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7-Transmission Media. DR. JOHN ABRAHAM UNIVERSITY OF TEXAS PANAM. THEORETICAL BASIS. See previous lesson. Transmission Media. Guided – exact path – physical media Unguided – radio transmission. Taxonomy by forms of Energy. Electromagnetic, light, electrical Use my notes. - PowerPoint PPT Presentation
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7-Transmission Media
DR. JOHN ABRAHAM
UNIVERSITY OF TEXAS PANAM
Transmission Media
Guided – exact path – physical media Unguided – radio transmission
Taxonomy by forms of Energy
Electromagnetic, light, electrical
Background Radiation and electrical Noise Random electromagnetic radiation (noise). When electrical signals propagate down a wire,
electromagnetic energy is radiated (i.e., the wire acts like an antenna)
When electromagnetic radiation encounters metal, a small electrical current is induced that can interfere with signals being carried on the wire
When an electrical pulse is sent down an unterminated wire, reflection comes back
When a signal passes across the connection between two wires, reflection and loss occur Note: a network diagnostic tool uses reflection to find the
distance to the point where a cable has been cut
Twisted pair
Unshielded UTP
Shielded STP
Both wires in a twisted pair is affected equally in case of Noise giving a net difference of 0.
In parallel wires the one closer to the noise source will be affected more, giving a net difference.
Twisted Pair Ten Base-T UTP Connector Type RJ-45 Cat 3 up to 16MHz Cat 4 up to 20MHz Cat 5 up to 100 MHz
More twists per cm and teflon insulation Cat 5e noise immunity 125 mbps Cat 6 – 200 mbps Cat 7 foil shielded around the entire set of wires. 600 Mbpps
Twisted pair wiring scheme
1. Orange white2. Orange3. Green white4. blue5. Blue white6. Green7. Brown white8. Brown
1 White/Orange White/Green 1
2 Orange Green 2
3 White/Green White/Orange 3
4 Blue White/Brown 4
5 White/Blue Brown 5
6 Green Orange 6
7 White/Brown Blue 7
8 Brown White/Blue 8
Hub is a multiport repeater (operates in Layer1 OSI)
Every transmission from one port is amplified and retransmitted on all other ports
The maximum length of any segment is 100 meters
UTP contd
Using FDM coaxial can carry over 10,000 voice channels
When FDM is used CATV is called Broadband Good for both analog and digital signals Greater attenuation of signals, therefore amplifiers
and repeaters are used frequently. 50 ohm cable is for digital transmission 75 ohm for
TV
Coaxial cable
Single line - multiple connections FDM - frequency division - most widespread
A number of signals can be carried simultaneously if each signal is modulated onto a different carrier frequency
Multiplexing
Each modulated signal requires a certain bandwidth (called a channel)
Channels are separated by bands of unused portions
Broadcast TV - each channel requires 6Mhz. Coaxial cable has 500 MHz bandwidth Voice only requres 4 KHz
Synchronous Time Division Multiplexing Possible when the available data rate of a
medium exceeds the data rate of a digital signal to be transmitted.
Interleave bits or blocks at a time
TDM
Time Division Multiplexing The general alternative to FDM is
time division multiplexing (TDM)
In TDM sources share a medium by ``taking turns''
There are two types of TDM: Synchronous Time Division Multiplexing
(STDM)arranges for sources to proceed in a round-robin
manneralso known as Slotted Time Division Multiplexing
Statistical Multiplexing
Works similar to STDM, but if a given source does not have data to send, the multiplexor skips that source
Most NW use a form of statistical multiplexing because computers do not all generate data at exactly the same rate
Thick 10base5 up to 1650 feet -requires trnsceivers
High Bandwidth - use FDM or TDM Thin Coax 10base2 - up to 607 feet
T-connectors and 50 ohm resitors No more 30 devices on a segment No more than 5 segments in a single LAN Only 3 of these segments may have devices
(90) others are repeaters.
Coaxial cable contd
Greater capacity 2 Gbps over tens of kilometers Repeaters needed only every 8 KM Smaller size & weight Materials used
Plastic (short haul) Glass Fused Silica (best)
Fiber Optics
http://www.datacottage.com/nch/fibre.htm lower attenuation electromagnetic isolation Use LED or ILD
light emitting diode, Injection Laser diode Use Photodiode to detect
PIN photodiode APD photodiode
One - short pulse of light, Zero-absence of light
Fiber contd
Core Cladding
optical properties differ between core and cladding. Cladding has lower refractive index
Jacket to protect against moisture, crushing, etc.
Fiber contd
Light propagates from one end to another in one of the following ways mono mode (straight line)
the source is laser Most expensive
Multimode stepped index the source is LED Bounces of cladding
Multimode graded index The cladding refractive index increases as it moves away from the
core
Fiber contd
Fiber Optic Networks
Taps are difficult Two types of interface
Passive interface one end has an LED or laser diode The other end has photodiode
Active interface incoming light is converted to electric signal Signal is generated to full strength Tap into the signal generator
Wireless Transmission
Radio Microwave Infrared Laser light
Telephone
We skip most of it
The phone system is divided into 2 partsOutside plant
Local loops and trunks
Inside plantSwitches
Stop here
Switching1. Circuit SwitchingA physical connection (circuit) is established between the sender
and the receiver. (Similar to operator plugging in – old days)This path is called an end-to-end path.Time used to find the path adds enormous overhead. Entire
bandwidth is reserved even when there are gaps in communiction.
2. Message SwitchingNo physical path is established.The data is sent to the first switching office.Stored, forwarded later, one hop at a time.
Switching continued.
This is known as store-and-forward network.The message could be typed and saved to punched tape and
forwarded later.There was no block size limit. Therefore, one sender can
monopolize the system.3. Packet SwitchingBlock size has upper limit.No one can monopolize more than a fraction of a sec.Suited for interactive traffic.Each router should have sufficient memory to store data.
Switching continued
In packet switching each packet can be examined and format changed if need to be.
Packets may arrive at different order. Will have to be rearranged.
Types of switches
Hierarchical
Crossbar
Space Division
Time Division
ISDN
Narrow band
Broad band
Narrow Band ISDN
Primary goal was integration of voice and data.
Telephones can be connected to a computer for statistics.
Voice and data can be sent concurrently
Caller ID
ISDN System Architecture
ISDN is a bit pipe
All bits can flow in either direction.
Does not matter where the bit comes from – voice, computer, fax, etc.
Additional bit pipes can be added and combined.
ISDN continued
For each ISDN service a terminating device is need at your location such as NT1.
Up to 8 devices can be added to an NT1, provided you have sufficient bandwidth (pipes).
ISDN interface
Multiple channels can be interleaved by time division multiplexing.
The Channels that are standardized is given on page 142 of the text book.
Basic rate comes 2B and 1 DPrimary rate: 23B +1Hybrid: 1A +1C
N-ISDN
Narrow ISDN focused on 64Kbps channels.
Directed at telephone customers
Big failure
BROADBAND ISDN AND ATM
156 Mbps
This data rate is enough for HDTV
Developed based on ATM technology
ATM is a packet switching technology