MAYAH Communications

Technology Highlights

IP Overhead

At IP-transmissions the data stream consists of Payload (pure audio data e.g. one or more MPEG frame) and IP Overhead. In case of UDP protocol the absolute overhead is as large as 46 Bytes / packet and it consists of 8 Bytes UDP header, 20 Bytes IP header and 18 Bytes IEEE802.3 (Ethernet). RTP protocol has 58 Bytes overhead per packet. 12 Bytes - RTP, 8 Bytes UDP, 20 Bytes IP and 18 Bytes IEEE802.3.

Please note, that the RTP header used by MAYAH Audio Gateway Codecs is 12 Byte and not 16 Byte long since no contribution source identifiers are used.

The relative IP Overhead is calculated in percents of the original payload.

If the packet size mode is set variable then the payload is also rounded to the next full audio frame (MPEG) or audio block (Linear, apt-X/Eapt-X, ADPCM etc).

Here is one example of an IP overhead calculation for UDP connections.

Let's take one of the most popular algorithms MPEG L3 with a sample rate of 48 kHz and a bit rate of 256 Kbit/s. First of all we must find out the real frame length.
Frame length = 256 (bit rate) /48 (sample rate) * 144 (Byte) = 768 Byte
IP Overhead = ((768 Byte + 46 Byte)/768 Byte –1) * 100 % = approx. 6 %

For apt-X /Eapt-X algorithms there is a fixed block size instead of MPEG frame length as it was in the previous example. So the relative IP overhead calculation for Eapt-X with 20 Bit Stereo at the UDP packet size of 180 Bytes would be the following:

Payload = (180 [packet size] / 80 [block size] rounded up to the next integer) * 80 = 240 Byte
IP Overhead = ((240 Byte + 46 Byte)/240 Byte –1) * 100 % = approx. 19,7 %

Following you find the typical IP overhead rates for MPEG algorithms and apt-X/Eapt-X algorithms. Please note that packet size of 180 Bytes is set as default by MAYAH Audio Gateway Codecs. You can change it freely in the range from 2 to 1536 Bytes.

There is also a possibility of so called “synthesized packet mode size” which means that the operator can set the packet size individually, e.g. to adapt to an IP encapsulator or router. In that specific case, a complete MPEG frame will not be always in one packet.

For more details on MAYAH Audio and Video Codecs please turn to our specialists
by phone: +49 811 55 6 0, fax: +49 811 - 55 16 - 55 or e-mail: info@mayah.com