Tech-Trek
Wireless Datacom
Wireless Data Communications: The increasing demand for access to information services anytime, anywhere, has created a new emphasis on taking advantage of existing and emerging analog and digital wireless technologies and expanding them for the future.
Wireless Data: An Information Access Solution for a Mobile Society Access to information anytime, anywhere, is becoming a key component of today's business environment. By expanding into the wireless marketplace, service providers can bring information access closer to the customer and support the increasing demand for mobile communications. As more companies begin to support telecommuting and work-at-home programs for their employees -- in addition to the usual business demands of those on the road who need immediate access to information -- convenient, reliable, robust, and untethered connectivity is becoming essential for the successful employee of the future.
Wireless data communication addresses this constant and growing need by enabling service providers to offer remote information applications such as access to the Internet and on-line services, messaging, e-mail and databases. Given their ability to provide these and other important ways to access information, both existing and emerging wireless data technologies from client devices to infrastructure solutions are gaining momentum. There are several viable wireless communication technologies that are able to provide the necessary performance standards for transmitting data. Currently, the most widely used platform is analog Circuit-Switched Cellular (CSC), which is available to about 96 percent of the United States. In addition, other wireless technologies are emerging to support information access, including Cellular Digital Packet Data (CDPD), RAM Mobile Data, Global System for Mobile Communications (GSM), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA), all of which are digital cellular technologies that are expected to play a major role in wireless communications in the future.
Transmitting Data in an Analog CSC System In order to support efficient and reliable data services, analog CSC wireless service providers (WSPs) need to implement modem pools into their networks. The modem pool serves as a gateway that routes data between a WSP's network and a land-based network. Data services supported by modem pools vary with the type of wireless network and can include asynchronous data and fax, as well as direct access to Internets. Data can be transmitted over analog cellular networks in packets over circuit-switched channels. Although data communications over analog cellular voice channels has been technologically possible for many years, data throughput was minimal when using standard wireline modems because CSC networks were primarily designed for voice transmission.
There are three basic CSC data transmission modes: 1) calls connected directly to the host modem, 2) calls utilizing modem pools in the cellular network for reliable PSTN connectivity, and 3) calls directed to the Internet or other information networks via modem pools. In the first mode, data moves directly from cellular switch to the Public Switched Telephone Network (PSTN) if error correcting protocols exist at both the client and host modems. In the second mode, a modem pool is used between the cellular switch and the PSTN to reduce or eliminate incompatibility issues between the remote cellular modem and host landline modems. This also provides the WSP with a platform to offer additional billing and service packages for wireless data usage. The final mode is the most exciting and fastest growing wireless data opportunity for WSPs. By integrating a modem pool with the proper gateway technology, WSPs can offer customers direct access into data stores via the Internet, X.25 networks, and other networks that bypass the PSTN. In a typical mobile-to-land scenario, the cellular subscriber dials the land-based network. The call is routed by the WSP's switch to a modem pool, such as the Total Control Wireless Access System. A cellular modem within the access system answers the call, then makes a second call over the PSTN to the destination land-based modem. Once the land modem answers the call, a two-way connection is made between the cellular modem and the land modem. The process works in reverse when a land-based modem calls a cellular subscriber. Several emerging end-user trends - economic and equipment-based - are shining a positive light on the potential growth of CSC acceptance for wireless data transmission: Decreasing air-time charges for CSC use ; Falling prices for mobile computing equipment; Increasing shipments of highly powered portable PCs and PC Card (PCMCIA) modems; Growing demand for access to various information services; Continuing corporate support of telecommuting and mobile worker connectivity; Increasing corporate use of the Internet . In addition, with the progress and proliferation of new software applications and end-user devices designed to support CSC, the U.S. subscriber base is expected to grow. The wireless data communications arena may be considered in its infancy, but a number of factors are speeding its growth: a growing subscriber base, a corporate workforce that is becoming more mobile, the existing cellular platform of analog CSC, and emerging digital technologies such as CDMA and GSM. Wireless data is a viable, convenient, cost-effective solution for providing information access anytime, anywhere. --Saumitra [D9]
DVD Drives
As we are moving towards 21st century the complexity and the vastness of the data at our disposal is increasing. To compete with this ever increasing data and to store such vast amount of data we need a device with large storing capacity, DVD is one such option. DVD stands for ‘Digital Versatile Disc’.
A DVD which would look no bigger than a conventional CD can hold as much as 26 times more information than a CD . A normal CD can store to a maximum of 730 MB; which stores the data in form of microscopic pits the variations in the pits and flats on the recording surface are proportional to the data signal. The vast increase in the storage capacity of DVD is achieved by reducing the size and the space between the individual storage element this allows more data to be placed in same space. DVDs can have two layers of information in one sided disc, these two layers are separated by a semi-transparent layer which allows reading of both layers to be read by player.
All the existing CDs & other types of disc can be read using DVD player. DVD can be single sided or double sided and are structured as opposite track path & parallel track path. Parallel track path disc, the first layer is read from inside to outside & second layer is read from the same direction. In case of opposite track the disc is inside to outside with the middle area connecting the first track to the other, second track is read from outside to inside. The disc has special ‘lead in’ area which tells the player what the disc contains &’lead out ‘area which signals end of program.
The digital video and audio compressing is done by using technique called MPEG2 encoding . A Variable Bit Rate Encoding is used because the same can be used for audio & video. — Prasad [TE Elecs]
