1 kyung hee university chapter 14 local area networks : ethernet
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Chapter 14 Chapter 14 Local Area Networks : EthernetLocal Area Networks : Ethernet
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IntroductionIntroduction
Three Generations of Ethernet
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14.1 Traditional Ethernet14.1 Traditional Ethernet Mac Sublayer
Physical Layer
Physical Layer Implementation
Bridged Ethernet
Switched Ethernet
Full-Duplex Ethernet
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Traditional EthernetTraditional Ethernet
Designed to operate at 10 Mbps
Access through CSMA/CD
Media shared between all stations
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802.3 MAC frame
• Preamble – 7 bytes of alternating 0s and 1s to alert the receiver and allow it to synchronize
• Start Frame Delimiter (SFD) – 1 byte – 10101011 signals the beginning of a frame, last chance for synchronization – last 2 bits are 11
• Destination address (DA) – 6 bytes – contains the physical address of the destination station or stations
• Source address (SA) – 6 bytes – contains the physical address of the sender
• Length/type – if less than 1518 then it defines the length of the data field – if more than 1536 then it defines the type of the PDU packet that is encapsulated
• Data – data encapsulated from upper-layer protocols : 46 ~ 1500 bytes
• CRC – CRC-32
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Minimum and maximum length of a Frame
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Addressing Addressing
Ethernet addresses in hexadecimal notation
Each station on an Ethernet network has its own netwo
rk interface card (NIC)
NIC provides the station with a 6-byte physical address
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Unicast and Multicast and Broadcast Address Unicast and Multicast and Broadcast Address
Source address is always unicast
Destination can be unicast, multicast, or broadcast
Unicast specifies one recipient
Multicast specifies multiple recipients
Broadcast sends to all stations on the network – destination address is forty-eight 1s
•
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Physical LayerPhysical Layer
Physical layer for 10-Mbps Ethernet
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Physical Layer Signalling(PLS)Physical Layer Signalling(PLS)
PLS sublayer encodes and decodes data
Using Manchester Encoding
Data rate of 10 Mbps
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Attachment Unit Interface (AUI)Attachment Unit Interface (AUI)
A Specification that defines the interface between the P
LS and MAU.
Developed to create a kind of medium-independent inte
rface interface.
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Medium Attachment Unit (MAU)Medium Attachment Unit (MAU) MAU (transceiver) : transmitter and receiver
Transmitting signals over the medium; receiving signals over the medium; detecting collisions
Medium dependent
Transceiver is a transmitter and receiver, can be external or internal
Position and Functions
of a Transceiver
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Medium Dependent Interface (MDI) Medium Dependent Interface (MDI)
To connect the transceiver (internal, external) to
medium, we need a MDI.
For an external transceiver, it can be a tap or a tee
connector.
For an internal transceiver, it can be a jack.
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Physical Layer ImplementationPhysical Layer Implementation
Categories of traditional Ethernet
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10Base5 : Thick Ethernet10Base5 : Thick Ethernet
thick Ethernet or Thicknet
bus topology, external transceiver
Connection of a station to the medium using 10Base5
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10Base2 : Thin Ethernet10Base2 : Thin Ethernet Connection if stations to the medium using 10Base2
Thin Ethernet or Cheapernet
bus topology, internal transceiver or a point-to-point connection via an external transceiver
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10Base-T : Twisted Pair Ethernet10Base-T : Twisted Pair Ethernet
physical star topology
stations connected to a hub with internal or external
transceiver
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10Base-FL : Fiber Link Ethernet10Base-FL : Fiber Link Ethernet fiber link Ethernet
uses star topology to connect stations to a hub
normally implemented with external transceiver having
two pairs of fiber-optic cables connecting it to the hub
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Bridged EthernetBridged Ethernet
Raising the bandwidth
Separating collision domains
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Sharing BandwidthSharing Bandwidth
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Raising the BandwidthRaising the Bandwidth
A Network with and without a Bridge
10/6 Mbps vs 10/12 Mbps in case that traffic is not going through the bridge
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Separating Collision DomainsSeparating Collision Domains
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Switched EthernetSwitched Ethernet
Bandwidth is shared only between the station and the
switch (5 Mbps each)
N-port switch; Switched Ethernet
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Full-Duplex EthernetFull-Duplex Ethernet A Limitation of 10Base5 and 10Base2 half-duplex.
Evolution : switched Ethernet full duplex Switched Ethenet
10Base-T is always Full-duplex.
Full duplex mode increases the capacity of each domain from 10 to 20 Mpbs.
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Full-Duplex EthernetFull-Duplex Ethernet
No need for CSMA/CD, this functionality can be turned
off.
Each link is a point-to-point dedicated path between the station and the switch.
For flow and error control
Adding a sublayer called MAC Control between MAC sublayer and LLC sublayer
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14.2 Fast Ethernet14.2 Fast Ethernet
Evolution from 10 to 100 Mpbs doesn’t change the MA
C sublayer.
Access method is CSMA/CD, which is kept for backwar
d compatibility.
Frame format, minimum and maximum frame lengths,
and addressing are the same.
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AutonegotiationAutonegotiation
Allowing two devices to negotiate the mode or data
rate of operation.
To allow incompatible devices to connect to one another. For example, between 10 Mbps-device and 100 Mbps-device
To allow one device to have multiple capabilities
To allow a station to check a hub’s capabilities
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Physical LayerPhysical Layer
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ReconciliationReconciliation
Replacing PLS sublayer in 10 Mbps Ethernet
But, encoding and decoding, which were performed by the PLS, are moved to the PHY sublayer (transceiver), because encoding in Fast Ethernet is medium-dependent.
Is responsible for passing of data in 4-bit format (nibbl
e) to the MII.
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MIIMII
The AUI is replaced with the medium-independent inter
face (MII)
Can be used with both a 10-and 100Mbps data rate
Features a parallel data (4 bit at a time) path between t
he PHY sublayer and the reconciliation sublayer
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PHY (Transceiver) and MDIPHY (Transceiver) and MDI
Transceiver is responsible for encoding and decoding.
MDI is need to connect the transceiver to the medium.
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Physical Layer ImplementationPhysical Layer Implementation
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100Base-TX Implementation100Base-TX Implementation
Uses two pairs of twisted-pair cable
Physical star topology
Internal or external transceiver
Transceiver – responsible for transmitting, receiving, detecting
collisions, and encoding/decoding data
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Encoding and decoding in 100Base-TX
Encoding/decoding – first performs block encoding usi
ng 4B/5B, then encoded using MLT-3 (multiline transmi
ssion, three level)
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100Base-T4100Base-T4
uses category 3 (voice-grade twisted pair) or higher UTP
uses 4 pairs
Encoding/Decoding – 8B/6T
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Transmission Using Four WiresTransmission Using Four Wires
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Giga-bit EthernetGiga-bit Ethernet
No longer possible to keep the MAC sublayer untouche
d
Two distinctive approaches: half-duplex using CSMA/C
D or full-duplex with no need for CSMA/CD
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Physical Layer in Gigabit EthenetPhysical Layer in Gigabit Ethenet
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Physical Layer in Gigabit EthenetPhysical Layer in Gigabit Ethenet
RS – reconciliation sublayer – sends 8-bit parallel data to the PHY sublayer via GMII interface
GMII – gigabit medium-independent interface) defines how reconciliation sublayer is to be connected to the PHY sublayer (transceiver)
does not exist outside the NIC
operates only at 1 Gbps
no connecter or cable
PHY (transceiver) – medium-dependent – encodes and decodes – can only be internal
MDI medium-dependent interface – connects transceiver to the medium – RJ-45 AND fiber-optic connectors
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Gigabit Ethernet ImplementationGigabit Ethernet Implementation
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1000Base-X implementation1000Base-X implementation
uses two fiber-optic cables
internal transceiver
encoding – 8B/10B then NRZ
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Encoding in 1000Base-X
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1000Base-T implementation
designed to use category 5 UTP
four twisted pairs
encoding – 4D-PAM5 (4-dimensional, 5-level pulse amplitude
modulation)
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Encoding in 1000Base-T
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Questions !Questions !