Method and apparatus to determine the amount of delay in the transfer of data associated with a TCP zero window event or set of TCP zero window events
View Patent ↗Network monitoring method and apparatus determines the zero window event data transfer delay, reporting the amount of data transfer delay caused thereby. Non-data-transfer-delaying zero window events can be separated from those causing actual delay, allowing reporting of actual delay events separate from non-delay causing events.
1. A method of monitoring network zero window events via an interface connection to a network for observing traffic, comprising:
determining a zero window event advertised by a receiver;
determining whether a sender withheld data transmission until the end of the zero window event;
determining whether the zero window event caused said data transmission to be withheld; and
reporting a duration of a zero window delay only when it is determined the sender withheld said data transmission until the end of the zero window event.
2. The method according to claim 1 , further comprising:
determining a start time of the zero window event from a receiver, and determining an end time of the zero window event.
3. The method according to claim 2 , wherein said reporting a duration of a zero window delay comprises determining the amount of time between said start time and end time.
4. The method according to claim 2 , wherein said determining whether a zero window event caused said data transmission to be withheld comprises determining whether a subsequent transmission after said end time was a data transmission delayed during said time between said zero window start time and said zero window end time.
5. A network test instrument for determining zero window delay, comprising: a network interface for observing network traffic; and
a processor, said processor including employing observed network traffic to:
determine a start time of a zero window event advertisement from a receiver:
determine an end time of the zero window event;
determine whether a sender withheld data transmission until the end of the zero window event;
determine whether the zero window event caused said data transmission to be withheld; and
report a duration of a zero window delay only when it is determined the sender withheld said data transmission until the end of the zero window event.
6. A network test instrument according to claim 5 , wherein said processor determines whether the zero window event caused said data transmission to be withheld by determining whether a subsequent transmission after said end time was a data transmission that was delayed between said zero window start time and said zero window end time and wherein said processor reports a duration of the zero window delay by:
determining the amount of time between said start time and end time; and
if said determining whether a subsequent transmission after said end time was a data transmission that was delayed results in a determination of delay, reporting the duration of the zero window delay based on said determined amount of time between said start time and end time.
7. A system for determining zero window delay, comprising:
a network monitor for observing network traffic at a first location on a network; and
a processor at a second location on the network different from said first location, said processor including employing observed network traffic to:
determine a start time of a zero window event advertisement from a receiver,
determine an end time of the zero window event;
determine whether a sender withheld data transmission until the end of the zero window event;
determine whether the zero window event caused said data transmission to be withheld; and
report a duration of a zero window delay only when it is determined the sender withheld said data transmission until the end of the zero window event.
8. A system test instrument according to claim 7 , wherein said processor determines whether the zero window event caused said data transmission to be withheld by determining whether a subsequent transmission after said end time was a data transmission that was delayed between said zero window event start time and said zero window event end time; and if said determining whether a subsequent transmission after said end time was a data transmission that was delayed results in a determination of delay, said processor reports the zero window delay based on an amount of time between said start time and end time.