1. Chapter 2 Network Topology
Computer Networking From LANs to WANs: Hardware, Software, and Security
Chapter 2
Network Topology
Cengage Learning: Computer Networking from LANs to WANs

2. Cengage Learning: Computer Networking from LANs to WANs
Objectives
Describe the difference between physical topology and logical topology
Sketch the physical topologies of bus, star, ring, fully connected, and hybrid networks
Explain what is meant by network hierarchy
Describe how a subnet is used to manage addresses on a network
Explain what a network access point is
Discuss the differences between a public network and a private network
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3. Physical Topology Vs Logical Topology
RECAP – Chapter 1
Topology – The way things are connected.
Computer Network Topology - How individual computers (devices, nodes) are connected
Chapter 2
Network Topology - Structure of connections between network computers
Physical topology
Intermediate network nodes, machines, and connection between intermediate nodes
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4. Physical Topology Vs Logical Topology
A path of data packet network
Cloud
Graphic symbol describing network
Does not specify nature of connections
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5. Physical Topology Vs Logical Topology
Figure 2-1 Network cloud connecting three machines
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6. Physical Topology Vs Logical Topology
Five connections exist between the four intermediate nodes (W,X,Y,Z)
Provided through dedicated phone lines, twisted pair cable, fiber optic cable, line-of-sight microwave RF, ATM, or other form of electronic connection.
Figure 2-2 Physical network topology
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7. Physical Topology Vs Logical Topology
Four intermediates network nodes (W,X, Y, Z) are responsible for relaying data between each of the three network machines A, B, and C.
Sometimes the relaying data not as what we expected – too busy, the broken up of links, too noise.
Packet out of order, or arrive with errors, corrupted during transmission and might not arrive at all.
Figure 2-2 Physical network topology
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8. Physical Topology Vs Logical Topology
Network software protocols
Properly reassemble packets into correct sequence
Eliminate duplicated information
When a large amount of data must be sent between machines in on a network, it is possible to setup a virtual connection:
Virtual circuit
Virtual Private Network
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9. Physical Topology Vs Logical Topology
Virtual circuit between machines
Prearranged network path so that all packets will travel for a particular session between machines
Virtual private network (VPN)
Uses public network connections (internet or telephone systems) to establish private communication by encrypts the data transmitted between two computers at the end of the connection.
The data travel in tunnel – logical connection between the nodes of the VPN
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10. Physical Topology Vs Logical Topology
Special switches allow virtual LANs (VLANs)
Example for Table 2-1:
Twenty computers connected to three VLAN-capable switches
Grouped into two or more VLANs
Table 2-1 Grouping of 20 PCs into 3 virtual LANs
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11. Fully Connected Networks
Refer to figure 2-3(a)
Most expensive to build
Figure 2-3 Network topologies
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12. Fully Connected Networks
Table 2-2 Number of links in a fully connected network
Number of links (L) required in fully connected network of N nodes:
Number of connections at each node
Equals total number of nodes minus one
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13. Cengage Learning: Computer Networking from LANs to WANs
Star Networks
Refer to figure 2-3(b)
All nodes connect to central communications hub (also concentrator)
Small networks
Require only single hub
Four, eight, 16, 32, or more connections available
Large networks
Require multiple hubs
Increases hardware, cabling costs
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14. Cengage Learning: Computer Networking from LANs to WANs
Star Networks
Advantage
Can isolate failing nodes- if a node on the network fails, the switch will isolate it so that the other nodes are not affected.
Hub characteristic
Broadcasts data received on one port to all other ports
Each network node has opportunity to see each packet
Switch
Learns where to send data
Eliminates data broadcast traffic
Provides star topology
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15. Cengage Learning: Computer Networking from LANs to WANs
Bus Networks
Refer figure 2-3(c)
All nodes on common bus (cable) compete for possession
Broadcast data when an idle bus is detected
Collision
Two or more nodes transmit data at the same time
Handled by Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
Nodes stop, wait before retransmitting
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16. Cengage Learning: Computer Networking from LANs to WANs
Bus Network
Bus wiring not difficult
Daisy-chained via T-connectors into one long segment
Problem with daisy-chain that may cause intermittent, excessive collisions
Bad crimps on BNC connectors
Poor connections in T-connectors
Improperly terminated cable segment
Time domain reflectometer (TDR) used in troubleshooting – to send pulse down the coaxial cable segment and determine where the fault is
Bus network is easy to set up and cost-efficient
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17. Cengage Learning: Computer Networking from LANs to WANs
Ring Topology
Refer to figure 2-3(d)
Each node connected to exactly two other nodes
Data circulates in ring
Number of links
Same as number of nodes (similar to Star)
No central hub (difference from Star)
If a link fails, the worst-case scenario:
Message travels completely around ring (takes time)
Star – one link fails, only one node on that link is out of service
Central multi-station access units (MAUs) for token-ring networks
Physical star connection outside
Physical ring connection inside
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18. Cengage Learning: Computer Networking from LANs to WANs
Hybrid Networks
Combines two or more network topologies components
Requires careful planning
Various rules dictate how individual components are connected and used
Logical viewpoint and overall organization must be planned
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19. Cengage Learning: Computer Networking from LANs to WANs
Hybrid Networks
Figure 2-4 Hybrid network
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20. Cengage Learning: Computer Networking from LANs to WANs
Network Hierarchy
Hierarchy
Layered organization
Switches act like hubs
Differ by forwarding data selectively
Switches enforce hierarchy
Learn where data packets should be forwarded
Based on destination addresses
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21. Cengage Learning: Computer Networking from LANs to WANs
Network Hierarchy
Figure 2-5 Hybrid network with hierarchy
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22. Cengage Learning: Computer Networking from LANs to WANs
Network Hierarchy
* Notes :
Replacing a hub with a switch leads to better performance because the switch provides dedicated bandwidth, whereas a hub provides shared bandwidth. Imagine 10 users on a 10-Mbps shared Ethernet LAN. In fairness, each user should have 1-Mbps of bandwidth available to them. In a 10-Mbps switched Ethernet LAN, each user has 10-Mbps of bandwidth available.
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23. Cengage Learning: Computer Networking from LANs to WANs
Subnets
Important to understand the IP address and Subnet Mask in determining the device is residing on the same network or remote network.
IP address
Unique for each network node
32-bit number
Locates, identifies Internet nodes
E.g. Computer A –
B –
Subnetting: logical activity
Accomplished using special subnet mask
Logically ANDed with IP address to determine network address
Subnet mask separates IP address
Network portion and host portion
Nodes on different logical subnets require router
through
through
through
through
Same network
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24. Cengage Learning: Computer Networking from LANs to WANs

25. Network Access Points (NAPs)
Provide access to national, global network traffic
Companies can install independent communication networks
Connect to one or more NAPs
Act as NAPs themselves
Companies connected to a NAP
Enter into peering agreements with each other
Allows traffic exchange
If traffic Internet-based
Connection called a point-of-presence (POP)
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26. Network Access Points (NAPs)
Figure 2-6 RWA Software national backbone
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27. Public Networks Vs Private Networks
Two most pervasive public networks
Public Switched Telephone Network (PSTN)
Broadband cable (TV cable, Internet access and digital voice communication)
Public access requires limitations
User bandwidth, legal matters, user location
Private networks
Bandwidth limitations dependent on monetary network infrastructure investment
Higher maintenance costs per user
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28. Public Networks Vs Private Networks
Ways to keep network private
Keep all components inside locked building
No Internet connection
Allow Internet access through managed firewall
Encrypt all information needing to remain private
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29. Troubleshooting Techniques
Intentional harm to network:
Know what is required to partition network
Prevents communication
Disrupts normal network operation
Negatively affects security, reliability
Network troubleshooting requirements:
Knowledge of topology
Both physical and logical
Understanding of how network is partitioned
Testing and repairing can proceed smoothly
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30. Troubleshooting Techniques
Figure 2-7 Partitioning a network
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31. Cengage Learning: Computer Networking from LANs to WANs
Summary
Network cloud
Describes network without specifying nature of connections
Computer network connection views
Physical
Logical
VPN tunnel
VLANs may exist on same physical network
Network topologies
Fully connected, star, bus, ring, and hybrid
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32. Cengage Learning: Computer Networking from LANs to WANs
Summary
Switch provides dedicated bandwidth
Hub provides shared bandwidth
Router required for nodes on different logical subnets to talk to each other
Network Access Points (NAPs)
Provide access to national, global network traffic
POP
Internet-based NAP connections
Public networks: PSTN, broadband cable
Private network: owned and managed by private organization
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