| Introduction The term VoIP refers to the transfer of | | | | caused when dealing with several software packages |
| Voice over the Internet Protocol (IP) of the TCP/IP | | | | and platforms. |
| protocol suite. Using "VoIP" technology we can make | | | | ü Maintenance (Upgrades to existing services or |
| traditional telephone calls from either computer or | | | | introducing new services) can be easily done, as most |
| phone to other computer or phone using both public | | | | applications are actually software based and do not |
| switched telephone network (PSTN) and internet | | | | require any hardware replacements and configuration. |
| (which is packet switched network). All you need is an | | | | ü Smart Net - Being software based, VoIP |
| Internet connection for VoIP. This technology really | | | | products and services enable various smart solutions. |
| changes everything because it allows people to | | | | Achieving the same management capabilities on |
| receive phone calls from anywhere that an internet | | | | standard PSTN requires substantial hardware changes |
| connection exists, just in the same way you can | | | | whilst most of the VoIP solutions can easily managed |
| receive your emails anywhere that you can connect | | | | by a click of a mouse. An example could be the |
| to the internet. | | | | routing of a phone call to a subscriber in a predefined |
| The term "VoIP technology" covers a range of | | | | way: a schedule is set, and all phone calls are diverted |
| technologies, including voice-over-IP (VoIP) and | | | | to different locations (e.g. Home, Cellular, Business, and |
| fax-over-IP services, which are carried over both the | | | | Voicemail) according to this schedule. Performing this |
| Internet and private IP-based networks. VoIP is part of | | | | capability in VoIP networks is trivial (Software solution), |
| packet voice, which includes | | | | while achieving the same functionality on standard |
| voice-over-asynchronous-transmission-mode (ATM) | | | | PSTN requires a great deal of effort. |
| and frame-relay networks, which run faster than IP but | | | | ü New age multimedia - Because we treat voice |
| are less common. VoIP connects across combinations | | | | as data and due to the fact that we can use voice |
| of PCs, Web-based telephones, and phones | | | | services and telephony services from our PC, We can |
| connected via public telephone lines to remote voice | | | | use voice applications as another application on our |
| gateways. Because information travels in discrete | | | | computer. In that way we can use the same |
| packets, it doesn't need to rely on a continuously | | | | hardware to browse the net, talk over the phone and |
| available switched circuit. | | | | work on other applications at the same time and |
| Using VoIP we can enhance the traditional PBX by | | | | without having to switch between devices. This idea is |
| combining voice and data services onto a single | | | | also part of the convergence advantage that was |
| network. The end user devices (also called client | | | | brought up here in this section. |
| device) are normally referred to as VoIP phone are | | | | ü Evolution towards better communication |
| used in VoIP. Development of the 'VoIPphone' will | | | | services - For all the reasons mentioned above, VoIP |
| require the development of a ' system on a chip' which | | | | is an evolution towards better communication services. |
| combines digital signal processing (DSP) functions, | | | | We can combine voice with streaming video for |
| micro-controller (MCU) functions, analog interface, | | | | conference calls, allow better multimedia by using all |
| telephone user interface and associated glue logic. | | | | sorts of web applications and offer customers with |
| Uses of VoIP VoIP service is deployed in enterprise | | | | better communication services (such as the smart net) |
| and service provider network for various reasons. | | | | in order to get a communication package that will be |
| Most of these can be categorized into following. | | | | adjustable and will be configured to supply every |
| Ø Better bandwidth utilization by: | | | | customer needs. |
| § Using compression | | | | Main Issues of VoIP For VoIP to become popular, |
| § Exploiting silence periods during conversations | | | | some key issues need to be resolved. Some of these |
| § Sharing of equipment for voice and data traffic | | | | issues stem from the fact that IP was designed for |
| (unified processing) | | | | transporting data while some issues have arisen |
| Ø Introduction of new services: | | | | because the vendors are not conforming to the |
| § Conferences, distance learning, etc. | | | | standards [3]. |
| Working of VoIPThe basic steps involved in originating | | | | The key issues are discussed below. |
| an VoIP call are conversion of the analog voice signal | | | | Interoperability In a public network environment, |
| to digital format and compression/translation of the | | | | products from different vendors need to operate with |
| signal into Internet protocol (IP) packets for | | | | each other if Voice over IP is to become common |
| transmission over the Internet; the process is then | | | | among users. To achieve interoperability, standards are |
| reversed at the receiving end -- switching the digital | | | | being devised and the most common standard for |
| format back to analog so the telephone call goes | | | | VoIP is the H.323 standard. |
| through as normal.VoIP calls originate on any | | | | Security This problem exists because in the Internet, |
| broadband line: coaxial cable, DSL (Digital Subscriber | | | | anyone can capture the packets meant for someone |
| Line), wireless or even satellite. The call is routed to the | | | | else. Using encryption and tunneling can provide some |
| VoIP Company, where a computer converts the | | | | security. The common tunneling protocol used is Layer |
| sound into data packets - similar to the packets used | | | | 2 Tunneling protocol and the common encryption |
| to transfer internet data such as email. Sending data | | | | mechanism used is Secure Sockets Layer (SSL). |
| by packets is far more efficient as it enables the | | | | Integration with Public Switched Telephone Network |
| same line to handle more information simultaneously. | | | | (PSTN) While Internet telephony is being introduced; it |
| These data packets are sent through any of the | | | | will need to work in conjunction with PSTN for a few |
| Internet's multiple networks to a recipient of the call. | | | | years. We need to make the PSTN and IP telephony |
| The caller can receive the call via a wireless provider, | | | | network appear as a single network to the users of |
| a broadband provider, or a local phone carrier. In order | | | | this service. |
| to understand VoIP it is essential to have a complete | | | | Scalability As researchers are working to provide the |
| understanding of what the difference between circuit | | | | same quality over IP as normal telephone calls but at a |
| switching and packet switching. A normal telephone | | | | much lower cost, so there is a great potential for high |
| uses circuit switching for phone calls, which involves | | | | growth rates in VoIP systems. VoIP systems need to |
| routing of your call through the switch at your local | | | | be flexible enough to grow to large user market and |
| carrier to the person you is calling. The connection of | | | | allow a mix of private and public services. |
| two points in both directions is known as circuit. Packet | | | | VoIP technology can yield big cost savings to both |
| switching on the other hand is more efficient in | | | | corporations and consumers. It is more efficient than |
| transmitting data since small amount of data, which is | | | | the plain old telephone service (POTS) and is poised to |
| called a packet, is sent from one system to another. In | | | | undergo huge growth. Before that growth can occur, |
| a VoIP system, once the called party answers, voice | | | | however, designers have to address the issues listed |
| must be transmitted by converting the voice into | | | | above. |
| digitized form, then segmenting the voice signal into a | | | | Along with the issues listed above, providing better |
| stream of packets. The first step in this process is | | | | voice quality to the customer is another major |
| converting analog voice signals to digital, using an | | | | challenge. VoIP introduces a number of potential |
| analog-digital converter. Since digitized voice requires a | | | | impairments that can impact voice quality adversely, |
| large number of bits, a compression algorithm can be | | | | such as the use of lossy low-bit-rate codec's, the |
| used to reduce the volume of data to be transmitted. | | | | effects of tandem encoding/transcoding, longer delays, |
| Next, voice samples are inserted into data packets to | | | | and packet loss. Most of these impairments are either |
| be carried on the Internet. The protocol for the voice | | | | not present or are negligible in circuit switched |
| packets is typically the Real-time Transport Protocol | | | | networks. Thus new techniques for delivering and |
| (RTP). RTP packets have special header fields that | | | | maintaining voice quality are needed for VoIP |
| hold data needed to correctly re-assemble the | | | | networks. The impairments that a voice call |
| packets into a voice signal on the other end. However, | | | | experiences can be classified as either architectural or |
| voice packets will be carried as payload by UDP (User | | | | load dependent. |
| datagram protocol) protocols that are also used for | | | | Architectural components include IP phone codec's and |
| ordinary data transmission. | | | | their configuration parameter settings as well as fixed |
| ADVANTAGES The following are some of the | | | | components of delay such as processing delays at |
| advantages of VoIP: | | | | each network element along the path and the |
| ü VoIP is cost effective - using VoIP products | | | | end-to-end propagation delay. These architectural |
| long distance phone calls and international calls can be | | | | components define an upper bound on the best voice |
| made within the price of a local call. The caller simply | | | | quality that could be achieved in a given network. If the |
| connects to the Internet (with the price of a call to his | | | | upper bound is unacceptable, then changes in |
| local Internet provider) and using the appropriate | | | | equipment and configurations will be required. In general, |
| software, calls other computers running similar VoIP | | | | if the architecture is satisfactory, then low packet loss |
| applications, or even other telephones anywhere in the | | | | and delay are sufficient to ensure good voice quality. |
| world. (Performing a PC-2-Phone conversation | | | | Load dependent impairments include packet loss, |
| requires a VoIP Gateway to be present at the remote | | | | queuing delay, and jitter. As load increases, these |
| location). | | | | parameters deteriorate and begin to degrade voice |
| A growing amount of communication operators | | | | quality. The voice quality a user experiences depends |
| throughout the world utilize VoIP as the modern | | | | on the behavior of the entire end-to-end connection. |
| communication method for long distance calls, enabling | | | | This connection may cross multiple network domains |
| a full Phone-2-Phone conversation, which is carried | | | | each with its own set of controls and management |
| over an IP network. (Fully transparent to the caller) | | | | methods. Since impairments across the connection are |
| Using the IP networks for voice transportation allows | | | | cumulative, it is possible that each network domain |
| for a greater deal of phone calls to be made | | | | delivers acceptable voice quality while the end-to-end |
| simultaneously, thus reducing the operators' costs. | | | | connection does not. |
| Furthermore, large companies can use their intranet as | | | | The networks service offering to the end applications |
| their internal enterprise phone network (iPBX). This | | | | can be measured quantitatively and qualitatively by |
| enables lower maintenance fees, and cheap | | | | means defining network Quality of Service. Managing |
| communication to remote sites and branches of the | | | | voice Quality of Service across multiple domains |
| organization. | | | | requires SLAs (Service Level Agreements) between |
| ü Convergence - By using VoIP, a company can | | | | service providers and use of signaling protocols to |
| have one comprehensive solution handling both data | | | | indicate the desired QoS. |
| and telephone communication, all on the same platform | | | | In the next chapter we have discussed about QoS, |
| and supported by a single vendor. This allows | | | | and requirements of QoS for voice. The minimum QoS |
| companies to use a single system for all their | | | | requirements needed for better voice quality in VoIP |
| communication needs and prevents the overhead | | | | networks. |