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Network 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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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
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
Advantages of Bus Topology • Works well for small networks • Relatively inexpensive to implement • Easy to add to it
Disadvantages ofBus Topology • Management costs can be high • Potential for congestion with network traffic
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
Advantages of Ring Topology • Easier to manage; easier to locate a defective node or cable problem • Well-suited for transmitting signals over long distances on a LAN • Handles high-volume network traffic • Enables reliable communication
Disadvantages ofRing Topology • Expensive • Requires more cable and network equipment at the start • Not used as widely as bus topology • Fewer equipment options • Fewer options for expansion to high-speed communication
Simple Physical Topologies • Star topology • Every node on the network is connected through a central device
Advantages of Star Topology • Good option for modern networks • Low startup costs • Easy to manage • Offers opportunities for expansion • Most popular topology in use; wide variety of equipment available
Disadvantages ofStar Topology • Hub is a single point of failure • Requires more cable than the bus
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
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
Hybrid Physical Topologies • Daisy-Chained • A Daisy chain is linked series of devices
Hybrid Physical Topologies • Hierarchical hybrid topology • Uses layers to separate devices by priority or function
Enterprise-Wide Topologies • Enterprise • An entire organization • Backbone networks • Serial backbone • Distributed backbone • Collapsed backbone • Parallel backbone
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
Enterprise-Wide Topologies • Collapsed backbone • Uses a router or switch as the single central connection point for multiple subnetworks
Enterprise-Wide Topologies • Parallel Backbone • Collapsed backbone arrangement that consists of more than one connection from central router or switch to each network segment
Enterprise-Wide Topologies • Mesh networks • Routers are interconnected with other routers, with at least two pathways connecting each router
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
Wide Area Network (WAN) Topologies • Ring WAN topology • Each site is connected to two other sites so that entire WAN forms a ring pattern
Wide Area Network (WAN) Topologies • Star WAN topology • Single site acts as the central connection point for several other points
Wide Area Network (WAN) Topologies • Mesh WAN topology • Many directly interconnected locations forming a complex mesh
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
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
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
Ethernet CSMA/CD process
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
Ethernet • Demand priority • Method for data transmission used by 100BaseVG Ethernet networks • Demand priority requires an intelligent hub CSMA/CD versus demand priority
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
Ethernet A switched Ethernet network
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
Design Considerations for Ethernet Networks • Cabling • Connectivity devices • Number of stations • Speed • Scalability • Topology
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
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
Token Ring • Multistation Access Unit (MAU) • Regenerates signals Interconnected Token Ring MAUs
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
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 Type 1 IBM and DB-9 Token Ring connectors
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 A Token Ring media filter
Design Considerations for Token Ring Networks • Cabling • Connectivity devices • Number of stations • Speed • Scalability • Topology
Fiber Distributed Data Interface (FDDI) • Logical topology whose standard was originally specified by ANSI in mid-1980s and later refined by ISO
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
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)