|Latin America III 2001
|Too Many Wires
|Director of Business Development
|Hughes Software Systems, USA
Urban growth in Latin America has outpaced the growth of voice, data and video telecommunications services. These services tend to be expensive, lack reliability and are hard to obtain. One solution is the convergence of data, voice and video services on to single high-bandwidth lines using ATM technology to help maximise the traffic-handling capacity of existing networks. This solution, nevertheless, presents a series of challenges which the ITU, by providing effective standards, has helped to minimise.
The steady growth of urban areas in Latin American countries has exposed the serious lack of resources available for telephone and Internet connectivity expansion within these regions. Numerous businesses are finding it difficult to obtain the bandwidth, phone lines and telephony services they need to conduct business and manage their day-to-day activities. Additionally, the services they can obtain are expensive and not necessarily reliable. Too Many Wires In a traditional circuit-switched network, a path is dedicated to a call for the duration of the call. While in use, this path cannot be utilised by other calls, even during periods of silence in the conversation. Although the presence of a dedicated path guarantees reliable and immediate transmission of voice, the utilisation of bandwidth is not efficient. For each concurrent conversation occurring, another dedicated line is required. Large businesses, or small businesses with heavy call traffic, require dozens of expensive phone lines that each require a physical connection to the telephony network. The high costs associated with multiple lines and the difficulty in securing these multiple connections can be prohibitive even in large cities. Additionally, the often necessary requirement of connecting multiple corporate offices to a single circuit to share calls can be complex. A solution is needed that can reduce telephony network costs, make better use of bandwidth, and solve the complicated logistical issues of physical wires for each phone line. The ATM Solution Asynchronous Transfer Mode (ATM) is a multi-service, high-speed, scalable technology that has been designed to carry voice and all types of data, such as facsimile and multimedia over a single fibre line. Voice over ATM (VoATM) provides a platform for the transport of plain old telephone service over a digital, broadband access network. VoATM can support toll-quality voice, a Quality of Service parameter associated with traditional circuit-switched networks. In addition, ATM provides efficient use of band-width, high network efficiency and, therefore, lower operational costs. The Wide Area Network (WAN) environment today is made up of a variety of services fulfilling the requirements of a multiplicity of applications. Each service provides unique benefits for certain communication needs. However, ATM, being a multimedia, multi-service technology, has the potential to support all network applications more efficiently than any other single internetworking protocol. This leads to improved performance and lower communication costs for both the service provider and the user. With the standards already evolved, ATM’s capacity to transport voice and deliver high-quality speech has been recognised. The advantages of ATM are: ,b>Maximum network utilisation: ATM provides virtual networking, making statistical multiplexing of traffic over any network resource possible. Virtual networking attempts to utilise as much of the network as possible, thus conserving relatively limited WAN fibre. Network capacity is shared among the numerous phone calls and data services occurring on a network at any one time. Considering that typical networks utilise only 35 per cent of the available bandwidth and waste the rest during idle, quiet, times ATM networks can take full advantage of network bandwidth by allocating resources and bandwidth to a user only when required. This allows the network to support more users, usually twice the number of users that a typical Time Division Multiplexed network can support. High-quality phone service: ATM supports extensive Quality of Service, which ensures the reliable transmission of voice traffic across a network. While typical Voice over IP (Internet Protocol) conversations are filled with static and echoes, VoATM supports clear, full duplex conversations that are undistinguishable from standard phone quality. Traffic management built in: ATM switches have been designed with effective traffic management capabilities. For example, call admission control, usage parameter control and traffic shaping are supported. Supports multiple services on a single line: ATM supports the transfer of voice, data and video signals. ATM can easily inter-network with the Public-Switched Telephone Network. In addition, different ATM Adaptation Layers provide support for different service class capabilities. No longer do you need separate networks and separate services for your voice and data needs. ATM brings true convergence to your telephone and networks needs. However, Not All Is Rosy While ATM does provide low cost, single line solutions to many of the challenges facing businesses and homeowners in Latin American countries, the transport of voice across an ATM network requires that a number of technical challenges be successfully managed if the network is to provide an effective voice transport mechanism. The convergence of data and voice traffic on a single network yields significant economic benefits, but, at the same time, it presents technical challenges. Must Cut Down Delays Have you ever made an international phone call and had a 2-3 second delay or loud echo within your conversation? While this still occurs, typical phone circuits now contain echo cancellors to reduce the echo and delay that occurs during a conversation. In a VoATM environment this problem must be managed ‘up front’ for the service to be acceptable. There are a number of issues that must be addressed to make ATM delays acceptable to end-users. Because ATM networks transfer voice and data in packets, there are delays created in encoding the packets, buffering the data, and filling the packets with the correct amount of data. A method is needed to reduce the time ATM networks spends encoding data and creating the necessary packets. Silence suppression The characteristics of voice can be employed to advantage for optimal use of available bandwidth. A normal flow of conversation consists of pauses between sentences and periods of silence when there is no speech. Voice communication is typically half-duplex-that is, one person is silent while the other speaks. These characteristics can be used to save bandwidth by halting the transmission of packets during such periods of silence. This is known as silence suppression. ATM implantations must take advantage of silence gaps in conversations to increase network utilisation. Synchronisation When voice is transported across a network, it is important to synchronise the data that is transmitted from the speaker to the listener. This can be achieved by employing standard mechanisms. In case of ATM, the easiest solution (owing to the availability of the global timing standards) is to adopt an externally synchronised model, where each node is synchronised to some external clock source. ATM services must have these synchronisation features built in to make them usable. The Emergence of a Standard The International Telecommunications Union/Telecommunication Standardisation Sector (the ITU-T) has created a standard for ATM data/voice usage known as AAL2. AAL2 provides for the bandwidth-efficient transmission of low-rate, short and variable packets for delay-sensitive applications. AAL2 also provides bandwidth reduction support because of voice compression, silence detection /suppression and idle voice channel removal. AAL2 supports multiple-user channels on a single ATM virtual circuit and also supports varying traffic conditions for individual users or channels. User Benefits of AAL2 A major benefit of ATM trunking using AAL2 for narrowband services is bandwidth savings. This can be achieved by: o Compressing voice. When voice is compressed, lesser bandwidth is allocated per call. o Releasing bandwidth when the voice application does not need it. Bandwidth can be released when the talker is silent or when the call is completed. o Routing and switching narrowband calls on a per call basis. This leads to further improvements in performance and efficiency. The result is a usable, practical ATM solution that can bring voice and data convergence on a single line to end-users around the world. The Future Telecommunications companies around the world are beginning to build solutions around the AAL2 protocol. Telephonic software companies have now developed software stacks and tools that are making it easier to build, support and implement ATM solutions based on AAL2. One such solution, called Loop Emulation Service (LES), drastically reduces the developer’s time to market and provides rapid application development for VoATM-based product development. Besides being a modular, scalable, portable stack, a LES stack can be customised for national specifications. A reference model of LES, which uses AAL2, is depicted in the Figure. The reference model consists of three main components: o AAL2-enabled Customer Premises Equipment/Customer Premises Inter-working function (CPE/CP-IWF). This gives voice packets priority over data calls, ensures toll-quality voice delivery and sends the packets over Digital Subscribers Link (DSL) lines. o ATM-based switched or permanent virtual circuits, which are used to connect the customers premise with the central office. o Voice gateway, which ‘unpacks’ voice packets and converts them to a standard format for transmission to a voice terminal. What it Means for your Business… Owing to its low operational costs, multi-service capability and higher network efficiency, ATM is emerging as a solution for service providers and network operators, especially in the WAN environment. These solutions will especially help companies in areas of the world such as Latin America that do not have the infrastructure in place to lay additional phone lines and provide the necessary services. Mr. Ajay Kumar Gupta is the Vice-President and General Manager of Hughes Software Systems Operations in the Americas. Mr. Kumar has been working in the field of communications for over 14 years and has been involved with both RF and Terrestrial communications. Conclusion Previously, Mr. Kumar worked with Hughes Network Systems (India). He was responsible for the Business Development of the Wireless Local Loop Product line of Hughes in and around India. He was also involved in setting up Hughes Ispat Limited, the basic telephony operator in the state of Maharashtra. Mr. Ajay Kumar Gupta has done his Masters in Systems Engineering from the Indian Institute of Technology Kharagpur and Bachelors in Electrical Engineering (Communications) from Jawahar Lal Nehru University.