Packetizer

RTP Payload Types (Q9)


The information in this article applies to: H.323, H.225.0, H.245, RTP (RFC 3550)

If there is a static payload type defined for a media, it must be used. Several endpoints currently violate this requirement. Here are the relevant passages in H.225.0v2. 6.2.1: "Payload Type(PT): Only ITU-T payload types such as (0)[PCMU], (8)[PCMA], (9)[G722], and (15)[G728] shall be used. Dynamic payload types exchanged using H.245 signaling shall be used for any ITU-T payload types not listed in Annex B." 6.2.2: "Payload Type(PT): Only ITU-T payload types such as that for H.261 shall be used. Dynamic payload types may be used for H.263 or other ITU-T algorithms for which payload types do not exist." (A payload has been defined for H.263 since this was written, so now the static payload type of 34 must be used for H.263.)

    PT         encoding      audio/video    clock rate    channels
               name          (A/V)          (Hz)          (audio)
 
    0          PCMU          A              8000          1
    8          PCMA          A              8000          1
    9          G722          A              8000          1
    4          G723          A              8000          1
    15         G728          A              8000          1
    18         G729          A              8000          1
    31         H261          V              90000
    34         H263          V              90000
    96--127    dynamic       ?
 
    Table 2/Annex B-H.225.0:
    Payload types (PT) for standard audio and video encodings