Question on Data and Voice Packets

WilliamK99

I am reviewing some Transcender Flash Cards, and ran into a question I knew nothing about, the question is

Which uses less overhead, data or voice packets?

Considering Data uses TCP and Voice uses UDP, I figured this was a sure thing and guessed Voice, come to find out it was data. I did a little research and could not find out why Data packets have less overhead. By using TCP, there is already substantial overhead, so I am curious how this is the case.

Thanks...

networker050184

Data can use UDP or TCP, so that is not a determination. The question is most likely referring to the RTP header as the extra overhead. Voice packets will also have a much smaller payload to overhead ratio than data packets.

fieldmonkey

WilliamK99 wrote: »

I am reviewing some Transcender Flash Cards, and ran into a question I knew nothing about, the question is

Which uses less overhead, data or voice packets?

Considering Data uses TCP and Voice uses UDP, I figured this was a sure thing and guessed Voice, come to find out it was data. I did a little research and could not find out why Data packets have less overhead. By using TCP, there is already substantial overhead, so I am curious how this is the case.

Thanks...

just stabbing at this one ... but ...

UDP is flooding the port, were as TCP would be receiving / sending ACK's... a controlled transmission?

kalebksp

networker is correct. Since data is (generally) not time sensitive, maximum sized packets can be sent, therefor the overhead to data ratio is small. Because voice traffic is time sensitive it must be sent in many small packets, resulting in a high overhead to data ratio.

For example, compare a 1460 byte data packets to a 20 byte G729a voice packet (20 bytes is fairly standard for G729a) over Ethernet:

The data uses 58 bytes of overhead in this case (20 bytes TCP + 20 bytes IP + 18 bytes Ethernet), and voice will also use 58 bytes (12 bytes RTP + 8 bytes UDP + 20 bytes IP + 18 bytes Ethernet).

58 / 1518 = ~4% of the data packet is overhead
58 / 78 = ~74% of the voice packet is overhead

Obviously the overhead for the voice is much greater. Of course this is way more detailed than you need to know for CCNA, but hopefully it clarifies the answer to that question for you.

fleck

Only studying Network+ right now but I immediately thought voice. Only because it seemed logical.