1. Physical and Logical Topologies
Chapter Five
Physical and Logical Topologies

2. Objectives
Describe the basic and hybrid LAN physical topologies, their uses, advantages, and disadvantages
Describe a variety of enterprise-wide and WAN physical topologies, their uses, advantages, and disadvantages
Compare the different types of switching used in data transmission
Understand the transmission methods, or logical topologies, underlying Ethernet, Token Ring, LocalTalk, and FDDI networks

3. Simple Physical Topologies
Physical topology
Physical layout of a network
A Bus topology consists of a single cable—called a bus— connecting all nodes on a network without intervening connectivity devices
Figure 5-1: Bus topology network

4. Simple Physical Topologies
Figure 5-2: A terminated bus network

5. Simple Physical Topologies
Ring topology
Each node is connected to the two nearest nodes so the entire network forms a circle
One method for passing data on ring networks is token passing
Active topology
Each workstation transmits data
Figure 5-3: A typical ring network

6. Simple Physical Topologies
Star topology
Every node on the network is connected through a central device
Figure 5-4: A typical star topology network

7. Hybrid Physical Topologies
Hybrid topology
Complex combination of the simple physical topologies
Star-wired ring
Star-wired topologies use physical layout of a star in conjunction with token ring-passing data transmission method
Figure 5-5: A star-wired ring topology network

8. Hybrid Physical Topologies
Star-wired bus
In a star-wired bus topology, groups of workstations are star-connected to hubs and then networked via a single bus
Figure 5-6: A star-wired bus network topology

9. Hybrid Physical Topologies
Daisy-Chained
A Daisy chain is linked series of devices
Figure 5-7: A daisy-chained star-wired bus topology

10. Hybrid Physical Topologies
Hierarchical hybrid topology
Uses layers to separate devices by priority or function
Figure 5-8: A hierarchical ring topology

11. Enterprise-Wide Topologies
An entire organization
Backbone networks
Serial backbone
Distributed backbone
Collapsed backbone
Parallel backbone

12. Enterprise-Wide Topologies
Serial backbone
Two or more hubs connected to each other by a single cable
Distributed backbone
Hubs connected to a series of central hubs or routers in a hierarchy
Figure 5-9: A simple distributed backbone network

13. Enterprise-Wide Topologies
Figure 5-10: A distributed backbone connecting multiple LANs

14. Enterprise-Wide Topologies
Collapsed backbone
Uses a router or switch as the single central connection point for multiple subnetworks
Figure 5-11: A collapsed backbone network

15. Enterprise-Wide Topologies
Parallel Backbone
Collapsed backbone arrangement that consists of more than one connection from central router or switch to each network segment
Figure 5-12: A parallel backbone network

16. Enterprise-Wide Topologies
Mesh networks
Routers are interconnected with other routers, with at least two pathways connecting each router
Figure 5-13: An example of a mesh network

17. Wide Area Network (WAN) Topologies
Peer-to-peer topology
WAN with single interconnection points for each location
Dedicated circuits
Continuous physical or logical connections between two access points that are leased from a communication provider
Figure 5-14: A peer-to-peer WAN

18. Wide Area Network (WAN) Topologies
Ring WAN topology
Each site is connected to two other sites so that entire WAN forms a ring pattern
Figure 5-15: A ring-configured WAN

19. Wide Area Network (WAN) Topologies
Star WAN topology
Single site acts as the central connection point for several other points
Figure 5-16: A star-configured WAN

20. Wide Area Network (WAN) Topologies
Mesh WAN topology
Many directly interconnected locations forming a complex mesh
Figure 5-17: Full-mesh and partial-mesh WANs

21. Wide Area Network (WAN) Topologies
Tiered WAN topology
Sites connected in star or ring formations are interconnected at different levels, with interconnection points organized into layers
Figure 5-18: A tiered WAN topology

22. Logical Topologies
Refers to the way in which data are transmitted between nodes
Describes the way:
Data are packaged in frames
Electrical pulses are sent over network’s physical media
Logical topology may also be called network transport system

23. Switching
Component of network’s logical topology that determines how connections are created between nodes
Circuit switching
Connection is established between two network nodes before they begin transmitting data
Message switching
Establishes connection between two devices, transfers information to second device, and then breaks connection
Packet switching
Breaks data into packets before they are transmitted

24. Ethernet
Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
The access method used in Ethernet
Collision
In Ethernet networks, the interference of one network node’s data transmission with another network node’s data transmission
Jamming
Part of CSMA/CD in which, upon detection of collision, station issues special 32-bit sequence to indicate to all nodes on Ethernet segment that its previously transmitted frame has suffered a collision and should be considered faulty

25. Figure 5-19: CSMA/CD process
Ethernet
Figure 5-19: CSMA/CD process

26. Ethernet
On an Ethernet network, an individual network segment is known as a collision domain
Portion of network in which collisions will occur if two nodes transmit data at same time
Data propagation delay
Length of time data take to travel from one point on the segment to another point

27. Figure 5-20: CSMA/CD versus demand priority
Ethernet
Demand priority
Method for data transmission used by 100BaseVG Ethernet networks
Demand priority requires an intelligent hub
Figure 5-20: CSMA/CD versus demand priority

28. Ethernet
Traditional Ethernet LANs, called shared Ethernet, supply fixed amount of bandwidth that must be shared by all devices on a segment
Switch
Device that can separate network segments into smaller segments, with each segment being independent of the others and supporting its own traffic
Switched Ethernet
Newer Ethernet model that enables multiple nodes to simultaneously transmit and receive data over logical network segments

29. Figure 5-21: A switched Ethernet network

30. Ethernet Gigabit Ethernet 1 Gigabit Ethernet 10 Gigabit Ethernet
Ethernet standard for networks that achieve 1-Gbps maximum throughput
10 Gigabit Ethernet
Standard currently being defined by IEEE 802.3ae committee
Will allow 10-Gbps throughput
Will include full-duplexing and multimode fiber requirements

31. Ethernet Padding Ethernet frame types:
Bytes added to data portion of an Ethernet frame to make sure this field is at least 46 bytes in size
Ethernet frame types:
IEEE (“Ethernet 802.2” or “LLC”)
Novell proprietary frame (or “Ethernet 802.3”)
Ethernet II frame
IEEE SNAP frame

32. IEEE 802.3 (“Ethernet 802.2” or “LLC”)
Default frame type for versions 4.x and higher of Novell NetWare network operating system
Sometimes called LLC frame
In Novell’s lexicon, this frame is called Ethernet frame
Figure 5-22: An IEEE frame

33. IEEE 802.3 (“Ethernet 802.2” or “LLC”)
Service Access Point (SAP)
Identifies node or internal process that uses LLC protocol
Frame Check Sequence (FCS)
This field ensures that data are received just as they were sent
Cyclical Redundancy Check (CRC)
Algorithm used by FCS field in Ethernet frames

34. Novell Proprietary 802.3 (or “Ethernet 802.3”)
Original NetWare frame type
Also called:
802.3 Raw
Ethernet frame
Figure 5-23: A Novell proprietary frame

35. Ethernet II
Original Ethernet frame type developed by DEC, Intel and Xerox, before IEEE began to standardize Ethernet
Figure 5-24: An Ethernet II frame

36. IEEE 802.3 SNAP Adaptation of IEEE 802.3 and Ethernet II
SNAP stands for Sub-Network Access Protocol
Figure 5-25: An IEEE SNAP frame

37. Understanding Frame Types
Learning about networks is analogous to learning a foreign language, with the frame type being the language’s syntax
Just as you may know the Japanese word for go but how to use it in a sentence, you may know all about the IPX/SPX protocol but not how devices handle it
Autosense
Feature of modern NICs that enables a NIC to automatically sense what types of frames are running on a network and set itself to that specification

38. Design Considerations for Ethernet Networks
Cabling
Connectivity devices
Number of stations
Speed
Scalability
Topology

39. LocalTalk Logical topology designed by Apple Computer, Inc.
Uses a transmission method called Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA)
A teleconnector is a transceiver used on a LocalTalk network
Macintosh version of TCP/IP is called MacTCP

40. Token Ring
Token Ring networks use the token passing routine and a star-ring hybrid physical topology
The 100-Mbps Token Ring standard is known as High-Speed Token Ring (HSTR)
On a Token Ring network, one workstation, called the active monitor, acts as the controller for token passing

41. Token Ring Multistation Access Unit (MAU) Regenerates signals
Figure 5-26: Interconnected Token Ring MAUs

42. Token Ring Control Access Unit (CAU) Lobe Attachment Module (LAM)
Connectivity device used on a Token Ring network
Lobe Attachment Module (LAM)
Device that attaches to a CAU to expand the capacity of that device

43. Token Ring
Token Ring networks with STP cabling may use a type 1 IBM connector
A DB-9 connector is another type of connector found on STP Token Ring networks
Figure 5-27: Type 1 IBM and DB-9 Token Ring connectors

44. Token Ring Media filter Token Ring media filter
Device that enables two types of cables or connectors to be linked
Token Ring media filter
Enables DB-9 cable and type 1 IBM cable to be connected
Figure 5-28: A Token Ring media filter

45. Token Ring Token Ring switching Token Ring frames
Like Ethernet networks, Token Ring networks can take advantage of switching to better utilize limited bandwidth
Token Ring frames
IEEE Token Ring frame
IBM Token Ring frame
Figure 5-29: An IBM Token Ring frame

46. Design Considerations for Token Ring Networks
Cabling
Connectivity devices
Number of stations
Speed
Scalability
Topology

47. Fiber Distributed Data Interface (FDDI)
Logical topology whose standard was originally specified by ANSI in mid-1980s and later refined by ISO
Figure 5-30: A FDDI network

48. Asynchronous Transfer Mode (ATM)
Logical topology that relies on a fixed packet size to achieve data transfer rates up to 9953 Mbps
The fixed packet in ATM is called a cell
A unique aspect of ATM technology is that it relies on virtual circuits

49. Asynchronous Transfer Mode (ATM)
ATM uses circuit switching, which allows ATM to guarantee a specific quality of service (QOS)
ATM technology can be integrated with Ethernet or Token Ring networks through the use of LAN Emulation (LANE)

50. Chapter Summary A physical topology is the basic layout of a network
Physical topologies are categorized into three fundamental geometric shapes: bus, ring, and star
Few LANs use the simple physical topologies in their pure form
Hubs that service star-wired bus or star-wired ring topologies can be daisy-chained to form a more complex hybrid topology
Hierarchical hybrid topology can designate hubs at different layers to perform different functions

51. Chapter Summary Cabling that connects each hub is called the backbone
In mesh networks, routers are interconnected with other routers so at least two pathways connect each node
WAN topologies use LAN and enterprise-wide topologies as building blocks, but add more complexity
Network logical topologies encompass a set of rules specifying which data are packaged and transmitted over network media

52. Chapter Summary
Switching is a component of a network’s logical topology that manages the filtering and forwarding of packets between nodes on a network
Ethernet is a networking technology and is by far the most popular logical topology for LANs today
Ethernet follows a network access method called CSMA/CD
On heavily trafficked Ethernet networks, collisions are not uncommon
A switch is a device that can separate a network into smaller segments, each independent of each other and supporting its own traffic

53. Chapter Summary
Token Ring networks currently run at either 4 or 16 Mbps, as specified by IEEE 802.5
Token Ring networks use the token-passing routine and a star-ring hybrid physical topology
FDDI is a networking standard originally specified by ANSI in mid-1980s and later refined by ISO
ATM relies on a fixed packet size to achieve data transfer rates up to 9953 Mbps
ATM relies on virtual circuits to determine the optimal path between sender and receiver