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Интерактивная система просмотра системных руководств (man-ов)

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radio (6)
  • radio (1) ( Linux man: Команды и прикладные программы пользовательского уровня )
  • >> radio (6) ( Solaris man: Игры )
  • Ключ radio обнаружен в базе ключевых слов.
         radio - Radio Free Ethernet receiver
         radio [ -h host
         ] [ -s service ] [
         This program is furnished on an AS IS basis as a  demonstra-
         tion of audio applications programming.
         Radio Free Ethernet (RFE) is a  network  audio  broadcasting
         system. It consists of programs and tools that allow packets
         of audio data to be transmitted around a network.  The  sys-
         tem  is  best understood by using the analogy of traditional
         radio broadcasting.
         A radio station takes audio data from a variety  of  sources
         (e.g.,  CDs,  tapes, a microphone in front of a disc jockey,
         the telephone, etc.) and broadcasts it  in  the  atmosphere.
         Similarly,  a  workstation may take audio data from an audio
         file or input device (e.g., a microphone or CD plugged  into
         the  audio cable of a workstation) and broadcast it over the
         local area network.  Each such workstation becomes  a  radio
         station,  and  must  broadcast  on a distinct 'frequency' in
         order to be differentiated from other active radio stations.
         Individual radios function as  receivers  for  radio  broad-
         casts.   To  listen  to  a radio station, you must tune your
         radio to its frequency.  At that point, the  broadcast  data
         is  converted to an audio signal and may be played through a
         speaker.  In the same fashion, a workstation  may  scan  the
         network  for  RFE broadcasts and 'tune in' a particular sta-
         tion by routing its audio data to the  audio  output  device
         (e.g.,  the speaker). Multiple stations may broadcast on the
         same network; it is up to the receiver program to select the
         radio  station  of  interest and discard any other broadcast
         As with conventional radios, a receiver may be requested  to
         scan the network and tune in to the next detected radio sta-
         tion.  One of the advantages of the computer  implementation
         is  the  ability  to  display a list of all the active radio
         stations and allow the user to select from among them.
         In traditional radio, a regulation agency  allocates  broad-
         cast  frequencies,  and  associates a station identification
         name with each frequency. In Radio Free Ethernet, the broad-
         cast  frequency  is  directly  derived from the station call
         letters; that is, the ASCII code for a  four-character  sta-
         tion name becomes a 32-bit broadcast frequency. Each network
         radio packet contains a 12-byte header that  identifies  the
         frequency, packet type, sequence number, and the low order 3
         bytes of the broadcaster's network id.  This information  is
         used  to differentiate radio broadcasts and to detect multi-
         ple stations (workstations) that may be broadcasting on  the
         same  frequency  (call letters).  At the network level, each
         packet also contains a  port  number  corresponding  to  the
         Radio  Free Ethernet port.  Ordinarily, this port is identi-
         fied by looking up the service named radio in the  NIS  ser-
         vices map.
         In  addition  to  its  audio  data  packets,  each   station
         transmits  a  Station  Identification packet once every five
         seconds.  This packet contains  detailed  information  about
         the  station  and disc-jockey (i.e., the host and user ids).
         Station Identification is also used  to  recognize  stations
         that  are  On-The-Air,  but  are  not currently broadcasting
         audio data.
         This can occur when a transmitter detects silent audio input
         and  squelches  it  (see radio_xmit(6)).  For instance, if a
         user is broadcasting from a microphone, the station  may  be
         squelched when the microphone is switched off.
         When a radio station goes Off-The-Air, it broadcasts a final
         sign-off  message to alert the receiver programs that broad-
         casting has ceased.
         One of the pitfalls of the radio analogy is that users  seem
         to  expect  that  they can always tune in some radio station
         when they start up a receiver program. Do not  be  deceived.
         If nobody is broadcasting, there are no stations to tune in.
         As with radio in the early 20th century, the  usefulness  of
         the  radio  is only as good as the quantity (and quality) of
         Another common mistake is to assume that  traditional  radio
         broadcasts  will  somehow be available on the network.  Keep
         in mind that the transmitter only broadcasts data  from  its
         audio input source.
          If you connect the line-level  or  headphone  output  of  a
         radio  to  the workstation audio input, then in fact you can
         broadcast traditional radio over  the  network.   (Interest-
         ingly,  the  8khz  data rate provides roughly the same audio
         quality as AM radio.)  But if you  connect  no  audio  input
         source, then you will not broadcast anything.
         In order for Radio Free Ethernet to function  properly,  the
         following entry should be present in the NIS services map:
              radio    5002/udp        # Radio Free Ethernet
         This entry specifies the port number that is used  to  iden-
         tify  RFE broadcast data.  If this entry is not present, the
         port number may be specified as a command-line option.
         Radio Free Ethernet can  be  configured  to  broadcast  data
         either  in  UDP  Broadcast packets or using IP Multicasting.
         These techniques differ in subtle but important ways.
         UDP Broadcast packets are broadcast only  within  the  local
         subnetwork.  Network  gateway  routers  do not forward these
         packets to other networks. When a UDP  Broadcast  packet  is
         issued,  every machine on the subnet receives the packet and
         discards it, unless a program is specifically registered  to
         listen for that particular packet type.  Though the overhead
         of processing such packets is small,  it  is  normally  con-
         sidered  unfriendly to issue many UDP Broadcast packets on a
         network (RFE normally broadcasts approximately eight packets
         per  second,  each containing around 1000 bytes). UDP Broad-
         cast is available for the time being only because older ver-
         sions of the operating system do not support IP Multicast.
         IP Multicasting is an improvement over broadcast techniques.
         By sending network packets to a particular well-known multi-
         cast address, only machines that have registered interest in
         that address will receive the data (packet filtering is usu-
         ally performed in the  network  interface  hardware).   Some
         experimental  IP  routers  exist that will forward multicast
         packets to other networks. Such forwarding is only performed
         when  there  is  a  listener on the destination network, and
         when the packet itself is identified as forwardable.
         In order for Radio Free Ethernet to function  properly,  the
         following entry should be present in the NIS hosts map:
              RadioFreeEthernet    # IP Multicast address
         This entry specifies the base address used for  RFE  station
         broadcasts.  For  more information on how IP Multicasting is
         used, please refer to the radio_xmit(6) manual page.
         The Radio Free Ethernet tools have been designed to  provide
         a  limited  kind  of audio conferencing capability.  Since a
         workstation may broadcast on one frequency while receiving a
         different  one,  clever  assignment of radio stations can be
         constructed to implement  2-way  conferencing.   Multi-party
         conferencing  may be enabled by modifying the radio receiver
         to sum the audio data from multiple radio stations together,
         thus achieving a simple audio mix.
         radio is the window-based Radio Free Ethernet  receiver.  It
         functions as a graphical front-end to the radio_recv(6) pro-
         gram, which it uses to scan the  network  for  active  radio
         stations  and  to  play  audio  data from the network on the
         audio device. It also provides six preset  buttons,  similar
         to  the  presets  on  a car radio, that may be programmed to
         specific radio station names.
         Ordinarily, the program scans for radio  stations  that  are
         broadcasting  to  the IP Multicast address identified by the
         host name RadioFreeEthernet found in the NIS hosts map (sta-
         tions  using  UDP  Broadcast are also received). The -h host
         command-line option may be used to specify an alternate host
         address or name to use for the default IP Multicast address.
         The Radio Free Ethernet tools use the port number identified
         by the service name radio found in the NIS services map. The
         -s service command-line option may be  used  to  specify  an
         alternate service name or port number to use.
         The following sections describe the  individual  panel  con-
         trols.  In addition, online help is available by positioning
         the pointer over the item in question  and  pressing  the  <
         HELP > key.
         Power toggles the state of the receiver on  and  off.  Since
               this involves communicating with a running copy of the
               radio_recv program, this  operation  may  take  a  few
               seconds to complete.
         Scan  initiates a scan for the next active radio station. By
               pressing this button repeatedly, you can browse all of
               the active stations.
               brings up a menu of the radio stations that have  been
               detected. Selecting a station from this menu will tune
               in that station. Station names are enclosed in  square
               brackets if the station is determined to be on-the-air
               but has not broadcast any data for  some  time.   This
               can  occur when the transmitter squelches silent audio
         DJ    displays the username and hostname of the disc  jockey
               for the current radio station.
         Set   establishes a station preset button.  It uses the name
               in  the  Preset Station item or, if that is blank, the
               name of the current station. Once  a  preset  is  pro-
               grammed, pressing the button forces the radio tuner to
               scan for that particular station. Set also causes  the
               current  program  parameters and presets to be written
               out to the initialization file.
         Clear clears a station preset button. It uses  the  name  in
               the Preset Station item or, if that is blank, the name
               of the current station. Clear also causes the  current
               program  parameters  and  presets to be written out to
               the initialization file.
               starts up an Audio Control Panel (see gaintool(6)).
         Props brings up a property sheet for the program that allows
               various  operating  parameters  to be set.  Changes to
               the tool properties do not take effect until the Apply
               button  is pressed. Apply also causes the current pro-
               gram parameters and presets to  be written out to  the
               initialization file.  The Reset button on the property
               sheet restores the controls to their current state.
         The following sections describe the property sheet controls:
         Auto Scan
               When this feature is enabled,  the  radio  tuner  will
               scan  for  a  new  radio station when no broadcast has
               been received from the current station for  a  certain
               amount  of  time  (specified, in seconds, by a numeric
         Allow Device Release
               When this feature is enabled,  the  radio  tuner  will
               relinquish  the  audio  output device whenever another
               process tries to use it.  This allows  other  applica-
               tions, such as AudioTool, the opportunity to interrupt
               the playing of a radio station in order to  play  what
               is presumed to be more important audio data.
         Audio Output
               This property sheet item indicates  the  audio  output
               device that is used to play a radio broadcast.
         If radio (or radio_recv) are run more than once on a  single
         workstation,  subsequent  invocations  may display the error
         message: Radio receiver socket is  busy.   This  is  because
         there may only be one program listening to a particular net-
         work port at a time.
               startup initialization file for radio and xmit
         gaintool(6), radio_recv(6), radio_xmit(6), xmit(6)
         RFC 1256, Network  Information  Center,  SRI  International,
         Menlo Park, Calif., September 1991.
         The Radio Free Ethernet tools were inspired by similar  pro-
         grams originally developed by Stephen Uhler and Peter Langs-
         ton at Bellcore.

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