You send commands that are post-dated into the future.

1. Calculate the average-worse (right-ish side N-percentile of the bell curve) ping time in ticks with a small margin (eg: 10 tick ping +2 ticks variation)
2. Client send input/command to the server scheduled for now_tick + ping_ticks
3. Server receives the command (ping_ticks / 2) later, relays it to the clients
4. Clients (hopefully) receive commands before they're due and execute command on now_tick + ping_ticks

When packets are delayed there is two ways around it:

1. all clients/servers agree that commands will be received at most every N ticks with a delay of M ticks and will simply wait if no packet is received (use an empty keep-alive packet when no commands are to be sent). More packets can be sent more frequently.
2. Clients/servers will rewind in time and recalculate (fast-forward) once delayed packets are received. So all clients/servers keep a periodic backup of the entire game state at N ticks granularity for as far back as M (ping-delay) ticks can be accepted.

Usually a mix of both is used.

You send commands that are post-dated into the future.

1. Calculate the average-worse (right-ish side N-percentile of the bell curve) ping time in ticks with a small margin (eg: 10 tick ping +2 ticks variation)
2. Client send input/command to the server scheduled for (now_tick + ping_ticks) (eg: now 50 + ping 5 = tick 55)
3. Server receives the command (ping_ticks / 2) later, relays it to the clients
4. Clients (hopefully) receive commands before they're due (eg: received on tick 53) and execute command on the tick that was calculated as the post-date (eg: tick 55) so everyone is in sync.

When packets are delayed there is two ways around it:

1. all clients/servers agree that commands will be received at most every N ticks with a delay of M ticks and will simply wait if no packet is received (use an empty keep-alive packet when no commands are to be sent). More packets can be sent more frequently.
2. Clients/servers will rewind in time and recalculate (fast-forward) once delayed packets are received. So all clients/servers keep a periodic backup of the entire game state at N ticks granularity for as far back as M (ping-delay) ticks can be accepted.

Usually a mix of both is used.