1. Chapter 4 Signal Transmission Network Media

2. Signal Transmission
Signaling—the way data is transmitted across the media
Digital signaling
Two discrete states
0 or 1, on or off
Analog signaling
Constantly changing electromagnetic waves

3. Digital Signaling
Two different voltages are used. One voltage to represent on and another voltage to represent off

4. Analog Signaling Constantly changing electromagnetic wave
Characteristics:
Amplitude
Strength of signal (height of wave)
Frequency
Amount of time needed to complete one cycle of the wave
Phase
Relative state of one wave in reference to another wave
Can be divided into multiple channels to allow greater bandwidth

5. Attenuation/Noise
Loss of signal strength as signal travels across media
Signal must be amplified or regenerated to ensure that data is transmitted correctly
Noise on media can disrupt data signal
Static, cross-talk, etc.
Electromagnetic interference (EMI)
Radio frequency interference (RFI)
Amplifiers and regenerators are used to increase the distance that signals can travel

6. Converting Analog to Digital
Modems
At sending computer, convert computer digital signal to analog signal for transmission via media
At receiving computer, convert analog signal to digital signal
Modulator/Demodulator

7. Transmission Direction
Simplex—transmission of data in one direction only (television)
Half-duplex—transmission of data in both directions but only one direction at a time (CB radio)
Full-duplex—simultaneous sending and receiving of data (telephone)
Full-duplex is used on data networks by using multiple channels
one wire used for sending and another wire for receiving

8. Multiplexers
Enables multiple signals to travel simultaneously by combining two or more separate signals and transmitting them together.
Multiplexer (mux) at sending end combines signals and demultiplexer (demux) at receiving end separates signals
Example: Cable TV--numerous signals travel through coaxial cable; circuitry in the TV, VCR, or cable box separate the signals into different channels

9. Multiplexing Methods Time Division Multiplexing
Divides channel into time slots--each device is allotted a time slot
Statistical Multiplexing
Number of time slots allotted for each device varies depending on priority and need
Wavelength Division Multiplexing
Used for fiber-optic (light); different wavelength used for each channel

10. Throughput/Bandwidth
Throughput is the amount of data that can be sent across the network media in a given time.
Measured in bits per second
Bandwidth is the range of frequencies that the media can transmit
Frequently throughput and bandwidth are used interchangable
Two methods for allocating bandwidth:
Baseband
Broadband

11. Baseband Transmission signals use the entire media bandwidth.
Commonly used for digital signaling.
Most LANs use baseband signaling

12. Broadband Media bandwidth is divided into multiple channels.
Each channel can carry different analog signals
Broadband networks support multiple simultaneous signals over a single transmission medium
Cable TV is an example of broadband transmission.
Many channels are broadcast over the same media all the time.
You select which channel you want to watch.

13. Network Adapters (NICs or NACs)
Provide the physical connection between your computer and the network media
Transmit and receive data
Prepare data for the network cable
Send the data to another computer or device
Control the flow of data between the computer and the network media

14. Media Characteristics
Throughput/bandwidth
Cost
Installation—cable cost, ease of installation
Maintenance—troubleshooting, repairing, replacing
Scalability
Node Capacity—max # of node,
Attenuation—max length of segment, max number of segments
Noise immunity
electromagnetic interference, radio frequency interference, and eavesdropping
Connectors

15. Network Media Anything that carries the message through the network
Copper
Coaxial cable
Twisted-pair cable
Glass
Fiber-optic cable
Wireless (Air)
Radio waves
Microwaves
Infrared
Transmission media—Physical path through which computers send and receive signals

16. Coaxial Cable (Coax) Copper core surrounded by insulation and a sheath
Shielding makes it more resistant to interference
Two types of coax cable used in networks
Thinnet (10Base2)—RG 58 A/U
Thicknet (10Base5)—RG 62
Thinnet
Thicknet

17. Coaxial cable showing various layers
Outer shield
Insulation (PVC, Teflon)
Conducting core
Copper wire mesh or
aluminum sleeve

18. Thicknet cable transceiver with detail of a vampire tap piercing the core
Drop Cable

19. Coaxial Cable
Terminators used at both ends of network to prevent signal bounce back
Used with bus topology
BNC cable connector used for Thinnet cable; n-connectors are used for Thicknet
BNC T-connector
BNC cable connector
BNC Terminator

20. Coaxial Characteristics

21. Twisted-Pair Cable Similar to telephone wiring
Color-coded pairs of wire; twisted and encased in plastic coating
Unshielded twisted-pair and shielded twisted-pair cables
UTP
Twisted to reduce crosstalk (signal traveling one pair being hear by another pair or from another cable)
More twisted the higher quality of wire (twist ratio).
Shielded twisted pair has added layer of insulation such as a foil or metal shield
STP
Shielding

22. RJ-45 connector and jack

23. Twisted Pair Cable Categories
Category 1-2: Voice communications and low speed data communications.
Category 3: Suitable for computer networks. Data transmission rates up to 10 Mbps. Currently used for phone installations (home)
Category 4: Data transmission rates up to 20 Mbps
Category 5: Data transmission rates up to 100 Mbps. Very popular for LANs.
Category 5E: Higher speeds are possible (200 Mbps); more twists
Category 6: Speeds up to six times faster than Cat 5
Category 7: Speeds up to 1 Ghz (Gigabit)

24. UTP Characteristics
Cost: Relatively inexpensive; depends on grade of copper and any enhancements
Installation: Easy to install
Bandwidth: Mbps (Cat 5)
Higher speeds are possible (up to 1000Mbps—Cat5E, Cat 6 and Cat 7)
Node Capacity: Two (computer to hub)
Attenuation: 100 meters
EMI: Very susceptible to EMI and eavesdropping
Connector: RJ-45

25. STP Characteristics
Cost: Relatively inexpensive (more UTP, less than Thicknet or fiber-optic.
Installation: Slightly more difficult than UTP
Bandwidth: same as UTP
Node Capacity: Two
Attenuation: 100 meters
EMI: Susceptible to EMI (but less susceptible than UTP) and eavesdropping
Connector: RJ-45

26. Plenum Cable
A plenum is the space between the false ceiling and the floor above.
Plenum-grade cable is fire resistant and produces a minimum of smoke
More expensive than PVC cable and less flexible
May be required by fire code

27. Fiber-optic cable Contains one or more glass fibers (core)
Data transmitted via pulsing light
Two categories: Single-mode and multi-mode
Optical fiber (core)
Glass cladding
One or more glass fibers surrounded by glass cladding and an outer sheath.
Transmits light pulses
-Single-mode cable—carries one frequency of light—faster and longer distances but more expenses
-Multi-mode cable—carries several frequencies of light—more often used because its cheaper
Fiber is expected to replace UTP in networks over the next decade
Currently still more expensive and difficult to work with but prices are coming down.
Fiber-optic connectors:
ST and SC
Protective outer sheath
(jacket)

28. Fiber-optic Characteristics
Cost: More expensive than copper cable
Installation: More difficult than copper cable
Bandwidth: 100 Mbps to 1 Gbps
Node: 2
Attenuation: Several kilometers
EMI: Not subject to EMI; immune to eavesdropping
Connectors: ST and SC are popular

29. Cable Media Comparison

30. Wireless Media (Atmospheric)
Infrared
Radio Frequency (RF)
Narrow-band
Spread-spectrum
Microwaves

31. Wireless portable computer using an infrared light beam to print

32. Infrared Transmission Systems
Use infrared light to transmit signals
Point-to-Point (Direct) or Broadcast (Indirect)
Point-to-Point (Direct)—highly focused and directed at a specific target
Line of Site
Broadcast—spread the signal to cover a wider area and allow reception of signal by several receivers
Signal can be bounced off walls and ceilings

33. Infrared Characteristics
Line of site
Light must be able to reach target
Bandwidth: 100 Kbps to 16 Mbps
Tested at up to 100Mbps but slower speeds are currently standard
Attenuation: Depends upon the quality of light and atmospheric conditions
EMI: Can be affected by intense light. Point-to-Point transmissions are fairly immune to eavesdropping. However, broadcast transmission are more easily intercepted.

34. Wireless portable computer connecting to a cabled network access point

35. Radio Frequencies Characteristics

36. Wireless bridge connecting two LANs

37. Microwave Transmission
Terrestrial Microwave
Line of site (max distance ~ 23 miles)
Transmission can be affected by atmospheric conditions (rain/fog). Vulnerable to EMI, jamming and eavesdropping
Bandwidth 1-10 Mbps
Satellite Microwave
Can transmit data over vast distances
Extremely expensive if you put up your own satellite

38. Example of Network Wiring
Horizontal cabling is the twisted-pair or fiber network media that connects the workstations and the wiring closets.
Workstation area cable (or patch cable) connects the workstation to the wall outlet, and the telecommunications connector is found at the wall outlet.
Horizontal cable runs between the wiring closet and the wall outlet. Last, horizontal cross connects connect devices in the wiring closet.
patch cable

39. Example Wiring Closet
Patch cables used between workstation and wall jack
Cable (often plenum grade) runs in walls and ceilings to patch panels
Patch cables run from patch panels to hubs, switches, and routers
Different color cable is often used to signify different cable runs
In a large network, several closets containing the patch panels and hubs may be located throughout the building(s)
Often fiber-optic cable is used between floors or buildings to increase speed (backbone)