CS601 GDB

GDB OF CS-601
DATA COMMUNICATION
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Because 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 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. The Data Link Layer is concerned with local
delivery of frames between devices on the same LAN. Data Link frames, as these
protocol data units are called, do not cross the boundaries of a local network. Internetwork
routing and global addressing are higher layer functions, allowing Data Link
protocols to focus on local delivery, addressing, and media arbitration. In this way, the
Data Link layer is analogous to a neighborhood traffic cop; it endeavors to arbitrate
between parties contending for access to a medium. The data link thus provides data
transfer across the physical link. That transfer can be reliable or unreliable; many data
link protocols do not have acknowledgments of successful frame reception and
acceptance, and some data link protocols might not even have any form of checksum to
check for transmission errors. In those cases, higher-level protocols must provide flow
control, error checking, and acknowledgments and retransmission. The Data Link Layer
protocols respond to service requests from the Network Layer and they perform their
function by issuing service requests to the Physical Layer. The Data Link Layer is often
implemented in software as a "network card driver". The operating system will have a
defined software interface between the data link and the network transport stack above.
This interface is not a layer itself, but rather a definition for interfacing between layers.
The data link thus provides data transfer across the physical link. That transfer can be
reliable or unreliable; many data link protocols do not have acknowledgments of
successful frame reception and acceptance, and some data link protocols might not even
have any form of checksum to check for transmission errors. In those cases, higher-level
protocols must provide flow control, error checking, and acknowledgments and
retransmission.