Changes between Version 5 and Version 6 of 802.11/MAC/Upper/MACHighFramework/TX_queue


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Timestamp:
Dec 2, 2013, 7:55:22 AM (10 years ago)
Author:
murphpo
Comment:

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  • 802.11/MAC/Upper/MACHighFramework/TX_queue

    v5 v6  
    77= Wireless Transmit Queue =
    88
    9 The MAC High Framework provides a queue for outgoing wireless transmissions. The storage of this queue is in the DRAM SODIMM on the WARP v3 board provided it is plugged into the board (otherwise, a much smaller queue is created inside local BRAM). The MAC High Framework maintains a pool a free queue elements that can be checked out by the upper-level MAC. Furthermore, it maintains a series of full queue elements that are tied to any number of independent queues. This allows, for example, an upper-level MAC like an Access Point to queue packets for each station independently.
     9The low-level MAC running in CPU Low handles one packet at a time. The high-level MAC in CPU High manages many packets at once via a series of queues. In the reference implementation one queue is created per associated node plus one queue for all broadcast traffic. Whenever the low-level MAC finishes transmission of a packet the next available packet is dequeued from the appropriate queue and passed to CPU Low for transmission.
    1010
    11 The wireless transmission process is the following:
     11The packet queues use the DDR3 SO-DIMM on WARP v3 for storage. If the SO-DIMM is not installed a much smaller queue will be implemented using on-chip BRAM.
    1212
    13 1. A free queue element is checked out and, if available, filled in with a packet payload.
    14 2. The upper-level MAC decides which outgoing queue, if any, the packet should be added to and notifies the framework to add it to the end of that particular queue.
    15 3. The upper-level MAC checks each of the outgoing queues when the lower-level MAC is ready for another packet. At this point, the upper-level MAC can implement any number of queuing structures. In our implementation, we have used a round-robin scheme where the upper-level MAC cycles through the queues of associated devices. We intend for this design to be modified by users if a more complex queueing scheme is required. Once a packet is selected, the upper-level MAC notifies the MAC High Framework to send from a particular queue.
    16 4. Once sent, the queue element is returned back to the free pool so it can be checked out and filled in with a new payload in the future.
     13The queueing system is implemented in the MAC High Framework. At boot the framework creates a fixed number of free queue elements. When new packets requiring wireless transmission are received or generated a free queue element is checked out from the framework, populated with the new packet, then added to the tail of the queue associated with the node to which the packet is addressed. Broadcast packets are added to a dedicated queue.
     14
     15When the low-level MAC is ready for a new packet the high-level queue framework removes the head element from the next queue and passes it to the low-level MAC for transmission. By default the next queue is selected via round robin. More sophisticated queue management schemes (i.e. to support QoS) can be implemented in place of round robin.
     16
     17When the low-level MAC completes transmission of a packet the high-level framework clears the associated queue entry and returns it to the pool of available queue entries for future re-use.
     18