The chart below shows message rates for UQDF which carries quotes for Nasdaq stocks.
You can see the odd cycling behavior that lasts for exaclty 1 second and is followed
by a surge.
This was due to the feed being overloaded.
One result of that overload was trades appearing before quotes, like in MSFT.
UQDF is sent on 6 multicast lines which are grouped by the symbols first character
Line 1: A-B
Line 2: C-D
Line 3: E-I
Line 4: J-N
Line 5: O-R
Line 6: S-Z
UQDF overload on October 21, 2011
UQDF overload on June 24, 2011
Close-up of UQDF overload on June 24, 2011
UQDF overload on July 1, 2011
UQDF overload on July 5, 2011
UQDF overload on July 13, 2011
UQDF overload on October 24, 2011