[core] Init reorder tolerance with maximum value.

See #901.

docs/statistics.md

@@ -7,10 +7,10 @@ and are not exchanged between peers, unless explicitly stated.
 
 The following API functions can be used to retrieve statistics on an SRT socket.
 Refer to the documentation of the [API functions](API-functions.md) for usage instructions.
+
 * `int srt_bstats(SRTSOCKET u, SRT_TRACEBSTATS * perf, int clear)`
 * `int srt_bistats(SRTSOCKET u, SRT_TRACEBSTATS * perf, int clear, int instantaneous)`
 
-
 # Total accumulated measurements
 
 ## msTimeStamp
@@ -39,22 +39,22 @@ The total number of data packets detected lost on the receiver's side.
 
 Includes packets that failed to be decrypted (only as of SRT version 1.4.0).
 
-If a packet was received out of order, the gap (sequence discontinuity) is also 
+If a packet was received out of order, the gap (sequence discontinuity) is also
 treated as lost packets, independent of the reorder tolerance value.
 
-Loss detection is based on gaps in Sequence Numbers of SRT DATA packets. Detection 
-of a packet loss is triggered by a newly received packet. An offset is calculated 
-between sequence numbers of the newly arrived DATA packet and previously received 
-DATA packet (the received packet with highest sequence number). Receiving older 
-packets does not affect this value. The packets from that gap are considered lost, 
-and that number is added to this `pktRcvLossTotal` measurement. In the case where 
-the offset is negative, the packet is considered late, meaning that it was either 
-already acknowledged or dropped by TSBPD as too late to be delivered. Such late 
+Loss detection is based on gaps in Sequence Numbers of SRT DATA packets. Detection
+of a packet loss is triggered by a newly received packet. An offset is calculated
+between sequence numbers of the newly arrived DATA packet and previously received
+DATA packet (the received packet with highest sequence number). Receiving older
+packets does not affect this value. The packets from that gap are considered lost,
+and that number is added to this `pktRcvLossTotal` measurement. In the case where
+the offset is negative, the packet is considered late, meaning that it was either
+already acknowledged or dropped by TSBPD as too late to be delivered. Such late
 packets are ignored.
 
 ## pktRetransTotal
 
-The total number of retransmitted packets. Calculated on the sender's side only. 
+The total number of retransmitted packets. Calculated on the sender's side only.
 Not exchanged with the receiver.
 
 ## pktSentACKTotal
@@ -256,12 +256,21 @@ Same as `usSndDurationTotal`, but measured on a specified interval.
 
 ## pktReorderDistance
 
-`SRTO_LOSSMAXTTL` sets the maximum reorder tolerance value. The internal algorithm 
-checks the order of incoming packets and adjusts the tolerance based on the reorder 
+The distance in sequence numbers between the two original (not retransmitted) packets,
+that were received out of order. Receiver only.
+
+The traceable distance values are limited by the maximum reorder tolerance set by  `SRTO_LOSSMAXTTL`.
+`SRTO_LOSSMAXTTL` sets the maximum reorder tolerance value, or the time-to-live for the original packet,
+that was received after with a gap in the sequence of incoming packets. Those missing packets
+are expected to come out of order, therefore no loss is reported.
+The TTL value specifies the number of packet to receive further, before considering the preceding packets lost,
+and sending the loss report.
+
+The internal algorithm checks the order of incoming packets and adjusts the tolerance based on the reorder
 distance, but not to a value higher than the maximum.
 
-SRT starts from 0 tolerance. Once it receives the first 
-reordered packet, it increases the tolerance to the distance in the sequence
+SRT starts from tolerance value set in `SRTO_LOSSMAXTTL` (initial tolerance is set to 0 in SRT v1.4.0 and prior versions).
+Once the receiver receives the first reordered packet, it increases the tolerance to the distance in the sequence
 discontinuity of the two packets. \
 After 10 consecutive original (not retransmitted) packets come in order, the reorder distance
 is decreased by 1 for every such packet.

srtcore/core.cpp

@@ -328,6 +328,7 @@ CUDT::CUDT(const CUDT &ancestor)
     m_bTLPktDrop            = ancestor.m_bTLPktDrop;
     m_bMessageAPI           = ancestor.m_bMessageAPI;
     m_iIpV6Only             = ancestor.m_iIpV6Only;
+    m_iReorderTolerance     = ancestor.m_iMaxReorderTolerance;  // Initialize with maximum value
     m_iMaxReorderTolerance  = ancestor.m_iMaxReorderTolerance;
     // Runtime
     m_bRcvNakReport             = ancestor.m_bRcvNakReport;
@@ -708,6 +709,8 @@ void CUDT::setOpt(SRT_SOCKOPT optName, const void *optval, int optlen)
 
     case SRTO_LOSSMAXTTL:
         m_iMaxReorderTolerance = *(int *)optval;
+        if (!m_bConnected)
+            m_iReorderTolerance = m_iMaxReorderTolerance;
         break;
 
     case SRTO_VERSION: