An effective online teaching-learning should incorporate all the vital components/features (2). Some of them are as follows:

The online teaching-learning system must be easy to use in terms of navigation and interface design. Various types of users with different backgrounds use this system, so it must be user-centered, customizable and understandable by every group. Navigation to the different pages, features or settings should be clear and easy. The interface design should also be simple, specific and to the point without fancying simple things.

Reliability of software is defined as the probability of the program working without failure. In this case, it is referred to as consistency over time, and dependability of the system. In software engineering, a simple measurement of reliability is mean-time-between-failure (MTBF) (11).

MTBF = MTFF + MTRR

Where MTTF and MTRR are mean-time-to-failure and mean-time-to-repair.

It shows that the system is performing as desired or not in terms of request responses, server responses, execution time and accessibility.

Nowadays, almost all digital devices are smart. With the advancement of smartphones, tablets and PC, a lot of possibilities have emerged. But it has also increased the task of the developers as these devices use different operating systems. So, developers have to design and maintain the application for different platforms.

Scalability is the ability of the system to cope with the growing needs. If the number of users increases, the system should also adapt according to the users and if the system is to be migrated to a large enterprise from a small enterprise, it must be scaled according to the needs of the organization.

Security and privacy are the major issues in this digital era. The online teaching learning platforms are also prone to various attacks and data manipulation. Security breaches such as Man in the middle attack (MITM), Cross-site scripting (XSS), Ip spoofing, Session hijacking, Brute force and DOS attacks, etc., are very common nowadays and online systems must have the mechanism and manpower to defend against such attacks. Preventing unauthorized access, Password protection, Data encryption, Using antimalware, and using a secured protocol (HTTPS and SSH) for online transmission and remote access are some of the preventive measures.

The system should be consistent and provide quality services to the users. The system should not behave differently under varying circumstances. Quality services and system optimization must be done in order to achieve smooth performance.

Online teaching learning is meant to reduce the boredom of the existing traditional classroom-style teaching process. But in some cases, it turned out to be passive as lecturers only provide resources which are not attractive and understandable completely. Lengthy texts, MCQs, and complex choices of words fail to engage students. It is more like e-reading rather than e-learning.

Some online platforms are not accessible by most people. Moreover, students don’t have enough resources to participate in OTL. The absence of connectivity or the internet is one of the many reasons for this. The time factor is also another cause where students are not able to attend the class in real-time. In many regions, the complete course resources are not accessible to everyone.

Infrastructures needed for OTL are not within everyone’s reach. In poor and developing countries students lack basic hardware and software requirements. In some regions, there are cellular network problems, low bandwidth/poor internet connection and continuous 24-hour electricity service is also not available. Such problems make real-time interaction impossible.

Security is a major concern in any online application. Privacy is more valuable than anything in this digital world. Making a platform and all the connections secure is a tough task. Various technologies contribute to the management of security protocols on the application. Maintaining those technologies requires software and manpower. If the online system doesn’t pay enough attention to security, there are chances of user data and course resources being breached exposing the entire community.

Entering a new online learning environment can be more intimidating than entering a new physical learning environment. It takes time and effort to completely adapt to a new style of learning so there must be enough guidelines, tips, and examples in order to ease the students and instructors to adapt to the platform.

Familiarity with hardware, software, and computer networks is a major key element in implementing OTL systems. Many students lack computer literacy and feel difficult to work with basic programs like PowerPoint, Word, etc. Not only students, but instructors who are more comfortable with traditional teaching-learning systems also are prone to lack these skills as well. They are also not able to troubleshoot minor problems and handle basic errors. OTL systems require students and teachers to manage files, assignments, and course materials in an organized manner.

Synchronous learning is based on a synchronous mode of data transfer in which the client waits until the server responds with the processed data. It requires the instructor and students to interact in real-time simultaneously. It is similar to a webinar where participants interact with each other through text, audio or video. In synchronous learning, a group of students and instructors are engaged at the same time. Real-time interactions such as live chat, online instant messaging and video conferencing are supported by synchronous learning. Figure 7 depicts the working of synchronous learning in an online teaching learning system. Based on the needs of learning, synchronous learning is also known as web-conferencing.

Web conferencing refers to a virtual meeting hosted on a server. Those server providers are third-party suppliers. Web conferencing is different from video conferencing as anyone with the link can join from any location as long as they have the link to the meeting or a meeting code (17). Some of the web conferencing platforms are Zoom, Google Meet, Cisco WebEx, Skype, Microsoft Team, etc. All these applications follow the process shown in Figure 8. The UI, presentation, and pricing policy may differ but the basic architecture of all these applications are similar (18).

The working of real-time meeting/web conferencing (19, 20) is shown in Figure 8. The system works in three steps.

The features of the web conferencing platform include face-to-face meetings over the web, screen share and whiteboard services, collaboration on the same screen using a virtual whiteboard, recording and saving meetings, calendar, chat and online instant messaging, strong security and privacy, etc.

Asynchronous learning is a self-paced learning strategy based on the asynchronous mode of data transfer in which the client does not wait until the server responds. The client-side program proceeds further while the server request is being processed in the background. In this type of learning, the course interaction does not take place in real time. It is an online practice in which students are provided with all the resources and can interact with the learning management system at any time according to their convenience. It supports both online and offline features as shown in Figure 9. Based on the need for learning, asynchronous learning is categorized into three types.

Digital Learning Management system is a platform/software where online courses and training materials are delivered to students/participants and helps to manage online courses, their participants, their evaluation technique and the effectiveness of the course (21). All kinds of organizations benefit from LMS. Learning Management Systems are used by large enterprises, small and medium businesses and freelancers as well. In this digital era, the education system depends on LMS to provide education online. Many colleges and universities use LMS for remote access to courses online. In the education and higher education markets, an LMS will include a variety of functionalities that are similar to those of the corporate sector but will have features such as instructor-facilitated learning, a discussion board and often the use of a syllabus.

The learning management system with required components and features are shown in Figure 10. LMS deals with the overall management of the teaching-learning process. The teachers and students are authenticated using a login management system. After successful login, the users can perform various course-related and management activities. Students and teachers have different functions and work according to the availability and access to the LMS. The LMS supports online class lectures and group involve-ment/discussion. Various activities in LMS are managed by different components according to their functionalities. The assignment management component manages all the assignment-related activities. Similarly, other management components manage their respective activities. The LMS system also tracks the activity of students and provides various evaluation measures. The Learning Management System is categorized into two types based on deployment and licensing (22). LMS is categorized on such a basis because there are a lot of different types of digital devices such as smartphones, and PCs with different architectures and the LMS system comes with a wide range of prices. Based on deployment, the LMS can be categorized into four groups.

MOOC refers to Massive Open Online Course. They are massive courses where a large number of enrollments are possible which are open to everyone and anyone can access the course online for free. MOOC is a platform where a large group of participants with similar interests in a topic can interact, learn new skills, and advance their careers (25). Millions of people around the world use MOOCs for career development, college preparation, supplemental learning, e-learning, and more. MOOCs provide interactive courses with user forums or social media discussions to support community interactions among students, professors, and teaching assistants (26). It also supports immediate feedback on quick quizzes and assignments.

Self-directed learning is a process where individuals take the initiative, with or without the assistance of others, in diagnosing their learning needs, formulating learning goals, identifying human and material resources for learning, choosing and implementing appropriate learning strategies, and evaluating learning outcomes (1975, Malcolm Shepherd) (29). Self-directed learning uses a learning management system to provide resources such as videos, slideshows, texts, and quizzes. The reason behind the concept of self-learning is the desire to be in control of deciding what to learn and how to learn it. In self-directed learning, the earner can decide what to learn, how to learn, and what should be the outcome of learning. It applies to different contexts of learning whether it is learning to ride a bike, play a musical instrument, cook, learn academic content or learn a new language. In summary, the main elements of self-directed learning (30) include students acting alone without any interaction with teachers or peer groups and being available at any time. Self-directed learning with respect to an online college student incorporates (31) the following.

According to ISO usability is the extent to which a product can be used by specified users to achieve specific goals with effectiveness, efficiency, and satisfaction. Technical usability and learning usability best define/justify the usability of online teaching learning (OTL) systems. Technical usability deals with the ease of interaction with the learning platform such as UI, navigation, and plugins whereas learning usability is about minimizing the learning-related frustration for users. Based on these facts, usability (Technical and Learning can be rated as High, Moderate, and Low).

Scalability is a parameter that justifies the system’s ability to handle growing amounts of work and be flexible to accommodate that growth (32). In this context, the system is an online teaching-learning system. It deals with growing the application significantly as the size and complexity of the software increases. Scalability gives answers to some questions such as

With changes in needs, the OTL system should be able to adapt according to it by managing a large amount of data, a large number of users, response time, and system needs. Based on these facts, scalability can be rated as High, Moderate, and Low.

Online teaching learning systems should come with highly secure protocols and technologies. In this digital era, security is a major concern in every field. Authentication, restriction, Encryption, backup, Malware protection, and cyber-attack protection are some of the essential elements of security in OTLs (34). Attacks such as Man-in-the-middle attack (MITM), Cross-site scripting(XSS), Rootkits, Session hijacking, SQL injection, Bruteforce, and DOS are some of the security risks proposed by attackers. Based on such capabilities of the system to defend against such attacks, the security of OTLs can be rated as

An OTL system provides services to share multimedia such as texts, videos, audio, pdfs, live streaming, and screen share. OTL systems are of different types and support different multimedia types based on their functionality. For instance, web conferencing OTLs provide video streaming, live screen sharing, and online Instant Messaging facilities, LMS provides asynchronous file transfer rather than live streams, and MOOC delivers video lectures and discussion forums only.

Online teaching learning platforms have to deal with heterogeneous data. Heterogeneous data such as graphical data, voice/video, text, and numerical data contained in a compound document should be organized and accessed as a single data structure rather than a collection of separate files.

Reliability in OTLs refers to consistency over time, dependability, the efficiency of the system, and its capability to achieve its goal. The main objective of OTLs is to effectively deliver online training materials and facilitate easy interaction between instructors and learners without failure (35). Reliability of such systems can be measured by incorporating some of the following points:

Based on these facts and issues reliability of OTLs can be rated as:

Availability of a system/program in terms of e-learning refers to whether the program/course can be accessed. If the program/course can be accessed then, what will be the basis for its availability. System availability can be categorized as follows.

Privacy and security are different and it has a different and transparent set of policies. In the OTL system, teachers and students should have a private place to perform their activities online. While doing so, teachers should be able to criticize without fear and students should not fear to comment freely on controversial matters (36). Moreover, the OTL system should protect the personal data collection of students by the private sector for commercial use and prevent government agencies from tracking student learning activities. Personal details of users (students and teachers) should not be exposed without permission and data should be encrypted while transferring from client to server. With all these factors in mind, the privacy of the OTL systems can be categorized as Strong, Moderate, and Weak.

Online systems provide a more affordable option than traditional colleges. LMS used by colleges and universities provides online education for their students’ college fees whereas some LMS is provided free of charge by some colleges and universities. In some cases, course resources such as textbooks are available online at no cost. Many MOOC courses provide course resources and materials for free but charge for certifications. These OTL platforms come up with different pricing options. Based on the cost of the OTL system it can be categorized as

Quality of Service in OTLs refers to the measure of the overall performance of the learning system (37). There are various factors contributing to the quality of services but in this case, we mainly consider three parameters (38): Service quality, Information quality, and System quality. Service quality incorporates reliability, assurance, tangibility, and responsiveness of OTL systems. Information quality deals with quality learning content such as presentation, structure, interactivity, and delivery modes and system quality refers to the quality of website/software in terms of UI, Navigation, and ease of use. Based on these facts, QoS can be categorized as Good, Average, and Poor.

Online teaching-learning platforms come with various types of platform support. The platforms are based on the architecture of the system/hardware. Based on the popularity and most used operating system, some of the platforms are Linux, Mac, and Windows.

Based on the deployment of software on various platforms and architectures (23), OTL systems can be categorized as Cloud-based, Self-hosted, Mobile application, and Desktop applications.

The e-learning systems have various types of customers based on the functionality and need of the system. Some of the customers using these systems are Academic institutions, Freelancers, Non-Profit organizations, Public, Administration.

Training refers to the materials to learn and be familiar with the e-learning systems. These systems are used by various industries as per their need and requirements. Some of the industries using OTL systems are Banking, Education, Management, and e-Learning.

The online teaching-learning systems provide various support to the customers in case of errors, training, and usage of the system. Some services provided by OTL systems for support are 24/7 helpline, Email, FAQ, Knowledge Base, Live Online, and Online Community.

Interactivity has long been seen as a necessary and fundamental mechanism for knowledge acquisition (Sims 1997). Students interact with various objects in the system to participate in the learning process. Interactive labels and tools should be provided with enough guidelines and well- labeled components. The Interactive Numeric Exercises tool allows the creation of interactive exercises in any subject domain that requires the user to follow a set algorithm to solve a numeric problem.

A platform with discussion boards, file sharing, and Virtual chats enable learners to collaborate and share ideas. Collaborating learning describes a variety of different learning situations. It supports the discussion of groups of students and instructors about a concept using online forums. Collaborative learning increases the cognitive and intellectual capabilities of the participants.

Many tasks such as file download, transfer, video playback, and web conferencing may fail at any time depending on whether the user is mishandling data, or the server is overloaded with requests which may trigger software or hardware failure. For instance, a user may accidentally try to login again after being logged in which creates a double session for the current user. This may bring unnecessary problems to both the user and the system.

Reliability of software is defined as the probability of the program working without failure. In this case, it is referred to as consistency over time, and dependability of the system. Scalability is the ability of the system to cope with growing needs. The online teaching learning system should be reliable and scalable. Reliability and scalability also facilitate management and administrative teams to monitor and maintain the system effectively. Response time, execution time, adaptability, accessibility, and usability help to determine the reliability and scalability of the system.

Students and teachers that are involved in an online teaching-learning system should master a complex range of skills to achieve their goals. Various cognitive tools - computer applications such as computer conferencing, expert systems, databases, and spreadsheets are used which requires users to interpret and organize personal knowledge.

Security and privacy are major issues because data should be confidential and server reliable. Users should be provided with privileges according to their needs. Students and teachers should be provided with the necessary security and privacy services such as authentication and data encryption whereas system managers and administrators should be given the necessary tools to defend against attacks.

IT law (cyberlaw) is related to information technology and activities on the internet. It deals with the legal and illegal issues in the IT field. IT law is related to law and order and its consequences if anything illegal or unauthorized activities are done using the world wide web or the internet. IT laws have sections and subsections for different types of unofficial, violating, or theft issues and impose necessary punishment according to the crime. Online teaching-learning (OTL) systems are operated on the top of the internet so there is a high chance of security breaches, privacy theft, and data manipulation issues. In case any illegal or violating activities in the OTL system leads to cybercrime, necessary punishments are imposed on the guilty.

Basic infrastructures such as electricity, internet connection, and cellular service are needed for running an online system. The government and private sectors have worked on and proposed plans and policies in the communication sectors. Various government and private Internet Service Providers (ISPs) have emerged in recent years. Cellular network companies have also facilitated connectivity in different regions. But there are still some problems such as availability of hardware and software, poor connection, low bandwidth, and poor cellular networks, which make it difficult for users to access the OTL’s at any time. The internet service is expensive in developing countries and 24/7 electricity service is also not available in various regions.