Service Discovery Protocol in Wireless Sensor Networks

Sensor network is a novel technology about acquiring and processing information. This paper introduces the basic interaction patterns between requesters and providers of services during a typical Service Discovery task. It discusses existing service discovery protocols and provides a preliminary analysis of the mechanisms for service and resource discovery in the Wireless Sensor Network domain. 1.Intruduction The recently research of wireless sensor networks touch upon the technology of service discovery. Service discovery protocols play a key role in wireless sensor networks. Service discovery protocols enable service providers to advertise capabilities to potential clients, while also providing to clients and service providers a means for entering into relationship. Service Location Protocol (SLP), Jini, Bluetooth’s Service Discovery Protocol (SDP), Salutation, and Universal Plug and Play (UPnP) are protocols addressing service discovery. 2. Service Discovery Entities and interaction patterns The basic interaction pattern between requesters and providers of services during a typical service discovery task, as shown in Figure 1. After a successful discovery phase, additional communication between client and provider will be necessary in most cases. This information exchange is modeled by a Service Invocation and Invocation Acknowledgment handshake. Naturally, more or other data messages can be exchanged. End to end routing of data messages between client and provider will be needed. 3. Service Discovery Protocols Service discovery protocols play a key role in wireless sensor networks. They provide to the mobile nodes a functionality that enables them to advertise and discover service providers. There is a number of existing service discovery protocols. These include Sun Microsystems’ Jini, IETF’s Service Location Protocol, and Bluetooth’s Service Discovery Protocol. Figure1 : Entity Interactions 3.1 Jini Sun Microsystems has developed a distributed service-oriented architecture called Jini for the Java programming environment. It runs above RMI (TCP and IP). Service providers look for and register offers with lookup servers. Registration means uploading, in a lookup server, a service object and values of descriptive service attributes.Clients look for services by contacting the lookup servers and sending requests with conditions on service attributes. When requests can be granted, service objects are downloaded in the clients. They serve as local proxies to remote service providers. Jini can work without lookup servers by using a technique called peer lookup. With the peer lookup approach, the clients request particular services by sending messages called identification. Registration messages are returned directly by the service providers to the clients, which hence get the service object and service attributes. 3.2 Service Location Protocol(SLP) The Service Location Protocol is a service discovery protocol designed for IP networks. It runs above UDP. SLP defines three types of agents: User Agent (UA), Service Agent (SA), and Directory Agent (DA). UAs are clients, SAs are service providers, and DAs are repositories of service advertisements. The flow of interactions in SLP is as follows. DAs advertise their presence to UAs or SAs with the Directory Agent Advertisement (DAAdvert) message. SAs respond to this message using the Service Registration (SrvReg) message to register service offers. A service offer consists of a URL and values of descriptive attributes. A URL is a service access point (SAP) to a service provider, in Service