Changes between Version 4 and Version 5 of 802.11/MAC/Support_HW

Timestamp:

Jun 19, 2015, 11:43:58 AM (9 years ago)

Author:

chunter

Comment:

--

802.11/MAC/Support_HW

@@ -23 +23 @@
 == MAC CFG Tx Core A ==
 
-The Tx Core A is fundamentally different than Tx Core B in that its transmission can be qualified on medium idleness. Additionally, it is the transmission state that is capable of honoring a post-Tx timeout interval in which a reception is expected by the MAC state. The DCF implementation uses this core for three different purposes:
+Tx Core A is capable of honoring a post-Tx timeout interval in which a reception is expected by the MAC state. The DCF implementation uses this core for three different purposes:
 
-1. Transmission and retransmission of MPDU frames
-1. Transmission and retransmission of RTS frames
-1. Transmission of CTS frames
+1. Transmission of "short" MPDU frames (i.e. MPDUs that required no RTS medium reservation)
+1. Transmission of RTS frames
+1. Transmission of "long" MPDU frames (i.e. MPDUs that were preceded by an RTS/CTS handshake)
 
-The unifying trait of each of the above transmissions is a condition on medium idleness prior to each. Furthermore, each of the above transmissions utilizes a post-Tx timeout window during which a response is expected.
+The unifying trait of each of the above transmissions is the need for a post-Tx timeout window during which a response is expected.
 
 === Implementation Details ===
 
+[[Image(tx_core_a.png, width=1000)]]
+
+The above image gives a more detailed view on the state machine implemented in Tx Core A. Prior to actually transmitting, the core is capable of starting a backoff or deferring to an already running backoff when the medium is not idle. Alternatively, it can wait for a deterministic interval before transmitting. This interval is defined by either the '''postRxTimer1''' or '''postTxTimer1''' timers described above.
+
+For the DCF implementation, short MPDU and RTS transmissions do not employ the green deterministic-wait state. These transmission do employ the purple and blue backoff deferral states. Long MPDU transmissions, however, must occur a deterministic SIFS interval after the previous CTS reception. As such, these transmissions use the green deterministic-wait states.
+
 == MAC CFG Tx Core B ==
 
+The Tx Core B is simpler than Tx Core A. After a transmission is complete, the core is done and does not need to start any kind of post-Tx timeout interval. Optionally, Tx Core B can condition its transmission on medium idleness. The DCF implementation uses this core for two purposes:
+
+1. Transmission of CTS frames
+1. Transmission of ACK frames
+
+Both of the above transmissions have the common trait of being "fire and forget." They are slightly different from one another in that ACK frames must be transmitted regardless of perceived medium busyness. This is not the case for CTS frames, which are only sent when the medium is deemed idle.
+
 === Implementation Details ===
+
+[[Image(tx_core_b.png, width=1000)]]
+
+Like Tx Core A, the green section of the above state machine forces the core to wait for a deterministic amount of time prior to a transmission. The DCF uses this to schedule CTS and ACK transmissions a SIFS interval after the previous reception. The CTS case additionally instructs the core to condition transmission on medium idleness.