Mobile ad hoc networks (MANET)
Mobile ad hoc networks (MANET)
Mobile ad hoc networks (MANET)
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Problem of hidden terminals<br />
Hidden terminal<br />
A sends to B<br />
C does not receive A anymore<br />
C wants so send to B, Medium is free for C (CS fails)<br />
Collision at B, A does not recognize this (CD fails)<br />
A is „hidden“ for C<br />
A<br />
B<br />
C<br />
<strong>Mobile</strong> <strong>ad</strong> <strong>hoc</strong> <strong>networks</strong> 11<br />
www.tm.uka.de<br />
MAC-layer: DCF with RTS/CTS<br />
Request-to-Send (RTS)/Cleat-to-Send (CTS) option<br />
Sender tansmits RTS first<br />
contains Network Allocation Vector (NAV)<br />
Receiver replies with CTS (after SIFS)<br />
Sender sends data frame and receivers sends ack (after SIFS)<br />
Other stations store NAV<br />
Virtual reservation<br />
Sender<br />
DIFS<br />
RTS<br />
data<br />
Receiver<br />
SIFS<br />
CTS<br />
SIFS<br />
SIFS<br />
ACK<br />
Other<br />
Stations<br />
NAV (RTS)<br />
NAV (CTS)<br />
Waiting time<br />
Backoff<br />
DIFS<br />
data<br />
t<br />
<strong>Mobile</strong> <strong>ad</strong> <strong>hoc</strong> <strong>networks</strong> 12<br />
www.tm.uka.de
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