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Chapter Five

Chapter Five. Physical and Logical Topologies. Simple Physical Topologies. What does physical topology mean? The physical layout of the network nodes Bus, Ring, & Star What does logical topology mean? Network transmission methods Ethernet, Token Ring, LocalTalk, FDDI, ATM.

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Chapter Five

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  1. Chapter Five Physical and Logical Topologies

  2. Simple Physical Topologies • What does physical topology mean? • The physical layout of the network nodes • Bus, Ring, & Star • What does logical topology mean? • Network transmission methods • Ethernet, Token Ring, LocalTalk, FDDI, ATM

  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 • Three byte token used to pass data • Active topology • Each workstation transmits data Figure 5-3: A typical ring network

  6. Simple Physical Topologies • Token passing process: • Computer ready to transmit • Computer picks up the token packet • Adds control and data information plus the destination node’s address (the token is now a data frame) • The token is then passed to the next node • Once received by the destination, an acknowledgment is sent to the originating node • After the originating node receives the acknowledgement, it releases a new free token which is sent down the ring

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

  8. 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 • Fault tolerance of star – reliability of token passing Figure 5-5: A star-wired ring topology network

  9. 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 • More expensive that star or bus • Basis for modern Ethernet networks Figure 5-6: A star-wired bus network topology

  10. Hybrid Physical Topologies • Daisy-Chained • A Daisy chain is linked series of devices • Drawback – Large # of hubs may affect transmission integrity Figure 5-7: A daisy-chained star-wired bus topology

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

  12. Enterprise-Wide Topologies • Enterprise • An entire organization • Backbone networks (commonly fiber, but may be CAT5 wiring) • Serial backbone • Distributed backbone • Collapsed backbone • Parallel backbone

  13. Enterprise-Wide Topologies • Serial backbone (identical to daisy-chained networks) • Two or more hubs connected to each other by a single cable • Not suitable for large networks • Distributed backbone • Hubs connected to a series of central hubs or routers in a hierarchy Figure 5-9: A simple distributed backbone network

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

  15. Enterprise-Wide Topologies • Collapsed backbone • Uses a router or switch as the single central connection point for multiple subnetworks (subnetworks may be different types) Figure 5-11: A collapsed backbone network

  16. 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

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

  18. 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 telecommunication provider Figure 5-14: A peer-to-peer WAN

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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 • Examples include: Ethernet, Token Ring, LocalTalk, FDDI, and ATM

  24. 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 • Monopolized bandwidth between two nodes (not efficient) • PC - ISP • Message switching • Establishes connection between two devices, transfers information to second device, and then breaks connection • E-mail systems • Packet switching • Breaks data into packets before they are transmitted • Ethernet and FDDI (including the Internet)

  25. 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 • Collision rate > 5% is unusual • 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

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

  27. 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 • If to long, cannot identify collisions accurately

  28. 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

  29. 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

  30. Ethernet Figure 5-21: A switched Ethernet network * Increase the effective bandwidth of a network segment

  31. 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

  32. Ethernet • 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 • Padding • Bytes added to data portion of an Ethernet frame to make sure this field is at least 46 bytes in size

  33. 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 (Logical Link Control) frame • In Novell’s lingo, this frame is called Ethernet 802.2 frame Figure 5-22: An IEEE 802.3 frame

  34. 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

  35. Novell Proprietary 802.3 (or “Ethernet 802.3”) • Original NetWare frame type (NetWare 3.12-) • Also called: • 802.3 Raw • Ethernet 802.3 frame • Rarely used anymore Figure 5-23: A Novell proprietary 802.3 frame

  36. 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

  37. IEEE 802.3 SNAP • Adaptation of IEEE 802.3 and Ethernet II • SNAP stands for Sub-Network Access Protocol • Organization ID (OUI) – identifies network type • Rarely used on current networks Figure 5-25: An IEEE 802.3 SNAP frame

  38. 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

  39. Design Considerations for Ethernet Networks • Cabling – coax or twisted-pair • Connectivity devices – less expensive than comparable Token Ring or LocalTalk • Number of stations – 10BaseT/100BaseTX limited to 1024 • Speed – 10/100 Mbps, 1 and 10 Gbps (soon) • Scalability – easily expandable • Topology – 10BaseT/100BaseTX use star-wired bus hybrid topology (highly fault tolerant)

  40. LocalTalk • Logical topology designed by Apple Computer, Inc. • Uses a transmission method called Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) • Similar to CSMA/CD, except node signals intent before it actually does • A teleconnector is a transceiver used on a LocalTalk network • Macintosh version of TCP/IP is called MacTCP

  41. 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

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

  43. Token Ring • Control Access Unit (CAU) • Connectivity device used on a Token Ring network, similar to MAU but more flexible and allows easier management of nodes • Lobe Attachment Module (LAM) • Device that attaches to a CAU to expand the capacity of that device

  44. 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

  45. 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

  46. 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

  47. Design Considerations for Token Ring Networks • Cabling – shielded/unshielded twisted pair • Connectivity devices – more expensive than Ethernet • Number of stations – 255 STP – 72 UTP • Speed – 4/16/100 Mbps • Scalability – Easily daisy-chain MAUs • Topology – Star-wired ring topology (highly fault-tolerant)

  48. Fiber Distributed Data Interface (FDDI) • Logical topology whose standard was originally specified by ANSI in mid-1980s and later refined by ISO • Double ring of multimode or single mode fiber to transmit data Figure 5-30: A FDDI network

  49. Asynchronous Transfer Mode (ATM) • Describes both a network access method & a multiplexing technique • Logical topology that relies on a fixed packet size to achieve data transfer rates up to 9,953 Mbps • Typically used on WANs • The fixed packet in ATM is called a cell • A unique aspect of ATM technology is that it relies on virtual circuits • Connections between network nodes logically appear to be direct, dedicated links between the two nodes

  50. Asynchronous Transfer Mode (ATM) • ATM uses circuit switching, which allows ATM to guarantee a specific quality of service (QoS) • QoS – standard that specifies that data will be delivered within a certain period of time after the transmission • ATM technology can be integrated with Ethernet or Token Ring networks through the use of LAN Emulation (LANE) • ATM is very expensive • Gigabit Ethernet is a better choice

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