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correct processes running on each computer. A sequence number allows the datagrams to
be rebuilt in the correct order in the receiving computer, and a checksum verifies that the
data received is the same as the data sent. In addition to these fields, the TCP header
contains
the
following
informa tion:
acknowledgement
number,
offset,
reserved
flags,
window size, urgent pointer, option, and padding [6].
2.2.2.2 UDP
UDP
stands
for
User
Datagram
Protocol.
The
connectionless,
transport-
level
protocol
used
in
the
TCP/IP
suite
of
protocols,
usually
bundled
with
IP- layer
software.
Because
UDP does not add overhead, as does connection-oriented
TCP,
UDP
is
often
used
with
SNMP (Simple Network Management Protocol) applications. Multicast applications,
such as Mbone and the Real-time Transport Protocol that delivers
audio
and
video
streams use UDP as their delivery mechanism because the acknowledgment and
retransmission services offered by TCP are not needed and add too much overhead. If a
packet of audio data is lost, retransmission is neither practical nor desirable [6].
2.2.3 Internet Layer
In
internet
layer,
IP
(Internet
Protocol,
The
session- layer
protocol
that
regulates
packet
forwarding by tracking addresses, routing outgoing messages, and recognizing incoming
messages
in
TCP/IP
networks
and
the
Internet)
[6]
consider to be the most important
protocol
in this
layer. Main
function of this
layer
is to send packets
from one device
to
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