> For the complete documentation index, see [llms.txt](https://numerous-networks.gitbook.io/noversight-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://numerous-networks.gitbook.io/noversight-docs/noversight-tutorial/noversight-macos-analysis/noversight-wi-fi-analysis/analysis-views-bottom-half/session-timeline.md).
# Session Timeline
Exploring Wi-Fi using sessions is powerful to help understand which APs are working well, where the stresses are on the network and where performance issues are showing.
The essence of the Session Timeline is to display the associations made by a device across time - providing a powerful way to quickly navigate towards issues.
{% hint style="info" %}
When looking at a Session Timeline, here are the main things you would look out for
* Are there any APs which had low signal strength for long periods
* Are there situations where a session change moves to an AP with low signal strength
* Are there situations where the device ping-pongs between APs
* Are there times where congestion is consistently high and/or retries are significant
* Are the PHY rates as you would expect them to be all the time?
{% endhint %}
### Session-aligned signal quality
Vertical marker bars are used to identify where sessions change, aligning the RSSI and physical layer metrics to the session bars below. This makes it easier to understand how these metrics are changing around the time the network changes between APs
The physical layer performance charts show
* Tx and Rx Retry Ratios. These are a metric of packet retries. In the Apple logs, retry rates can go above 100% following periods where errors repeatedly occur and retries compound. The charts are capped at 100% retry ratio to ensure they remain readable (and do not go off the scale)
* Tx and Rx rates. These are the negotiated PHY rates and are helpful in understanding the quality of the link and observing when the link needs to adapt, indicating potential concerns in the network.
{% hint style="info" %}
As MCS is not reported by the iPhone and iPad devices, PHY rates, SNR and bandwidth are the other metrics we have available
{% endhint %}
### Session detail
Selecting a session bar reveals some key details about the AP, the join and leave/roam times and reasons.
Roam duration is indicated as a percentage as a high roam duration proves to be in indicator of a session which needed to roam but could not (roam attempts were failing or being abandoned)
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