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Introduction |
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The project is design and builds a data link simulator of the various data link control protocols and parameters. Where it is designing a transmitter-receiver pair of programs, one system send information to another system. The system will look for the error occurrence and immediately made detection, control, and report the errors. It is achieved with impose a layer of control in each communicating device that provides functions for flow control, error detection and error control.
Techniques to control the flow of data from a sender to receiver
are Stop-and-Wait flow control and Sliding Windows flow controls. The
Stop-and-Wait data flow control allow one message to be transmitted
checked for errors with techniques such as VRC or LRC, and an appropriate
ACK or NAK returned to sending station, no other data messages can be
transmitted until the receiving station sends back a reply. The inefficiency
of the Stop-and-Wait data flow control resulted in the development of
technique to provide for the overlapping of data message and their corresponding
continuous message.
But sometimes errors may occur during transmission of frames
as a result of lost frame or damaged frame, so we design the error detection
algorithms, which are Parity Check and Cyclic Redundancy Check (CRC)
to handle this problem. Parity Check is the simplest error detection
scheme to append a parity bit to the end of a block of data, such as
ASCII transmission, parity bit attached to 7 bit ASCII character, and
the character has an odd and even number of 1.CRC is quite widely used
today, the CRC approach entails the division of the user data stream
by a predetermined binary number, the remainder of the number is appended
to message as FCS field. The data stream at the receiving side has another
calculation performed and compared to the FCS field. If the remainder
is zero, the message is accepted as correct. When there is a damaged frame that have not been acknowledged, or retransmission is requested, we will use the Automatic repeat request (ARQ), that is a protocol for error control in data transmission. When the receiver detects an error in a packet, it automatically requests the transmitter to resend the packet. This process is repeated until the packet is error free or the error continues beyond a predetermined number of transmissions. ARQ is sometimes used with Global System for Mobile (GSM) communication to guarantee data integrity. ARQ is responsible to turn an unreliable data link into a reliable one. |
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Methodology |
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System development methodology is a standard process followed in an organization to conduct all the steps necessary to analyze, design, implement and maintain information systems. After discussion, we decided to choose System Development Life Cycle (SDLC) as our system development methodology that used to develop, maintain and replace information systems.
SDLC is divided into six phases such as Initiation, Analysis,
Design, Implementation, Review and Maintenance phase. The specific steps
and their sequence are meant to adapt as required for a project, consistent
with management approach. The system can be thought of as a circular
process which end of one system leads to the beginning of another project
that will develop new version or replace and existing system altogether.
Basically we choose this methodology because of we is familiar
with this approach, which we been used many times before in other projects.
The main reason we choose this approach because it is easy to handle
and it is all about teamwork. Besides, the effectiveness of it wills
more to guide us step by step and this way able to product a good result.
Further more, by separate part by part we not easily get confused instead
we able to do in efficiently. Other than that, it allows us to find more information needed and gain more knowledge to understand the purpose of the project by does some research. Consequently, it brings us into nearer to the objectives and achieves the goals. |
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