31-03-2010, 08:22 PM
Multiplexing and Transmission Media
MULTIPLEXING
Whenever the bandwidth of a medium linking two devices is greater than the bandwidth needs of the devices, the page link
can be shared. Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals
across a single data link. As data and telecommunications use increases, so does traffic.
Frequency Division Multiplexing
¢ Each signal is modulated to a different carrier frequency
¢ Carrier frequencies separated so signals do not overlap (guard bands)
¢ Channel allocated even if no data
¢ each channel occupies a fraction of the bandwidth of the link
¢ a channel is defined by its center frequency, and its bandwidth.
¢ Example: radio and television signal transmission
Wavelength Division Multiplexing
¢ Multiple beams of light at different frequency
¢ Carried by optical fiber
¢ A form of FDM
¢ Each color of light (wavelength) carries separate data channel
¢ 1997 Bell Labs
“ 100 beams
“ Each at 10 Gbps
“ Giving 1 terabit per second (Tbps)
WDM Operation
¢ Same general architecture as other FDM
¢ Number of sources generating laser beams at different frequencies
¢ Multiplexer consolidates sources for transmission over single fiber
¢ Optical amplifiers amplify all wavelengths
“ Typically tens of km apart
¢ Demux separates channels at the destination
Transmission Media
A transmission medium can be broadly defined as anything that can carry information from a source to a destination.
The transmission medium is usually free space, metallic cable or fiber “ optic cable.
GUIDED MEDIA
Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable,
coaxial cable, and fiber-optic cable. Out of these twisted-pair cable, coaxial cable transport signals in the form
of electric signals and fiber-optic cable transport signals in the form of light.
Coaxial cable
Coaxial cable carries signals of higher frequency ranges than those in twisted-pair cable, in part because the two
media are constructed quite differently.
Fiber-Optic Cable
A fiber-optic cable is made of glass or plastic and transmits signals in the form of light. Light travels in a
straight line as long as it is moving through a single uniform substance. If a ray of light traveling through one
substance suddenly enters another substance, the ray changes direction.
Fiber-optic cable connectors
Subscriber Channel (SC) Connector is used for cable TV. It uses a push/pull locking system
Straight “ tip (ST) Connector is used for connecting cable to networking devices. It uses a bayonet locking system
and is more reliable than SC.
MT-RJ is a connector that is the same size as RJ45.
UNGUIDED MEDIA: WIRELESS
Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is
often referred to as wireless communication.
CIRCUIT-SWITCHED NETWORKS
A circuit-switched network consists of a set of switches connected by physical links. A connection between two
stations is a dedicated path made of one or more links. However, each connection uses only one dedicated channel on
each link. Each page link is normally divided into n channels by using FDM or TDM.
DATAGRAM NETWORKS
In data communications, we need to send messages from one end system to another. If the message is going to pass
through a packet-switched network, it needs to be divided into packets of fixed or variable size. The size of the
packet is determined by the network and the governing protocol.
please read more
http://cs.virginia.edu/~zaher/classes/CS...ysical.pdf
http://cs.umsl.edu/~sanjiv/cs373/lectures/media.pdf
http://medusa.sdsu.edu/network/CS678/Lec...ndix_A.pdf