[ns] TCP/UDP overhead questions

[Xiang Fan]

Hi there,

I am doing some simulations over wlan 802.11.

If I use TCP protocol, I see that when tcp source packetSize_ is set, say x, 
the length of the packet through ether is

x+40(tcp)+20(ip)+52 (PLCP preamble(16)+PLCP header(8)+mac(28, in same BSS, 
802.11 Spec 7.2.2) in bytes.

When UDP is used and packetSize_ is set, say y,

The total length is
y+20+52,

The length of packets can be seen in both .tr and .nam files ..
I have two questions,
1. why is there a TCP overhead of 40 instead of 20,
2. Why is the UDP header of 8 bytes not included? bug?

any suggestions? many thanks in advance!

Xiang

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