Differences between version 2 and predecessor to the previous major change of Interleaving.
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| Newer page: | version 2 | Last edited on Tuesday, October 10, 2006 8:21:44 pm | by DrewCalcott | Revert |
| Older page: | version 1 | Last edited on Wednesday, October 6, 2004 12:09:11 am | by PerryLorier | Revert |
@@ -7,7 +7,7 @@
There are a lot of myths going around as to what interleaving is and how it works. The best explaination was able to find is that Interleaving was basically reed solomon error correction, which is __wrong__.
I've been through and read the [ITU] specification on DSL (G.992) to discover what Interleaving actually is.
-A DSL frame is broken into two sections a "Fast" section and a
"Interleave" section. In the fast section packets are sent with the [FEC] information sent directly after the packets. In the interleave section packets are all sent, then the FEC information is sent for each packet. This means that with interleaved packets you must wait for the entire frame to arrive before you can process any packets, but it moves the error correction information away from the data so data corruption is unlikely to take out both the FEC and the actual data. With Interleaving disabled, the FEC is sent directly after the packet, so a packet can be dispatched immediately after it's recieved (you don't have to wait for the entire frame to arrive), however the FEC is close to the payload data and if the data is corrupted then the FEC is probably corrupt as well and thus it's unable to correct the data.
+A DSL frame is broken into two sections a "Fast" section and an
"Interleave" section. In the fast section packets are sent with the [FEC] information sent directly after the packets. In the interleave section packets are all sent, then the FEC information is sent for each packet. This means that with interleaved packets you must wait for the entire frame to arrive before you can process any packets, but it moves the error correction information away from the data so data corruption is unlikely to take out both the FEC and the actual data. With Interleaving disabled, the FEC is sent directly after the packet, so a packet can be dispatched immediately after it's recieved (you don't have to wait for the entire frame to arrive), however the FEC is close to the payload data and if the data is corrupted then the FEC is probably corrupt as well and thus it's unable to correct the data.
The spec suggests that disabling Interleaving can increase the dropped packet rate to 50% of all packets recieved (which I think would be a miracle if FEC was able to recover that much data!).
