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Network Topologies
04/10/23 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
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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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Advantages of Bus Topology
• Works well for small networks
• Relatively inexpensive to implement
• Easy to add to it
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Disadvantages ofBus Topology
• Management costs can be high
• Potential for congestion with network traffic
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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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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
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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
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Simple Physical Topologies
• Star topology– Every node on the network is connected through
a central device
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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
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Disadvantages ofStar Topology
• Hub is a single point of failure
• Requires more cable than the bus
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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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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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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
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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
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Ethernet
CSMA/CD process
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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
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Ethernet
• Demand priority– Method for data transmission used by 100BaseVG Ethernet networks– Demand priority requires an intelligent hub
CSMA/CD versus demand priority
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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
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Ethernet
A switched Ethernet network
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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
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Design Considerations for Ethernet Networks
• Cabling
• Connectivity devices
• Number of stations
• Speed
• Scalability
• Topology
04/10/23 35
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
04/10/23 36
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
Interconnected Token Ring MAUs
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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
Type 1 IBM and DB-9 Token Ring connectors
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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
A Token Ring media filter
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Design Considerations for Token Ring Networks
• Cabling
• Connectivity devices
• Number of stations
• Speed
• Scalability
• Topology
04/10/23 42
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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