Wireless Local Area Network

WLAN

Wireless Local Area Network

WLAN Overview

Content & Scope 

Wireless LAN Overview  



Optional: Ethernet & TCP/IP Basics



Mobile & Wireless Basics



IEEE 802.11





Introduction



Media Access  



Frame Format  



Management Operations



Physical Layers



Deployment  

Miscellaneous – 

IEEE 802.11n, IEEE 802.16, & RadioTap



Lab Exercises



Next generation WLAN

©NetProWise

WLAN Overview

Pre-Requisites 

Computer Organization – bits, bytes, memory, integer representation,…



Desktop terminologies – file, delete, …



Operating System (Windows, Linux) – compile, shell, command, …



OSI Architecture – Layering,….



TCP/IP



Ethernet

©NetProWise

WLAN

Module 1 WLAN, Wired Ethernet & TCP/IP Overview

WLAN Overview

Wireless LAN 

LANs that use wireless medium



Connected to regular LANs for better reach



Allows limited Mobility



Unique Challenges & Issues



Benefits

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WLAN Overview

WLAN – Advantages     

Mobility Flexible Planning Design Robustness

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WLAN Overview

WLAN Standards 

IEEE 802.11 

  

Infra-red

HIPERLAN/2 Bluetooth …

©NetProWise

WLAN Overview

History 

802.11 standard first ratified in July 1997 

3 PHY’s specified (FHSS, DSSS, and IR) with 1 & 2 Mbps



2 High Rate PHY’s ratified in Sept 1999 

802.11a 6 to 54 Mbps in 5 GHz ISM band using OFDM



802.11b 5.5 to 11 Mbps in 2.4 GHz band using DSSS

©NetProWise

WLAN Overview

Companion or Evolution Specifications 

802.11c – support for 802.11 frames



802.11d – support for 802.11 frames, new regulations



802.11e – QoS enhancements in the MAC



802.11f – Inter Access Point Protocol



802.11g – High Rate or Turbo Mode – 2.4GHz bandwidth extension to 22Mbps



802.11h – Dynamic Channel Selection and Transmit Power Control



802.11i – Security Enhancement in the MAC ©NetProWise

Overview

IEEE 802.11 WLAN - Architecture

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Overview

Infrastructure & Independent WLANs

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802.11 Layer Description

802.2

New Overview

Data Link Layer

802.11 MAC DS

FH

IR

©NetProWise

Physical Layer

IEEE 802.11 Frame with LLC & MAC IEEE 802.11 Frame

New OverView

IEEE 802.11

MAC

LLC

Ethernet Frame MAC New Overview

©NetProWise

Data

Data

Link Layer – CSMA/CA   

Carrier Sense (CS) Media Access (MA) Collision Avoidance (CA)

New OverView ©NetProWise

Physical Layers 

Radio 

New OverView 

Spread Spectrum Technology 

Direct Sequence Spread Spectrum (DSSS)



Frequency Hopping Spread Spectrum (FHSS)

Infra Red (IR)

©NetProWise

Challenges & Issues        

Error Prone Medium Inherently Shared Medium Natural limitations Unique problems – Hidden & Exposed Stations Mobility Regulation Cost Inter-working

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WLAN Design Goals   

New OverView

     

Global Operation Low Power License-free operation Robust transmission technology Simplified Spontaneous co-operation Easy to use Protection of investment Safety and Security Transparency of application

©NetProWise

WLAN Applications   

New OverView

   

Inventory Control Hospital Hotel Training Trade Shows Networking old buildings IP-Zone

©NetProWise

WLAN Vendors 

WLAN Equipment (AP, Adaptors, Card) Vendors 

New OverView



WLAN Chip Vendors 



Cisco, Nortel, NetGear, Belkin, D-Link, Linksys,…

Broadcom, Lucent, Intel, …

WLAN Software Vendors – Mostly Mobile IP development (Home Agent, Foreign Agent, & Protocol) 

Cisco, Nortel, …

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IEEE 802.11 Market Size

New OverView ©NetProWise

Demo 

Infrastructure Network  

New OverView

  

Two One One One One

Wireless stations Switch/hub AP Wired station Wireless adaptor (for monitoring)

AirPcap Adaptor

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File Transfer Application  

New Overview



Transfer a file from one wireless station to another Capture some IEEE 802.11 frames using the adaptor & Wireshark Brief review of the IEEE 802.11 frame

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WireShark Tutorial

©NetProWise

Content

New Overview



Wireless LAN Overview  



Ethernet Basics



Mobile & Wireless Basics



Introduction to IEEE 802.11  



IEEE 802.11 Media Access  



IEEE 802.11 Frame Format  



IEEE 802.11 Management Operations



IEEE 802.11 Physical Layers



IEEE 802.11 Deployment  



Lab Exercises

©NetProWise

Relation to OSI Reference Model

New Overview ©NetProWise

LAN Standards

New Overview

• 802.1

Overview.

• 802.2

LLC.

• 802.3

CSMA/CD (Ethernet).

• 802.4

Token Bus.

• 802.5

Token Ring.

• 802.6

DQDB (Distributed Queue Dual Bus MAN standard)

• FDDI • 802.11

Wireless LANs 802.2 LLC

802.3

802.4

802.5

802.6

CSMA/CD

Token Bus

Token Ring

DQDB

©NetProWise

FDDI

IEEE 802.2 Encapsulation

New Overview ©NetProWise

Basic Ethernet Frame Format

22

MAC Header

©NetProWise

Ethernet Address   

   



Six Octets in size Hard coded to NIC and unique Represented in hexadecimal form  Example: 08:56:27:6f:2b:9c Most significant 3 octets code vendor id The other 3 octets are vendor generated All octets set to “ff” to indicate broadcast “01:00:5e” in most significant octets indicates multicast : Example: Multicast address derived from multicast IP address (Class D)

©NetProWise

Extending LAN Segments 





Due to noise and attenuation, length of LAN segments are limited to few hundred meters. Several different networking elements are used to extend the span of LANs. These enhancements still have to satisfy the round trip constraint and other constraints suggested by the standards.

©NetProWise

Repeater 

 

Repeater is bidirectional Analog amplifier that amplifies and retransmits signals. Layer 1 Device. Can double the size of a LAN segment.

Segment 1

Segment 2

6

R

©NetProWise

6

Repeater 

   

Standard suggests a limit of 4 Repeaters between any two stations on LAN. A maximum of 5 segments. Repeaters don’t understand frame formats. Collision affect the entire extended network. Noise propagates throughout the extended network.

©NetProWise

Hub  

Hub is a multilink repeater with star topology In other respects, a hub is similar to a repeater Stations

Hub

©NetProWise

Bridge 





Bridge is a device that connects two or more LAN segments. Unlike Repeater, Bridge receives, processes, and retransmits frames. Bridge is invisible to the other attached computers.

Segment 1

Segment 2 P1

B

P2 P3

©NetProWise

Segment 3

Bridge Characteristics   

Layer 2 Device. Can do frame filtering. Isolate collision and noise.

©NetProWise

Bridging   



Bridge uses a forwarding table to forward frames. Initially, this table is empty. Table populated by examining the source address in frames received. If there is no forwarding entry for a frame, then is forwarded to all the other ports.

©NetProWise

Switches 



 

Switch is a bridge that is configured to work like a hub in a star topology. Frame received in port is processed and forwarded to the right port using a forwarding table. Each computer thinks it is on segment by itself. Unlike bridges, switches support large number of ports.

… P1

P32

Switch To Uplink ©NetProWise

Bridge versus Switch 

Bridge: 









Supports less than 5 ports (interfaces) Software implementation can easily handle the traffic Interface connects to a LAN segment Price per port is higher than comparable switch ©NetProWise

Switch:  The

workgroup switch, one of the smallest, can support 16/32/64 ports  Port volume requires hardware solution  Interface connects to a computer  Price per port is very low

Broadcast Storm

©NetProWise

Invalid Bridging Entry

©NetProWise

Spanning Tree Algorithm(STA)  

Converts a graph with cycle to a rooted tree. There are a number of algorithms in the literature:

Root

STA

Bridge

©NetProWise

Content 

Wireless LAN Overview  



Ethernet & TCP/IP Basics



Mobile & Wireless Basics



Introduction to IEEE 802.11  



IEEE 802.11 Media Access  



IEEE 802.11 Frame Format  



IEEE 802.11 Management Operations



IEEE 802.11 Physical Layers



IEEE 802.11 Deployment  



Lab Exercises

©NetProWise

Mobile and Wireless Concepts

Characteristics    

Fixed and wired Mobile and wired Fixed and wireless Mobile and wireless

©NetProWise

Signal, Carrier, and Medium signal

source

destination

V Carrier T • • • • • • • •

Audio signal travel as Variations in air pressure This variation is converted to Variations in Voltage levels to send signal farther Carrier is a repeating voltage (wave) – repetition period is known to both ends Carrier can travel farther without getting corrupted compared to direct voltage Carrier is modified by the signal at the source end in some form This modified Carrier – can transport the original signal from source to destination To send the modified carrier from source to destination we need a medium Using this medium we can direct (and control) the signal to its destination ©NetProWise

Modulation, Multiplexing, and Coding 











Modulation is the process of modifying the carrier with signal before transmitting it to destination. Demodulation is the process of extracting the signal from the modified carrier at the destination. Multiplexing is the process of mixing multiple signals at the source so that all these signals can be sent in the medium concurrently. Demultiplexing is the process of separating individual signals at the destination. Coding is the digital equivalent of modulation. It maps one form digital signal to another form of digital signal. Coding is done for security and easier transmission at the source. Decoding the reverse mapping of extracting original digital signal from the coded signal at the destination.

©NetProWise

RF and IR Transport 2.4GHz

I-Band 902 MHz

2.48GHz

S-Band 928 MHz

M-Band 5.725GHz

ISM Frequencies IR Spectrum: 850 to 950 nanometers

©NetProWise

5.85GHz

WLAN frequency band

©NetProWise

Signal Representation 

Time domain representation



Frequency domain representation



Phase domain representation

©NetProWise

Time domain representation of a signal Periodic signals: g (t)=At sin(2∏ftt + ϕ t) Fourier: ∞

∞

g (t)= ½ c+n=1 Σ an Cos(2∏nft)+n=1 Σ bn Sin(2∏nft)

T

f = 1/T

360

0

ϕ A

90 ©NetProWise

0

180

0

0

270 360

0

Square in terms of Sine waves

©NetProWise

Wireless transmission

Frequency Spectrum

©NetProWise

Examples for Frequency allocations

Wireless transmission

Europe

Mobile phones

Cordless telephones

Wireless LANs

US

NMT 453-457MHz 463-467MHz GSM 890-915 MHz, 935-960 MHZ; 1710-1785 MHz, 1805-1880 MHz

AMPS,TDMA,CDMA 824-849 MHz 869-894MHz; GSM,TDMA,CDMA 1850-1910 MHz 1930-1990MHz

CT1+ 885-887 MHz 930-932 MHZ CT2 864-868 MHz; DECT 1880-1900 MHz; IEEE802.11 2400-2483MHz HIPERLAN1 5176-5270MHz ©NetProWise

PACS 1850-1910MHz 1930-1990MHz PACS-UB 1910-1930MHz

IEEE802.11 2400-2483MHz

JAPAN PDC 810-826MHz, 940-956MHz 1429-1465MHz, 1477-1513MHZ

PHS 1895-1918MHz; JCT 254-380MHz

IEEE 802.11 2471-2497MHz

Signal Representation in different domains f1 T

f2

f = 1/T

Amplitude frequency A

Frequency Domain MCosφ Φ

Time Domain

Phase Domain

©NetProWise

Path Loss & Other effects*           

Line of sight (LOS) Free Space Loss Effect of weather Long waves versus Short waves Shadowing or Blocking Scattering Reflection Refraction Diffraction Multi-path propagation Delay-Spread ©NetProWise

Multiplexing 



Basic Multiplexing techniques 

Space division multiplexing



Time division multiplexing



Frequency division multiplexing



Code division multiplexing

Combinations of the above

©NetProWise

Analog Modulation 

Basic Analog

Time

Amplitude

V modulation techniques 

Amplitude modulation



Frequency modulation





T f = 1/T

Phase modulation

90

0

180

0

0

270 360

Phase

Combinations of the

Carrier Wave

above

©NetProWise

0

0

90

180

0

0

0

270 360

Digital Modulation 



Basic digital modulation techniques 

Amplitude Shift Keying



Frequency Shift Keying



Phase Shift Keying

Combinations of the above

©NetProWise

Digital Amplitude Modulation 

We can code  

Zero amplitude as 0 or 1 Non-zero amplitude as 1 or 0

©NetProWise

Frequency Shift Keying

©NetProWise

Phase Shift Keying

©NetProWise

QPSK in the phase domain Q 10 1

0

I

Q

11

I

00

©NetProWise

01

QPSK in the time domain

©NetProWise

Quadrature amplitude modulation

Amplitude Phase

©NetProWise

Minimum Shift Keying (data 1011010) Data

1

0

1

1

0

1 0

Even bits Odd bits Low frequency High frequency MSK signal

t ©NetProWise

Spread spectrum p

p

f

p

f p

f

p

f

f

User signal Broadband interface

Narrowband interface

©NetProWise

CDMA - Spreading with DSSS

©NetProWise

CDMA - Frequency Hopping Spread Spectrum tb User data

f f3 f2

0

1 td

0

1

1

t

Slow hopping (3 bits/hop)

f1 f

td

t

f3 fast hopping (3 hops/bit)

f2 f1 t

©NetProWise

CDM Background   

Vector Vector dot-product Orthogonality

Binary (11) in vector form: (1, 1) Vector dot Product: (1,1).(1,-1) = 1.1+1.-1 = 1+-1 = 0

©NetProWise

4 Mutually Orthogonal or vectors u:

1

1

1

1

v:

1

1

-1

-1

w:

1

-1

-1

1

x:

1

-1

1

-1

©NetProWise

CDM - Background For vectors a and b

The square root of a.a is a real number, and is important. We write

Suppose vectors a and b are orthogonal. Then:

©NetProWise

Code Division Multiplexing • • • •

• • • •

•

Data to be transmitted: 1, 0, 1, 1 Chip Code 1: b – (1,-1); -b – (-1, 1) Code data to be transmitted with b Transmitted Vector • 1, -1, -1, 1, 1, -1, 1, -1

2 Orthogonal Chip Codes

a:

1

1

b: 1

-1

Data to be transmitted: 0, 0, 1, 1 Chip Code 2: a – (1,1); -a – (-1, -1) Code data to be transmitted with a Transmitted Vector • -1, -1, -1, -1, 1, 1, 1, 1 •

Sum of the transmission vector • 0, -2, -2, 0, 2, 0 , 2, 0 ©NetProWise

Receiver decoding for b: • (1, -1).(0, -2) = 0+2 = 2 > 0 • (1, 1).(0, -2) = 0+-2 = -2 < 0

CDMA versus TDMA, FDMA 

Unlike TDMA, CDMA transmits data from all the input channels simultaneously!



Unlike FDMA, CDMA uses single frequency to transmit all the input channels simultaneously!

©NetProWise

CDMA Limitation 

It assumes all the channels start and stop their transmission synchronously!

©NetProWise

Asynchronous CDMA 

CDM assumes all transmitted vectors start at the same time.



This limits CDM for transmission from base-to-mobile where all transmitted vectors can be synchronized



CDM Asynchronous is used for transmission from mobileto-base



It is an enhancement of CDM



Unique, Orthogonal, Pseudo Noise signals are used for arbitrary random starting points.

©NetProWise

CDMA Summary 

CDMA operates by: 

Encoding the each input channel data using a unique (chip) code



Summing the encoded data from all the channels



Transmitting the resulting sum



On reception, each channel data is separated using the respective chip (code) from the sum and decoded

©NetProWise

Orthogonal Frequency Division Multiplexing (OFDM)  





 

OFDM is based on FDM & TDM Carrier Channel is divided into multiple sub carrier channels Each channel carries a portion of the user information. Each sub carrier channel is orthogonal with every other sub carrier OFDM is also referred to as Multi-tone modulation Applications: DSL, WLAN, BT, DAB, Powerline Ethernet

©NetProWise

OFDM – Frequency Domain Representation

©NetProWise

OFDM versus CDMA 



 

The mathematics underlying the CDMA is more complicated than in OFDM OFDM encodes a single transmission into multiple sub carriers. CDMA encodes multiple transmissions onto a single carrier. OFDM handles multi-path spread better. Both make use of orthogonal property in multiplexing signals.

©NetProWise

Hidden and exposed terminals

A

B

C

A can hear B C can hear B A cannot hear C C cannot hear A sending data ©NetProWise

Near and far terminals

A

B

©NetProWise

C

Content 

Wireless LAN Overview  



Ethernet & TCP/IP Basics



Mobile & Wireless Basics



Introduction to IEEE 802.11  



IEEE 802.11 Media Access  



IEEE 802.11 Frame Format  



IEEE 802.11 Management Operations



IEEE 802.11 Physical Layers



IEEE 802.11 Deployment  



Lab Exercises

©NetProWise

IEEE 802 Network Technology Family Tree 802 Overview 802.1 And architecture Management

Data Link Layer LLC sublayer

802.2 Logical Link control(LLC)

802.3

802.5

802.11

802.3 MAC

802.5 MAC

802.11 MAC

802.3 PHY

802.5 PHY

802.11 FHSS PHY

©NetProWise

802.11 DSSS PHY

802.11a OFDM PHY

MAC sublayer

802.11b HR/DSSS PHY

Physical Layer

IEEE 802.2 Encapsulation

©NetProWise

Basic Ethernet Frame Format

22

MAC Header

©NetProWise

MAC

MAC management

PLCP

PHY management

PMD

©NetProWise

Station management

DLC

LLC

PHY

IEEE 802.11 protocol architecture and management

Components of 802.11 LANs Distribution System

Wireless Medium )))) Access Point

)))) Access Point

©NetProWise

Stations

Independent and Infrastructure BSSs

Independent BSS

Infrastructure BSS ©NetProWise

Extended Service Set

BSS1 BSS3 BSS2

BSS4

Router Internet

©NetProWise

Distribution system in common 802.11 access points implementation Backbone network

Bridge Bridge Distribution system Wireless medium

Station A

©NetProWise

Station B

Station C

Network Services 1. 2. 3. 4. 5. 6. 7. 8. 9.

Distribution Integration Association Reassociation Disassociation Authentication De-authentication Privacy MSDU (MAC Service Data Unit) Delivery

©NetProWise

Overlapping BSSs in an ESS

BSS1 BSS2

BSS3

BSS4

©NetProWise

Overlapping Network Types AP’s Basic Service area

©NetProWise

BSS transition DS

BSS1,ESS1

T=1

BSS2,ESS2

T=2

©NetProWise

BSS3,ESS3

Inter AP Protocol (IAPP) 

Protocol for handling roaming



No standard! 



Inter-operability is an issue

Status of IEEE 802.11f not clear

©NetProWise

ESS transition

ESS1

BSS2

ESS2

BSS1

BSS4 BSS3

Seamless transition not supported

©NetProWise

Content 

Wireless LAN Overview  



Ethernet & TCP/IP Basics



Mobile & Wireless Basics



Introduction to IEEE 802.11  



IEEE 802.11 Media Access- Distributed Coordinated Function (DCF)  



IEEE 802.11 Frame Format  



IEEE 802.11 Management Operations



IEEE 802.11 Physical Layers



IEEE 802.11 Deployment  



Lab Exercises

©NetProWise

Challenges for the MAC   

RF Link Quality Hidden Node Problem Exposed Node Problem

©NetProWise

Positive acknowledgment of data transmissions

Time

Frame

ACK

©NetProWise

Nodes 1 and 3 are hidden Area reachable Node 3

Area reachable Node 1

1

2

3

©NetProWise

RTS/CTS clearing 1

2

RTS 1) RTS 1 4) ACK

3) Frame

3

CTS Frame

ACK

2) CTS 2 ©NetProWise

Power Save 

Battery power is premium in wireless devices



To Conserve battery WLAN stations alternate between Active and Power-save modes



Access Point buffers data for a WLAN station that is in Power-save mode



IEEE 802.11 protocol includes provision to implement WLAN station Power Savings

©NetProWise

MAC Access Modes  

Distributed Coordination Function (DCF) Point Coordination Function (PCF) Contention-free delivery

“Normal” Delivery

PCF

DCF

©NetProWise

Using the NAV for virtual carrier sensing

RTS Sender

data SIFS CTS

SIFS

SIFS

ACK1

t

receiver NAV

NAV(RTS)

DIFS NAV(CTS)

Defer access

Contention Window

Carrier Sensing 1. Physical Carrier Sensing 2. Virtual Carrier Sensing NAV – Network Allocation Vector ©NetProWise

Interframe spacing relationship

Contention window(randomized back-off mechanism)

DIFS

DIFS

Medium busy

PIFS SIFS

frame transmission

Otherstationbuffer anddeferframes

Slot time

©NetProWise

Contention Based Access using DCF 

If the medium has been idle for longer than DIFS, transmission can begin immediately. Both carrier-sensing are employed 

Delivery/non-delivery of the last frame decides whether to wait DIFS or EIFS.



If the medium is busy, then access deferral is applied.



Error Recovery is the responsibility of the sender



Sender expects acknowledgement for all transmitted frames. Specifically, for all unicast frames.



Retransmit frame until it is successful.



Multi frame sequence may update the NAV



RTS Threshold, Fragmentation threshold decide when to use RTS and when to fragment respectively.

©NetProWise

Error Recovery with the DCF   

Short Retry Counter Long Retry Counter Lifetime Counter

©NetProWise

MAC – Flow Chart

©NetProWise

Other Rules Applied 

Error Recovery is the responsibility of the sender



Sender expects acknowledgement for all transmitted frames.



Retransmit frame until it is successful.



Multi-frame Sequence can update NAV with each step.



Fragments get the same priority as CTS/RTS, ACK



Packets that are larger than configured RTS threshold must have RTS/CTS exchange (Extended Frame Sequence).



Packets larger than fragmentation threshold must be fragmented.

©NetProWise

Error Recovery with DCF   

Error indication – Lack of positive ACK or NAK Short Retry Counter Long Retry Counter

©NetProWise

Back-off with the DCF      

Contention Window or back-off window follows DIFS Contention Window is divided into slots. Slot length medium (speed) dependent Stations Randomly choose a slot All slots are equally likely selections Station that picks the earliest slot wins

©NetProWise

DSSS contention window size Initial attempt

Previous frame

DIFS

Previous frame

DIFS

2nd transmission

Previous frame

DIFS

3rd transmission

Previous frame

DIFS

4th transmission

Previous frame

1st transmission

DIFS

31 slots

63 slots

127 slots

255 slots

511 slots

Contention window =1,023slots 5th transmission

Previous frame

DIFS Contention window =1,023slots

6th transmission

Previous frame

DIFS

©NetProWise

Fragmentation and Reassembly DIFS SIFS

Sender

Fragment0

RTS receiver

SIFS

CTS

NAV

Fragment1 ACK0

Fragment2 ACK1

SIFS

SIFS

SIFS Block of slots

SIFS

SIFS

RTS

Fragment0

CTS

ACK0

©NetProWise

ACK2

t

SIFS

Fragment1 ACK1

t

Content 

Wireless LAN Overview  



Ethernet & TCP/IP Basics



Mobile & Wireless Basics



Introduction to IEEE 802.11  



IEEE 802.11 Media Access  



IEEE 802.11 Frame Format  



IEEE 802.11 Management Operations



IEEE 802.11 Physical Layers



IEEE 802.11 Deployment  



Lab Exercises

©NetProWise

Generic 802.11 MAC frame Direction of Transmission

bytes 2 Frame control

Most Significant bit

Least Significant bit 2

6

Duration Address ID 1

6 Address 2

6

2

Sequence Address control 3

©NetProWise

6

02312

Address Frame 4 body

4 FCS

Frame control field bytes 2 Frame control

bits

2

6

Duration Address ID 1

2

2

protocol Type=data b2

6

6

Address 2

4 Sub type

6

2

Address Sequence control 3

1

1

To DS From DS

b3

©NetProWise

02312

1

4

Address Frame 4 body

1

1

1

FCS

1

1

More Retry Pwr More WEP frag Mgmt Data

order

Type field 

Type field encodes (b3 b2)    

Management Frames (00) Control Frames (01) Data Frames (10) Reserved (11)

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Management Subtypes (00)        

  

Association Request (0000 – b7 b6 b5 b4) Association Response (0001) Reassociation Request (0010) Reassociation Response (0011) Probe Request (0100) Probe Response (0101) Beacon (1000) ATIM - Announcement Traffic Indication Message (1001) Disassociation (1010) Authentication (1011) Deauthentication (1100)

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Control Frame (01)      

Power Save (PS)-Poll (1010 – b7 b6 b5 b4) RTS (1011) CTS (1100) Acknowledgment –ACK (1101) Contention-Free(CF)-End (1110) CF-End+CF-Ack (1111)

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Data Frames (10)        

Data (0000 b7 b6 b5 b4) Data+CF-Ack (0001) Data+CF-Poll (0010) Data+CF-Ack+CF-Poll (0011) Null data (no data transmitted) (0100) CF-Ack (no data transmitted) (0101) CF-Poll (no data transmitted) (0110) Data+CF-Ack+CF-Poll (0111)

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ToDS and FromDS bits ToDS =0

F ro m D S = 0 F ro m D S = 1

ToDS = 1 D ata fram es W ireles s S tation of A ll fram es of IB S S Infras tru c ture netw ork D ata fram es rec eived for a W ireles s s tation in an infras truc tu re netw D ata ork fram es on "w ireles s bridg e"

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More Fragments bit 

Behaves like IP Fragmentation flag

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Retry bit

WLAN Overview

 

This bit is set to 1 in retransmitted frames Receiver can eliminate duplicate frames using this bit

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Power Management bit

WLAN Overview WLAN Overview

 



Used to conserve battery life If set to 1 indicates that the sender will be in powersaving mode after this atomic exchange. Access points cannot be in power-saving mode

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More data bit

WLAN Overview





Indicates that there is at least one frame available for a dozing station. Set by an AP

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WEP (Wired Equivalent Privacy) bit

WLAN Overview



Indicates that the frame has gone through WEP processing

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Order bit Frames and fragments can be transmitted in order

WLAN Overview



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Duration /ID Field

WLAN Overview

Duration (NAV) 0

1

2

3

4

5

6

7

8

9

10

11

Least significant

PS-Poll frames 0

0

1

0

2

0

3

0

4

13

14

15 0

Most significant

Contention Free Period frames 0 1 2 3 4 5 0

12

0

5

6

7

8

9

10

0

0

0

0

0

6

7

8

10

0

12 0

11

0

12

13

14

15

0

0

1

13

14

15

AID (range: 1-2007) Least significant Most significant

1

1

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9

11

WLAN Overview

Sequence control field bytes 2 Frame control

bits

2

6

Duration Address ID 1

6

6

Address 2

6

2

Address Sequence Address control 3 4

4

12

Fragment number

Sequence number

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02312 Frame body

4 FCS

Address Fields

WLAN Overview

 

4 – Address Fields Destination, Source, Receiver, Transmitter, & BSSID

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WLAN Overview

Frame Check Sequence 

FCS is checked by the receiver



The result of this checking is sent as an acknowledgement by the receiver



Recalculated during hop.

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IP Encapsulation in 802.11 6

WLAN Overview

Ethernet

Destination MAC

12 802.1h

MAC headers

1 SNAP DSAP 0xAA

6 Source MAC

1 SNAP DSAP 0xAA

12 RFC1042

SNAP MAC DSAP headers 0xAA

Variable

2 Type 0X800(IP) 0X0806(ARP)

1 Control 0x03(UI)

IP Packet

3 Ethernet Tunnel 0x00-00F8

Copy

4 FCS

Recalculate Copy

Type

IP Packet

FCS

Type

IP Packet

FCS

Type

IP Packet

SNAP header SNAP DSAP 0xAA

Control 0x03(UI)

RFC 1042 Encapsulation 0x00-00-00

24 or 30 802.11

802.11 SNAP MAC DSAP headers 0xAA

SNAP DSAP 0xAA

Control 0x03(UI)

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RFC 1042 Encapsulation 0x00-00-00

FCS

Contention-Based Data Services  

Broadcast and Multicast Frames Directed Frames    



Basic Fragmented RTS/CTS Lockout RTS/CTS Fragmented

Power Savings Mode

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Broadcast/multicast data and broad cast management atomic frame exchange

DIFS DIFS End or prior SIFS Frame data exchange NAV

Contention window

Prior exchange

Data(bc/mc) Management(bc)

Contention window For next exchange

t

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Basic positive acknowledgment of data(unicast frames) DIFS SIFS data

station2 station1

SIFS data ACK

t

SIFS

NAV

station2

ACK+SIFS t

station1

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Fragmentation SIFS data

station2 station1

Data frag1

SIFS

Data frag2

Data frag3

ACK1

ACK2

SIFS

SIFS

ACK3

t

SIFS NAV3=ACK+SIFS

NAV2=data3+2xACK+3xSIFS

NAV

station2 station1

NAV1=data2+2xACK+3xSIFS ACK1=data2+2xACK

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NAV2=data3+2xACK

t

RTS/CTS lockout

SIFS data

data

RTS

ACK

CTS SIFS

t

SIFS Data= ACK+SIFS

RTS=3xSIFS+Data+ACK NAV CTS=RTS-(CTS+SIFS)

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t

RTS/CTS with fragmentation SIFS data

station2 station1

RTS

SIFS

Data frag1 CTS

Data frag2 ACK2

ACK1

SIFS

t

SIFS

SIFS

Data2

Data1 NAV

station2 station1

RTS CTS

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ACK1

t

Immediate power-saving(ps)poll response

SIFS data

PS-poll Station Access point

ACK data

t

SIFS

Medium seized by data frame NAV

Station Access point

Implied: SIFS+ACK data

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t

Immediate power-saving(ps)poll response with fragmentation

SIFS

SIFS data

PS-poll Station Access point

ACK2

ACK1 data1

data1

t

SIFS

Medium seized by data frame NAV

Station Access point

Implied: NAV

ACK1 data1

t data2

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Deferred PS-poll response example one or more atomic frame exchanges

data

station Access Point

PS-poll

NAV

Zzz..

ACK ACK SIFS

station

SIFS

DIFS

Data

Frame Contention window

Beacon

DIFS

t

DIFS

Implied

Access Point

Data

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t

Generic Data Frame 2

2

6

6

6

2

6

02,312

F r a m De u r a At i od nd r Ae sd sd 1r Ae sd sd 2r Se se sq 3- AC dt l d r Fe sr as m4 e C o n t Ir Do l ( r e c e ( vSi ee r n) (d Fe i rl t) e r i n g ) ( O p t i Bo no ad ly)

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4

Duration setting on final fragment DIFS SIFS

Last fragment station1 station1

Contention window

ACK SIFS

Second to Last fragment NAV

Fragment: SIFS+ACK

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Duration settings on nonfinal fragment SIFS fragmentX fragmentX+1

station1 station2

ACKX

ACKX+1

SIFS

NAV

SIFS

Duration in FragmentX:fragmentx+1+3xSIFs+2xACK

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Use of the Address Fields

Func tion ToDS IB S S 0 To A P (infra) 1 From A P (infra) 0 W DS (bridge) 1

A ddres s 1 A ddres s 2 From DS (rec eiver) (trans m itter) A ddres s 3 0 DA SA B S S ID 0 B S S ID SA DA 1 DA B S S ID SA 1 RA TA DA

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A ddres s 4 not us ed not us ed not us ed SA

BSSID   



 

Each BSS is assigned a BSSID 48-bit binary identifier In infrastructure BSS, the BSSID is the MAC address of the wireless interface in the AP. IBSS must create its BSSID using random generation The Universal/Local bit is set to 1 The Individual/Group bit is set to 0

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Address Field Usage in Frames to the Distribution System RA(BSSID)

SA/TA

DS

)))) AP

DA

Client Sever

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Address Field Usage in Frames from the Distribution System TA(BSSID)

RA/DA

DS

)))) AP

SA

Client Sever

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Wireless Distribution Systems RA SA

802.11 TA

)))) AP

DA

Client Sever

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Data Frame of subtype Null Mobile Station

Header

Access Point

FCS Null frame;PM = 1

Frame Control

ACK Power Management = 1

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Mobile station is resting, begin buffering frames

Frame Types   

Data Control Management

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IBSS data Frame bytes 2

2

6

6

2

6

4

F r a m e D u r a t io nR e ID c e i veSr o u r c eB S S ID S e q - c Ft l r a m e C o n t ro l a d r e s s /a d d r e s s B ody D e s t in a t io n a d d re s s

bits 2 2

4

1

1

1

1

FCS

02,312

1

1

1

P r o t oT cy op l e S= u db a tTTayo pD e sF r o m MD os r e R Fe rt ar yPg w r M og rme Wt E PO r d e r 0 0 0 1 0 0 D a ta 0000,Data 0010,Null ©NetProWise

1

Data Frames from the AP bytes 2 2

6

6

2

6

02,312

F r a mD eu r a tRi o An / DS I DAo u rB c Se S S I De q -F cr at lm e C o n tro l a d d re s s B ody bits 2 2

4

1

1

1

1

1

4

FC S

1

1

P r o t oT cy op l e S= u db a tTTayo pD e sF r o m MD os r e R Fe rt ar yPg w r M og rme Wt E PO r d e r 0 0 0 1 0 1 D a ta 0000:Data 1000:Data + CF - ACK 0100:Data + CF - Poll 1100:Data + CF – ACK + CF - Poll 1010: CF – ACK 0110:CF - Poll 1110: CF – ACK + CF - Poll ©NetProWise

1

Data Frames to the AP bytes 2 2

6

6

6

2

02,312

F r a mD eu r a tRi o An S I DA / DT A S e q -F cr at lm e C o n t r o l ( B S S ID ) B ody bits 2

2

4

1

1

1

1

1

4

FC S

1

1

P r o t oT cy op l e S= u db a tTTayo pD e sF r o m MD os r e R Fe rt ar yPg w r M og rme Wt E PO r d e r 0 0 0 1 1 0 D a ta 0000:Data 0100:Data + CF - ACK 0010:Null 1010: CF – ACK (no data)

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1

WDS (Wireless DS) Frame bytes 2 2

6

6

6

2

6

02,312

F r a mD ue r a R t i Ao n T A I DD A S e q S - Ac tF l r a m e C o n tro l B ody bits 2

2

4

1

1

1

1

4

F C S

1

1

1

P r o t oT cy op l e S= u db a tTTayo pD e sF r o m MD os r e R Fe rt ar yPg w r M og rme Wt E PO r d e r 0 1 0 0 1 1 D a ta

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1

Frame Control Field in Control Frames Bits 2

2

4

1

1

1

1

1

1

1

P r o t To yc po el S = u bd aTT t oya Dp eFs r o mM Do sr e RF er at rgPy w r MM go mr e tW D Ea tPOa r d e r 0 1 0 00 0 0 0 0 0 0

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1

RTS Frame MAC header

Bytes 2

2

6

6

4

F ra m e D u ra t io n R e c e ive r A d d reTra s s n s m it t e r A d d reF sCsS C o n t ro l bits 2 2

4

1

1

1

1

1

1

P r o t o cT oy lp e S= u b T y p e T=o DR sTFSr o m D Ms o r e RF er at rgy P w r MM g omr et D Wa t Ea P O r d e r 0 C 0o n t r o1 l 1 0 1 0 0 0 0 0 0 0 1 0

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1

1

Duration field in RTS frame SIFS

Expected frame

RTS

transmission

station1 station2

CTS

ACK

SIFS

NAV

SIFS

Duration in RTS:3xSIFs+ACK+frametime

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CTS Frame MAC header

Bytes 2

2

6

Frame Control

Duration

Receiver Address

bits 2

2

4

4

1

FCS

1

1

1

1

1

1

P r o t o cT oy lp e S= u b T y p e T =o DCs TF Sr o m D Ms o r e RF er at rgy P w r MMg omr et D Wa t Ea P O r d e r 0 C 0o n t r o0 l 0 1 1 0 0 0 0 0 0 0 1 0

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1

CTS duration SIFS

RTS

Expected frame transmission

station1 station2

CTS

ACK

SIFS

NAV

SIFS

Duration in CTS:RTS-CTS-1xSIFS Duration in RTS:3xSIFs+ACK+frametime

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ACK Frame MAC header

Bytes 2

2

6

4

Frame Control

Duration

Receiver Address

FCS

bits 1 1 1 1 2 4 1 2 1 1 P r o t oT cy op l e S =u b T y p Te o =D sA C K F r0o m MD so r e R Fe rt ar yPg w r M og rme t WD aE t aPO r d e r 0 C o 0n t 1r o 0l 1 1 0 0 0 0 0 1 0

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1

Duration in non-final ACK frames SIFS fragmentX fragmentX+1

station1 station2

ACKX

ACKX+1

SIFS

SIFS

Station 1’s previous duration Duration in FragmentX=coverage to end of ACK+1 NAV

Station 2’s previous duration

Duration in ACKX=Fragment X duration-ACK1xSIFS

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PS-Poll Frame MAC header

Bytes 2 Fram e Control

bits 2

2

6

A s s oc iati B S S ID on ID (A ID)

2

4

6

4

Trans m itter A ddres sFCS

1

1

1

1

1

1

P r o t o cT oy lp e S= u b T y p e T=o DA sCF Kr o m D Ms o r e RF er at rgy P w r MMg omr et D Wa t Ea P O r d e r 0 C 0o n t r o0 l 1 0 1 0 0 0 0 0 0 0 1 0

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1

1

Generic Management Frame Information elements and Fixed fields

MAC header 2

2

6

6

6

2

F r a m eD u r a t iDo nA S A B S S ID S e q - C Ft lr a m e C o n tro l B ody

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0-2,312

FCS

4

Authentication Algorithm Number Field 16 Bits Authentication algorithm Least Significant number

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Most Significant

Authentication transaction sequence number field 16 Bits Authentication transaction Least Significant sequence number

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Most Significant

Beacon Interval Field 16 Bits Least Significant

Beacon interval

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Most Significant

Capability Information Field Bits ESS

IB S S C F - P o l la b leP r iva c Sy h o r t P B C C C h a n n e l aRg ei lsi t ey r ve d P r e a m b (l 8e 0 2 . 1 1( 8b 0) 2 . 1 1 b )

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Current AP Address Field Bytes Current AP (MAC)

Bit 0

Bit 47

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Listen interval Field Bits Least Significant

Listen interval

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Most Significant

Association ID Field Bits

1-13 Association ID

14

15

1

1

Most Significant

Least Significant

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Timestamp Field Bytes Least Significant

1-7 Timestamp

Bits 0

Most Significant

Bits 63

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Reason Code Field Bits Least Significant

Reason Code

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Most Significant

Status Code Field

Least Significant

Status Code

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Most Significant

Generic management frame information element

bytes

1

Length(in bytes)

1

E l e m e n t ID le n g t h

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Service Set Identity Information Element

Bytes

1

1

0-32

E l e m e nL te ID n g t hS S ID 0

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Supported Rates information element Element ID 1

length

Data rate label least most significant significant Mandatory

Data rate element

D a t a r a t e 1= 2 DM a bt ap 1Ms r a bt epo =sp 1t i o n a l 0

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FH Parameter Set information Element Bytes

1

1

2

1

1

1

E l e m eL ne tn gI DtDh w e l l HT oi mp eHs oe pt p Ha tot pe r Inn d e x 0 5

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DS Parameter Set information element Bytes

1

1

1

E l e m eL ne t n IDg t Ch u r r e n t 3 1 Channel

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Traffic Indication Map Information Element Bytes

1

1

1

1

2

2

E l e m Le en nt gI DCt h F P C Fo uP nC t F P MC FA PX D u r 3 1 P e r i oD du r a t iRo en m a i n i n g

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IBSS Parameter Set Information Element

Bytes

1

1

2

E le m e n Lt eIDn g t h A T IM 3 1 W in d o w

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Challenge Text Information Element

Bytes

1

1

1-253

E le m e n tL ID e n g t h C h a lle n g e 3 1 Tex t

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Beacon frame bytes

MAC header

2 2 F ra m e D u ra t io n c o n t ro l DA bytes

8

2

6

SA

2

6

6

2

4

Variable

B S S ID s e q c t rl F ra m e B o d y F C S

Variable

7

2

8

Tim e s t a mB pe a c o Cn a p a b ilit y FH DS CF IB S S In t e rva in l fo S S ID p a ra m e t e rspeatra m e t e rspeatra m e t e rspeat ra m e t e rsTIM et

Mandatory

optional

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4

Variable

Probe Request Frame Bytes 2

Frame body

MAC header 2

6

6

2

F r a m D e u r aD t iAo n S A B S S SI D e q -S c S t l I D C o n tro l

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Variable

Variable

S u p p o rte d F C S R a te s

4

Probe Response Frame bytes

MAC header

2 2 F ra m e D u ra t io n c o n t ro l DA bytes

8

2

6

SA

2

6

6

2

4

Variable

B S S ID s e q c t rl F ra m e B o d y F C S

Variable

7

2

8

Tim e s t a mB pe t w e e nC a p a b ilit y FH DS CF IB S S In t e rva l in fo S S ID p a ra m e t e rsp ea tra m e t e rsp ea tra m e t e rspeatra m e t e rs e t

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4

Variable

ATIM Frame Bytes 2

MAC header 2

F r a m De u r a Dt i Ao n C o n tro l

6

SA

6

6

2

B S S IDS e q - Fc Ct l S

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4

Disassociation and Deauthentication Frames Bytes 2

MAC header 2

F r a m De u r a Dt i oA n C o n tro l

6

SA

6

6

2

2

B S S ISD e q - Bc Ot l D YF C S

Bits Reason Code

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4

Association Request Frame MAC header

Bytes 2

2

6

6

6

2

2

Frame body 2

F r a Dm u e rDa At i oS n A B S SS eI DqC - a cp Lt a li sb Sit lei St ny I D C o n tro l In fo In t e r v a l

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variable

variable

S u p p o r t e Fd C S R a te s

4

Reassociation Request Frame Bytes 2

Frame body

MAC header 2

6

6

6

2

2

2

6

F r a mD ue r Da tA i o Sn A B S SS I eD q C - ac ptL la i sb ti Clei t nuy r r Se nS t I AD P C o n tro l I n f o I n t e Ar v da dl r e s s

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Variable

Variable

4

S u p p o rte dF C S R a te s

(Re)Association Response Frame Bytes 2

Frame body

MAC header 2

6

6

6

2

2

2

2

variable

F r a m D eu r Da tAi o n S A B S S SI De q -C ca tpl aS bt ai lAit tusy ss o Sc ui ap t pi oo nr t e d F C S C o n tro l I n f o c o d I De R a te s

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4

Authentication Frames Frame body

MAC header 2

2

F r a m e D u r a t io D An C o n tro l

6

6 SA

6

2

2

2

2

B S S ID S e q - c At l u t h e n t icAa ut iot hne n t i cSa t aiot un s C h a lle n g e A lg o r i t h m T r a n s a c t ioC no d e T e x t N u m b e r S e q .N o

©NetProWise

variable FCS

4

Overall 802.11 State Diagrams Class 1,2, and 3 frames

State3

Authenticated and Associated

Successful [re] association Class 1 and 2 frames or [re] association failure

Disassociation

State2

Authenticated and Unassociated

Successful [re] authentication Class 1 frames or authentication failure

Deauthorization

State1

Unauthenticated and Unassociated ©NetProWise

Deauthorization

Content 

Wireless LAN Overview  



Ethernet & TCP/IP Basics



Mobile & Wireless Basics



Introduction to IEEE 802.11  



IEEE 802.11 Media Access  



IEEE 802.11 Frame Format  



IEEE 802.11 Management Operations



IEEE 802.11 Physical Layers



IEEE 802.11 Deployment - Security 



Lab Exercises

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Two Approaches  

Wired Equivalent Protocol (WEP) IEEE 802.1X

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Security Objectives   

Confidentiality Authentication Integrity

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Cryptography with Wired Equivalent Protocol (WEP)  

Employs RC4 PRNG to Encrypt/Decrypt data RC4 PRNG   



 



Symmetric Algorithm 40 bit encryption key + 24 bit initialization vector 64 bit string is used as seed to PRNG to generate a “key sequence”

ICV (integrity check value) is computed for plaintext (CRC-32) ICV is concatenated to data stream Key Sequence is XORéd to data stream to create ciphertext. Ciphertext and IV (24 bits) are sent to receiver

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Generic Stream Cipher operation D ata 0 1 0 1 1 0 0 0 .

s ourc e K ey s tream 1 1 1 0 0 1 0 1 .

c iphers tream 1 0 1 1 1 1 0 1 .

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D es tination K ey s tream R ec eived data 1 0 1 1 1 0 0 1 0 1 1 0 0 0 1 0 . .

Keyed stream cipher operation

Source

Key

Destination

Cipher PRNG

Cipher text

Key

Cipher PRNG Data

Data XOR

XOR

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WEP operations – Confidentiality & Integrity 24-bitIV 40-bit WEP key

+

ICV

64-bitRC4 RC4 algorithm

=

Integrity check

RC4 key stream (as long as frame+ICV)

24-bitIV Cipher frame+ICV

Frame header

IV header (4bytes)

Clear

Frame Body

ICV trailer (4 bytes)

Encrypted

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FCS

Clear

WEP Keying  

Uses a set of up to four default keys May also use pairwise mapped keys

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WEP frame extension

IVheader

F ra m e In it ia lis a t io n In t e g r i t y c h e c k P a d K e y ID F ra m e b o d y FCS h e a d e r ve c to r V a lu e

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Limitations of WEP 

Integrity check 



  

Reuse of key stream is a major weakness IV field is not encrypted. Key distribution 

  



It is based on CRC, predictable; effective in finding single-bit alterations with high probability It should be based on hashing (unpredictable)

Key must be distributed to all stations participating in an 802.11 service set. 802.11 fails to specify a key distribution mechanism Manually configuring the keys is not scalable Users can view these keys

Keys can be accessed through SNMP interface!

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Some Solutions for WEP       

Change default key change WEP key frequently Password Protect Client Drives and Folders Change Default SSID Use Sessions Keys If Available Use MAC Filtering If Available Use A VPN

©NetProWise

Two Approaches  

Wired Equivalent Protocol (WEP) IEEE 802.1X

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IEEE 802.1x 

Based on IETF’s Extensible Authentication Protocol (EAP) – RFC 2284



Simply an Authentication protocol; Secrecy and Integrity are not provided



User is authenticated, however, the network is not authenticated; user might end up giving his/her credentials to the wrong network

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EAP Architecture Methods

TLS

AKA/ SIM

Token card

EAP EAP

Link Layers

PPP

802.3

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802.11

EAP Packet Format

Bytes

1

1

2

Variable

C o d eI d e n Lt ief i ne gr t Dh a t a

©NetProWise

EAP Request and Response Packets

Bytes 1

1

2

1

Variable C

e

d

o

e

d

I

t

n

i i

r

e

h

f

t

g

n

e

L

y

T

e

p

a

©NetProWise

p

y

t

a

D

-

e

2: Response

T

1: Request

EAP Success and Failure Frames Bytes

1

C ode

1

2

IdentifierL ength 3: Success

4

4: Failure

©NetProWise

Sample EAP Exchange Authenticator

End-User System

1:Request / Identity 2:Response / Identity 3:Request / MD5 - Challenge 4:Response/NAK,generic token card 5:Request/ Generic token card 6:Response/ Generic token card (bad) 7:Request/ Generic token card 8:Response/ Generic token card (good) 9:Success

©NetProWise

802.1x Architecture Authenticator Supplicant

EAPOL (PAE)

RADIUS

Authentication Sever

(PAE)

Enterprise edge/ ISP access

Enterprise Core/ ISP backbone

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EAPOL Frame Format MAC header Bytes

6

6

2

1

1

2

Des tination S ourc e E thernetV ers ionP ac k etP ac k etP ac k et A ddres s A ddres sTy pe 1 Ty pe B ody B ody 88-8E Length

©NetProWise

variable F CS

4

Typical EAPOL Exchange Authenticator

Supplicant

EAPOL

Radius

RADIUS

1:EAPOL - Start 2:Request / Identify 3:Response/ Identify 4:EAP - Request 5:EAP- Response

3:Radius – Access - Request 4: Radius – Access - Challenge 5: Radius – Access - Request

6:EAP- Success

6: Radius – Access - Accept

(Access allowed ) 7:EAP – Logoff (Access blocked ) ©NetProWise

EAPOL Exchange on an 802.11 Network Supplicant

Authenticator

802.11 1:Association request 2:Association response EAPOL

3:EAPOL - Start 4: Request / Identity 5:EAP- Response/ Identify 6:EAP- Request

Radius

RADIUS

3:Radius – Access - Request 4: Radius – Access - Challenge 5: Radius – Access - Request 6: Radius – Access - Accept

7:EAP – Response 8:EAP – Success 9:EAPOL – Key (WEP) ©NetProWise

802.11x Supporting Public Ethernet Ports Client

1: Authenticate

ISP RADIUS 6: Billing

Corporate Finance

4: Allow

2: Authenticate

5: Accounting

3: Allow

Internet

Corporate RADIUS

AP ©NetProWise

Content 

Wireless LAN Overview  



Ethernet & TCP/IP Basics



Mobile & Wireless Basics



Introduction to IEEE 802.11  



IEEE 802.11 Media Access  



IEEE 802.11 Frame Format  



IEEE 802.11 Management Operations



IEEE 802.11 Physical Layers



IEEE 802.11 Deployment - Security 



Lab Exercises

©NetProWise

Relationship Between Management Entities

MLME MAC

MAC MIB PLME

PHY

PHY MIB

©NetProWise

SME

Management Operations   

Scanning Scan Report Joining

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Scanning 



Scanning is the first activity when a station wants to join a service set. The following parameters are used in scanning:        

BSSType (independent, infrastructure, or both) BSSID (individual or broadcast) SSID (“network name”) Scan Type (active or passive) ChannelList ProbeDelay MinChannelTime MaxChannelTime

©NetProWise

Passive Scanning Client

Beacon ))))

AP1

AP2 Found BSSs: BSS1,AP1 BSS2,AP2 BSS3,AP3

AP3 AP4 )))) ©NetProWise

Active scanning Probe response Probe request

Mobile station (scanner)

DIFS

Minimum response time

Probe Request

SIFS

SIFS DIFS

ACKX

ACKX t

Probe Response AP1

Contention window

t

Probe Response

AP2 ©NetProWise

t

Scanning Report  

At the end of scanning a report is produced This report includes       



BSSID SSID BSSType Beacon interval (integer) DTIM period (integer) Timing parameters PHY parameters, CF parameters, and IBSS parameters BSSBasicRateSet

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Joining   

Joining is a precursor to association User intervention or automatic Automatic then the decision based on power level and signal strength

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Authentication

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Open- system authentication Exchange Client

1: Form – source (Identity) Authentication algorithm – 0 (open system) Sequence number - 1

AP

2:Authentication algorithm – 0 (open system) Sequence number – 2 Status code

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Shared-Key Authentication Exchange 1: Form – source (Identity) Authentication algorithm – 1 (Shared Key) Sequence number - 1

Client

2:Authentication algorithm – 2 (Shared Key) Sequence number – 2 Status code –0 (Successful) Challenge text (clear) AP

3:Authentication algorithm – 2 (Shared Key) Sequence number – 3 Challenge text

4:Authentication algorithm – 2 (Shared Key) Sequence number – 4 Status code

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Time savings of preauthentication 5

AP2

AP1

1

4 3

BSS1

BSS2

2 A. No preauthorization ©NetProWise

Scan Report     

Beacon interval DTIM period Timing parameters PHY parameters, CF parameters, IBSS parameters BSSBasicRateSet

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Joining 

Choosing which BSS to join  

User intervention Automatic

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Time Savings of Preauthentication 3 AP2

AP1

2

1.5 1

BSS1

BSS2

2 A. No preauthorization

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Association Procedure 1: Association request Client

2: Association response “Here is your association ID.”

3:Traffic AP

©NetProWise

Reassociation Procedure 1:Reassociation request “My old AP WAS..” Client

2: Reassociation response “I am your new AP, and here is Your new association ID.”

Old AP 3:IAPP “Please send Any buffered Frames for..”

5:(Optional ) “Here are some frames Buffered from your old AP New AP

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4: IAPP “Why certainly ..”

Reassociation with the same access point BSS

1

3: Reassociation Exchange 2

©NetProWise

AP

PS-Poll Frame Retrieval AP

PS-Poll

Time

Frame 1, more data

ACK PS-Poll Frame 1, more data

ACK PS-Poll Frame 2

ACK

©NetProWise

Buffered frame retrieval process Beacon interval TIM-Frame TIM-Frame for 1 for 1and2

TIM-Frame TIM-Frame for 2 for 1and2

TIM-No TIM-No Frame Frame Busy

t

AP Pspoll

Pspoll

t

CW frame

station1

Busy CW defer

station2

©NetProWise

t

Multicast and Broadcast buffer transmission after DTIMS

Beacon interval TIM

DTIM Interval DTIM

TIM BC

TIM

DTIM BC

MC

TIM

MC

AP

t

station1

t

©NetProWise

ATIM Usage ATIM “Don’t Sleep, I have data for you.”

A

C

B

a.Unicast or directional ©NetProWise

ATIM Usage ATIM “Don’t sleep, I have data for all Of you”

A

B

E

C

D

B. Multicast ©NetProWise

ATIM window

Target beacon times Peacon interval Busy ATM Window

ATM Window

ATM Window

©NetProWise

ATM Window

t

ATM effects on Power-saving modes Target beacon transmission

ATM Window

ATM Window

ATM Window

t

station1

©NetProWise

Effect ATIM on power-saving modes in an IBSS network ATM Window ATM to 2,3, and 4

ATM Window

Frame to 2,3, and 4

ATM Window Sleep

ATM Window Sleep

station1

t

ATM to 4 Frame to 4

Sleep

station2

t ATM to 4

ATM to 4 Frame to 4

station3

t ACK to 3 ACK to 2 Frame to 1

station4

ACK to 3

Frame to 3

t

©NetProWise

Matching the local timer to a network timer Beacon/ Probe Response

Timestamp + Local offset

Network Time

Local offset

Local timer

Time

Save TSF Value

Begin Join Process

©NetProWise

Distributed Beacon generation Awake period TBIT

Transmission canceled

station1

t Beacon

station2

t Transmission canceled

station3

t

©NetProWise

Content 

Wireless LAN Overview  



Ethernet & TCP/IP Basics



Mobile & Wireless Basics



Introduction to IEEE 802.11  



IEEE 802.11 Media Access  - Point Coordinated Function (PCF)



IEEE 802.11 Frame Format  



IEEE 802.11 Management Operations



IEEE 802.11 Physical Layers



IEEE 802.11 Deployment - Security 



Lab Exercises

©NetProWise

Using the PCF Contention-free repetition interval Contention-free period SIFS

SIFS

CFBeacon poll(to statio n1) Other

PC

NAV

Frame from #1 plus CFACK

PIFS CF-poll(to Station2)+ CF-ACK(to Station1)

SIFS

Data to Stn4+CFpoll

Contention period

CF-END t CF-ACK

SIFS

SIFS Set by Beacon

Released CF-End CFMaxduration

©NetProWise

t

Data+CF-Ack and Data+CF-poll usage CFP end DIFS CFP Frame

Beacon

Frame ACK SIFS

CP

ACK

t

SIFS CFP foreshortening CFPMaxduration

©NetProWise

Actual CFP start

Data + CF – ACK Usage SIFS

Mobile Station frames Access Point frames

Data + CF - ACK

Data + CF – Poll to MS1

SIFS

©NetProWise

Point Coordination resumes

Usage of Data+CF-ACK-ACK+CF-poll

SIFS

Mobile stations

Data+CF-ACK From MS1

Data+CF-ACK From MS2 Data+CF-ACK +CF-poll to MS2

Access points SIFS

©NetProWise

CF-poll framing usage

PIFS SIFS

SIFS

Mobile stations Access points

Data from MS2 CF-poll

CF-poll to MS2

©NetProWise

CF – ACK + CF – Poll Usage SIFS

Mobile Stations Access Points

SIFS

Data + CF – ACK From MS1 Data + CF - Poll to MS 1

Data From MS2 CF-ACK+ CF-Poll To MS2

SIFS

©NetProWise

CF- End Frame MAC header Bytes

2

2

6

4

6

Frame Duration Receiver Address BSSID FCS Control 00x00 - 0xFF-FF-FF-FF-FF 00

bits 2

2

4

1

1

1

1

1

P rotoc olTy pe = c ontrol S ub Ty pe = C F - E nd ToD s F rom D sM ore F ragR etry P w r M oreW E P O rder 0 01 0 0 1 1 1 0 0 0 0 M gm t D ata 0 0 0

©NetProWise

1

1

CF-End + CF – ACK Frame MAC header Bytes 2

2

6

4

6

Frame Duration Receiver Address BSSID FCS Control 00x00 - 0xFF-FF-FF-FF-FF 00

bits 2

2

4

1

1

1

1

1

P rotoc olTy pe = c ontrol S ub Ty pe = C F - E nd ToD s F rom D sM ore F ragR etry P w r M oreW E P O rder 0 01 0 + C F -A C K 0 0 0 0 M gm t D ata 0 0 0 1 1 1 0

©NetProWise

1

1

CF Parameter Set Information Element Bytes

1

Element ID

1 Length 6

1 CFP Count

1 CFP Period

CFP MaxDuration

©NetProWise

2 CFP DurRemaining

2

Mobile IP Network COA Home Network

Router HA

Router FA

MN Foreign network

Internet

CN

Router

©NetProWise

Packet Delivery 3 Home Network

Router HA

Router FA

2

MN 4

Internet 1

CN

Router

©NetProWise

Foreign network

Mobile Transport (TCP) Access Point 1

Socket Migration & State Transfer

Mobile Host

Access Point 2

©NetProWise

Internet

Next Generation WLAN – IEEE 802.11n

Comparing IEEE 802.11 Amendments

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IEEE 802.11b versus BlueTooth

©NetProWise

IEEE 802.11n       



IEEE 802.11g (up to 30 m & 54 Mbps) IEEE 802.11a (up to 30 m & 54 Mbps) IEEE 802.11b (up to 30 m & 11 Mbps) IEEE 802.11n (up to 50 m & 600 Mbps) Developed by IEEE Task Group n (TGn) Chip Vendors – Broadcom, Intel, Atheros, and Marvell. Switch and Adaptor Vendors – Belkin, D-Link, Linksys, and Netgear Some of the other vendors who are contributing to IEEE 802.11n – AirGo, Atheros, Intel, Nortel Networks, Panasonic, Philips Electronics, Qualcomm, Samsung, and Sony

©NetProWise

How IEEE 802.11n works   

Adds MIMO to the earlier 802.11g technology Makes use of the multi-path propagation. Bonds several existing channels for sending and receiving Object

Transmitter With MIMO Signal Processing

Antenna

Receiver With MIMO Signal Processing

©NetProWise

RadioTap 

What is RadioTap 



Addresses the limitations of PrismAVS header format 



Mechanism to exchange frame information between user application and driver

Using RadioTap arbitrary number of fields can be specified.

Example: One could specify/retrieve FCS for/from a frame.

©NetProWise

RadioTap Header The radiotap capture format starts with a radiotap header: struct ieee80211_radiotap_header { u_int8_t it_version; /* set to 0 */ u_int8_t it_pad; u_int16_t it_len; /* entire length */ u_int32_t it_present; /* fields present */ } __attribute__((__packed__));

©NetProWise

Some of the Header fields enum ieee80211_radiotap_type { IEEE80211_RADIOTAP_TSFT = 0, IEEE80211_RADIOTAP_FLAGS = 1, IEEE80211_RADIOTAP_RATE = 2, IEEE80211_RADIOTAP_CHANNEL = 3, IEEE80211_RADIOTAP_FHSS = 4, … IEEE80211_RADIOTAP_DBM_TX_POWER = 10, IEEE80211_RADIOTAP_ANTENNA = 11, IEEE80211_RADIOTAP_DB_ANTSIGNAL = 12, IEEE80211_RADIOTAP_DB_ANTNOISE = 13, IEEE80211_RADIOTAP_FCS = 14, IEEE80211_RADIOTAP_EXT = 31, };

©NetProWise

Important Characteristics of RadioTap 

   



Fields are in strict order (as they are specified in the it_present bitmask) Data is specified in little endian order Field Lengths are implicit Variable length fields are not supported If bit 31 of the it_present field is set, an extended it_present bit_mask is present Natural alignment field requirement – 16, 32,48, …

©NetProWise

Summary

©NetProWise

Summary Slide 

Mobile Transport (TCP)

©NetProWise

Historical background of FHSS Look at the notes section

©NetProWise

FHSS close

©NetProWise

Overview

Ethernet

BasicsWireless

©NetProWise

BasicsIEEE 802.11 Nextgen WLAN

Content 

Wireless LAN Overview  



Ethernet & TCP/IP Basics



Mobile & Wireless Basics



Introduction to IEEE 802.11  



IEEE 802.11 Media Access  



IEEE 802.11 Frame Format  



IEEE 802.11 Management Operations



IEEE 802.11 Physical Layers



IEEE 802.11 Deployment  



Lab Exercises

©NetProWise

Some TCP/IP Concepts          

Layering Protocol Data Units (PDUs) Encapsulation Multiplexing/Demultiplexing IP Address Class Domain Name System (DNS) Client-Server Model Some Tools Routing versus Switching Connection Oriented versus Connectionless

©NetProWise

TCP/IP Layers

Application/Layer

Transport Layer UDP or TCP Networking Layer (IP) Link Layer

Physical Layer

©NetProWise

Network

Protocol Data Units (PDU) & Encapsulation A p p lic a t io n D a t a message datagram segment

packet

IP Header

Ethernet IP Header frame Hdr

14

20

A p p lic a t io n A p p lic a t io n D a t a Header

TCP Header

TCP Header

TCP Header

application

Data

TCP

Data

Data

20 46-1500 ©NetProWise

IP Ethernet Trailer

Ethernet

4 Physical Medium

Demultiplexing and Multiplexing TCP Applications

UDP Applications

Stack/suite TCP ICMP

Port no

UDP

IGMP

… IPX

IP

Ethernet Incoming Frame ©NetProWise

ARP/RARP

Frame type

protocol type

Data Networks - Standards  

IEEE – 802.3, 802.5, 802.11, FDDC, … Internet Society (ISOC) 

Internet Architecture Board (IAB)    



IETF – Engineering Task Force IRTF – Research Task Force IANA – Assigned Number Authority InterNIC – IP Address distribution

Request for Comment (RFCs)

©NetProWise

Addresses used 

Four types are addresses are used:    



Domain Name IP Address Link Layer Address Port Number

They all complement each other in sending and receiving messages.

©NetProWise

Subnet 

Host A starting an FTP session with Server B.

Rest of the network

LAN segment 3

B

A

LAN segment 1

LAN segment 2

©NetProWise

Address Structure 

Domain name: yahoo, google, alcatel, etc.



Networking Layer Address - IP Address - unique, but likely to change and move 



Link Layer Address - MAC Address - unique & fixed 



Example: 192.168.1.128

Example: 08:56:27:6f:2b:9c

Port Numbers – Identifies individual program in a computer 

80

©NetProWise

Domain Name System (DNS) 







DNS permits meaningful host names to be used instead of host of IP addresses. It’s a distributed database that provides a mapping between host names and IP addresses. There is a function to do IP to host name, another function to do host name to IP mapping. www.touchtelindia.net maps to class C address 202.56.228.42.

©NetProWise

Port Address   

 



Identifies a service entity. 16 bit in size Well Known Server Ports - 0 to 1023 FTP Port 21, Telnet port 23 Registered Ports - 1024 to 49151 Dynamic or Ephemeral Ports – 49152 to 65535

©NetProWise

21

23

FTP

Telnet

TCP IP 192.168.0.1 Ethernet

00:50:eb:0e:14:7a

Ethernet

Client Server 

  



Networking applications are mostly client-server applications. Iterative server or Concurrent Server. Iterative server handles one client at a time. Concurrent server handles multiple clients concurrently. TCP servers are usually concurrent and UDP servers are usually iterative.

©NetProWise

IPCONFIG  

List IP configuration for a host Usage  



ipconfig ipconfig /all

Exercise 1: Explore different options of ipconfig. Find out ipconfig equivalent in Linux/Unix.

©NetProWise

Ping Command  

Checking for IP connectivity Usage:   



ping localhost ping ping

Loopback 127.0.0.1

Loopback Interface  

Used for Inter Process Communication (IPC) Loopback address 127.*.*.*

©NetProWise

Netstat

©NetProWise

ARP

©NetProWise

Networking Hierarchy     

Computer LAN segments Subnets Networks Interconnected Networks

©NetProWise

Subnet 

Host A starting an FTP session with Server B.

B

A ©NetProWise

Network    

Hosts and Router ports within a subnet share the same subnet ID. Subnet is a link layer broadcast domain Router is the gateway between subnets Router terminates subnet broadcast

192.168.1 192.168.2

Router Port 192.168.3 192.168.9 ©NetProWise

Packet Switching and Routing 1. Switching Network sender

receiver

X.25, ATM, FR

2. Routing

Network sender

©NetProWise

receiver

IP, IPX

Connection Oriented Messaging Establishes a dedicated pipe first exchange between A & B

A S Sequencing guaranteed S

S

S

S

S After the message exchange, pipe is removed

Global address not needed in message

No Need for big transfer tables ©NetProWise

Ideal for 1-to-1 communication

B

Connectionless Messaging No dedicated pipe between A & B Pipe is shared

A R Sequencing not guaranteed R

Global address needed R

R

R

R Inherently robust

Needs big transfer tables ©NetProWise

Ideal for 1-to-n communication

B

Connection Oriented & Connectionless Networking with IP  



IP is connectionless networking Both connection-oriented and connectionless transport could be offered on top IP. TCP is a connection-oriented protocol, UDP is connectionless protocol

©NetProWise

IP Packet Routing in a Subnet 1.

2.

3.

4. 5.

Host A checks if Server B is in the same subnet. It is. Host A sends a broadcast frame asking for the MAC address of Server B (IP Address). This request frame is seen by all hosts & servers within the subnet. Server B responds to Host A with its MAC address. Host A saves the Server’s IP address and MAC address in its ARP table and starts sending /receiving frames to/from Server B.

©NetProWise

ARP Table or ARP Cache  



ARP stands for Address Resolution Protocol Each entry in an ARP table contains an IP Address and the corresponding MAC Address. ARP entries live only for a short duration - 2 to 10 mins Microsoft Windows XP [Version 5.1.2600] (C) Copyright 1985-2001 Microsoft Corp.

C:\Documents and Settings\hari>arp -a

Interface: 10.0.0.224 --- 0x2 Internet Address

Physical Address

Type

10.0.0.2

00-80-c6-f9-29-a7

dynamic

C:\Documents and Settings\hari> ©NetProWise

Out of Subnet Packet Routing 1.

2.

3.

4.

5.

6.

Host A checks if Server B is in the same subnet. It is not. Host A sends a broadcast frame asking for the MAC address of Gateway (Router Port). This request frame is seen by all hosts & servers within the subnet. Router A responds to Host A with its Port 1 MAC address. Host A saves the Server’s IP address and Router Port 1 MAC address in its ARP table and starts sending /receiving frames to/from Router A. Router A Routes packets from host A to Server.

©NetProWise

Physical Layer 

Restricted to Wireline

©NetProWise

Network Interface Controller (NIC)

on

ne

ct

or

Ethernet Cables

IC



NIC Card RJ45 Connector, Cable

PC



RJ45 Socket

©NetProWise

RJ45 10Base-T

Crossover Cable RJ-45 PIN RJ-45 PIN 1 Rc+ 3 Tx+ 2 Rc6 Tx3 Tx+ 1 Rc+ 6 Tx2 Rc-

Straight Through Cable RJ-45 PIN RJ-45 PIN 1 Tx+ 1 Rc+ 2 Tx2 Rc3 Rc+ 3 Tx+ 6 Rc6 Tx©NetProWise

Notes Page

©NetProWise

Link Layer 

Responsible for  

Creating a frame and sending it to next node Receiving a frame and Processing it    

Error check Flow control De-multiplexing Class of Service

©NetProWise

Link Layers       

Ethernet IEEE 802 Encapsulation FDDI CDDI PPP SLIP ATM

©NetProWise

Serial Line IP (SLIP RFC 1055) 

Motivation

Versus

©NetProWise

SLIP Frame Format (RFC 1055) 

  

END (0xC0) and ESC (0xdb) are used to create the frame. No type field! IP address issue No Frame Check Sequence (FCS) or CRC!

IP Datagram c0 c0

db

db dc

©NetProWise

db dd

c0

PPP Motivated by the deficiencies of SLIP. Includes type field. IP address could be exchanged Includes Frame Check Sequence (FCS) or CRC!

©NetProWise

PPP Encapsulation Format (RFC 1548) flag 7E

addr FF

ctl 03

protocol

1

1

2

1

protocol 0021

Information

Upto 1500

CRC

flag 7E

2

1

IP Data gram

2

protocol C021

Link Control Data

2

protocol 8021

Escape Sequence: 7D and 5E 7E 7D

Network Control Data

2

©NetProWise

7D and 5D

Loopback IP Interface 127.0.0.1 is Loopback IP Interface. This allows a client to communicate with a server on the same host. Any packet sent to this IP address will be looped back to the same host from the host’s Link layer. DNS maps localhost to 127.0.0.1. Datagrams that are multicast and broadcast are looped back to localhost. Anything sent to host’s IP address is sent to localhost. Datagrams sent only to localhost do not appear on the network! ©NetProWise

Loopback Interface IP output function

IP input function

YES

Place on IP input Queue

Dest IP Multicast/Broadcast?

Place on IP input Queue

NO YES

Loopback Driver

Dest IP is local IP? NO

Ethernet Driver

IP ARP

send

Ethernet ©NetProWise

ARP

Demultiplex

receive

Local Area Network (LAN) 



Initial LANs provided connectivity between computers which are co-located within a short distance of few meters using shared medium. This solution of interconnecting computers does not scale well. Thus, it is still limited to computers that are in physical proximity.

©NetProWise

What is Ethernet?      

 

Ethernet is a LAN Link Layer Standard Most popular LAN standard Least Expensive Comes in Half-duplex and Full-duplex forms Comes in several speeds 10/100/1000/10000 Mbps Comes with several media options (wireless, fiber, coaxial, twisted pair,…) Wireless LAN variations 802.11x (CSMACA) Initial competition from Token Ring, later from ATM, now none!

©NetProWise

Ethernet History     



Developed by Xerox Corporation. Initially controlled by DEC, Intel, and Xerox. IEEE started its standardization in late 80s. IEEE 802.2 Specifies LAN Message Format. IEEE 802.3 Specifies Ethernet Hardware standard for Ethernet. Issue with Internet TCP/IP standard!

©NetProWise

Typical Ethernet Configuration

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Media Access – Carrier Sense Multiple Access Collision Detection (CSMA-CD) 

Sense the media (Carrier Sense). If the medium is idle, transmit, otherwise go to next step.



If the medium is busy, continue to listen until medium is idle, then transmit immediately.



If a collision is detected during transmission:





Transmit a jam signal for one slot.



Wait for a random time and reattempt (up to 16 times).



Random time generated according to exponential back-off .

Collision is detected by monitoring the voltage, high voltage ⇒ two or more transmitters are colliding. ©NetProWise

IP Layer

IPv4 Header Format (RFC 791)

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Subnet Addressing

subnetid

netid

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hostid

Subnets 

IP Address is divided into 3 parts 

 

Network Id, Subnet Id, Host Id

Subnet Id need not start on 8 bit boundaries Applies to Class A, B, and C

254 subnets

254 hosts

8-bits Subnet Id

8-bits Host Id

16-bits Net Id

Subnetting a Class B Address ©NetProWise

Subnet Mask    



Each host needs to know its IP addresses Host also must know its subnet Ids Subnet Id is Specified with 32 bit mask Subnet Mask is also represented by dotted decimal notation Examples: 16 bits

8 bits

8 bits

netid 11111111 11111111

subnetid hostid 11111111 00000000

netid 11111111 11111111

subnetid 1111111111 ©NetProWise

= 255.255.255.0

hostid 000000 = 255.255.255.192

Host Sending 



 

Host  knows its IP address and subnet id  knows its MAC address  knows its Gateway’s IP address Application provides Server’s  (Destination) IP address IP/Link Layer maintains ARP cache Server’s MAC address is required to complete the datagram

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Host Receiving IP datagrams  

IP layer on host can be configured to do routing in addition to acting as host When IP datagram is received, IP layer checks if the destination IP is one of its own IP addresses or an IP broadcast  

If so the datagram is delivered to protocol module specified in the protocol field in datagram If not then  If the host is configured as a router, then the datagram is forwarded using the IP routing table  Else the datagram is silently dropped

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Address Resolution Protocol (ARP) 











ARP finds the physical address of a host given its IP address by issuing an ARP broadcast within the subnet This information stored in ARP cache and used in IP datagram transmission ARP cache is a table where each entry contains host’s IP address and corresponding physical address ARP entries also contain host name and expiration counter. Default expiration time is 20 mins ARP command can be used to list the entries of an ARP cache - Example: arp –a ARP request timeout, Proxy ARP, Gratuitous ARP

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hostname

hostname

(1)

Resolver

FTP

IP address

(2)

Establish connection with IP address

TCP (4)

(5)ARP (6) ARP Request (Ethernet broadcast)

Ethernet Driver

ARP

(8)

Ethernet Driver

(3) IP (9)

Ethernet Driver

(7)ARP ©NetProWise

IP

Send IP datagram to IP address

IP Fragmentation 

Transport layer can send datagrams which are larger than MTU



Larger datagrams are fragmented at the source by IP layer



Assembled at the destination IP layer



Fragments can be fragmented recursively



IP fragmentation strongly discouraged!

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Characteristics of TCP  

Connection-oriented (state based) Reliable 



Exchanges Byte Stream 



Timeout, Buffering, Checksum, Acknowledge Different from message exchange, message transparent

Duplex

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TCP Header Format (RFC 793) IP Header

20

4

TCP Header

20

6

TCP Segment

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TCP data

18

TCP Message Flags 

    

SYN

Synchronize Sequence Numbers to initiate connection. RSTReset Connection. PSH Push data to receiving process ASAP. URG Urgent pointer is valid. ACK Acknowledgement is valid. FIN Sender is finished sending.

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TCP - Connection Establishment 1.

2.

3.

SYN: Requesting end (client) sends the destination port and source initial sequence number (ISN) with SYN flag Client set. 1. SY N ACK & SYN: The server ACKs this with its own ISN, the YN S , next expected sequence K C A 2. number from the client with SYN flag set. 3 . AC K ACK: The client must ACK this SYN with server’s ISN time plus 1.

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Server

TCP data flow

Client

Open Connection … databyt e

time

Ack for databyte databyte Ack for databyte

… Close Connection ©NetProWise

Server

TCP – Connection Termination 1. 2.

3. 4.

Server

FIN: Client sends a FIN ACK: Server ACKs client’s FIN FIN: Server sends a FIN ACK: Client ACKs server’s FIN

Client 1 . F IN

2. ACK

time

. . . 3. FIN 4 . AC

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K

Some TCP Terminologies 







Half-open: Server is waiting for SYN requests from client Half-close: Client has no more requests and sent its FIN and Server has even ACKed the FIN. But Server has some more data to send to the client. Active/Passive close: It is said that the first host to issue a FIN performs the active close , then the other and second one becomes the passive close. Maximum Segment Size (MSS)

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Sliding Window 

Sliding Window parameter is used to:  Guarantee the reliable delivery of data.  Ensure the that the data is delivered in order.  Enforces flow control between the sender and receiver.

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