Proxim Harmony 802.11a Network Adapter 802.11a Guida di Installazione Scaricare il pdf (Pagina 165)

Wireless Guide 151

Advanced Features for Wireless Analysis

 1 — Unspecified reason.

 4 — Disassociated due to inactivity.

 5 — Disassociated because the access point is unable to handle

all currently associated stations.

 7 — Class 3 frame received from non-associated station.

 8 — Disassociated because sending station is leaving (or has left)

the network.

 9 — Station requesting (re)association is not authenticated with

responding station.

Mcast/Bcast Fragmentation

The Expert generates the Mcast/Bcast Fragmentation alarm when it detects

an 802.11 frame with a multicast or broadcast destination address and

fragmentation indicated in the MAC header. This is a violation of the 802.11

specification.

Wireless networks commonly implement the fragmentation and

defragmentation services provided by the 802.11 MAC layer to increase

transmission reliability. However, the 802.11 specification does not allow

fragmentation for broadcast or multicast frames because of the overhead this

would cause for the network as a whole.

Missing Fragment Number

The Expert generates the Missing Fragment Number alarm when it detects

a jump in the fragment number of an 802.11 frame, indicating that a portion of

a fragmented data unit is at least temporarily missing.

Wireless networks commonly implement the fragmentation and

defragmentation services provided by the 802.11 MAC layer to increase

transmission reliability. When a unicast frame’s length exceeds an internal

threshold in the MAC’s MIB, the MAC will break up the frame into smaller

constituent frames — fragments — with the same sequence number.

Each fragment of a larger data unit is identified with a fragment number

indicating its intended ordered position within the reassembled data unit at the

receiving station. The Expert observes each transmitted fragment and stores

the fragment numbers. If it observes a jump in the fragment number for the

transmission of fragments with the same sequence number, it generates this

alarm.

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Proxim Harmony 802.11a Network Adapter 802.11a Guida di Installazione Pagina 165