Date post: | 22-Apr-2015 |
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Transmission media
Guided mediaThose that provide a conduit from one device to
another.Types include:
◦ Twisted pair◦ Coaxial◦ Fiber optic
A signal travelling along these medium is directed and contained by the physical limits of the medium.
Twisted pair and coaxial cable use metallic conductors, transporting signals in electrical current
Optical fiber is a glass or plastic cable that accepts and transports signals in form of light.
Twisted pair Cable Types:
◦unshielded twisted pair(UTP)◦Shielded twisted pair(STP)
Coaxial Cable
Categories of coaxial cables
Category Impedance Use
RG-59 75 W Cable TV
RG-58 50 W Thin Ethernet
RG-11 50 W Thick Ethernet
OPTICAL FIBER
An optical fiber (or fibre) is a
glass or plastic fiber (pipe) that
carries light along its length.
Light is kept in the "core" of the
optical fiber by
total internal reflection.
Unguided Media: WirelessRadio Waves
Microwaves
Infrared
Band Range Propagation Application
VLF 3–30 KHz Ground Long-range radio navigation
LF 30–300 KHz GroundRadio beacons and
navigational locators
MF 300 KHz–3 MHz Sky AM radio
HF 3–30 MHz SkyCitizens band (CB),
ship/aircraft communication
VHF 30–300 MHzSky and
line-of-sightVHF TV, FM radio
UHF 300 MHz–3 GHz Line-of-sightUHF TV, cellular phones,
paging, satellite
SHF 3–30 GHz Line-of-sight Satellite communication
EHF 30–300 GHz Line-of-sight Long-range radio navigation
Radio waves are used for multicast communications, such as radio and television, and paging systems.
Note:
Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.
Note:
Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.
Note:
Switching How to connect multiple devices so as
one to one communication is possible?Solution: different topologiesDrawbacks of different topologiesSwitched network consists of series of
interlinked nodes called switches.Switches are hardware and/or software
devices capable of creating temporary connections between two or more devices linked to the switch
Types of switchingCircuit switchingPacket switchingMessage switching
Circuit SwitchingCreates a direct physical
connection between two devicesIt may have n inputs and m
inputsMay implement space division
switching or time division switching
A circuit switch
Packet SwitchingDrawbacks of circuit switch
◦Less suited for data communication ◦Data rate is slow◦System is inflexible
In packet switch, data are transmitted in discrete units of variable length blocks called packets
Types:◦Datagram approach◦Virtual circuit approach
Datagram approachIn this approach, Each packet is treated
independently, here each packet is referred to as datagram
Each message is divided into several datagrams, and each datagram may go different paths to reach their destination
This can cause datagrams to arrive at destination out of order. The transport layer takes the responsibility of reordering these out of order datagrams before they are given to destination port
Virtual circuit approachHere the relationship between
each packet is maintainedWhen data is sent, all packets of
the transmission travel one after the another along a dedicated route
Can be implemented in two formats:◦Switched virtual circuit◦Permanent virtual circuit
Similar to circuit switching, in SVC, a virtual circuit is created whenever it is required and this connection exists only for the duration of the transmission
Only one route is established in SVCIn the case of PVC, the same virtual
circuit is established between two users but on a continuous basis
Much like a dedicated link to dedicated users
Message switchingIt is best known otherwise as
STORE AND FORWARDHere a node receives messages,
stores it until an appropriate route is free and then it sends it.
Not much in use today, due to requirement of large storage capacity and delays.