Data Link Layer:-
The study of design principles of Data Link Layer deals with the algorithms for achieving reliable, efficient communication between ‘2’ adjacent machines at DLL.
adjacent means those two machines are connected by a wire— a co-axial cable, telephone line (or) point-to point wireless channel.
The essential property of a channel –wire like— means sending the bits in the same order as they are sent .
Let us suppose we have a system A and machine B and these two are connected by a wire and assume that there is no means of any software in any machine then the picture seems to be as follows
as A just puts the bits on the wire and B just takes off the bits.
i.e, they have only a finite data rate and there is a non-zero propagation delay between the time a bit is sent and the time it is received and the communication devices makes errors occasionally.
these are the limitations that have been taken care for the efficiency of the data transfer.
The protocols used for communications must take all these factors into consideration.
i.e design issues and also the nature of errors , their causes and how they can be detected and corrected are all taken care in DLL.
Design issues of DLL:-
The DLL has specific functions to carryout those are
- Providing a well-defined service interface to the N/w layer.
- Dealing with the transmission errors.
- Regulating the flow of data so that slow receivers are not swamped by fast senders.
i.e, DLL takes the packets coming from N/W layer and are encapsulated into frames for Transmission.
each frame contains a frame header and a trailer and a payload field for holding the packet.
the heart of DLL does the frame formation.
Services provided to the N/W Layer:-
The function of DLL is to provide services to N/W layer