Surveyor User's Guide

10-49
Expert Features
Transport Layer
10
TCP Long Ack
Counter
The TCP Long Ack counter increments when the TCP acknowledgment for a
connection is not seen for greater than a threshold value, measured in milliseconds.
A count of all TCP Long Ack events displays in the
Overview counters of Expert
View. A threshold for this counter can be set in Expert Alarms.
Expert Symptom
TCP Long Acks are automatically logged as expert symptoms. The
Symptom
Summary field provides information about the acknowledgment time and the well-
known ports (WKP) involved, including the port number and the IP address. For
example:
Ack Time=[300 ms] between [206.250.228.69]/[TCP/IP
WKP:1988] and [206.250.228.11]/[SMTP]
The time required to acknowledge a TCP/IP packet is calculated for every packet.
When a value exceeds a threshold value, the event is logged as an Expert Symptom.
The threshold for this symptom can be changed. The default threshold is no
acknowledgment for 200 milliseconds.
Diagnostic Details
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Problem Description:
A TCP/IP ACK (Acknowledgment) has taken longer than threshold value to reach the
sender.
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Probable Cause(s):
1. The receiver which generated the ACK was very busy.
2. The network is overloaded.
3. The path to the sender from the receiver has long delays.
4. There may be a problem with the receiver’s TCP/IP stack.
5. There may be an overloaded switch or router in the path.
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Recommended Action(s):
1. Load balance your network.
2. If you see repeated delays and long acknowledgments,
your receiver may need upgrading.