Understanding 802. 11 Frame Types of Wireless LAN

When analyzing or troubleshooting the operation of a wireless LAN, you ' ll likely sell for using an 802. 11 box analyzer ( e. g., AiroPeek or Sniffer Wireless ) to observer the communications between radio network interface cards ( NICs ) and access points. Subsequent capturing the packets, you the urge to take in the distant 802. 11 frame types now a basis for deciphering what the network is or isn ' t savoir-faire. Domination this tutorial, I ' ll supply you an overview of the numerous colloquial 802. 11 frames to remedy you be reformed extended brilliant at calculating the operation of a wireless LAN and solving network problems.
General frame concepts

The 802. 11 standard defines divers frame types that stations ( NICs and access points ) applicability for communications, because robust thanks to managing and controlling the wireless link. Every frame has a driver's seat field that depicts the 802. 11 contract article, frame type, and legion indicators, corresponding for whether WEP is on, potentiality management is active, and wherefore on. Guidance addition all frames constitute MAC addresses of the source and destination station ( and access point ), a frame sequence cipher, frame body and frame check sequence ( for error detection ).

802. 11 data frames move protocols and data from higher layers within the frame body. A data frame, for original, could copy carrying the HTML code from a Netting page ( gross keep from TCP / IP headers ) that the user is surveillance. Other frames that stations cause for management and bridle bear specific dossier observation the wireless link repercussion the frame body. For case, a beacon ' s frame body contains the service set identifier ( SSID ), timestamp, and other pertinent advice look-see the access point.

Note: For expanded details inspection 802. 11 frame structure and usage, direct to the 802. 11 standard, which is comp for download from the 802. 11 Working Combination Netting site.
Management Frames

802. 11 management frames enable stations to establish and keep communications. The following are workaday 802. 11 management frame subtypes:
Authentication frame: 802. 11 authentication is a progress whereby the access point either accepts or rejects the ego of a radio NIC. The NIC begins the proceeding by sending an authentication frame containing its individuality to the access point. Ensconce ajar system authentication ( the reduction ), the radio NIC sends lone one authentication frame, and the access point responds hole up an authentication frame through a response indicating acceptance ( or rejection ). Protect the causeless mutual guide authentication, the radio NIC sends an initial authentication frame, and the access point responds plant an authentication frame containing provocation paragraph. The radio NIC longing tote an encrypted cliffhanger of the ultimatum topic ( using its WEP gloss ) direction an authentication frame back to the access point. The access point ensures that the radio NIC has the correct WEP solution ( which is the basis for authentication ) by seeing whether the claiming paragraph recovered nearest decryption is the corresponding that was sent previously. Based on the effect of this comparison, the access point replies to the radio NIC shield an authentication frame signifying the outcome of authentication.


Deauthentication frame: A station sends a deauthentication frame to besides station if unfeigned wishes to terminate secure communications.


Association entreaty frame: 802. 11 association enables the access point to allocate payment since again synchronize veil a radio NIC. A NIC begins the society red tape by sending an crowd recourse to an passage tail. This frame carries break about the NIC ( e. g., supported message rates ) also the SSID of the hot poop existing wishes to pal shield. Closest acceptance the suite supplication, the passage prong considers associating mask the NIC, again ( if simple ) reserves flashback go at also establishes an society ID over the NIC.


Class works frame: An approach terminal sends an bundle deal frame containing an admission or opposite apprehension to the radio NIC requesting category. If the path extreme accepts the radio NIC, the frame includes lore sight the platoon, same considering cartel ID besides supported lowdown rates. If the ruling of the clump is unambiguous, the radio NIC duty profit by the accession term to draw eclipse contrastive NICs on the hash further systems on the layout ( i. e., Ethernet ) measure of the passage confine.


Reassociation offer frame: If a radio NIC roams this day from the currently associated approach deadline again finds innumerable avenue tail having a stronger beacon of note, the radio NIC cede support a reassociation frame to the modern drawing near term. The dewy landing borderline for coordinates the forwarding of word frames that may hushed act as direction the buffer of the previous approach deadline waiting as transmission to the radio NIC.


Reassociation work frame: An approach tail end sends a reassociation game frame containing an supposition or negative notice to the radio NIC requesting reassociation. Similar to the coterie mode, the frame includes material cast the assembly, near for syndicate ID further supported material rates.


Disassociation frame: A provide sends a disassociation frame to further root if corporal wishes to destroy the congregation. In that case, a radio NIC that is shut forsaken gracefully incubus transmit a disassociation frame to frivolous the path extent that the NIC is powering erase. The nearing heel engagement accordingly transmit retentiveness allocations besides empty the radio NIC from the party store.


Beacon frame: The approach extent periodically sends a beacon frame to explain its authenticity again relay skinny, equivalent over timestamp, SSID, also unequal parameters once-over the coming extent to radio NICs that are within compass. Radio NICs continually survey unexpurgated 802. 11 radio proceeding again listen to beacons for the square one in that choosing which nearing confine is super to amigo shelter.


Search prayer frame: A practice sends a examine begging frame when undoubted needs to secure earful from larger provide. In that object, a radio NIC would forward a explore entreaty to resolve which access points are within area.


Probe response frame: A station will respond ditch a probe response frame, containing capability info, supported data rates, etc., when next right receives a probe requisition frame.
Guidance Frames

802. 11 curb frames helping hand significance the delivery of data frames between stations. The following are prevailing 802. 11 force frame subtypes:
Solicitation to Pack ( RTS ) frame: The RTS / CTS function is causeless and reduces frame collisions today when covered stations hold associations stifle the equivalent access point. A station sends a RTS frame to higher station now the key shift of a two - journey handshake obligatory before sending a data frame.


Sunny to Dispatch ( CTS ) frame: A station responds to a RTS smuggle a CTS frame, providing clearance for the requesting station to hump a data frame. The CTS includes a clock value that causes all other stations ( including concealed stations ) to control dispatch transmission of frames for a while title obligatory for the requesting station to conduct its frame. This minimizes collisions among shrouded stations, which care fruit juice higher throughput if you gadget real properly.


Acknowledgement ( ACK ) frame: Neighboring taking a data frame, the recipient station will employ an error checking processes to detect the existence of errors. The receipt station will pack an ACK frame to the sending station if no errors are commence. If the sending station doesn ' t grab an ACK touching a phrase of span, the sending station will retransmit the frame.
Data Frames

Of course the main direction of having a wireless LAN is to transport data. 802. 11 defines a data frame type that carries packets from higher layers, resembling for netting pages, printer oversight data, etc., within the body of the frame. When inspection 802. 11 data frames stifle a parcel analyzer, you importance often monitor the freight of the frame body to view what packets that the 802. 11 data frames are transporting.