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- 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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- 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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- 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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- Star topology
- Every node on the network is connected through a central device
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- 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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- 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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- Daisy-Chained
- A Daisy chain is linked series of devices
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- Hierarchical hybrid topology
- Uses layers to separate devices by priority or function
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- Enterprise
- Backbone networks
- Serial backbone
- Distributed backbone
- Collapsed backbone
- Parallel backbone
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- 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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- Collapsed backbone
- Uses a router or switch as the single central connection point for
multiple subnetworks
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- 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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- Mesh networks
- Routers are interconnected with other routers, with at least two
pathways connecting each router
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- 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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- Ring WAN topology
- Each site is connected to two other sites so that entire WAN forms a
ring pattern
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- Star WAN topology
- Single site acts as the central connection point for several other
points
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- Mesh WAN topology
- Many directly interconnected locations forming a complex mesh
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- 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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- 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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- 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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- 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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- Original NetWare frame type
- Also called:
- 802.3 Raw
- Ethernet 802.3 frame
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- 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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- 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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- 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 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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- Multistation Access Unit (MAU)
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- 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 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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- 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 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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- Cabling
- Connectivity devices
- Number of stations
- Speed
- Scalability
- Topology
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- Logical topology whose standard was originally specified by ANSI in
mid-1980s and later refined by ISO
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- 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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- 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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- 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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- 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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- 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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- 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
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