1. Physical Layer Issues - Transmission Media and Network Cabling
Hitesh lad

2. What is Cable? Transmission Media
Transmission medium is the physical path between the transmitter and receiver.
It is the Transmission medium through which information usually moves from one network device to another.
In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types.
Understanding the characteristics of different types of transmission media and how they relate to other aspects of a network is necessary for the development of a successful network.

4. Factors to Select Transmission Media
Data Rate and Bandwidth (BPS and Hz)
Distance and Attenuation (meters, dB/km)
Interference Characteristics
Number of receivers (broadcast vs. point to point)
Cost - Remember cabling is a long term investment!

5. Transmission Impairments
Impairments exist in all forms of data transmission media
Analog signal impairments result in random modifications that impair signal quality
Digital signal impairments result in bit errors (1s and 0s transposed)

6. Types of Media Two major classes Conducted or guided media
use a conductor such as a wire or a fiber optic cable to move the signal from sender to receiver.
Energy is confined to the medium and guided by it
Wireless or unguided media
use radio waves of different frequencies and do not need a wire or cable conductor to transmit signals
Energy spreads out and is not confined

7. Media Sub-types Guided Media Unguided Media
Unshielded Twisted Pair (UTP) Cable
Shielded Twisted Pair (STP) Cable
Coaxial Cable
Fiber Optic Cable
Unguided Media
Terrestrial microwave transmission
Satellite transmission
Broadcast radio
Infrared

8. Twisted Pair Wires
Consists of two insulated copper wires arranged in a regular spiral pattern to minimize the electromagnetic interference between adjacent pairs
Often used at customer facilities and also over distances to carry voice as well as data communications
Low frequency transmission medium
Two varieties
STP (shielded twisted pair)
the pair is wrapped with metallic foil or braid to insulate the pair from electromagnetic interference
UTP (unshielded twisted pair)
each wire is insulated with plastic wrap, but the pair is encased in an outer covering

9. Twisted Pair
One difference between the different categories of UTP is the tightness of the twisting of the copper pairs. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot.
Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices.

10. Categories of Unshielded Twisted Pair
The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated five categories of wire.
Type Use
Category 1 Voice Only (Telephone Wire)
Category 2 Data to 4 Mbps (LocalTalk)
Category 3 Data to 10 Mbps (Ethernet)
Category 4 Data to 20 Mbps (16 Mbps Token Ring)
Category 5 Data to 100 Mbps (Fast Ethernet)
Category 5e Data to 1000 Mbps (Gigabit Ethernet)
Category 6 Data to 1000 Mbps (Gigabit Ethernet)
Category 7 ?

11. Benefits of UTP Disadvantages of UTP Inexpensive and readily available
Flexible and light weight
Easy to work with and install
Disadvantages of UTP
Susceptibility to interference and noise
Attenuation problem
For analog, repeaters needed every 5-6km
For digital, repeaters needed every 2-3km
Relatively low bandwidth (3000Hz)

13. Twisted Pair - Applications
Telephone network
Between house and local exchange (subscriber loop/local loop)
Within buildings
To private branch exchange (PBX)
For local area networks (LAN)
10Mbps or 100Mbps or 1000 Mbps

14. Unshielded Twisted Pair Connector
The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector (See figure).
A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.

15. The RJ-45 Connector

16. Shielded Twisted Pair (STP) Cable
A disadvantage of UTP is that it may be susceptible to radio and electrical frequency interference (RFI, EFI).
Shielded twisted pair (STP) is suitable for environments with electrical interference; however, the extra shielding can make the cables quite bulky.
Shielded twisted pair is often used on networks using Token Ring topology.
More expensive, harder to work with.

17. Shielded Twisted Pair (STP) Cable

18. Coaxial Cable
Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield (See figure). The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers.
Both conductors share a common center axis, hence the term “co-axial”

19. Coax Layers outer jacket (polyethylene) shield (braided wire)
insulating material
copper or aluminum
conductor

20. Pros and Cons Coax Advantages Coax Disadvantages Higher bandwidth
400 to 600MHz
up to 10,800 voice conversations
Can be tapped easily (pros and cons)
Much less susceptible to interference than twisted pair
Greater cable lengths between network devices than twisted pair cable.
Coax Disadvantages
High attenuation rate makes it expensive over long distance
Bulky - coaxial cabling is difficult to install

21. Coaxial Cable Applications
Most versatile medium
Television distribution
Ariel to TV
Cable TV
Long distance telephone transmission
Can carry 10,000 voice calls simultaneously
Being replaced by fiber optic
Short distance computer systems links
Local area networks

22. Types of Coaxial Cable Thin Coax Thick Coax
Thin coaxial cable is also referred to as thinnet. Thin coaxial cable is popular in linear bus networks.
Thick Coax
Thick coaxial cable is also referred to as thicknet.
Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. This makes thick coaxial a great choice when running longer lengths in a linear bus network.
One disadvantage of thick coaxial is that it does not bend easily and is difficult to install.

23. Coaxial Cable Connectors
The most common type of connector used with coaxial cables is the Bayone-Neill-Concelman (BNC) connector (See figure). Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid problems with your network, always use the BNC connectors that crimp, rather than screw, onto the cable.

24. Fiber Optic Cable
Relatively new transmission medium used by telephone companies in place of long-distance trunk lines
Also used by private companies in implementing local data communications networks
Require a light source with injection laser diode (ILD) or light-emitting diodes (LED)

25. Fiber Optic Cable
Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials.
It transmits light rather than electronic signals, eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference.
It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting.

26. Fiber Optic Layers consists of three concentric sections
plastic jacket
glass or plastic
cladding
fiber core

27. Optical Fiber

28. Armored Cable

29. Facts About Fiber Optic Cables
Outer insulating jacket is made of Teflon or PVC.
Kevlar fiber helps to strengthen the cable and prevent breakage.
A plastic coating is used to cushion the fiber center.
Center (core) is made of glass or plastic fibers.

30. Fiber Optic Cable
Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair.
It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services.
The cost of fiber optic cabling is comparable to copper cabling; however, it is more difficult to install and modify.

31. Optical Fiber - Transmission Characteristics
Act as wave guide for 1014 to 1015 Hz
Portions of infrared and visible spectrum
Light Emitting Diode (LED)
Cheaper
Wider operating temp range
Last longer
Injection Laser Diode (ILD)
More efficient
Greater data rate
Wavelength Division Multiplexing

32. Fiber Optic Types Multimode step-index fiber
the reflective walls of the fiber move the light pulses to the receiver
Multimode graded-index fiber
acts to refract the light toward the center of the fiber by variations in the density
Single mode fiber
the light is guided down the center of an extremely narrow core

33. Optical Fiber Transmission Modes

34. Fiber Optic Signals fiber optic multimode step-index
graded-index
fiber optic single mode

35. Pros and Cons Fiber Optic Advantages Fiber Optic Disadvantages
Greater capacity - data rates of hundreds of Gbps
Smaller size and lighter weight
Lower attenuation
Electromagnetic isolation - immunity to environmental interference and highly secure due to tap difficulty and lack of signal radiation
Greater repeater spacing - 10s of km at least
Fiber Optic Disadvantages
Expensive over short distance
Requires highly skilled installers
Adding additional nodes is difficult

36. Optical Fiber - Applications
Long-haul trunks
Metropolitan trunks
Rural exchange trunks
Subscriber loops (FTTH, FTTC)
LANs (generally backbone connections)

37. Fiber Optic Connector
The most common connector used with fiber optic cable is an ST connector. It is barrel shaped, similar to a BNC connector. A newer connector, the SC, is becoming more popular. It has a squared face and is easier to connect in a confined space.

38. Comparison of the Three Guided Media Types
1000 THz
1 THz
1 GHz
1 MHz
Optical Fiber
1 kHz
0.1
3/8” Coaxial Cable
22-gauge Twisted Pair
Frequency
dB/km 1 10
100

39. Wireless (Unguided Media)
Transmission
Transmission and reception are achieved by means of an antenna
Directional
transmitting antenna puts out focused beam
transmitter and receiver must be aligned
Omnidirectional
signal spreads out in all directions
can be received by many antennas

40. Wireless (Unguided Media) Frequencies
Three general ranges of frequencies
30MHz to 1GHz
Broadcast radio
Omnidirectional
2GHz to 40GHz microwave frequencies
Microwave
Highly directional
Point to point
Satellite
3 x 1011 to 2 x 1014
Infrared

41. Propagation of Radio Frequencies

42. Propagation of Radio Frequencies (continued)

43. Terrestrial Microwave Transmission
Uses the radio frequency spectrum, commonly from 2 to 40 GHz
Transmitter is a parabolic dish, mounted as high as possible
Used by common carriers as well as by private networks
Requires unobstructed line of sight between source and receiver
Curvature of the earth requires stations (called repeaters) to be ~30 miles apart

44. Terrestrial Microwave Transmission
Distance between antennas:
d = 7.14 (Kh)1/2 , d = distance in km, h is antenna height in meters, K = constant = 4/3

45. Terrestrial Microwave Applications
Long-haul telecommunications service for both voice and television transmission
Short point-to-point links between buildings for closed-circuit TV or a data link between LANs

46. Terrestrial Microwave Communications

47. Pros and Cons Microwave Transmission Advantages
No cabling needed between sites
Wide bandwidth
Multi-channel transmissions
Used for long haul or high capacity short haul
Requires fewer amplifiers and repeaters
Microwave Transmission Disadvantages
Line of sight requirement
Expensive towers and repeaters
Subject to interference such as passing airplanes and rain
Frequency bands are regulated

48. Satellite Microwave Transmission
Satellite is a microwave relay station in space
Can relay signals over long distances
Geostationary satellites
remain above the equator at a height of 22,300 miles (geosynchronous orbit)
travel around the earth in exactly the time the earth takes to rotate
Earth stations communicate by sending signals to the satellite on an uplink
The satellite then repeats those signals on a downlink
The broadcast nature of the downlink makes it attractive for services such as the distribution of television programming

50. Satellite Transmission Process
transponder
dish
dish
22,300 miles
uplink station
downlink station

51. Satellite Transmission Applications
Television distribution
a network provides programming from a central location
direct broadcast satellite (DBS)
Long-distance telephone transmission
high-usage international trunks
Private business networks

52. Principal Satellite Transmission Bands
C band: 4(downlink) - 6(uplink) GHz
the first to be designated
Ku band: 12(downlink) -14(uplink) GHz
rain interference is the major problem
Ka band: 19(downlink) - 29(uplink) GHz
equipment needed to use the band is still very expensive

53. Pros and Cons Satellite Advantages Satellite Disadvantages
Can reach a large geographical area
High bandwidth
Cheaper over long distances
Satellite Disadvantages
High initial cost
Susceptible to noise and interference
Propagation delay (0.25 sec) - requires sophisticated flow control

56. Broadcast Radio Broadcast radio is omnidirectional
Covers 30MHz to 1 GHz (FM, UHF, VHF)
Need line of sight. Ionosphere is transparent above 30MHz, hence no atmospheric reflection
Advantages
Less sensitive to attenuation from rainfall
Disadvantages
Multipath interference is significant

57. Infrared
Transceivers operate with line of sight or reflection from light-colored surface
Modulate noncoherent infrared light
e.g. TV remote control, IRD port
Advantages
Does not penetrate walls - enhanced security
No licensing of frequencies
Disadvantages
Operate on limited distances

58. Summary

59. The RS-232 Serial Interface and Ethernet 10/100BaseT

60. DB-25 Connectors
DB-25/DB-9 is an old standard family of connectors which are used for various interface standards such as RS-232 (Serial), Parallel and SCSI interfaces.
The DB-25 male and female connectors are shown in the figure. Please note the way the pins are numbered.

61. What is a Null Modem Cable?
A specially designed cable that allows you to connect two computers directly to each other via their communications ports (RS-232 ports).
Null modems are particularly useful with portable computers because they enable the portable computer to exchange data with a larger system.

62. What is a Null Modem Cable?
The purpose of a null-modem cable is to permit two RS-232 "DTE" devices to communicate with each other without modems or other communication devices (i.e., "DCE"s) between them.
To achieve this, the most obvious connection is that the TD signal of one device must be connected to the RD input of the other device (and vice versa).
Also, however, many DTE devices use other RS-232 pins for out-of-band (i.e., "hardware") flow control. One of the most common schemes is for the DTE (the PC) to assert the RTS signal if it is ready to receive data (yes, it DOES sound backwards, but that's how it works), and for the DCE (the modem) to assert CTS when it is able to accept data. By connecting the RTS pin of one DTE to the CTS pin of the other DTE, we can simulate this handshake.
Also, it is common convention for many DTE devices to assert the DTR signal when they are powered on, and for many DCE devices to assert the DSR signal when they are powered on, and to assert the CD signal when they are connected. By connecting the DTR signal of one DTE to both the CD and DSR inputs of the other DTE (and vice versa), we are able to trick each DTE into thinking that it is connected to a DCE that is powered up and online. As a general rule, the Ring Indicate (RI) signal is not passed through a null-modem connection

63. DB-25 and DB-9 male and female connectors, as viewed from the pin side (not the solder side).

64. DB-9 connectors on both ends

65. DB-25 connectors on both ends

66. DB-9 connector on one end, DB-25 on the other end

67. RS-232 Signals The RS-232 standard: DB-25 DCE DB-9 1 AA x
Protective Ground 2
TXD 3 BA I
Transmitted Data
RXD BB O
Received Data 4
RTS 7 CA
Request To Send 5
CTS 8 CB
Clear To Send 6
DSR CC
Data Set Ready
GND AB
Signal Ground CD CF
Received Line Signal Detector 9 --
Reserved for data set testing 10 11
Unassigned 12
SCF
Secndry Rcvd Line Signl Detctr 13
SCB
Secondary Clear to Send 14
SBA
Secondary Transmitted Data 15 DB
Transmisn Signl Elemnt Timng 16
SBB
Secondary Received Data 17 DD
Receiver Signal Element Timing 18 19
SCA
Secondary Request to Send 20
DTR
Data Terminal Ready 21 CG
Signal Quality Detector 22 CE
Ring Indicator 23
CH/CI
I/O
Data Signal Rate Selector 24 DA
Transmit Signal Element Timing 25

68. Common Null-Modem Connection
25 Pin
9 Pin
FG (Frame Ground) 1 - X FG
TD (Transmit Data) 2 3 RD
RD (Receive Data) TD
RTS (Request To Send) 4 7 8 5
CTS
CTS (Clear To Send)
RTS
SG (Signal Ground) SG
DSR (Data Set Ready) 6 20
DTR
DTR (Data Terminal Ready)
DSR

69. RJ-45 Connector
The RJ-45 connector is commonly used for network cabling and for telephony applications. 
It's also used for serial connections in special cases. 

70. RJ-45 Connector for LAN
Also, please note that it is very important that a single pair be used for pins 3 and 6.  If one conductor from one pair is used for pin 3 and a conductor from another pair is used for pin 6, performance will degrade.  See the following figure.

72. RJ-45 Connector in Non LAN Applications
RJ-45 Pinout for RocketPort
The following chart shows the pinout for RJ-45 connectors used on certain RocketPort serial interface cards (manufactured by Comtrol).
The following chart shows the pinout for RJ-45 connectors used on certain ISDN S/T interfaces.  For more info, see ANSI T1.605.
Pinouts for ISDN
Here's an ISDN BRI U port pinout for a Cisco 750 series router:

73. Straight Through Cable vs. Crossover Cable
In general, the patch cords that you use with your Ethernet connections are "straight-through", which means that pin 1 of the plug on one end is connected to pin 1 of the plug on the other end. In this particular case it is not then important to wire them as above. Pin 1 is Pin 1 etc etc. However for the sake of uniformity it may be best to wire your cables with the same colour sequence.
Cross-Over cables are "crossed" end to end data cables aren't. If you have a network hub that has an uplink port on it then you do not need to make (or purchase a cross-over cable). Just switch the port on the hub to the 'uplink' mode.
If your hub does not have an 'uplink' port on it then the only way to cascade another hub or attach a cable modem is to use a cross-over cable. It helps for future reference to mark or attach a tag to the cross-over cable so that you do not attempt to use it as a 'normal' patch lead at some time in the future.

74. Straight Through Cable vs. Crossover Cable

75. Straight Through Cable vs. Crossover Cable

76. The Uses of RJ-45 Connector and Cat5 UTP Cable