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4.7. VoIP Metrics Report Block

4.7. VoIP Metrics Report Block​

The VoIP Metrics Report Block provides metrics for monitoring voice over IP (VoIP) calls. These metrics include packet loss and discard metrics, delay metrics, analog metrics, and voice quality metrics. The block reports separately on packets lost on the IP channel, and those that have been received but then discarded by the receiving jitter buffer. It also reports on the combined effect of losses and discards, as both have equal effect on call quality.

In order to properly assess the quality of a Voice over IP call, it is desirable to consider the degree of burstiness of packet loss [14]. Following a Gilbert-Elliott model [3], a period of time, bounded by lost and/or discarded packets with a high rate of losses and/or discards, is a "burst", and a period of time between two bursts is a "gap". Bursts correspond to periods of time during which the packet loss rate is high enough to produce noticeable degradation in audio quality. Gaps correspond to periods of time during which only isolated lost packets may occur, and in general these can be masked by packet loss concealment. Delay reports include the transit delay between RTP end points and the VoIP end system processing delays, both of which contribute to the user perceived delay. Additional metrics include signal, echo, noise, and distortion levels. Call quality metrics include R factors (as described by the E Model defined in [6,3]) and mean opinion scores (MOS scores).

Implementations MUST provide values for all the fields defined here. For certain metrics, if the value is undefined or unknown, then the specified default or unknown field value MUST be provided.

The block is encoded as seven 32-bit words:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     BT=7      |   reserved    |       block length = 8        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        SSRC of source                         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   loss rate   | discard rate  | burst density |  gap density  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       burst duration          |         gap duration          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     round trip delay          |       end system delay        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| signal level  |  noise level  |     RERL      |     Gmin      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   R factor    | ext. R factor |    MOS-LQ     |    MOS-CQ     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   RX config   |   reserved    |          JB nominal           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          JB maximum           |          JB abs max           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

block type (BT): 8 bits A VoIP Metrics Report Block is identified by the constant 7.

reserved: 8 bits This field is reserved for future definition. In the absence of such a definition, the bits in this field MUST be set to zero and MUST be ignored by the receiver.

block length: 16 bits The constant 8, in accordance with the definition of this field in Section 3.

SSRC of source: 32 bits As defined in Section 4.1.

The remaining fields are described in the following six sections: Packet Loss and Discard Metrics, Delay Metrics, Signal Related Metrics, Call Quality or Transmission Quality Metrics, Configuration Metrics, and Jitter Buffer Parameters.

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