A04 IEEE 802.11 Architecture

8/21/2019 A04 IEEE 802.11 Architecture

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A04 - IEEE 802.11 Architecture

IEEE 802.11 Architecture


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Module contents

IEEE 802.11 Terminology

IEEE 802.11 MAC Frames

Operational Processes

Configuration parameters


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IEEE 802 .11 Term ino logySTA (Station)

Station (STA) Architecture:

Device that contains IEEE 802.11

conformant MAC and PHY interface to the

wireless medium, but does not provide

access to a distribution system

Most often end-stations available in

terminals (work-stations, laptops etc.)

Implemented in ORiNOCO IEEE 802.11

PC-Card

Ethernet-like driver interface

supports virtually all protocol stacks

Frame translation according to IEEE Std

802.1H IEEE 802.3 frames: translated to 802.11 Maximum Data limited to 1500 octets

Transparent bridging to Ethernet

Platform

Computer

PC-Card

HardwareRadio

Hardware

WMAC controller with

Station Firmware

(WNIC-STA)

Driver

Software

(STADr)

802.11 frame format

802.3 frame format

Ethernet V2.0 / 802.3frame format

Protocol Stack


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IEEE 802 .11 Term ino logyAP (Access Point)

Access-Point (AP) Architecture:

Device that contains IEEE 802.11

conformant MAC and PHY interface to the

wireless medium, providing access to a

distribution system for associated stations

Most often infra-structure products that

connect to wired backbones

Implemented in ORiNOCO IEEE 802.11

PC-Card inserted in AP-500, AP-1000,

AP-2000

STAs select an AP and associate with it

APs :

Support roaming Provide time synchronization (beaconing)

Provide Power Management support

Bridge

Software

PC-Card

HardwareRadio

Hardware

WMAC controller with

Access Point Firmware

(WNIC-AP)

Driver

Software

(APDr)

802.11 frame format

802.3 frame format

Ethernet V2.0 / 802.3

frame format

Kernel Software (APK)

Bridge

Hardware

Ethernet

Interface


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IEEE 802 .11 Term ino logyBasic Service Set (BSS)

Basic Service Set (BSS):

A set of stations controlled by a single

Coordination Function (=the logical

function that determines when a station

can transmit or receive)

Similar to a cell in Cellular networkterminology

A BSS can have an Access-Point (both in

standalone networks and in building-wide

configurations), or can run without and

Access-Point (in standalone networks

only) Station-to-Station traffic is relayed by the

Access Point

BSS


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IEEE 802 .11 Term ino logyIndependent Basic Service Set (IBSS)

Independent Basic Service Set (IBSS):

A Basic Service Set (BSS) which forms a

self-contained network in which no access

to a Distribution System is available

A BSS without an Access-Point

Station-to-station traffic flows directly

without any relay action

All stations in the cell will be able to

receive frames transmitted by another

station in the cell (filtering of traffic for

subsequent processing is based on MACaddress of the receiver)

IBSS


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IEEE 802 .11 Term ino logyExtended Service Set (ESS) - Integrated DS

Extended Service Set (ESS):

A set of one or more Basic Service Sets

interconnected by a Distribution System

(DS)

Traffic always flows via Access-Point

Distribution System (DS): A system to interconnect a set of Basic

Service Sets

Integrated;A single Access-Point in a

standalone network

Wired; Using cable to interconnect the

Access-Points

Wireless; Using wireless to interconnectthe Access-Points

BSS


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IEEE 802 .11 Term ino logyExtended Service Set (ESS) - Wired DS




(DS)



Service Sets

Integrated; A single Access-Point in a

standalone network

Wired;Using cable to interconnect the

Access-Points

Wireless; Using wireless to interconnectthe Access-Points

BSS

BSS


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IEEE 802 .11 Term ino logyExtended Service Set (ESS) - Wireless DS




(DS)



Service Sets

Integrated; A single Access-Point in a

standalone network

Wired; Using cable to interconnect the

Access-Points

Wireless;Using wireless to interconnectthe Access-Points

BSS

BSS


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IEEE 802 .11 Term ino logySSID (Network name)

Service Set Identifier (SSID):

Network name

One network (ESS or IBSS) has one SSID

32 octets long string

Needed to separate one network from the

other Used during initial establishment of

communication between STA and AP to

allow STA to select the correct AP

Can be viewed as Security Provision in

combination with so-called Closed Option

(not providing the correct SSID means no

access to the network)

BSS

BSS

BSSID = xx-xx-xx-xx-xx-xx

BSSID = yy-yy-yy-yy-yy-yySSID = ABCD


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IEEE 802 .11 Term ino logyBSSID (Cell Identifier)

Basic Service Set Identifier (BSSID)

cell identifier

One BSS has one BSSID

6 octets long (MAC address format)

In ESS is the same as the MAC address of

the radio in the AP In IBSS the value of BSSID will be

randomly generated, and with local-bit on

Used as filter for multi-cast traffic and for

traffic from other networks (in IBSS

networks)

Used during hand-over (roaming) to other

AP, in identifying the old AP

BSS

BSS

BSSID = xx-xx-xx-xx-xx-xx

BSSID = yy-yy-yy-yy-yy-yySSID = ABCD


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IEEE 802.11 MAC FramesFrame Formats

MAC Header format differs per Type: Control Frames (several fields are omitted)

Management Frames

Data Frames

FrameControl

DurationID

Addr 1 Addr 2 Addr 3 Addr 4SequenceControl

CRCFrameBody

2 2 6 6 6 62 0-2312 4

802.11 MAC Header

Bytes:

Protocol

VersionType SubType

To

DSRetry

Pwr

Mgt

More

DataWEP Rsvd

Frame Control Field

Bits: 2 2 4 1 1 1 1 1 1 1 1

DS

From More

Frag


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IEEE 802.11 MAC FramesAddress Field Description

Addr. 1 = All stations filter on this address.

Addr. 2 = Transmitter Address (TA), Identifies transmitter to address the ACK frame to.

Addr. 3 = Dependent on Toand From DS bits.

Addr. 4 = Needed to identify the original source of WDS (Wireless Distribution System)

frames

Protocol

VersionType SubType

To

DSRetry

Pwr

Mgt

More

DataWEP Rsvd

Frame Control Field

Bits: 2 2 4 1 1 1 1 1 1 1 1

DS

From More

Frag

To DS

0

0

1

1

From DS

0

1

0

1

Address 1

DA

DA

BSSID

RA

Address 2

SA

BSSID

SA

TA

Address 3

BSSID

SA

DA

DA

Address 4

N/A

N/A

N/A

SA


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IEEE 802.11 MAC FramesType field descriptions

Type and subtype identify the function of the frame:

Type=00 Management Frame

Beacon (Re)Association

Probe (De)Authentication

Power Management

Type=01 Control Frame

RTS/CTS ACK

Type=10 Data Frame

Protocol

VersionType SubType

To

DSRetry

Pwr

Mgt

More

DataWEP Rsvd

Frame Control Field

Bits: 2 2 4 1 1 1 1 1 1 1 1

DS

From More

Frag


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IEEE 802.11 MAC FramesManagement Frames

Beacon

Timestamp, Beacon Interval,Capabilities, SSID, Supported Rates,parameters, Traffic Indication Map

Probe

SSID, Capabilities, Supported Rates

Probe Response Timestamp, Beacon Interval,

Capabilities, SSID, Supported Rates,parameters

same for Beacon except for TIM

Dis-association

Reason code

Authentication

Algorithm, Sequence, Status,

Challenge Text

Association Request

Capability, Listen Interval, SSID,

Supported Rates

Association Response

Capability, Status Code, Station ID,

Supported Rates Re-association Request

Capability, Listen Interval, SSID,

Supported Rates, Current AP

Address

Re-association Response

Capability, Status Code, Station ID,Supported Rates

De-authentication

Reason


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Operat ional processesAssociation

Process within an ESS where an STA establishes a relationship with an

AP

Before a STA can access an ESS, Association has to be completed

STA will scan the available channels in the 2.4 GHz band to select AP

(with matching SSID) that has the best communications quality

Active Scan (sending a Probe request on specific channels and assess response)

Passive Scan (assessing communications quality from beacon message)

AP maintains list of associate stations in MAC FW

Record station capability (data-rate)

To allow inter-BSS relay

Stations MAC address is also maintained in bridge learn table in theAccess Point associated with the port it is located on


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Operat ional processesAuthentication

Process within an ESS to control access to the network

Stations need to identify themselves to other Access-Points prior to data

traffic or association

Open System Authentication

Uses null authentication algorithm

Default

Shared Key Authentication

Uses WEP privacy algorithm

Optional


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Operat ional processesStarting an ESS

The infrastructure network is identified by its SSID (network name)

All APs have to be configured to use this SSID

ORiNOCO wireless stations will be configured to set their desired SSID to

the value of SSID configured in the APs

On power up stations will issue Probe Requests and will locate the APthat they will associate with:

best Access-Point with matching SSID

best Access-Point if the desired SSID has been set to ANY or a blank (empty)

string (known as the broadcast SSID


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Operat ional processesStarting an IBSS

Station configured for IBSS operation will: Scan the band (using Probe requests) using the SSID it was configured with

Received Probe Responses that match the SSID contain indication about sender of theProbe Response:

If sender is an AP, the station will associate to the AP

If sender is another STA in IBSS mode, the station will join this IBSS, and will

obtain the BSSID of the starter to be able to filter traffic (for network separation) When no Probe Responses are received with matching Network Name, Station will start

the IBSS network:

Set an BSSID (randomly generated, in MAC address format with local bit on)

Start sending Beacons

All Stations in an IBSS network will participate in sending beacons. All stations start a random timer prior to the point in time when next Beacon is to be

sent.

First station whose random timer expires will send the next beacon


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DIFSContention Window

Slot time

Defer Access

Backoff-Window Next Frame

Select Slot and Decrement Backoff as long

as medium is idle.

SIFS

PIFSDIFS

Free access when medium

is free longer than DIFS

Busy Medium

Operat ional processesTraffic Flow

On transmit:

STA that wants to send makes an Clear-

Medium check to see if the medium is

available

After Busy Medium condition has cleared,

STA will await for DIFS and contends for

the medium

When winning the contention, STA will

transmit the frame.

The Address 1 field of the frame contains:

The BSSID (when STA operates in an

ESS)

The MAC address of the recipient or a

Multi-cast address (when STA operates in

an IBSS)


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Operat ional processesTraffic Flow

On receive:

RF receivers on the same channel

will process first part of frame (Frame

header) and examine Address1 When the STA is in ESS operation and the

Addr1 is uni-cast it is matched to its own

MAC address, and accepted when the same

When the STA is IBSS operation and the

Addr1 is a uni-cast and matching its own

MAC address, Addr3 (the BSSID) is

compared to the BSSID obtained during

IBSS set-up (has to to be the same)

When Addr1 is multi-cast, the receiver will

accept the frame, when Addr3 (the BSSID)

matches the one obtained during association

to the AP or during IBSS creation

Uni-cast frames are replied to with

ACK after observing the SIFS period

Ack

Data

Next MPDU

Src

Dest

Other

Contention Window

Defer Access Backoff after Defer

DIFS

SIFS

DIFS

FrameControl

DurationID


CRCFrameBody

2 2 6 6 6 62 0-2312 4

802.11 MAC Header

Bytes:

To DS0

0

1

1

From DS0

1

0

1

Address 1DA

DA

BSSID

RA

Address 2SA

BSSID

SA

TA

Address 3BSSID

SA

DA

DA

Address 4N/A

N/A

N/A

SA


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Operat ional processesTraffic flow - bridging and relaying

STA-2

yyy

AP-500, AP-1000,

AP-2000

ORiNOCO PC-Card

Association table

Intra-BSS

Relay

Bridge learn table

MAC addr. Port #.

xxx

yyy

2

2

STA-1

STA-2

STA-1

xxx

On STA Association: STA is recorded in Association Table within PC

card FW

STAs MAC address is recorded in the Bridge

Learn table of the AP-500, AP-1000, AP-2000

correlated to the port is was detected on:

1 = Ethernet

2 = PC card (Slot-A on dual slot AP) 3 = PC card in Slot-B

4-15 = WDS ports (on AP-2000)

Intra-BSS traffic handled by FW in

PC Card, without consulting Bridge

Learn table except for: AP-2000 (always checks bridge table for port #)

AP-500/AP-1000 with so-called Access Controlenabled, to prevent non-authenticated STAs

accessing other stations in the BSS


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Operat ional processesTraffic flow - WDS operation

At this time implemented in the AP-2000

Up to 6 WDS links can be maintained by a

single ORiNOCO PC Card within the AP

Each link is associated with a separate

port within the bridge learn table

Linkage is established by identifying the

MAC address of the PC Card at the otherend of the link (at both ends)

Frames on the WDS link use all 4

addresses in the MAC header

Received frames transferred on the WDS

link are filtered on first address

Addr3 and Addr4 are used as addresspair in 802.3 frame and passed to bridge

Channel 6

Channel 11

Channel 1

FrameControl

DurationID


CRCFrameBody

2 2 6 6 6 62 0-2312 4

802.11 MAC Header

Bytes:

To DS0

0

1

1

From DS0

1

0

1

Address 1DA

DA

BSSID

RA

Address 2SA

BSSID

SA

TA

Address 3BSSID

SA

DA

DA

Address 4N/A

N/A

N/A

SA


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Operat ional processesTraffic flow - Intra-BSS

AP-500, AP-1000

ORiNOCO PC-Card

Association table

Intra-BSS

Relay

Bridge learn

table

STA-1

xxx

BSS-A

Associate

STA-2

yyy

AssociatePacket for STA-2ACK Packet for STA-2

ACK

xxx

STA-1

2

STA-2

yyy 2


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Operat ional processesTraffic flow - Inter-BSS with wired DS

STA-1

xxx

STA-2

yyyBSS-A

BSS-B

Packet for STA-2

ACK

Packet for STA-2

ACK

AP-500, AP-1000

or AP-2000

ORiNOCO PC-Card

Association table

Bridge learn

table

AP-500, AP-1000or AP-2000

ORiNOCO PC-Card

Association table

Bridge learntable

STA-1

yyy 1

xxx

yyy

xxx

2STA-2

2

1


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Operat ional processesTraffic flow - Inter-BSS with wireless DS

STA-1

xxx

STA-2

yyyBSS-A

BSS-B

Packet for STA-2

ACK

Packet for STA-2

ACK

AP-2000

ORiNOCO PC-Card

Association table

Bridge learn

table

AP-2000

ORiNOCO PC-Card

Association table

Bridge learntable

STA-1

yyy 4

xxx

yyy

xxx

2

STA-2

2

4

WDS Relay

Packet for STA-2

ACK

WDS Relay


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Operat ional processesCoalescence of IBSS networks

Different IBSS networks with same SSID

might exist, if cell members are out of

each others radio-range, when they start

up.

Two networks are shown with different

BSSIDs: BSSID-a and BSSID-b

Both networks are configured with the

same SSID (SSID-a)

BSSID-b

SSID-x

SSID-x

BSSID-a


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When a station moves it might get into

radio-range of a neighboring cell (from

BSSID-a to BSSID-b)

It will receive the Beacons from the

neighboring cell, and examines these for

the SSID.

It will find that these Beacons contain the

same SSID

Based on time-stamp information in all

Beacon messages received (fromBSSID-a and BSSID-b) the station might

decide to join the other networkBSSID-b

SSID-x

SSID-x

BSSID-a


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To join the network it will obtain the

BSSID from the frame header of the

Beacon message

Once joined it will participate in sending

beacons according to the coordination of

the new cell, and using the new BSSID

Other stations close to the last one that

joined the new cell, will be able to receive

the beacons now as well

BSSID-a

BSSID-b

SSID-x

SSID-x


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The process repeats itself and another

station might add itself to the network

This can continue until all stations might

have joined the cell

BSSID-b

SSID-x

SSID-x

BSSID-a


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The two cells have grown to one; this is

known as Coalescence.

When a station in this large cell will not

hear Beacons anymore (if no Beacons

have been received for 10 seconds), the

station assumes that it is alone and

restarts as IBSS station

Scans all channels

May find another AP or Station that sends

Probe Responses with matching SSID, and

connects

Or starts new IBSS (with new BSSID)

BSSID-b

SSID-x

SSID-x

BSSID-a

C fi ti P t


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Conf igu ration Parameters

ORiNOCO PC-Card are used in client station and Access Point, butbehaves differently based on the parent unit When inserted in AP- 500, AP-1000 or AP-2000, AP firmware is downloaded into the

PC-Card (Note: this is ORiNOCO/MAC FW, not Bridge FW)

When inserted in client station, STA firmware is active (default FW)

Requires different configuration parameter sets to support the

different behavior

Configuration can be performed by: Setting parameters at driver installation (Station)

Changing parameters in property settings via control panel on config file (Station)

Using ORiNOCO AP Manager (for AP-500, AP-1000)

Browser based configuration tool (AP-2000)

Using CLI procedures (All APs)


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Conf igu ration ParametersAP-500/1000/2000

Netwo rk Name (SSID)

ASCII string to identify the network that

the Access-Point is part of

Frequency (channel)

To indicate the frequency channel that the

AP-500/1000/2000 will use for its cell.

The channel is selected from the set thatis allowed in the regulatory domain.

Medium Reservat ion

To enable/disable the RTS/CTS

handshake.

Threshold value 0-2346 (value=2347

disables Medium Reservation)

Microwave Oven Robustness

Check box to enable/disable data-ratefallback delay-mechanism to allowimproved performance in presence ofmicrowave ovens

Distance between APs

To specify the coverage of a cell interms of the distance between the

Access-Points

Large

Medium

Small

Mult icast Rate

To specify data-rate used for transmittingMulticast frames


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Conf igu ration ParametersAP-500/1000/2000

Closed System (AP)

To enable rejection of association

requests from stations with Network

Name set to ANY

Enable Encrypt ion

To enable/disable Encryption

Encrypt ion keys Four fields to store up to four different

encryption keys

Encrypt ion key index

Index identifying which of the four keys isthe active one

WDS

MAC address of the corresponding AP in

a WDS link

DTIM

Power Management related parameter tospecify the timing of the delivery ofmulticast traffic to stations that haveindicated to receive multicast messageswhile under power management.

Example:

DTIM=1 means multicast traffic when itarrives at the AP is passed through afterevery beacon

DTIM=3 means multicast traffic is passedthrough after every 3rd beacon message

C fi ti P t


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Station parameters

Netwo rk Name (SSID)

ASCII string to identify the network thatthe station wants to connect to

Type of Operat ion

To identify the kind of network that the

station will be part of

Network centered around APs

Residential Gateway networks

IBSS (peer-to-peer network)

Card Power Management

Check box to enable/disable PowerManagement

Enable Encrypt ion

To enable/disable Encryption

Encrypt ion keys

Four fields to store up to four different

encryption keys

Entries take up to 5 ASCII or 10 hexa-

decimal values (when using 64 WEP)

Encrypt ion key index Index identifying which of the four keys is

the active one

Station parameters are specified per so-called profile

Up to 99 different profiles can be defined each having their set of parameters

Values for parameters that have a dependency on similar ones in the APs are dynamicallytransferred to the STA as part of the (re)-association response.

Parameters that can be entered locally:

C fi ti P t


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Dynamically assigned station parameters

Cell specific parameters are dynamically

transferred to the STA as part of the (re)-

association response.

Part of the Association response can be

Vendor defined

Agere OUI (= Organizational Unique

Identifier), identifies the frame asORiNOCO specific Value is x601D

Agere Element ID identifies the type of

information represented: Medium Density Parameters (x80)

Load Balancing Information (x81)

Capability

Info

2 bytes

Statuscode

2 bytes

Associatn

ID

2 bytes

Supported

Rates

3-11

bytes

Vendor

specificinfo

15

bytes

(Re) association response

Agere

ElementID

1 byte

Length

1 byte

AgereOU

I

3 bytes

Medium

Density

7 bytes

RTS/CTS

Threshold

2 bytes

interference

Robustness

1 byte

Cell Parameters

Conf ig ration Parameters


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Dynamically assigned station parameters

RTS/CTS Threshold

Interference Robustness switch

Medium Density Parameters:

Distance between APs

Energy Detect Threshold

Carrier Detect Threshold

Defer Threshold

Cell Search Threshold

Out of Range Threshold

Delta SNR

Capability

Info

2 bytes

Statuscode

2 bytes

Associatn

ID

2 bytes

Supported

Rates

3-11

bytes

Vendor

specificinfo

15

bytes

(Re) association response

Agere

ElementID

1 byte

Length

1 byte

AgereOU

I

3 bytes

Medium

Density

7 bytes

RTS/CTS

Threshold

2 bytes

interferenc

e

Robustness

1 byte

Cell Parameters

Module contents


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Module contents

IEEE 802.11 Terminology

IEEE 802.11 MAC Frames

Operational Processes

Configuration parameters


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Your Mobile Broadband Connection

A04 IEEE 802.11 Architecture

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