1. Chapter 4: Connecting Through a Cabled Network

2. Communications Media Types
OSI Layer 1: communication media and interfaces
Five basic communication media types
Coaxial cable: based on copper wire
Twisted-pair cable: based on copper wire
Fiber-optic cable: glass or plastic cable
Hybrid fiber/coax: combines copper and fiber
Wireless technologies: radio or microwaves
The suitability of media varies with different networks
Example: uses of coaxial cable
Older LANs
LANs in areas with signal interference strong
Connecting wireless antenna to network device

3. Communications Media Types
When choosing the best medium for a LAN or WAN consider capabilities and limitations of media
Factors affecting the choice of LAN or WAN medium
Data transfer speed
Use in specific network topologies
Distance requirements
Cable and cable component costs
Additional network equipment that might be required
Flexibility and ease of installation
Immunity to interference from outside sources
Upgrade options
Security

4. Communications Media Types
Backbone cabling: cable that runs between network equipment rooms, floors, and buildings and is often used to connect network devices
Plenum cable: Teflon-coated cable that does not emit a toxic vapor when burned
Used in locations such as a false ceiling through which circulating air reaches other parts of a building
Impedance: total amount of opposition to the flow of current and is measured in ohms

5. Coaxial Cable
Coaxial cable was the first media type defined with Ethernet standards (early 1980s)
Two types of coaxial cable (coax)
Thick: used in early networks, typically as backbone
Thin: used to connect desktops to LANs
Has much smaller diameter than thick coax
Use of both thick and thin coaxial cables declining

6. Thick Coax Cable Thick coax cable (thickwire, thicknet, RG-8)
Has relatively large .4-inch diameter
Copper or copper-clad aluminum conductor at core
Conductor surrounded by insulation
Aluminum sleeve wrapped around insulation
PVC or Teflon jacket covers aluminum sleeve
The cable jacket is marked every 2.5 m to show where a network-connecting device can be attached
If devices are attached more closely than 2.5 meters, the signal can be impaired and errors may occur
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7. Figure 4-1 Thick coax (RG-8) cable
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8. Thick Coax Cable Media access unit (MAU) transceiver
Connecting device driven by small current (.5 amps)
Has 15-pin attachment unit interface (AUI) connector
AUI connects via cable to network cable
Thick AUI cable up to 50 meters long
Impedance of thick coax cable is 50 ohms
Maximum cable segment length is 500 meters
10Base5
10 = the cable transmission rate is 10 Mbps
Base = that baseband transmission is used
5 = 500 meters for the longest cable run
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9. Figure 4-2 Connecting to thick coax cable
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10. Table 4-1 Thick coax cable (10Base5) properties for Ethernet applications
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11. Thin Coax Cable Ethernet specifications for thin coax cable
50 ohms of impedance (RG-58A/U or Radio Grade 58)
Meets criteria in 10Base2 designation
Maximum theoretical speed of 10Mbps
Wire runs up to 185 meters (formerly 200)
Used for baseband (Base) data transmission
Thin coax has a smaller diameter than thick coax (.2")
Implementing thin coax cable:
Cable is attached to a bayonet nut connector (BNC)
BNC is connected to a T-connector
Middle of T-connector is attached to a NIC
Terminator may be attached to one end of a T-connector
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12. Figure 4-3 A BNC T-connector with a terminator at one end
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13. Thin Coax Cable Advantages of thin coax cable
Easier and cheaper to install than thick coax
More resistant to EMI and RFI (interferences) than twisted pair
Coax is still found on some legacy networks and in places subject to very high EMI/RFI
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14. Table 4-2 Thin coax cable (10Base2) properties for Ethernet applications
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15. Twisted Pair Cable Twisted-pair cable
Contains pairs of insulated copper wires
Outer insulating jacket covers wires
Communication specific properties
Copper wires twisted to reduce EMI and RFI
Length: up to 100 meters
Transmission speed: up to 10 Gbps
RJ-45 plug-in connector attaches cable to device
Less expensive and more flexible than T-connectors
Two kinds of twisted pair cable: shielded and unshielded (preferred)
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16. Figure 4-4 Twisted-pair cable with an RJ-45 plug-in connector
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17. Shielded Twisted Pair Cable
Shielded Twisted Pair Cable (STP)
Surrounded by braided or corrugated shielding
Shielding reduces interference due to EMI and RFI
Further reducing impact of EMI and RFI
Interval of twists (lay length) in each pair should differ
Connectors and wall outlets should be shielded
Have proper grounding
Use medium when strong interference sources nearby
Example: heavy electrical equipment
Shielded cable and associated equipment is more expensive than unshielded cable
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18. Figure 4-5 STP and UTP cables
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19. Unshielded Twisted-Pair Cable
Unshielded Twisted-Pair Cable (UTP)
Consists of wire pairs within insulated outer covering
Has no shielding between wires and encasement
UTP is the most frequently used network cable
Reducing EMI and RFI
Twist interior strands (like STP)
Built-in media filter into network equipment, workstation, and file connection servers
UTP cables used in 10BaseT networks
Category 3: transmission rates up to 16 Mbps
Category 4: transmission rates up to 20 Mbps
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20. Unshielded Twisted-Pair Cable
Category 5 UTP has 100 Mbps transmission rate
Category 5e (enhanced) UTP vs. Category 5 UTP
1 Gbps transmission rate
Uses better-quality copper
Has a higher twist ratio for better EMI/RFI protection
Category 6 UTP
Wire pairs are wrapped within insulating foil
Has fire resistant plastic sheath
Category 7 UTP
Extremely resistant to EMI/RFI but it requires special connectors and is not as flexible
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21. Table 4-3 Ethernet twisted-pair cable standards
Table 4-3 Ethernet twisted-pair cable standards
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22. Unshielded Twisted-Pair Cable
Reasons for preferring UTP over STP
Fewer points of failure
Has no shield that can tear (up through Category 5e)
Connectors and wall outlets do not need shielding
Proper grounding not as critical to purity of signal
Horizontal cabling (defined by EIA/TIA-568 standard)
Cabling connecting workstations/servers in work area
Implemented with Categories 5e, 6, and 6e UTPs
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23. Table 4-4 10BaseT (and in general 100BaseX) unshielded
twisted-pair Ethernet specifications
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24. Table 4-5 10BaseT (and in general 100BaseX) shielded
twisted-pair Ethernet specifications
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25. Figure 4-7 Twisted-pair cable connected to an RJ-45 connector
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26. Fiber-Optic Cable Fiber-optic cable
One or more glass or plastic fiber cores encased in glass tube (cladding)
Fiber cores and cladding are surrounded by PVC cover
Signal transmissions consist of light (usually infrared)
Three commonly used fiber-optic cable sizes
50/125 micron
Micron (μm): millionth of a meter
50 represents core diameter
125 represents cladding diameter
62.5/125 micron
100/140 micron
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27. Figure 4-9 Fiber-optic cable
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28. Fiber-Optic Cable Uses of fiber-optic cables Cable-plant backbones
Fat pipe: high bandwidth backbone between floors
Connect different buildings in campus environment
Joining spread-out LANs into a WAN
Advantages of fiber-optic cables
Each cable type has multimode transmission capacity
Transmission speeds from 100 Mbps - over 100 Gbps
No EMI or RFI problems, data travels by light pulse
Low attenuation (attenuation: signal loss during travel)
Secure from unauthorized taps
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29. Fiber-Optic Cable Disadvantages of fiber-optic cables Fragile
More expensive than UTP
Requires specialized training to install
Basic characteristics of light transmission
Light wavelength is measured in nanometers (nm)
Infrared light travels in the range of nm
Three ideal wavelengths (windows): 850 nm, 1300 nm, 1550 nm
High-speed transmission typically use the 1300 nm window
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30. Fiber-Optic Cable Fiber-optic cable comes in two modes
Single-mode: used for long-distance communication
8-10/125 micron cable transmits one wave at a time
Communications signal is laser light
Multimode: supports multiple waves (broadband)
Comes in two varieties: step index and graded index
Cable diameter between 50 and 115 microns
Source for multimode cable is light-emitting diode (LED)
Three connector types used with fiber-optic cables
Subscriber connector (SC)
Straight tip (ST)
MTRJ
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31. Table 4-6 EIA/TIA-568-B specifications for single-mode
fiber-optic cable in a cable-plant backbone
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32. Table 4-7 EIA/TIA-568-B specification for multimode
fiber-optic cable in a cable-plant backbone
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33. Hybrid Fiber/Coax Cables
Hybrid fiber/coax (HFC) cable
Single sheath containing fibers and copper cables
Different combinations for different implementations
How HFC cables improve cable networks
Increase upstream bandwidth and reduce noise
HFC drawbacks: expensive and not fully installed
Services possible using HFC cables
Plain old telephone service (POTS)
Over 200 digital TV channels
Over 400 digital point channels
High-speed, two-way digital data link for PCs
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34. High-speed Technologies For Twisted-Pair And Fiber-Optic Cable
High-speed threshold: 10 Mbps
Three technologies enhancing cables for high-speed
Fast Ethernet
Gigabit Ethernet
10 Gigabit Ethernet
40 and 100 Gigabit Ethernet
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35. Fast Ethernet
Fast Ethernet: 100 Mbps data transfer over twisted-pair cable
Two Fast Ethernet technologies
100BaseVG or 100VG-AnyLAN
100BaseX
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36. The IEEE 802.3u Standard
IEEE 802.3u (100BaseX): standard for Fast Ethernet
Versions of 100BaseX: 100BaseT, 100BaseTX, 100BaseT4, 100BaseT2, 100BaseFX
Common properties of standards (except 100BaseT2)
All use CSMA/CD media access methods
All propagate signal in more than one direction
100BaseT2 transmits signal in timed-delay manner
Signal transmitted with twisted-pair or fiber-optic cable
Limitations and restrictions
Signal can only go through one Class I repeater or two Class II repeaters
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37. The IEEE 802.3u Standard
A Class I repeater introduces delays when performing the Fast Ethernet conversion
For this reason, only one Class I repeater can be put in a single, Fast Ethernet LAN segment
Class II repeaters have all ports of the same Fast Ethernet media type so there is no need for a conversion
Very little delay is introduced by the quick movement of data
For this reason, two Class II repeaters are allowed per Fast Ethernet segment
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38. Table 4-8 100BaseX communication options
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39. The IEEE 802.12 Standard IEEE 802.12: (100BaseVG/100VG-AnyLAN)
Abandons CSMA/CD for demand priority
Demand priority
Ensures signal travels in one direction
Used in star networks linked by a central switch
Grants requests one by one
Benefits of demand priority
Enables packet travel up to 100 Mbps
Security: packet visible only to receiving node
Prioritizes multimedia and time sensitive transmissions
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40. Figure 4-13 Using demand priority
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41. Gigabit Ethernet Gigabit Ethernet (1000BaseX)
Provides data transfer of up to 1 Gbps
Uses CSMA/CD access methods
Upgrade path for 100BaseX Ethernet networks
Uses of Gigabit Ethernet
Alternative for backbone LAN congestion
Attract token ring users with star-based topologies
Gigabit Ethernet target
Installations using Layer 3 routed communications
Separate standards for fiber-optic and twisted-pair cables
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42. Table 4-9 Gigabit Ethernet specifications
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43. 10 Gigabit Ethernet 10 Gigabit Ethernet or 10GBaseX
High-speed networking protocol
Competes with other high-speed MANs and WANs
Provides fast backbone networking in LANs
True Ethernet with some differences
Operates at full duplex (transmission in two directions)
Does not need to employ CSMA/CD
No packet collisions by design
How to distinguish various standards
By interfaces and transmission characteristics
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44. 40 and 100 Gigabit Ethernet
40 Gigabit (40GBaseX/40GBaseE) and 100 Gigabit (100GBaseX/100GBaseE) are relatively new high-speed Ethernet options
Both are intended to serve two purposes:
Enable faster computing services, such as through faster backbone speeds
Provide faster communications for network aggregation points, such as links to servers and network storage
Shared resources such as Internet Protocol television (IPTV) and streaming media require faster backbone speeds
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45. 40 and 100 Gigabit Ethernet
Network aggregation – refers to central resources such as servers and network storage
Gigabit Ethernet is intended to remove network transport bottlenecks surrounding these aggregated resources
Table Gigabit Ethernet specifications
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46. Table 4-12 100 Gigabit Ethernet specifications
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47. Connecting Computers to a Cabled Network
Network Interface Card (NIC)
Enables node to connect to cabled network
Matches transport methods, bus types, and media
Network connection requires four components
Appropriate connector for network medium
Hardware and protocol control firmware and drivers
Transceiver
Controller to support MAC sublayer of Data Link layer
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48. The NIC Connector Connector designed for specific medium type
Examples: twisted-pair, fiber-optic cable, wireless
Older combination NICs have multiple connectors
May be used with different media
Newer combination NICs have single connector
Select one among: 10BaseT, 100BaseX, 1000BaseTX
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49. The Role of Firmware and NIC Drivers
Firmware and NIC driver support communications
Firmware: software stored on a chip, such as ROM
NIC Driver: manages how packets or frames sent
Firmware or driver may automatically detect media
Some NIC drivers can be signed
Driver signing: placing digital signature in driver
Functions of digital signature
Ensures driver compatible with operating system
Certifies that driver tested for defects or viruses
Ensures that driver cannot overwrite new driver
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50. Using a Transceiver
Cable connector is attached to transceiver Transceiver: device that transmits and receives signals on a communications cable Transceiver may be internal or external to NIC
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51. The Role of the MAC Controller Unit
MAC controller unit and firmware work together to encapsulate:
Source and destination address information
Data to be transported
CRC error control information
MAC Controller operates at two sublayers of Layer 2
MAC sublayer: formats frames
LLC sublayer: initiates and maintains link between nodes and ensures the communications link is not broken and remains reliable after it is established
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52. Half- and Full-Duplex NIC Communications
Two transmission modes for NIC and network equipment
Half-duplex: cannot send and receive at the same time
Full-duplex: can send and receive simultaneously
Made possible by buffering at NIC
Buffering: temporarily storing information
Full-duplex is a good choice on networks
Usually faster than half-duplex
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53. Buses and NICs Bus: data pathway inside the computer
Common bus types (standards)
Industry Standard Architecture (ISA)
Extended Industry Standard Architecture (EISA)
Microchannel Architecture (MCA)
Peripheral Computer Interface (PCI)
SPARC Bus (SBUS)
Universal Serial Bus (USB)
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54. Choosing a NIC Every NIC is critical for effective communication
Questions to consider when purchasing a NIC
Is NIC for host computer, server, or workstation?
What kind of throughput does the computer require?
What network media and transport methods are in use?
Who manufactures the NIC?
What is the computer or network equipment bus type?
What operating system is used by the computer?
Are half-duplex or full-duplex communications used?
If NIC is for a special application, how does it attach?
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55. Designing a Cabled Network
Design choices applicable to most networks
Use Ethernet as the transport method
Use twisted pair to the desktop
Employ fiber-optic cable for the backbone
Connect servers to the network at 1 Gbps or 10 Gbps
Use the best and fastest options within budget
Scenario: small credit union in two story building
Use star-bus hybrid topology
Run 100BaseT to computers on both floors
Fiber-optic cable run for backbone between floors
Connect servers using 1000BaseTX or 10GBaseF
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56. Figure 4-18 Designing a network for a small credit union
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57. Summary
High-speed technologies for twisted-pair and fiber-optic cabling include Fast Ethernet, Gigabit Ethernet, 10 Gigabit Ethernet, 40 Gigabit Ethernet, and 100 Gigabit Ethernet NICs have an important role on networks because these devices connect computers and network devices to network cable. Important NIC components on a cabled network include a connector, firmware and drivers, a transceiver, and a MAC controller.
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