Compare and contrast flow control and
error control in data transmission. Also, suggest the solutions for each.
Ans
Data communication requires at least
two devices working together, one to send and the other to receive. Even such a
basic arrangement requires a great deal of coordination for a clear exchange to
occur. The most important responsibilities of the data link layer are flow
control and error control.
Flow Control
Flow control coordinates the amount
of data that can be sent before receiving an acknowledgment and is one of the
most important duties of the data link layer. In most protocols, flow control
is a set of procedures that tells the sender how much data it can transmit
before it must wait for an acknowledgment from the receiver. The flow of data
must not be allowed to overwhelm the receiver. Any receiving device has a
limited speed at which it can process incoming data and a limited amount of
memory in which to store incoming data. The receiving device must be able to
inform the sending device before those limits are reached and to request that
the transmitting device send fewer frames or stop temporarily. Incoming data
must be checked and processed before they can be used. The rate of such
processing is often slower than the rate of transmission. For this reason, each
receiving device has a block of memory, called a buffer, reserved for storing
incoming data until they are processed. If the buffer begins to fill up, the
receiver must be able to tell the sender to halt transmission until it is once
again able to receive.
Flow control refers to a set of
procedures used to restrict the amount of data that the sender can send before
waiting for acknowledgment.
Error Control
Error control is both error detection
and error correction. It allows the receiver to inform the sender of any frames
lost or damaged in transmission and coordinates the retransmission of those
frames by the sender. In the data link layer, the term error control refers
primarily to methods of error detection and retransmission. Error control in
the data link layer is often implemented simply: Any time an error is detected
in an exchange, specified frames are retransmitted. This process is called
automatic repeat request (ARQ).
Error control in the data link layer
is based on automatic repeat request, which is the retransmission of data.
The Internet provides a platform for
rapid and timely information exchange among adisparate array of clients and
servers. TCP and IP are separately designed and closelytied protocols that
define the rules of communication between end hosts, and are themost commonly
used protocol suite for data transfer in the Internet. The combinationof TCP/IP
dominates today’s communication in various networks from the wiredbackbone to
the heterogeneous network due to its remarkable simplicity andreliability. TCP
has become the de facto standard used in most applications rangingfrom interactive
sessions such as Telnet and HTTP, to bulk data transfer like FTP.TCP was
originally designed primarily for wired networks. In a wired network,random bit
error rate, a characteristic usually more pronounced in the wirelessnetwork, is
negligible, and congestion is the main cause of packet loss. The
emergingwireless applications, especially high-speed multimedia services and
the advent of wireless IP communications carried by the Internet, call for
calibration andsophisticated enhancement or modifications of this protocol
suite for improvedperformance. Many studies have shown that the unmodified
standard TCP performspoorly in a wireless environment due to its inability to
distinguish packet lossescaused by network congestion from those attributed
to transmission errors.
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