TCP method
General
The TCP method relates to the transmission control protocl (TCP). A single measurement sends a TCP request to the specified target hostname and measures the round-trip-time. By default port 443 is used. The general validity of the returned TLS certificate (e.g. that it is trusted and not expired) can optionally be checked.
When to use the TCP method
Usually services use HTTP to transfer their data. But some services just use TCP (e.g. IMAP, LDAP) for the data exchange. To monitor the performance and availability of those services it is best to send TCP packets and measure their round-trip-time. If a service uses HTTP but you are only interested in the availability of that service rather than its performance you can also use TCP to monitor that service.
Parameters
These are the parameters that are configurable for each test using the TCP method.
Hostname
Specifies the hostname of the target service.
Examples: example.comt, worldaz.tr.teams.microsoft.com
Port
Specifies the port at which the target service is running.
Default: 443 (HTTPS)
Allowed inputs: 1 - 65535
Validate TLS certificate
If this option is checked, a TLS handshake is executed once per test run. The returned certificate is validated regarding e.g. the expiration date and checks if it legitimate and links back to a Root certificate authority (CA) on the client.
Default: unchecked
Number of measurements
Specifies the number of TCP requests send per minute. To measure the performance a value between 5 and 10 measurements is recommended. It is also recommended to have not more than 20 requests to not overload the client or service. To measure the availability one or two requests are sufficient.
Allowed inputs: 1 - 58
Warning/critical threshold
The thresholds define the latency beyond which a measurement gets the status warning or critical. TCP requests to a (nearby) servers usually take between 20ms to 100ms. It is unusual for a TCP request to take more than 200ms. The TCP requests time out after 20s.
Base warning threshold: 100ms
Base critical threshold: 200ms
Allowed inputs: 1 - 10.000 and has to be less than the critical threshold.
Status percentage
See Status percentage. Around two slow TCP requests per test run are normal and generally not noticeable for the experienced performance.
Allowed inputs: 1 - 100.
Limitations and recommondations
- HTTP requests might go to a proxy while TCP packets do not over a proxy. Keep that in mind when monitoring a service with TCP that usually uses HTTP.
- The underlying operating system limits the number of concurrent TCP connections in pending which can impact the client. Therefore do not execute too many TCP-based tests on one client. It is recommended to have not more than 10 TCP-based tests.
Example test
The Teams audio/video (TCP) test measures the latency to the Teams TURN server using TCP. As teams uses