Transcript Chapter 5

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
Simple Physical Topologies
Physical topology
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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
Simple Physical Topologies
Figure 5-2: A terminated bus network
Simple Physical Topologies
Ring topology
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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
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Each workstation transmits data
Figure 5-3:
A typical
ring
network
Simple Physical Topologies
Token passing process:
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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
Simple Physical Topologies
Star topology
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Every node on the network is connected through
a central device
Figure 5-4:
A typical
star
topology
network
Hybrid Physical Topologies
Hybrid topology
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Complex combination of the simple physical topologies
Star-wired ring
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Star-wired topologies use physical layout of a star in
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conjunction with token ring-passing data transmission
method
Fault tolerance of star – reliability of token passing
Figure 5-5:
A starwired ring
topology
network
Hybrid Physical Topologies
Star-wired bus
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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
Hybrid Physical Topologies
Daisy-Chained
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A Daisy chain is linked series of devices
Drawback – Large # of hubs may affect
transmission integrity
Figure 5-7:
A daisychained
star-wired
bus
topology
Hybrid Physical Topologies
Hierarchical hybrid topology
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Uses layers to separate devices by priority or function
Figure 5-8: A hierarchical ring topology
Enterprise-Wide Topologies
Enterprise
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An entire organization
Backbone networks (commonly fiber, but
may be CAT5 wiring)
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Serial backbone
Distributed backbone
Collapsed backbone
Parallel backbone
Enterprise-Wide Topologies
Serial backbone (identical to daisy-chained networks)
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Two or more hubs connected to each other by a single cable
Not suitable for large networks
Distributed backbone
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Hubs connected to a series of central hubs or routers in a
hierarchy
Figure 5-9:
A simple
distributed
backbone
network
Enterprise-Wide Topologies
Figure 5-10: A distributed backbone connecting multiple LANs
Enterprise-Wide Topologies
Collapsed backbone
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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
Enterprise-Wide Topologies
Parallel Backbone
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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
Enterprise-Wide Topologies
Mesh networks
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Routers are interconnected with other routers, with at least two
pathways connecting each router
Internet
Figure 5-13:
An example of
a mesh
network
Wide Area Network (WAN)
Topologies
Peer-to-peer topology
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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
Wide Area Network (WAN)
Topologies
Ring WAN topology
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Each site is connected to two other sites so that entire
WAN forms a ring pattern
Figure 5-15: A ring-configured WAN
Wide Area Network (WAN)
Topologies
Star WAN topology
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Single site acts as the central connection point for several
other points
Figure 5-16:
A starconfigured
WAN
Wide Area Network (WAN)
Topologies
Mesh WAN topology
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Many directly interconnected locations forming a complex mesh
Figure 5-17: Full-mesh and partial-mesh WANs
Wide Area Network (WAN)
Topologies
Tiered WAN topology
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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
Logical Topologies
Refers to the way in which data are transmitted
between nodes
Describes the way:
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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
Switching
Component of network’s logical topology that
determines how connections are created
between nodes
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Circuit switching
Connection is established between two network nodes
before they begin transmitting data
Monopolized bandwidth between two nodes (not efficient)
PC - ISP
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Message switching
Establishes connection between two devices, transfers
information to second device, and then breaks connection
E-mail systems
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Packet switching
Breaks data into packets before they are transmitted
Ethernet and FDDI (including the Internet)
Ethernet
Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)
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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
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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
Figure 5-19: CSMA/CD process
Ethernet
On an Ethernet network, an individual
network segment is known as a collision
domain
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Portion of network in which collisions will occur if
two nodes transmit data at same time
Data propagation delay
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Length of time data take to travel from one point
on the segment to another point
If to long, cannot identify collisions accurately
Ethernet
Demand priority
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Method for data transmission used by 100BaseVG Ethernet
networks
Demand priority requires an intelligent hub
Figure 5-20:
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
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Device that can separate network segments into
smaller segments, with each segment being
independent of the others and supporting its own
traffic
Switched Ethernet
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Newer Ethernet model that enables multiple nodes to
simultaneously transmit and receive data over logical
network segments
Ethernet
Figure 5-21: A switched Ethernet network
* Increase the effective bandwidth of a network segment
Ethernet
Gigabit Ethernet
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1 Gigabit Ethernet
Ethernet standard for networks that achieve 1Gbps maximum throughput
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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
Ethernet
Ethernet frame types:
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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
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Bytes added to data portion of an Ethernet frame to
make sure this field is at least 46 bytes in size
IEEE 802.3 (“Ethernet 802.2” or
“LLC”)
Default frame type for versions 4.x and higher of
Novell NetWare network operating system
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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
IEEE 802.3 (“Ethernet 802.2” or
“LLC”)
Service Access Point (SAP)
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Identifies node or internal process that uses LLC
protocol
Frame Check Sequence (FCS)
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This field ensures that data are received just as
they were sent
Cyclical Redundancy Check (CRC)
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Algorithm used by FCS field in Ethernet frames
Novell Proprietary 802.3 (or
“Ethernet 802.3”)
Original NetWare frame type (NetWare 3.12-)
Also called:
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802.3 Raw
Ethernet 802.3 frame
Rarely used anymore
Figure 5-23: A Novell proprietary 802.3 frame
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
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
Understanding Frame Types
Learning about networks is analogous to
learning a foreign language, with the frame type
being the language’s syntax
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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
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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
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)
LocalTalk
Logical topology designed by Apple
Computer, Inc.
Uses a transmission method called Carrier
Sense Multiple Access/Collision
Avoidance (CSMA/CA)
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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
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)
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Regenerates signals
Figure 5-26: Interconnected Token Ring MAUs
Token Ring
Control Access Unit (CAU)
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Connectivity device used on a Token Ring
network, similar to MAU but more flexible and
allows easier management of nodes
Lobe Attachment Module (LAM)
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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
Figure 5-27: Type 1 IBM and DB-9 Token Ring connectors
Token Ring
Media filter
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Device that enables two types of cables or connectors to be
linked
Token Ring media filter
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Enables DB-9 cable and type 1 IBM cable to be connected
Figure 5-28: A Token Ring media filter
Token Ring
Token Ring switching
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Like Ethernet networks, Token Ring networks can take
advantage of switching to better utilize limited bandwidth
Token Ring frames
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IEEE 802.5 Token Ring frame
IBM Token Ring frame
Figure 5-29: An IBM Token Ring frame
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)
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
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
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Connections between network nodes logically appear
to be direct, dedicated links between the two nodes
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