitations.

Protocols

As one of the core elements in the introduction of Centrex, the use of available protocols must be taken into account in the net. Was there in private networks using private nodes clear separation between private and public communication protocols to mix these two worlds at Centrex essentially extent. So the ISDN protocol used in Germany DSS -1 is limited prepared for functions of telephone systems. In the world of telephone systems therefore work with the manufacturers own proprietary protocols, which are not available at Centrex in the public network. This translates Centrex a number of limitations with respect to the telephone equipment available on the market.

Applications

Due to the special architecture of the public network, additional services may be provided in private groups with Centrex, are not so private systems usually possible. These applications made so far is a large part of the appeal of Centrex and will play a central role in IP Centrex.

Wide Area Centrex ( WAC)

In the network, this feature may be combined in various locations to a common private group, referred to as inter-site networking or as a Virtual Private Network (VPN). With this function, a distributed group appears as if it is located at one site. This allows for uniform value-added services at all ports of this group use alike.

Special features of all solutions with Wide Area Centrex are:

Consistent representation of the entire network under a common number block,
Common functions and services across the network,
Treatment of all connections within the WAC group as in a shared private telephone system,
Joint administration of all sites,
No bottlenecks or excess capacity through access to network capacity of the carrier,
Reduced risk of interference between sites over leased lines rented by the denser meshing of public network operators,
Tailored to customer requirements tariff variations between sites.

All functions of the Wide Area Centrex based on communication processes in the systems of public network operator. Recognized the groups in different network nodes in the network WAC by evaluating the BGID from the ISDN User Part of SS7 signaling protocol. The messages contained there then solve the corresponding functions within the group. Currently, however, neither this nor the evaluation of BGID other functions are standardized so that only manufacturer-specific messages are exchanged. This are currently no Centrex groups realized that span network nodes from different manufacturers. Likewise, so is the structure of groups is impossible, extending over different network operators. Currently in Germany, only the systems EWSD Siemens AG across multiple sites as a basis for Centrex operation. With use of the SS7 ISUP V2 field (ISUP ) this system provides a vendor-specific and limited number of messages for communication between two network nodes. Alternatively, of course, would also Intelligent WAC possible - there are the available messages in the INAP but still much less focused on the use of a complex Centrex solution, so that especially the numbering between the sites is organized in this way. So at least the operation of various systems are possible as a limited solution.

Now comes the interconnection between PSTN and NGN into play arises again the problem of incompatible message formats. Currently going providers in particular the assumption that the potential customers of IP Centrex begin ideally without existing telecommunications infrastructure on greenfield sites, the reality is something different. For many users, IP Centrex would be an ideal migration path from PSTN to NGN - without communication between the two worlds but that remains a pipe dream. A possible solution would be to rely more on the protocols of the IP world that has, for example with SIP over an open platform that other services could absorb them. Without a harmonized approach by all market participants in this project will not be feasible at this time.

Call Center

One of the still insignificant applications are virtual call center. Under the terms of IP Centrex, this image should convert but since this is where the communication can better link with the required data. Focus of the solutions currently used, the use of a central ACD services a plurality of stations with Wide Area Centrex. Here a central call management is provided by the loading of the individual agents is controlled from one point. Similarly, the use of CTI is also provided; due to the very complicated handling, there were, until now no cases. In conjunction with Centrex Call Center Solutions, the following services can use:

Central switchboard

Centralized exchanges, in which more than pure queries from callers as the call center also has an active call treatment is possible, form an essential building block in many of the currently operating Centrex solutions. So it is in a Wide Area Centrex sense to edit various locations centrally. This can not only streamline communication processes but also use staff more effectively. In conjunction with network-wide ACD solutions, the users get a versatile application with this system. Since the ZVPL based on public networks, the functions differ in some respects from those of private systems: In a location of the Centrex Group, the central dial is set as a direct connection to ZVPL. In addition, calls can be redirected to the ZVPL also to the other places with the " Do Not Disturb ". Gets now an external subscriber one of these connections or want to be sent to the central dial a general inquiry, this connection is redirected on the web directly without the involvement of the connecting cables of the customer directly to ZVPL. There, both the caller's number as well as the originally selected target are displayed. This can directly react so be as if located at the originally selected location of the ZVPL. In the next step can be both finally processed as in a call center or relayed within the Centrex group on ZVPL the call. If necessary, the ZVPL - and only he, and only in this case - to break through the " Do Not Disturb " in which participants initially chosen and transfer the call to this place on. With the outlined functions, the user has a number of services available that can be readily prepared as a private system does not. In this context, the function of the centrex complex plays an interesting role. So that several private groups under Centrex from a central service provider can provide you with a ZVPL - a function as it is not possible with a telephone system.

Teleworkstation

Centrex offers in this area a simple answer that other systems is superior in many respects. Therefore, first of all the currently available solutions are presented. In ISDN-based Centrex, these benefits result:

After application of the teleworker to his native work all the functions of his office workstation are available to him.
At the office workplace incoming calls are forwarded directly in the network to the remote workers without a line is seized in the company.
As a full member of the Private Communications Group, the so incoming calls can be arranged by teleworkers to the corporate site on.
Outgoing calls the teleworker are marked with the office number, so not the origin of the call from a home office can be seen for the called party.
Logs from the remote workers from the group 's outgoing calls are again displayed as private calls and billed.
Additionally, it is possible to integrate data links in this process, and thus to establish a VPN in the ISDN. With IP Centrex, this variant is significantly simplified.
For the telework place, there is a signaling, indicating the status of the external workplace. This allows the presence of the teleworker settle. With this feature active teleworking can also be integrated into a call distribution when needed.
It is also possible that the teleworker is only partially involved in a so-called mini - Centrex solution in the communicative events in his company.

So far has been realized with this solution, especially the integration of teleworkers as " overflow " for virtual call centers. Ensure that the operator of a call center can without much effort and waiving own investments additional jobs - regardless of location - integrated into existing groups.

Conditions of use

Centrex requires in contrast to projects with private systems, a different approach. It is always the views of the users noted that has grown from those same systems of telephone systems and leased lines out. A complete reorientation of customers ultimately leads only to confusion. Despite everything, some conditions must be considered when using Centrex, which are not found in traditional projects.

Organization

Focus is on outsourcing, the costs and the impact on the processes. The following items will play a role:

There are no investments of customers necessary
Shorter contract terms than a telephone system are possible,
Heterogeneous solutions from PBX and Centrex require special support services,
With special function packages the customer can reduce its costs by paying only really needed services,
The user will be charged only the really undrawn uses of the network,
It can be special pricing models negotiate, make a charge internal links as opposed to telephone systems,
The user must not provide facilities for the abandonment of its own technology,
For internal calls can incur costs and
For large companies to the classic Centrex is only conditionally suitable.

Technology

The use of Centrex offers in comparison to other systems, a number of technical features:

The reliability is significantly higher than would be possible with private systems in public networks and network nodes.
Public network operators offer a higher level of security than private systems due to their system structures.
They also run a very high cost for system maintenance, administration and maintenance.
With support on a public network nodes uniform growth without intermediate steps is possible.
Public networks are clearly blocking poorer than would ever be possible with private systems generally.

User Equipment

The interplay between Centrex and existing user systems, there are some advantages:

Telephone systems can be extended to other ports, regardless of the location of the system.
Virtual networking of existing telephone systems are possible.
In addition, application servers in the network to expand the capabilities of existing private schemes.

In addition, there is the interaction of telephone systems and Centrex also some disadvantages and problems:

Comfort features are not available across the system, as to the absence of standardized protocols.
Call forwarding is not possible in some configurations.
Disclosure of compounds or call forwarding between the systems can overload the private line routes.
CTI systems are system-wide not possible as third-party applications.

Dissemination

In North America Centrex achieved a market share of about 30% of the internal ports in companies and administrations. Along with IP Centrex dominated the "principle Centrex " there now about half of the market. Widespread Centrex is also in Scandinavia, Great Britain, New Zealand, Australia and Japan. Regionally active against all - - Also in Germany the product of different network operators is offered. Because of newly developed features and the possible merger with IP technologies ( IP Centrex ) and broadband applications, the service is predicted one until recently held for possible renaissance.

History

Originally there were only Centrex worldwide since own telephone systems at the customer in the early years of telecommunications were not admitted. It was not until 1900 developed from the technical necessity telephone systems, which then market were decisive in the sequence. For an understanding of current development, a look into the history is very helpful. Centrex was originally developed in the USA. Early fifties turned AT & T fixed at market research that could support the business processes of the customer only partially with the facilities of private extension systems, while the public switching equipment were not equal more powerful. On the basis of this discovery began at Bell Labs as a subsidiary of AT & T first studies how public agencies can accommodate private group communication. The aim was to provide especially high-volume large companies with more benefits. The Bell Labs led by 1958 first in Colorado Springs tests that a year later led then into regular operation in Chicago. There, suddenly revealed the unexpected situation that instead of the expected target groups more and more small and medium-sized enterprises for Centrex interested in wholesale. This demand for inexpensive corporate networks brought then in the following years a certain flowering period for Centrex in the USA. In the seventies, this boom broke with the advent of powerful private extension systems again. The market then was revived by a turn in the entire communications market: the break-up of AT & T into small business units. These so-called Baby Bells saw in Centrex an excellent opportunity to gain access to lucrative business potential customers. Thus, for some RBOCs Centrex really the key product for their own survival in the market. Bell Atlantic, eg reaching nearly half of its business customers with this solution. In the race for market share by public or private solutions then applied - again, in the U.S. - digital systems, a new generation of benefits and services. Other states then moved in the eighties and nineties slowly but never reached the density of Centrex connections as it is found throughout North America today. In Germany tried after deregulation in 1998, also some regional suppliers with Centrex to score with business customers. However, the first promising approaches initially failed due to technical problems and later at the lack of understanding by the network operator for the market of telephone systems. In the period since 2006, in a second attempt in the German market a range of specialist providers established. Condition for their emergence was the highly -advanced meantime spread of broadband connections, even for small and medium-sized enterprises. Today's solutions are typically configured by the user via the Web. The range of features corresponds to the quality of traditional phone systems.

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