我有一个简单的 802.15.4 模拟程序（2 个节点，CBR 流量）。
如果 CBR 数据包的大小小于 100，则可以毫无问题地传递数据包，但一旦增加数据包大小，所有数据包都会被丢弃。
我猜这是因为默认情况下不会发生碎片（802.15.4 上的最大大小为 127 个八位字节）。真的吗？我应该如何修复我的模拟程序（因为我认为碎片发生在现实世界中）？
set val(chan) Channel/WirelessChannel ;# channel type
set val(prop) Propagation/TwoRayGround ;# radio-propagation model
set val(netif) Phy/WirelessPhy/802_15_4 ;# network interface type
set val(mac) Mac/802_15_4 ;# MAC type
set val(ifq) Queue/DropTail/PriQueue ;# interface queue type
set val(ll) LL ;# link layer type
set val(ant) Antenna/OmniAntenna ;# antenna model
set val(ifqlen) 100 ;# max packet in ifq
set val(nn) 2 ;# number of mobilenodes
set val(rp) AODV ;# protocol tye
set val(x) 40 ;# X dimension of topography
set val(y) 40 ;# Y dimension of topography
set val(stop) 500 ;# simulation period
set val(energymodel) EnergyModel ;# Energy Model
set val(initialenergy) 100 ;# value
set ns [new Simulator]
set tracefd [open aodv1.tr w]
set namtrace [open aodv1.nam w]
$ns use-newtrace
$ns trace-all $tracefd
$ns namtrace-all-wireless $namtrace $val(x) $val(y)
set dist(35m) 1.56962e-07
set dist(40m) 1.20174e-07
Phy/WirelessPhy set CSThresh_ $dist(40m)
Phy/WirelessPhy set RXThresh_ $dist(40m)
# set up topography object
set topo [new Topography]
$topo load_flatgrid $val(x) $val(y)
create-god $val(nn)
# configure the nodes
$ns node-config -adhocRouting $val(rp) \
-llType $val(ll) \
-macType $val(mac) \
-ifqType $val(ifq) \
-ifqLen $val(ifqlen) \
-antType $val(ant) \
-propType $val(prop) \
-phyType $val(netif) \
-channel [new $val(chan)] \
-topoInstance $topo \
-agentTrace ON \
-routerTrace OFF \
-macTrace OFF \
-movementTrace OFF \
-energyModel $val(energymodel) \
-initialEnergy $val(initialenergy) \
-rxPower 35.28e-3 \
-txPower 31.32e-3 \
-idlePower 712e-6 \
-sleepPower 144e-9
#-IncomingErrProc MultistateErrorProc \
#-OutgoingErrProc MultistateErrorProc
for {set i 0} {$i < $val(nn) } { incr i } {
set mnode_($i) [$ns node]
}
for {set i 1} {$i < $val(nn) } { incr i } {
$mnode_($i) set X_ [ expr {$val(x) * rand()} ]
$mnode_($i) set Y_ [ expr {$val(y) * rand()} ]
$mnode_($i) set Z_ 0
}
# Position of Sink
$mnode_(0) set X_ [ expr {$val(x)/2} ]
$mnode_(0) set Y_ [ expr {$val(y)/2} ]
$mnode_(0) set Z_ 0.0
$mnode_(0) label "Sink"
for {set i 0} {$i < $val(nn)} { incr i } {
$ns initial_node_pos $mnode_($i) 10
}
#Setup a UDP connection
set udp [new Agent/UDP]
$ns attach-agent $mnode_(1) $udp
set sink [new Agent/Null]
$ns attach-agent $mnode_(0) $sink
$ns connect $udp $sink
$udp set fid_ 2
#Setup a CBR over UDP connection
set cbr [new Application/Traffic/CBR]
$cbr attach-agent $udp
$cbr set type_ CBR
$cbr set packet_size_ 100
$cbr set rate_ 0.1Mb
$cbr set interval_ 2
#$cbr set random_ false
$ns at 5.0 "$cbr start"
$ns at [expr $val(stop) - 5] "$cbr stop"
# Telling nodes when the simulation ends
for {set i 0} {$i < $val(nn) } { incr i } {
$ns at $val(stop) "$mnode_($i) reset;"
}
# ending nam and the simulation
$ns at $val(stop) "$ns nam-end-wireless $val(stop)"
$ns at $val(stop) "stop"
$ns at [expr $val(stop) + 0.01] "puts \"end simulation\"; $ns halt"
proc stop {} {
global ns tracefd namtrace
$ns flush-trace
close $tracefd
close $namtrace
}
$ns run