1.Explain the services provided by transport layer
Answer:
Services Provided to the Upper Layers:
The ultimate goal of the transport layer is to provide efficient, reliable, and cost-effective data transmission service to its users, normally processes in the application layer. To achieve this, the
transport layer makes use of the services provided by the network layer. The software and/or
hardware within the transport layer that does the work is called the transport entity. The transport
entity can be located in the operating system kernel, in a library package bound into network
applications, in a separate user process, or even on the network interface card. The first two options
are most common on the Internet. The (logical) relationship of the network, transport, and application
layers is illustrated in Fig
- Connection-oriented communication: It is quite easy for the application to interpret the
connection as a data stream instead of having to cope up with the connectionless models that
underlie it. For example, internet protocol (IP) and the UDP’s datagram protocol. - Byte orientation: Processing the data stream is quite easy when compared with using the
communication system format for processing the messages. Because of such simplification, it
becomes possible for the applications to work up on message formats that underlie. - Same order delivery: Usually, it is not guaranteed by the transport layer that the data packets
will be received in the same order in which they were sent. But this is one of the desired
features of the transport layer. Segment numbering is used for incorporating this feature. The
data packets are thus passed on to the receiver in order. Head of line blocking is a
consequence of implementing this. - Reliability: During transportation some data packets might be lost because of errors and
problems such as network congestion. By using error detection mechanism such as CRC
(cyclic redundancy check), the data might be checked by the transport protocol for any
corruption and for the verification whether the correct reception of the data by either sending
a NACK or an ACK signal to the sending host. Some schemes such as the ARR (automatic
repeat request) are sometimes used for the retransmission of the corrupted or the lost data. - Flow control: The rate at which the data is transmitted between two nodes is managed for
preventing a sending host with a fast speed from the transmission of data more than what the
receiver’s data buffer can take at a time. Otherwise, it might cause a buffer overrun. - Congestion avoidance: Traffic entry into the network can be controlled by means of
congestion control by avoiding congestive collapse. The network might be kept in a state of
congestive collapse by automatic repeat requests.