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A White Paper on Telephony to Voice over Wireless LAN(VoWL)

Filed under: Pbx

By: Vijay Kaul

Telephony to Voice Over Wireless LAN.
A complete piece of apparatus for making and receiving calls is called a Telephone Instrument.
Analog and Digital Telephone Instruments.
Analog information-- like sound-- is, in a physical sense, a waveform. Digital information is simply numbers, ones and zeros. Analog phone lines carry waveforms, while digital phone lines carry bits. (A bit is either a zero or a one.)The conversion of analog to digital then, is the conversion of waveforms to bits. Analog information needs to be represented in binary numbers (1 and 0) in order for the computer to understand. This means that the analog information is divided into sections that are assigned numbers. For example, a continuous wave of a tone would be represented by a large number of squares that, from a distance, resolves into what appears to be a smooth curve, but up close you can see that it isn't really continuous, like a picture in a newspaper. From far away, you see complete pictures, but the closer you look you see that it's just made up of dots. And with the way the mind works, if you get a significant amount of those dots, it looks like a continuous picture.
This holds true for sounds as well. A record is analog data. The voice, or musical sound, goes into an amplifier, which then moves the needle to carve the sound waves in vinyl. When you play back the record, the needle jiggles and is amplified and heard as sound waves.
Digital information is not a perfect representation of sound data, but if you do a high-enough number of samples, it's indistinguishable from the wave form. One advantage to digital sound information is that you can process the digital information in a number of ways and you can store more data on a smaller amount of space. Most importantly, however, digital information is more resistant to degradation and errors. Analog signals get noisy over time and distance, digital signals are just ones and zeros, so they don't get "fuzzy."
KTS-Key Telephone Systems
Often referred to as just KTS, a key telephone system is a premises telephone system that is best known by the phones that have buttons for calling inside an organization and for placing calls outside through the public telephone network. A key telephone system is in the same category as a PBX (private branch exchange), except that key systems rely on the telephone company switching equipment, while PBXs rely on a central control unit located at the customer site. In other words, with a key system, the dial tone is generated at the telephone company central office. A full PBX generates its own dial tones.
Key systems also do not require dialing a number to gain an outside line since all lines are already directly connected to the telephone company central office. On a PBX system, lines are connected to the PBX, and the PBX makes connections to the central office when the outside number is dialed
Designed primarily for small and medium businesses requiring from two to 130 multi-functional telephone sets and/or line combinations. The system resides on the customer's premises and can operate either on its own or in conjunction with a Private Branch Exchange (PBX). A key system or key telephone system is a multiline telephone system typically used in small office environments.
Key systems are noted for their expandability and having individual line selection buttons for each connected phone line, however some features of a PBX such as dialable intercoms may also commonly be present.
PBX (Private Branch eXchange) is a privately owned telephone switching system for handling multiple telephone lines without having to pay the phone company to lease each line separately.
Normally a telephone line is connected to the phone company's local Central Office through "a trunk." The Central Office is responsible for routing incoming and outgoing calls. It also provides other services like voice mail, call forwarding, caller ID and so on. For this service the phone company receives a monthly fee. A company requiring dozens or even hundreds of phones would quickly incur a very large phone bill!
A PBX essentially takes the place of the phone company's Central Office within the company by acting as the exchange point, routing calls. With a PBX in place, each phone only needs an extension, not a phone number, and the PBX handles all calls made from desk-to-desk within the company.
When an outside call is required, an access number is dialed first. The PBX then transfers the call to the phone company's Central Office. From there the call is routed normally.
A PBX reduces cost because the company only pays for the number of lines liable to be connected at any given time to the outside. If a company has 100 telephones, it's unlikely everyone will be making an outside call at once. Perhaps only 10%25 will require an outside line at any given time. Therefore the company would lease 10 lines from the phone company rather than 100.PBX systems can be bare bones or feature-rich, depending on what the customer is willing to pay. Voice mail, call forwarding, conferencing, intercoming, and transferring are just some of the options available.In a typical office environment, the PBX system connects multiple incoming phone lines to multiple telephone extensions.
Centrex
Before the advent of VoIP there were, broadly speaking, two ways to provide office workers with telephone service, an organization can install a PBX which switches calls within the office, connects the office phones with the larger telephone network, and delivers services such as voice mail and automated attendant. an organization can contract with the telephone company to provide the same services using the switch installed at the telephone company's premises. This service (telephone company hosted switch) is called Centrex.
Advantages of Centrex over a PBX?
Centrex is offered by a service provider who is responsible for purchasing, installing, maintaining, and operating the necessary equipment...In contrast having a PBX means in essence being your own telephone company. You become responsible for everything although, of course, you can subcontract any or all of these responsibilities. Which is less expensive depends on many factors and requires a careful analysis to determine the approach best for each situation The availability of Centrex provides an exciting new alternative to existing approaches to provide telephone services to organizations professionally.
IP telephony
IP telephony, also known as Voice over IP (VoIP), is the use of Internet protocols to carry telephone calls. Previously all telephone calls travelled over wires and circuits dedicated to voice communications. With VoIP, telephone calls are converted into data and then the data travels over circuits along with other data such as email, web traffic, and file transfers.
There are many advantages to using IP telephony over traditional approaches to voice communications:
1. The cost of sending data over the Internet is insensitive to distance. An email across the Atlantic costs the same as an email across the office. By converting voice calls into data, VoIP can exploit this distance-insensitive pricing model enjoyed by email.
2. The cost of installing two separate sets of wires in the office, one for voice (the telephone circuits) and one for data (the LAN) becomes redundant. Organisations can reduce costs and improve efficiencies by only needing one communications infrastructure.
3. Until recently the cost of the computing power to switch telephone calls was sufficiently high that it made sense to put all the intelligence into a central switch (the central office or PBX) and make telephones particularly dumb. Now, however, microprocessors are cheap and phones can be very intelligent. But that intelligence needs an equally flexible infrastructure. Telephone wires cannot provide that.
Four product migration paths are currently available to PBX customers to move to IP.
They are:
1.IP-enabled circuit-switched PBX.
2. Pure client/server IP-PBX designs.
3. Converged IP-PBX designs.
4. IP-PBX capping: working behind a circuit-switched PBX
Hybrid keyphone systems-IP-KTS
Into the 21st century, the distinction between key systems and PBX has become increasingly confusing. Early electronic key systems used dedicated handsets which displayed and allowed access to all connected PSTN lines and stations. The modern key system now supports ISDN, analogue handsets (in addition to its own dedicated handsets - usually digital) as well as a raft of features more traditionally found on larger PBX systems. The fact that they support both analogue and digital signalling types gives rise to the "Hybrid" designation.
The IP/KTS is best thought of as a specialized network server offering VOIP (Voice Over Internet Protocol) services to users and allowing data and voice communications to share the same common infrastructure. Sharing the existing data networking infrastructure primarily provides cost savings but also offers several tangible benefits, such as:
IP Centrex
IP Centrex is a service which provides full-featured telephone service to office workers over the Internet from a switch located at the service provider's facility. The primary difference between traditional Centrex and IP Centrex is that the old-fashioned service required every phone in the office to be connected by separate circuits to the telephone company's central office (CO). This reliance on the wires from the CO limited the number of companies that could offer the service and increased the costs. IP Centrex is delivered over the Internet which eliminates the choke hold the telcos have on traditional Centrex. The result is a more competitively priced offering with more features.Because IP Centrex is not tied to traditional telephone circuits, it is easy to provide service to geographically distributed operations. A company with branch offices can all be part of the same service.IP Centrex does not require the considerable investment in circuits to connect the office phones to the central office and therefore can be offered by many more companies (i.e. increased competition) and at a lower cost (because it does not require the same infrastructure)
IP Centrex is free of the geographical contraints of traditional telephone services making it easy to integrate remote offices, home workers, telecommuters, and indeed travellers in hotels with the office phone system IP phones know their identity (unlike older analog phones) and the maintenance costs associated with office moves is eliminated.Changing offices? Merely take your phone with you and your calls follow! Travelling to New York. Take your phone with you, plug it into the hotel's network and make and receive calls as if you never left the office.
W-PBX
Wireless PBX is Equipment that allows employees or customers within a building or limited area to use wireless handsets connected to an office's Private Branch Exchange system. The various ways this is implemented is explained below.
Wireless LANS
A wireless LAN (WLAN) is a flexible data communication network used as an extension to, or an alternative for, a wired LAN in a building. WLANs are useful when employees are on the move, in temporary locations or where cabling may hinder the installation of wired LANs. WLANs may also be used to connect terminals to printers and other devices. The technology avoids the use of costly T1 leased lines often employed in inter-building connections (including WLAN point-of-sale applications such as setting up cash registers in a seasonal display area). They are easy to install, offer the same transmission rates as wired LANs and adequate security. However, the market is widely viewed as vendor-driven and many potential users need to be convinced the products are worthwhile.
VoWLAN
It is currently estimated that up to 80%25 of workers are potentially mobile around their workplace and may have a need to access wireless voice communications onsite. The implementation of wireless LANs (predominantly based on 802.11b and 802.11g standards operating in the 2.4 GHz band) to carry data has lead some vendors to eagerly promote the idea that adding IP enabled wireless handsets to a data network is a relatively simple, inexpensive and reliable method of delivering voice over wireless LAN (VoWLAN). This has lead to declarations that DECT systems, traditionally used for wireless PABX, will not be able to survive in the medium term.
Despite this hype, the consensus of panellists at the Wi-Fi VoIP Futures Summit at the VON trade show held in Boston in September 2003 was that "...there are a number of challenges that must be met before voice over Wi-Fi goes mainstream....VoWLAN won't see widespread adoption until certain technical hurdles are addressed."1 This paper seeks to dispel some of the hype and highlight some of the limitations potential users should be aware of that are inherent in the 802.11 solutions being offered today.
Wireless Voice - User Requirements
As a starting point, it is useful to summarise the minimum requirements that users in large enterprises demand for wireless voice applications. We will then examine whether these requirements are met by 802.11b/g WLAN standards.· Equipment should be based on uniform industry standards, with interoperability between equipment from all vendors to ensure users are not locked into costly proprietary systems.· A consistently high level of voice quality of service (QoS) is absolutely paramount,particularly with calls to external customers or in critical applications such as healthcare or manufacturing control.
System performance cannot be compromised by interference from other technologies sharing the frequency band or by system load.· Seamless handover of calls on the move between base stations / access points is an essential component of voice QoS.· Radio coverage needs to extend to wherever mobile workers may be. This may include store rooms, canteens, loading docks and outside smoking areas typically not covered by WLAN.
· Users expect their wireless system to be able to be configured to be able to make or receive a mobile phone call on demand.· The wireless network should be totally secure, with encryption of calls considered essential.· Handset performance such as battery life, robustness and the delivery of PABX functionality must match commercial and industrial user expectations.

Vijay Kaul is a Technology man doing Business Analytics, Consulting and Project Management for the Information %26 Communication Technology Practice of A Growth Consulting M.N.C. as an Industry Analyst .Vijay's greatest asset is his domain knowledge of both Telecom %26 I.T. domains and his understanding of the Markets in the Asia-Pacific. With his past experience of about 14 years, Vijay is all set to face new challenges globally in the fields of mar