1. CIS 1140 Network Fundamentals
Chapter 5 – Topologies and Ethernet Standards
Collected and Compiled
By JD Willard
MCSE, MCSA, Network+,
Microsoft IT Academy Administrator
Computer Information Systems Instructor
Albany Technical College

2. Attention: Accessing Demos
This course presents many demos.
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To access and log in to the Virtual Technical College web site:
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If you should click on the demo link and you get an Access Denied it is because you have not logged in to vtc.com or you need to log out and log back in.
If you should click on the demo link and you are taken to the VTC.com web site page you should do a search in the search box for the CompTIA Network+ (2009 Objectives) Course and run the video from within that page.

3. Objectives
Describe the basic and hybrid LAN physical topologies, and their uses, advantages, and disadvantages
Describe the backbone structures that form the foundation for most networks
Compare the different types of switching used in data transmission
Explain how nodes on Ethernet networks share a communications channel
Identify the characteristics of several Ethernet standards

4. Network Topology Basics Demo
Network Topologies
Topology is the term used to describe how devices are connected and how messages flow from device to device
There are two types of network topologies:
Physical topology is the physical layout of the network, including cable and device configuration
Logical topology refers to the method used to communicate between the devices
It is important to understand the physical topology before designing networks, because they can affect the logical topology chosen, how the building is cabled, and what kind of media is used
Network Topology Basics Demo

5. Simple Physical Topologies
Physical topology
Physical layout of nodes on a network
Depicts broad scope
Does not specify:
Device types
Connectivity methods
Addressing schemes
Topology integral to type of network, cabling infrastructure, and transmission media used
Fundamental shapes
Bus, ring, star
Hybrid
Physical Topologies Demo

6. Topologies pt. 1 Demo
Topologies pt. 2 Demo

7. Bus Bus topology Physical medium Passive topology Single cable
The single cable is called the bus and supports one channel, where each node shares total capacity
Connects all network nodes
No intervening connectivity devices
One shared communication channel
Physical medium
Coaxial cable
Passive topology
Node listens for, accepts data
Uses broadcast to send
Bus Topology Demo

8. Basic Ethernet Bus
An Ethernet network where all machines are daisy chained using coaxial cable (Thin Ethernet/Thin-net or Thick Ethernet/Thick-net).
Machine 2 wants to send a message to machine 4.
First it 'listens' to make sure no one else is using the network.
If it is all clear it starts to transmit its data on to the network (represented by the yellow flashing screens).
Each packet of data contains the destination address, the senders address, and of course the data to be transmitted.
The signal moves down the cable and is received by every machine on the network but because it is only addressed to number 4, the other machines ignore it.
Machine 4 then sends a message back to number 2 acknowledging receipt of the data (represented by the purple flashing screens).

9. Terminators Signal bounce One end grounded
Bus requires a terminator at each end of cable
50-ohm resistors
Stop signal at end of wire
Prevents signal bounce
Signal bounce
Signal travels endlessly between two network ends
One end grounded
Removes static electricity
A terminated bus topology network

10. Bus (cont’d.) Bus topology advantage Disadvantages
Easy to install and add devices
Relatively inexpensive
Requires less cable
Disadvantages
Requires 50 ohm terminators at each end of the cable
Requires grounding loop
Does not scale well
Difficult to troubleshoot
Not very fault tolerant
Entire network shuts down if the cable breaks (signal bounce)

11. Ring Ring topology Node connects to nearest two nodes Circular network
Clockwise data transmission
One direction (unidirectional) around ring
Token passing
Token Ring and FDDI networks
Active topology
Workstation participates in data delivery
Data stops at destination
Physical medium
Twisted pair or fiber-optic cabling
Ring Topology Demo

12. Ring (cont’d.) Ring advantages Drawbacks No network collisions
Malfunctioning workstation can disable network
Not very flexible or scalable
A ring topology network

13. Star Star topology Physical medium
Node connects through central device
Hub, Router or switch
Physical medium
Twisted pair or fiber-optic cabling
Single cable connects only two devices
Star Topology Demo
A star topology network

14. Star Most popular fundamental layout
Modern Ethernet networks based on star topology
1024 addressable logical network nodes maximum
How Ethenet accesses the cable and transmits using a hub.

15. Star (cont’d.) Star advantages Star disadvantages Fault tolerant
Easier to troubleshoot
A break in the cable does not shut down the network
Higher reliability
Flexible
No terminators required
Star disadvantages
Uses more cable than ring or bus networks
Connectivity devices more expensive than terminators
Connectivity device failures take down entire LAN segments
Any single cable connects only two devices, Cabling problems affect two nodes at most

16. Hybrid Topologies Pure bus, ring, star topologies Hybrid topology
Rarely exist because too restrictive
Hybrid topology
More likely
Complex combination of pure topologies
Several options
Hybrid Topology Demo
Hybrid Topologies Demo

17. Star-Wired Ring Star-wired ring topology Star physical topology
Ring logical topology
Token passing data transmission method
Benefit
Star fault tolerance
Reliability of token passing
Network use
Token Ring networks
IEEE 802.5

18. Star-Wired Ring (cont’d.)
Token Ring MAUs can be connected together using straight-through patch cables to connect the Ring Out port of one MAU and the Ring In port of the next MAU until the network of MAUs forms a circle.
Up to 255 stations can be connected to the network when using Shielded Twisted Pair cable and 72 when using Unshielded Twisted Pair cable.

19. MAU Showing Internal Ring
A Token Ring hub (MAU) changes the topology from a physical ring to a star wired ring.
MAU can automatically bypass any ports that are disconnected or have a cabling fault.

20. Star-Wired Bus Star-wired bus topology Advantage Drawback
Workstation groups
Star-connected devices
Networked via single bus
Advantage
Cover longer distances
Easily interconnect, isolate different segments
Drawback
Cabling, connectivity device expense
Basis for modern Ethernet networks

21. Star-Wired Bus (cont’d.)
A star-wired bus topology network

22. Logical Topologies
Logical topology: how data is transmitted between nodes
May not match physical topology
Bus logical topology: signals travel from one network device to all other devices on network
Required by bus, star, star-wired physical topologies
Ring logical topology: signals follow circular path between sender and receiver
Required by ring, star-wired ring topologies
Broadcast domain
All nodes connected to single repeating device or switch
Logical Topologies Demo

23. Logical Topology
Physical Topology
Description
Bus
Messages are sent to all devices connected to the bus.
Star
Ring
Messages are sent from device-to-device in a predetermined order until they reach the destination device.
Messages are sent directly to (and only to) the destination device.

24. Backbone Networks Cabling connecting hubs, switches, routers
More throughput
Large organizations
Fiber-optic backbone
Cat 5 or better for hubs, switches
Enterprise-wide network backbones
Complex, difficult to plan
Enterprise
Entire organization
Significant building block: backbone

25. Serial Backbone Simplest backbone Daisy-chain Benefit
Two or more devices
Connect using single medium in daisy-chain fashion
Daisy-chain
Linked series of devices
Benefit
Logical growth solution
Modular additions
Low-cost LAN infrastructure expansion
Easily attach switches

26. Serial Backbone (cont’d.)
Backbone components
Gateways, routers, switches
Serial connection of repeating devices
Limited distance spanned between each
Standards
Define number of repeating devices allowed
Exceed standards
Intermittent, unpredictable data transmission errors
Not used in modern networks

27. Distributed Backbone Connectivity devices Benefit
Connected to hierarchy of central connectivity devices
Benefit
Simple expansion, limited capital outlay
More complicated distributed backbone
Connects multiple LANs, LAN segments using routers
Additional benefits
Workgroup segregation
May include daisy-chain linked repeating devices
Consider length
Drawback
Potential for single failure points

28. Collapsed Backbone Uses router or switch Highest layer
Single central connection point for multiple subnetworks
Highest layer
Single router or switch with multiprocessors
Central router failure risk
Routers may slow transmission
Advantages
Interconnect different subnetwork types
Central management

29. Parallel Backbone Most robust network backbone
More than one central router, switch
Connects to each network segment
Requires duplicate connections between connectivity devices
Advantage
Redundant links
Increased performance
Better fault tolerance

30. Switching Logical network topology component
Determines connection creation between nodes
Three methods
Circuit switching
Packet switching
Multiprotocol label switching
Circuit Switching and Packet Switching (3:30)

31. Circuit Switching Connection established between two network nodes
Before transmitting data
Dedicated bandwidth
Data follows same initial path selected by switch
Monopolizes bandwidth while connected
Resource wasted
Uses
Live audio, videoconferencing
Traditional telephone calls
Most popular

32. Packet Switching Breaks data into packets before transporting Packets
Travel any network path to destination
Find fastest circuit available at any instant
Need not follow each other
Need not arrive in sequence
Reassembled at destination
Requires speedy connections for live audio, video transmission
Examples
Ethernet networks
Internet

33. MPLS (Multiprotocol Label Switching)
Introduced by IETF in 1999
Enables multiple types of Layer 3 protocols:
To travel over any one of several Layer 2 protocols
Most often supports IP
Common use
Layer 2 WAN protocols
Offers potentially faster transmission than packet- or circuit-switched networks
Advantages
Use packet-switched technologies over traditionally circuit switched networks
Create end-to-end paths
Addresses traditional packet switching limitations
Better QoS (quality of service)

34. Ethernet Most popular networking technology used on modern LANs
Benefits
Flexible
Can run on various network media
Excellent throughput
Reasonable cost
All variations
Share common access method
CSMA/CD
What is Ethernet? Demo
Ethernet Demo

35. CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
Network access method
Controls how nodes access communications channel
Necessary to share finite bandwidth
Carrier sense
Ethernet NICs listen, wait until free channel detected
Multiple access
Ethernet nodes simultaneously monitor traffic, access media
CSMA / CD Demo
CSMA/CD Access Method demo

36. CSMA/CD (cont’d.) Collision Two nodes simultaneously:
Check channel, determine it is free, begin transmission
Collision detection
Manner nodes respond to collision
Requires collision detection routine
Enacted if node detects collision
Jamming
NIC issues
32-bit sequence
Indicates
previous
message faulty

37. CSMA/CD (cont’d.) Heavily trafficked network segments Segment growth
Collisions common
Segment growth
Performance suffers
“Critical mass” number dependencies
Data type and volume regularly transmitted
Collisions corrupt data, truncate data frames
Network must detect and compensate
CSMA/CD process
CSMA/CD and CSMA/CA (5:33)

38. CSMA/CD (cont’d.) Collision domain Ethernet network design
Portion of network where collisions occur
Ethernet network design
Repeaters repeat collisions
Result in larger collision domain
Switches and routers
Separate collision domains
Collision domains differ from broadcast domains
Broadcast domains and collision domains
Collision Domains Demo

39. CSMA/CD (cont’d.) Ethernet cabling distance limitations
Effected by collision domains
Data propagation delay
Data travel time too long
Cannot identify collisions accurately
100 or 1000 Mbps networks
Three segment maximum connected with two repeating devices
10 Mbps buses
Five segment maximum connected with four repeating devices

40. Ethernet Standards for Copper Cable
IEEE Physical layer standards
Specify how signals transmit to media
Differ significantly in signal encoding
Affect maximum throughput, segment length, wiring requirements
Ethernet Network Types Demo
BASE Terminology Demo
Ethernet Topologies (7:32)

41. Ethernet Standards for Copper Cable (cont’d.)
10Base-T
10 represents maximum throughput: 10 Mbps
Base indicates baseband transmission
T stands for twisted pair
Requires CAT3 or higher UTP
Two pairs of wires: transmit and receive
Full-duplex transmission

42. Follows 5-4-3 rule of networking
A 10Base-T network
Follows rule of networking
Five network segments
Maximum segment length is 100 meters
Four repeating devices (hubs)
Three populated segments maximum

43. Ethernet Standards for Copper Cable (cont’d.)
100Base-T (Fast Ethernet)
IEEE 802.3u standard
Similarities with 10Base-T
Baseband transmission, star topology, RJ-45 connectors
100Base-TX
100-Mbps throughput over twisted pair
Full-duplex transmission: doubles effective bandwidth
Fast Ethernet Demo

44. A 100Base-T network Supports three network segments maximum
Connected with two repeating devices
100 meter segment length limit between nodes

45. Ethernet Standards for Copper Cable (cont’d.)
1000Base-T (Gigabit Ethernet)
IEEE 802.3ab standard
1000 represents 1000 Mbps
Base indicates baseband transmission
T indicates twisted pair wiring
Four pairs of wires in Cat 5 or higher cable
Transmit and receive signals
Data encoding scheme: different from 100Base-T
Standards can be combined
Maximum segment length: 100 meters, one repeater
Gigabit Ethernet Demo

46. Ethernet Standards for Copper Cable (cont’d.)
10GBase-T
IEEE 802.3an
Pushing limits of twisted pair
Requires Cat 6, 6a, or 7 cabling
Maximum segment length: 100 meters
Benefits
Very fast data transmission
Cheaper than fiber-optic
Uses
Connect network devices
Connect servers, workstations to LAN
Even Faster Ethernet Demo

47. Ethernet Over Copper Summary
Category
Standard
Bandwidth
Cable Type
Maximum Segment Length
Ethernet
10BaseT
10 Mbps (half duplex) 20 Mbps (full duplex)
Twisted pair (Cat3, 4, or 5)
100 meters
Fast Ethernet
100BaseTX
100 Mbps (half duplex) Mbps (full duplex)
Twisted pair (Cat5 or higher) Uses 2 pairs of wires
Gigabit Ethernet
1000BaseT
1,000 Mbps (half duplex) 2,000 Mbps (full duplex)
Twisted pair (Cat5 or higher)
10 Gigabit Ethernet
10GBaseT
10 Gbps (full duplex only)
Twisted pair (Cat5e, 6, or 7)

48. Ethernet Standards for Fiber-Optic Cable
100Base-FX (Fast Ethernet)
100-Mbps throughput, baseband, fiber-optic cabling
Multimode fiber containing at least two strands
Half-duplex mode
One strand receives; one strand transmits
412 meters segment length
Full duplex-mode
Both strands send and receive
2000 meters segment length
One repeater maximum
IEEE 802.3u standard

49. Ethernet Standards for Fiber-Optic Cable (cont’d.)
1000Base-LX (1-Gigabit Ethernet)
IEEE 802.3z standard
1000: 1000-Mbps throughput
Base: baseband transmission
LX: reliance on 1300 nanometers wavelengths
Longer reach than any other 1-gigabit technology
Single-mode fiber: 5000 meters maximum segment
Multimode fiber: 550 meters maximum segment
One repeater between segments
Excellent choice for long backbones

50. Ethernet Standards for Fiber-Optic Cable (cont’d.)
1000Base-SX (1-Gigabit Ethernet)
Differences from 1000Base-LX
Multimode fiber-optic cable (installation less expensive)
Uses short wavelengths (850 nanometers)
Maximum segment length dependencies
Fiber diameter, modal bandwidth used to transmit signals

51. Ethernet Standards for Fiber-Optic Cable (cont’d.)
1000Base-SX (cont’d.)
Modal bandwidth measurement
Highest frequency of multimode fiber signal (over specific distance)
MHz-km
Higher modal bandwidth, multimode fiber caries signal reliably longer
50 micron fibers: 550 meter maximum length
62.5 micron fibers: 275 meter maximum length
One repeater between segments
Best suited for shorter network runs

52. 10-Gigabit Fiber-Optic Standards
Extraordinary potential for fiber-optic cable
Pushing limits
802.3ae standard
Fiber-optic Ethernet networks
Transmitting data at 10 Gbps
Several variations
Common characteristics
Star topology, allow one repeater, full-duplex mode
Differences
Signal’s light wavelength; maximum allowable segment length

53. 10-Gigabit Fiber-Optic Standards (cont’d.)
10GBase-SR and 10GBase-SW
10G: 10 Gbps
Base: baseband transmission
S: short reach
Physical layer encoding
R works with LAN fiber connections
W works with SONET fiber connections
Multimode fiber: 850 nanometer signal transmission
Maximum segment length
Depends on fiber diameter

54. 10-Gigabit Fiber-Optic Standards (cont’d.)
10GBase-LR and 10GBase-LW
10G: 10 Gbps
Base: baseband transmission
L: long reach
Single-mode fiber: 1310 nanometer signal transmission
Maximum segment length
10,000 meters
10GBase-LR: WAN or MAN
10GBase-LW: SONET WAN links

55. 10-Gigabit Fiber-Optic Standards (cont’d.)
10GBase-ER and 10GBase-EW
E: extended reach
Single-mode fiber
Transmit signals with 1550 nanometer wavelengths
Longest fiber-optic segment reach
40,000 meters (25 miles)
10GBase-EW
Encoding for SONET
Best suited for WAN use

56. Ethernet Over Fiber Summary
Category
Standard
Bandwidth
Cable Type
Maximum Segment Length
Fast Ethernet
100BaseFX
100 Mbps (multimode cable)
Fiber optic
412 meters
Gigabit Ethernet
1000BaseSX (short)
1,000 Mbps (half duplex) 2,000 Mbps (full duplex)
220 to 550 meters depending on cable quality
1000BaseLX (long)
550 meters (multimode) 10 kilometers (single-mode)
10 Gigabit Ethernet
10GBaseSR/10GBaseSW
10 Gbps (full duplex only)
Multimode fiber optic
300 meters
10GBaseLR/10GBaseLW
Single mode fiber optic
10 kilometers
10GBaseER/10GBaseEW
40 kilometers

57. Multiple types of Ethernet on a WAN

58. Ethernet Frames Four types Frame types differ slightly
Ethernet_802.2 (Raw)
Ethernet_802.3 (Novell proprietary)
Ethernet_II (DIX)
Ethernet_SNAP
Frame types differ slightly
Coding and decoding packets
No relation to topology, cabling characteristics
Framing
Independent of higher-level layers

59. Using and Configuring Frames
Ensure all devices use same, correct frame type
Node communication
Ethernet_II used today
Frame type configuration
Specified using NIC configuration software
NIC autodetect
Importance
Know frame type for troubleshooting

60. Frame Fields Common fields
7-byte preamble, 1-byte start-of-frame delimiter
SFD (start-of-frame delimiter) identifies where data field begins
14-byte header
4-byte FCS (frame check sequence)
Frame size range: 64 to 1518 total bytes
Larger frame sizes result in faster throughput
Improve network performance
Properly manage frames

61. Ethernet_II (DIX) Ethernet Frames Demo
Developed by DEC, Intel, Xerox (abbreviated DIX)
Before IEEE
Most commonly used on contemporary Ethernet networks
Ethernet Frames Demo
The preamble is a set of alternating ones and zeroes terminated by two ones (i.e., 11) that marks it as a frame.
The destination address identifies the receiving host's MAC address.
The source address identifies the sending host's MAC address.
The 2-byte type field identifies the Network layer protocol
The data, or the information that needs to be transmitted from one host to the other.
Optional bits to pad the frame. Ethernet frames are sized between 64 and 1518 bytes. If the frame is smaller than 64 bytes, the sending NIC places "junk" data in the pad to make it the required 64 bytes.
The FCS/CRC (frame check sequence/cyclic redundancy check) is the result of a mathematical calculation performed on the frame. The CRC helps verify that the frame contents have arrived uncorrupted.

62. PoE (Power over Ethernet)
IEEE 802.3af standard
Supplying electrical power over Ethernet connections
Two device types
PSE (power sourcing equipment)
PDs (powered devices)
Requires Cat 5 or better copper cable
Connectivity devices must support PoE
Compatible with current installations
PoE capable switch
PoE adapters
Power over Ethernet (3:45)

63. Summary Physical topology describes basic network physical layout
Examples: bus, ring, star, hybrid
Logical topology describes signal transmission
Network backbones
Serial, distributed, collapsed, parallel
Switching
Manages packet filtering, forwarding
Ethernet
Cabling specifications, data frames, PoE

64. The End