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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 l.jpg

Chapter Five

Physical and Logical Topologies

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  • 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

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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

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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

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Simple Physical Topologies

  • Star topology

    • Every node on the network is connected through a central device

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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

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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

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Hybrid Physical Topologies

  • Daisy-Chained

    • A Daisy chain is linked series of devices

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Hybrid Physical Topologies

  • Hierarchical hybrid topology

    • Uses layers to separate devices by priority or function

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Enterprise-Wide Topologies

  • Enterprise

    • An entire organization

  • Backbone networks

    • Serial backbone

    • Distributed backbone

    • Collapsed backbone

    • Parallel backbone

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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

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Enterprise-Wide Topologies

  • Collapsed backbone

    • Uses a router or switch as the single central connection point for multiple subnetworks

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Enterprise-Wide Topologies

  • Parallel Backbone

    • Collapsed backbone arrangement that consists of more than one connection from central router or switch to each network segment

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Enterprise-Wide Topologies

  • Mesh networks

    • Routers are interconnected with other routers, with at least two pathways connecting each router

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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

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Wide Area Network (WAN) Topologies

  • Ring WAN topology

    • Each site is connected to two other sites so that entire WAN forms a ring pattern

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Wide Area Network (WAN) Topologies

  • Star WAN topology

    • Single site acts as the central connection point for several other points

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Wide Area Network (WAN) Topologies

  • Mesh WAN topology

    • Many directly interconnected locations forming a complex mesh

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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

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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

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  • 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

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  • 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

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  • 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

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  • Demand priority

    • Method for data transmission used by 100BaseVG Ethernet networks

    • Demand priority requires an intelligent hub

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  • 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

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  • 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

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  • 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

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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

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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

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Novell Proprietary 802.3 (or “Ethernet 802.3”)

  • Original NetWare frame type

  • Also called:

    • 802.3 Raw

    • Ethernet 802.3 frame

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Ethernet II

  • Original Ethernet frame type developed by DEC, Intel and Xerox, before IEEE began to standardize Ethernet

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  • Adaptation of IEEE 802.3 and Ethernet II

  • SNAP stands for Sub-Network Access Protocol

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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

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Design Considerations for Ethernet Networks

  • Cabling

  • Connectivity devices

  • Number of stations

  • Speed

  • Scalability

  • Topology

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  • 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

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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

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Token Ring

  • Multistation Access Unit (MAU)

    • Regenerates signals

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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

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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

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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

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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

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Design Considerations for Token Ring Networks

  • Cabling

  • Connectivity devices

  • Number of stations

  • Speed

  • Scalability

  • Topology

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Fiber Distributed Data Interface (FDDI)

  • Logical topology whose standard was originally specified by ANSI in mid-1980s and later refined by ISO

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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

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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)

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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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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

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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

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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