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data-link layer and physical layer protocols establish an error-free communication
of raw bits between two nodes.
The network layer is responsible for setting up a logical path between two nodes
for communication to take place. It encapsulates frames into packets that can be
transmitted from one node to another using a high-level addressing and routing scheme. That is, routing is the primary job of the network layer and the routing
algorithm forms the main part of the network layer protocols of the network.
Two popular network layer protocols are the X.25 Protocol and the Internet
Protocol (called IP). The X.25 is a connection-oriented protocol that is based on
the concept of establishing a virtual circuit between the sender and receiver before
the actual communication starts between them. In this protocol, a request for
connection is first sent to the destination, which can either be accepted or rejected.
If the connection is accepted, the requesting party is given a connection identifier
to use in subsequent requests. During the connection establishment phase, a route
between the two parties is also decided that is used for the transmission of
On the other hand, IP is a connectionless protocol in which no connection is
established between the sender and receiver before sending a message. Therefore,
each packet of the message is transmitted independently and may take a different
route. IP is part of the DoD (U.S. Department of Defense) protocol suite.
Notice that the functions performed at the network layer are primarily required in
WANs. In a single LAN, the network layer is largely redundant because packets
can be transmitted directly from any node on the network to any other node.
Therefore the network layer, if present, has little work to do.
The job of the transport layer is to provide node-to-node communication and to
hide all the details of the communication subnet from the session layer by
providing a networ...
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- Spring '14