Voice Over IP – Per Call Bandwidth Consumption

Bandwidth Calculation Formulas

These calculations are used:

  • Total packet size = (L2 header: MP or FRF.12 or Ethernet) + (IP/UDP/RTP header) + (voice payload size)
  • PPS = (codec bit rate) / (voice payload size)
  • Bandwidth = total packet size * PPS

Sample Calculation

For example, the required bandwidth for a G.729 call (8 Kbps codec bit rate) with cRTP, MP and the default 20 bytes of voice payload is:

  • Total packet size (bytes) = (MP header of 6 bytes) + ( compressed IP/UDP/RTP header of 2 bytes) + (voice payload of 20 bytes) = 28 bytes
  • Total packet size (bits) = (28 bytes) * 8 bits per byte = 224 bits
  • PPS = (8 Kbps codec bit rate) / (160 bits) = 50 pps

    Note: 160 bits = 20 bytes (default voice payload) * 8 bits per byte

  • Bandwidth per call = voice packet size (224 bits) * 50 pps = 11.2 Kbps

Ref:http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080094ae2.shtml

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