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+QUIC Statistics Manager
+=======================
+
+The statistics manager keeps track of RTT statistics for use by the QUIC
+implementation.
+
+It provides the following interface:
+
+Instantiation
+-------------
+
+The QUIC statistics manager is instantiated as follows:
+
+```c
+typedef struct ossl_statm_st {
+    ...
+} OSSL_STATM;
+
+int ossl_statm_init(OSSL_STATM *statm);
+
+void ossl_statm_destroy(OSSL_STATM *statm);
+```
+
+The structure is defined in headers, so it may be initialised without needing
+its own memory allocation. However, other code should not examine the fields of
+`OSSL_STATM` directly.
+
+Get RTT Info
+------------
+
+The current RTT info is retrieved using the function `ossl_statm_get_rtt_info`,
+which fills an `OSSL_RTT_INFO` structure:
+
+```c
+typedef struct ossl_rtt_info_st {
+    /* As defined in RFC 9002. */
+    OSSL_TIME smoothed_rtt, latest_rtt, rtt_variance, min_rtt,
+              max_ack_delay;
+} OSSL_RTT_INFO;
+
+void ossl_statm_get_rtt_info(OSSL_STATM *statm, OSSL_RTT_INFO *rtt_info);
+```
+
+Update RTT
+----------
+
+New RTT samples are provided using the  `ossl_statm_update_rtt` function:
+
+  - `ack_delay`. This is the ACK Delay value; see RFC 9000.
+
+  - `override_latest_rtt` provides a new latest RTT sample. If it is
+    `OSSL_TIME_ZERO`, the existing Latest RTT value is used when updating the
+    RTT.
+
+The maximum ACK delay configured using `ossl_statm_set_max_ack_delay` is not
+enforced automatically on the `ack_delay` argument as the circumstances where
+this should be enforced are context sensitive. It is the caller's responsibility
+to retrieve the value and enforce the maximum ACK delay if appropriate.
+
+```c
+void ossl_statm_update_rtt(OSSL_STATM *statm,
+                           OSSL_TIME ack_delay,
+                           OSSL_TIME override_latest_rtt);
+```
+
+Set Max. Ack Delay
+------------------
+
+Sets the maximum ACK delay field reported by `OSSL_RTT_INFO`.
+
+```c
+void ossl_statm_set_max_ack_delay(OSSL_STATM *statm, OSSL_TIME max_ack_delay);
+```