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C1.2.3. Disadvantages:
•
Greater complexity of the intermediate switching devices, which need to have higher
speed and greater calculating capacity to determine the appropriate route for each
packet.
•
Packet duplication. If a packet takes too long to reach its destination, the receiving
device may conclude that it has been lost, in which case it will send a packet
retransmission request to the sender, which gives rise to the arrival of duplicate
packets.
•
If the routing calculations account for an appreciable percentage of the transmission
time, the channel throughput (useful information / transmitted information) decreases.
•
Variations in the mean transit delay of a packet in the network. Parameter known as
jitter.
C2. IP Protocol.
The Internet Protocol (IP) is a non-connection oriented protocol used both by the origin and the
destination in data transmission over a switched packet network.
The data in an IP-based network are sent in blocks known as packets or datagrams (in the IP
protocol these terms are used interchangeably). In particular, in IP there is no need for
configuration before a device attempts to send packets to another with which it has not
communicated previously.
The Internet Protocol provides an unreliable datagram service called UDP (User Datagram
Protocol), also known as “best effort”, a phrase that expresses good intentions but offers few
guarantees. IP does not offer any mechanism to determine whether a packet reaches its
destination, and only provides security (by means of checksums) to cover its headers, and not
the transmitted data. For example, since it gives no guarantee that the packet will reach its
destination, it could arrive damaged, in the wrong order with respect to other packets,
duplicated, or simply not arrive. If reliability is needed, it is provided by transport layer protocols
such as TCP (Transport Control Protocol).
Reliability over TCP is obtained through the use of retransmissions. Real-time applications such
as an audio link, with the timing requirements inherent in the information contained in the link,
do not offer any useful guarantee. Since the data that are not received, and whose
retransmission is requested of the sender by the receiver, will in most cases arrive out of order,
they will end up as useless information that will have served only to overload the network. For
all these reasons, the protocol selected to serve as a communication substrate in real-time
applications is UDP.
UDP Datagram
The protocols for transport over IP, independently of the reliability they offer, add new
functionalities to the basic ones provided by IP, such as packet numbering to facilitate, on the
receiving end, the detection of losses (although not their correction) and of disorder in the
information received; and the advent of the port concept as an identifier of different logic
connections over the same IP interface.
For complete information on IP protocol, we recommend consulting:
http://tools.ietf.org/html/rfc791
http://www.iana.org/assignments/port-numbers
