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Local Area Networks
LANs are designed to: Operate within a limited geographic area Allow multi-access to high-bandwidth media Control the network privately under local
administration Provide full-time connectivity to local services Connect physically adjacent devices
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Local-Area Network LAN
What is a LAN? A collection of computers, printers, modems,
and other devices that can communicate witheach other in a small area (< ~ 1000 feet)
Small area-low cost, high speed, reliablecommunication is possible.
How is a LAN controlled? Protocols Formal sets of rules that govern
how devices on a network exchangeinformation
Standards
Sets of rules or procedures thatare either widely used or officially specified-
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Connector Port
PC or Workstation
Loaded with NOS
Network InterfaceCard (NIC)
Network Interface Card Amplifies electronic signals Packages data for transmission Physically connects computer to
transmission media (cable)
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Network Interface Card
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OSI Model and Project 802
1985 IEEE started with a project, to set standards to enable interconnectivity.
Does not seek to replace modelsWay of specifying functions of the physical layer &data link layer of LAN protocols.
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Project 802
ach subdivision is identified with a number.
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PDU Format
Defines the upper layer protocol at the source and destination that uses these LLC.
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PDU Control Field
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MAC Frame
46 to 1500 bytes
frame
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Common LAN Technologies
Ethernet
Token Ring
FDDIFiber Distributed Data Interface
FDDIDual Ring
TokenRing
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How media access is controlled?- how devices access thecommunication channel in LAN.
Multiple users have unregulatedaccess to channel. LAN needs mechanism to coordinate
traffic and reduce collision. Accessmechanism used in Ethernet CSMA/CD.
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MEDIA ACCESS
Random access protocols Controlled access protocols Token
passing Cannelization protocols- FDMA , TDMA
Random access- all devices have equalaccess to medium.
2 features:-1) there is no scheduled time fora device to transmit.
2) No rule concerning which device shouldtransmit first.
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When should a device attempt toaccess the medium?
What should a system do if it wishes tosend a data frame and the medium isbusy?
How should a device determine whetherthe transmission was successful? How a device know when a collision has
occurred? When a collision occurs, how a device
know if it was involved in it? What should a device do if it detect a
collision.
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Evolution of CSMA/CDALOHA was the 1 st random access usedFor broadband wireless LAN
Developed by university of Hawaii in 1970.
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Ethernet Operation
AA BB CC DD
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Ethernet Operation
AA BB CC DD
D
Data LinkNetworkTransportSession
PresentationApplication
Physical
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Ethernet Operation
AA BB CC DD
D
Data LinkNetworkTransportSession
PresentationApplication
Physical
B and C
Data LinkNetworkTransportSession
PresentationApplication
Physical
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Ethernet Broadcast
D
Data LinkNetworkTransportSessionPresentationApplication
Physical
C
Data LinkNetworkTransportSessionPresentationApplication
Physical
B
Data LinkNetworkTransportSessionPresentationApplication
Physical
A
Data LinkNetworkTransportSessionPresentationApplication
Physical
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Ethernet Reliability
B C DA
B C DA Figure 1
Figure 2
Collision
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Ethernet Reliability
Collision
C
B C DA
BA D
JAMJAMJAMJAMJAM JAM
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Ethernet Reliability
B C DA
Collision
B C DA
JAMJAMJAMJAMJAM JAM
Carrier sense multiple access with
collision detection (CSMA/CD)
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Project 802
ach subdivision is identified with a number.
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10
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Base band systems use Manchester digitalcoding.
Ethernet LANs can support data ratesbetween 1 and 10Mbps.
IEEE defines types of cable, connectionsand signals that are to be used in each offive different Ethernet implementations.
All Ethernet LANs are configured as logicalbuses, although they may be physicallyimplemented in bus or star topologies.
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Ethernet and IEEE 802.3 Benefits and background
Ethernet is the most popular physical layer LANtechnology because it strikes a good balancebetween speed, cost, and ease of installation
Supports virtually all network protocols Revisions of Ethernet specification
Fast Ethernet (IEEE 802.3u) raises speed from
10 Mbps to 100 Mbps Gigabit Ethernet is an extension of IEEE 802.3
which increases speeds to 1 Gbps
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LANspeed (Mbps)
100BaseFX
Base = baseband Broad = broadband
Indicates type of cableand maximum length.If a number,
max. length = # x 100 m
Ethernet Protocol Names
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Bus topology LAN
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10BASE5
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Ethernet Segments
Attachment unit interface transceiver cable. AUIs are restricted to a maximumlength of 50 meters.Medium attachment unit transceiver. Performs CSMA/CD function.
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10BASE2
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10BASET
Instead of individual transceivers, 10 Base T Ethernet places all of its networking
Operations in an Intelligent hub with a port for each station.
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Unshielded Twisted-Pair Cable
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Schemes to improve performanceand speed of Ethernet LAN
Bridged Ethernet
Switched Ethernet Fast Ethernet Gigabit Ethernet
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Switched Ethernet
Entire media is involved in each transmission.- one transmission uses the entirecapacity of 10Mbps.
We can theoretically increase the capacity of network with N devices to N X 10Mbps.
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Fast Ethernet operates at 100 mbps. It is easy to increase the speed if the
collision domain is decreased.
Collision domain of ethernet is limited to2500meters. Needed to achieve data rate
of 10Mbps using the CSMA/CD accessmethod.
U hi ld d T i t d P i
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Unshielded Twisted-Pair(UTP)
Speed and throughput: 10 100 Mbps Average cost per node: Least expensive Media and connector size: Small Maximum cable length: 100 m (short)
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USES TWISTED PAIR CABLE
Star LAN
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1BASE5
Daisy chaining starLAN allows as many as 10 stations to be linked, each to the next,In a chain in which only the lead device connects to the hub.
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Switched Ethernet
Entire media is involved in each transmission.- one transmission uses the entirecapacity of 10Mbps.
We can theoretically increase the capacity of network with N devices to N X 10Mbps.
MAC F
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MAC Frame
46 to 1500 bytes
frame
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Minimum size of frame 72 bytes .ie 576 bits.To send 576bits at data rate of 10 mbps takes57.6 us.
Collision must be detected during 57.6us. Thistime is sufficient to allow a signal to make around trip of 5000 meters at a propagationspeed in a typical medium.
To increase data rate without changingminimum size of frame . We decrease round
trip time. With 100mbps the round trip timereduces to 5.76us(576 bits/100mbps). Thismeans collision domain must be decreased 10times, from 2500 to 250 meters.
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Printer (Also has a NIC)
NIC
PC or WorkstationLoaded with NOS
Wiring Hub
Cables or Transmission Media
Physical environments through
which transmission signals pass Twisted pair Coaxial cable
Connectors (RJ-11, RJ-45, etc.)
Cable
Fiber-optic cable Atmosphere
Connectors
RJ-45Connector
RJ = Registered Jack
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Network Cabling Media connecting network components
NIC cards take turns transmitting on the cable LAN cables only carry one signal at a time WAN cables can carry multiple signals simultaneously
Three primary types of cabling Twisted-pair (or copper) Coaxial cable Fiber-optic cable
Twisted-Pair Cable
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Twisted-Pair Cable
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Twisted-Pair (UTP and STP)
Speed and throughput: 10/100 Mbps
Relative cost: Least costly
Media and connector size: Small
Maximum cable length: 100 m
RJ-45Connector
Color-CodedPlastic Insulation
Twisted-Pair
Outer Jacket
STP only:Shielded Insulationto Reduce EMI
EMI = Electromagnetic Interference
Unshielded Twisted Pair
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Unshielded Twisted-Pair(UTP)
Speed and throughput: 10 100 Mbps Average cost per node: Least expensive Media and connector size: Small Maximum cable length: 100 m (short)
1 2 3 6 normally used for data transmission.
Most common UTPConnector.Registered jack
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The Electronic Industries association hasdeveloped standards to grade UTP cables byquality. With 1 the lowest and 5 as highest.
Category1 basic twisted pair cabling used intelephone systems. This level of quality is finefor voice communication.
Category2 next higher grade, suitable for voiceand data transmission up to 4 Mbps.
Category3 used for data transmission of up to10 Mbps.
Category4 up to 16Mbps Category5 used for data transmission up to
100Mbps
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UTP Connectors
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Shielded Twisted-Pair (STP)
Speed and throughput: 10 100 Mbps Average cost per node: Moderately expensive Media and connector size: Medium to Large Maximum cable length: 100 m (short)
Coaxial Cable
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Coaxial Cable
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Coaxial Cable
Speed and throughput: 10/100 MbpsRelative cost: More than UTP, but still low
Media and connector size: Medium
Maximum cable length: 200/500 m
Outer Jacket Braided Copper ShieldingPlastic Insulation
Copper Conductor
BNC Connector
BNC = Bayonet Neill Concelman
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Fiber-Optic CableOuter Jacket Kevlar ReinforcingMaterial
PlasticShield Glass Fiber
and Cladding
Single mode: One stream of laser-generated light (100 km)
Multimode: Multiple streams of LED-generated light (2 km)
Speed and throughput: 100+ MbpsAverage cost per node: Most expensive
Media and connector size: Small
Maximum cable length: Up to 2 km
MultimodeConnector
LED = Light Emitting Diode
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LANspeed (Mbps)
100BaseFX
Base = baseband Broad = broadband
Indicates type of cableand maximum length.If a number,max. length = # x 100 m
Ethernet Protocol Names
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10BASE5
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10BASE5
Transceiver
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Transceiver
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10BASET
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10BASET
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Unshielded Twisted-Pair Cable
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Go back-N Damaged Frame
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g
Selective Reject
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Selective Reject
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L t F
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Lost Frame