Which of the following OSI layers establishes, manages, and terminates the connections between
the local and remote applications?

A.
Data Link layer

B.
Network layer

C.
Application layer

D.
Session layer

Explanation:

The session layer of the OSI/RM controls the dialogues (connections) between computers. It
establishes, manages and terminates the connections between the local and remote application. It
provides for full-duplex, half-duplex, or simplex operation, and establishes checkpointing,
adjournment, termination, and restart procedures. The OSI model made this layer responsible for
graceful close of sessions, which is a property of the Transmission Control Protocol, and also for
session checkpointing and recovery, which is not usually used in the Internet Protocol Suite. The
Session Layer is commonly implemented explicitly in application environments that use remote
procedure calls.
Answer option C is incorrect. The Application Layer of TCP/IP model refers to the higher-level
protocols used by most applications for network communication. Examples of application layer
protocols include the File Transfer Protocol (FTP) and the Simple Mail Transfer Protocol (SMTP).
Data coded according to application layer protocols are then encapsulated into one or more
transport layer protocols, which in turn use lower layer protocols to affect actual data transfer.
Answer option A is incorrect. The Data Link Layer is Layer 2 of the seven-layer OSI model of
computer networking. It corresponds to or is part of the link layer of the TCP/IP reference model.
The Data Link Layer is the protocol layer which transfers data between adjacent network nodes in
a wide area network or between nodes on the same local area network segment. The Data Link
Layer provides the functional and procedural means to transfer data between network entities and
might provide the means to detect and possibly correct errors that may occur in the Physical
Layer. Examples of data link protocols are Ethernet for local area networks (multi-node), the Pointto-Point Protocol (PPP), HDLC, and ADCCP for point-to-point (dual-node) connections.
Answer option B is incorrect. The network layer controls the operation of subnet, deciding which
physical path the data should take, based on network conditions, priority of service, and other
factors. Routers work on the Network layer of the OSI stack.