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Network topologies
Unit objective
 Describe different logical and physical
network topologies
 Compare and contrast different LAN
technologies
 Categorize WAN technology types and
properties
 Identify virtual network components
Topic A
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Topic A: Network topologies
Topic B: LAN technologies
Topic C: WAN technologies
Topic D: Virtual networks
Local area networks
 Located within a
confined area
 Connected by
wires or radio
waves
 Node: any network
device
 Host: always a
computer
 Can be connected
to the Internet
 Requires host OS
Network topologies
 Networks defined by logical and
physical topologies
 Logical — The path that data takes
between nodes
 Physical — The material layout of
network wiring and locations of nodes
Logical network topologies
 Two basic LANs:
– Peer-to-peer
– Client/server
 Extend LAN remotely:
– Virtual private network (VPN)
Peer-to-peer model
 Simple file and resource sharing
 Home or small office
 Computers have:
– NIC for wired or wireless connections
– Client OS that supports network
connectivity; hosts can have different
OSs
 Fewer than a dozen hosts
– Client OSs have connection limits
Decentralized
 All hosts have equal authority
 Each host controls its own resources
 Individual user responsibility
Peer-to-peer authentication
 User account includes
– User name
– Password
– Permissions
 User account exists on single computer
 Valid user credentials for computer use
 User name and password for
authentication, validation, logging on
 Can create additional user accounts
 Can share local resources with other users
Client/server model
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Servers hold data and provide services
Scales larger than peer-to-peer network
Network operating system on server
Servers manage resources
Unlimited connections
NOS provides:
– Network directory services
– Network security, monitoring, and auditing
features
– Architectural framework (APIs) to support
server-based applications
A client/server LAN
Client/server authentication
 Client OS sends login information to
directory server
 Directory server responsible for user
authentication
 Login process — Client communicates
with NOS on server
Activity A-1
Describing network models
Star topology
 Nodes connected to central network
connectivity device
 Central device distributes
information packets
 Single break
doesn’t affect
other nodes
 If central device
fails, all
communication
fails
Bus topology
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Continuous line is formed
Nodes connected to next in line
Coaxial and T-connectors
End of line uses terminating device
Terminator absorbs the data signal
Information passes through each node once
Node determines if data is addressed to it
Simple and inexpensive design
Single break in line stops all communication
Ring topology
 Each node is connected to two nodes on
either side of it
 All nodes form a continuous loop
 Data token passes around the ring
 Node can transmit data if it has the token
Mesh topology
 All nodes have
independent
connections to
all other nodes
 Very fault-tolerant
and scalable design
 Nodes need
multiple network
cards
 Complex wiring scheme
 Most often wide-area
or campus links
 Might not be fully meshed
Hybrid topology
 Two or more types of network
topologies combined into one network
Point-to-point vs. point-to-multipoint
 Point-to-point:
– Dedicated connection between two nodes
– Only those two nodes communicate over the connection
 Point-to-multipoint:
– Multiple connections from single node to multiple nodes
MPLS
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Multiprotocol Label Switching
Uses labels to move data
Protocol-agnostic network
Operates between OSI Layers 2 and 3
Can carry different types of traffic for both
circuit- and packet-switching clients
 Provides traffic management and QoS
support
 Simple traffic shaping and Layer 3 VPNs
Label Edge Routers
 Assign each data packet an MPLS
header
 Header contains one or more labels
called a stack
 Label stack is a 32-bit field
 Label contains four elements:
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–
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20-bit label value
3-bit traffic class field
1-bit bottom-of-stack flag
8-bit time-to-live (TTL) field
Activity A-2
Describing physical network topologies
Topic B
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Topic A: Network topologies
Topic B: LAN technologies
Topic C: WAN technologies
Topic D: Virtual networks
Ethernet
 10 Gigabit Ethernet (10GbE)
– Fastest Ethernet standard
– Data rate of 10 gigabits per second
 1000-Mbps Ethernet (Gigabit Ethernet)
– Data rate of 1000 Mbps (1 gigabit per second)
– Used for large, high-speed LANs and heavy-traffic server
connections
 100-Mbps Ethernet (Fast Ethernet)
– Data rate of 100 Mbps
 10-Mbps Ethernet (Twisted-pair Ethernet)
– Data rate of 10 Mbps
– Became known as Ethernet IEEE 802.3
– All subsequent Ethernet architectures conform to IEEE
802.3
Ethernet media
 BASE-R — Fiber optic cable
 BASE-W — Wide Area Network Physical
Layer (WAN PHY)
– Fiber optic cables
– Same types of fiber and support the same
distances as 10GBASE-R
– Ethernet frames encapsulated in SONET
frames
 BASE-T — STP or UTP
 BASE-C — Shielded copper twisted-pair
continued
Ethernet media, continued
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F typically identifies fiber optic cabling
R refers to LAN technologies
W refers to WAN encodings
S, L, and E designate wavelength
10-Gigabit Ethernet standards
Standard
Medium
Distance
10GBASE-T
Copper twistedpair, shielded or
unshielded
100 meters with
CAT6a; up to 55
meters with CAT6
10GBASE-SR,
10GBASE-SW
Multi-mode fiber
26 or 82 meters,
depending on cable
type
Notes
Preferred choice
for optical cabling
within buildings.
300 meters over 50
microns at 2000 MHz
per km with OM3
multi-mode fiber
10GBASE-LR,
10GBASE-LW
Single-mode fiber
10 km
10GBASE-ER,
10GBASE-EW
Single-mode fiber
40 km
Used to connect
transceivers.
Gigabit Ethernet standards
Standard
Medium
Distance
Notes
1000BASE-T
Unshielded twistedpair: CAT5, CAT5e,
or CAT6
100 meters per
network segment
Requires all four wire
pairs.
1000BASE-CX
Balanced copper
25 meters
shielded twisted-pair
An initial standard for
Gigabit Ethernet
connections.
1000BASE-LX
Single-mode optic
fiber
5 km*
(See the notes below this
table in course book.)
1000BASE-LX10
Single-mode optic
fiber
10 km
Wavelength of 1270 to
1355 nm.
1000BASE-BX10
Single-mode fiber,
over single-strand
fiber
10 km
Different wavelength
going in each direction—
1490 nm downstream,
1310 nm upstream.
1000BASE-SX
Multi-mode optic
fiber
500 meters
Fast Ethernet standards
Standard
Medium
Distance
Notes
100BASE-TX
Twisted-pair
copper, CAT5
or above
100 meters per
network segment
Runs over two pairs:
one pair of twisted
wires in each direction.
The most common
Fast Ethernet.
100BASE-FX
Single- or
multi-mode
fiber
400 meters for halfduplex
2 km for full-duplex
over MMF
Uses two strands: one
for receiving and one
for transmitting.
Not compatible with
10BASE-FL.
10BASE-T
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10 Mbps
Copper twisted-pair cable
Up to 100 meters
Easier to install than coax Ethernet
Ethernet bonding
 Combines bandwidth of two NICs
 Increases bandwidth
 Provides fault tolerance
Data transmission
 Ethernet LANs are broadcast domains
 Wire is a shared transmission system
 All nodes detect the data transmission
on the network
 Only the node to which the data was
addressed receives it
Data collisions
Channel access methods
 Determine physical methodology by
which data is sent across transmitting
media
 CSMA/CD
– Carrier sensing
– Multiple access
– Collision detection
 CSMA/CA
– Avoids collisions; does not detect them
– Uses alert messages
Activity B-1
Describing Ethernet standards
Topic C
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Topic A: Network topologies
Topic B: LAN technologies
Topic C: WAN technologies
Topic D: Virtual networks
Wide area networks
 Span larger geographical distances
 Connect multiple LANs using high-speed
communication lines
 Expand beyond own premises
 Typically lease data lines from public carrier
Packet vs. circuit switching
 Packet switching:
– Data grouped into packets before being sent
over shared network
– Packets can contain a variety of data types
– Packets can be buffered and queued
– Can result in transmission delays
– Examples: LAN and Internet
 Circuit switching:
– Dedicated path for data transmission between
two nodes
– Transfer moves at non-stop rate
– Path unavailable for other traffic until it’s
released
– Examples: PSTN and ISDN
WAN connections
WAN connection
Description
Dial-up networking
(DUN)
Uses a modem to connect through regular analog
phone lines.
Digital Subscriber Line
(DSL)
High-speed connections made over regular analog
phone lines.
Cable
Connections made over the same lines that carry
cable television signals.
Satellite
Connections made by sending signals to and
receiving signals from satellites in orbit around the
earth.
Wireless
Connections made through infrared light or radio
waves. Wireless connections can also be made over
cellular telephone networks or via satellite.
Cellular
Connections made through a cell phone or laptop’s
cellular network PC Card on a cellular phone network.
continued
WAN connections, continued
 Used to connect:
– Small ISP or large business to regional
ISP
– Regional ISP to an Internet backbone
 T lines and E lines
 X.25 and frame relay
 ATM
POTS/PSTN
 Dial-up system over telephone lines
 Connection isn’t continuous
 Phone and data share line; only one can be used at
a time
 Max data speed 56 Kbps
 Modem bonding combines speed of multiple
modems
ISDN
 Uses phone lines
– 2 data channels
– Control signal channel
 Data not converted to analog
 Terminal adapter
 Each data channel can transmit data at up
to 64 Kbps
 Two channels can be combined to move
data at speed of 128 Kbps
 Basic Rate Interface (BRI)
 PRI: 23 channels + control channel
DSL
 High-speed data and voice
transmission line
 Uses telephone wires for data
transmission
 Carries digital data at frequencies
above voice transmission
 Can transmit voice and digital data on
same line at same time
 Typical speeds: 1.5 Mbps in both
directions
continued
DSL, continued
 ADSL — Up to 640 Kbps upstream
and 7.1 Mbps downstream
 SDSL — Up to 1.544 Mbps
 HDSL — Up to 1.5 Mbps
 VDSL — Up to 52 Mbps downstream
and 16 Mbps upstream
 DSL Lite or G.Lite — Up to 384 Kbps
upstream and 6 Mbps downstream
 Can bond multiple DSL lines for higher
bandwidth
Cable
 Uses transceiver (cable modem) to send and
receive data
 Uses same line as cable TV
 Different frequencies
 Speed examples: 500 Kbps up to 10 Mbps
 Optional VoIP
Satellite
 Useful in rural areas
 Uses dish mounted on building to communicate
with stationary satellite in orbit
 Downlink uses satellite (up to 1.5 Mbps)
 Uplink sometimes dial-up
Wireless
 Technologies that don’t use cables
 Public radio, cell phones, one-way paging, satellite,
infrared, and private, proprietary radio
 More expensive to install and use
 Health concerns; wireless network can interfere
with other devices
 Two types: fixed-point wireless and mobile wireless
WiMAX
 802.16 Air Interface Standard
 Worldwide Interoperability of Microwave
Access
 Provides DSL and T1-level service
 Point-to-multipoint broadband wireless
access standard
 Used for WANs and MANs
 10–66 GHz licensed; 2–11 GHz unlicensed
 70 Mbps
 Max of 31 miles
 Doesn’t require a line of sight
Cellular
 Provided by major cell phone companies
 Access via cell signal with Internet-capable
phone or laptop using cellular network PC
card
 Faster than dial-up; slower than DSL or
cable
T and E lines
 First digitized voice transmission
 Work with leased digital
communications line
 Transmit both voice and data
 T1
– 24 channels
– 64 Kbps each
– Total of 1.544 Mbps
 T3
– 672 channels
– Total of 44.736 Mbps
continued
T and E lines, continued
 E carrier: European equivalent of T
line
– E1: 2.048 Mbps
– E3: 34.368 Mbps
 T and E use 4 wires: 2 for receiving
and 2 for sending
 Fiber optic and STP preferred over
coaxial
 Repeaters every 6000 ft.
continued
T and E lines, continued
 Business lines
– T1: coaxial, microwave, or fiber optic
– T3: microwave or fiber optic
 Can lease fractional line
– T1: 64 Kbps increments
– T3: 1.544 Mbps increments
 D3 (Digital Signal 3): Digital T3 or E3
line
X.25 and frame relay
 Packet-switching communication
protocols
 Designed for long-distance data
transmission
 Packet-switching technology
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Divides data into packets
Sends each packet separately
Used on Internet
Uses bandwidth efficiently
continued
X.25 and frame relay, continued
 Frame relay
– Digital
– T1 or T3 lines
– Speeds from 64 Kbps to 44.736 Mbps
 X.25
– Analog
– Up to 56 Kbps
 Both use a permanent virtual circuit
(PVC)
continued
X.25 and frame relay, continued
 PVCs aren’t dedicated lines
– You specify
 Nodes (two endpoints)
 Amount of bandwidth required
– Carrier sends data along any number of
paths between the two endpoints
 Advantage: pay for only the amount of
bandwidth you need
 International businesses use frame
relay
ATM
 Very fast network technology
 Used with LANs and WANs
 Uses cells to transmit data, voice, video,
and frame relay traffic
 Each cell is 53 bytes
– 48 bytes of data
– 5-byte header
 Uses virtual circuits
– PVCs
– SVCs
 Throughput of 622 Mbps
 Best with fiber optic cable; can use TP
SONET and SDH
 Synchronous Optical Network
 ANSI standard for signal transmission on
optical networks
 Signal Digital Hierarchy: European
counterpart to SONET
 Categories: Signal
Rate
STS-1, OC-1
51.8 Mbps
STS-3, OC-3
155.5 Mbps
STS-12, OC-12
622.0 Mbps
STS-48, OC-48
2.48 Gbps
STS-192, OC-192
9.95 Gbps
STS-768, OC-768
39.81 Gbps
DWDM
 Dense wavelength division
multiplexing
 Increases data capacity of fiber
networks such as SONET and SDM
 Assigns optical signals to specific
frequencies of light within a band
 Can carry multiple protocols without a
common signal format
PON
 Passive optical network
 Shared point-to-multipoint fiber
network
continued
PON, continued
Activity C-1
Discussing WAN bandwidth technologies
Topic D
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Topic A: Network topologies
Topic B: LAN technologies
Topic C: WAN technologies
Topic D: Virtual networks
Virtual computers
 Virtual applications
 Virtual desktops
 Virtual servers
 Virtual PBX
Virtualization concerns and risks
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Compliance with security standards
Rogue VMs
Orphaned VMs
Legal and regulatory compliance
Activity D-1
Exploring the benefits and risks of
virtualization
Cloud computing
 Key features
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Elastic provisioning
Cost benefits
Standardized API
Simplified installation
Multi-tenancy
Reliability and redundancy
Cloud deployment
 Public cloud
 Private cloud
 Mixed cloud
Cloud categories
 Software as a Service
 Platform as a Service
 Infrastructure as a Service
Risks and concerns
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Data residing outside your network
Privacy and data loss
Compliance with laws and regulations
Intellectual property agreements
Activity D-2
Exploring the benefits and risks of
cloud computing
Unit summary
 Described different logical and
physical network topologies
 Compared and contrasted different
LAN technologies
 Categorized WAN technology types
and properties
 Identified virtual network components