RTCP XR Report Block for Packet Delay Variation Metric Reporting

Metrics in this block report on packet delay variation in the stream arriving at the RTP system.

block type (BT): 8 bits A Packet Delay Variation Metrics Report Block is identified by the constant NJB. [Note to RFC Editor: please replace NPDV with the IANA provided RTCP XR block type for this block.] Interval Metric flag (I): 1 bit This field is used to indicate whether the Packet Delay Variation metrics block is an Interval or a Cumulative report, that is, whether the reported values apply to the most recent measurement interval duration between successive metrics reports (I=1) (the Interval Duration) or to the accumulation period characteristic of cumulative measurements (I=0) (the Cumulative Duration). Numerical values for both these intervals are provided in the Measurement Identifier block referenced by the tag field below. Measurement Identifier association (tag): 3 bits This field is used to identify the Measurement Identifier block which describes this measurement. The relevant Measurement Identifier block has the same tag value as the Packet Delay Variation Metrics block. Note that there may be more than one Measurement Identifier block per RTCP packet. Packet Delay Variation Metric Type (pdvtyp): 4 bits This field is used to identify the Packet Delay Variation Metric Type used in this report block, according to the following code:

bits 014-017 0: PPDV according to [RFC3550], 1: MAPDV according to [G.1020], 2: IPDV according to [Y.1540] Other values reserved block length: 16 bits The length of this report block in 32-bit words, minus one. For the Packet Delay Variation Metrics block, the block length is equal to 3. Positive Threshold/Peak PDV: 16 bit, S11:4 format The PDV associated with the Positive PDV percentile expressed in milliseconds. The term Positive is associated with packets arriving later than the expected time. If the measured value is more negative than -2047.9375 (the value which would be coded as 0x8001), the value 0x8000 SHOULD be reported to indicate an over-range negative measurement. If the measured value is more positive than +2047.8125 (the value which would be coded as 0x7FFD), the value 0x7FFE SHOULD be reported to indicate an over-range positive measurement. If the measurement is unavailable, the value 0x7FFF SHOULD be reported. Positive PDV Percentile: 16 bit, 8:8 format The percentage of packets on the call for which individual packet delays were less than the Positive Threshold PDV. If the measurement is unavailable, the value 0xFFFF SHOULD be reported. Negative Threshold/Peak PDV: 16 bit, S11:4 format The PDV associated with the Negative PDV percentile expressed in milliseconds. The term Negative is associated with packets arriving earlier than the expected time. If the measured value is more negative than -2047.9375 (the value which would be coded as 0x8001), the value 0x8000 SHOULD be reported to indicate an over-range negative measurement. If the measured value is more positive than +2047.8125 (the value which would be coded as 0x7FFD), the value 0x7FFE SHOULD be reported to indicate an over-range positive measurement. If the measurement is unavailable, the value 0x7FFF SHOULD be reported. Negative PDV Percentile: 16 bit, 8:8 format The percentage of packets on the call for which individual packet delays were more than the Negative Threshold PDV. If the measurement is unavailable, the value 0xFFFF SHOULD be reported. If the PDV Type indicated is IPDV and the Positive and Negative PDV Percentiles are set to 100.0 then the Positive and Negative Threshold/Peak PDV values are the peak values measured during the reporting interval (which may be from the start of the call for cumulative reports). In this case, the difference between the Positive and Negative Threshold/Peak values defines the range of IPDV. Mean PDV: (16 bit, S11:4 format) expressed in milliseconds For MAPDV this value is generated according to . For interval reports the MAPDV value is reset at the start of the interval. For PPDV the value reported is the value of J(i) calculated according to at the time the report is generated. For IPDV, the value reported is the mean of per-packet IPDV values. This metric indicates the arrival time of the first media packet of the session with respect to the mean of the arrival times of every packet of the session. A single value of the metric (for a single session) may not be useful by itself, but its average over a number of sessions may be useful in diagnosing media delay at session startup. For example, this might occur if media packets are often delayed behind signalling packets due to head-of-line blocking. If the measured value is more negative than -2047.9375 (the value which would be coded as 0x8001), the value 0x8000 SHOULD be reported to indicate an over-range negative measurement. If the measured value is more positive than +2047.8125 (the value which would be coded as 0x7FFD), the value 0x7FFE SHOULD be reported to indicate an over-range positive measurement. If the measurement is unavailable, the value 0x7FFF SHOULD be reported. unused: 16 bits These bits are unused. They SHOULD be set to zero by the sender and MUST be ignored by the receiver.

(a) To report PPDV (RFC3550): Threshold PDV = FFFF (Undefined); PDV Percentile = FFFF (Undefined); PDV type = 0 (PPDV) causes PPDV to be reported in the Mean PDV field. (b) To report MAPDV (G.1020): Pos Threshold PDV = 50.0; Pos PDV Percentile = 95.3; Neg Threshold PDV = 50.0 (note - implies -50ms); Neg PDV Percentile = 98.4; PDV type = 1 (MAPDV) causes average MAPDV to be reported in the Mean PDV field. Note that implementations may either fix the reported percentile and calculate the associated PDV level OR may fix a threshold PDV level and calculate the associated percentile. From a practical implementation perspective it is simpler to use the second of these approaches (except of course in the extreme case of a 100% percentile). IPDV, according to Y.1540 is the difference in delay between the current packet and the first packet of the stream. If the sending and receiving clocks are not synchronized, this metric includes the effect of relative timing drift.