Rohde & Schwarz AMU-K48, Руководство по эксплуатации

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WLAN User Interface IEEE 802.11 (a/b/g)
36 Operating Manual 1171.5283.12 ─ 18
The sequence control field has a length of 2 bytes and is divided in two parts, the frag-
ment number (4 bits) and the sequence number (12 bits) field. A long user data stream
to be transmitted is first split up into MSDUs (MAC service data units). The MSDUs can
either be transmitted as PSDU frames or further divided into fragments. The sequence
number and the fragment number are then used to number the individual subpackets
of the user data stream to be transmitted. Thus, all PSDUs are assigned a consecutive
number. The technique allows the receiver to arrange the data packets in the correct
order, to determine whether an incorrectly transmitted packet was retransmitted and to
find out whether packets are missing.
If the receiver can detect a packet without an error and does not request a retransmis-
sion, the sequence number is incremented by 1 for each packet (the field is reset to 0
at the latest after a count of 4095). The fragment number field is incremented by 1
when another fragment of the current MPDU is transmitted. The start count for the
transmission (normally 0) and the number of packets required to increment the corre-
sponding counter can be defined for both numbers. This is done with the parameters
"Start Number" and "Incremented every ... packet(s)" (see below).
Example:
An error-free transmission of 50 packets (no packet retransmission) is to be simulated.
The sequence number should be incremented by 1 for each packet. Since no packet is
fragmented, the fragment counter can always remain at 0. In this case the following
values have to be set:
If it is to be simulated that some packets are received incorrectly or if the response of
the receiver should be tested when the same packet arrives several times, the number
of packets required to increment the sequence number can be set to 2, for example.
Each packet will then automatically be sent twice (with identical data).
Remote command:
[:SOURce<hw>]:BB:WLAN:PSDU:MAC:SCONtrol:STATe
on page 83
[:SOURce<hw>]:BB:WLAN:PSDU:MAC:SCONtrol:FRAGment:STARt
on page 82
[:SOURce<hw>]:BB:WLAN:PSDU:MAC:SCONtrol:SEQuence:STARt
on page 83
[:SOURce<hw>]:BB:WLAN:PSDU:MAC:SCONtrol:FRAGment:INCRement
on page 82
[:SOURce<hw>]:BB:WLAN:PSDU:MAC:SCONtrol:SEQuence:INCRement
on page 82
Start Number
Sets the start number of the fragment bits or the sequence bits of the sequence con-
trol.
MAC Header and FCS Configuration