Lec-7 Transport Layer

Transport Layer Protocols (7.1)
As previously discussed, for communication to occur between source and destination, a set of rules
or protocols must be followed.
Transportation of Data (7.1.1)
In the TCP/IP model, data that originates from application programs is passed to the application layer,
which in turn passes the data to the transport layer.
Role of the Transport Layer (7.1.1.1, 7.1.1.2)
The transport layer is responsible for establishing a temporary communication session between two
applications and delivering data between them. An application generates data that is sent from an
application on a source host to an application on a destination host, without regard to the destination
host type, the type of media over which the data must travel, the path taken by the data, the congestion
on a link, or the size of the network. As shown in Figure 7-1, the transport layer is the link between
the application layer and the lower layers that are responsible for network transmission.
The transport layer provides a method of delivering data across the network in a way that ensures that
the data can be properly put back together on the receiving end. The transport layer provides the
segmentation of data and the controls necessary to reassemble these segments into the various
communication streams. In TCP/IP, these segmentation and reassembly processes can be achieved
using two very different transport layer protocols: Transmission Control Protocol (TCP) and User
Datagram Protocol (UDP).
The primary responsibilities of transport layer protocols are
Tracking the individual communication between applications on the source and destination
hosts
Segmenting data for manageability and reassembling segmented data into streams of application
data at the destination
Identifying the proper application for each communication stream
Tracking Individual Conversations
At the transport layer, each particular set of data flowing between a source application and a
destination application is known as a conversation. A host can have multiple applications that are
communicating across the network simultaneously. Each of these applications communicates with one
or more applications on one or more remote hosts. It is the responsibility of the transport layer to
maintain and track these multiple conversations.