Changes between Version 18 and Version 19 of 802.11/MAC/Lower/Retransmissions

Timestamp:

May 5, 2015, 3:40:18 PM (9 years ago)

Author:

chunter

Comment:

--

802.11/MAC/Lower/Retransmissions

@@ -112 +112 @@
 
 The above example shows the ideal scenario the transmission of 2 MPDUs. Each MPDU transmission is initiated with an RTS control frame. A successful CTS response to that RTS transmission instructs the originator to attempt a transmission of the MPDU. A reception of a successful ACK in response to that MPDU transmission keeps all counts and contention window at station at their minimum values.
+
+== Example L.2 ==
+
+{{{
+#!div style="overflow-x:scroll; border:1pt solid"
+[[Image(ex_l_2.png)]]
+}}}
+
+This example shows the first type of failure that can occur in the transmission of a long MPDU. A failure is inferred if a CTS is not received after the transmission of an RTS.
+
+  '''''Excerpt C from 9.3.4.4 of 802.11-2012''''
+
+  ''After an RTS frame is transmitted, the STA shall perform the CTS procedure, as defined in 9.3.2.6. If the RTS transmission fails, the SRC for the MSDU or MMPDU and the SSRC are incremented.''
+
+Furthermore, '''''Excerpt A from 9.3.3 of 802.11-2012'''' in [#ExampleS.1 Example S.1] applies here as well, so the contention window immediately increases to 31 after the post-RTS timeout. The second attempt of the first MPDU begins with a new RTS transmission. When a CTS is received in response to that RTS, the following excerpt instructs our behavior:
+
+  '''''Excerpt D from 9.3.3 of 802.11-2012'''''
+
+  '' The SSRC shall be reset to 0 when a CTS frame is received in response to an RTS frame ... .''
+
+Note that resetting the SSRC to 0 does not indicate that the contention window shall be reset. As such, the CW remains at 31 during the transmission of the MPDU. Upon the reception of the MPDU's ACK, the CW is reset to its minimum value according to '''''Excerpt B of Section 9.3.3 of 802.11-2012''''' from [#ExampleS.1 Example S.1].