1. Transmission medium
We can say that transmission media belong to layer zero

2. Transmission medium
Transmission media can be divided into two broad categories:
Guided media include twisted-pair cable, coaxial cable, and fiber-optic
Unguided media is usually air

3. 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.
A signal traveling along guided media is directed and contained by the physical limits of the medium
Twisted-pair and coaxial cable use metallic (copper) conductors that accept an transport signals in the form of electric current
Optical fiber is a glass cable that accepts and transports signals in the form of light

4. Twisted-Pair Cable Consists of two conductors (normally copper)
each with its own plastic insulation
twisted together

5. Twisted-Pair Cable
One of the wires is used to carry signals to the receiver
And the other is used as a ground reference
Receiver uses the difference between the two level
Interference (noise) and crosstalk may affect both wires and create unwanted signals
Receiver operates only on the difference between these unwanted signals
If the two wires are affected by noise or crosstalk equally
Receiver is immune (the difference is zero)
If the two wires are parallel
The effect of these unwanted signals is not the same in both wires (one close and one farther)
By twisting the pairs, a balance is maintained

6. Twisted-Pair Cable
The number of twists per unit of the length (e.g. inch) determines the quality of the cable
More twists mean better quality

7. Unshielded versus Shielded
Two common twisted-pair cable used in communications
Unshielded twisted-pair (UTP)
Shielded twisted-pair (STP)
STP has a metal foil or braided-mesh covering
Preventing the penetration of noise or crosstalk
It is bulkier and more expensive

8. Categories
EIA: the Electronic Industries association classifies unshielded twisted-pair cable into seven categories which determined by quality (1 lowest and 7 highest)

9. Connectors Most common UTP connector is RJ45
R J stands for Registered Jack

10. Performance One way measure performance is to compare
attenuation vs. frequency and distance.
A twisted-pair can pass a wide range of frequencies.
Figure 7.6 shows with increasing frequency, attenuation in decibels per kilometer (dB/km), sharply increase with frequency above 100 kHz.
Gauge is a measure of the thickness of the wire.

11. Application Used in telephone Lines (UTP) DSL lines (UTP)
Local area networks

12. Coaxial Cable
Carries signals of higher frequency ranges than twisted-pair cable
Coax has a central core conductor of solid or stranded wire (usually copper)
Encased in an outer conductor of metal foil, braid, or a combination of the two
The outer metallic wrapping
Outer conductor is also enclosed in an insulating sheath
Whole cable is protected by a plastic cover

14. Coaxial Cable Standards
Coaxial cables are categorized by their radio government (RG) ratings
Each RG number denotes a unique set of physical specifications
Wire gauge of the inner conductor
Thickness and type of the inner insulator
Construction of the shield
Size and type of the outer casing
Each RG ratings is adapted for a specialized function

15. Coaxial Cable Connectors
Coaxial cable connector is BNC (Bayone-Neill-Concelman)
Figure shows the BNC connector, the BNC T connector, and the BNC terminator

16. Applications
It was used in analog and digital telephone networks (replaced by fiber-optic)
Cable TV networks (replaced by fiber-optic)
Traditional Ethernet Lans

17. Fiber-Optic Cable
It is made of glass or plastic and transmits signals in the form of light
If a ray pf light traveling through one substance and enters another (more or less dense), the ray changes directions
Optical fibers use reflection to guide light through a channel

18. Fiber-Optic Cable
Glass or plastic core is surrounded by a cladding of less dense glass or plastic

19. Propagation Modes
Current technology supports two modes (multimode and single mode) for propagating light along optical channels
Multimode: multiple beams from a light source move through the core in different paths
Multimode can be implemented in two forms:
Step-index
Graded-index

20. Propagation Modes

21. Fiber Sizes
By the ratio of the diameter of their core to the diameter of their clading [micrometers]

22. Cable compostion

23. Fiber-Optic Connections
Fiber-optic use three different type of connectors
Subscriber Channel (SC) connector
Used in cable TV and it uses a push/pull locking system
The Straight-Tip (ST) connector
Used for connecting cable to networking devices
MT-RJ in new connector with the same size as RJ45

24. Fiber-Optic Connections
Applications
It used in backbone networks
For cable TV with coaxial cable (a hybrid network)

25. Advantages and Disadvantages of Optical
Advantages over twisted-pair and coaxial
Higher bandwidth
Less signal attenuation
Signal with fiber-optic can run for 50 km with requiring regeneration
5 km for coaxial or twisted-pair cable
Immunity to electromagnetic interference
Electromagnetic noise cannot affect fiber-optic cables
Resistance to corrosive materials
Glass is more resistant to corrosive materials than copper
Light weight
More immune to tapping
Fiber-optic cables definitely more immune to tapping than copper cables

26. Advantages and Disadvantages of Optical
Installation/maintenance
Because it is new technology, need expertise
Unidirectional
If we need bidirectional we need two fibers
Cost
The cables and interfaces are expensive

27. UNGUIDED MEDIA: WIRELESS
Unguided media: transport electromagnetic waves without using a physical conductor (wireless communication)
Signal broadcast through air

28. UNGUIDED MEDIA: WIRELESS
Unguided signals can travel from the source to destination in several ways:
Ground propagation
Sky propagation
Line-of-sight propagation

29. UNGUIDED MEDIA: WIRELESS
Ground propagation (below 2 MHz)
Radio waves travel through the lowest portion of atmosphere
Waves emanate in all directions from the transmitting antenna
Distance depends on the amount of power in the signal
Sky propagation ( MHz)
Higher frequency radio waves radiate upward into ionosphere where they reflected back to earth
This type of transmission allows for greater distance with lower power output

30. UNGUIDED MEDIA: WIRELESS
Line-of-sight propagation (above 30 MHz)
Very high-frequency signals are transmitted in straight lines directly from antenna to antenna
Antennas must be directional
Facing each other
Either tall enough or close enough

31. UNGUIDED MEDIA: WIRELESS
Electromagnetic spectrum defined as radio waves and microwaves is divided into eight ranges, called bands:

32. UNGUIDED MEDIA: WIRELESS
Wireless transmission can be divided into:
Radio waves
Microwaves
Infrared waves

33. UNGUIDED MEDIA: WIRELESS
Radio waves
Radio waves: waves range in frequencies between 3 KHz and 1 GHz
Microwaves: waves ranging in frequencies between 1 and 300 GHz
Radio waves are omnidirectional (propagated in all directions)
The sending and receiving antennas do not have to be aligned
Disadvantage
One antenna interferences another antenna when they using same frequency
Radio waves that propagate in the sky mode, can travel long distance [AM radio]
Radio waves [low and medium frequencies] can penetrate walls inside a building
Advantage: an AM radio can be received inside a building
Disadvantage: we cannot isolate a communication to just inside or outside a building
Applications
Useful for multicasting: Radio, television. Cordless phones and paging system

34. UNGUIDED MEDIA: WIRELESS
Microwaves
Microwaves are unidirectional
Antenna need to be aligned
Advantage: pair of antenna can be aligned without interfering with another pair
Microwave propagation is line-of-sight
For long distance communication
Very tall towers
Repeater
Very high-frequency microwaves cannot penetrate walls
Disadvantage if receiver inside a building

35. UNGUIDED MEDIA: WIRELESS
Applications
Due to unidirectional properties, microwaves useful when unicasting (one-to-one) communication
Cellular phones
Satellite networks
Wireles LANs

36. UNGUIDED MEDIA: WIRELESS
Infrared
From 300 GHz to 400 THz (wavelengths from 1 mm to 770 nm)
Use for short-range communication
It has high frequency, cannot penetrate walls
Prevents interference between one system and another
Remote control not interfere with our neighbors
Can not be used outside because sun’s rays contain infrared waves (interference)
(IrDA) Infrared Data Association established standards for communicating between devices:
Keyboards, mice, PCs and printers