[ns] Mac/Tdma Fragmentation-related
yucigou at hotmail.com
Tue May 25 09:24:55 PDT 2004
Now I use the Mac/Tdma protocol in ns2, there seems to be some problems with
it. One of the problems is related to packet fragmentation. Every Tdma frame
is divided into 3 time slots in my experiment. Let's just look at outbound
packets at the base station. Packets type and their size in byte are listed
Mobile IP Advertisement 120
Mobile IP Registration Reply 144
TCP control packets 92
TCP data packets 604
1. When I set slot_packet_len_ to 124, the time it takes for each packet
except TCP data packets and Registration Replies is 3 time slots;
TCP data packets 9 time slots
Mobile IP Registration Replies 6 time slots
2. When I set slot_packet_len_ to 145, which is one byte bigger than the
size of Registration Replies, the time it takes for each packet except TCP
data packets is 3 time slots;
TCP data packets, 9 time slot.
It seems that TDMA does take fragmentation into account. But what I don't
understand is 9 time slots are not enough for TCP data packets of 604 bytes.
In both cases, the number of time slot should be 15, i.e. ceil(604 / 145) *
3 = 15, ceil(604 / 125) * 3 = 15
(NB: y = ceil(x) rounds x to the nearest integer greater than or equal to
Could you please explain why it happens like that?
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