hey, I have this exercice for the advanced network if someone can help me with it.
We configured the adhoc wireless network in the figure below with nodes A, B, C, and X (access
point). The range of each node is illustrated with the circle around it. We can notice how node A
and B cannot sense each other existence since their domains do not intersect. On the other hand,
nodes X and C can hear the other three nodes.
1. At a first stage, we will consider that RTS/CTS are not used and the inter-frame-spacing
(IFS) and the time required for ACK (transmission and propagation time) are ignored.
Besides, the back-off time for each node is the same as the DIFS assigned to it.
• Suppose X is transmitting a packet at time 0 and finishes sending it at time 100 μs.
(all other nodes can hear X)
• Node A gets a packet to send at time 50 that takes 100 μs to send and is assigned a
DIFS of 100 μs.
• B gets a packet to send at time 70 that takes 200 μs and is assigned a DIFS of 50
μs.
• C gets a packet to send at time 90 that takes 150 μs and is assigned a DIFS of 150
μs.
From time t=0, for each of the three hosts, what time do they start sending their packets?
And what time do they finish? So you are asked to provide the following and explain your
calculation:
• A start transmitting time and A end transmitting time:
• B start transmitting time and B end transmitting time:
• C start transmitting time and C end transmitting time:
Reminder: do not forget that DIFS is a timer that starts counting down only when the
channel is sensed idle, and it freezes whenever it senses any other signal on the channel.
It continues counting down whenever the channel is idle again until reaching 0 so the
node can send.
2. Of the three packets sent, which are successfully delivered on the first attempt?
3. Now, suppose RTS/CTS are enabled. In this case, when will each host be able to reserve
the channel (so be able to start sending its data packet)? And when does it finish? You may
assume that the time needed to send RTS, CTS and ACK packets is negligible. So you are
asked to provide the following and explain your calculation:
• A start transmitting time and A end transmitting time:
• B start transmitting time and B end transmitting time:
• C start transmitting time and C end transmitting time:
here the schema:
