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  • Acleris' -- Telecommunications Glossary -- T1 to TVRO
    and many more innovative new network architecture approaches for voice video graphics data etc Fully supports T 120 suite and a variety of coding and transmission methods T 131 ITU T recommendation describing Real Time Stream Multipoint Communications Service T 132 ITU T recommendation describing Real time Link Management T 133 ITU T recommendation describing an Audio Video Control Applications Protocol T 134 ITU T recommendation describing a text chat application entity T 135 ITU T recommendation describing user to reservation system transactions within T 120 conferences T 136 ITU T recommendation describing a remote device control application protocol T 137 ITU T recommendation describing virtual meeting room management services and protocol T 140 ITU T recommendation describing a protocol for multimedia application text conversation Tail time In acoustic echo cancellers telephony echo cancellers and related devices the sampling window size in milliseconds used for the electroacoustic model of all the echo sources Related to the more complex AFIRF taps parameter TCP IP Transmission Control Protocol Internet Protocol Networking protocols providing communications across interconnected networks including Internet and Intranets The networks may incorporate diverse hardware architecture computers and various operating systems TCP IP includes communication connection and routing standard protocols TDD Time Division Duplex part of DECT modulation scheme TDM Time Division Multiplex the sharing of a transmission network by a number of users versus time TDMA Time Division Multiple Access the sharing of a satellite transmission network by a number of locations versus time TEC Telephony Echo Canceller an echo canceller used to eliminate echoes on the line side of AECs and other telecommunications voice equipment Telco Jargon for TELephone COmpany Temporal Filtering In video compression the recursive removal of redundant pixels on a frame to frame basis a major factor controlling final image quality Timebase Corrector TBC A

    Original URL path: http://acleris.com/info/glossary4-t.html (2016-04-29)
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  • Acleris' -- Telecommunications Glossary -- UPS to VSAT
    characteristics for balanced double current interchange circuits operating at data signaling rates up to 10 Mbps V 24 ITU T rec listing definitions for interchange circuits between terminal equipment DTE and data circuit terminating equipment DCE V Vertical Volts Velocity VAPC Vector Adaptive Predictive Coding A proprietary audio coding algorithm primarily intended for use at the lowest transmission aggregate bit rates VDSL Video or Very high bit rate Digital Subscriber Line the fastest form of xDSL it provides asymmetrical full duplex connectivity at 52 Mbps to the subscriber and 16 Mbps from the subscriber over distances of up to 1 2 Km 0 75 miles over a single pair This type of transmission does not support telephony over the same physical pair as do ADSL and RADSL Video Server An audio and video file server often with multiple terabyte hard disk capacities connected to LANs and WANs with high speed facilities like ATM or FDDI Depending on use may employ H 320 H 323 MPEG2 MPEG4 or Motion JPEG video compression for broadcasting training on demand to the desktop and many other corporate purposes including marketing Also a key technology for VoD which see VIRIS A BellCore developed VIdeo Reference Impairment System a subset of RISV useful for determining acceptable impairment levels for compression schemes including MPEG1 MPEG2 and MPEG4 H 320 H 323 and others VIRIS may be used as the preparatory phase of a P 910 subjective testing program VoD Video on Demand a combination of video servers networks infrastructure supporting software and user interface to provide broadcast pay TV training or reference data on demand Some applications also use IRD hardware as a user terminal VoDSL Voice over Digital Subscriber Loop techniques permitting transmission of telephony over DSL VoIP Voice over Internet Protocol a series of techniques

    Original URL path: http://acleris.com/info/glossary4-uv.html (2016-04-29)
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  • Acleris' -- Telecommunications Glossary -- WAN to XML
    U V W X Y Z W WAN Wide Area Network typically an inter city network Wavelet image coding Unlike the broadband DCT used for video compression for applications like videoconferencing and DBS in algorithms like H 263 and MPEG2 wavelet coding is generally narrow band with the coding and filtering tailored to a specific application Wavelet coding is especially efficient and powerful when applied to phenomena with discontinuous or spiky data Some wavelet applications include compression of well defined data sets such as signatures and fingerprints At the other extreme wavelet coding may be used for machine vision and more complex applications In addition to image processing the wavelet mathematical functions are widely used for digital signal processing for diverse applications ranging from astronomy to seismology X Y Z xDSL An unspecified type of Digital Subscriber Line May be one of ADSL HDSL IDSL MSDSL RADSL SDSL or VDSL which see XLR A circular three conductor shielded connector commonly used in professional applications for connection of low level balanced audio signals to and from equipment XML eXtensible Markup Language descends from SGML and is a standard for the exchange of structured and networked data on the Web XML documents

    Original URL path: http://acleris.com/info/glossary4-wxyz.html (2016-04-29)
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  • Acleris' Direct Broadcast Satellite (DBS), Rainfall, Fading and Attenuation
    or simply rain fade For similar reasons the satellite operators need to carefully monitor their transmit or uplink signal strength from the transmit earth station to each satellite because these higher frequency signals are also attenuated when passing through rain However when there is rain fade in the uplink the attenuation affects all subscribers The solution to this is to automatically increase the uplink transmit power by an amount sufficient to overcome the fade effects The approximate rainfall attenuation at 12 5 GHz assuming that one mile or 1 6 Km of the path from satellite to receiver passes through rain is shown below Downlink Attenuation Rainfall Attenuation Description 0 02 0 5 mm hour 0 01 dB drizzle 0 1 2 5 mm hour 0 1 dB light rain 0 5 12 7 mm hour 0 9 dB heavy rain 1 0 25 4 mm hour 2 3 dB 4 0 100 mm hour 12 dB cloudburst 10 0 250 mm hour 43 dB To help put things into perspective attenuation is measured in dB or decibels a base 10 logarithmic relative power scale This means that 3 0dB attenuation or loss equates to a loss of one half

    Original URL path: http://acleris.com/info/mpeg2b.html (2016-04-29)
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  • Acleris' Direct Broadcast Satellite (DBS) -- Forward Error Correction (FEC)
    will request that the sending modem re transmit the block of data in error a useful error control technique when two way communications is possible and just two sites are involved However with DBS the receiver can t initiate a request to re send of lost data from the sending location Consequently a technique is needed that is able to correct most received errors independently without any intervention by the transmit site This technique is known as forward error correction When a signal from the satellite passes through heavy rain on its way to the receiver the signal is considerably attenuated or weakened perhaps to one one thousandth of its fair weather strength This loss of receive signal level in turn results in significant errors being introduced into the received digital signal analogous to a snowy analog TV picture The presence of the FEC information transmitted together with the compressed video usually provides the means to automatically keep the recovered signals looking and sounding error free But during the heaviest rain or when the receiver s dish is covered with melting snow the receive signal level can drop to a very low value resulting in an extremely high bit error rate When this happens the forward error correction can run out of range exposing the viewer to artifacts like incorrectly placed small picture blocks blocks of colored snow rainbows or other visual anomalies Static like clicking sounds may also be heard When the signal finally fades to a point beyond the FEC s capabilities the receiver automatically mutes turns off the sound and video Occasionally muted video may temporarily appear as a frozen image As the rainfall rate decreases the signal level gradually increases The receiver eventually reaches a threshold where it can lock on to the incoming satellite signals

    Original URL path: http://acleris.com/info/mpeg2c.html (2016-04-29)
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  • Acleris' Using Large Antennas for Direct Broadcast Satellite (DBS)
    and tightly focussed As the diameter of an antenna is increased its beam width becomes narrower making pointing the antenna more critical The standard antenna s half power beamwidth angle is halved with a 3 foot 0 91 meter diameter antenna while at the same time the antenna gain is increased by about 6 dB With a 10 foot 3 meter diameter antenna the half power beam width is only about 0 55 degrees with an increase in gain of about 16 dB over the standard antenna With such a large antenna and forward error correction there will still be outages during periods of heavy rain but the outages will be somewhat shorter Also accurate pointing or aiming of the dish becomes very difficult with a 10 foot 3 meter diameter antenna an important consideration A problem with large antennas is caused by our planet s daily wobble about its axis A geostationary satellite viewed from the earth over a 24 hour period describes a small figure 8 in the sky Aiming a large dish will need to be done when the satellite is in the middle of the 8 Professional satellite systems with large diameter antennas use a steerable sub reflector to compensate for the earth s wobble Wind loading becomes a problem as the antenna size is increased as a satellite antenna acts like a sail In a 50 mile per hour wind 80 Km hour the standard DBS antenna wind loading or maximum thrust is about 35 pounds 16 Kg With a ten foot 3 meter diameter antenna the thrust increases to a huge 850 pounds 386 Kg Unless you have mounted your large antenna on a concrete secured mast with lots of steel bracing the twist and tilt of the antenna during high winds will cause

    Original URL path: http://acleris.com/info/mpeg2d.html (2016-04-29)
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  • Acleris' Video, Compression, Codecs and Encoding for Direct Broadcast Satellite (DBS)
    thermal noise present on the video signal which otherwise also needs to be encoded Generally the premium channels are allocated more samples per line than the lower cost programming Human vision is quite limited under some circumstances For example as the angular motion of an object increases the eye s ability to see detail falls off Video compression takes advantage of this by providing low pass filtering or sometimes called subsampling which may increase automatically as the angular momentum increases If the detail is beyond the limits of visual acuity why waste the extra bits And at the receive location the image can be adequately approximated using motion prediction see below Also on program material like news or quiz shows the true video frame rate can be dropped from about 30 frames per second fps to some lower value The missing information can again be approximated using the motion prediction mentioned below Color information as distinguished from the luminance or monochrome information is subsampled at half the number of samples used for the luminance channel Once again this is a human visual acuity aspect that is exploited by modern video compression Perhaps the most powerful compression is then done by first forming the video data stream into 8 x 8 picture element pixel blocks Each block is then scanned diagonally in a serpentine manner and then a discrete two dimensional cosine transform is performed on each block s data This converts the temporal and spatial domains into the frequency or transform domain The less significant coefficients are then truncated discarded This process can also reduce noise in the image by a small amount the discontinuous data in each block tends to be included in the truncated data Another key part of compression is quantization the reduction of the number of shades of gray available for each pixel from 256 shades to some lower value This is achieved by combining two or three or more adjacent gray scale values into a new single value But when over done this can significantly degrade an image s subjective quality Another important part of video compression is called motion prediction motion compensation or loop filtering depending upon the context or the particular standards document The transmit codec buffers or temporary bit storage stores two frames of video and compares the video blocks between both frames Having been analyzed the blocks or groups of blocks can then be assigned a vector amplitude direction and rate of change This information is then passed along allowing the receive decoder to predict motion for various parts of the television image The prediction information is much more compact than the actual new image data Sometimes if the codec is incorrectly set up in a low bitrate environment and with high contrast lighting this can produce interesting received artifacts like a nose periodically detaching from a person s face The final coding technique used is called Huffman coding where the statistically most common digital patterns in the data stream are

    Original URL path: http://acleris.com/info/mpeg2e.html (2016-04-29)
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  • Acleris' MPEG Codec Hardware for Direct Broadcast Satellite (DBS) and Broadcasting Using Video Compression
    MPEG4 is gradually being introduced MPEG2 provides high quality video and stereo audio transmission at a variety of bit rates from 1 5 Mbps to 15 Mbps Initially DirecTV used two basic encoding rates centered at 3 Mbps and 7 5 Mbps High motion program material such as sports was allocated a nominal 7 5 Mbps while more sedate material such as talk shows used about 3 Mbps Several channels were then combined using a statistical multiplexer a device combining a number of digital television signals into a single transponder signal At this stage it s important to understand that the video encoder or transmit codec produces variable amounts of data over relative short periods of time depending upon the amount of motion the amount of image detail and other factors relating to the television signal The bit rates can vary between just a few hundred kilobits per second up to the system s programmed maximum in this example 3 0 or 7 5 Mbps Within the DBS context there is only 23 Mbps available per transponder shared by a group of encoders The statistical multiplexer can help maximize the utilization of each transponder by controlling each codec s bit rate For example if a codec only needs half of its available nominal assigned bandwidth for a period of time the rest of its allotted bandwidth can be borrowed by another or several encoder s If the system has been correctly programmed this will provide better motion handling and or picture definition for one or more of the other signals Such dynamic bandwidth allocation is a very effective way of providing what seems like more bandwidth than the actual 23 Mbps available but only if the types of services sharing each transponder have been chosen with care On the other

    Original URL path: http://acleris.com/info/mpeg2f.html (2016-04-29)
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