need help about question

You know, what worries me most about this question is the assumption in it that VoIP uses UDP because of lower overheads.

If you students want to stand out, challenge that statement in your answers. It is an oversimplification made by someone who has little understanding of the technology.

Over their heads I guess. What do you think guys 😉

Really? Why are you all asking exactly the same question then? It seems to be question 7 on your list.

I have no problem helping students. But, this is a place for open an constructive discussion.

as far i know…it is not possible to give exat percentage gain……’coz it will depend on RTT, delays, etc., What do u say Sir ,TOM

1)UDP has an 8 byte header, and TCP usually has a 20 byte header.
Let payload is x bytes

Throughput of voip will be given by formula:
(Payload+ udp/tcp header + rtp header + ip header) * 8 * (voip bitrate/payload in bits)

Terms :
Payload is constant as specified in problem
BitRate = bitrate defined by codec (ex. 8Kbps in G.729 )
Packets per second= (bitrate / payload in bits )
Num of packets required(dependent on payload) to send per second to maintain bitrate .
Header = RTP header( 12 bytes) + TCP/UDP header(20/8 bytes) + IP header(20 bytes).

Effective BW required by Voip call = (pay load + headers) * 8 * packets per second
= (payload + rtp header + IP header+ TCP/UDP header) *8 * (bitrate / (payload *8))
= ( pay load + 12+20+ TCP/UDP header) * 8 *(bitrate / (payload *8))

BW gain = 1-{( pay load + 32+ 8) * 8 *(bitrate / (payload *8))}/{ ( pay load + 32+20) * 8 *(bitrate / (payload *8))}
Bw gain=1-{pay load + 40}/{payload+52}
Lets take payload = 20 bytes as in case of G.729
Bw gain= 1-60/72
=.1666
=16.66% is the gain by using udp over tcp
(gain is calculated over tcp)
2) for each packet send tcp receives a ACK packet .
this features wastes BW in case of real time applications like VOIP and media streaming
because packet will be discarded at receiver if it is received late , but even then ACK packet will be sent by TCP. There is no such problem in UDP.

3) Udp never decreses its send rate . while TCP can decrease its send rate because of its congestion control algorithm, which is an overhead in case of VOIP.