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library subroutines in the user's address space, and the application layer in the
user's address space, and the application layer in the user’s program.
The physical layer is responsible for transmitting raw bit streams between two
nodes. That is, it may convert the sequence of binary digits into electric signals,
light signals, or electromagnetic signals depending on whether t two nodes are on
a cable circuit, fiber-optic circuit, or microwave/radio circuit, respectively.
Electrical details such as how many volts to use for 0 and 1, how many bits can be
sent per second, and whether transmission can take place only in one direction or
in both directions simultaneously are also decided by the physical layer take place
only in one direction or in both directions simultaneously are also decided by the
physical layer protocols. In addition, the physical layer protocols also deal with the
mechanical details such as the size and shape of the connecting plugs, the number
of pins in the plugs, and the function of each pin. In short, the physical layer
protocols deal with the mechanical, electrical, procedural, and functional
characteristics of transmission of raw bit streams between two sites. RS232-C is a
popular physical layer standard for serial communication lines.
The physical layer simply transmits the data from the sender's node to the
receiver's node as raw bits. It is the responsibility of the data-link layer to detect
and correct any errors in the transmitted data. Since the physical layer is only
concerned with a raw bit stream, the data-link layer partitions it into frames so that
error detection and correction can be performed independently for each frame. The
data-link layer also performs flow control of frames between two sites to ensure
that a sender does not overwhelm a receiver by sending frames at a rate faster than
the receiver can process. Therefore, the error control and flow control mechanisms
of a network form the data-link layer protocols in the OSI model. Notice that th...
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- Spring '14