svromp
07-16-2003, 11:02 AM
The 802.11 standard describes 2 architectures: IBSS and BSS
Consider the following scenario: 2 wireless stations (sta1, sta2) are connected to one ap. sta1 sends packets to sta2 which flow through the ap.
So every packet that sta1 sends has its ToDS bit enabled and its FromDS bit disabled. When the packets arrive at the ap, the ap relays the packets to sta2 after inspecting the Destination Adress and enabling the FromDS bit and disabling the ToDS bit. So the ap waits untill a packet of sta1 fully arrives and then it just transmits the packet to sta2, which will normally respond with an Ack packet.
Does the ap wait untill a packet from sta1 fully arrives or does it commence its transmission to sta2 earlier?
If the ap waits, does it also use the CSMA/CA mechanism before sending the packet? (Because sta1 just finished its transmission and the medium should be idle)
If it does, the AckTimeOut value of the MAC protocol of sta1 should be set differently for the BSS case and the IBSS case, because it just takes longer to send the data from sta1 to sta2 via the ap in the BSS case compared to the IBSS case where sta1 just sends its packets directly to sta2 or is the AckTimeOut value fixed in the 802.11 standard? It is not very clear to me what the value of the AckTimeOut should be?
So the performance (Goodput) of the BSS architecture is worse than its IBSS counterpart, given the fact that all stations hear eachother.
Could someone please clarify this problem/misunderstanding,
Thanks
Consider the following scenario: 2 wireless stations (sta1, sta2) are connected to one ap. sta1 sends packets to sta2 which flow through the ap.
So every packet that sta1 sends has its ToDS bit enabled and its FromDS bit disabled. When the packets arrive at the ap, the ap relays the packets to sta2 after inspecting the Destination Adress and enabling the FromDS bit and disabling the ToDS bit. So the ap waits untill a packet of sta1 fully arrives and then it just transmits the packet to sta2, which will normally respond with an Ack packet.
Does the ap wait untill a packet from sta1 fully arrives or does it commence its transmission to sta2 earlier?
If the ap waits, does it also use the CSMA/CA mechanism before sending the packet? (Because sta1 just finished its transmission and the medium should be idle)
If it does, the AckTimeOut value of the MAC protocol of sta1 should be set differently for the BSS case and the IBSS case, because it just takes longer to send the data from sta1 to sta2 via the ap in the BSS case compared to the IBSS case where sta1 just sends its packets directly to sta2 or is the AckTimeOut value fixed in the 802.11 standard? It is not very clear to me what the value of the AckTimeOut should be?
So the performance (Goodput) of the BSS architecture is worse than its IBSS counterpart, given the fact that all stations hear eachother.
Could someone please clarify this problem/misunderstanding,
Thanks