[PPT] - C o m p u t e r N e t w o r k s - X a r x e s PowerPoint Presentation

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C

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Outline

Course Syllabus Unit 1: Introduction Unit 2. IP Networks Unit 3. LANs Unit 4. TCP Unit 5. Network applications

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Unit 3. Local Area Networks, LANs

Outline

Introduction IEEE LAN Architecture Ethernet Ethernet Switches Wireless LANs

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Unit 3. Local Area Networks, LANs

Introduction – WAN and LAN differences

WANs:

Main goal: scalability. Switched network with mesh topology.

LANs:

Multy-access network with shared media. A Medium Access Control (MAC) protocol is needed.

Wireless

BUS Tx Rx Rx

Ring

Rx Tx Rx Rx Tx Rx Rx Tx Tx

l

c

a l l

p

s w i t c h e s ( C e n t r a l O ffj c e )

S w i t c h e d m e d i a

m

d

e m m u l t i p l e x e d l i n e s m

d

e m

WA N ( P S T N ) L A N s

S h a r e d m e d i a

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Unit 3. Local Area Networks, LANs

Outline

Introduction IEEE LAN Architecture Ethernet Ethernet Switches Wireless LANs

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Unit 3. Local Area Networks, LANs

IEEE LAN Architecture

Me d i u m A c c e s s C

n

t r

l

( MA C ) P h y s i c a l L

g

i c a l L i n k C

n

t r

l

( L L C ) I E E E L A N R e f e r e n c e m

d

e l O S I R e f e r e n c e m

d

e l :

7 application 6 presentation 5 session 4 transport 3 network 2 data link 1 physical

I E E E L A N s t a n d a r d s ( 8 2 . x )

LLC sublayer (802.2): Common to all 802.x MAC standards. Define the interface with the upper layer and specifies several services (operational modes): (i) unacknowledged connectionless, (ii) connection oriented, (iii) acknowledged connectionless. MAC sublayer: Define the medium access protocol. It is different for each LAN technology.

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Unit 3. Local Area Networks, LANs

IEEE LAN Architecture – IEEE 802 standards (some)

802.1: LAN/MAN architecture. 802.2 Logical Link Control (LLC) 802.3 Ethernet 802.4 Token Bus 802.5 Token Ring 802.8 FDDI 802.11 WiFi: Wireless LANs. 802.15 Personal Area Networks or short distance wireless networks (WPAN) 802.15.1 Bluetooth 802.15.4 low data rate and low cost sensor devices 802.16 WiMAX: broadband Wireless Metropolitan Area Networks. See: http://grouper.ieee.org/groups/802/1, 2, …

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Unit 3. Local Area Networks, LANs

IEEE LAN Architecture – LAN encapsulation

MA C h e a d e r L L C h e a d e r C R C h i g h e r l a y e r P D U

... physical layer

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Unit 3. Local Area Networks, LANs

IEEE LAN Architecture – LLC header

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 bits +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Destination SAP| Source SAP | Control / | | | 8 or 16 bits / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

S e r v i c e A c c e s s P

i

n t ( S A P ) : I d e n t i fj e s t h e u p p e r l a y e r p r

t
c
l

. C

n

t r

l

: I d e n t i fj e s t h e f r a m e t y p e . I t c a n b e 8

r

1 6 b i t s l

n

g , 8 b i t s f

r

u n n u m b e r e d f r a m e s ( u s e d i n c

n

n e c t i

n

l e s s m

d

e s ) .

SAP (hex) Protocol 06 ARPANET Internet Protocol (IP) 08 SNA 42 3IEEE 802.1 Bridge Spanning Tree Protocol 98 ARPANET Address Resolution Protocol (ARP) AA E0 F0 FF Global LSAP Example of some IEEE SAP values. SubNetwork Access Protocol (SNAP) Novell Netware IBM NetBIOS

3 / 4 b y t e s

S N A P : u s e d i n T C P / I P

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Unit 3. Local Area Networks, LANs

Outline

Introduction IEEE LAN Architecture Ethernet Ethernet Switches Wireless LANs

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Unit 3. Local Area Networks, LANs

Ethernet – Introduction Designed by Bob Metcalfe at Xerox in mid-70s. Initially was commercialized by Digital, Intel and Xerox consortium (DIX). Ethernet was standardized by IEEE (802.3) in 1983. Nowadays Ethernet is the leading LAN technology. There are numerous Ethernet standards with different transmission mediums, and line bitrates. There are several active Ethernet working groups inside IEEE 802.3.

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Unit 3. Local Area Networks, LANs

Types of MACs Token Passing: Only the station having the token can transmit. After transmission the token is passed to another station. Examples: FDDI and Token-Ring Random: There is no token. Instead, there is a non null collision

probability. In case of collision, the frame is retransmitted

after a random backoff time. Examples: Ethernet

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Unit 3. Local Area Networks, LANs

Carrier Sense Multiple Access/Collision Detection (CSMA/CD) Is a random MAC where the stations “listen” the medium (carrier sense) before transmission. When the medium is becomes free the frame is transmitted immediately, and the medium is listened to detect collisions. In case of collision, the frame is retransmitted after a random backoff time.

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Unit 3. Local Area Networks, LANs

Ethernet – CSMA/CD Ethernet protocol (simplified)

m e d i u m b u s y ? y e s n

wait IPG

transmit 1 bit c

l

l i s i

n

? n

n
e

n d T x ? y e s init Tx Transmit the JAM r e t r i e s > 1 6 ? wait backoff y e s discard the frame y e s n

transmit the preamble

n

y

e s c

l

l i s i

n

?

Legend: InterPacket Gap (IPG): 96 bits. JAM: 32 bits that produce an erroneus CRC. backoff = n T512 T512:SlotTime (51,2 s at 10 Mbps) n = random{0, 2min{N, 10}-1}, N: number of retransmission of the same frame (1, 2…) The transmitting station must detect the collision (no ack is sent).

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Unit 3. Local Area Networks, LANs

Ethernet – Collision example Stations A y B have frames ready to Tx:

P J P J T 2

I P G

i n i t T 2 T x b a c k

fg

= S l

t

T i m e ( s ) b a c k

fg

= 1 S l

t

T i m e t t i n i t T 3 T x i n i t T 3 T x  I

P G I P G

A B P T 1 T 3 p r e a m b l e f r a m e i J a m L e g e n d : c

l

l i s i

n

d e t e c t i

n

P J T i  l a t e n c y

A B

N O T E : T h e p r e a m b l e i s n

t

i n t e r r u p t e d i n c a s e

f

c

l

l i s i

n

, a n d t h e J A M i s T x i m m e d i a t e l y a f t e r .

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Unit 3. Local Area Networks, LANs

Ethernet – Half Duplex and full-duplex

Half Duplex: Using CSMA/CD only one NIC can be simultaneously transmitting into the medium. Full Duplex: When 2 Ethernet NICs are connected point-to-point, some Ethernet standards allow a full-duplex Tx, . Ethernet NICs have an auto-negotiation mechanism to detect the full-duplex availability. In full-duplex mode Ethernet NICs deactivate CSMA/CD (no collisions can occur).

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Unit 3. Local Area Networks, LANs

Ethernet – Frames Ethernet II (DIX): IEEE 802.3 Preamble: Give time to detect, synchronize and start reception. Type: Identifies the upper layer protocol (IP, ARP, etc. RFC 1700, Assigned numbers). This value is always > 1500. Length: Payload size (0~1500).

+-----------+-----------+----------+----------+-----------+----------+ |Preamble |Destination|Source MAC|Frame type| Payload | CRC | |(8 bytes) |MAC Address|Address |(2 bytes) |(46 to |(4 bytes) | | |(6 bytes) |(6 bytes) | |1500 bytes)| | +-----------+-----------+----------+----------+-----------+----------+ +-----------+-----------+----------+----------+-----------+----------+ |Preamble |Destination|Source MAC|Length of | Payload | CRC | |(8 bytes) |MAC Address|Address |the frame |(46 to |(4 bytes) | | |(6 bytes) |(6 bytes) |(2 bytes) |1500 bytes)| | +-----------+-----------+----------+----------+-----------+----------+

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Unit 3. Local Area Networks, LANs

Ethernet – IEEE Sub-Network Access Protocol (SNAP) Allows the specification of protocols, and vendor-private identifiers, not supported by the 8-bit 802.2 Service Access Point (SAP) field. It is used to encapsulate TCP/IP protocols over IEEE 802.2 (LLC) with OUI=0x000000 and Type equal to the RFC 1700 (used for DIX). Note: The MSS indicated by TCP would be of 1460 if DIX, and 1452 if IEEE encapsulation is used.

8 2 . 3 S N A P F r a m e

+-------+------+------+------+--------+------+-----------+----------+ | MAC | DSAP | SSAP |Contr.| OUI | Type |upper layer| CRC | | 802.3 | 0xAA | 0xAA | 0x03 |0x000000|2bytes| PDU |(4 bytes) | +-------+------+------+------+--------+------+-----------+----------+

L L C h e a d e r ( 3 b y t e s ) S N A P h e a d e r ( 5 b y t e s ) ≤ 1 4 9 2

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Unit 3. Local Area Networks, LANs

Ethernet – Different Ethernet Standards (some)

bps Standard year Name Cabling Connector Codification segment distance* Half duplex Full duplex Ethernet 10Mbps 802.3 1983 10Base5 Coax-thick

AUI

Manchester 500m n/a 802.3a 1985 10Base2 Coax-thin

BNC

Manchester 185m n/a 802.3i 1990 10BaseT UTP-cat.3 2 RJ45 Manchester 100m 100m 802.3j 1993 10BASE-FL FO 2 SC

n/off Manchester

2000m >2000m 100Mbps 802.3u 1995 100BaseTX UTP-cat.5 2 RJ45 4B/5B 100m 100m 802.3u 1995 100BaseFX FO 2 SC 4B/5B 412m 2000m TIA/EIA-785 1999 100BaseSX FO/led 2 SC 4B/5B 300m 300m Gigabit-Eth. 1Gbps 802.3z 1998 1000BaseSX FO 2 SC 8B/10B 275-316m 275-550m 802.3z 1998 1000BaseLX FO 2 SC 8B/10B 316m 550-10000m 802.3z 1998 1000BaseLH FO 2 SC 8B/10B n/a 100km 802.3ab 1999 1000BaseT UTP-cat. 5e 4 RJ45 PAM5 100m 100m 10Gbps 802.3ae 2002 10GBASE-CX4 InfiniBand 4 CX4 8B/10B n/a 15m 802.3ae 2002 10GBASE-SR FO 2 SC 64B/66B n/a 26-300m 802.3ae 2002 10GBASE-LR FO 2 SC 64B/66B n/a 10km 802.3ae 2002 ... FO 2 SC ... n/a ... *With OF the distance depends on the OF type. Commercial name UTP/OF Pairs Fast Ethernet 10Gigabit- Eth.

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Unit 3. Local Area Networks, LANs

Ethernet – Different Ethernet Standards

x B a s e y

D e n

m

i n a t i

n

:

L i n e b i t r a t e : 1 : 1 Mb p s 1 : 1 Mb p s 1 : 1 Mb p s ( 1 G b p s ) 1 G : 1 G b p s B a s e b a n d s i g n a l . B r

a

d : t r a n s l a t e d b a n d s i g n a l . V a r i

u

s m e a n i n g s : Number: Maximum segment distant in hundreds of m. Reference to the medium type: T: UTP F: Optical Fiber Other: T4: Uses 4 UTP pairs. TX: Full Duplex ...

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Unit 3. Local Area Networks, LANs

Ethernet – Different Ethernet Standards: 10BaseT

h u b

N I C “ c

m

b

”

: S u p p

r

t s 1 B a s e 5 , 1 B a s e 2 , 1 B a s e T T r a n s c e i v e r s A U I

B

N C / A U I

R

J 4 5

U T P c a b l e , R J 4 5 c

n

n e c t

r

s 1 m m a x i m u m 1 B a s e T s e g m e n t s

R J 4 5 D B 1 5 B N C 1 B a s e T 1 B a s e 5 ( A U I ) 1 B a s e 2

1 9 9 . C a b l e U T P

c

a t 3 . H u b : I s a m u l t i

p
r

t r e p e a t e r ( l a y e r 1 ) . The signal received in 1 port is retransmitted by all the others.

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Unit 3. Local Area Networks, LANs

Ethernet – Different Ethernet Standards: after 10BaseT

A l l s t a n d a r d s u s e U T P

O

F ( e x c e p t 1 G B a s e C X 4 ) : Fast Ethernet (1995). 100BaseTX: UTP-cat. 5 Gigabit Ethernet (1998). 1000BaseT: UTP-cat 5e 10Gigabit Ethernet (2002). Uses optical fiber. The only copper standard is Infiniband with segment size  15m.

I n fj n i b a n d c a b l e w i t h C X 4 c

n

n e c t

r

s N I C 1 / 1 – R J 4 5 10BaseT-100BaseTX $11.99 N I C 1 / 1 / 1

S

C 1 B a s e F L

1

B a s e F X

1

B a s e

S

X $ 1 5 1 N I C 1 G b p s – C X 4 1 G B a s e C X 4 $ 7 9 5

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Unit 3. Local Area Networks, LANs

Outline

Introduction IEEE LAN Architecture Ethernet Ethernet Switches Wireless LANs

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Unit 3. Local Area Networks, LANs

Ethernet Switches - Introduction Hub problem: If many stations are connected, may be inefficient due to collisions. Solution: bridges and switches. Ethernet bridge:

“plug and play” layer 2 device. In each port there is a NIC in “promiscuous” mode: Capturing all frames. The source address is used to “learn” which MAC is present in each port (MAC table). Each entry has the MAC and the port numbers. The destination MAC is used to decide whether the frame needs to be retransmitted by another port. Segments the “collision domain”.

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Unit 3. Local Area Networks, LANs

Ethernet Switches - Bridges

h u b h u b

MAC address Port 00:00:00:00:00:11 1 00:00:00:00:00:33 1 00:00:00:00:00:44 2 MAC Table

1 2 00:00:00:00:00:11 00:00:00:00:00:22 00:00:00:00:00:33 00:00:00:00:00:44 00:00:00:00:00:55 00:00:00:00:00:66 b r i d g e

c

l

l i s i

n

d

m

a i n 1 ( D 1 ) c

l

l i s i

n

d

m

a i n 2 ( D 2 )

H

w

t h e b r i d g e w

r

k s : If a frame is received with a source address not in the MAC table, it is added (learning bridge). If a frame from D1 is received with a destination address that: (i) is in D2, (ii) it is not in the table, (iii) it is broadcast: It is sent into D2 (flooding). If it is received a frame from D1 addressed to another station from D1, it is discarded (filtering). The entries have an aging timer. Each time an entry is used, it is refreshed. If the aging timer expires, the entry is removed. Advantages: Segments the collision domain (less collisions). Clients in D1 and D2 can simultaneously send frames to their servers.

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Unit 3. Local Area Networks, LANs

Ethernet Switches - Switch Architecture

fm

w

c

n

t r

l

p 2 p 4 p 6 p 5 p 3 p

r

t : 1 : A C : : 1 9 : 2 2

. . . . . .

MA C a d d r e s s MA C t a b l e t r a n s m i s s i

n

q u e u e

. . . . . .

p 1 s w i t c h f a b r i c Switch#show mac-address-table Address Dest Interface

00D0.5868.F583 FastEthernet 2

00E0.1E74.6ADA FastEthernet 1 00E0.1E74.6AC0 FastEthernet 1 0060.47D5.2770 FastEthernet 3 00D0.5868.F580 FastEthernet 5

MA C T a b l e i n a C I S C O S w i t c h

r e c e p t i

n

q u e u e

E d g e a n d b a c k b

n

e C I S C O s w i t c h e s .

H

w

t h e s w i t c h w

r

k s : It is equivalent to a “multiport bridge”. When a frame is received with a source address not in the table, it is added. If a frame is received with a destination address: (i) not in the table, (ii) broadcast or multicast: copy the frame in all transmission buffer of the other ports (flooding). If a frame is received with the address from another port: It is switched as fast as possible the the transmission buffer of that port. If receives a frame addressed to another station from the same port, it is discarded (filtering).

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Unit 3. Local Area Networks, LANs

Ethernet Switches - Switch Capabilities

s w i t c h

F u l l D u p l e x P

r

t s

E a c h p

r

t i s d i fg e r e n t a c

l

l i s i

n

d

m

a i n ( l e s s c

l

l i s i

n

s ) . D i fg e r e n t p

r

t s c a n b e s i m u l t a n e

u

s l y T x / R x . P

r

t s c a n h a v e d i fg e r e n t b i t r a t e s . P

r

t s m a y b e f u l l

d

u p l e x ( u s a b l e i f

n

l y

n

e h

s

t i s c

n

n e c t e d ) . T h e r e c a n b e p

r

t s s i m u l t a n e

u

l y i n h a l f

r

f u l l d u p l e x m

d

e . L i n k a g g r e g a t i

n

: B i t r a t e c a n b e i n c r e a s e d b y a g g e g a t i n g s e v e r a l l i n k s , w h i c h b e h a v e a s a s l i n g l e

n

e ( e t h e r c h a n n e l i n C I S C O ) . S e c u r i t y : S t a t i

n

s c a n

n

l y c a p t u r e t h e t r a ffj c

f

t h e i r c

l

l i s i

n

d

m

a i n . . . .

1 Mb p s 1 Mb p s

S i m u l t a n e

u

s T r a n s m i s s i

n

s

1 Mb p s 1 Mb p s 1 G b p s s w i t c h s w i t c h

P

r

t s w i t h D i fg e r e n t b i t r a t e s

SLIDE 27

2 7

L l

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A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

router

Unit 3. Local Area Networks, LANs

Ethernet Switches - Broadcast and Collision Domains

Broadcast Domain: Set of stations that will received a broadcast frame sent by any of them. Unless Virtual LANs are used, a switch does not segment the broadcast domain. A router segment the broadcast domain. The broadcast reachability is important because allows reaching stations having one hop connectivity (with ARP).

h u b s w i t c h s w i t c h

C

l

l i s i

n

D

m

a i n B r

a

d c a s t D

m

a i n

A R P r e q u e s t ( b r

a

d c a s t ) r e q u e s t i n g a n @I P ( t h e r

u

t e r @I P ) A R P r e p l y ( u n i c a s t ) A R P c a n n

t

s

l

v e a n @I P

u

t

f

t h e b r

a

d c a s t d

m

a i n . T

l

e a v e t h e b r

a

d c a s t d

m

a i n a r

u

t e r i s r e q u i r e d .

SLIDE 28

2 8

L l

r

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A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Ethernet Switches – Flow Control

Switch Flow Control: Consists of adapting the rate at which the switch receives the frames, and the rate at which the switch can send them. Examples: Flow control techniques (back pressure):

Jabber signal (half duplex): The switch sends a signal into the port which need to be throttled down, such that CSMA see the medium busy. Pause frames (full duplex): The switch send special pause frames. These frames have an integer (2 bytes) indicating the number of slot-times (512 bits) that the NICs receiving the frame must be silent.

1 B a s e T ( 1 G b p s ) 1 B a s e T X ( 1 Mb p s ) 1 B a s e T X ( 1 Mb p s )

I f n

fm
w

c

n

t r

l

i s u s e d , f r a m e s c

u

l d b e l

s

t b y b u fg e r

v

e r fm

w

.

SLIDE 29

2 9

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A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Ethernet Switches – Problems of Flow Control

Flow Control can introduce inefficiencies (head of line blocking):

We would expect a download of approximately 90 Mbps for PC1 and 10 Mbps for PC2. However, the flow control can make the PC1 throughput to be significantly lower. Switches allow disabling the flow control in a link (In CISCO: Switch(config-if)# flowcontrol send off). If flow control is disabled, traffic is assumed to be controlled by TCP.

If not otherwise stated, we shall assume an ideal flow control in the problems, which allow achieving the maximum throughput.

1 Mb p s

T h e s l

w

l i n k m a y t r i g g e r t h e fm

w

c

n

t r

l

a n d s e n d p a u s e f r a m e s t

w

a r d s t h e s e r v e r , c a u s i n g u n d e r

u

t i l i z a t i

n
f

t h e s w i t c h

s

e r v e r l i n k .

1 Mb p s 1 Mb p s

d

w

n l

a

d P C 1 P C 2 P C 1

SLIDE 30

3

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A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Ethernet Switches – Line bitrate sharing

Hub: If the hub is the bottleneck for all the active ports, the capacity is equally shared between all ports where frames are transmitted. Switch: If one congested port is the bottleneck for all ports sending traffic to it, the port bit rate is equally shared between all ports sending traffic to it. Example:

h u b

A B S C

1 B a s e T X ( 1 Mb p s )

I f A , B a n d C s i m u l t a n e

u

s l y t r a n s m i t t

S

: t h r

u

g h p u t C  1 Mb p s / 2 = 5 Mb p s t h r

u

g h p u t A = t h r

u

g h p u t B  ( 1 Mb p s / 2 ) / 2 = 2 5 Mb p s

SLIDE 31

3 1

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l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Ethernet Switches – Spanning Tree Protocol (STP)

The basic principle of the “layer 2 routing” done by Ethernet switches is based on having a unique port to forward the frame towards the

destination. Therefore, loops are not allowed.

In practice loops can appear because:

They are introduced by accident. The are desirable to have redundant path (fault tolerance).

If loops are introduced without protection a broadcast storm is produced, and the network blocks:

3 2 ' 2 5 5 ' 1 3 ' 4 ' 4 5 5 '

. . . . . . . . . . . .

F r a m e s m u l t i p l y a n d r e m a i n t u r n i n g i n d e fj n i t e l y i n t h e l

p

! S

l

u t i

n

: I E E E 8 2 . 1 D S p a n n i n g T r e e P r

t
c
l

( S T P )  O t h e r p r

b

l e m s : R e c e p t i

n
f

d u p l i c a t e d f r a m e s MA C T a b l e s i n s t a b i l i t y

SLIDE 32

3 2

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A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Ethernet Switches – Spanning Tree Protocol (STP)

STP goal: Build a loop free topology (STP-tree) with optimal paths. The ports that do not belong to the STP tree are blocked. The switches send 802.1D messages to their neighbors to build up the STP-tree. If the topology changes (e.g. due to a link failure), a new STP-tree is setup.

S p a n n i n g t r e e  l

p

s r e d u n d a n t l i n k s

h u b h u b

SLIDE 33

3 3

L l

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A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Ethernet Switches – Virtual LANs, VLANs

Motivation:

Grouping related servers and hosts in different broadcast domains.

How VLANs work:

Each switch port belongs to a VLAN. The switch isolates different VLANs: The switch flooding is done

nly towards the ports of

the same VLAN. Each VLAN is equivalent to a different physical switch. A router is needed to send traffic to a different VLAN.

P r

g

r a m m e r s D i r e c t i

n

P r a c t i c e Wo r k e r s 1 9 2 . 1 6 8 . . / 2 4 1 9 2 . 1 6 8 . 1 . / 2 4 1 9 2 . 1 6 8 . 1 . / 2 4

. . .

. . . . . . . . .

P

r

t c

n

fj g u r e d i n V L A N 1 I D F

1

. . . . . . . . .

2 3 1 I D F

2

1 2 211 2 3 321 1 2 1 321 2 3 1 2 3 1 MD F 1 9 2 . 1 6 8 . . / 2 4 1 9 2 . 1 6 8 . 1 . / 2 4 1 9 2 . 1 6 8 . 1 . / 2 4

 L

g

i c T

p
l
g

y P h y s i c a l T

p
l
g

y

router router

P r a c t i c e Wo r k e r s P r

g

r a m m e r s D i r e c t i

n

SLIDE 34

3 4

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r

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A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Ethernet Switches – Virtual LANs, VLANs

Advantages:

Flexibility of the physical placement of the devices. Facilitates the network grow. Facilitates the network management: Changing the topology, adding new subnetworks, moving ports from one network to another.

NOTE: Since each VLAN is a different broadcast domain, usually a different STP instantiation is used for each VLAN. Thus, a different STP-tree is build in each VLAN.

SLIDE 35

3 5

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A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Ethernet Switches – VLAN Trunking

Problem:

Why connecting several ports between the same devices?

Trunking:

The port configured as trunk belongs to several VLANs (maybe all). The traffic sent in one VLAN is also sent to the trunk the VLAN belongs to. A tagging mechanism is used in the trunk to discriminate the traffic from different VLANs.



I D F

1

. . . . . . . . .

2 3 1 I D F

2

1 2 211 2 3 321 1 2 1 321 2 3 1 2 3 1 MD F 1 9 2 . 1 6 8 . . / 2 4 1 9 2 . 1 6 8 . 1 . / 2 4 1 9 2 . 1 6 8 . 1 . / 2 4 I D F

1

. . . . . . . . .

I D F

2

211 321 321 MD F 1 9 2 . 1 6 8 . . / 2 4 1 9 2 . 1 6 8 . 1 . / 2 4 1 9 2 . 1 6 8 . 1 . / 2 4

t r u n k s

P r a c t i c e Wo r k e r s P r

g

r a m m e r s D i r e c t i

n

P r a c t i c e Wo r k e r s P r

g

r a m m e r s D i r e c t i

n

P

r

t c

n

fj g u r e d i n V L A N 1

router router

SLIDE 36

3 6

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r

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A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Ethernet Switches – VLAN Trunking

Trunking Protocols:

Inter-Switch Link (ISL). CISCO propietary protocol. IEEE-802.1Q.

I E E E

8

2 . 3 f r a m e w i t h t h e 8 2 . 1 Q t a g .

Legend:

Tag Protocol Identifier (TPID): Field with the hex. value 8100 for an Ethernet frame. Tag Control Information (TCI): Contains several fields. The most important is the VLAN ID (12 bits), which identify the VLAN.

SLIDE 37

3 7

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A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Outline

Introduction IEEE LAN Architecture Ethernet Ethernet Switches Wireless LANs

SLIDE 38

3 8

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A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Wireless LANs (WLANs) – Brief WLAN History

1971: Prof. Norman Abramson develops ALOHANET for the University of Hawaii 1990: many companies develop proprietary WLANs products. 1996: ETSI approves HIPERLAN/1 and 1997 IEEE approves 802.11 Late 90 and 2000: Wi-Fi Alliance, tremendous growth of 802.11 products. 1999: 802.11a, 802.11b. 2003: 802.11g. 2009: 802.11n...

8 2 . 1 1 i n d

r

A P s 8 2 . 1 1 N I C s 8 2 . 1 1

u

t d

r

SLIDE 39

3 9

L l

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e n ç C e r d à

A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Wireless LANs (WLANs) – 802.11

802.2 (LLC) 802.11 (MAC)

S t a n d a r d B i t r a t e I S M b a n d 8 2 . 1 1 1 , 2 Mb p s 2 . 4 G H z 8 2 . 1 1 b u p t

1

1 Mb p s 2 . 4 G H z 8 2 . 1 1 a u p t

5

4 Mb p s 5 G H z 8 2 . 1 1 g u p t

5

4 Mb p s 2 . 4 G H z 8 2 . 1 1 n u p t

6

Mp b s 2 . 4

r

5 G H z

802.11 802.11a 802.11b 802.11g

I S M: I n d u s t r i a l S c i e n t i fj c a n d Me d i c a l . N

l

i c e n c e r e q u i r e d f

r

n

n

c

m

m e r c i a l u s a g e .

802.11n

SLIDE 40

4

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r

e n ç C e r d à

A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Wireless LANs (WLANs) – 802.11 Components

Distribution System (DS):

Used by APs to exchange frames with one another and with wired

networks. (e.g. an ethernet switch).

Access Point (AP)

Simplify communication between stations. All transmissions go through the AP. APs are bridges and may have a collocated router.

A P

A c c e s s P

i

n t ( A P ) u s e d a s a b r i d g e . S t a t i

n

Wi r e l e s s m e d i u m D i s t r i b u t i

n

S y s t e m ( D S )

A P

A c c e s s P

i

n t ( A P ) w i t h a c

l

l

c

a t e d r

u

t e r . S t a t i

n

Wi r e l e s s m e d i u m I n t e r n e t

ISP

A D S L

SLIDE 41

4 1

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A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Wireless LANs (WLANs) – 802.11 Components

Basic Service Set (BSS) Set of stations communicating with each other. Are identified by: (i) a Service Set identifier (SSID), or Network name: String with <32 characters; and (ii) a BSS Identifier (BSSID): 48 bits number. If the network is composed of more than 1 BSS it is called Extended Service Set (ESS).

I n d e p e n d e n t B S S , I B S S ( a d

h
c

m

d

e )

A P

I n f r a s t r u c t u r e B S S ( i n f r a s t r u c t u r e m

d

e ) A n s t a t i

n

m u s t a s s

c

i a t e w i t h a n A P . A l l t r a n s m i s s i

n

s g

t

h r

u

g h t h e A P s .

B S S 1 B S S 2 B S S 3 E S S D S

E x t e n d e d S e r v i c e S e t ( E S S )

A P A P A P

SLIDE 42

4 2

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A

l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Wireless LANs (WLANs) – 802.11 Addresses

Designed to be compatible with ethernet. Use non overlapping ranges with ethernet. The frame may have up to 4 addresses. The meaning of the addresses is specified by the bits to-DS and from-DS of the control. The BSSID is always present to identify frames belonging to the BSS

G e n e r i c f r a m e f

r

m a t

Frame Control Duration Address 1

Address 2 Address 3

Seq Ctrl FCS Payload 2 2 6 6 2 Variable: 0-2312 4 6

Address 4

6

Wireless LANs (WLANs) – 802.11 MAC

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA): In contrast to CSMA/CD, always wait a random backoff before Tx. Acks are needed to detect whether a transmitted frame collided. CSMA/CD is not used because collisions can hardly be detected in wireless (because in the antenna the Tx power is orders of magnitude higher than Rx power).

SLIDE 43

4 3

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G r a u e n e n g i n y e r i a i n f

r

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X

a r x e s d e C

m

p u t a d

r

s ( X C

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Unit 3. Local Area Networks, LANs

Wireless LANs (WLANs) – 802.11 Addresses

Scenario Usage Address1 Address2 Address3 Address4 STA→STA DA SA BSSID

STA→AP

Infrastructure 1 BSSID SA DA

AP→STA

Infrastructure 1 DA BSSID SA

AP→AP

WDS 1 1 RA TA DA SA Legend: Destination Address (DA), Source Address (SA), Receiver Address (RA), Transmitter Address (TA) to-DS from-DS Ad-hoc

E x a m p l e :

M# ping S

A P

B S S D S M S

L e g e n d , f r a m e s 8 2 . 1 1 : ME S S A G E

T

Y P E ( t

D

S , f r

m
D

S , A d d r e s s 1 , A d d r e s s 2 , A d d r e s s 3 ) L e g e n d , f r a m e s e t h e r n e t : ME S S A G E

T

Y P E ( d e s t i n a t i

n

a d d r e s s , s

u

r c e a d d r e s s ) F F i s t h e b r

a

d c a s t a d d r e s s

M A R P

R

E Q ( 1 , , B S S I D , M , F F ) S A P A R P

R

E Q ( , 1 , F F , B S S I D , M ) A R P

R

E Q ( F F , M ) A R P

R

E P ( M , S ) A R P

R

E P ( , 1 , M , B S S I D , S ) E C H O

R

E Q ( 1 , , B S S I D , M , S ) E C H O

R

E Q ( S , M ) E C H O

R

E P ( M , S ) E C H O

R

E P ( , 1 , M , B S S I D , S )

t t t

SLIDE 44

4 4

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l a b e r n

G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

r

s ( X C

g

r a u )

Unit 3. Local Area Networks, LANs

Wireless LANs (WLANs) – 802.11 Addresses

Scenario Usage Address1 Address2 Address3 Address4 STA→STA DA SA BSSID

STA→AP

Infrastructure 1 BSSID SA DA

AP→STA

Infrastructure 1 DA BSSID SA

AP→AP

WDS 1 1 RA TA DA SA Legend: Destination Address (DA), Source Address (SA), Receiver Address (FA), Transmitter Address (TA) to-DS from-DS Ad-hoc

A P

D S

L e g e n d , f r a m e s 8 2 . 1 1 : f r a m e ( t

D

S , f r

m
D

S , A d d r e s s 1 , A d d r e s s 2 , A d d r e s s 3 , A d d r e s s 4 ) L e g e n d , f r a m e s e t h e r n e t : f r a m e ( d e s t i n a t i

n

a d d r e s s , s

u

r c e a d d r e s s )

A P

D S H 2 A P 1 A P 2

f r a m e ( H 2 , H 1 ) H 1 A P 1 f r a m e ( 1 , 1 , A P 2 , A P 1 , H 2 , H 1 ) f r a m e ( H 2 , H 1 ) H 2 A P 2

H 1

t t t t

SLIDE 45

4 5

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G r a u e n e n g i n y e r i a i n f

r

m à t i c a

X

a r x e s d e C

m

p u t a d

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s ( X C

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r a u )

Unit 3. Local Area Networks, LANs

Wireless LANs (WLANs) – Hidden Node Problem

Node A is in coverage with AP and C A and B cannot hear each other When A transmits to AP, B cannot detect the transmission using the carrier sense mechanism If B transmits, a collision will occur at AP

A P

A A P B C

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G r a u e n e n g i n y e r i a i n f

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X

a r x e s d e C

m

p u t a d

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Unit 3. Local Area Networks, LANs

Wireless LANs (WLANs) – 802.11 RTS/CTS

Optional mechanism to solve the hidden node problem.

S I F S R T S C T S S I F S D A T A A C K t t t H 1 A P H 2 S I F S D u r a t i

n

i n d i c a t e d i n R T S D u r a t i

n

i n d i c a t e d i n C T S

A P

H 1 H 2 A P

RTS is sent using the basic access mechanism. Upon receiving a RTS/CTS, the station set the Network Allocation Vector (NAV) to the indicated duration. While the NAV is non zero, the virtual carrier sensing indicates that the medium is busy. RTS/CTS is only used for unicast Tx. There is a threshold indicating the minimum frame size for using RTS/CTS.