How does round-trip estimate if last send report packet lost in RTCP?

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From RFC 3550 we can use RTCP Sender report and Receiver report to estimate the round-trip time.

Quote from section 6.4.1:

delay since last SR (DLSR): 32 bits
  The delay, expressed in units of 1/65536 seconds, between
  receiving the last SR packet from source SSRC_n and sending this
  reception report block.  If no SR packet has been received yet
  from SSRC_n, the DLSR field is set to zero.

  Let SSRC_r denote the receiver issuing this receiver report.
  Source SSRC_n can compute the round-trip propagation delay to
  SSRC_r by recording the time A when this reception report block is
  received.  It calculates the total round-trip time A-LSR using the
  last SR timestamp (LSR) field, and then subtracting this field to
  leave the round-trip propagation delay as (A - LSR - DLSR).  This
  is illustrated in Fig. 2.  Times are shown in both a hexadecimal
  representation of the 32-bit fields and the equivalent floating-
  point decimal representation.  Colons indicate a 32-bit field
  divided into a 16-bit integer part and 16-bit fraction part.

  This may be used as an approximate measure of distance to cluster
  receivers, although some links have very asymmetric delays.

But how about if last sender report got lost, then the RTT calculate from above formula will not correct. Do I understand it correctly?

asked 48 secs ago

ZijingWu

642