The corporate head office has a teleconferencing system that uses VOIP(voice over IP)
technology. This system uses UDP as the transport for the data transmissions. If these UDP
datagrams arrive at their destination out of sequence, what will happen?

A.
UDP will send an ICMP information Request to the source host.

B.
UDP will pass the information in the datagrams up to the next OSI layer in the order that they
arrive.

C.
UDP will drop the datagrams.

D.
UDP will use the sequence numbers in the datagram headers to reassemble the data in the
correct order.

Explanation:
VOIP systems utilize UDP because it is faster and uses less overhead. In addition, the reliable
transport mechanism used in TCP is useless to VOIP because if a packet gets dropped and needs
to be resent, it will be already too late.
UDP provides a service for applications to exchange messages. Unlike TCP, UDP is
connectionless and provides no reliability, no windowing, and no reordering of the received data
. However, UDP provides some functions of TCP , such as data transfer, segmentation, and
multiplexing using port numbers, and it does so with fewer bytes of overhead and with less
processing required. UDP data transfer differs from TCP data transfer in that no reordering or
recovery is accomplished. Applications that use UDP are tolerant of lost data, or they have some
application mechanism to recover data loss.
ReferencE. CCNA Self-Study CCNA INTRO exam certification Guide (Cisco Press, ISBN 1-
58720-094-5) Page 161.