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Chapter Five

Chapter Five. Physical and Logical Topologies. 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

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Chapter Five

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  1. 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 • Enterprise • 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. 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. 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. Ethernet Figure 5-21: A switched Ethernet network

  30. Ethernet • Gigabit Ethernet • 1 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 • 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 802.3 (“Ethernet 802.2” or “LLC”) • Novell proprietary 802.3 frame (or “Ethernet 802.3”) • Ethernet II frame • IEEE 802.3 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 802.2 frame Figure 5-22: An IEEE 802.3 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 802.3 frame Figure 5-23: A Novell proprietary 802.3 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 802.3 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) • 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 • 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 • Like Ethernet networks, Token Ring networks can take advantage of switching to better utilize limited bandwidth • Token Ring frames • IEEE 802.5 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

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