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Expert Features
Transport Layer
10
TCP Frozen Window
Counter
The TCP Frozen Window counter increments when the TCP window is frozen for
greater than a threshold value, measured in seconds. A count of all TCP Window
Frozen events displays in the
Overview counters of Expert View. A threshold for
this counter can be set in Expert Alarms.
Expert Symptom
TCP Frozen Window events are automatically logged as expert symptoms. The
Symptom Summary field provides information about the frozen window size,
duration, and the well-known ports (WKP) involved, including the port number and
the IP address. For example:
Frozen at 29909 for [19 ms] between [206.250.228.69]/[TCP
WKP:1988] and [206.250.228.11]/[SMTP]
A frozen window event is defined as the TCP window size remaining the same for
all packets over a threshold interval for one connection in one direction. If only one
packet is detected over the threshold interval, it is logged as a TCP frozen window
event. Events of this type can indicate when a problem with the TCP/IP connection
or excessive network traffic.
The threshold for this symptom can be changed. The default threshold is a frozen
window of 5 seconds.
Diagnostic Details
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Problem Description:
A TCP/IP packet has the window size stuck for longer than the threshold interval.
If the window size is less than the maximum, the flow of data is restricted. The
sender will not exceed the receiver’s window size.
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Probable Cause(s):
1. The receiver is overloaded.
2. The receiver has run out of buffer space.
3. There may be a problem with the receiver’s TCP/IP stack.
4. There may too many connections to the receiver resulting in reduced buffer space.