TCP ACK problem [CentOS4 (kernel-2.6.9-78.0.1.EL) to VxWorks]

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I am investigating a TCP problem involving linux, and wonder whether 
anyone can help me with a diagnosis, or reference to further relevant 
information on-line.

The problem can be seen in the tshark output segment below. The packet 
capture was done at the switch attached to 172.16.139.1 (VxWorks end).

This packet is received over and over again:

172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] Seq=24113 Ack=30625 Win=64240 Len=0

By my understanding though, this earlier packet (74783 3494.378842) 
renders that packet unexpected (inappropriate and anomolous):

172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [PSH, ACK] Seq=24113 Ack=30801 Win=8576 Len=176

Any help appreciated, thanks.

...
74264 3470.401388 172.16.139.1 -> 172.16.5.161 TCP 6802 > 59762 [ACK] 
Seq=30625 Ack=24113 Win=8760 Len=0
74781 3494.233084 172.16.139.1 -> 172.16.5.161 TCP 6802 > 59762 [PSH, ACK] 
Seq=30625 Ack=24113 Win=8760 Len=176
74782 3494.274405 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30801 Win=8576 Len=0
74783 3494.378842 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [PSH, ACK] 
Seq=24113 Ack=30801 Win=8576 Len=176
74784 3494.401937 172.16.139.1 -> 172.16.5.161 TCP 6802 > 59762 [ACK] 
Seq=30801 Ack=24289 Win=8760 Len=0
75160 3518.233618 172.16.139.1 -> 172.16.5.161 TCP 6802 > 59762 [PSH, ACK] 
Seq=30801 Ack=24289 Win=8760 Len=176
75161 3518.276229 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24289 Ack=30977 Win=8576 Len=0
75162 3518.379056 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [PSH, ACK] 
Seq=24289 Ack=30977 Win=8576 Len=176
75163 3518.402481 172.16.139.1 -> 172.16.5.161 TCP 6802 > 59762 [ACK] 
Seq=30977 Ack=24465 Win=8760 Len=0
75563 3542.233655 172.16.139.1 -> 172.16.5.161 TCP 6802 > 59762 [PSH, ACK] 
Seq=30977 Ack=24465 Win=8760 Len=176
75564 3542.233744 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
75565 3542.234024 172.16.139.1 -> 172.16.5.161 TCP [TCP Dup ACK 75563#1] 
6802 > 59762 [ACK] Seq=31153 Ack=24465 Win=8760 Len=0
75573 3543.473192 172.16.139.1 -> 172.16.5.161 TCP [TCP Retransmission] 
6802 > 59762 [PSH, ACK] Seq=30977 Ack=24465 Win=8760 Len=176
75574 3543.473295 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
75575 3543.473737 172.16.139.1 -> 172.16.5.161 TCP [TCP Dup ACK 75573#1] 
6802 > 59762 [ACK] Seq=31153 Ack=24465 Win=8760 Len=0
75606 3546.473831 172.16.139.1 -> 172.16.5.161 TCP [TCP Retransmission] 
6802 > 59762 [PSH, ACK] Seq=30977 Ack=24465 Win=8760 Len=176
75607 3546.473835 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
75609 3546.474273 172.16.139.1 -> 172.16.5.161 TCP [TCP Dup ACK 75606#1] 
6802 > 59762 [ACK] Seq=31153 Ack=24465 Win=8760 Len=0
75666 3551.568975 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [PSH, ACK] 
Seq=24465 Ack=30625 Win=64240 Len=176
75667 3551.643178 172.16.139.1 -> 172.16.5.161 TCP 6802 > 59762 [ACK] 
Seq=31153 Ack=24641 Win=8760 Len=0
75672 3552.473540 172.16.139.1 -> 172.16.5.161 TCP [TCP Retransmission] 
6802 > 59762 [PSH, ACK] Seq=30977 Ack=24641 Win=8760 Len=176
75673 3552.473544 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
75674 3552.473997 172.16.139.1 -> 172.16.5.161 TCP [TCP Dup ACK 75672#1] 
6802 > 59762 [ACK] Seq=31153 Ack=24641 Win=8760 Len=0
75676 3552.525237 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
75677 3552.525532 172.16.139.1 -> 172.16.5.161 TCP [TCP Dup ACK 75672#2] 
6802 > 59762 [ACK] Seq=31153 Ack=24641 Win=8760 Len=0
75679 3552.573863 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
75680 3552.574158 172.16.139.1 -> 172.16.5.161 TCP [TCP Dup ACK 75672#3] 
6802 > 59762 [ACK] Seq=31153 Ack=24641 Win=8760 Len=0
75681 3552.623862 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
75682 3552.624178 172.16.139.1 -> 172.16.5.161 TCP [TCP Dup ACK 75672#4] 
6802 > 59762 [ACK] Seq=31153 Ack=24641 Win=8760 Len=0
75685 3552.673734 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
75686 3552.674024 172.16.139.1 -> 172.16.5.161 TCP [TCP Dup ACK 75672#5] 
6802 > 59762 [ACK] Seq=31153 Ack=24641 Win=8760 Len=0
75687 3552.721872 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
75688 3552.722120 172.16.139.1 -> 172.16.5.161 TCP [TCP Dup ACK 75672#6] 
6802 > 59762 [ACK] Seq=31153 Ack=24641 Win=8760 Len=0
75689 3552.771840 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
75690 3552.772107 172.16.139.1 -> 172.16.5.161 TCP [TCP Dup ACK 75672#7] 
6802 > 59762 [ACK] Seq=31153 Ack=24641 Win=8760 Len=0
75691 3552.821832 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
75692 3552.822097 172.16.139.1 -> 172.16.5.161 TCP [TCP Dup ACK 75672#8] 
6802 > 59762 [ACK] Seq=31153 Ack=24641 Win=8760 Len=0
75694 3552.871999 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
75695 3552.872269 172.16.139.1 -> 172.16.5.161 TCP [TCP Dup ACK 75672#9] 
6802 > 59762 [ACK] Seq=31153 Ack=24641 Win=8760 Len=0
75696 3552.922255 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
75697 3552.922506 172.16.139.1 -> 172.16.5.161 TCP [TCP Dup ACK 75672#10] 
6802 > 59762 [ACK] Seq=31153 Ack=24641 Win=8760 Len=0
75698 3552.972003 172.16.5.161 -> 172.16.139.1 TCP 59762 > 6802 [ACK] 
Seq=24113 Ack=30625 Win=64240 Len=0
...
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