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MAX 4000 - Collisions at the 10 Mbit port.

The green "ACT" network LED flashs like extreme high traffic.

In 1997 when RDE did start with the first MAX 4000 in our POP here in Wiesbaden, we have been very disappointed to have so many collisions on the 10 Mbit Ethernet LAN port, running one E1 port as dial in only. You can see this watching the yellow "COL" LED (close to the red arrow)

check this LED

The test :

With a MAX 6000 (10/100 Mbit) we did request 3 x 2 MBit data from a web-server at the MAX 4000´s end using its 10 Mbit Ethernet, a total of 6 MBit.


We did see so many collisions, but the data rate was absolutely sufficient and there have been no data errors or "resend´s".


So, whats that ???

The answer:

Talking to the old Ascend people, we got the information, that this is a legal (but tricky) way to force the sender (the server at 10 Mbit end) to stop immediately and hold on sending.


No data is lost and the E1 WAN connection is not overstressed. Even on a 10/100 switch port the MAX 4000 uses this protocol trick to manage the data flow.


As we found out looking to to logs of our switches, this seems to be a "no danger error" with the option, it may be ignored.

Another text to understand whats going on:

You need to know that the max by this way is blocking to much traffic comming from the 10 MBit line passed to the 2 Mbit line by creating synthetic Ethernet collisions and forcing the next hub or switch to wait sending the next block of data until the current block of data is passed through the 2 Mbit line.


This means a server is strongly pushing requested data into the 10 Mbit line of the MAX and the MAX

cannot handle so much transfer traffic because the bottleneck of the 2Mbit WAN line is only 20% of the 10 Mbit line.


If this trick would not be successful, the MAX had to drop the packets with the result that the receiver on the other end would send requests for repeatedly sending the whole file or sum of blocks again and again and again. (= extremely much traffic but no success)


And this trick costs some little CPU power, nothing else.

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