Communication Channels 2.5 2000/07/27 2004/08/04 15:41:43.220 GMT-5 Don Johnson dhj@rice.edu Don Johnson dhj@rice.edu Joe Montgomery montgom@rice.edu Adan Galvan jago@rice.edu Erin Snavely ernsnave@alumni.rice.edu John Austin Cottrell jac3@rice.edu point-to-point broadcast wireline wireless communication channels information communication A brief introduction to the two types of communication channels. Electrical communications channels are either wireline or wireless channels (see the Circuit Models module). Wireline channels physically connect transmitter to receiver connection with a "wire," which could be twisted pair, coaxial cable or optic fiber. Consequently, wireline channels are more private and much less prone to interference. Simple wireline channels connect a single transmitter to a single receiver: a point-to-point connection as with the telephone. Some wireline channels operate in broadcast modes: one or more transmitter is connected to several receivers. One simple example of this situation is cable television. Computer networks can be found that operate in point-to-point or in broadcast modes. Wireless channels are much more public, with a transmitter's antenna radiating a signal that can be received by any antenna sufficiently close enough. In contrast to wireline channels where the receiver takes in only the transmitter's signal, the receiver's antenna will react to electromagnetic radiation coming from any source. This feature has two faces: The smiley face says that a receiver can take in transmissions from any source, letting receiver electronics select wanted signals and disregarding others, thereby allowing portable transmission and reception. You will hear the term "tetherless networking" applied to completely wireless computer networks, while the frowny face says that interference and noise are much more prevalent than in wireline situations. A noisier channel subject to interference compromises the flexibility of wireless communication.