Other LAN Technologies
Chapter 5
Copyright 2003 Prentice-HallPanko’s Business Data Networks and Telecommunications, 4th edition
2
Other LAN Technologies
Large Ethernet networks
Wireless LANs
ATM LANS and QoS
Legacy LANs Token-Ring Networks
10 Mbps Ethernet co-axial cable LANs
3
Figure 5.1: Multi-Switch Ethernet LAN
Switch 2
Switch 1 Switch 3
Port 5 on Switch 1to Port 3 on Switch 2
Port 7 on Switch 2to Port 4 on Switch 3
C3-2D-55-3B-A9-4FSwitch 2, Port 5
A1-44-D5-1F-AA-4CSwitch 1, Port 2
E5-BB-47-21-D3-56Switch 3, Port 6
D4-55-C4-B6-9FSwitch 3, Port 2
B2-CD-13-5B-E4-65Switch 1, Port 7
4
Switching Table Switch 1Port Station
2 A1-44-D5-1F-AA-4C7 B2-CD-13-5B-E4-655 C3-2D-55-3B-A9-4F5 D4-47-55-C4-B6-9F5 E5-BB-47-21-D3-56
Figure 5.1: Multi-Switch Ethernet LAN
Switch 2
Switch 1
Port 5 on Switch 1to Port 3 on Switch 2
A1-44-D5-1F-AA-4CSwitch 1, Port 2
B2-CD-13-5B-E4-65Switch 1, Port 7
E5-BB-47-21-D3-56Switch 3, Port 6
5
Figure 5.1: Multi-Switch Ethernet LAN
Switch 2
Switch 1 Switch 3
Port 5 on Switch 1to Port 3 on Switch 2
Port 7 on Switch 2to Port 4 on Switch 3
C3-2D-55-3B-A9-4FSwitch 2, Port 5
Switching Table Switch 2Port Station
3 A1-44-D5-1F-AA-4C3 B2-CD-13-5B-E4-655 C3-2D-55-3B-A9-4F7 D4-47-55-C4-B6-9F7 E5-BB-47-21-D3-56 E5-BB-47-21-D3-56
Switch 3, Port 6
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Figure 5.1: Multi-Switch Ethernet LAN
Switch 2
Switch 3
Port 7 on Switch 2to Port 4 on Switch 3
A1-44-D5-1F-AA-4CSwitch 1, Port 2
D4-55-C4-B6-9FSwitch 3, Port 2
Switching Table Switch 3Port Station
4 A1-44-D5-1F-AA-4C4 B2-CD-13-5B-E4-654 C3-2D-55-3B-A9-4F2 D4-47-55-C4-B6-9F6 E5-BB-47-21-D3-56
E5-BB-47-21-D3-56Switch 3, Port 6
7
Figure 5.2: Hierarchical Ethernet LAN
Ethernet Switch F
Server YServer X
Client PC1
Only OnePossible Path
BetweenAny TwoStations
PC Client 2
EthernetSwitch E
EthernetSwitch D
EthernetSwitch B
EthernetSwitch A
EthernetSwitch C
8
Figure 5.3: Single Point of Failure in a Switch Hierarchy
No CommunicationNo Communication
Switch 1
Switch 2
Switch 3
Switch Fails
A1-44-D5-1F-AA-4C
B2-CD-13-5B-E4-65
C3-2D-55-3B-A9-4F
D4-47-55-C4-B6-9F
E5-BB-47-21-D3-56
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Figure C.10: 802.1D Spanning Tree Protocol
Switch 1
Switch 2
Switch 3
A1-44-D5-1F-AA-4C
B2-CD-13-5B-E4-65
C3-2D-55-3B-A9-4F
D4-47-55-C4-B6-9F
E5-BB-47-21-D3-56
Activated
Activated
Deactivated
Normal OperationLoop, but Spanning Tree ProtocolDeactivates One Link
Module C
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Figure C.10: 802.1D Spanning Tree Protocol
Switch 1
Switch 2
Switch 3
A1-44-D5-1F-AA-4C
B2-CD-13-5B-E4-65
C3-2D-55-3B-A9-4F
D4-47-55-C4-B6-9F
E5-BB-47-21-D3-56
Deactivated Deactivated
Activated
Switch 2 FailsModule C
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Figure 5.2: Hierarchical Ethernet LAN
Core
WorkgroupEthernet Switch F
Server YServer XClient PC1
PC Client 2
WorkgroupEthernetSwitch E
WorkgroupEthernetSwitch D
Core EthernetSwitch B
CoreEthernetSwitch A
Core EthernetSwitch C
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Figure C.8: Switching Matrix with Queue
Switch Matrix
Input Queue
IncomingSignal
OutgoingSignal
Port1
Port2
Port3
Port4
Port5
Port6
Port7
Port8
Module C
13
Figure 5.4: Workgroup Switches versus Core Switches
Ports = 4
Speed = 1 Gbps
Maximum input = 4 Gbps
Nonblocking switch matrix capacity = 4 Gbps
1 Gbps
1 Gbps
1 Gbps1 Gbps
Switching Matrix4Gbps
Nonblocking
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Figure 5.4: Workgroup Switches versus Core Switches
Connects
Typical PortSpeeds
Switching Matrix
Workgroup Switches
Client or Server to theEthernet Network via An access line
10/100 Mbps
Lower Percentage ofNonblocking CapacityBut not less than 25%
Core Switches
Ethernet Switchesto One Another viaA trunk line
100 Mbps, Gigabit Ethernet,10 Gbps Ethernet
80% or More ofNonblocking Capacity
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Client A
Client B
Client C
Server D Server E
ServerBroadcast
Figure 5.5: Virtual LAN with Ethernet Switches
Server Broadcasting without VLANS
Frame is BroadcastGoes to all stationsCreates congestion
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Figure 5.5: Virtual LAN with Ethernet Switches
Server Multicasting with VLANS
Client Aon VLAN1
Client Bon VLAN2
Client Con VLAN1
Server Don VLAN2
Server Eon VLAN1
ServerBroadcast
VLANs are collections of servers and their clients
Multicasting (some), not Broadcasting (all)
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Figure 5.6: Tagged Ethernet Frame
Source Address (6 Octets)
Length (2 Octets)Length of Data Field in
Octets1,500 (Decimal) Maximum
Tag Protocol ID (2 Octets)1000000100000000
81-00 hex; 33,024 decimalLarger than 1,500, So not
A Length
By lookingat the value
in the 2octets after
theaddresses,the switchcan tell ifthis frameis basic(value < 1,500)
or tagged(value = 33,024)
Basic 802.3 MAC Frame Tagged 802.3 MAC Frame
Source Address (6 Octets)
Tag Control Information(2 Octets) Priority Level (0-7)
(3 bits); VLAN ID (12 bits)(1 other bit)
Length (2 Octets)
Data Field (variable)
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Figure 5.7: Ethernet Physical Layer Standards
Physical LayerStandard
SpeedMaximum
Run Length
UTP
10Base-T
100Base-TX
10 Mbps
100 Mbps
100 meters
100 meters
Medium
4-pair Category 3, 4, or 5
4-pair Category 5
1000Base-T 1,000 Mbps 100 meters4-pair Category 5, 4-pairEnhanced Category 5 is
preferred
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Figure 5.7: Ethernet Physical Layer Standards
Physical LayerStandard
SpeedMaximum
Run Length
Optical Fiber
Medium
10Base-F* 10 Mbps UP to 2 km*62.5/125 micron
multimode, 850 nm.
100Base-FX 100 Mbps 412 m62.5/125 multimode,
1,300 nm, hub
100 Base-FX 100 Mbps 2 km62.5/125 multimode,
1,300 nm, switch
* Several 10 Mbps fiber standards were defined in 10Base-F.
Wireless LANs
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Figure 5.8: Typical 802.11 Wireless LAN Operation with Access Points
Switch
Client PCServer
Large Wired LAN
AccessPoint A
AccessPoint B
UTP Radio Link
HandoffIf mobile computermoves to another
access point,it switches serviceto that access point
Notebook
CSMA/CA+ACK
UTP
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Figure 5.8: Typical 802.11 Wireless LAN Operation with Access Points
WirelessNotebook
NIC
Access Point
IndustryStandard
CoffeeCup
To EthernetSwitch
Antenna(Fan) PC Card
Connector
23
Figure 5.8: Typical 802.11 Wireless LAN Operation with Access Points
D-LinkWirelessAccessPoint
Using Two Antennas Reduces Multipath Interference (See Ch. 3)
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LinksysSwitchWith
Built-InWirelessAccess Point
Using Two Antennas Reduces Multipath Interference (See Ch. 3)
Figure 5.8: Typical 802.11 Wireless LAN Operation with Access Points
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Figure 5.8: Typical 802.11 Wireless LAN Operation with Access Points
The Wireless Station sends an 802.11 frame to a server via the access point
The access point is a bridge that converts the 802.11 frame into an 802.3 Ethernet frame and sends the frame to the server
MobileStation
AccessPoint
EthernetSwitch
Server
802.11Frame
802.3Frame
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Figure 5.8: Typical 802.11 Wireless LAN Operation with Access Points
The server responds, sending an 802.3 frame to the access point
The access point converts the 802.3 frame into an 802.11 frame and sends the frame to the mobile station.
MobileStation
AccessPoint
EthernetSwitch
Server
802.11Frame
802.3Frame
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802.11 Wireless LAN Speeds
802.11 2 Mbps (rare)2.4 GHz band (limited in bandwidth)
802.11b 11 Mbps, 2.4 GHz3 channels/access point
802.11a 54 Mbps, 5 GHz (> bandwidth than 2.4 GHz)11 channels/access point
802.11g 54 Mbps, 2.4 GHzlimited bandwidth
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802.11 Broadcast Operation
The Wireless Stations and Access Points Broadcast their Signals. Only one access point or wireless station may
transmit at any moment or signals will become scrambled.
CollisionAbout toOccurAccess
Point
WirelessStation
WirelessStation
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Figure 5.9: CSMA/CA + ACK in 802.11 Wireless LANs
CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) Station or access point sender listens for traffic
If there is no traffic, can send if there has been no traffic for a specified amount of time
If the specified amount of time has not been met, must wait for the specified amount of time. Can then send if the line is still clear
Correction
30
Figure 5.9: CSMA/CA + ACK in 802.11 Wireless LANs
CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) Station or access point sender listens for traffic
If there is traffic, the sender must wait until traffic stops
The sender must then set a random timer and must wait while the timer is running
If there is no traffic when the station or access point finishes the wait, it may send
Correction
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Figure 5.9: CSMA/CA + ACK in 802.11 Wireless LANs
ACK (Acknowledgement) Receiver immediately sends back an
acknowledgement; no waiting because ACKs have highest priority
If sender does not receive the acknowledgement, retransmits using CSMA/CA
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Who Implements CSMA/CA+ACK?
Stations (when they send)
Access Points (when they send)
MobileStation
AccessPoint
802.11Frame
CSMA/CA+ACK
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Request to Send (RTS) / Clear to Send (CTS)
There is a widely used option we should cover.
After a station may send, its first message may be a Request-to-Send (RTS) message instead of a data message
Only if the other party sends a Clear-to-Send (CTS) message does the sender begin sending data
MobileStation
AccessPoint
RTS
CTS
New
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Ad Hoc 802.11 Networks
Ad Hoc Mode There is no access point. Stations broadcast to one another directly Not scalable but can be useful for SOHO use NICs automatically come up in ad hoc mode
Module C
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Wired Core / Wireless to the Desktop
Normal Networks: Core & Workgroup Switches
Core
WorkgroupEthernet Switch FWorkgroup
EthernetSwitch D
Core EthernetSwitch B
CoreEthernetSwitch A
Core EthernetSwitch CWorkgroup
SwitchesAttach toStationsBy UTP
Module C
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Wired Core / Wireless to the Desktop
With High-Speed Wireless LANs, Replace Workgroup Switches with Access Points
Core
AccessPoint 2
AccessPoint 1
Core EthernetSwitch B
CoreEthernetSwitch A
Core EthernetSwitch CAccess
PointsServe
Stations
Module C
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802.11 Security
Attackers can lurk outside your premises In “war driving,” drive around sniffing out unprotected
wireless LANs
In “drive by hacking,” eavesdrop on conversations or mount active attacks.
Site with 802.11 WLAN
OutsideAttacker
New
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802.11 Security
By default, security on 802.11 WLAN NICs and access points is turned off, making external attacks trivial
WLAN vendors offer Wired Equivalent Privacy (WEP), but this is weak and easily broken.
The 802.11 Working Group is working on a temporary replacement (TKIP) and longer-term security replacement, 802.11i
Even if corporate access points can be secured, many departments create unauthorized rogue access points that are seldom secured.
New
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Personal Area Networks (PANs)
Connect Devices On or Near a Single User’s Desk PC, Printer, PDA, Notebook Computer,
Cellphone
Connect Devices On or Near a Single User’s Body Notebook Computer, Printer, PDA,
Cellphone
The Goal is Cable Elimination
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Personal Area Networks (PANs)
There May be Multiple PANs in an Area May overlap
Also called piconets
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Figure 5.10: 802.11 versus Bluetooth LANs
Focus
Speed
802.11 Bluetooth
Large WLANs Personal Area Network
11 Mbps to 54 MbpsIn both directions
722 kbps with backchannel of 56 kbps.
May increase.
Distance100 meters for 802.11b(but shorter in reality)
Shorter of 802.11a
Numberof Devices
Limited in practice onlyby bandwidth and traffic
Only 10 piconets,each with
8 devices maximum
10 meters(may increase)
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Figure 5.10: 802.11 versus Bluetooth LANs
Scalability
Cost
Battery Drain
802.11 Bluetooth
Good through havingmultiple access points
Poor(but may get
access points)
Probably higher Probably Lower
Higher Lower
Discovery No Yes
Discovery allows devices to figure out how to work together automatically
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Figure 5.11: Bluetooth Operation
File Synchronization
Client PCSlave
NotebookMaster
Printer SlavePrinting
Cellphone
Telephone
Piconet 1
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Figure 5.11: Bluetooth Operation
Client PC
Notebook
Printer SlavePrinting
Call Through CompanyPhone System
CellphoneMaster
Telephone Slave
Piconet 2
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Figure 5.11: Bluetooth Operation
File Synchronization
Client PCSlave
NotebookMaster
Printer SlavePrinting
Call Through CompanyPhone System
CellphoneMaster
Telephone Slave
Piconet 1
Piconet 2
46
Figure 5.12: Normal Radio Transmission and Spread Spectrum Transmission
Channel BandwidthRequired for a specificSignal speed
Normal Radio:Use only the requiredBandwidth to conserveThe frequency spectrum
Note: Height of Box Indicates Bandwidth of Channel
Shannon’s Law: W = B log2 (1/S/N)
Defines minimum bandwidth needed for a signal of a specific speed.
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Figure 5.12: Normal Radio Transmission and Spread Spectrum Transmission
Channel BandwidthRequired for Signal
Frequency HoppingSpread Spectrum (FHSS)
802.11
Direct SequenceSpread Spectrum (DSSS)
802.11b
Note: Height of Box Indicates Bandwidth of Channel
Wideband but Low-Intensity Signal
48
Figure 5.13: Code Division Multiple Access (CDMA) Spread Spectrum Transmission
Client PC 1
Client PC 2
Low-Density Orthogonal Signal 1
Low-Density Orthogonal Signal 2
Server A
Server B
Radio Spectrum
Used in Some Cellular Telephone Systems
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OFDM
Orthogonal Frequency Division Multiplexing (OFDM) Divide a large channel into many subchannels Send part of the signal in each channel Stops using channels with impairment Used in 802.11a, 802.11g at 54 Mbps
Module B
Channel
Subchannel
ImpairedSubchannel(Not Used)
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Spread Spectrum Methods
Spread Spectrum Techniques
DSSS FHSS(Original802.11)
802.11bDSSS
CDMA(Cellular
Telephony)
OFDM(802.11a,802.11g)
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Ultrawideband (UWB)
EWB Uses Extremely Wide Channels
EWB channels are enormously wide—often cutting across several entire service bands
Extremely high speeds are possible
Can travel through thick walls
Because of concerns that EWB may it interfere with services in the service bands spanned, regulators require power to be kept extremely low
NewNot in Book
52
ATM (Asynchronous Transfer Mode)
Ethernet competitor for switched LANs
Quality of Service (QoS) for telephony and multimedia transmissions
As scalable in speed as Ethernet
Highly complex and expensive to buy and manage
Not selling well for LANs
Increasingly popular for WANs
53
Figure 5.15: Handling Brief Traffic Peaks
Traffic
Network Capacity
Momentary Traffic Peak:Congestion and Latency
Time
Congestion and Latency
54
Figure 5.15: Handling Brief Traffic Peaks
Traffic
Network Capacity
Traffic Peak
Time
Quality of Service (QoS) Guarantees in ATM
Traffic with ReservedCapacity Always Goes(Voice)
Other Traffic Must Wait(Data)
55
Figure 5.15: Handling Brief Traffic Peaks
Traffic
Overprovisioned Network CapacityTraffic Peak:No Congestion or Latency
Time
Overprovisioned Traffic Capacity in Ethernet
56
Figure 5.15: Handling Brief Traffic Peaks
Traffic
Network Capacity
Peak Load
Time
Priority in Ethernet
High-Priority Traffic FirstLow-Priority Waits
57
Figure 5.16: ATM Network with Virtual Circuits
Server
Client PC
ATM Switch 1 ATM Switch 2
ATMSwitch 3
ATM Switch 4
ATM Switch 5ATM switches can be arranged in amesh, so there are alternative paths. This makes switching slow and expensive.
58
Figure 5.16: ATM Network with Virtual Circuits
Server
Client PC
ATM Switch 1 ATM Switch 2
ATMSwitch 3
ATM Switch 4
ATM Switch 5
VirtualCircuit
VirtualCircuit
ATM selects a single path, called aVirtual circuit, before two stationsBegin transmitting. This simplifiesSwitching and so lowers switching cost
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Figure 5.16: ATM Network with Virtual Circuits
Server
Client PC
ATM Switch 1 ATM Switch 2
ATMSwitch 3
ATM Switch 4
ATM Switch 5
VirtualCircuit
VirtualCircuit
Virtual CircuitA . . .B . . .C . . .D . . .
Port1234
Switch 4 Switching Table
ATM switching tables are as simple asEthernet switching tables
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ATM Reduces Switching Costs
Virtual circuits simplify switching, reducing switching costs
ATM (like Ethernet) is unreliable, also reducing switching costs by avoiding the expense of step-by-step error correction
Switches are the most expensive element in most networks, so minimizing switching cost usually is a major goal in network standards
61
Figure 5.17: Virtual Circuit with VPI and VCI
Virtual Path is a Path to a SiteVirtual Channel is a Connection to a Particular Computer at the Site
Switches in Backbone Only Have to Look at the Virtual Path Indicator (VPI)
VirtualChannels Virtual Path
Site 1 Site 2
ATM Backbone
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Figure 5.17: ATM Cell
Bit 1 Bit 4Bit 3Bit 2 Bit 8Bit 7Bit 6Bit 5
Virtual Channel Identifier
Virtual Path Identifier Virtual Channel Identifier
Virtual Channel Identifier ReservedCall LossPriority
Payload Type
Header Error Check
Payload(48 Octets)
Virtual Path Identifier
VPI: Specifies a VC to siteVCI: Specifies a station at siteSwitches between sites only look at VPI
5 octets of header48 octets of payload53 octets total
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ATM Cells
ATM frames are short and fixed in length; called cells Only 53 octets long 5 octets of header 48 octets of data
Short length reduces latency at switches Switch may have to wait until entire frame arrives
before sending it back out—faster with short cells
Fixed length gives predictability for faster processing
Token-Ring Networks
Legacy LAN Technologies
65
Token-Ring Networks
Ring Topology
Inner Ring Outer Ring
Frame
NormalOperation
Dual Ring; normally only one is used
66
Token-Ring Networks
Ring is wrapped if there is a break The wrapped ring is still a full ring
BreakWrapped Ring
67
Token-Ring Networks
Special Frame Called Token Circulates when no station is transmitting For access control, station must have token to send
Inner Ring Outer Ring
Token
68
Ring Network Technologies
802.5 Token-Ring Network
FDDI (Fiber Distributed Data Interchange)
SONET/SDH
16 Mbps 100 Mbps: 200 km circumference
54 Mbps to several Gbps
Small to Mid-size LANs
LAN Backbones Telephony
Lost out to cheaper and eventually faster Ethernet
Lost out to faster gigabit Ethernet
Growing rapidly in the telephone network core
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Figure 5.19: 802.5 Token-Ring Network
STP or UTP
STPOr Fiber
Wiring hubs are called multistation access units (MAUs).
Prefers to use shielded twisted pair (STP) wire for runs to stations and to link MAUs but will use UTP for stations and fiber for trunks.
STP has two twisted pairs. There is a metal mesh around each pair and around both pairs to reduce interference. STP is bulky and expensive.
MultistationAccess Unit
(MAU)
70
Figure 5.18: Major Legacy Networks
Early Ethernet Standards General
Only 10 Mbps—shared by all stations
Before switches and hubs
Used coaxial cable (central wire surrounded by a conducting cylinder) You use this to connect your TV to your VCR
InnerWire
Outer Conductor Wrapped in Jacket
71
Figure 5.18: Major Legacy Networks
Early Ethernet Standards 10Base5
Multidrop topologyThick trunk cable uses coaxial cable
technology; 500-meter limitDrop cable has 15 wiresNIC has 15-hole Attachment Unit Interface
(AUI) port
Trunk CableDrop Cable
15-HoleAUI Port
72
Figure 5.18: Major Legacy Networks
Early Ethernet Standards 10Base2
Daisy chain topologyThin coaxial cable between stationsCircular BNC connector
BNCConnector
73
Figure 5.18: Major Legacy Networks
Ethernet 10Base2
To NextStation
T-Connector to Link NIC to next segments
NIC
74
Figure 5.18: Major Legacy Networks
RJ-45UTP
Connectors
BNC Connector10Base2T-Connector
UTP
ThinCoax
Ethernet 10Base2: UTP versus BNC Connectors
75
Figure 5.18: Major Legacy Networks
Ethernet 10Base2
BNC Connector
T-ConnectorTo NextStation
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