1. OSI
Model
All People Seem To Need Data Processing
All People Seem To Need Data Processing
All - Application
People - Presentation
Seems - Session
People - Presentation
Seems - Session
To - Transport
Need - Network
Need - Network
Data - Data
Processing - Physical
2. Full
Form of WiFi?
Wireless
Fidelity.
3. Example
of other IEEE standards?
802.3 is a standard specification for Ethernet, a method of physical communication in a local area network (LAN), which is maintained by the Institute of Electrical and Electronics Engineers (IEEE). In general, 802.3 specifies the physical media and the working characteristics of Ethernet.
802.3 is a standard specification for Ethernet, a method of physical communication in a local area network (LAN), which is maintained by the Institute of Electrical and Electronics Engineers (IEEE). In general, 802.3 specifies the physical media and the working characteristics of Ethernet.
4. Standards of WiFi?
IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specifications for implementing wireless local area network (WLAN) computer communication in the 900 MHz and 2.4, 3.6, 5, and 60 GHz frequency bands
IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specifications for implementing wireless local area network (WLAN) computer communication in the 900 MHz and 2.4, 3.6, 5, and 60 GHz frequency bands
5. Wireless Stations?
All wireless devices that join a Wi-Fi network, whether mobile, portable or fixed, are called wireless stations (STAs). A wireless station might be a PC, a laptop, a PDA or a phone.
All wireless devices that join a Wi-Fi network, whether mobile, portable or fixed, are called wireless stations (STAs). A wireless station might be a PC, a laptop, a PDA or a phone.
6. AP?
AP stands for access point. An AP is a wireless station (STA) with additional functionality.
AP stands for access point. An AP is a wireless station (STA) with additional functionality.
A
major role of an AP is a to extend access to wired networks for the clients of
a wireless network.
7. Basic Service Set?
When two or more STAs are wirelessly connected, they form a basic service set (BSS). This is the basic building block of a Wi-Fi network.
When two or more STAs are wirelessly connected, they form a basic service set (BSS). This is the basic building block of a Wi-Fi network.
8. Co-Ordination Function?
The Coordination Function (CF) is a logical function that determines when a STA transmits and when it receives. A basic service set (BSS) is a set of STAs controlled by a single coordination function (CF).
The Coordination Function (CF) is a logical function that determines when a STA transmits and when it receives. A basic service set (BSS) is a set of STAs controlled by a single coordination function (CF).
9. Why Coverage area is Oval?
While a circle may represent the idealized coverage area of a single radio, it is not very accurate in real world situations. Environmental factors cause dramatic variations to the coverage area. For example, a STA with an omnidirectional antenna placed in the corner of a building may have most of its coverage area outside the building and in the adjacent parking lot.
While a circle may represent the idealized coverage area of a single radio, it is not very accurate in real world situations. Environmental factors cause dramatic variations to the coverage area. For example, a STA with an omnidirectional antenna placed in the corner of a building may have most of its coverage area outside the building and in the adjacent parking lot.
10. Operating Mode's of WiFi?
There are 2 operating modes of WiFi according IEEE 802.11 standard
a. ad-hoc mode
There are 2 operating modes of WiFi according IEEE 802.11 standard
a. ad-hoc mode
b. infrastructure mode
The
operating mode is selected during the configuration of the wireless station , all
wireless stations must select an operating mode before
attempting to create or join a Wi-Fi network
11. Ad-hoc mode?
This
is peer to peer mode . Each wireless node can communicate directly with each of
the other nodes in the network (without wireless Access Point). It follows MESH
network topology. Independent Basic Service Set (IBSS) , a group of nodes communicating in ad-hoc mode.
12. Infrastructure Mode?
All wirless node or stations
communicate to one another via Wireless Access Point.
Follows STAR network tropology. Basic
Service Set (BSS) a group of nodes communicating in infrastructure mode. A BSS
has one wireless access point . Extended Basic Service Set (EBSS) two or more
BSS that can communicate to one another. An EBSS contains two or more Aireless
Access Point.
13. BSS , IBSS, EBSS, ESS?
BSS- Basic Service Set
Basic Service Set (BSS) a group of
nodes communicating in infrastructure mode. A BSS has one wireless access point.
IBSS- Independent Basic Service Set
IBSS- Independent Basic Service Set
Independent
Basic Service Set (IBSS) , a group of nodes
communicating in ad-hoc mode.
EBSS- Extended Basic Service Set
Extended Basic Service Set (EBSS)
two or more BSS that can communicate to one another. An EBSS contains two or
more Aireless Access Point.
ESS- Extended Service Set
14. Distributed System (DS)?
All
wireless devices trying to join the BSS must associate with the AP. An AP
provides access to its associated STAs
to what is called the distribution system (DS). The DS is an architectural component that allows communication among APs.
The
IEEE 802.11 specification does not define any physical characteristics or
physical implementations for the
DS. Instead, it defines services that the DS must provide.
15. Extended Service Set (ESS)?
A common distribution system (DS) and two or more BSSs create what is called an extended service set(ESS). An ESS is a Wi-Fi network of arbitrary size and complexity. In figure a representation of an ESS comprised of BSS 1,2,3.
A common distribution system (DS) and two or more BSSs create what is called an extended service set(ESS). An ESS is a Wi-Fi network of arbitrary size and complexity. In figure a representation of an ESS comprised of BSS 1,2,3.
The
Distribution System (DS) is not part of the ESS.
The
network name, or SSID, must be the same for all APs participating in the same
ESS.
16. Understanding with Five layer TCP
Model
IEEE 802.11
and it's extension defines only two layers in the five layer TCP.
Data Link Layer and Physical Layer.
This are the same two layer which has been defined by IEEE 802.3 (Ethernet).
Data Link Layer and Physical Layer.
This are the same two layer which has been defined by IEEE 802.3 (Ethernet).
Here Data
Link Layer is comprised of two sub layer - Logical Link Control (LLC) and Media
Access Control (MAC).
IEEE 802.11 specification defines MAC sub layer and Physical Layer.
IEEE 802.11 specification defines MAC sub layer and Physical Layer.
17. IEEE 802.11 Media Access Control
Layer - MAC
Here
MAC layer is technically a sub layer of Data Link Layer.
It rides above the physical layer. Controls
transmissions of data and providing interaction with the backbone - wired
network , if exists.
The
MAC layer also provides services related to radio and mobility management.
18.
Carrier
Sense Multiple Access/Collision Avoidance (CSMA/CA)
To
move data packets across a shared channel, the MAC layer uses CSMA/CA (Carrier
Sense Multiple Access/Collision Avoidance), which is very similar to the strategy
used in 802.3 MAC layers: CSMA/CD (Collision Detection). They are both
peer-to-peer protocols, but unlike CSMA/CD, which deals with transmissions after
a collision has occurred, CSMA/CA
acts
to prevent collisions before they happen.
19. IEEE 802.11 Physical Layer - PHY
There are several physical layers described in the 802.11 specification and its extensions. The PHY is responsible for such things as modulation methods, encoding schemes and the actual transmission of radio signals through space.
There are several physical layers described in the 802.11 specification and its extensions. The PHY is responsible for such things as modulation methods, encoding schemes and the actual transmission of radio signals through space.
20. Services
Provided by Stations (e.g. Mobile)
IEEE 802.11 compliance service station should provide/implement 4 services as defined in the IEEE specification.
IEEE 802.11 compliance service station should provide/implement 4 services as defined in the IEEE specification.
a.
Authentication
A
wireless station needs to be identified before it can access network services.
This process is called authentication. It is a required state that comes before
the STA may enter the association state.
b.
De-authentication
This
service voids an existing authentication.
c. Privacy
A wireless station must be able to encrypt frames in order to protect message content so that only the intended recipient can read it.
A wireless station must be able to encrypt frames in order to protect message content so that only the intended recipient can read it.
d.
MSDU (MAC
Service Data Unit) Delivery
An MSDU is a data frame that must
be transmitted to the proper destination.
21. Services
Provided by Access Point (Distributes Systems)
A wireless station that functions as an Access Point must implement the 4 services of stations plus below system services:
A wireless station that functions as an Access Point must implement the 4 services of stations plus below system services:
a. Association
This service establishes an AP/STA mapping after mutually agreeable authentication has taken place between the two wireless stations. A STA can only associate with one AP at a time. This service is always initiated by the wireless station and when successfully completed enables station access to the DSS.
This service establishes an AP/STA mapping after mutually agreeable authentication has taken place between the two wireless stations. A STA can only associate with one AP at a time. This service is always initiated by the wireless station and when successfully completed enables station access to the DSS.
b. Re-association
This service moves a current association from one AP to another AP.
This service moves a current association from one AP to another AP.
c. Disassociation
This service voids a current association.
This service voids a current association.
d. Distribution
This service handles delivery of MSDUs within the distribution system; i.e., the exchange of data frames between APs in an extended service set (ESS).
This service handles delivery of MSDUs within the distribution system; i.e., the exchange of data frames between APs in an extended service set (ESS).
e. Integration
This service handles delivery of MSDUs between the distribution system and a wired LAN on the other side of a portal. Basically this is the bridging function between wireless and wired networks.
This service handles delivery of MSDUs between the distribution system and a wired LAN on the other side of a portal. Basically this is the bridging function between wireless and wired networks.
22. State Variables
Each wireless station maintains two state variables.
Each wireless station maintains two state variables.
For Authentication and for
Association. A wireless station is authenticated or unauthenticated.
Once in an authenticated state,
the STA is either associated or un-associated.
These variables create three
states:
a. State 1: Unauthenticated and un-associated.
b. State 2: Authenticated, not
associated.
c. State 3: Authenticated and
associated.
The state of the wireless station determines which MAC frames are admissible. This information could be useful when debugging with a packet sniffer.
23. Type of MAC frame - MPDU's
There
are three types of frame which traverse through MAC
a. Control
b. Data
c. Management
24. Address Fields in MAC Frame
A MAC frame has up to four, but usually three, address fields. Each address field is the same format as an IEEE 802 MAC address. The following five address types are used:
A MAC frame has up to four, but usually three, address fields. Each address field is the same format as an IEEE 802 MAC address. The following five address types are used:
a. BSS Identifier (BSSID)
Identifies the AP of an infrastructure BSS. For an IBSS (ad hoc network) this is a locally-administered random number.
Identifies the AP of an infrastructure BSS. For an IBSS (ad hoc network) this is a locally-administered random number.
b. Destination Address (DA)
Identifies the final recipient(s) of the frame.
Identifies the final recipient(s) of the frame.
c. Source Address (SA)
Identifies the initial source of the frame.
Identifies the initial source of the frame.
d. Receiver Address (RA)
Identifies the immediate recipient AP(s) on the wireless DS.
Identifies the immediate recipient AP(s) on the wireless DS.
e. Transmitter Address (TA)
Identifies the AP that transmitted the frame onto the wireless DS.
Identifies the AP that transmitted the frame onto the wireless DS.
Addr 1: this is always the recipient
address, which is the wireless station in the BSS who is the next
receiver of the frame.
Addr 2: this is always the wireless
station that is physically transmitting the frame.
Addr 3: this is either the original
source address or the intended destination address.
Addr 4: this is the final source
address for a frame that is both transmitted and received on a wireless
distribution system.
In the above table, the first row defines the address fields for frames travelling between an access point and its associated stations. The second and third rows define the address fields for frames travelling between an access point and the distribution system. The fourth row defines the special case of when the immediate addresses for both transmitting and receiving are via a wireless distribution system, thus requiring two additional address fields for the final source and destination addresses.
In the above table, the first row defines the address fields for frames travelling between an access point and its associated stations. The second and third rows define the address fields for frames travelling between an access point and the distribution system. The fourth row defines the special case of when the immediate addresses for both transmitting and receiving are via a wireless distribution system, thus requiring two additional address fields for the final source and destination addresses.
25. Comparison of 802.11 Networks
WiFi Parameter
|
IEEE 802.11
Protocols
|
|||||
802.11
|
802.11a
|
802.11b
|
802.11g
|
802.11n
|
802.11ac
|
|
Operating Frequency
|
5.3 & 5.8GHz
|
2.4GHz
|
2.4GHz
|
2.4 GHz /
5 GHz |
2.4 GHz /
5 GHz |
|
Avg Signal Range
|
75Feet
|
115Feet
|
125Feet
|
230Feet
|
>500Feet
|
|
Available BW per
Channel
|
||||||
Data Rate (Max)
|
2 Mbps
|
54 Mbps
|
11 Mbps
|
54 Mbps
|
600 Mbps
|
1.7~2.5Gbps
|
Supported Data
Rates
|
1, 2 Mbps
|
6, 9, 12, 18, 24, 36, 48, 54
Mbps
6, 12, and 24 Mbps
are mandatory
|
1, 2, 5.5, 11 Mbps
|
1, 2, 5.5, 11, 6, 9, 12, 18,
22, 24, 33, 36, 48, 54 Mbps
1, 2, 5.5, 11, 6, 12 and 24
Mbps are mandatory
22 and 33 Mbps are typically
not supported
|
1, 2, 5.5, 6, 9, 11, 12, 18,
24, 36, 48, 54, 121.5, 130,
144.44, 270, 300 ,600
Mbps
|
|
Typical Tpt for MAX
Data Rate
|
||||||
Modulation
Technique
|
OFDM
|
CCK /DSSS
|
OFDM
|
OFDM using
MIMO and CB
|
||
Channels
|
36, 40, 44, 48, 52,
56, 60, 64, 149,
153, 157, 161
|
1-11
|
3 non-overlapping
channels in ISM
frequency band at
2.4 GHz
12 non-overlapping
UNII channels
in 5 GHz
frequency band
with and without
CB
|
|||
Special Considerations
|
Higher fq
signals have more
trouble with physical
obstruction
|
2.4 GHz subject to interference
from:
Bluetooth products, cordless
phones,
microwaves, radar, remote
controls,
ZigBee networks,
etc.
|
||||
26. Some 802.11 Add-Ons
a.
802.11e
Defines a set of QOS enhancements that are of critical importance to applications that cannot tolerate delays, such as streaming multimedia or voice over IP.
Defines a set of QOS enhancements that are of critical importance to applications that cannot tolerate delays, such as streaming multimedia or voice over IP.
b.
802.11i
Security extension.
Security extension.
c.
802.11p
Adds support for data exchange between high-speed vehicles and between vehicles and roadside.
Adds support for data exchange between high-speed vehicles and between vehicles and roadside.
27. ISM and U-NII Band
ISM - Industrial Scientific and Medical Band
ISM - Industrial Scientific and Medical Band
Apart from Wi-Fi , Microwave Ovens, Cordless Phones, Medical Diathermy
Devices,
Military Radars, Industrial heaters are some more example which
operates on ISM band.
U-NII - Unlicensed National Information Infrastructure
It Operates over several ranges as follows.
28. Operating Frequency of Wi-Fi
There are two signalling frequencies currently used by Wi-Fi networks:
2.4 GHz - Comprises 14 channels, each with a bandwidth of approximately 20 to 22 MHz operating in the ISM band. 802.11b/g networks operate in the 2.4 GHz band. It is a crowded frequency because many devices other than 802.11 devices operate in it. For example, Bluetooth as well as many consumer products such as microwaves, telephones, garage door openers, baby monitors, etc.
5 GHz - Comprises 13 channels, each with a bandwidth of approximately 20 MHz operating in the U-NII band. 802.11a networks operate in the 5 GHz band. Currently, this band is less crowded than 2.4 GHz, but this is likely to change as the wireless market continues to grow.
There are two signalling frequencies currently used by Wi-Fi networks:
2.4 GHz - Comprises 14 channels, each with a bandwidth of approximately 20 to 22 MHz operating in the ISM band. 802.11b/g networks operate in the 2.4 GHz band. It is a crowded frequency because many devices other than 802.11 devices operate in it. For example, Bluetooth as well as many consumer products such as microwaves, telephones, garage door openers, baby monitors, etc.
5 GHz - Comprises 13 channels, each with a bandwidth of approximately 20 MHz operating in the U-NII band. 802.11a networks operate in the 5 GHz band. Currently, this band is less crowded than 2.4 GHz, but this is likely to change as the wireless market continues to grow.
29. Tips for improving SNR (Signal to
Noise Ratio)
Position
wireless AP or router in a good spot. Off the floor to start and as far away as
possible from any known sources of interference.
Use a
high-gain antenna, especially on the AP, but also on STAs with marginal SNRs.
Antennas provide gain with very little additional noise of their own. Use
directional antennas to help filter out interfering noise sources.
30. Configuration Parameters
a. Operating Mode-
ad-hoc and infrastructure mode.
ad-hoc and infrastructure mode.
b. Operating Channel-
The 802.11 extension in use (a, b, g, n...) and country regulatory agencies determine
The 802.11 extension in use (a, b, g, n...) and country regulatory agencies determine
the
channels available to the network. For access points that are within range of
one another, set each one to a different channel to avoid interference from one
another.
c. Network Name- SSID
the Service Set Identifier (SSID) is essentially the name of a Wi-Fi network. Some networks broadcast their SSIDs to wireless devices in range. SSIDs are up to 32 bytes long.
the Service Set Identifier (SSID) is essentially the name of a Wi-Fi network. Some networks broadcast their SSIDs to wireless devices in range. SSIDs are up to 32 bytes long.
31. Scanning for a Network
Basically, a scan is
a search for available networks within range of the scanning device.
The
device can be directed to search on a particular channel or all channels. Likewise,
a wireless device can search for a particular SSID or it can be directed to “not
care” about the SSID of the network.
Access points transmit management MAC frames called beacons for the purpose of announcing their network to any interested Wi-Fi device in range. Beacon frames are what the wireless device is looking for when it passively scans. Active scanning is used to shorten the time spent waiting for beacons for each potential SSID. Beacons from an AP are typically sent every 100 ms, but an AP will respond immediately to an active probe request from a STA.
Access points transmit management MAC frames called beacons for the purpose of announcing their network to any interested Wi-Fi device in range. Beacon frames are what the wireless device is looking for when it passively scans. Active scanning is used to shorten the time spent waiting for beacons for each potential SSID. Beacons from an AP are typically sent every 100 ms, but an AP will respond immediately to an active probe request from a STA.
32. Wireless Access Points and
Routers
The 802.11 specification defines an access point (or, AP, for short) as a wireless station (STA) that provides access to the distribution service (DS). A wireless router that claims to be 802.11 compliant also provides access to the distribution service because it contains AP functionality.
The key difference between an access point and a router is that routers allow wireless clients access to multiple networks and strictly speaking APs allow access to a single network. However, in practice many APs these days have routing capabilities.
The 802.11 specification defines an access point (or, AP, for short) as a wireless station (STA) that provides access to the distribution service (DS). A wireless router that claims to be 802.11 compliant also provides access to the distribution service because it contains AP functionality.
The key difference between an access point and a router is that routers allow wireless clients access to multiple networks and strictly speaking APs allow access to a single network. However, in practice many APs these days have routing capabilities.
Wireless
routers often have more functionality than an access point in addition to being
able to route across subnets. Here is a list of possible features a wireless
router may implement:
a. DHCP Server
b.
NAT
/ Firewall Protection
c.
VPN
Pass-Through
d.
RIP1
e.
DMZ
Support
f.
Built-in
DSL or Cable Modem
33. SOHO
SOHO - Small Offices and Home Offices
SOHO - Small Offices and Home Offices
34. Fat AP and Thin AP
Fat APs are part of a
distributed architecture, in that they operate independently of one another.
They are access points that have the full AP functionality physically present
in the device. Fat APs have the intelligence to control traffic flow, manage
the association of wireless stations, and enforce security policies.
Thin
APs are part of a centralized architecture. They function more like Ethernet
hubs, having little intelligence themselves and passing responsibility to a
central switch or controller.
35. AP Client Capability
a. Limit placed by device
manufacturer
The device may have a hard-coded limit on the number of associations that it will allow.
The device may have a hard-coded limit on the number of associations that it will allow.
b. Channel Capacity
Since channels are shared resources, the sum of all traffic cannot exceed the channel's capacity.
Since channels are shared resources, the sum of all traffic cannot exceed the channel's capacity.
c. Client Configured Security Option
Selecting Open authentication will typically allow for more clients than selecting a configuration that includes TKIP.
Selecting Open authentication will typically allow for more clients than selecting a configuration that includes TKIP.
d. Application Complexity
Data transactions, busty in nature, have less stringent requirements for service
Data transactions, busty in nature, have less stringent requirements for service
than
the more complex applications, such as video or voice.
The number of clients associated with an AP has a direct impact on the network throughput, since all communication must go through one device. It is well-documented that as the number of client associations increase, aggregate throughput decreases.
The number of clients associated with an AP has a direct impact on the network throughput, since all communication must go through one device. It is well-documented that as the number of client associations increase, aggregate throughput decreases.
36. Network Planning and Maintenance
a. Physical
Location
The physical location of a wireless network has a major influence on it. Everything
The physical location of a wireless network has a major influence on it. Everything
from atmospheric conditions to
buildings and trees may change the strength and direction of RF signals. Information
about the network’s physical location may include such things as floor plans or
blueprints. It should also include any available information about other
potential networks that are in the same location or range.
b.
Coverage Area.
This is the area wherein a client can expect to be able to sustain a connection
with an access point at a minimum data rate. RF signal propagation is
unpredictable, which makes the coverage area somewhat unpredictable as well.
There are differences in the coverage area when the network is outside versus
inside. Obstacles and interference affect coverage area, as does the transmit
power of the access point. The coverage area for the highest link rate is the
smallest and for the lowest link rate it is the largest. The coverage area is
sometimes referred to as a cell in the wireless LAN.
c.
Bandwidth Requirements. Getting this part of the design
right will enhance the experience of using the network. How much bandwidth is
required, where is it required, and when is it required, are all questions that
need to be answered. Bandwidth is affected by the number of associated
stations, client contention, collisions, physical channel errors, application
requirements and protocol overhead. Some of these factors can be mitigated,
others, such as physical channel errors and protocol overhead, are just the
cost of doing business.
d.
Security Requirements. The over-the-air transmissions in wireless
networks introduce security risks not present in wired networks. With the
release of IEEE 802.11i, there are now strong security options available for
Wi-Fi networks.
37. Types of RF Interference
Networks
using 2.4GHz band have more potential source of interference than networks
operating on 5GHz band. Because 2.4GHz is more crowded with consumer
electronics.
a. Other 802.11 networks
b. Bluetooth Devices
c. Consumer Electronics
Cordless Phone, Wireless Camera,
Microwave Ovens
d. Building Materials
Metal, Brick, Concrete
(Wood , Plaster, Glass Doesn't affect
RF transmissions much to worry about)
e. Environmental Factors\
Dense Forest/Plantation, Large
bodies of water, Extreme Weather
38. Minimizing or Eliminating RF
Interference
IEEE 802.11 does not specify how to deal with interference.
IEEE 802.11 does not specify how to deal with interference.
a. AP
Position
Wireless routers and APs should be placed as high as possible. They should be placed as far away as possible from metal, concrete, stone, water heaters, water tanks, large house plants, and even large CD collections.
Wireless routers and APs should be placed as high as possible. They should be placed as far away as possible from metal, concrete, stone, water heaters, water tanks, large house plants, and even large CD collections.
b. Channel
Selection
Changing the channel for your network may eliminate interference from networks transmitting in your vicinity
Changing the channel for your network may eliminate interference from networks transmitting in your vicinity
c. Good
Cell Coverage
Ensure the wireless LAN has strong signals throughout the areas where users will need it.
Ensure the wireless LAN has strong signals throughout the areas where users will need it.
d. Transmit
Power Setting
The transmit power of the AP should be set to reach only the desired coverage area. Besides being less likely to interfere with your neighbours wireless LAN, a smaller coverage area will be less likely to exhibit the hidden node problem. The hidden node problem is when clients on opposite sides of the AP are unable to “hear” one another. This allows the clients to transmit at the same time, thus increasing the chance of a collision.
The transmit power of the AP should be set to reach only the desired coverage area. Besides being less likely to interfere with your neighbours wireless LAN, a smaller coverage area will be less likely to exhibit the hidden node problem. The hidden node problem is when clients on opposite sides of the AP are unable to “hear” one another. This allows the clients to transmit at the same time, thus increasing the chance of a collision.
e. Define
an RF Policy
Where possible, define, and thus limit, the devices allowed in the coverage area. Minimize other wireless devices in the coverage area. For example, newer microwave ovens produce less noise than older models.
Where possible, define, and thus limit, the devices allowed in the coverage area. Minimize other wireless devices in the coverage area. For example, newer microwave ovens produce less noise than older models.
