This page describes all known channels, including those in extensions.  Part of the benefit is so that people implementing new channels can look at how others have done it. - DL

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'''Built-in Channels'''

   file:   File/device/process channel (create with open)
   sock:   TCP channel (create with socket)

'''Extension Channels'''

   exp:   Pty/process channel (create with spawn).   Expect extension.  [http://expect.nist.gov] [Don Libes]
   tls:   SSL channel (create with tls::socket).  TLS extension.  [http://www.sensus.org/tcl/tls.htm]
   x25:   X.25 switched virtual circuit (create with x25::socket).  x25 extension. [http://millibits.com/djh/tcl/index.html#x25]
   memchan:   In-memory channel. Memchan extension [http://www.purl.org/NET/akupries/soft/memchan/] [Andreas Kupries]
   fifo:    In-memory channel, fifo-behaviour. Memchan extension (s.a.)
   mod_dtcl:	mod_dtcl has a file channel built in to interact with Apache [http://tcl.apache.org/mod_dtcl/]

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'''Other documentation'''

See the Tcl documentation at SourceForge [http://sourceforge.net/docman/?group_id=10894],
specifically ''The Tcl I/O system as seen by a driver (channel type)'' [http://sourceforge.net/docman/display_doc.php?docid=1791&group_id=10894]