Question

15. When all devices in an 802.11 WLAN are within range of each other and the access point, the frame exchange protocol is sufficient to establish reliable data delivery.

TRUE or FALSE

17. DCF (distributed coordination function)uses a binary exponential backoff, which means that if a station attempts to transmit after a series of repeated collisions, then the delay time (backoff) is doubled after each collision.

TRUE or FALSE

Answer 1

Answer 15) True. When all the devices are within range with each other and that of the access point, the relaible data transfer can be done through Frame Exchange Protocol.

The Frame exchange protocol is a more efficient to handle the errors at MAC level. The working of frame exchange protocol is as follows-

• Source station sends the data.
• The Destination then responds with acknowledgment (ACK).
• If the source station doesn’t receive ACK, it then retransmits the frame again.

Answer 17) TRUE, DCF or Distributed Coordination function uses a CSMA-CA(Carrier Sense Multiple Access - Collision Avoidance) algorithm and also employs a exponential backoff algorithm.

The working is given below-

• DCF starts sesnsing to check if the carrier channel if it is busy or not.
• If it is found to be busy, the carrier stops its transmission.
• There are multiple such carriers waiting to send data on the same channel.
• So, if all carrier start transmission at same time when channels becomes free, collision may occur.
• Hence, exponential backoff algorithm is used, in which the waiitng time is doubled for a carrier after any collision occurs.