IP-Centrex System : Features and Applications

The effective use of features (within the phone system) and applications (attached to the phone system) is the key benefit promised by IP-Centrex. With legacy PBX systems and Centrex services, most users do not know what features are available and are uncomfortable with some that they do know (e.g., establishing a three-way conference call). Additionally, the integration of desired applications has proven to be complex and expensive with PBXs, and almost impossible with Centrex, due to management and physical separation.

With the next generation networks, as typified by IP-Centrex, voice service features and applications will be created by a wide range of developers, including specialist software companies, the service providers, system manufacturers, and the user community. These improvements can be grouped into three categories:

High-volume services for many users will reside on centralized application servers, next to the carrier's softswitch. These will include address/number translations and other directory services, toll-free number services, nationwide number portability, and links to wireless services.

Applications for work groups that need specialized services, such as contact centers, but that are also physically distributed and frequently changing. A wide variety of occupations, such as brokers of all types, public relations personnel, sale executives, and consultants, spend much of their day on the phone and are highly mobile. These applications need to be flexible and logically distributed, but will mostly be implemented on shared, centralized servers.

Personalized features will involve customization at the endpoint, with an intelligent device. These include features such as call blocking of specific codes or numbers, user-specific icons or audio interfaces, and caller-identifying ring patterns.

Hosted Internet protocol (HIP) telephony is an almost ideal application service provider business model, in that voice services do not involve customization for particular vertical markets. At the same time, other applications, such as CRM and enterprise resource planning (ERP) can be attached to the voice services and tailored to specific industries. Most users of the features and applications that will be delivered through IP-Centrex will need an IP telephone, while some will be served by a softphone within a PC.

IP Centrex System : Cisco Systems & Sylantro Systems

Cisco Systems
Cisco Systems' CallManager server had been installed by at least three service providers as of mid-2002, to provide IP-Centrex services. Pingtel, one of these competitive service providers, delivers IP-Centrex from CallManager installations in New York City, Philadelphia, and Washington, DC. This service has proved most successful with small businesses that have from 100 to 500 users at a site.

This is a development that we expect will be followed by other service providers, both large and small, as an alternative to the use of more powerful softswitches from the established Centrex manufacturers.

Sylantro Systems
Sylantro Systems sells an application switch that offers hosted PBX and IP-Centrex features to competitive service providers. Sylantro claimed to have sold systems with more than 10,000 user ports within the first year that its system was available.

Tacqua Systems
Tacqua Systems has created its OCX softswitch with class 5 capabilities, specifically so that CLECs can deliver local telecom services with significantly reduced initial and ongoing costs of ownership. Tacqua delivers a kernel of telephony features, while encouraging other software developers to use its intelligent network (IN), application programming interface (API), and SIP interfaces.

IP-Centrex System : Siemens ICN

Siemens ICN sells its Centrex product under the name GeoCENTREX. GeoCENTREX is based on the Siemens EWSD central office switch. The EWSD is the most widely sold such system in the world, supplying 250 million analog and digital ports. A single EWSD system can process 16 million BHCAs, have up to 240,000 ports, and handle 100,000 Erlangs of traffic. Siemens holds a distant third place in the North American market and is still a minor player in the Centrex field.

Siemens intends to provide an end-to-end IP-Centrex solution through a combination of its own technology and vendor partnerships, as shown in Figure 3.5, which illustrates the use of an IAD to link analog stations or KTS/PBX systems to IP-Centrex.


Figure 3.5: Next generation local switch services.

In mid-2002, Siemens sold its controlling share in Unisphere to Juniper Networks and is no longer directly involved in the data router and switch market. However, since Siemens' IP phones work to open standards, the customer and service provider could use any standards-based router. Siemens has retained the name of the Unisphere SRX for its family of softswitches and obtains its IP-Centrex software from Broadsoft Inc.

The Broadworks package can be deployed in a totally packet-based architecture such as full IP-Centrex or work as an extension of a preexisting class 5 switch. The system can support more than 1 million customers per network and process up to 6 million BHCA, based on a cluster of Sun computers, divided into the three classes of application, media, and network servers.

This software enables service providers to manage a nationwide IP-Centrex system centrally, delivering a uniform service to distributed enterprises and optimizing network management resources.

The Broadworks package provides Web portals for five types of service management:

- Service providers with complete system administration capabilities;

- Resellers that can create and manage their own groups of customers, under contract with the service provider;

- Enterprise administrators with access for configuration and management of multilocation dialing plans, for specific organizations:

- Group administrators, within one enterprise, that can perform modification, addition, and deletion of features and users;

- End users within a calling group that can personalize calling services and features.

IP-Centrex System : Nortel Networks

Nortel Networks is the world's largest vendor of Centrex systems and has been responsible for most of the development of these services outside North America over the past decade. There are nearly 100 million lines on Nortel's DMS switches worldwide and of these well over 10 million are for Centrex. Nortel has announced a family of softswitches under the name of Succession, based on Sun computing platforms. The CS2000 can process 300,000 BHCA with a pair of servers, supporting both asynchronous transfer mode (ATM) and IP, together with H.323 and SIP standards. Nortel's concept of IP-Centrex, delivered either from a legacy DMS switch through gateways and from the CS2000 softswitch, is illustrated in Figure 4.


Figure 4: Centrex IP for extended service reach. (Reproduced with the permission of Nortel Networks. Copyright © 2002 Nortel Networks, All rights reserved.)

Nortel Networks conducted a number of IP-Centrex technology trials in North America and Europe during 2001 and 2002. Then, in late 2001, Telstra announced that it would offer CustomNet IP in the major cities of Australia, using Nortel-made gateways to link IP-based endpoints to the existing CustomNet (i.e., digital Centrex) service. Telstra stated that CustomNet IP would also use data services, such as dial connect, cable, asynchronous digital subscriber line (ADSL), or ATM, to provide access to its DMS-based CustomNet. This is the first product set to be released under Telstra's Next Generation Telephony project, but the actual start-up date for this service was not announced.

IP-Centrex Systems : Lucent Technologies

Lucent Technologies is the second-largest supplier of Centrex systems, based on its 5ESS digital central office, which has been installed in a number of countries. Lucent made an early start in 2000 with its iCentrex product, which is based on the iMerge gateway, extending Centrex over IP and wireless networks. The iCentrex solution is actually switch independent and could work with other vendors' central offices. This product allows for the use of a mobile phone with Centrex dialing and other features when the user is in the Centrex service area. Sharing one voice mailbox between wireless and wireline Centrex services is also possible, with more than 1,000 wireless handsets feasible in one building.

Lucent claims that its 5ESS switch has the least downtime of any CO system in the U.S. public networks. The iCentrex development relies on the 7R/E Packet Driver software to deliver full PBX-like parity, including call transfer to voice mail and auto attendant. The wireless Centrex features work with either code-division multiple access (CDMA) or time-division multiple access (TDMA) technologies.

The iMerge Centrex Feature Gateway (CFG) enables users to enjoy worldwide Centrex service, as emphasized in Figure 3.


Figure 3.3: Worldwide IP-Centrex.
Lucent identifies the benefits of worldwide IP-Centrex as including a single dialing plan and uniform telephone system at all locations, including mobile and at-home workers, as well as branch plants or offices. IMerge enables a customer to be freed from service area boundaries with the delivery of existing Centrex and new services across a packet network.

Based on the encouraging results from field trials of Lucent's iMerge product SBC Communications launched commercial IP-Centrex service in September 2002, starting with availability in five major cities across the United States. SBC claimed that it was the first major carrier to bring these new IP-Centrex capabilities to the market.

IP-Centrex Systems : Ericsson

Ericsson became interested in Centrex over 10 years ago, when the service was first introduced to Europe, but has not become a significant player in wireline Centrex. However, Ericsson makes three major contributions to the overall IP-Centrex market, as follows:

- A product known as G-Nexus, or GSM Mobile Centrex, delivers PBX-like functionality over a public mobile phone network, using GSM technology, which is the most widely deployed wireless standard in the world. Ericsson-made equipment supports over one-half of the world's GSM users, and its G-Nexus has IP access facilities, with a managed IP network between the enterprise and the Centrex node at the network operator's site. This mobile or fixed access to G-Nexus uses an H.323 media gateway to link to the AXE-based Centrex node, providing business group communications. The latest version of Ericsson's central office, the AXE Local 7.2, is a UNIX-based system that is really a transition product, partway between a legacy circuit switch and a softswitch. Ericsson's softswitch product, known as the IPT 2.1, has an all-IP architecture, supports H.323 protocol, and is intended as a signaling processor for multimedia service delivery. This is illustrated in Figure 2.


Figure 2: Ericsson's IPT 2.1 domains.

- Ericsson was an early starter in the VoIP (transmission) market during 1997 and is now one of the largest suppliers of VoIP gateways.

- Ericsson has become the most successful supplier of in-building wireless phone sets, which can work with PBXs and Centrex services from other suppliers, such as Siemens and Nortel.

IP-Centrex Systems : Alcatel

Five major telecommunications equipment manufacturers, namely Alcatel, Ericsson, Lucent, Nortel, and Siemens have been able to supply Centrex solutions, based on their respective digital CO systems, for the last decade. Three other significant public exchange manufacturers—Fujitsu, Marconi, and NEC—have not supplied Centrex software in the past and do not appear to be interested in delivering IP-Centrex systems (although NEC was one of the early suppliers of IP-PBXs).

The product descriptions that follow are not intended to be exhaustive but should give a good indication of what systems are available to deliver hybrid and full IP-Centrex from a number of vendors. The hybrid, evolutionary approach extends the life and depreciation time of legacy class 5 switches, but retains proprietary technology in the network and limits the integration of new applications. The softswitch-based, full IP-Centrex, approach can be disruptive for the service provider and its customers. This approach may also be risky if the softswitch comes from a smaller company that has had time only to develop a limited set of the popular Centrex features.

Alcatel includes a Centrex offering on its model 1000 central office, but at the time of this writing had not made any announcement regarding IP-Centrex. Alcatel is not a major vendor of Centrex systems; it has implemented a limited form of Centrex in a few countries and planned for Centrex service with several South American telcos.

The company has developed the powerful 5000 series of softswitch platforms, of which the 5020 is a signaling server and the 5424 is designed for off-loading switched data traffic from the voice network to the Internet. The model 5000 is a class 5 switch server, with a typical network topology as shown in Figure 1.


Figure 1: Network topology with Alcatel 5000 softswitch.

This 5000 softswitch can process 5 million busy hour call attempts (BHCA) and grow to 1 million virtual ports, delivering voice over IP or ATM and interfaces to the SS7 network. The softswitch in Figure 3.1 is shown with integrated access devices (IAD) on the customers' premises, providing 16 voice channels over one digital subscriber line (DSL).

Deployment Strategies for IP-Centrex

The arrival of credible IP-Centrex services presents different scenarios to corporate decision-makers, depending on the state of their telecom infrastructures and on the alternative offerings in their marketplace. These situations fall into one or more of three classes:

1. Controlled Migration to IP-Centrex. Many organizations will wish to add IP phones to an existing Centrex configuration (i.e., the hybrid approach). Two possible reasons for this might be:

- To implement a contact center as a managed service;

- To extend fully featured, multimedia service to remote or mobile worders.

For these solutions the organization will need to use a wellmanaged IP network, which may be provided by the ILEC, that currently operates the Centrex service, or may be from another service provider (e.g., an international telco with a wider-ranging network, such as AT&T or BT).

The use of two or more IP-WANs presents a further choice to the customer, as the customer may prefer to have access directly to the competitive long-haul network through a switch at the customer's site, rather than via the IP-Centrex service provider's own network access. This alternative is shown in Figure 1.


Figure 1:Controlled migration to IP-Centrex.

2. Greenfield IP-Centrex Implementation. On the reasonable assumption that the average digital PBX needs to be replaced (not just enhanced) after a 10-year life, or that long-term Centrex contracts never last more than a decade, about 10% of all organizations will face a crucial greenfield telephone services decision each year.

3. Move to a Competitive Service Provider. Many organizations obtain their Internet or VPN connections through an ISP and/or rent Web server hosting facilities from a service provider other than the incumbent telco. In many of these cases this service provider is a good candidate to become the customer's communications application service provider (CASP), in preference to the ILEC.

When considering whether or not to entrust its in-house voice and video communications to a CASP, an organization's management must evaluate the following topics:

- The specific IP-Centrex design being deployed by the CASP;

- The match between the feature set available, from the competitive IP-Centrex service, and that needed by the users;

- The local access technology being offered to the WAN and its scalability to accommodate growth (or, occasionally, contraction) of bandwidth needs;

- The perceived financial stability of the service provider, in a time when the finances of some long-established, large telcos also have been seriously questioned.

Network Considerations for IP-Centrex

Requirements for VolP
The IP-based systems and networks that will be used for voice or video transmission over IP must meet several criteria to deliver a signal of the same quality that has been available through circuit-switched, digital systems and with which the users are satisfied.

Because of the real-time, interactive nature of VoIP the average transit time (i.e., latency) between source and destination is most important. As shown in Table 2.1, ideally one-way latency should be less than 100 ms. If the round trip delay on a voice conversation exceeds three-tenths of one second, then it becomes difficult to continue an intelligent dialog, as many have experienced when a telephone call was routed through a geostationary satellite.

Jitter is the variability of packet arrival times at the receiver and is generally caused by large bursts of data interfering with the real-time traffic in the network. Although modest jitter delays have not been considered serious to real-time conversation, yet significant jitter (i.e. delays approaching 60 ms) leads to unintelligible speech patterns and ruins video displays.

Packet loss corresponds to link dropouts, which is a common experience with mobile/cell phones in congested areas and also results in unsatisfactory voice or video communications.

The bandwidth, or bit rate, requirements for VoIP depend on the type of encoding/decoding (i.e., codec) technique that is used in the digital signal processor (DSP) in the end stations. A reasonably good guideline, with current technology, is to allow 20 Kbps in the network or the access link for each simultaneous voice conversation, or 200 Kbps for a small-group video conference session.

LAN Requirements
In a large office complex there may be a correspondingly large number of simultaneous voice calls on the LAN, in the busy hour of the week. This traffic volume depends on the peak telephone utilization level in the organization, which may be 25% in many offices, but rise to nearly 100% of the population in some highly sales-oriented businesses, such as a stock brokerage. Even if there are 1,000 concurrent voice calls on the LAN, this probably represents an added load of only 20 Mbps, which is insignificant on a gigabit backbone.

However, if the in-building network is to carry IP-based video traffic, as will increasingly be the case as multimedia applications are implemented, then a major LAN upgrade is much more likely to be needed. If we assume a minimum bit rate of around 200 Kbps for two-way video interaction and up to 2 Mbps for higher definition, full motion, video displays, then a number of simultaneous video sessions will put a heavy load on the LAN. In some early installations for IP-based video conferencing a separate LAN that went all the way to the main edge router for the building was dedicated to the video outlets.

WAN Requirements
An existing metropolitan area network (MAN) or WAN will certainly be more challenged by the added burden of carrying VoIP packets than a LAN. The transit and jitter delays and bit rate requirements will each have to be seriously addressed across all stages of the larger network. Generally a data network that runs on frame relay (FR) technology will not meet the latency criteria that we have specified. There may be some exceptions if the FR virtual circuit involves only two frame switches. The regular Internet is definitely not suitable for corporate VoIP traffic and only a managed network can meet the requirements.

A managed IP network is one where the service provider(s) monitor and control the QoS, outside the customer's own environment, to minimize latency and jitter, while ensuring that sufficient bandwidth is available for busy traffic. In a managed network the VoIP packets pass through the least number of nodes and the QoS is guaranteed, going beyond just "best effort" engineering.

The characteristics of the access links between the LANs and WAN must also be well defined and managed to fit within the overall criteria budget from source to destination.