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how to calculate number of byte send in UDP

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rps rathore
rps rathore 2015-8-14
评论： rps rathore 2015-8-21
i send data in udp call.
u = udp('127.0.0.1', 8000);
fopen(u);
x = (0:999) .* 8 * pi / 1000;
data = sin(x);
fwrite(u, data, 'float32');
how many byte is sent in this fwrite call.
how to calculate byte using this call
please explain
similarly
fread(u, datas, 'float32');
how many byte is received in this fread call.
how to calculate byte using this call
thanks
  1 个评论
rps rathore
rps rathore 2015-8-14
thanks for replying. how many bytes is taken by object u also. how many total bytes including data plus u

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回答（2 个）

Uladzimir
Uladzimir 2015-8-14
fwrite(u, data, 'float32') Here are numel(data)*4 bytes.
fread(u, datas, 'float32') Here are datas*4 bytes
Walter Roberson
Walter Roberson 2015-8-14
http://www.tenouk.com/Module43.html
udp takes 2*32 bits = 8 bytes, plus the length of the data (which here would be 4 bytes). But udp packets have to be embedded in IP packets, which take 5*32 bits = 20 bytes before the UDP packet.
But IP packets have to be embedded in a physical transport layer such as ethernet which require a number of bytes around the IP packet. The structure of Wi-Fi 802.11 packets is not the same as for Ethernet; more at http://www.wildpackets.com/resources/compendium/wireless_lan/wlan_packets#wp1000999
You need to decide on a particular physical transmission standard, and you need to decide what you want to include in your count. Do you count the preamble (historically it was allowed for some of the bytes to go missing in transit)? The Frame Check Sequence (a lot of people forget but it really should be included)? The Interpacket Gap (arguable, since it is a mandatory gap in transmission rather than data being transmitted)

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