Data Link Protocol and Communication Networks
What are the functions of data link?
Why and where is flow control needed? Explain its parameters.
Explain stop-and-wait flow control with special reference to the handling of (i) a damaged frame (ii) a lost frame.
Explain HDLC. What are the categories of HDLC stations?
What is the configuration and modes of HDLC?
What does “switching” mean? Explain the three possible switching methods.
Data Link Protocol and Communication Networks
Datalink
The data link, as its name suggests, makes sure that information packets are free of errors s they are passed on. It ensures that there is an appropriate physical protocol assigned to the data. The data link layer in the OSI model is classified as the second layer. The OSI or rather the Open Systems Interconnection is a model used to give knowledge on how systems or networks operate since they are quite complicated. The model has seven layers, which are the data link layer, physical layer, transport layer, network layer, presentation layer, session layer, and application layer. The data link layer performs three main functions. These functions include regulating the data flow, dealing with transmission errors, and providing an interface that is well defined to the network layer.
Sequence numbers and timers are used by the data link layer to transfer the data to the next sheet, which is the network layer. That is to make sure that all data is received successfully. Different services and protocols are used by the data link layer to complete its task. Protocols are defined as rules that are necessary for passing data to the next layer successfully (ComputerNetworkingNotes, 2010). The postal service is more comparable to the data link layer, where a package is brought by the sender to deliver to a specific place. The packages are relatable to frames of data. The first phase, which in this case is a postal worker inputs the packages into the system. That is to enable a connection. Also, the input of the variables required to keep track as it travels to the receiver.
Flow control
Flow control can be easily confused with control flow. Flow control is under data communications, which is the process of managing data transmission rates between two nodes. That is to prevent a slow receiver from being overwhelmed by a fast sender. Flow control and congestion control also differ. Congestion control is used to control the flow data in case congestion occurs. Mechanisms of flow control could be classified depending on how the feedback is sent by the receiving node to the sending node. The main agenda of flow control is to enable transmission of information through a sending computer at a rate faster than how a destination computer can process it after it is received. If there is a heavy traffic load on the receiving networks than the sending network, then that can happen. Also, if there is less processing power in the receiving computer than the sending computer.
There are different types of flow control, such as transmit flow control. It may happen between data terminal equipment and a switching center, through data circuit terminating equipment. Transmit flow control is categorized as hardware flow control and software flow control. The hardware flow control is handled by DTE or master end because first asserts or raises its line to command in the case of DTE sets its RTS, RTS control flow, which gives a signal to the opposite side to start monitoring the data input line. The software flow control is found in data links, and it uses codes that are special transmitted in-band over the primary communications channel.
The second type of flow control is open-loop flow control. It is characterized by not having feedback between the transmitter and the receiver. Allocation of its resources is enabled at the setup of a connection by the connection admission control (CAC). It is also used by asynchronous transfer mode (ATM) in its VBR, UBR, and CBR services. It contains the regulator and the controller, which are types of controls. The third type of flow control is the closed-loop flow control mechanism. It is characterized by how the network reports pending network congestion back to the transmitter. The transmitter then uses the information to adapt its functions to network conditions that already exist. The system contains the essential control elements like the controller, regulator, sensor, and transmitter.
Stop-and-wait flow control
When sending data, the transmission might experience an error or damage in the process of delivery. The error control is connected to a mechanism that detects and corrects errors in the frame transmission. There are two types of errors, which are the lost frame, which a frame that fails to reach the other side, and the damaged frame, which is a frame that has arrived but has errors. Stop-and-wait is a method of automatic repeat request that is used to correct such errors while sending the frame during transmission time (Ramadhan & Siahaan, 2016). The sending and receiving computers are used for data transmission. The method makes sure that information is not lost due to packet drops and that the packet received is in the right order. The stop-and-wait method fixes corrupted or lost data that occurs in the process of transmission automatically.
HDLC
HDLC is specified using an event-driven process model between two communicating protocol entities. The verification of the protocol is done using the projections method. The HDLC protocol has two characteristics contained in most real-life communication protocols (Singh & Sharma, 2015). These are, it operates under constraints of real-time that are important for its logical behavior that is correct and performance. Again, the HDLC protocol contains several main functions, which include one way of transferring data between protocol entities and management of connection. The HDLC has three types of stations which are primary station, secondary station, and combined station. The primary station has absolute control of the link. The secondary station sends responses while the combined station acts as either the primary or secondary station.
Switching
There are two main transfer modes used in different configurations of the HDLC. These are the normal response mode and asynchronous balanced mode. The station configuration is unbalanced in the normal response mode. There are several secondary stations and just a single primary station. A switch is a type of hardware that connects devices on a network by the use of packet switching to pass data to the desired device and receive it (He, Yan & Filipovic, 2015). There are several switching methods, which include the store-and-forward method. It processes frames that are in a good state. Second, the cut-through switching method, where the switch starts the frame processing just when it reads the MAC address of the destination. Third, the fragment-free switching method, where the switch begins the frame processing after it has recited the first sixty-four bytes of the frame.
In conclusion, the data link protocol is used in networking and communications. It is the transmission of a data unit. It is calibrated in frame or packet, from a node to another. Stop-and-wait is a method of automatic repeat request that is used to correct such errors while sending the frame during transmission time. The importance of flow control is to allow transmission of information through a sending computer at a rate faster than how a destination computer can process it after it is received. A network switch contains multiple ports, or instead, it is a multiport bridge of network that uses specifically MAC address in forwarding data at the OSI model data link.
References
(2010, January 12). computer networkingNotes. https://www.computernetworkingnotes.com/
Ramadhan, Z., & Siahaan, A. P. U. (2016). Stop-and-Wait ARQ Technique for Repairing Frame and Acknowledgment Transmission. International Journal of Engineering Trends and Technology, 38(7), 384-387.
Singh, V., & Sharma, N. (2015). Improving Performance Parameters of Error Detection and Correction in HDLC Protocol by using Hamming Method. International Journal of Computer Applications, 126(1).
He, N., Yan, H., & Filipovic, D. F. (2015). U.S. Patent No. 9,118,108. Washington, DC: U.S. Patent and Trademark Office.
