Local Access Facilities

With an MPLS-based WAN providing the public network links for IP-Centrex, the customer is essentially concerned about the bandwidth to and from the network. The typical IP-VPN service provider defines a committed access rate (CAR), which is comparable to the more familiar committed information rate that was defined for frame relay services. For VoIP the CAR should be a minimum of 20 Kbps for each active voice conversation over a symmetrical, digital bit stream, and with an Ethernet interface at the customer's premises.

For a single user (e.g., at home) with a PC, a standard, analog dial-up connection and a 56-Kbps modem are adequate to handle voice conversations through the IP-Centrex service. Where video communications are used this minimum bit rate requirement rises to 200 Kbps. At sites with multiple users (i.e., anywhere other than the smallest home office) the local access is now generally described as a broadband link, or a "fat pipe." This is in contrast to legacy Centrex, which in most cases is delivered by each phone line using one of the copper wire pairs (which are utilized as "thin" pipes in this case, as a bandwidth of only 4 kHz or 64 Kbps is required).

Broadband used to be defined, over the past decade, as bit rates above 45 Mbps (DS-3) in North America, or 34 Mbps (E-3) in other countries. But common usage now seems to define broadband as referring to any bit rates higher than 128 Kbps. An informal survey of documents from 14 countries showed that the lower threshold considered for broadband ranged from 200 Kbps to 30 Mbps.

We can assume that today's multimedia applications demand a symmetrical 1 Mbps per active individual user. Table 3.3 shows the desirable available access bit rate for different types of premises.

Managed Networks

The voice and video traffic that is directed by an IP-Centrex controller travels over the LAN inside a building or campus generally at a nominal bit rate of 100 Mbps to and from the desktop. Increasingly, Ethernet links are being created over virtual local area networks (VLANs) between buildings in an urban area, with an operating range of up to at least 20 miles (30 km). In this way metropolitan area networks have been absorbed into VLANs, so that building boundaries have become invisible. The transport of VoIP packets over WANs is still a challenge and requires careful consideration.

LAN Considerations
Most LANs will need some enhancement to support VoIP, if only to provide the in-line power for telephone sets. The LAN for voice/video over IP must be switched, not shared, and any device used in the LAN should be QoS-aware and/or -capable. Admissions control to the LAN will be done in a gateway.

The voice or video bandwidth requirements depend on the codec used in the endpoints. The two voice encoding standards that are commonly used in IP phones are G.711, which was the original ITU recommendation for pulse code modulation and usually generates 64 Kbps per speaker, and G.729 Annex A, for which 8 Kbps must be reserved for each voice transmission.

The G.723.1 recommendation has been extensively used as a low bit-rate encoding algorithm in VoIP gateways, running at 5.3 or 6.3 Kbps, but it is processing-intensive (at around 30 Mips) and therefore has not been widely implemented in IP telephone sets.

If we add some consideration for packeting overhead and round up the numbers somewhat, for bandwidth estimating purposes the figures of 80 Kbps for G.711 and 20 Kbps for G.729A are reasonable.

It is essential to have coding conversion capability at the transition point from one network to another, to allow for telephones, softphones, or video units with differing codecs. This conversion may take place in a separate subsystem, known as a transcoder, or it might be a DSP card in a slot of a router at the edge of a LAN. A practical budget of $30 to $200 per port (i.e., per user) should be allowed for LAN upgrades. Some reprogramming of the edge router will be needed for voice or video, as no PSTN access was likely when the network handled only data.

E911 service requires that local dial tone be provided to each physical location, which will usually be a discrete LAN, and may then be easily identified. However, if each location is just one domain within a larger VLAN (which spans multiple sites), then identification of a specific location will be much more difficult. For details regarding the challenge of meeting E.911 requirements with IP-Centrex

WAN Requirements
The predominant service for carrying VoIP traffic is the VPN. A VPN delivers multiple service classes and interoperates well with the customer's own IP networks, at lower costs than a customer-managed network. A typical example of the four classes of service in an international VPN appears in Table 1.

Contact Center Applications

Simple uniform call distribution (UCD) has been available for some 20 years on digital Centrex offerings. The limited features with UCD are suitable only for some small call centers and are not widely used.

Full-scale ACD, based on Centrex, was first launched by NYNEX in New York City in 1990. The vital core of an ACD service for a contact center (or a multimedia call center) is the management information system (MIS) system, which delivers real-time statistics to the supervisors, and printed, historical reports to management and the system administrator. BT (formerly British Telecom), for example, identifies "FeatureNet Call Centres" as a major part of its digital Centrex service.

The design and implementation of contact centers has been one of the busiest parts of the telecommunications industry in the past decade, employing much of the talent available. The acceptance of Centrex-based ACD services has been disappointing and has not nearly matched the growth rate of premise-based contact centers over the past few years in North America. This lack of enthusiasm was due to the perceived problems of integrating in-house systems and software with a remote switch, together with concerns over the lack of administrative control.

The generally accepted allocation of operating costs for a contact center is 50% for network services, 40% for personnel, and 10% for equipment maintenance. A CO-based Centrex-ACD service can save up to one-half of the trunks that would be needed for a separate ACD system on the customer's premises. This savings is made possible because the call queuing occurs in software at the CO, rather than farther out in the network.

Also, a CO-based service can grow one line at a time, up to an open ended maximum. It is easy to handle seasonal business with Centrex, since lines can be turned up and down at short notice, adjusting costs in line with demand. The staffing aspects of contact center operation can be addressed through Centrex by taking the work to the agents, rather than bringing the agents to the center. A standby, part-time pool of agents, who work from their homes, can be easily arranged over a managed IP-WAN.

The availability of IP-Centrex, based on a common voice-data network, should remove management's inhibitions regarding Centrex-based contact centers. In the IP-based environment the physical locations of applications, including call management and customer relationship software, and of agents, are no longer significant concerns.

The shortage and cost of competent people to implement and maintain complex contact center configurations can, hopefully, be addressed by the service provider and not remain as a problem for the customer. The outsourcing of contact center business, which now employs 5% of the working population

Unified Messaging : Speech-Enabled Call Routing

Autoattendant services, which are usually available as a standard part of a voice-mail package, have not been as widely used with Centrex as with PBX systems. However, there are some mass-market Centrex applications where it is important to have an autoattendant front end.

Call routing systems are now available that have high-performance automatic speech recognition (ASR) abilities and that can work well for large, distributed organizations with hundreds of users. Such a system can be very useful for inbound, outbound, and internal calls.

For inbound communications, ASR is easier and faster to use than touch-tone dialing. Internal callers can control some features, such as initiating conference calls and forwarding calls to selected destinations, without using specific codes or keys. On outbound calls users do not need to remember dialing codes or long number sequences to call the required party. For all callers, an ASR system provides round-the-clock assistance and can be cost-effectively integrated with an IP-Centrex softswitch.

Unified Messaging

Unified messaging (UM) assembles all e-mail, fax, and voice mail messages (for both wireline and wireless devices) into a single mailbox for one user. While UM systems have been available from several vendors, for about a decade, their acceptance in the market has been quite poor, at much less than 10% of corporate users, compared with the universal utilization of voice mail. This reluctance to invest in UM can be explained by the relatively high cost of software licenses and, perhaps more importantly, the perceived cost of system management.

The proponents of UM claim that a mobile worker, with multiple single-purpose mailboxes, can greatly optimize communications management and save at least 30 minutes of working time each day. With UM, users can review, manage, and answer any electronic messages, using a desktop or mobile phone, or a PDA.

A major capability of UM is that messages can be translated to the most useful medium, so that text message and facsimile headers can be read by a synthesized voice and voice messages can be played through a laptop. A user can point and click through all the message titles and selectively listen to a desired message while quickly deleting junk mail. The possibility of outsourcing the provision and administration of UM to a service provider is one of the prime justifications for IP-Centrex.

Table 1 shows estimates of the first-year costs for implementing and operating an in-house UM system for 500 users. The continuing costs, from the second year onward, will include hardware and software maintenance (at 10% of initial costs), a system administration person, and software upgrades, all of which may amount to $1 10,000 each year.


Table 1: First-Year Costs of UM System

The total monthly fee for UM from a competitive service provider would likely be in the $20 to $30 range, or perhaps $12,000 for 500 users (i.e., $150,000 annually).

The large first-year costs for acquisition and installation so outweigh the outsourced charges that the managed UM service linked to IP-Centrex shows a worthwhile savings even after 7 years, which probably exceeds the viable system lifetime. Some advantages from owning an on-site UM system, such as better security control and immediate system management action, can be identified. These should be evaluated against the relief from management headaches that a well-managed service can provide and the choice can then be based on the organization's requirements and culture.

Wireless Capabilities

The availability of IP-Centrex, based on a common voice-data network, should remove management's inhibitions regarding Centrex-based contact centers. In the IP-based environment the physical locations of applications, including call management and customer relationship software, and of agents, are no longer significant concerns.

We can classify the solutions for in-building, wireless access to IP-Centrex into these three categories:

1. Wireless IP phones, based on the IEEE 802.11b standard, can communicate (as a data device) with wireless access points within the building. A few companies, such as Spectralink and Symbol, have been making this type of phone for a while.

2. Wireless-enabled data devices, such as PDAs, laptop PCs, and voice-capable pagers are available with IEEE802.11b and/or Bluetooth capability.

3. Multipurpose wireless handset that can work outside a building as cell phones (with GSM, CDMS, or TDMA systems), but that can also operate to proprietary in-building standards (e.g., Ericsson's Freephone) have not become widely accepted yet. These phones would need an IP gateway between the wireless access points and the IP-Centrex system.

The IEEE 802.11b standard, frequently known as "Wi-Fi," has become the dominant standard for high-rate wireless LANs and employs direct sequence spread spectrum at the physical layer. Wi-Fi operates in an unlicensed 2.4-GHz band in most countries, at a nominal bit rate of 11 Mbps, and delivers a throughput of from 5 to 7 Mbps. An extension known as 802.1 lg offers a nominal bit rate of 22 Mbps.

Although IEEE 802.11a was ratified at the same time as 802.11b (in 1999), this standard has not yet been widely adopted because it involves a radically different modulation technology. IEEE 802.11a wireless systems are intended to operate in the 5-GHz band, where 300 MHz of unlicensed spectrum should be available in most countries.

The disadvantage of moving to a higher radio frequency than that used for IEEE 802.11b is a reduced operating range, which means that the required number of APs may be quadrupled. To compensate for this, the 802.11a standard increases the recommended output to 50 mW and employs coded orthogonal frequency division multiplexing.

As the demand for wireless LAN access grows, it is likely that we will see a mixed-standard enterprise environment develop, where users' devices will be able to roam between 802.11b and 802.1la networks. As equipment prices fall, dual-mode clients and APs will become prevalent.

Equipment made to 802.11b standards can interoperate with earlier 802.11 devices, which may deliver only 1 or 2 Mbps. Most Wi-Fi transmitters radiate at a power level of 30 mW, but the standards do allow for an output of up lW, for use outdoors. There are always concerns regarding security when wireless transmission is used for telecommunications, but the 802. lx standard, which defines the authentication and encryption techniques to be employed, has strengthened the security walls around 802.11 systems.

For over a decade the widespread use of wireless LANs has been a promise for "next year" that never seems to be fulfilled. However, the combination of a powerful array of wireless voice terminals and the capabilities of IP-Centrex may lead to a growth in usage more like that of cellular radio than of wireless data networks.

Attendant Consoles

Because of the inherent DID feature with Centrex, there is less of a need for console attendants than there is with PBX. The availability of autoattendant service, to assist "lost" callers, further reduces the need for attendant personnel. Some requirements for operator assistance still remain with IP-Centrex, especially in institutions that have a highly mobile workforce, such as hospitals and universities. In that environment a PC-based console, closely integrated with the organization's directories and on-line personal diaries, is the best solution. At the departmental level, an attendant answering position based on a midlevel IP phone, with add-on programmable key modules that usually come in 48-button units, is a good solution.

Examples of IP Phones

The large telecom equipment manufacturers, such as Lucent and Nortel, are addressing the IP phone market with just one or two models, compared with the wide variety of telephones that they previously made for their legacy Centrex and PBXs. Presumably these vendors hope to rationalize their production line and minimize the costs of making large quantities of a standard set. The first generation of IP phones from these large companies, including Cisco, were proprietary devices that could only be used with that vendor's switches. The trend now is to produce sets that are based on the SIP or Megaco standards, or both.

Other independent phone suppliers (such as Aastra, Avanti, Pingtel, Telcordia, and Telrad) are offering intelligent, voice-over-IP phones to complement the features of IP-Centrex. Well-established, high-volume handset producers, such as Samsung and Sony, are also supplying this market.

Two telecom manufacturers, Mite1 and Siemens, have earned a reputation for ergonomically excellent telephone terminals, and both produce a range of IP phones. Mitel has five IP phone models, including a low-cost, single-port unit and the 5140 IP Appliance, which is pictured in Figure 3. The more expensive device has a 320-by-240 pixel display and an infrared adapter (IrDA) interface, which provides a link to (personal digital assistants) PDAs. This phone enables users to define icons to represent telephony features, using the Palm-based graphical interface.


Figure 3: Mitel's 5140 IP Appliance. (Reproduced with the permission of Mitel Networks.)

The Mitel 5140 also has a built-in Hypertext Markup Language (HTML) browser and integrated directory management capabilities. It can be used as an agent's or supervisor's workstation in an automatic call distribution (ACD) configuration.

An interesting and forward-looking type of IP phone is one that is essentially a PDA cradle, built to accommodate a Palm Pilot or a similar device. The PDA provides a color screen display and most of the processing power, as well as its built-in operating system, applications, and database. This keeps the cost of the phone itself very low and provides a powerful desktop terminal.

The Siemens IP phone brand is optiPoint; these were the first sets from a major telecom manufacturer to support SIP. The optiPoint 100, for example, has both 10 Mbps Ethernet and RJ-45 interfaces and includes the G.711 (64 Kbps) and G.723.1 (5.3 Kbps) voice encoding algorithms. It has a two-line, 24-character display and is a hands-free, speakerphone set.

A major advantage with IP phones is that, when moved, these phones automatically reregister with the communication system, providing access to the voice services within a few seconds. Most IP phones also integrate with HTTP-based system management packages to allow for fast and intuitive moves, adds, and changes (MAC).

Telephone Sets and Consoles

Some users will be satisfied with having a softphone as their only voice terminal, but we cannot assume that the PC, with added software, headset, and speakers, will largely replace telephone sets, as the PC is awkward to use, not always switched on, and certainly less reliable than a single-purpose phone. Most users still seem to prefer having a real telephone, with which they can dial, talk, and listen in a familiar fashion.

Numerous manufacturers are attempting to fill the need for IP-compatible phones and most of those will be based on the SIP standard. Some years ago there were predictions that ISDN-compatible telephones would become commonplace, low-cost devices, in conjunction with PBXs or Centrex. This has not happened because ISDN is an expensive technology to implement and this type of phone has not become a high-volume production item.

IP telephones are akin to ISDN sets in that they cannot easily be supplied with DC power from the central office and must be powered locally. Commonly an ac plug-in power cube is used for each phone, but a better method is to install a power supply unit (PSU) in the closest telecom closet (TC). The DC power is supplied to a number of sets over the LAN wiring and the PSU can be backed up by a small UPS in the TC.

However, the $100-IP phone became a reality in the early days of IP-Centrex, as Ethernet NICs and SIP chip sets both cost just a few dollars. The IP-Centrex service providers cannot expect to generate revenue from the rental of IP phones in the future, because these will become commodity items and will be mostly purchased from highly competitive retailers.

A two-level market in IP phones has developed as the less-demanding users' needs can be met by generic sets that implement just the requirements of the SIP standard. At the higher level of sophistication, manufacturers add their own features on top of SIP and therefore create proprietary sets that cost significantly more. The market for IP phones will simply reflect that for mobile/cell phones, most customers pay less than $100 for a handset, but some users (perhaps 20% of the total) are willing and able to pay well over $200 for a feature-rich handset.

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.