US Robotics USR2450 Información técnica descargar pdf (Pagina 97)

V 2.2 Copyright SystemExperts 2001,2002,2003

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Glossary(cont.)

GPRS (general packet radio service) A technology that sends packets of data across a wireless network at speeds of up to

114Kbps. It is a step up from the circuit-switched method; wireless users do not have to dial in to networks to download

information. With GPRS, wireless devices are always on—they can receive and send information without dial-ins. GPRS

is designed to work with GSM.

GSM (global system for mobile communications) A standard for how data is coded and transferred through the wireless

spectrum. The European wireless standard also used in Asia, GSM is an alternative to CDMA. GSM digitizes and

compresses data and sends it down a channel with two other streams of user data. The standard is based on time division

multiple access.

HDML (handheld device markup language) It uses hypertext transfer protocol (HTTP, the underlying protocol for the Web)

to allow for the display of text versions of webpages on wireless devices. Unlike wireless markup language, HDML is not

based on XML. HDML also does not allow developers to use scripts, while WML employs its own version of JavaScript.

Phone.com, now part of Openwave Systems, developed HDML and offers it free of charge. Website developers using

HDML must recode their webpages in this language to tailor them for the smaller screens of handhelds.

iDEN (Integrated Digital Enhanced Network) A Motorola-enhanced mobile radio network technology that integrates two-

way radio, telephone, text messaging, and data transmission into a single network.

I-Mode A wildly popular service in Japan for transferring packet-based data to handheld devices. I-Mode is based on a

compact version of HTML and does not use WAP, setting it apart from other widely used transmission method.

Industrial, Scientific, and Medical (ISM) An unlicensed Radio Frequency spectrum used primarily for industrial, scientific,

medical, domestic or similar purposes, excluding applications in the field of telecommunications These bands support

spread spectrum operation on a non-interference unlicensed basis. Operation in this band is authorized under FCC Rule

Part 15.247. Spread spectrum systems share these bands on a non-interference basis with systems supporting critical

government requirements, secondary only to ISM equipment operated under the provisions of Part 18. Many of these

government systems are airborne radiolocation systems that emit a high ERP, which can cause interference to other users.

Multipath Effect The effect that occurs when a transmitted signal is reflected from objects resulting in multiple copies of a

given transmission arriving at the receiver at different moments in time. Thus the receiver receives multiple copies of the

same signal with many different signal strengths or powers.

OFDM (Orthogonal Frequency Division Multiplexing) A multi-carrier transmission technique, which divides the available

spectrum into many carriers, each one being modulated by a low rate data stream. This is the basis for ADSL as well

PCS (personal communications services) An alternative to cellular, PCS works like cellular technology because it sends calls

from transmitter to transmitter as a caller moves. But PCS uses its own network, not a cellular network, and offers fewer

"blind spots"—areas in which access to calls is not available—than cellular. PCS transmitters are generally closer

together than their cellular counterparts.

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Glossary(cont.)

PDA (personal digital assistant) Mobile, handheld devices—such as the Palm series and Handspring Visors—that give users

access to text-based information. Users can synchronize their PDAs with a PC or network; some models support wireless

communication to retrieve and send e-mail and get information from the Web.

Physical Layer Convergence Protocol (PLCP) A protocol specified within the Transmission Convergence layer that specifies

exactly how cells are formatted within a data stream for a particular type of transmission facility.

Physical Medium Dependent (PMD) Performs wireless encoding

Satellite phone Phones that connect callers via satellite. The idea behind a satellite phone is to give users a worldwide

alternative to sometimes unreliable digital and analog connections.

Service Set Identifier (SSID) An identifier attached to packets sent over the WLAN that functions as a "password" for joining

a particular radio network (BSS). All radios and access points within the same BSS must use the same SSID, or their

packets will be ignored

SMS (short messaging service) A service through which users can send text-based messages from one device to another. The

message—up to 160 characters—appears on the screen of the receiving device. SMS works with GSM networks.

Symbol A term for the information contained in a message. I can be though of as a discrete block of digital information.

TDMA (time division multiple access) This protocol allows large numbers of users to access one radio frequency by

allocating time slots for use to multiple voice or data calls. TDMA breaks down data transmission, such as a phone

conversation, into fragments and transmits each fragment in a short burst, assigning each fragment a time slot. With a cell

phone, the caller would not detect this fragmentation. Whereas CDMA (which is used more frequently in the United

States) breaks down calls on a signal by codes, TDMA breaks them down by time. The result in both cases: increased

network capacity for the wireless carrier and a lack of interference for the caller. TDMA works with GSM and digital

cellular services.

WAP (wireless application protocol) WAP is a set of protocols that lets users of mobile phones and other digital wireless

devices access Internet content, check voice mail and e-mail, receive text of faxes and conduct transactions. WAP works

with multiple standards, including CDMA and GSM. Not all mobile devices support WAP.

WASP (wireless application service provider) These vendors provide hosted wireless applications so that companies will not

have to build their own sophisticated wireless infrastructures.

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