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ecomraendation H.320
Scope
NARROW-BAND VISUAL TELEPHONE SYSTEMS
AND TERMINAL EQÜIPMENT
(Geneva, J990; revised ai Helsinki, ¡993)
'hís Recommendation covers I he teehnical requiremenls for narro w-band visual lelephone services defined
i H.200/AV.120-Series Recommendalions, where channel rales do nol exeeed 1920 kbtl/s.
NOTE - It ís anlicipaled ihal ihis Recommendalion will he extended lo a numlier of Recomrnendations each of whích would
over a single videoconferenclng or vídeophone service (narrow-band, broadband, ele.). Ilowever, large parts of these
ecommendalions would have idenlical wordíny, while in ihe pninis of divergence [he actual cholees beiween allcmaiives have not yel
een made; for the lime being, iherefore, ti is convenieni lo [real al! [he Icxl in a single Rtícommendalion.
'he servíce requiremenl.s for visual Itikphone servicies are. pre.senled \\\s F.72U for videolelephony and
'.730 for vídeoconferttiuití; video and audio «oding sysiem.s and oiher ieL-.hnit:al sel aspcícts uommon lo audiovisual
ervíces are covered in othcr Recommendalinns in Ihe H.20Ü/A V.2í)0-Series.
\í
:or the purpose of this Recommendalion, Ihe following definilions apply:
i¡t-rate allocatian sígnal (RAS): 8 hils posilioned wilhín ihe framt; slrueiure of H.221 lo transmil, e.g. commands,
onlrol and indicaiion signáis, capabililitís.
:ontrol and indication (C&I): end-lo-e.nd signalling heiween I e rm i na I.s uonsisliiig of i: mitro I whic-h causes a si al e change
n Ihe receiver and indicalion which pruvides for informal ion as lo ihe funclíoning of I he syslem, see also
lecommendalion H.230.
lata port: ínpui/ouipui gaie for ihe ustír dala iransmiiled wilhin .service channel or suh-tih aunéis accordíng lo
lecommendation H.221.
ip synchronixation; operation lo provide feeling ihal .speaking nioiion nf the di.splayed person i.s .synchronixed wilh the
(he person makes.
n-band signalling: sígnalling via BAS of Ihe H.221 j'ramt: .striuiiure.
nultipoint control unit (MCU): a píete nf equipmenl localed ¡n a node of Ihe neiwork or in a terminal which receives
leveral channels from acces.s pnrls and, ar.cording 10 c'.ertain «rileria, proces.se.s audiovisual signáis and distrilniles ihem lo
he connecled channels.
nan-raachine interface (MMI): niuii-manhine inierfane helween user and lerniinal/syslem which consisls of a physícal
leclíon (electro-acouslic, electro-opiic iransducer, key.s, ele.) and a logical seclitin dealing wilh runctional operalion staies.
larrow-band: bil rales ranging from 64 khil/s lo 192Ü khil/.s. Thís channel capacíly may be provided as a single
3/Ho/Hn/H[2-channeI or muliiple B/Hf)-«hanneIs in KSDN.
out-band signalling: signalling via a channel nol hc-ing parí of ihe B/H|)/H i i/H [2-channel (due lo !.400-Ser¡es
Recomrnendalions).
visual telephone services: a group of audiovisual .serviles inHuding videophone defined in Recommendalion F.721 and
videoconferencing defined in (he Rettommendaiion F.730.
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RecommendaEion H.320 (03/93) 1