The transport layer manages the transport of messages at the application level between the client and the pages of the application server by adapting the data transmission over the network and the service required by the user. It performs a multiplexing of data between different processes, fragmenting packets from the top layers into packets whose size is adapted to the network. Depending on the type of data to be transmitted, there are two types of transport protocols. In the connection mode, the service includes guaranteed transmission of messages at the application level; There is no loss of package and the packages received are correct. This can lead to significant transmission delays. In unconnected mode, packages are transmitted only once by the transmitter and there is no confirmation procedure on the packages. It`s a slight delay, but risky transmission. At this level, the package can take two names. It is called a datagram if the protocol is unconnected (p.B.

UDP) or segment if it is oriented to the connection (z.B. TCP). Modern information systems rarely operate in isolation and, like other types of organizations, federal authorities often integrate two or more systems to exchange data or exchange information resources. A system connection is a direct link between information systems; Information system holders must document all system connections in the system security plan and set appropriate security measures for each connection [51]. System owners must document system connections between different information systems within the same agency or beyond agency boundaries and describe, for systems at both ends of the connection, the name of the system, the organizational unit responsible for the system, the type of interconnection, all agreements concluded and their validity dates, the stage of security categorization. , the status of the security authority and the name of the authorized official [51]. Agency government boards require the identification and documentation of system connections [14], whether these links integrate systems into a single agency, two different agencies or between an agency and an external service provider. Figure 4.3 shows the diversity of types of system connections.

In many agencies, information system holders use other methods of formal liaison agreements when affiliated systems are placed under the control of the same ordering system. Federal system consolidation guidelines apply primarily to situations where each system is owned and operated by a different organization, including several parts of the same agency [52]. Before delving into the internal affairs of this model, let`s take a look at the types of data and see how marshalling and unmarshalling happens.