Problem on IP datagram

Question

In VOIP system, suppose h be the total number of header bytes added to each chunk, including UDP and IP header.

a)Supposing an IP datagram is emitted every 20 msec, find the transmission rate in bits per second for the datagrams generated by one side of the application.

b) What is the typical value when RTP is utilized?

Answer 1

A) Total number of header bytes = h
Let’s assume,
PCM-encoded voice: 64kbps=8000 bytes/s
8000 bytes/s * 20 msec/chunk = 160 bytes/chunk
(160 + h) bytes / datagram
1s / (20 msec) = 50 datagrams/s
Transmission rate = 50 * (160+h) bytes/s
= 0.4 * (160 + h) kbps
= (64 + 0.4h) kbps

B) IP header = 20 bytes
UDP header = 8 bytes
RTP header = 12 bytes
h = 40 bytes