Grow Wifi

The default Colouring Rule that Wireshark provides for WLAN packets is not the best one. People who are used to use Omnipeek, often find it difficult to use Wireshark to check WLAN packets. There are coloring rules in Wireshark that we can define to make WLAN captures look similar to Omnipeek. After applying the Rules, this is what WLAN capture looks like in Wireshark: If you are interested to have this look then follow the below procedure to have Omnipeek Look in Wireshark: Save the below text in a file in your computer: # DO NOT EDIT THIS FILE!  It was created by Wireshark @wlan.ba_req@wlan.fc.type_subtype == 0x18@[65535,65535,65535][50372,41120,0] @wlan.ps_poll@wlan.fc.type_subtype == 0x1a@[65535,65535,65535][36281,18871,45656] @wlan.qos_null@wlan.fc.type_subtype == 0x2c@[65535,65535,65535][36281,18871,45656] @wlan.null_data@wlan.fc.type_subtype == 0x24@[65535,65535,65535][36281,18871,45656] @EAPOL@eapol@[65535,65535,65535][8611,29490,4718] ...

AIFS Arbitration Inter-Frame Spacing (AIFS) defines different inter-frame gaps for traffic from each of the 4 priority queues. This replaces the original DCF Inter-Frame Spacing (DIFS) which defined only a single inter-frame gap value for all data frames. Using AIFS, each frame awaiting transmission must wait until the medium is declared to be available through Clear Channel Assessment (CCA) and the Network Allocation Vector (NAV). Once the medium is available, each logical station (one for each priority queue) must wait the defined inter-frame space time based on the queue to which the traffic is assigned. Each of the 4 priority queues has a defined inter-frame space value corresponding to the priority assigned to the queue. For example, the Voice queue is the highest priority and as such has the lowest inter-frame space timer. The AIFS timers assigned by IEEE 802.11e are all defined as 1 Short Inter-Frame Spacing (SIFS) value plus a variable number of slots times (AIFSN) wh...

Part 2 - IEEE 802.11e Principles 802.11e and WMM QoS Overview The initial 802.11 Standard did not give priority to different types of Traffic. This really doesn't works well in the real world. We would like to have more priority to traffics like Voice and Video over other type of Data, but this wasn't addressed initially. With 802.11e Amendment, it addressed this issue by giving more priority creating 8 priority classes for Traffic. This work was done as part of the IEEE 802.11e working group and was added as an amendment to the standard. Certifications of compliance with portions of this amendment are done by the WiFi Alliance through the WiFi Multimedia (WMM) certification process. 802.11e defines 8 user priorities for Quality of Service (QoS) of wireless traffic. These 8 user priorities are grouped into 4 Access Categories (AC) defined as Voice, Video, Best Effort, and Background. Each access category contains 2 different user priorities. The design of this priori...

Part 1 - Background Information - The Non QOS way... 802.11 had 2 ways of getting the medium for transmission: 1.  Point Co-ordinate Function  : To my knowledge it was not widely implemented. In this the AP would control the usage of medium, in other words, AP was the Point of control of who gets the Access to the medium. 2.  Distributed Co-ordinate Function  : In this, the access to medium is decided by CSMA/CA. Let us learn more about this: The basic principles of CSMA/CA: In CSMA/CA, when a wireless node has a packet to send, it first listens to the channel for any active transmissions. If there are no active transmission going on, then it sends the Packet. If there are any active transmission going on then, then the node backs off for a random interval of time and then again checks if the medium is clear. This random timer is called as Backoff timer. If it is clear, then the node sends the packet. If it finds the medium to be busy again, it increases ...

RTS CTS to the Rescue: Even with CSMA/CA, the collision can be tried to avoid but not be guaranteed. Let us look at the below scenario to understand the Problem: Node A sees that there is no active transmission going on and has data to send to Node B. At the same time Node C also sees that there is no active transmission and has to send data to Node B. Both Node A and Node C sees a clear channel and sends data to Node B. Node B will receive corrupted data from Node A and Node C and will not send ACK to either. Since Node A and Node C cannot listen each others transmission they find that the Channel to be free. This kind of problem is called as Hidden Node Problem where in the Nodes which aren't able to identify Channel utilisation at the receivers side, tend to assume that the channel is free and start Transmitting. This results in data corruption at the receivers end. Node B will receive corrupted data from Node A and Node C and will not send ACK to either. If ...

Why it is so Important? As you are aware that most of the Wifi Devices are Battery Operated such as Mobile Phones, Laptops etc. It is very important to consider the Power consumed of every component of such devices. If the device drains its battery too often, then it limits it mobility capability. It is very essential to conserve the battery when the device is not using any of such components. For Ex: Screen times out if there is no activity by User. Similarly when there is no active data transfer over Wifi, it is best to put it in a low power consumption mode to avoid Battery Wastage. Basic Mechanism: 1. STA sends out a packet to AP indicating that it is going to sleep mode. 2. AP Start buffering data for the client and indicates that there is data buffered in Beacon. 3. STA wakes up, listens to Beacon and sees if there is any data buffered for it. If no, go back to sleep. If yes, send a packet to AP to say that it is awake and send the buffered data. 4. AP after sending th...

Wifi Roaming Techniques: Roaming is one of the most crucial aspect of Wifi. Roaming in simple terms is Handing off Client connectivity from one Access point to another without losing connectivity. When the Client sees that the RSSI ( signal Strength ) of connected AP is decreasing, the Client does a roam Scan and sees if there are other APs with better RSSI. Once it identifies the better AP, it starts association with this AP. This process is called Roaming. Why is Roaming Important: Wifi is mostly used in devices which are mobile such as mobile phones, Laptops etc. User intend to use these device while moving from one place to another and it is expected that the devices are always connected to wifi and the user can continue his work seamlessly. It would not be desirable that wifi keeps disconnecting and connecting to other Access Point while the user is moving, there should be a way where in the client can remain connected to wifi network while it moves. This issue is add...