# Does a collision occur if two packets are sent at the same time in Slotted AHOLA?

There's something I don't really understand about the Slotted AHOLA protocol, and I hope you can help me: what happens if a station wants to send two packets at the same time? Will it be considered as a collision? If not, when will the first and second package be sent?

I did some research here but all I found was probability formulas that I haven't seen yet...

• no, this just can't happen. Each sender sends at most one packet at every slot. This is just the physics of the system. Mar 19 '15 at 20:22

## 2 Answers

A station is not allowed to send two packets at the same time. Each station is only allowed to send one packet at a time. If the station has multiple packets it wants to send, it can start sending one of them but it must queue the others and wait to send them later.

The protocol does not impose any requirements on how long a station must wait to send the other packets. Suppose Alice has two packets to send. Alice is required wait to send the second packet until some later point after she has finished sending the first packet. Beyond that, it's up to her exactly when he tries to send it. The protocol doesn't specify anything in particular. Some stations might try to send the second packet immediately after they finish sending the first packet. Other stations might wait a while (for whatever reason) in between. There are no guarantees and no requirements.

In a network interface you have always a transmission queue for the packets waiting to be transmitted. So if you have two or more packets at the same time to be transmitted, you transmit the first one and put the other ones in the transmission queue. When you have finished with the transmission of the packet (after eventual retransmissions), you dequeue another packet and transmit it.