Download CIS 1140 Network Fundamentals

CIS 1140 Network Fundamentals
Chapter 5 – Topologies and Ethernet Standards
Collected and Compiled
By JD Willard
MCSE, MCSA, Network+,
Microsoft IT Academy Administrator
Computer Information Systems Instructor
Albany Technical College
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Objectives
• Describe the basic and hybrid LAN
physical topologies, and their uses,
advantages, and disadvantages
• Describe the backbone structures that
form the foundation for most LANs
• Understand the transmission methods
underlying Ethernet networks
• Compare the different types of switching
used in data transmission
Network Topologies
• There are two types of network topologies:
– Physical topology is the physical layout of the
network, including cable and device configuration
– Logical topology refers to the method used to
communicate between the devices
– It is important to understand the physical topology
before designing networks, because they can affect
the logical topology chosen, how the building is
cabled, and what kind of media is used
– Physical topologies are classified according to
three geometric shapes: bus, ring and star
Types of Topologies Demo
Simple Physical Topologies
• Physical topology: physical layout of nodes on a network
• May create hybrid topologies
• Does not specify:
• Device types
• Connectivity methods
• Addressing schemes
• Topology integral to type of network, cabling infrastructure, and
transmission media used
• Three fundamental shapes:
– Bus
– Ring
– Star
Physical Topologies Demo
Topologies pt. 1 Demo
Topologies pt. 2 Demo
Bus
• Bus consists of a single cable that connects all the nodes of a
network without intervening connectivity devices, and requires a
terminator at each end
• The single cable is called the bus and supports one channel,
where each node shares total capacity
• Bus advantages: easy to install and add devices; requires less
cable; less expensive
• Bus disadvantages: requires 50 ohm terminators at each end of
the cable; entire network shuts down if the cable breaks; difficult
to troubleshoot; requires grounding loop
• Terminators stop signals after reaching end of wire
• Prevent signal bounce
• Inexpensive, not very scalable
• Difficult to troubleshoot, not fault-tolerant
The Bus Topology Demo
Basic Ethernet Bus
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An Ethernet network where all machines are daisy chained using coaxial cable (Thin
Ethernet/Thin-net or Thick Ethernet/Thick-net).
Machine 2 wants to send a message to machine 4.
1. First it 'listens' to make sure no one else is using the network.
2. If it is all clear it starts to transmit its data on to the network (represented by the
yellow flashing screens).
3. Each packet of data contains the destination address, the senders address, and
of course the data to be transmitted.
4. The signal moves down the cable and is received by every machine on the
network but because it is only addressed to number 4, the other machines ignore
it.
5. Machine 4 then sends a message back to number 2 acknowledging receipt of the
data (represented by the purple flashing screens).
Bus (continued)
A terminated bus topology network
Ring
• Ring is where each node is connected to the two
nearest nodes, effectively forming a circle
• Data is transmitted in one direction around the ring,
and is typically done so using token passing
• The ring is used by Token Ring and FDDI networks
• Ring advantages: no network collisions; each node
functions as a repeater; less cable required
• Ring disadvantages: Single malfunctioning node can
disable entire network; not flexible or scalable;
modifications requires network shutdown
The Ring Topology Demo
Ring
Star
• Star is where each node is connected through a central device, such
as a hub
• All nodes transmit data to the hub, which then retransmits the data to
the destination node
• Easily moved, isolated, or interconnected with other networks
• Scalable - Supports max of 1024 addressable nodes on logical
network
A typical star topology network
Star
•Any single cable connects
only two devices; Cabling
problems affect two nodes at
most
•More fault-tolerant
•Star advantages: a break in
the cable does not shut
down the network; higher
reliability; easier
troubleshooting; no
terminators required
•Star disadvantages: uses
more cable than ring or bus
networks; hubs are more
expensive than terminators;
hub failures take down entire
LAN segments
The Star Topology Demo
Hybrid Physical Topologies
• Pure bus, ring, star topologies
– Rarely exist
• Too restrictive
• Hybrid topology
– More likely
– Complex combination of pure topologies
– Several options
Hybrid Topologies Demo
Star-Wired Ring
The star-wired ring topology uses the physical
layout of a star in conjunction with the token–passing
data transmission method. Data are sent around the
star in a circular pattern. This hybrid topology benefits
from the fault tolerance of the star topology (data
transmission does not depend on each workstation to
act as a repeater) and the reliability of token passing.
Modern Token Ring networks, as specified in IEEE
802.5, use this hybrid topology.
Star-Wired Ring
Token Ring MAUs can be connected together using straightthrough patch cables to connect the Ring Out port of one MAU and
the Ring In port of the next MAU until the network of MAUs forms a
circle. Up to 255 stations can be connected to the network when
using Shielded Twisted Pair cable and 72 when using Unshielded
Twisted Pair cable.
MAU Showing Internal Ring
A Token Ring hub
(MAU) simply changes
the topology from a
physical ring to a star
wired ring. The Token
still circulates around
the network and is still
controlled in the same
manner, however,
using a hub or a switch
greatly improves
reliability because the
hub can automatically
bypass any ports that
are disconnected or
have a cabling fault.
31
Star-Wired Bus
A star-wired bus topology network
Star-wired Bus
In a star-wired bus topology, groups of workstations are starconnected to hubs and then networked via a single bus. With this
design, you can cover longer distances and easily interconnect or
isolate different network segments. One drawback is that this option
is more expensive than using either the star or, especially, the bus
topology alone because it requires more cabling and potentially
more connectivity devices. The star-wired bus topology commonly
forms the basis for modern Ethernet and Fast Ethernet networks.
Advantages and Disadvantages of the
different network topologies
Backbone Networks
• A network backbone is the cabling that connects the
hubs, switches, and routers on a network. Backbones
usually are capable of more throughput than the cabling
that connects workstations to hubs. This added capacity
is necessary because backbones carry more traffic than
any other cabling in the network. For example, an
increasing number of businesses are implementing fiberoptic backbone but continue to use CAT5 wiring for the
cabling from hubs to workstations.
• Although even the simplest LAN (including a star or bus
topology LAN) technically has a backbone, enterprisewide back-bones are more complex and more difficult to
plan.
• The backbone is the most significant building block of
these networks.
Serial Backbone
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A serial backbone is the simplest kind of backbone network. It consists of two or more
hubs connected to each other by a single cable. They are not suitable for large networks
or long distances. Although the serial backbone topology could be used for enterprisewide networks, it is rarely implemented for that purpose.
Daisy chain : linked series of devices
– Hubs and switches often connected in daisy chain to extend a network
Hubs, gateways, routers, switches, and bridges can form part of backbone
Benefit
– Logical growth solution
• Modular additions
– Low-cost LAN infrastructure
expansion
• Easily attach hubs
Serial connection of repeating devices
– Essential for distance communication
Standards
– Define number of hubs allowed
– Exceed standards
• Intermittent, unpredictable data transmission errors
Distributed Backbone
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Consists of a number of hubs connected to a series of central hubs or routers in a hierarchy
Allows for simple expansion and limited capital outlay for growth
Layers of hubs can be added to existing layers
A more complicated distributed backbone connects multiple LANs or LAN segments using routers
Provides network administrators with the ability to segregate workgroups and therefore manage
them more easily
Adapts well to an enterprise-wide network confined to a single building, where layers of hubs can
be assigned according to the floor or department
You must consider the maximum allowable distance between nodes and the server dictated by
the network media
Central point of failure is the hub at the uppermost layer
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Implementing can be relatively simple, quick, and inexpensive
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A distributed backbone
connecting multiple LANs
Collapsed Backbone
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Uses a router or switch as the single central connection point for multiple
sub-networks
A single router or switch is the highest layer of the backbone.
The dangers of using this arrangement relate to the fact that a failure in the
central router or switch can bring down the entire network
In addition, because routers cannot move traffic as quickly as hubs, using a
router may slow data transmission.
A substantial advantages is that this arrangement allows you to interconnect
different types of sub-networks.
You can also centrally manage maintenance and troubleshooting chores.
Parallel Backbone
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The most robust enterprise-wide topology.
This variation of the collapsed backbone arrangement consists of more than one
connection from the central router or switch to each network segment.
Each hub is connected to the router or switch by more than one cable.
The advantage of using a parallel backbone is that its redundant (duplicate) links
ensure network connectivity to any area of the enterprise.
Parallel backbones are more expensive than other enterprise-wide topologies
because they require much more cabling than the others. However, they make up for
the additional cost by offering increased performance.
As a network administrator, you might choose to implement parallel links to only
some of the most critical devices on your network. By selectively implementing the
parallel structure, you can lower connectivity costs and leave available additional
ports on the connectivity devices.
Most Reliable and Most
Expensive to Set UP
Logical Topologies
• Logical topology: how data is transmitted between
nodes
– May not match physical topology
• Bus logical topology: signals travel from one network
device to all other devices on network
– Required by bus, star, star-wired physical
topologies
• Ring logical topology: signals follow circular path
between sender and receiver
– Required by ring, star-wired ring topologies
Logical Topologies Demo
Switching: Circuit Switching
• Switching: component of network’s logical topology that
determines how connections are created between nodes
• Circuit switching: connection established between two
network nodes before transmission
– Bandwidth dedicated to connection
• Remains available until communication terminated
– While connected, all data follows same path initially
selected by switch
• Monopolizes bandwidth while connected
– Resource wasted
• Uses
– Live audio, videoconferencing
– Home modem connecting to ISP
Message Switching
• Establishes connection between two devices, transfers
information, then breaks connection
– Information then stored and forwarded from second
device to third device on path
– “Store and forward” routine continues until message
reaches destination
– All information follows same physical path
– Requires that each device in data’s path have
sufficient memory and processing power to accept
and store information
Packet Switching
• Breaks data into packets before transmission
– Packets can travel any network path
• Contain destination address and sequencing information
• Can attempt to find fastest circuit available
• When packets reach destination node, they are reassembled
– Based on control information
– Not optimal for live audio or video transmission
• Advantages
– No wasted bandwidth
– Devices do not process information
• Examples
– Ethernet networks
– Internet
MPLS (Multiprotocol Label Switching)
• IETF
– Introduced in 1999
• Multiple layer 3 protocols
– Travel over any one of several connection-oriented layer 2
protocols
• Supports IP
• Common use
– Layer 2 WAN protocols
• Advantages
– Use packet-switched technologies over traditionally circuit
switched networks
– Create end-to-end paths
• Act like circuit-switched connections
– Addresses traditional packet switching limitations
– Better QoS (quality of service)
802.3 Ethernet
Ethernet Demo
• Ethernet is a LAN standard that specifies an implementation of the
physical layer and the MAC sub-layer of the data link layer.
• An Ethernet network is a broadcast system; this means that when
a station transmits data, every other station receives the data. The
frames contain a destination address in the frame header and only
the station with that address will pick up the frame and pass it on to
upper-layer protocols to be processed.
• The access method –Carrier Sense Multiple Access/Collision
Detection (CSMA/CD).
Ethernet/Fast Ethernet/Gigabit Ethernet Demo
CSMA/CD (Carrier Sense Multiple Access
with Collision Detection)
• Network access method
– Controls how nodes access communications channel
– Necessary to share finite bandwidth
CSMA/CD Access Method demo
• Carrier sense
– Ethernet NICs listen, wait until free channel detected
• Multiple access
– Ethernet nodes simultaneously monitor traffic, access
media
CSMA/CD (cont’d.)
• Collision
– Two nodes simultaneously:
• Check channel, determine it is free, begin transmission
• Collision detection
– Manner nodes respond to collision
– Requires collision detection routine
• Enacted if node detects collision
– Jamming
• NIC issues
32-bit sequence
• Indicates
previous
message faulty
CSMA/CD (cont’d.)
• Heavily trafficked network segments
– Collisions common
• Segment growth
– Performance suffers
– “Critical mass” number dependencies
• Data type and volume regularly transmitted
• Collisions corrupt data, truncate data frames
– Network must compensate for them
• Collision domain
– Portion of network where collisions occur
• Ethernet network design
– Repeaters repeat collisions
• Result in larger collision domain
– Switches and routers
• Separate collision domains
CSMA/CD (cont’d.)
• Collision domains differ from broadcast domains
• Ethernet cabling distance limitations
– Effected by collision domains
• Data propagation delay
– Time for data to travel
• From one segment point to another point
– Too long
• Cannot identify collisions accurately
– 100 Mbps networks
• Three segment maximum connected with two hubs
– 10 Mbps buses
• Five segment maximum connected with four hubs
Collision Domain
• On an Ethernet network, an individual segment is known
as a collision domain, or a portion of a network in which
collisions will occur if two nodes transmit data at the
same time.
• The more nodes transmitting data on a network, the more
collisions will take place and you may see performance
suffer as a result of collisions.
• Collisions are likely to occur at the Physical Layer (on the
channel or wire).
• Repeaters and Hubs are Physical Layer devices and
therefore share the Ethernet channel.
• Portions of the network connected by repeaters or hubs
must share the bandwidth of the single Ethernet channel.
• Repeaters/Hubs simply regenerate any signal they
receive, they repeat collisions just as they repeat data.
• Networks can be separated into multiple collisions
domains by using switches.
Collision Domains Demo
10BASE-T
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The “10” represents its maximum throughput of 10Mbps, the “Base”
indicates that it uses baseband transmission, and the “T” stands for twisted
pair, the medium it uses.
On a 10BaseT network, one pair of wires in the UTP cable is used for
transmission, while a second pair of wires is used for reception. By using
two pairs of wires, 10BaseT networks use full-duplex transmission.
A 10BaseT network requires CAT3 or higher UTP.
Fault tolerance: capacity for component or system to continue functioning
despite damage or partial malfunction
Physical star configuration
Maximum cable length is 100 meters
Nodes connected via concentrator
Maximum of 1024 Nodes per logical segment
Passive Topology connect to Active Hubs
No external terminators
10Base-T Advantages: 1) the star wiring topology supports easier
maintenance and troubleshooting, 2) twisted pair wiring is inexpensive and
widely used, and 3) optionally supports full-duplex operation.
BASE Terminology Demo
10BASET 5-4-3 Rule
5-4-3 rule of networking: between two communicating nodes, network
cannot contain more than five network segments connected by four
repeating devices, and no more than three of the segments may be
populated
100BaseT Ethernet
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100Base-T (Fast Ethernet)
– IEEE 802.3u standard
– Similarities with 10Base-T
• Baseband transmission, star topology, RJ-45 connectors
• Requires CAT5 or higher UTP
– Supports three network segments maximum
• Connected with two repeating devices
• 100 meter segment length limit between nodes
• Maximum of 1024 Nodes per logical segment
– 100Base-TX
• 100-Mbps throughput over twisted pair
• Full-duplex transmission: doubles effective bandwidth
1000BaseT Gigabit Ethernet
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1000BASE-T or 802.3ab is a standard for
Gigabit Ethernet over copper wiring. It
requires, at a minimum, Cat 5e ("Category 5
enhanced") cable. Category 6 cable may also
be used. The 1000BASE-T standard was
approved by the IEEE 802.3 in 1999.
In a departure from both 10BASE-T and
100BASE-TX, 1000BASE-T uses all four
cable pairs to achieve full duplex
transmission. The aggregate data rate of
1000 Mb/s is achieved by transmission at a
data rate of 250 Mb/s over each wire pair.
Each network segment can have a maximum
distance of 100 meters. This usually consists
of 90 m horizontal (inside the building), 9 m at
the patch panel, and 1 m from the port to the
computer or node.
1000BaseT buses can practically support a
maximum of two network segments
connected with one hub and 1024 nodes per
logical segment.
10GBaseT Ethernet
• 10GBase-T
– IEEE 802.3an
– 10GBASE-T cable infrastructure can also be used for
1000BASE-T allowing a gradual upgrade from
1000BASE-T
– Pushing limits of twisted pair
• Requires Cat 6 or Cat 7 cabling
• Maximum segment length: 100 meters
– Benefit
• Very fast data transmission, lower cost than fiberoptic
– Use
• Connect network devices
• Connect servers, workstations to LAN
100Base-FX Ethernet
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100Base-FX supports a 100 Mb/s transmission rate over two multimode fiber optic
cables. One cable is used to transmit data, and the other is used to receive data.
It allows maximum segment lengths of 412 meters for half-duplex links, and 2000
meters or more for full-duplex links.
The 100Base-FX standard allows several types of fiber optic connectors to be used.
Duplex "SC" connectors are recommended, but "ST" and FDDI "MIC" connectors are
also permitted.
In full-duplex mode, 100Base-FL segment lengths can be increased from 412 meters
to 2000 meters. Even longer distances can be supported with the more expensive
single mode fiber (SMF).
The 100BaseFX standard uses a star topology, with its repeaters connected through
a bus with a maximum of two repeaters allowed to connect three segments.
2000
2000
Full
duplex
2000
6000
Full duplex
1000Base-LX Ethernet
• 1000Base-LX operates with a
1300nm laser over single and
multi-mode fiber
• The "L" in 1000Base-LX stands for
"long" as it uses long wavelength
lasers to transmit data over fiber
optic cable.
• Long wavelength lasers are more
expensive than short wavelength,
but have the advantage of being
able to drive longer distances.
• Maximum segment lengths range
from 550 meters using multimode
fiber to 5000 meters using single
mode.
• One repeater may be used to
connect two segments.
• Excellent choice for long
backbones
550m
using
MMF
to
5000m
using
SMF
1000Base-SX Ethernet
• 1000BASE-SX is a fiber optic gigabit
Ethernet standard.
• The "S" in 1000Base-SX stands for
"short" as it uses short wavelength
lasers to transmit data over fiber
optic cable. The short wavelength
lasers specified by the standard
operate at 850 nanometers. Less
expensive than long wavelength
lasers.
• Only multi-mode optical fiber is
supported.
• Maximum segment lengths range
from 275 meters (62.5 micron fibers)
to 550 meters (50 micron fibers)
depending on the diameter of the
fiber used.
• Only one repeater may be used
between two segments.
• Best suited for shorter network runs
275 to 550
meters
10Gigabit Ethernet (802.3ae)
• The IEEE 802.3ae standard specifies 10Gigabit
Ethernet, also referred to as 10GbE, over
multimode and single-mode fiber optics.
• 10GbE increases the maximum fiber optic cable
lengths up to 40 kilometers.
• All use SC or LC connectors.
– Common characteristics
• Star topology, allow one repeater, fullduplex mode
– Differences
• Signal’s light wavelength, maximum
allowable segment length
10GBase-SR and 10GBase-SW
• 10GBase-SR and 10GBase-SW
– 10G: 10 Gbps
– Base: baseband transmission
– S: short reach
– Physical layer encoding
• R works with LAN fiber connections
• W works with SONET fiber connections
– Multimode fiber: 850 nanometer signal
transmission
– Maximum segment length
• 300 meters using 50 micron fiber
• 66 meters using 62.5 micron fiber
10GBase-LR and 10GBase-LW
• 10GBase-LR and 10GBase-LW
– 10G: 10 Gbps
– Base: baseband transmission
– L: long reach
– Single-mode fiber: 1319 nanometer signal
transmission
– Maximum segment length
• 10,000 meters
– 10GBase-LR: WAN or MAN
– 10GBase-LW: SONET WAN links
10GBase-ER and 10GBase-EW
• 10GBase-ER and 10GBase-EW
– E: extended reach
– Single-mode fiber
• Transmit signals with 1550 nanometer
wavelengths
– Longest fiber-optic segment reach
• 40,000 meters (25 miles)
– 10GBase-EW
• Encoding for SONET
– Best suited for WAN use
Summary of Common Ethernet Standards
Ethernet Frames
• Ethernet networks may use one (or a combination) of
four kinds of data frames:
– Ethernet_802.2 (“Raw”)
– Ethernet_802.3 (“Novell proprietary”)
– Ethernet_II (“DIX”)
– Ethernet_SNAP
• Frame types differ in way they code and decode packets
of data
• Ethernet frame types have no relation to network’s
topology or cabling characteristics
Using and Configuring Frames
• Cannot expect interoperability between frame types
• Node’s Data Link layer services must be properly
configured for types of frames it might receive
– LAN administrators must ensure all devices use
same, correct frame type
– Most networks use Ethernet_II
• Frame types typically specified through device’s NIC
configuration software
– (AutoSense) Most NICs automatically sense frame
types running on network and adjust
Frame Fields
• Ethernet frame types share many common fields
• Every frame contains:
– 7-byte preamble and 1-byte start-of-frame
delimiter (SFD)
– 14-byte header
• Destination address
• Source address
• Additional field that varies in function and size
– 4-byte FCS field
– Data portion
• 46 to 1500 bytes of information
Ethernet_II (“DIX”) frame
Summary
• A physical topology is the basic physical layout of a network;
it does not specify devices, connectivity methods, or
addresses on the network
• A bus topology consists of a single cable connecting all
nodes on a network without intervening connectivity devices
• In a star topology, every node on the network is connected
through a central device, such as a hub
• LANs often employ a hybrid of more than one simple
physical topology
• Network backbones may follow serial, distributed, collapsed,
or parallel topologies
• Ethernet employs a network access method called
CSMA/CD
• Networks may use one (or a combination) of four kinds of
Ethernet data frames
The End