1 Kyung Hee University Chapter 14 Local Area Networks : Ethernet.

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Kyung Hee University

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

1010


Physical Layer Signalling(PLS)Physical Layer Signalling(PLS)

PLS sublayer encodes and decodes data

Using Manchester Encoding

Data rate of 10 Mbps

1111


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

3333


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

4141


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

4343


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 !

1 Kyung Hee University Chapter 14 Local Area Networks : Ethernet.

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