Wave Datacomm 2

7/26/2019 Wave Datacomm 2

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DATA COMMUNICATIONandCOMPUTER NETWORKS(Part 2)

Information

This is a continuation of Data Communication and Computer Networks (Part 1), which should be available

from the same source. This file is created for 1stSemester, 2011.

Chapter 8: Switching

Switching

Circuit-Switched ( )

Packet-Switched ()

o

Datagram network

o Virtual-circuit network

Message-Switched

Circuit-Switched Networks

( matrix switch) ( )

timing diagram 3 Setup (connect), data transfer Teardown (disconnect)

Figure 1 Timing diagram of circuit-switching


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Data Communication and Computer Networks, part 2 2

Datagram network

packet "" router routing table map ( layer 3)router routing (circuit switch)

datagram network () datagram network ( circuitswitch)

Figure 3 Timing diagram of datagram network

Virtual-circuit network

circuit switching datagram network packet-switched circuit-switched setup time ""

virtual circuit datagram "virtual-circuit identifier" (VCI) virtual circuit ""

address link

tablelookup waiting time

Figure 2 Routing Table


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Figure 4 data transmission using virtual-circuit switching

Figure 5 Timing diagram of virtual-circuit switched network

Switching Circuit-Switch Datagram Virtual-Circuit

Delay Time Connect/Disconnect Hop waiting-time Setup/Teardown

Yes No No

Yes No YesWaiting Time

(between hops)

None High Low

( Switching)

( VCI)

Switch crosspoint crosspoint /


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Figure 6A simple switch

(crosspoint)

Number of Crosspoints in a Switch

N M crosspoint N*N switch switching 3-stage switch

Figure 7 3-stage switch

3 stage () 1 N n crossbar N/n crossbar k stage 1 3 stage 3 stage 1

crosspoint

Stage 1 N/n n k

o crosspoint kN

Stage 2 k N/n N/n

o crosspoint k (N/n)2


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Number of Crosspoints for 3-stage switch

Example: Design a three-stage 200-by-200 switch (N=200) with k=4 and n=20 Crosspoint one-stage

Crossbar Stage () N/n = 200/20 = 10

Crossbar Stage k = 4

1-Stage Crosspoint 3-stage crosspoint 2000/40000 = 5% 1-stage

Clos Criterion

non-blocking Clos Criterion

Clos Criterion

( )Example: Clos Criterion

n = sqrt(200/2) = 10 ( "") k >= 2n-1 = 19 ()

stage 10 1920 (20*(10*19) points)

stage 19 10 10 (19*10*10 points)

stage stage


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9500 points ( "non-blocking")

crossbar 3-stage switching

Time-slot interchange & TST Switch

switching crossbar time-space-time switch

Figure 8Time-slot interchange

Packet Switch

circuit

switching fabric lookup table

Banyan Switch

binary switch switch

Chapter 10: Error Detection and Correction

forward error correction (

) retransmission

Data Corruption

Common Errors

Single-bit Error

00000010 00001010


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Burst Error

error 0100010001000011 0101110101100011 error ( error )

Basics / check digit extra bit

convolute code

Block Coding

2k

k bit n bit 2n ("" 2k)

Hamming Distance

bit pattern 2 XOR 1

d(000,011) = 2 000 XOR 011 = 011

d(10101,11110) = 3 10101 XOR 11110 = 01011

minimum Hamming distance Hamming distance

Data Codeword

00 000

01 011

10 101

11 110

Figure 9 Data-Codeword table

x,y (x!=y) d(x,y) = 2 minimum Hamming distance = 2 valid word 2 detect error error 1 ( error size minimum Hamming distance)

Data Codeword

00 00000

01 01011

10 01101

11 11110


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Figure 10 Revised table

minimum Hamming distance = 3 3 bit ( invalid word )

Rules of Hamming Distance

Minimum Hamming Distance Rules

Detect minimum s -> Distance s+1

Correct maximum t -> Distance 2t+1

Example: hamming distance dmin=4 ( -)

Detect: s+1 = 4 s=3

Correct: 2t+1 = 4 t=3/2 t=1

Linear Block Codes

Parity Checking

hamming distance = 2 1 "" "" 0 1

0000 -> 00000

0001 -> 00011

...

0110 -> 01100

( Even Parity 1 Odd Parity 1 ) 1 parity checker parity syndrome bit 0

dmin= 2 detect1 bit parity check error 11011 ---(3)---> 00111 --> 1 detect1

2D Parity parity

1 1 0 0 1 1 1 1


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3 bit

Parity 2D parity

Hamming Code

redundancy bit

Table 1 Hamming code bit positions (1-17)

Bit no. 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

Bit type d R16 d d d d d d d R8 d d d R4 d R2 R1

BitCoverage

R1 X X X X X X X X X

R2 X X X X X X X X

R4 X X X X X X X X

R8 X X X X X X X X

R16 X X

Redundancy (R) power-of-2 ( parity

parity )

m>=2 redundancy bit m 2m-m-1 data bits* parity parity 1, 2, 4 () 1+2+4=7

redundant bit ()

Cyclic Codes

Cyclic Code Cyclic Code modulo Cyclic Code modulo (0-1 = 1)

*http://en.wikipedia.org/wiki/Hamming_code

1 0 1 1 1 0 1 1

0 1 1 1 0 0 1 0

0 1 0 1 0 0 1 1

0 1 0 1 0 1 0 1

1 1 0 0 1 1 1 1

1 0 0 1 1 1 1 1

0 1 1 1 0 0 1 0

0 1 1 1 0 1 1 1

0 1 0 1 0 1 0 1
http://en.wikipedia.org/wiki/Hamming_codehttp://en.wikipedia.org/wiki/Hamming_codehttp://en.wikipedia.org/wiki/Hamming_codehttp://en.wikipedia.org/wiki/Hamming_code


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0-1=1 cyclic code CRC http://en.wikipedia.org/wiki/Cyclic_redundancy_check

codeword generator( 0 )

codeword 1001110 CRC generator = 1011

Binary as Polynomial

binary polynomial0b1000011 => x6+x+1 6 remainder 6 bit

polynomial

....
http://en.wikipedia.org/wiki/Cyclic_redundancy_checkhttp://en.wikipedia.org/wiki/Cyclic_redundancy_checkhttp://en.wikipedia.org/wiki/Cyclic_redundancy_checkhttp://en.wikipedia.org/wiki/Cyclic_redundancy_check


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Choosing a Generator

CRC codeword Codeword c(x) =M(x) + R(x) codeword (message + remainder)g(x) Generator

generator codeword g(x)|c(x)error detect g(x)|(c(x) + e(x)) g(x) | e(x) detect g(x) error g(x) = 1 1|e(x)

g(x) x0= 1 single-bit error x2+1

+1 polynomial x3+x2 x2(x+1) x2= 0b100 error 0b1000 0b100|0b1000 error detect

1 Example: g(x) error

x+1 ( 1)

x3( x3)

1 ( 1 )

Double Error

error generator xt+1 ( 0


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x5+x3+x+1 x+1 x6+x4+x2+x+x5+x3+x+1 (x+x=0 modulo) x+1 x+1|e(x)

Generator

Cyclic code Burst error generator detect shift

generator satisfy g(x)|e(x) burst error generator error 1-(1/2)(r-1) burst error generator error 1-(1/2)r

Polynomial

1 ( xn polynomial ) (single-bit error ) xt+1 2


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checksum 36+9 = 45 wrap 1011012 wrap 1101+10 = 1111 = 15 complement 0

Chapter 11: Data Link Control

Error Control (Detection/Correction codes) Data Link Layer Data LinkControl Data Link Error

Introduction

Transmission Time () Propagation Delay

"" Transmission Time Bit Rate Bit Rate * Propagation Delay Bandwidth Delay Product

file download propagation delay download transmission time

...

error

processing

Acknowledgement

() ...

o retransmission Automatic Repeat Request (ARQ)

Importance of Bandwidth Delay Product

delay ack

Framing

Frame Structure

o Flag


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o Header

o Trailer error control

Escaping

bit pattern Flag = 00110 00110 (escape sequence "\") stuffing

unstuffing

Flag Header Trailer Flag

... ... ... ... ...Flag ESC

... ... ... ... ...Flag ESCESCESC

From Network Layer

Stuff

Send

Flag Header Trailer Flag... ... ... ... ...Flag ESCESCESC

... ... ... ... ...Flag ESC

Unstuff

To Network Layer

Figure 11 Stuffing and Unstuffing

Bit-oriented protocol

Data Link

Protocols (actually "mechanisms")

Noiseless

o Simplest

o Stop-and-Wait

Noisy

o

Stop-and-Wait ARQ

o Go-Back-N ARQ

o Selective Repeat ARQ


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Noisy ARQ

Simplest Protocol

Sender: Wait from Network Layer -> Physical Layer

Receiver: Wait from Physical Layer -> Network Layer

Receiver

error control flow control

Stop-and-Wait

ACK

Figure 13 Stop-and-Wait protocol

Stop-and-Wait ARQ

Stop-and-Wait timeout ACK

ACK 0 1 ACK frame ( Frame 0 ACK 1)

Figure 12Simplest Protocol


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Figure 14 Stop-and-Wait ARQ

Go-Back-N ARQ

Stop-and-Wait ARQ send/receive window 0/1 Sending Window 2m-1 sequence number m

Figure 15Go-Back-N ARQ (Left one is good, right one is bad)


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Selective-Repeat ARQ

Go-Back-N ARQ ( Go-Back-N ARQ Receiving Window 1)

Figure 16 Selective-Repeat ARQ, m=2 (left: good, right: bad)

Sending Window Receiving Window 2m/2

Figure 17 Another example of Selective-Repeat ARQ (m=3)

ACK NAK (Negative-Acknowledge) Sender

Table 2 ARQs' Window Sizes

Component Stop-and-Wait ARQ Go-Back-N ARQ Selective-Repeat ARQ

Send Window 1 2m-1 2

m/2

Recv Window 1 1 2m

/2


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High-level Data Link Control (HDLC)

(bit-oriented)

HDLC point-to-point multipoint Normal Response Mode primary/secondary

Figure 19 HDLC Normal Response Mode

Asynchronous Balanced Mode

Figure 20HDLC Asynchronous Balanced Mode

HDLC Go-Back-N ARQ piggybacking ACK/NAK

Point-to-Point Protocol (PPP)

point-to-point (byte-oriented)

Figure 21 PPP Frame

Escape Byte 01111101 (Escape Byte Flag \n \t \r )

Figure 18 HDLC Piggybacking


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Figure 22 State diagram of PPP

PPP state state PPP

PAP

authenticate ( terminate)

Figure 23PAP

PAP user/pass

Challenge-Handshake Authentication Protocol (CHAP)

server Challenge user f(challengeValue, password) response server


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() f(challengeValue,password) password

Figure 24 CHAP

Chapter 12: Multiple Access

Multiple Access

Random Access

ALOHA

2Tframe

Figure 25Pure ALOHA vulnerable time (If frame A exists, cant send after-B-before-C)


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Load Factor

Load Factor 1 Load factor Throughput ALOHA Throughput S = G exp(-2G) Smax= 0.184 G=1/2 (50%)

G Smaxhttp://www.wolframalpha.com/input/?i=d+%28x+exp%28-2x%29%29+%2Fdx Show Steps

Algorithm

Figure 26 Algorithm for Pure ALOHA

Slotted ALOHA

ALOHA Vulnerable Time 2TframeTframeS = G exp(-G) Smax= 0.368 G=1

CSMA

Carrier-Sense Multiple Access

CSMA/CD

( .) propagation time ( padding )
http://www.google.com/url?sa=D&q=http%3A%2F%2Fwww.wolframalpha.com%2Finput%2F%3Fi%3Dd%2B%2528x%2Bexp%2528-2x%2529%2529%2B%252Fdxhttp://www.google.com/url?sa=D&q=http%3A%2F%2Fwww.wolframalpha.com%2Finput%2F%3Fi%3Dd%2B%2528x%2Bexp%2528-2x%2529%2529%2B%252Fdxhttp://www.google.com/url?sa=D&q=http%3A%2F%2Fwww.wolframalpha.com%2Finput%2F%3Fi%3Dd%2B%2528x%2Bexp%2528-2x%2529%2529%2B%252Fdxhttp://www.google.com/url?sa=D&q=http%3A%2F%2Fwww.wolframalpha.com%2Finput%2F%3Fi%3Dd%2B%2528x%2Bexp%2528-2x%2529%2529%2B%252Fdxhttp://www.google.com/url?sa=D&q=http%3A%2F%2Fwww.wolframalpha.com%2Finput%2F%3Fi%3Dd%2B%2528x%2Bexp%2528-2x%2529%2529%2B%252Fdxhttp://www.google.com/url?sa=D&q=http%3A%2F%2Fwww.wolframalpha.com%2Finput%2F%3Fi%3Dd%2B%2528x%2Bexp%2528-2x%2529%2529%2B%252Fdxhttp://www.google.com/url?sa=D&q=http%3A%2F%2Fwww.wolframalpha.com%2Finput%2F%3Fi%3Dd%2B%2528x%2Bexp%2528-2x%2529%2529%2B%252Fdx


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A B C

Collision NOT detected, but B cannot receive.

A B C

Solution

t1

t1+Tp

t1+Tf

t1+2Tp

Tframe>=2Tprop

Otherwise collision will slip and detection will

fail. See the diagram.

Figure 27 CSMA/CD Solution

frame 2Tp Tf>=2Tp

: CSMA/CD bandwidth 10Mbps propagation time 25.6us

Tp= 25.6us Tf>= 2TpTf>= 51.2us

Frame Size = Frame Time (s) * Data Rate (bps) = 51.2us * 10Mbps = 512 bits

TL Note: ( Unicode )

Figure 28 Flow diagram of CSMA/CD

Controlled Access

3


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Reservation 1 Select-Poll Slave/Master Master Select Slave

Poll Slave Token Ring

Ring Topology (logical order)

Channelization

TDMA & FDMA

Time multiplexing Frequency multiplexing multiple access

Time

Frequency

A B C D

Ch

Ch

Ch

Ch

Time

Frequency

A

B

C

DCh

Ch

Ch

Ch

Figure 29TDMA and FDMA

CDMA

[+1 +1] [+1 -1]

0 -1 1 +1 0

A [+1 +1] 1 ( 1) [+1 +1]B [+1 -1] 0 ( -1) [-1 +1]

[0 +2]

[0 +2]A [+1 +1] [0 +2] 2/2 = 1

B [+1 -1] [0 +2] -2/2 = -1


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Walsh Table

[ ]

[ ] [ ] * + [

] * + * +

* + * +

Channel (sum)

A:0

B:0

C:-

D:1

Code Result

(Nothing)

Figure 30 Mixing together (4 CDMA)

CDMA

Chapter 13: Ethernet

IEEE 802

IEEE


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Figure 31 OSI IEEE

IEEE 802.3: MAC Protocol

Preamble SFD Dest. Addr Source AddrLength/

TypeData & Padding CRC

Preamble = 56bytes 10101010

SFD = 10101011

7 Bytes 1B 6 Bytes 6 Bytes

Ethernet: Type

IEEE: Length

2 Bytes 4 Bytes

Payload Length: 46~1500B

Physical Layer Frame Length: 64~1518 Bytes

Figure 32 MAC Frame

Address MAC MAC Address

Ethernet (MAC) Address

6 bytes 06:01:02:01:2C:4B

OUI (Organizationally-Unique Identifier) ID NIC VendorOUI

OUI http://standards.ieee.org/develop/regauth/oui/public.html

OUI

Unicast and Multicast

OUI Unicast (0) Multicast (1) OUIYX:YY:YYX

Least Significant Bit ABCDEFG HIJKLMN GFEDCBA NMLKJIH Bit G Unicast/Multicast Bit

FF:FF:FF:FF:FF:FF broadcast

Wireshark ARP Request Broadcast
http://www.google.com/url?sa=D&q=http%3A%2F%2Fstandards.ieee.org%2Fdevelop%2Fregauth%2Foui%2Fpublic.htmlhttp://www.google.com/url?sa=D&q=http%3A%2F%2Fstandards.ieee.org%2Fdevelop%2Fregauth%2Foui%2Fpublic.htmlhttp://www.google.com/url?sa=D&q=http%3A%2F%2Fstandards.ieee.org%2Fdevelop%2Fregauth%2Foui%2Fpublic.htmlhttp://www.google.com/url?sa=D&q=http%3A%2F%2Fstandards.ieee.org%2Fdevelop%2Fregauth%2Foui%2Fpublic.html


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Standard Ethernet

Types

10Base5 coax 500m 10Base2 185m ( 2) 10Base-T TTwisted Pair UTP + Hub 10Base-F F Fiber

Standard Ethernet Manchester Encoding

Bridges & Switches

Hub Star bus bus

bandwidth

bridge

Bridge

collision domain

Bridge

Figure 33 Blue = Collision Domain

Fast Ethernet

Topology

point-to-point

Implementations

100Base-TX copper ( ) Cat5 UTP

100Base-FX fiber

100Base-T4 Cat3 hack Cat5

Encoding

Manchester baud/bit = 2 MLT-3 4B/5B

Gigabit Ethernet

Ethernet encoding block line encoding


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Chapter 14: 802.11: Wireless LANs

BSS and ESS

BSS (Basic Service Set) AP ad-hoc AP infrastructure network BSS 1 AP 1 AP ( KUWIN) BSS ESS(Extended Service Set) LAN Gateway

Figure 34 BSS and ESS

Access

Access

Controlled Access (Point coordination function)

Random Access (Distributed coordination function)

PCF DCF

Wi-Fi?

Wi-Fi Wireless Fidelity 802.11 Wi-Fi Certified ()

CSMA/CA with RTS/CTS

CSMA/CA () AP

RTS (Request to Send) AP

AP CTS (Clear to Send)


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o o

Data AP ACK

RTS

IFS

IFS Collision Avoidance priority

DIFS (Distributed IFS) SIFS (Short IFS)

DIFS > SIFS

Addressing

Addressing 4

To DS From DS Addr 1 Addr 2 Addr 3 Addr 4

0 0 Destination Source BSSID 0 1 Destination Sending AP Source AP

1 0 Receiving AP Source Destination AP1 1 Receiving AP Sending AP Destination Source AP AP

A AP1 AP2Data1

Data1

ToDS,FromDS=(1,0)

Address1= AP1

Address2= A

Address3= B

Address4= None

B

ToDS,FromDS=(1,1)

Address1= AP2

Address2= AP1

Address3= B

Address4= A

ToDS,FromDS=(0,1)

Address1= B

Address2= AP2

Address3= A

Address4= None

Data1

802.11 Addressing Mechanism

X

ToDS,FromDS=(0,0)

Address1= Y

Address2= X

Address3= BSSID

Address4= None

YData2

BSSID

Figure 36How to choose addressing

address MAC Address

Figure 35CSMA/CA with RTS/CTS


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RTS and CTS

Figure 37 RTS and CTS Frames

Hidden and Exposed Node

B A C

Hidden Node:

B and C cannot see each other

Figure 38 Hidden Node Problem

B C B C A A CSMA/CD CA

!

RTS/CTS (Request/Clear to Send) CTS (Timeout RTS) RTS/CTS ()

B A C D

Exposed Node:

C overhearsA-to-B Transmission

Figure 40Exposed Node

Exposed Station node A B C C D C A

MACA ( CSMA/CA Packet Radio) KA9Qhttp://www.ece.rice.edu/~camp/MAC/maca.pdf

Figure 39RTS and CTS
http://www.ece.rice.edu/~camp/MAC/maca.pdfhttp://www.ece.rice.edu/~camp/MAC/maca.pdfhttp://www.ece.rice.edu/~camp/MAC/maca.pdfhttp://www.ece.rice.edu/~camp/MAC/maca.pdfhttp://www.ece.rice.edu/~camp/MAC/maca.pdfhttp://www.ece.rice.edu/~camp/MAC/maca.pdf


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C ( ) Exposed Node

ISM Band

ISM (Industrial, Scientific and Medical) band ( .) 915MHz, 2.450GHz 5.800GHz ( ITU-R)

902-928 MHz 2.400-2.500 GHz 5.725-5.875 GHz

Source: http://www.itu.int/ITU-R/terrestrial/faq/index.html#g013

915MHz 2.450GHz 5.800GHz

Figure 41ISM Band

Bluetooth

Personal Area Network (PAN) Bluetooth Piconet Master 1 Slave 7( 7active7)

Slave Master Scatternet

Figure 42 Piconet and Scatternet

Bluetooth Frequency Hopping Spread Spectrum (FHSS)

Timeslot frequency hopping Poll-Select Slave timeslot

http://www.itu.int/ITU-R/terrestrial/faq/index.html#g013
http://www.itu.int/ITU-R/terrestrial/faq/index.html#g013http://www.itu.int/ITU-R/terrestrial/faq/index.html#g013http://www.itu.int/ITU-R/terrestrial/faq/index.html#g013http://www.itu.int/ITU-R/terrestrial/faq/index.html#g013


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timeslot frame 3 5 timeslot () max data capacity

Chapter 15: Connecting LANs

Physical Layer

Hub () Repeater Repeater Hub

Hub Repeater Collision Domain ()

A B Repeater C D

Collision Domain

Broadcast Domain

Figure 43 Repeater/Hub, Broadcast and Collision Domains

Repeater (noise )

Data Link Layer

Data Link Layer Bridge Switch Collision Domain

Bridge Switch MAC Address

(, )

node ( ) Bridge update

Bridge (Collision Domain ) Broadcast Broadcast Domain


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A B Bridge C D1 2Collision Domain Collision Domain

Broadcast Domain

Addr | Port

A | 1 B | 1

C | 2

D | 2

Spanning Tree Protocol

() Bridge Spanning Tree Protocol (STP)

Bridge Shortest Path Tree

Path Cost Bridge LAN Cost= 1 LAN Bridge Cost = 0

What about Switch?

Switch cut-through

Network Layer

Network Layer Router Bridge IP Address Broadcast Broadcast Domain

A B

Bridge

C D

Broadcast Domain

Router

E F

Bridge

G H

Broadcast Domain

Collision Domain Collision Domain

Collision Domain Collision Domain

Figure 45Bridge and Router

Figure 44STP


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Backbone Network

( ) LAN Star Networkhigh-speed switch LAN WAN Link LAN WAN RouterBackbone Network

VLAN

VLAN Bridge VLAN VLAN Switch

Switch A

A1

A2 A3

A4

A5 A6

Switch B

B1

B2

B3 B4

B5 B6

VLAN 1

VLAN 2

VLAN 3

Backbone

Figure 46 VLAN

VLAN IEEE 802.11q


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Data Communication and Computer Networks, part 2 A

Appendix

Line Coding Example

Check problem statement for level definitions, etc. before using this chart.

Data 01 1 1 0 0 1 1

Unipolar

NRZ

NRZ-I

RZ

Data 01 1 1 0 0 1 1

Manchester

Diff.

Manchester

Bipolar AMI

List of Standards (that we should know)

Name Description Common subset Related Names

IEEE 802.3 Ethernet LAN

IEEE 802.11 WLAN Wi-Fi Wi-Fi Alliance

IEEE 802.15 WPAN Bluetooth Bluetooth SIG

IEEE 802.16 Broadband Wireless Access WiMAX

List of Equations

Decibels:

o o o

Capacities & Bit Rate

o Nyquist: o Shannon:


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Data Communication and Computer Networks, part 2 B

Pulse Rate Quantization Noise Baud Bandwidth & Signal Rate

Multiplexing:

o Multiplexed Frame Rate = Channel Bit Rate

o Multiplexed Bit Rate = (Number of Channels) * (Bit Rate of Each Channel)

Switching:

o Crosspoints: o 3-Stage Crosspoints: o Clos Criteria:

(Worth reading: Page5)

Error Correction

o Detect minimum s -> Distance s+1

o Correct maximum t -> Distance 2t+1

ARQ Window Sizes: See Page17

Choose a CDMA Key: See Page24

WLAN Addressing: See Page28

See you in Network!

()

LunaticNeko4CPE23

Draft 4

2011-10-05 22:38:02

Documents

Wave Datacomm 2