Path: utzoo!utgpu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!ria!uwovax.uwo.ca!telecom-request From: bellutta@irst.it (Paolo Bellutta) Newsgroups: comp.dcom.telecom Subject: Re: Transporting a Bitstream on a Video Channel Message-ID: Date: 15 Jun 91 04:13:49 GMT Sender: Telecom@eecs.nwu.edu Organization: I.R.S.T. 38050 POVO (TRENTO) ITALY Lines: 48 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 454, Message 4 of 8 rmz@ifi.uio.no (Bj|rn Remseth) asks: > Does anyone know about existing hardware that puts a bitstream on a > video channel and let you extract the same bitstream out of the video > video signal, after it has been transmitted on standard video > transport media such as satellite links, video cassettes and cable TV > networks. > This kind of equipment could use spare capacity on local cable > networks and satellite sattelite links to spread e.g. usenet news > quite inexpensively. > But, the Big Question is: Does this hardware exist? Yes. There are several ways to do that. Let's list the various kinds of media you can use: 1) VCR 2) terrestrial link 3) satellite link 1) can make use of the SMPTE/EBU time code, this is a digital code inserted in the VBI (vertical blanking interval), and represents hours:minutes:seconds:frames plus some spare bits you can use for special purposes. Since this is written on video tape, low bit rates can be achieved. In the US (but not in Europe) they have CC (close captioning) encoding which can be recorded on tape (always in the VBI). 2) can make use of the same code that is used for teletext and VPS codes. Since the channel bandwidth is a bit larger than in a VCR, a higher bit rate can be achieved. An alternative way is to use the NICAM encoding (used for terrestrial TV digital audio). 3) satellite transponders have a very high bandwidth, therefore subcarriers are used to carry additional data (for example different languages audio). Subcarriers can usefully encoded to transmit data at high bit rates. Adam Smith has a large production of Time Code HW. Rohde & Schwarz have DGF and DEF (coder and decoder) for VBI, DCA and DDA for digital audio. This covers 1) and 2). Sit on a chair before asking prices ;) Paolo Bellutta I.R.S.T. vox: +39 461 814417 loc. Pante' di Povo fax: +39 461 810851 38050 POVO (TN) e-mail: bellutta@irst.it ITALY bellutta@irst.uucp