WLAN Power Save Modes

                Most of the Mobile devices like Laptops, Smart phones , and many more devices have battery crunch. As they will use more battery while using VOIP and Video applications on Wi-Fi.So they need to save the power when they are using in outside.So they use the power save techniques.

In WLAN we have 3 diffrent power save modes

1. Legacy power save mode
2. WMM power save mode
3. 11N power save mode

1. Legacy Power Save mode

• AP will manage the legacy power save mode clients by using the element id  "Traffic Indication Map(TIM)".
• The TIM shall identify the STAs for which traffic is pending and buffered in the AP. This information is coded in a partial virtual bitmap.
• TIM contain DTIM count and DTIM period for Multicast and Broadcast traffic.
• It will make use of "Traffic Indication Bit" , "Bit Map Offset" and "Partial Virtual Bmap" .
• Every AP  will have constant DTIM period and DTIM count will decrement for every Beacon.Whenever DTIM count reaches zero all the clients which are connected to that AP will wake up from Dozzing state.
• AP will send all Broadcast/Multicast traffic that is buffered in the AP.
• Every STA is assigned an AID by the AP as part of the association process. 
• AID 0 (zero) is reserved to indicate the presence of buffered broadcast/multicast MSDUs. 
• The AP shall identify those STAs for which it is prepared to deliver buffered MSDUs by setting bits in the TIM’s partial virtual bitmap that correspond to the appropriate AIDs.

See  below Diagram for the reference.

  See below picture for your reference for TIM in Beacon

In Legacy mode client will negotiate the "Listen interval" at the time of Association request. See below frame exchange in open authentication.

See below Association Request Frame which contains listen interval that will be negotiated during connection establishment.

• The client waits in receiving mode for a beacon frame from the base station. 
• The beacon frame includes Traffic Indication Map (TIM) information that tells the client whether there is any data available for download. 
• 
  

• If there is no data to download, the client can doze until the next beacon frame. 
• If there is data available, the client sends a PS-Poll (Power Save–Polling) frame to request a download of the data. After sending an acknowledgement frame, the access point starts transmitting frames with the data.

See below frame exchanges with PS-Poll messages.

• For each frame, the client sends a PS-Poll frame and an acknowledgement frame after the data has been received and receive an acknowledgement of its download request. 
• When the access point has downloaded the data to the client, it sends a bit in the last data frame that indicates it is the last. Upon receiving this, the client goes back to dozing mode.

Dis-advantages:

• A DCF (Distributed Coordination Function) delay is imposed between any two frames sent by the access point or the client, regardless of the type of traffic (e.g., voice, email downloading, or Internet browsing).
• As a result, for each data frame sent from the access point, two data frames are sent from the access point and from the client, and two DCF access delays are interleaved.
• Legacy power save operates in a ping-pong fashion that increases the latency for applications that require frequent data exchanges between the client and the access point, like VoIP, or voice and audio streaming. 

This is for several reasons:

•  The client has to wait for the beacon frame and cannot initiate transmission at shorter intervals.
•   Only one data frame is sent at a time and the client has to transmit and receive additional signalling frames for each data frame received.
• The dozing time is set by the client Wi-Fi driver regardless of which applications it runs, thus limiting the opportunity to tailor the client behaviour to the requirements of specific applications.

WMM power save mode and 11N power save will cover in separate topics.

Step by step process in connecting client to AP with dot1x

For connecting the client to AP with 802.1x involves sequence of steps. 
Below are sequence of steps.

1. Client started with Active scanning . Sends "Probe request"
2. AP responds with "Probe Response"
3. Client sends "Auth Request"
4. AP responds with "Auth Response"
5. Client sends "Assosiation Request"
6. AP responds with "Assosiation Resonse"
7. The station sends an "EAPOL - Start" message to the AP.This initiates the process of "EAP authentication".
8. The AP sends an "access request" on behalf of the client to the RADIUS server.
9. The AP replies with an "EAP Request/Identity" message.
10. The station sends an "EAP  Response/Identity" message containing its credentials (such as username) to the AP. This
 message will contain ID based on the EAP type such as "EAP-TLS", "EAP-TTLS", "EAP-PEAP", "EAP-LEAP", or "EAP-FAST".In a password-based EAP, the user.s password is NOT part of this
message.
11. The AP forwards the "user ID" to the "RADIUS server".
12. The "RADIUS server" responds with a "challenge message", which the access point forwards to the station as an EAP message.
13. The station encrypts the challenge message using its password (or other credential) as a secret key and sends the resulting value back to the AP.
14. The access point forwards the "encrypted challenge" to the "RADIUS server".
15. The RADIUS server uses the password (or other credential) that it has stored for the user to encrypt the same challenge message it sent to the station. If the resultant value and the value returned by
the station match, the RADIUS server sends a success message to the AP.
16. The AP forwards the "success/failure"  message to the station.
17. The station now sends a "challenge" to the "RADIUS server" to authenticate the AP (the network), and proceeds through the reverse authentication process.
18. If the network is successfully authenticated, the station passes a success message through the AP to the RADIUS server, which opens a port. The user is now LIVE on the network.
19. The station and RADIUS server each generate a dynamic unicast  key (which will match) from key material exchanged during the mutual authentication phase.
20. The RADIUS server sends the unicast WEP key to the AP in a RADIUS attribute. The attribute is encrypted using the shared key used between the AP and RADIUS server.
21. Now Client sends "DHCP" discover message if it is configured for DHCP IP address.
22. DHCP servers will respond with "DHCP offer " messages.
23. Client will respond for one of the "DHCP offer" Messages with "DHCP request"
24. Then corresponding "DHCP server" responds with "DHCP ACK" message for confirmation.
25. Now client is able to send data to the AP network.

Please see the above frame exchange for the sample 

802.11 Frame types

802.11 Frames are devided into three categories.

1. Managment Frames
2. Control frames.
3. Data Frames

1. Management Frames

•    Managment Frames are used by Wireless stations to join and Leave the Basic Service Set
•    Another name for Managment Frames is "MAC protocol Data Unit"(MMPDU)
•    There is no MSDU encapsulated in the MMPDU frame body , which carries only layer2 information fileds and information elements

   Following are the list of all 12 of the Managment frame subtypes as defined by 802.11 standard

    Assosiation Request
    Assosiation Response
    Reassosiation Request
    Reassosiation Response
    Probe request
    Probe Response
    Beacon
    Announcement Traffic Indication Message(ATIM)
    Disassosiation
    Authentication
    Deauthenication
    Action

2. Control Frames

•     802.11 Control frames assit with the delivery of the data frames. 
•     Control frames must be heard by all the stations, therefore they must be transmitted at one of the basic rates
•     Control frames are also used to clear the channel,acquire the channel and provide the unicast frame acknowledgements
•     They contain only header information

    Following are the list of control frame subtypes as defined by 802.11 standard

    Power Save(PS) Poll
    Request to Send (RTS)
    Clear to send (CTS)
    Acknowledgement(ACK)
    Contention-Free(CF)-End (PCF only)
    CF-End+CF-ACK (PCF only)
    Black-ACK(HCF)
    Black Ack Request(HCF)

3.Data Frames

•    Most of the Data Frames carry actual data that is passed down from higher layer protocols
•    Some 802.11 data frames contain no data at all but do have a specfific purpose within BSS
•    There are 15 data frame subtypes 

Data
Data+CF-Ack (PCF only)
Data+CF-Poll (PCF only)
Data+CF-Ack+CF-Poll (PCF only)
Null data (no data transmitted)
CF-Ack (no data transmitted) (PCF only)
CF-Poll (no data transmitted) (PCF only)
Data+CF-Ack+CF-Poll (PCF only)
Qos Data (HCF)
Qos Null (No Data) (HCF)
Qos Data+CF-Ack (HCF)
 Qos Data+CF-Poll (HCF)
 Qos Data+CF-Ack+CF-Poll (HCF)
Qos Cf-Poll(HCF)
Qos CF-ACK+CF-Poll (HCF)


See some of below combination for different frame types.

WLAN most common terms

In WLAN we use some common terms in explaning any scenarios. Below are the some of the most common terms that will be used in most of the time.

1. Basic Service Set (BSS)
2. Extended Service Set (ESS)
3. Independent Basic Service Set (IBSS)
4. Service Set Identifier(SSID)
5. Infrastructure mode
6. Adhoc Mode
7. Roaming


1. Basic Service Set (BSS)

     When one access point is connected to a wired network and a set of
wireless stations, the network configuration is referred to as a basic
service set (BSS).  A basic service set consists of only one access point
and one or more wireless clients, as shown in Figure .  A basic service
set uses "infrastructure mode" , a mode that requires use of an access point
and in which all of the wireless traffic traverses the access point.  No
direct client-to-client transmissions are allowed

2. Extended Service Set (ESS)

   An extended service set is defined as two or more basic service sets
connected by a common distribution system, as shown in Figure.
The distribution system can be either wired, wireless, LAN, WAN, or any
other method of network connectivity.  An ESS must have at least 2
access points operating in infrastructure mode.  Similar to a BSS, all
packets in an ESS must go through one of the access points.

3.Independent Basic Service Set (IBSS)

   An independent basic service set is also known as an "Ad hocnetwork".  An
IBSS has no access point or any other access to a distribution system, but
covers one single cell and has one SSID, as shown in Figure.  The
clients in an IBSS alternate the responsibility of sending beacons since
there is no access point to perform this task.
 

4. Service Set Identifier(SSID)

   The "Service set identifier" (SSID) is a unique, case sensitive, alphanumeric
value from 2-32 characters long used by wireless LANs as a network
name.  This naming handle is used for segmenting networks and in the process of joining a network.
The SSID value is sent in beacons, probe requests, probe responses, and other types of frames.  A client station must be configured for the correct
SSID in order to join a network.  The administrator configures the SSID
(sometimes called the ESSID) in each access point


5. Infrastructure mode
 
      In  "infrastructure mode" will use  an access point
and in which all of the wireless traffic traverses the access point.  No
direct client-to-client transmissions are allowed.

6. Adhoc Mode

          In this mode there will be no "Accesspoint" in that network. Communication will happen between the clients only directly.
Clients will send beacons between them for syncronization between them .


7. Roaming

   Roaming is the process or ability of a wireless client to move seamlessly
from one cell (or BSS) to another without losing network connectivity.
Access points hand the client off from one to another in a way that is
invisible to the client, ensuring unbroken connectivity.  Figure
illustrates a client roaming from one BSS to another BSS.
When any area in the building is within reception range of more than one
access point, the cells' coverage overlaps.  Overlapping coverage areas
are an important attribute of the wireless LAN setup, because it enables
seamless roaming between overlapping cells.  Roaming allows mobile
users with portable stations to move freely between overlapping cells,
constantly maintaining their network connection

 


 

Brief introduction of 802.11 standards from a -z

What is 802.11 Standards

IEEE 802.11, the Wi-Fi standard, denotes a set of Wireless LAN/WLAN standards developed by working group 11 of the IEEE LAN/MAN Standards Committee (IEEE 802). The term IEEE 802.11 is also used to refer to the original 802.11, which is now sometimes called "802.11 legacy.

IEEE 802.11 standard is continuously updated by means of amendments such as IEEE 802.11a, IEEE 802.11b etc. 802.11F and 802.11T are stand-alone documents, rather than amendments to the 802.11 standard.

Wi-Fi Alliance

• The Wi-Fi trademark, is intended to guarantee interoperability.
• Wi-Fi also includes the security standard Wi-Fi Protected Access or WPA.
• Eventually "Wi-Fi" will also mean equipment which implements the IEEE 802.11i security standard (also  known as WPA2).
• Products that say they are Wi-Fi are supposed to also indicate the frequency band in which they operate   (2.4 or 5 GHz).
• The most popular (and prolific) techniques are those defined by the b, a, and g amendments to the original  standard.
• Security was originally included and was later enhanced via the 802.11i amendment.
• 802.11n is another modulation technique under development. 
• Other standards in the family (c-f, h, j) are service enhancements and extensions or corrections to previous  specifications.
• 802.11b was the first widely accepted wireless networking standard, followed (somewhat counterintuitively) by 802.11a and 802.11g 

All of Amendments 802.11

IEEE 802.11 - The original 1 Mbit/s and 2 Mbit/s, 2.4 GHz RF and IR standard (1999) 

IEEE 802.11a - 54 Mbit/s, 5 GHz standard (1999, shipping products in 2001) 

IEEE 802.11b - Enhancements to 802.11 to support 5.5 and 11 Mbit/s (1999) 

IEEE 802.11c - Bridge operation procedures; included in the IEEE 802.1D standard (2001) 

IEEE 802.11d - International (country-to-country) roaming extensions (2001) 

IEEE 802.11e - Enhancements: QoS, including packet bursting (2005) 

IEEE 802.11F - Inter-Access Point Protocol (2003) Withdrawn February 2006 

IEEE 802.11g - 54 Mbit/s, 2.4 GHz standard (backwards compatible with b) (2003) 

IEEE 802.11h - Spectrum Managed 802.11a (5 GHz) for European compatibility (2004) 

IEEE 802.11i - Enhanced security (2004) 

IEEE 802.11j - Extensions for Japan (2004) 

IEEE 802.11k - Radio resource measurement enhancements 

IEEE 802.11l - (reserved and will not be used) 

IEEE 802.11m - Maintenance of the standard; odds and ends. 

IEEE 802.11n - Higher throughput improvements 

IEEE 802.11o - (reserved and will not be used) 

IEEE 802.11p - WAVE - Wireless Access for the Vehicular Environment (such as ambulances and 

                              passenger cars) 

IEEE 802.11q - (reserved and will not be used, can be confused with 802.1Q VLAN trunking) 

IEEE 802.11r - Fast roaming 

IEEE 802.11s - ESS Mesh Networking 

IEEE 802.11T - Wireless Performance Prediction (WPP) - test methods and metrics 

IEEE 802.11u - Interworking with non-802 networks (for example, cellular) 

IEEE 802.11v - Wireless network management 

IEEE 802.11w - Protected Management Frames 

IEEE 802.11x - (reserved and will not be used) 

IEEE 802.11y - 3650-3700 Operation in USA 

IEEE 802.11Z -Enhancements to DLS communications

IEEE 802.11 legacy

• IEEE 802.11 released in 1997
• Specifies two raw data rates of 1 and 2 (Mbit/s).
• It is infrared (IR) signals or by either Frequency hopping or Direct-sequence spread spectrum in                  the   Industrial Scientific Medical frequency band at 2.4 GHz. 

• IR remains a part of the standard but has no actual implementations.
• The original standard also defines Carrier Sense Multiple Access with Collision Avoidance                   (CSMA/CA) as the medium access method. 

      802.11 disadvantages

•       It offered so many choices that interoperability was sometimes challenging to realize.
• It is really more of a beta-specification than a rigid specification, allowing individual product vendors the

         flexibility to differentiate their products 

IEEE 802.11a

• It ratified in 1999.
• Operates in 5 GHz band.
• Uses a 52-subcarrier orthogonal frequency-division multiplexing (OFDM).
• Maximum raw data rate of 54 Mbit/s(mid-20 Mbit/s).
• The data rate is reduced to 48, 36, 24, 18, 12, 9 then 6 Mbit/s if required.
• 802.11a has 12 non-overlapping channels, 8 dedicated to indoor and 4 to point to point.
• Of the 52 OFDM subcarriers, 48 are for data and 4 are pilot subcarriers with a carrier separation of    0.3125 MHz (20 MHz/64).
• Each of these sub carriers can be a BPSK, QPSK, 16-QAM or 64-QAM. 

802.11a ad-dis advantages

• Less interference.
• It restricts the use of 802.11a to almost line of sight, necessitating the use of more access points
• It also means that 802.11a cannot penetrate as far as 802.11b since it is absorbed more readily, other   

           things (such as power) being equal.

IEEE 802.11b

• Ratified in 1999. 
• Maximum raw data rate of 11 Mbit/s.
• An application can achieve is about 5.9 Mbit/s over TCP and 7.1 Mbit/s over UDP. 
• 802.11b products appeared on the market very quickly.
• Since 802.11b is a direct extension of the DSSS (Direct-sequence spread spectrum) modulation                      technique defined in the original standard.

• Technically, the 802.11b standard uses Complementary code keying (CCK) as its modulation                  technique, which is a variation on CDMA.

• Hence, chipsets and products were easily upgraded to support the 802.11b enhancements.
• The dramatic increase in throughput of 802.11b (compared to the original standard) along with                  substantial price reductions led to the rapid acceptance of 802.11b.

802.11b advantages

•      Since the lower data rates use less complex and more redundant methods of encoding the data, they are less susceptible to corruption due to interference and signal attenuation.
•     Extensions have been made to the 802.11b protocol (for example, channel bonding and burst transmission techniques) in order to increase speed to 22, 33, and 44 Mbit/s.
•     But the extensions are proprietary and have not been endorsed by the IEEE.
•     Many companies call enhanced versions 802.11b+.
•    These extensions have been largely obviated by the development of 802.11g, which has data rates up to 56 Mbit/s and is backwards-compatible with 802.11b

IEEE 802.11g

• In June 2003,  802.11g. 
• This flavor works in the 2.4 GHz band (like 802.11b) .
• Maximum raw data rate of 54 Mbit/s, or about 24.7 Mbit/s net throughput like 802.11a.
• 802.11g hardware will work with 802.11b hardware. 
• Details of making b and g work well together occupied much of the lingering technical process. 
• The modulation scheme orthogonal frequency-division multiplexing (OFDM).
• The data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbit/s, and reverts to (like the 802.11b standard) CCK for 5.5 and 11 Mbit/s and DBPSK/DQPSK+DSSS for 1 and 2 Mbit/s. 
• The maximum range of 802.11g devices is slightly greater than that of 802.11b devices, but the range in which a client can achieve full (54 Mbit/s) data rate speed is much shorter than that of 802.11b.

IEEE 802.11n

• 802.11n builds upon previous 802.11 standards by adding MIMO (multiple-input multiple-output). 
• MIMO uses multiple transmitter and receiver antennas to allow for increased data throughput through spatial multiplexing and increased range by exploiting the spatial diversity, perhaps through coding schemes like Alamouti coding.

IEEE 802.11c

• IEEE 802.11c is a network interoperability standard that deals with bridging in wireless bridges or access points. This work is now part of IEEE 802.1D.
• This standard is complete and is a supplement to IEEE 802.1D that adds requirements associated with bridging the MAC layers.
• IEEE 802.1D that modifies this basic LAN standard to accommodate 802.11 frames. 
• In particular it adds a sub clause under 2.5 Support of the Internal Sublayer Service, to cover bridge operations with 802.11 MACs
• 802.1 covers the management features (and 802.1D specific to bridging) section of the overriding 802 LAN specifications.

IEEE 802.1D

• 802.1D is the IEEE MAC Bridges standard which includes Bridging, Spanning Tree, interworking for 802.11 and others. 
• It is standardized by the IEEE 802.1 working group.
• VLANs (virtual LANs) are not part of 802.1D, but specified in 802.1Q.

IEEE 802.11d

• The IEEE 802.11d standard is also referred to as the Global Harmonization standard.
• It is used in countries where systems using other standards in the IEEE 802.11 family are not allowed to operate.
• The standard defines physical layer requirements to satisfy regulatory domains not covered by the existing standards.
• In the other regulatory domains, the allowed frequencies, allowed power levels, and allowed signal bandwidth may be different.
• The specification eliminates the need for designing and manufacturing country specific products.
• Enabling IEEE 802.11d standard operation on the access point causes the AP to broadcast the ISO country code for the country it is operating in as a part of its beacons and probe responses. 
• If enabled, the client adjusts its frequencies, power levels and bandwidth accordingly
• This is particularly well suited for systems that want to provide global Roaming.

IEEE 802.11e

• IEEE 802.11e in 2005 .
• It defines a set of Quality of Service enhancements for LAN applications.
• The standard is considered of critical importance for delay-sensitive applications, such as Voice over Wireless IP and Streaming Multimedia.
• The protocol enhances the IEEE 802.11 Media Access Control (MAC) layer 

IEEE 802.11f

• IEEE 802.11F or Inter-Access Point Protocol is a recommendation that describes an optional extension to IEEE 802.11 that provides wireless access-point communications among multivendor systems .
• The 802.11 WG purposely didn't define this element in order to provide flexibility in working with different distribution systems (i.e., wired backbones that interconnect access points).
• The protocol is designed for the enforcement of unique association throughout an Extended Service Set and for secure exchange of station's security context between the current AP and the new AP during the handoff period. 
• Based on security level, communication session keys between APs are distributed by a RADIUS server.
• The RADIUS server also provides a mapping service between AP's MAC address and IP address.
• The 802.11F Recommendation has been ratified and published in 2003.

IEEE 802.11h

• IEEE 802.11h is the IEEE standard for Spectrum and Transmit Power Management Extensions. 
• It solves problems like interference with satellites and radar using the same 5 GHz frequency band.
• It was originally designed to address European regulations but is now applicable in many other countries.
• The standard provides Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) to the IEEE 802.11a MAC.
• DFS ensures that channels containing radar are avoided by an Access Point (AP) and energy is spread acoss the band to reduce interference to satellites. 
• TPC ensures that the average power is less than the regulatory maximum to reduce interference to satellites.

IEEE 802.11i

• IEEE 802.11i also known as WPA2.
• Is ratified on 24 June 2004.
• Supersedes the previous security specification, Wired Equivalent Privacy (WEP).
• WPA implemented a subset of 802.11i.
• The Wi-Fi Alliance refers to their approved, interoperable implementation of the full 802.11i as WPA2.
• 802.11i makes use of the Advanced Encryption Standard (AES) block cipher; WEP and WPA use the RC4 stream cipher.
• The 802.11i architecture contains the following components: 802.1X for authentication (entailing the use of EAP and an authentication server), RSN for keeping track of associations, and AES-based CCMP to provide confidentiality, integrity and origin authentication. 

IEEE 802.11j

• The 802.11j standard Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: 4.9 to 5 GHz Operation in Japan.
• Finalized in 2004.
• The standard works in the 4.9 GHz to 5 GHz band to conform to the Japanese rules for radio operation for indoor, outdoor and mobile applications.
• 802.11j defines uniform methods that let APs move to new frequencies or change channel width for better performance or capacity -- for example, to avoid interference with other wireless applications.
• In the USA, the 4.9 GHz band is reserved for use by public safety wireless applications. 
• The transmission mask is narrower for the public safety band than for consumer part 15 applications. 

IEEE 802.11k

• IEEE 802.11k is a proposed standard for radio resource management.
• It defines and exposes radio and network information to facilitate the management and maintenance of a mobile Wireless LAN. I
• EEE 802.11k and IEEE 802.11r are the key industry standards now in development that will enable seamless Basic Service Set (BSS) transitions in the WLAN environment.
• The 802.11k standard provides information to discover the best available access point.
• 802.11k is intended to improve the way traffic is distributed within a network. 
• In a network conforming to 802.11k, if the AP having the strongest signal is loaded to its full capacity, a wireless device is connected to one of the underutilized APs.
• Even though the signal may be weaker, the overall throughput is greater because more efficient use is made of the network resources.
• It is anticipated that the standard will be ratified by 2Q 2007.

IEEE 802.11m

• IEEE 802.11m is an initiative to perform editorial maintenance, corrections, improvements, clarifications, and interpretations relevant to documentation for the IEEE 802.11 family specifications.
• The term 802.11m also refers to the set of maintenance releases itself.
• The 802.11m initiative, sometimes called 802.11 housekeeping or 802.11 cleanup, was begun in 1999 by IEEE Task Group M, a part of the IEEE 802.11 Working Group.

IEEE 802.11o - (reserved and will not be used)

IEEE 802.11p

• IEEE 802.11p also referred to as Wireless Access for the Vehicular Environment (WAVE) defines enhancements to 802.11 required to support Intelligent Transportation Systems (ITS) applications.
• This includes data exchange between high-speed vehicles and between these vehicles and the roadside infrastructure in the licensed ITS band of 5.9 GHz (5.85-5.925 GHz).
• 802.11p will be used as the groundwork for DSRC (Dedicated Short Range Communications), a US Department of Transportation project - which will be emulated elsewhere - looking at vehicle- based communication networks, particularly for applications such as toll collection, vehicle safety services, and commerce transactions via cars. 
• The ultimate vision is a nationwide network that enables communications between vehicles and roadside access points or other vehicles. 
• The work builds on its predecessor, ASTN a2213-O3.
• The 802.11p Task Group is still active. 

IEEE 802.11q - (reserved and will not be used, can be confused with 802.1Q VLAN trunking)

IEEE 802.11r

• Specifies fast BSS (Basic Service Set) transitions. 
• This will permit connectivity aboard vehicles in motion, with fast handoffs from one base station to another managed in a seamless manner. 
• Handoffs are supported under the a, b and g implementations, but only for data (using IEEE 802.11f or Inter-Access Point Protocol commonly known in the wireless circles as IAPP). 
• The handover delay is too long to support applications like voice and video.
• The primary application currently envisioned for the 802.11r standard is VOIP (voice over IP, or Internet-based telephony) via mobile phones designed to work with wireless Internet networks, instead of (or in addition to) standard cellular networks.
• The delay that occurs during handoff cannot exceed about 50 msec, the interval that is detectable by the human ear.
• However, current roaming delays in 802.11 networks average in the hundreds of milliseconds.
• This can lead to transmission hiccups, loss of connectivity and degradation of voice quality. 
• Faster handoffs are essential for 802.11-based voice to become widely deployed.
• Another problem with current 802.11 wireless gear is that a mobile device cannot know if necessary QoS resources are available at a new
• The protocol allows a wireless client to establish a security and QoS state at a new access point before making a transition, which leads to minimal connectivity loss and application disruption. 
• The overall changes to the protocol do not introduce any new security vulnerabilities. This preserves the behavior of current stations and access points.
• Under 802.11r, clients can use the current access point as a conduit to other access points, allowing clients to minimize disruptions caused by changing channels.
• Until that time, however, enterprises will need to use proprietary hardware from vendors such as SpectraLink to get fast roaming for applications such as VoIP. 
• More secure encryption types such as TKIP or AES-CCM (CCMP) involve handshakes that happen after association, and they can typically take 30-40 milliseconds, potentially disrupting the call.

IEEE 802.11s

• 802.11s is the unapproved IEEE 802.11 standard for ESS Mesh Networking. 
• It specifies an extension to the IEEE 802.11 MAC to solve the interoperability problem by defining an architecture and protocol that support both broadcast/multicast and unicast delivery using radio-aware metrics over self-configuring multi-hop topologies.
• The purpose of the project is to provide a protocol for auto-configuring paths between access points over -configuring multi-hop topologies in a Wireless Distribution System (WDS) to support both broadcast/multicast and unicast traffic in an ESS Mesh using the four-address frame format or an extension.
• The call for proposals (CFP) for 802.11s ended in June 2005.

IEEE 802.11t

• The IEEE 802.11T is also referred to as the Wireless Performance Prediction (WPP) - test methods and metrics recommendation.
• Given the complexity of the IEEE 802.11 family of protocols, a test specification is particularly important so that products specifications and performance can be ascertained.
• The capital T in the name shows this is a recommended practice and not a standard.
• The goal of the 802.11T project is to provide a set of measurement methods, performance metrics, and test recommendations that enable manufacturers, independent test labs, service providers, and end users to measure the performance of IEEE 802.11 standard equipment and networks

IEEE 802.11u

• IEEE 802.11u to add features that improve interworking with external networks.
• IEEE 802.11u covers the cases where user is not pre-authorised.
• A network will be able to allow access based on the user's relationship with an external network (e.g. hotspot roaming agreements), or indicate that online enrollment is possible, or allow access to a strictly limited set of services such as emergency calls.
• Instead of being presented with a long list of largely meaningless SSIDs the user could be presented with a list of networks, the services they provide, and the conditions under which the user could access them.
• The IEEE 802.11u Proposal Requirements Specification contains requirements in the areas of enrolment, network selection, emergency call support, user traffic segmentation, and service advertisement.
• The 802.11u standard is in its proposal evaluation stages 

IEEE 802.11v

• IEEE 802.11v is the Wireless Network Management standard for the IEEE 802.11 family of standards.
• TGv is working on an amendment to the IEEE 802.11 standard to allow configuration of client devices while connected to IEEE 802.11 networks. 
• The standard may include cellular-like management paradigms.
• The 802.11v standard is still in its early proposal stages.

IEEE 802.11w

• IEEE 802.11w is the Protected Management Frames standard for the IEEE 802.11 family of standards. 
• TGw is working on improving the IEEE 802.11 Medium Access Control layer to increase the security of management frames.
• Wireless LANs send system management information in unprotected frames, which makes them vulnerable. 
• This standard will protect against network disruption caused by malicious systems that forge disassociation requests that appear to be sent by valid equipment.
• It is expected that 802.11w would extend IEEE 802.11i to apply to 802.11 management frames as well as data frames. 
• These extensions will have interactions with IEEE 802.11r and IEEE 802.11u [1]

IEEE 802.11x - (reserved and will not be used)

IEEE 802.11y

• IEEE 802.11y is the Contention Based Protocol .
• In July 2005, the FCC opened up the use of the 3.65-3.7 GHz band for public use, previously reserved for fixed satellite service networks.
• TGy will be working on amendments to IEEE 802.11 for operation in the 3650-3700 MHz Broadband Wireless Services allocation.
• IEEE 802.11y provides a standardized interference avoidance mechanism. 
• 802.11y also streamlines the adoption of new frequencies in the future.
• The PAR and Five Criteria for 802.11Y (Contention Based Protocols) were approved by ExCom in November 2005. 
• The 802.11y standard is in its early proposal stages.

IEEE 802.11z

The purpose is establish and standardize a Direct Link Step (DLS) mechanism to allow operation with non-DLS capable access-points.

DLS allows client stations to bypass the access-point and communicate with direct frame exchanges.

IEEE 802.11aa

Enhancements to 802.11 Media Access Control (MAC)  for robust audio streaming while maintaining  coexistence with other types of traffic.

Notes : all the above information is understanding from my previous readings.It may change over the period of time.

First check how much you know on WLAN?

Before writing the different topics for different WLAN concepts. I am starting with questions on WLAN. So that you know where you stand. Below are some of the frequently asking WLAN interview questions. See how much you know.



1. what are main diff between 11n and 802.11a/b/g feaures ?
2. what is A-MPDU and A-MSDU . Diffrence between them ?
3. what is lenghts supported on A-MSDU and A-MPDU ?
4. what are diffrences between a,b and g in range ,speed and all other aspects ?
5. How DFS will work ?
6. What are diff frames that will be exchanged at the time of channel switch announcement ?
7. what is dis-assosiation and de-authentication when they will happen ?
8. What is  diffrence between wpa1 and wpa2 auth key managemnet and how we can diffrentiate whther its psk or 802.1x ?
9. what are diffrenrent fileds in the  beaccon frames ?
10.what are three diffrent regulatory domains? what are the channels supported ?
11.what are rdaios suppotred in J domain?
12 what are diff auth methods supported in 802.1x ?
13. How client know open+none and open+wep ?
14. How legacy power save and u-apsd will work ?
15  How many AID's will support ?
16. How TXOP,ESOP will work ? when they will be negotiated ?
17. How fragmentation will affect with rts thresold it is configured on the AP.
18. What are address will update when frame sent from wired client to wireless client adress1 ,address2 and address3.
19. What is EIFS and what is the interval used ?
20. How RTS and CTS frame wil be sent how frgamentation thresold will impact ?
21. what are wps methods and how iot will work ?
22. what are values of throughput thresold getting with b/g network ?
23. How cckm will work ? what is wds ?
24. How leap will work ?
25. 802.1x process for leap ?
26. Four way hand shake process in 802.1x?
27. How PTK and GTK derived and what are the speps ?
28. what are different types of inter frame spacing ? which will be used and when ?
29. when will be used SIFS and DIFS ,EIFS ?
30. Why we need Qos and what are advantages of QOs ?
31. What are diffrent parameters involved in qos ?
32. How TXOP will work for sending the data ?
33. When we use wpa2 psk with wrong pass phrase which level it will fail ?
34. How A-nounce and S-nounce will be derived ?
35. What is MIMO ? how 2*3 antenna will work ? how 3 recievers will work ?
36. what is antennas diversity ?
37. With 2*3 what is maximum bandwidth we will get ?
38. For MCS what are the parameters will involved /
39. How b/g protection will work ?
40. What are diffrent types of power saves ? tell about legacy and u-apsd ?
41. How we can know wheter it is MSDU or A-msdu data ?
42. What will be fields of qos control data ?
43. What is guard interval ? how its implemented ?
44. what is need of preambles ? IFS ? guard intervals ?
45. What is hidden ap ?
46. What is hidden ssid how it will work ?
47. How erp protection will work ?
48. What is for ground scanning and what is back ground scanning ?
49. How 11n WPA TKIP will work ?
50. How DTIM will work ?
51. What is number of handshakes will happen in wpa1 and wpa2 ?
52. What are data rates used for ACK ? multicast ?
53. Diffrent type of data rates like basic ,supported ?
54. When open authentication it self will fail ?
55. When assosiation will fail ?
56. What is diff between ap reboot and radio reset actions ?
57. How 40/20 and 20 mhz co-location will work ?
58. What are diffrent types of ack mechanism used with A-msdu and A- mpdu ?
59. What is ATIM and how it will work ?
60. What are mandatory rates for a,b,g?
61. Diff between wep and TKIP ?

62. Will the force Change in centre frequency of channel effect the throughput?

63. what is the difference between pep0 and peap 1?
64. 1In WPA2 mixed what is the Group Wise Cipher and pairwise cipher used
65. What is the difference between AES and TKIP encryption in EAPOL handshake?
66. What replay protection mechanism?
67. In DFS is there is radar  signal  on 48 and client moved to next DFS 58.If radar seen in 58 will the client move to different DFS channel or move back to 48?
68. What is the Broadcast address for 192.168.1.10 with mask 255.255.255.0?
69.  What are the messages seen on wireshark when EAPOL 802.1x authentication is happening?
70. Which all the authentication does IAS server support?
71. What are software used in WMM-PS?
72. If the IP addrees class is changed from Class C to Class B in WMM-PS will there be any setup issues?
73  With 1x1,20Mhz,Long GI what is the Data Rate the client supports?
74  Which MCS index /Long GI 65Mbps is achievable?By configuring it to shortGI what is the difference in throughtput?
75. What are Different 11n Modes?



I will keep on adding what ever possible.