It is known that Billions of intelligent devices and networks will be integrated to perform a specific task. To perform a specific task without intervention of human is referred as smart application. To build IoT applications, Sensors perform major role. Sensors are mostly battery dependent, so it is important to consider energy consumption while developing the application. A traditional application layer protocol like HTTP is a heavyweight protocol, which consume lots of energy. In this paper, low weighted application layer protocol CoAP and some application where it can be used is mentioned. The applications where CoAP can be used for smart energy, smart grid, building control, intelligent lighting control, industrial control systems, and asset tracking, to environmental monitoring. To enable interaction between devices and to support IoT applications, CoAP is the standard protocol. The existing CoAP is analysed at initial level for smart parking in this paper.Keywords—IoT; CoAP; HTTP; Smart applicationI. INTRODUCTION (HEADING 1)The expression ‘The Internet of Things’ (IoT) was first mentioned by Kevin Ashton in 1999. It combines the general meaning of the term ‘Internet’ with (smart) objects, such as sensors, localization systems or RFID tags, called ‘Things’, and denotes a network of objects, identified by a unique address 1.Smart parking involves the use of low cost sensors, real-time data and application allow users to monitor available and unavailable parking spots. The goal is to automate and decrease time spent manually searching for optimal parking oor, spot and even Iot 1.Constrained Application Protocol (CoAP) is a transport service designed especially considering the requirement of constrained devices such as sensors and IoT devices 1. As CoAP has a short binary header, the header overhead in transferring data can be very low. On the other hand, a CoAP-HTTP proxy is needed to connect a CoAP client to an HTTP server or vice-versa. In addition, deploying proxies can have scalability issues 2.The intention is that such objects are able to gather information in a more accurate and efficient way than human. The captured information can be used to improve people’s lifestyle and well-being, as well as to protect the environment, or to automate designated processes (industrial automation) 3. One possible usage scenario for IoT, is pervasive healthcare, where wireless medical sensors can be associated with different personal area networks and used for health monitoring independent of location or time. Another widely discussed example is building control automation in order to directly control lighting, heating or security settings in a building through a mobile phone.Remotely accessing sensors is also a big deal. CoAP provide copper “cu” web browser client. Copper “cu” is an extension for browser which provide interfaces on browser to remotely manage sensor 1. Standard methods of CoAP protocol to manage sensor devices from the browser are GET, PUT, POST, and DELETE.II. RELATED WORKThe critical goal of the Internet of things (IoT) is to ensure effective communication between objects and build a sustained bond between them using different types of applications. The application layer is responsible for providing services and determines a set of protocols for message passing at the application level. In survey paper 2 author have discussed all application layer protocols which will be useful for smart application. Author have discussed CoAP, MQTT, and XMPP, RESTFUL services, DDS, AMQP and Web Socket are discussed. Also, the author has explained best suited application of this protocol. Out of all application layer protocols CoAP is best suited for client server based application 5.CoAP plays important role in applications like smart parking. In paper 1 smart parking is explained using CoAP. The novel idea in this work 1 is used of CoAP (Constrained Application Protocol) which is recently created by IETF, CoRE (Constrained RESTful Environment) group to develop a RESTful application layer protocol for communications within embedded wireless networks. This paper 2 deals with the enhanced CoAP protocol using multi hop flat topology, which makes the acuter feel soothed towards parking vehicles.One of the application of CoAP client-server architecture is explained in 13. A smart parking system with deeplearning is more efficient way to allocate a parking slot to the car. An artificial neural network used in case of light condition changes, presence of shadows, and partial occlusions. This paper explains real time availability of parking slots using a neural network algorithm running on on-board of a smart camera.III. METHODOLOGYA. Study of simulatorsFollowing are the some simulators which are helpful to build IoT applications? NS2: Network Simulator (Version 2), widely known as NS2, is simply an event-driven simulation tool that has proved useful in studying the dynamic nature of communication networks. Simulation of wired as well as wireless network functions and protocols (e.g., Routing algorithms, TCP, UDP) can be done using NS2. In general, NS2 provides users with a way of specifying such network protocols, and simulating their corresponding behaviors 7. There are different packages of NS2, which is used to simulate the network such as create a network topology, log events that happen under any load, analyze events to understand the network behavior.? NS3: NS3 is the advanced version of NS2 with more functionalities like PyViz and Net Anim. NS-3 has been developed to provide an open, extensible network simulation platform, for networking research and education. In brief, NS-3 provides models of how packet data networks work and perform, and provides a simulation engine for users to conduct simulation experiments 8. Some of the reasons to use NS-3 include performing studies that are more difficult or not possible to perform with real systems, to study system behavior in a highly controlled, reproducible environment, and to learn about how networks work. Users will note that the available model sets in NS-3 focus on modelling how Internet protocols and networks work, but NS-3 is not limited to Internet systems; several users are using NS-3 to model non-Internet-based systems? Tossim: TOSSIM simulates entire TinyOS applications 4. It works by replacing components with simulation implementations. The level at which components are replaced is very flexible: for example, there is a simulation implementation of millisecond timers that replaces HilTimerMilliC, while there is also an implementation for atmega128 platforms that replaces the HPL components of the hardware clocks. The former is general and can be used for any platform, but lacks the fidelity of capturing an actual chip’s behavior, as the latter does. Similarly, TOSSIM can replace a packet-level communication component of packet-level simulation, or replace a low-levelradio chip component for a more precise simulation of the code execution.? Cooja: COOJA is a flexible Java-based simulator designed for simulating networks of sensors running the Contiki operating system 9. COOJA simulates networks of sensor nodes where each node can be of a different type; differing not only in on-board software, but also in the simulated hardware. COOJA is flexible in that many parts of the simulator can be easily replaced or extended with additional functionality. Example parts that can be extended to include the simulated radio medium, simulated node hardware, and plug-ins for simulated input/output.Code development for wireless sensor networks is difficult and tedious. Reasons include the distributed nature of sensor networks, as well as the longer compile run-debug cycle caused by the need to transfer the compiled program onto the set of sensor nodes used for development and testing 10. So COOJA is best suited tool which provides code development for wireless sensor network.B. DesignCoAP based architecture is presented in following figure 3.1. CoAP communication is only in inter network communication that is between sensors and sink node. Inter-network follows IPV6 protocol, hence to communicate between IPV6 networks to internet i.e. IPV4 network Border router, gateway is used.Figure. 3.1The Data collection node is actual sensors where data is captured and the sensor will forward to Control server. Control server is working as sink node 11. The main task of CoAP protocol is in between sensors and control server.The Communication of CoAP protocol are explained in following figure. 3.2, where the client sends POST request to server and server response it with acknowledgment.All the above communications are client server based communication. CoAP gives best result for client server communication. In paper 6, study of application layerprotocol has mentioned and stated that each protocolgives best result in different field.Figure. 3.2C. ImplementationCoAP is RESTfull architecture. REST(representational state transfer) technology is generallypreferred to the more robust Simple Object AccessProtocol (SOAP) technology because REST leveragesless bandwidth, making it more suitable for internetusage. In system, at server REST resources are definedand that resources are called by client with either of GET,PUT, POST, DELETE method.Following figure 3.4 shows the sample declaration ofresources at server side. In C code, URI path is declaredas well as method by which client will call the resourcesare also defined.Figure 3.4Figure 3.5 shows the client side implementation ofCoAP. In client side, URI path defined and that path iscalled with payload as parking status with client ID.Figure 3.5Both the code is modified from example code ofcontiki/example/er-rest-examples folder.As this work is implemented on cooja simulator, tocreate an event button is used. In real life scenario, sensorwill detect the car and event is occurred.In any IoT smart application, there are many clientsand one server. Client requests for data and serverresponse it with data. In a given scenario, 3 client act as asensor node and 1 sink node. Whenever event occur atclient side, it sends CoAP POST method to sink node.Border router gatway is used connect simulated networkto real nework. The implementation of smart parking isrepresented is cooja simulator figure. 3.6.Figure. 3.6CoAP is RESTfull architecture i.e. resources aredefined at server side and client access that resources overIPV6 network. To access resource URI path is used. Inproposed system, URI path to access log of parking slotsiscoap://aaaa::212:7402:2:202:5683/sensors/button.As CoAP is application layer protocol, it is possibleto access resources on browser. As it is new technologybrowser doesn’t support directly. To make itunderstandable to browser, copper (cu) extension onfirefox browser available. Following figure. 3.7 representsthe available parking slot on GET request to URI.With the help of copper cu extension, browser is actas client node of CoAP network. So, in network with IPaddress anyone can manage the sensor nodes remotely.Remotely every sensor can be start or stop. Which is alsomore reliable to network administrator.Figure 3.7IV. RESULTSCoAP is optimized to be small, light and fast forM2M/IoT applications. Like HTTP, it has very little logicembedded in it, and instead uses a limited command set tocommunicate with RESTful server processes. UnlikeHTTP, it’s designed to work on the UDP protocol, insteadof TCP/IP. Hence, CoAP is best suited application layerprotocol for smart parking application.Following figure. 4.1 shows that on button clickevent sensor node send POST method with payload “41”.Payload is combination of sensor id and status of parkingslot. 4 is node id and 1 represents “parked” status. Node 4send CoAP message to node 2 and node to print it onsimulator output windows.Figure. 4.1In following figure. 4.2, Node 2 is sink node andNode 3, 4, 5 are sensor node. Node 3 is directly connectedto node 2 using wireless connectivity i.e. single hope. But,node 4 and node 5 are indirectly connected to node 2.Whenever node 4, 5 try to send data, they have to send itthrough node 3. Node 4 and node 5 are double hope andtriple hope connectivity.Figure. 4.2Table 4.2 represents the delay to send data in multihoping networking. Table shows that delay is increasedwith respect to increase in intermediate node to send datato node 2. The delay in mili sec are calculated in coojasimulator. It is observe that, as the number of hopesincrease then response time increase in linearly.Table 4.1Multi-hoping Single Hope DoublehopeTripleHopingNodenumberNode 3 Node 4 Node 5Delay (msec) 18 41 67Browser request to fetch all parking data from node 2using GET method requires 900 millisecond. But, thisdelay can be reduced using cachability of CoAP payloadat node 2.V. CONCLUSION AND FUTURE WORKTraditional application layer protocol http are not efficientfor IoT constrained devices, hence the new light weightprotocol CoAP are useful. The backbone of any smart IoTapplication is network i.e. Communication protocol. Manysmart IoT applications require fast response from sensors.Hence, protocol and packet size are efficient, so that responseare increased. Hence CoAP is used. CoAP has small headersize, time require to process header at nodes are less. Also itdecreases energy consumption of the nodes which increaseslife of nodes. The basic backbone of any IoT smart applicationis a client sends data to the server. For the client-serverapplication CoAP gives best result out of all application layerprotocols. The analyzed results are mentioned in this paper.The work presented in this paper can be extended to anyapplication where client-server communication requires. Theuse of cache memory at server node to increase responsespeed and to reduce delay. The cachability of CoAP messageswill be important in case of sleeping node configuration andpower limited node. And future conclusions can be made.