Lecture10-WLAN and LAN briges.pdf

7/21/2019 Lecture10-WLAN and LAN briges.pdf

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1

B i gi ng M ng Vi n thng

Tr n Xun Nam Khoa V tuy n i n t

H c vi n K thu t Qun s


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2

B i9 C c Giao th c i u khi n

Truy nh p Mi trngv M ng C c b

Part II: M ng C c b T ng quan v LANsEthernet

Token Ring and FDDI802.11 Wireless LAN

LAN Bridges


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3

B i9 C c Giao th c i u khi n

Truy nh p Mi trngv M ng C c b

Tng quan v L A N s


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4

Chapter 6 Medium Access Control

Protocols and Local AreaNetworks

802.11 Wireless L A N


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Tr n Xun Nam, Hc vin KTQS 5

Wireless Data Communications

Cc yu c u i v i wireless communicationsD tri n khai, chi ph thpMobility & roaming: truy nh p thng tin b t k ni u H tr cc thi t b c nhn

PDAs, laptops, data-cell-phones

H tr cc thi t b lin lcCameras, thi t b nh v , nh n d ng v tuyn

Kh khn C ng t n hi u bi n i theo khng gian & thi gian

T n hi u c th b thu trmPh t n b gi i h n v th ng b h n ch


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C c ch lin l c WLAN

Ch AdhocCc tr m l m vi c tr c ti p v i nhau khng qua tr mi u khi n trung tm (Access Point)

Ch c c u trc (Infrastructure)Cc tr m l m vi c thng qua m t tr m trung tm(Access Point)


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B D

C A

Ad Hoc Communications

Gn t m th i m t nh m cc trmTrong ph m vi lin l c c a gi a cc trmC n trao i thng tin VD: Tr nh chi u trong h i ngh , hay game n i mng


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A2 B2

B1 A1

AP1

AP2

Distribution SystemServer Gateway tothe InternetPortal

Portal

BSS A BSS B

Infrastructure Network

Cc Access Points c nh cung c p truy nh p ti Internet


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A transmits data frame

(a)

Data Frame Data Frame

A

B C

C transmits data frame& collides with A at B

(b)

C senses medium,

station A is hidden from C

Data Frame

B

C A

Hidden Terminal Problem

New MAC: CSMA with Collision Avoidance


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RTS

A requests to send

B

C

(a)

CTS CTS

A

B

C

B announces A ok to send

(b)

Data Frame

A sends

B

C remains quiet

(c)

CSMA with Collision Avoidance


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IEEE 802.11 Wireless LAN

S d ng bng t n khng c p ph p ( unlicensedspectrum )

U.S. Industrial, Scientific, Medical (ISM) bands902-928 MHz, 2.400-2.4835 GHz, 5.725-5.850 GHz

T c mong mu n ban u 20 Mbps Thi t k giao th c MAC cho WLAN t c cao M ng Ad Hoc & C u trc (Infrastructure) S d ng cc l p v t l khc nhau


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802.11 Definitions

Basic Service Set (BSS)Nh m cc tr m i u phi truy nh p s d ng m tphin b n c a MAC

t t i mt Basic Service Area (BSA)Cc tr m trong BSS c th lin l c vi nhauC th t n t i cc BSS trong c ng m t vng

Extended Service Set (ESS)Cc BSSs k t n i v i nhau qua Distribution System(DS)M i BSS nh m t cell v cc tr m trong BSS lin l cv i m t Access Point (AP)Cc portals g n v i DS cung c p truy nh p tiInternet


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A2 B2

B1 A1

AP1 AP2

Distribution SystemServer

Gateway tothe InternetPortal

Portal

BSS A BSS B

Infrastructure Network


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C c d ch v phn ph i

Cc tr m trong BSS c th lin l c th ng vinhauDS cung c p cc d ch v phn phi (distributionservices ):

Chuy n MAC SDUs gi a cc APs trong ESSChuy n MSDUs gi a cc portals & BSSs trong ESSChuy n MSDUs gi a cc tr m trong cng 1 BSS

Multicast, broadcast, theo t y ch n c a tr m

ESS gi ng nh m t BSS i v i lp con LLC


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C c D ch v C u trc

Ch n AP v thi t lp gn m ng (association ) v i APSau c th pht/thu cc frame qua AP & DS

Gn m ng l i (Reassociation service ) chuy n

t m t AP t i m t AP khcT ch m ng (Dissociation service) ng t g nm ngNh n thc (Authentication service) thit l pidentity c a cc tr m khcB o m t (Privacy service) gi b o m t n idung


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IEEE 802.11 MAC

Nhi m v ca MAC sublayerTruy nh p knh nh a ch PDU, nh d ng frame, ki m tra liPhn o n (fragmentation) & ti h p (reassembly) ccMAC SDUs

T y ch n d ch v an ton MAC Authentication & privacy

D ch v qu n lMACChuy n gi a cc AP (roaming) trong ph m vi ESSQu n l cng su t


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C c d ch v MACD ch v c nh tranh: Best effort (khng tin cy)

D ch v khng c nh tranh (contention-free): truy n gi i h n theo th igianMAC c th thay i gia Contention Periods (CPs) & Contention-Free Periods (CFPs)

Physical

Distribution coordination function(CSMA-CA)

Point coordinationfunction

Contention-free service

Contentionservice

MAC

MSDUs MSDUs


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Distributed Coordination Function (DCF)

DCF cung c p d ch v truy nh p c bnTruy n d li u best-effort khng ng b T t c cc tr m c nh tranh truy nh p mi trng

CSMA-CATr m s n s ng pht i khi k t th c truynT t c cc tr m ph i i m t khong Interframe Space (IFS)

DIFS

DIFS

PIFS

SIFS

Contention

window

Next frame

Defer access Wait forreattempt time

Time

Busy medium


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G n u tin qua Interframe Spacing

Cc frame u tin cao i kho ng th i gian ng n ShortIFS (SIFS)

Th ng k t th c trao i trao i d li u hi n ti ACKs, CTS, data frames c a cc MSDU phn o n etc .

PCF IFS (PIFS) kh i t o Contention-Free PeriodsDCF IFS (DIFS) pht d li u v& MPDUs

DIFS

DIFS

PIFS

SIFS

Contention

window

Next frame

Defer access Wait forreattempt time

Time

Busy medium


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Contention & Backoff Behavior

N u knh r i sau DIFS period, cc tr m s n s ng c thtruy n m t MPDU ban uN u knh b n tr c DIFS, tr m c n nh tr nh l i thigian backoff th l i

Backoff period l m t s nguyn l n cc timeslot c nh tranh riTr m ang ch pht gim st mi tr ng v gi m th i gian chm i khi c m t khe c nh tranh r i xy raTr m c th c nh tranh khi th i gian backoff k t thc

M t tr m v a k t th c truy n m t frame khng ctruy n ngay

Ph i th c hi n th tc backoff


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RTS

CTS CTS

Data Frame

A requests to send

B

C

A

A sends

B

B

C

C remains quiet

B announces A ok to send

(a)

(b)

(c)

ACK B(d)

ACK

B sends ACK


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Carrier Sensing in 802.11

C m nh n S ng mang V t l (Physical Carrier Sensing) Phn t ch t t c cc frame tch cGim st c ng t n hi u tng i t cc tr m khc

C m nh n S ng mang o (Virtual Carrier Sensing) l pMAC

Cc tr m ngu n thng bo cho cc tr m khc v th i giantruy n ( msec) cho m t MPDUThng tin v th i gian truy n c mang trngDuration c a RTS & CTSCc tr m i u ch nh Network Allocation Vector (tham s m ng c) bi t khi n o knh ri

Knh b n khi m t trong hai c m nh n cho bi t bn


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DataDIFS

SIFS

Defer AccessWait for

Reattempt Time

ACK

DIFS

NAV

Source

Destination

Other

Truy n MPDU khng s d ng RTS/CTS


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Data

SIFS

Defer access

Ack

DIFSNAV (RTS)

Source

Destination

Other

RTSDIFS

SIFS

CTS

SIFS

NAV (CTS)

NAV (Data)

Truy n MPDU c s d ng RTS/CTS


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Va ch m, M t khung & L i

Collision AvoidanceKhi tr m c m nh n knh b n, n i n t n khi knh r i chom t chu k DIFS & sau b t u t th i gian backoff ng unhin (theo n v slot ri)Tr m truy n frame khi th i gian backoff k t thcN u c va ch m x y ra, t nh l i backoff qua kho ng th i gian d ig p i

Cc tr m thu cc frame khng c l i truyn ACKTr m pht coi tr ng h p ACK khng n nh l mt khungTi n h nh backoff v sau truy n liCc tr m thu s d ng s th t xc nh cc frame thu p


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Point Coordination Function

PCF cung c p d ch v nh h ng k t n i,khng c nh tranh thng qua polling Point coordinator (PC) AP th c hi n PCFPolling table up to implementor

Chu k l p li CFP (Contention-Free Period)Xc nh t n xu t CFP xy raKh i t o b i beacon frame pht t PC APCh a CFP v CPTrong chu k n y cc tr m CFP ch c th truy n png l i m t poll t PC hay truyn ACK


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CFEnd

NAV

PIFS

B D1 +Poll

SIFS

U 1 +ACK

D2+Ack+Poll

SIFS SIFS

U 2 +ACK

SIFS SIFS

Contention-free repetition interval

Contention period

CF_Max_duration

Reset NAV

D1, D2 = frame sent by point coordinatorU1, U2 = frame sent by polled stationTBTT = target beacon transmission timeB = beacon frame

TBTT

PCF Frame Transfer


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C c ki u Frame

Management FrameStation association & disassociation with APTiming & synchronization

Authentication & deauthentication

Control framesHandshaking

ACKs during data transfer

Data framesData transfer


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Address2

FrameControl

Duration/ID

Address1

Address3

Sequencecontrol

Address4

Framebody CRC

2 2 6 6 6 2 6 0-2312 4MAC header (bytes)

Frame Structure

MAC Header: 30 bytesFrame Body: 0-2312 bytesCRC: CCITT-32 4 bytes CRC over MAC header

& frame body


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Address2

FrameControl

Duration/ID

Address1

Address3

Sequencecontrol

Address4

Framebody CRC

Protocolversion Type Subtype

ToDS

FromDS

Morefrag Retry

Pwrmgt

Moredata WEP Rsvd

2 2 6 6 6 2 6 0-2312 4

2 2

MAC header (bytes)

4 1 1 1 1 1 1 1 1

Frame Control (1)

Protocol version = 0

Type: Management (00), Control (01), Data (10)Subtype within frame typeType=00, subtype=association; Type=01, subtype=ACKMoreFrag=1 if another fragment of MSDU to follow


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ToDS

FromDS

Address1

Address2

Address3

Address4

0 0 DestinationaddressSourceaddress BSSID N/A

0 1 Destinationaddress BSSID Sourceaddress N/A

1 0 BSSID SourceaddressDestination

address N/A

1 1 ReceiveraddressTransmitter

addressDestination

addressSourceaddress

Meaning

Data frame from station tostation within a BSS

Data frame exiting the DS

Data frame destined for theDS

WDS frame being distributedfrom AP to AP

Address2

FrameControl

Duration/ID

Address1

Address3

Sequencecontrol

Address4

Framebody CRC


ToDS

FromDS

Morefrag Retry

Pwrmgt

Moredata WEP Rsvd

2 2 6 6 6 2 6 0-2312 4

2 2 4 1 1 1 1 1 1 1 1

To DS = 1 if frame goes to DS; From DS = 1 if frame exiting DS

Frame Control (2)


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Address2

FrameControl

Duration/ID

Address1

Address3

Sequencecontrol

Address4

Framebody CRC


ToDS

FromDS

Morefrag Retry

Pwrmgt

Moredata WEP Rsvd

2 2 6 6 6 2 6 0-2312 4

2 2

MAC header (bytes)

4 1 1 1 1 1 1 1 1

Frame Control (3)

Retry=1 if mgmt/control frame is a retransmissionPower Management used to put station in/out of sleepmodeMore Data =1 to tell station in power-save mode moredata buffered for it at APWEP=1 if frame body encrypted


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Physicallayer

LLC

Physical layerconvergence

procedure

Physical mediumdependent

MAClayer

PLCPpreamble

LLC PDU

MAC SDUMACheader CRC

PLCPheader

PLCP PDU

Physical Layers

802.11 designed toSupport LLCOperate over many physical layers


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IEEE 802.11b Channels

Channels khng gy nhi u


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IEEE 802.11 Physical Layer Options

FrequencyBand Bit Rate Modulation Scheme

802.11 2.4 GHz 1-2 Mbps Frequency-Hopping SpreadSpectrum, Direct SequenceSpread Spectrum

802.11b 2.4 GHz 11 Mbps Complementary Code Keying& QPSK

802.11g 2.4 GHz 54 Mbps Orthogonal Frequency DivisionMultiplexing

& CCK for backwardcompatibility with 802.11b

802.11a 5-6 GHz 54 Mbps Orthogonal Frequency DivisionMultiplexing


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36

Chapter 6 Medium Access Control

Protocols and Local AreaNetworks

LA N Br idges


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Hub

Station Station Station

Two TwistedPairs

Hubs, Bridges & Routers

Hub: Active central element in a star topologyTwisted Pair: inexpensive, easy to insallSimple repeater in Ethernet LANsIntelligent hub: fault isolation, net configuration, statistics Requirements that arise:

Hub


Two TwistedPairs

User community grows, need to interconnect hubs

?

Hubs are for different types of LANs

Hub


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Hub


Two TwistedPairs

Hubs, Bridges & RoutersInterconnecting Hubs

Repeater: Signal regeneration All traffic appears in both LANs

Bridge: MAC address filteringLocal traffic stays in own LAN

Routers: Internet routing

All traffic stays in own LAN

Hub


Two TwistedPairs

?

HigherScalability


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Operation at data link level implies capability to workwith multiple network layersHowever, must deal with

Difference in MAC formatsDifference in data rates; buffering; timersDifference in maximum frame length

PHY

MAC

LLC

Network Network

PHY

MAC

LLC

802.3 802.3 802.5 802.5

802.3

802.3

802.3 802.5

802.5

802.5

CSMA/CD Token Ring

General Bridge Issues


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Bridge

Network

Physical

Network

LLC

PhysicalPhysicalPhysical

LLC

MAC MACMAC MAC

Bridges of Same Type

Common case involves LANs of same typeBridging is done at MAC level


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Interconnection of IEEE LANs withcomplete transparencyUse table lookup, and

discard frame, if source & destinationin same LANforward frame, if source & destinationin different LANuse flooding, if destination unknown

Use backward learning to build tableobserve source address of arrivingLANs

handle topology changes by removingold entries

Transparent Bridges

Bridge

S1 S2

S4

S3

S5 S6

LAN1

LAN2


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B1

S1 S2

B2

S3 S4 S5

Port 1 Port 2 Port 1 Port 2

LAN1 LAN2 LAN3

Address Port Address Port

S


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B1

S1 S2

B2

S3 S4 S5


LAN1 LAN2 LAN3

Address Port

S1 1

Address Port

S1 1

S1 S5

S1 to S5 S1 to S5 S1 to S5 S1 to S5

S


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B1

S1 S2

B2

S3 S4 S5


LAN1 LAN2 LAN3

Address Port

S1 1S3 1

Address Port

S1 1S3 1

S3 S2

S3 S2S3 S2 S3 S2

S3 S2 S3 S2


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B1

S1 S2

B2

S3 S4 S5


LAN1 LAN2 LAN3

S4 S3

Address Port

S1 1S3 2S4 2

Address Port

S1 1S3 1S4 2

S4 S3

S4 S3

S4 S3S4 S3


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B1

S1 S2

B2

S3 S4 S5


LAN1 LAN2 LAN3

Address Port

S1 1S3 2S4 2S2 1

Address Port

S1 1S3 1S4 2

S2 S1

S2 S1

S2 S1


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Adaptive Learning

In a static network, tables eventually store alladdresses & learning stopsIn practice, stations are added & moved all thetime

Introduce timer (minutes) to age each entry & force itto be relearned periodicallyIf frame arrives on port that differs from frame address& port in table, update immediately


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Avoiding Loops

LAN1

LAN2

LAN3

B1 B2

B3

B4

B5

LAN4

(1)

(2)

(1)

l h


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Spanning Tree Algorithm

1. Select a root bridge among all the bridges. root bridge = the lowest bridge ID.

2. Determine the root port for each bridge except the rootbridge

root port = port with the least-cost path to the root bridge3. Select a designated bridge for each LAN

designated bridge = bridge has least-cost path from the LANto the root bridge.

designated port connects the LAN and the designated bridge4. All root ports and all designated ports are placed into a

forwarding state. These are the only ports that areallowed to forward frames. The other ports are placedinto a blocking state.


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LAN1

LAN2

LAN3

B1 B2

B3

B4

B5

LAN4

(1)

(2)

(1)

(1)

(1)

(1)

(2)

(2)

(2)

(2)

(3)


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LAN1

LAN2

LAN3

B1 B2

B3

B4

B5

LAN4

(1)

(2)

(1)

(1)

(1)

(1)

(2)

(2)

(2)

(2)

(3)

Bridge 1 selected as root bridge


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LAN1

LAN2

LAN3

B1 B2

B3

B4

B5

LAN4

(1)

(2)

(1)

(1)

(1)

(1)

(2)

(2)

(2)

(2)

(3)

Root port selected for everybridge except root port

R

R

R

R


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LAN1

LAN2

LAN3

B1 B2

B3

B4

B5

LAN4

(1)

(2)

(1)

(1)

(1)

(1)

(2)

(2)

(2)

(2)

(3)

Select designated bridgefor each LAN

R

R

R

R

D

D

D D


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LAN1

LAN2

LAN3

B1 B2

B3

B4

B5

LAN4

(1)

(2)

(1)

(1)

(1)

(1)

(2)

(2)

(2)

(2)

(3)

All root ports & designatedports put in forwarding state

R

R

R

R

D

D

D D

S R ti B id


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Source Routing Bridges

To interconnect IEEE 802.5 token ringsEach source station determines route todestinationRouting information inserted in frame

Routingcontrol

Route 1designator

Route 2designator

Route mdesignator

Destinationaddress

Sourceaddress

Routinginformation

Data FCS

2 bytes 2 bytes 2 bytes 2 bytes

R t Di


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Route Discovery

To discover route to a destination each stationbroadcasts a single-route broadcast frame Frame visits every LAN once & eventuallyreaches destination

Destination sends all-routes broadcast framewhich generates all routes back to sourceSource collects routes & picks best

D t il d R t Di


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Detailed Route Discovery

Bridges must be configured to

form a spanning treeSource sends single-route frame without route designator fieldBridges in first LAN add incomingLAN #, its bridge #, outgoing LAN# into frame & forwards frameEach subsequent bridge attachesits bridge # and outgoing LAN #Eventually, one single-route framearrives at destination

When destination receives single-

route broadcast frame it respondswith all-routes broadcast framewith no route designator fieldBridge at first hop inserts incomingLAN #, its bridge #, and outgoingLAN # and forwards to outgoingLAN

Subsequent bridges insert theirbridge # and outgoing LAN # andforwardBefore forwarding bridge checksto see if outgoing LAN already indesignator fieldSource eventually receives all

routes to destination station

Fi d t f S1 t S3


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B4

B6

B3 B7LAN 1

B1

B2

S1S2

S3

B5

LAN 2 LAN 4

LAN 3 LAN 5

Find routes from S1 to S3

LAN1 B1

B3

B4

LAN3 B6 LAN5

LAN4

LAN2

B4LAN 2 LAN 4


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B4

B6

B3 B7LAN 1

B1

B2

S1S2

S3

B5

LAN 2 LAN 4

LAN 3 LAN 5

LAN5

B6

B7

LAN3

LAN4

B2

B3

B5

LAN1 B1 LAN2B3

B4 LAN4 B5B7

LAN2 B1B4

LAN1 B2LAN4 B5

B7

LAN4 B4

B7

LAN2 B1B3

LAN1 B2

B4

B5

LAN2 B1

B3 LAN3B2B5B6

LAN1 B1LAN1 B2 LAN3

B3

B5B6

LAN3 B3B2

B6

LAN1

LAN2

B1 LAN2B3B4

B1B4

LAN1 B2

Virtual LAN


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Physicalpartition

Logical partition

Bridge

or

switch

VLAN 1 VLAN 2 VLAN 3

S17

2 3 4 5 61

8

9 Floor n 1

Floor n

Floor n + 1

S2

S3

S4

S5

S6

S7

S8

S9

Virtual LAN

Per Port VLANs


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Logical partition

Bridge

or

switch

VLAN 1 VLAN 2 VLAN 3

S172 3 4 5 61

8

9 Floor n 1

Floor n

Floor n + 1

S2

S3

S4

S5

S6

S7

S8

S9

Per-Port VLANs

Bridge only forwards frames to outgoing ports associated with same VLAN

Tagged VLANs


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Tagged VLANs

More flexible than Port-based VLANsInsert VLAN tag after source MAC address ineach frame

VLAN protocol ID + tag

VLAN-aware bridge forwards frames to outgoingports according to VLAN IDVLAN ID can be associated with a port staticallythrough configuration or dynamically through

bridge learningIEEE 802.1q

Documents

Lecture10-WLAN and LAN briges.pdf