1 Why are acknowledgments used in 80211 while TCP already ac

1) Why are acknowledgments used in 802.11 while TCP already acknowledges the packets?

2)  Let us assume that there are two wireless stations associated with the same AP and the stations cannot sense each other due to signal fading. Station1 has two packets to transmit and station 2 has 1 packet to transmit. Moreover assume that the two stations simultaneously decide to transmit to the channel. Kindly explain the steps CSMA/CA with RTS/CTS will take to transmit these packets to the AP

Solution

Answer :

1A).

      1. Acknowledgments used in 802.11 while TCP already ackowledges the packets because there are no packet loss in wired Ethernet.This is much more in a wireless.

      2.In an 802.11 network due to high rate of errors in wireless networks.

      3.Because of fading,collisions,signal loss and multi path propagation and interface.

      4.Robustness is increased through retransmissions.Due to that they can able to perform retransmissions ACKs are required.

    5.We think there is no knowledgements it sent back to the sender,the sender could nort recognize that the receiver receive the data.

         TCP uses cumulative acknowledement. The acknowledgement number that a receiver sends inside a TCP header is always the sequence number that the receiver wants to see next. To avoid sending too many data-free acknowledgement segments, a receiver is allowed to wait up to 500 ms (half a second) before sending an acknowledgement. If another segment comes in during that interval, a cumulative acknowledgement must be sent. For a steady stream of messages, therefore, cumulative ACKs need to be sent for every other packet. However, any out-of-order segments must be acknowledged upon receipt.