Zakaria Maamar , Wathiq Mansoor , and Qusay H. Mahmoud'
Section 2 motivates our work on m-services. Section 3 denes mobile combe oered need to be tailored to each device individually. Unfortunately, this wireless devices. sible. In an open environment with dieren t users and needs, looking for the puting and e-services. Section 4 presents our system of m-services. Section 5 advocate that m-services will be fetched on-demand from provider sites to users’ describes our system implementation. Section 6 presents related work. Section 7 and coordination, while important, do not fall in the scope of this paper. users where looking for the lowest common denominator between them is feafollow for systems designed to the wireless world. e-services into m-services is a necessity. M-services will have to consider the Having pre-installed services on users’ wireless devices is an option that could to wireless devices is more appropriate than pre-installing services. Enabling be considered. However, this option would have worked for a small number of concludes the paper. It is made clear at that level that issues such as negotiation common denominator is not trivial. Therefore, on-demand delivery of services goes against the e-services platform independence principle. Thus, leveraging the downloading of dynamically composed services is among the approaches to characteristics of the wireless devices on which they will be running. In fact, we 2 Motivating scenario before he leaves his oce this time he did not do wnload the appropriate software sentative working for a software company; it is based in country X but serves representative has to send "wirelessly" the required data. Later on, the server required data to the request he submitted in the rst time. Unfortunately , this one is to put his request in a waiting list. The second one is to send the required oce tools. Moreover, the representative uses the PDA to record the deals he applications to his PDA for execution. These applications transfer has to follow applications into his PDA. Consequently, he decides to proceed as follows. First, ing, the representative has to carry out specic operations such as simulating Server not "busy" - it accepts the request and processes it. To this end, the transmits "wirelessly" results to the representative’s PDA. If the representative customers from over the world. Since the representative is most of the time on is dicult to predict.
To motivate our work, we consider the following ctiv e scenario. A sales reprethe move visiting customers, he is equipped with a PDA, which provides basic he sends a "wireless" request to the company server. According to the workload made with customers. It may happen that in preparation for an important meetServer "busy" - it suggests two alternatives to the representative. The rst specic rules, as w e will discuss it. the consequences of this meeting on the company stock shares. Unfortunately, of the server, one of the following situations occurs. has known before that the server was not busy, he could have attached the 4 System of m-services 4.2 Architecture 3 Background 4.1 M-services operations because they lack appropriate facilities on their devices. Therefore, adaptable according to the wireless devices’ computing characteristics; and exeof using wireless communication mechanisms. Finally, a solution to 3) consists of using Software Agents (SAs) [6]. devices, and 3) to conduct the operations 1) and 2) in a transparent way. A socutable on wireless devices.
We consider an application component as an m-service if it is: transportable it becomes important to support such users by allowing them: 1) to search for lution to 1) consists of creating brokering mechanisms. A solution to 2) consists ties to wireless devices-oriented users. It happens that these users postpone their The rationale of designing and developing is to oer new opportuni- m-services2 through wireless networks; exible in term of composition with other m-services; additional facilities, when needed, 2) to fetch these facilities to their wireless If this is the rst time that a user-agent submits requests, the supervisoragent creates a user-delegate in the MI to be associated with that user-agent location. To download the m-services one at a time from the storage server to user-delegate the storage server to be used considering for example the server’s ting them to the user-delegate, the user-agent goes into a standby mode and "notify" performatives illustrating the interactions that take place between userThe user-agent keeps track of the execution of an m-service, before it asks the vice is deleted from the wireless device platform. Finally, the user-agent informs storage-agent to submit the next m-service. When it is received, the executed serthe user’s wireless device, the user-agent communicates with the storage-agent. the user about the completed requests.
User-oriented components User-agent resides in a wireless device. First, vice, m-services are put in a storage server. The MI supervisor-agent suggests to user-delegate (cf. Table 2). Table 1 and Table 2 use "submit", "reply", and m-services that satises the user’s requests. Before executing them on user’s dethe user communicates with his user-agent to arrange requests. After submitagents and supervisor-agent and between user-agents and delegate-agents. In waits for notications from its delegate. Notications concern the sequence of Table 1, "submit" performative has v e elds among them "Device"; it species (cf. Table 1). For the next requests, the user-agent interacts directly with the environment in which they meet and interact directly. The MI plays the role questers and providers may have to bypass the broker. They need a common instead of several user-agents. Security is increased for both users and providers.
Storage-servers are independent platforms where security control are conducted. delegates interact in a local and secure environment [9]. In an open environment, sibilities, among them: it monitors the interactions that occur within the MI; of this environment. In our system, the MI supervisor-agent has several responto a user’s wireless device one by one. Several advantages are obtained from the most of the interactions between requesters of services and providers of services for execution. According to our system execution’s principles, m-services are sent Its point of contact for getting the m-services is the storage-agent. The same use of storage-servers. A user-agent does not have to deal with several providers. thing applies to device-agents that will be interacting with few storage-agents less devices for execution. The rationale of having device-agents is to consider processor speed. it makes the MI a safe environment; and it directs user-delegates towards the are conducted through third parties, known as brokers. Despite its important role, a broker could easily become a bottleneck. To overcome this problem, reprovider-delegates that interest them.
The MI part is a software platform on which user-delegates and providerThe storage part receives the sequence of m-services that will be sent to users the dierences that exist between wireless devices, e.g. screen dimension and role of device-agents is to wrap m-services before they are sent to users’ wirefor two main reasons: even if we expect a big improvement in wireless devices’ delegate receives the user’s requests from the user-agent (cf. Table 2). Afterwards, it interacts with provider-delegates. The purpose is to match user’s reble 2). In Table 3, two relevant elds of "to-get-ready" performativ e are imporand shipping it to the MI, we suggested to undertake this operation in the MI noties the user-agen t about the sequence of m-services it has established (cf. Tam-services has been designed. "M-services" eld corresponds to the m-services device-agent. Instead of creating a user-delegate on a wireless-device platform resources, those resources have to be used in a "rationale" way; and the wireless the device-agent has to submit. To set up a sequence, the storage-agent knows is always a match), the user-delegate designs the sequence of m-services to be User-delegate resides in the MI, acting on behalf of user-agent. The userready to receive m-services from device-agents. Furthermore, the user-delegate quests with providers’ m-services. In case there is a match (we assume that there included in satisfying the user’s requests. Information about this sequence is the m-service that comes before and after the m-services to be submitted by a tant. "Destination" eld corresponds to the user-agen t for which the sequence of connection that transfers the user-delegate is avoided. sent to the storage-agent (cf. Table 3). The purpose is to make the storage-agent system, the provider-delegate is responsible for interacting with user-delegates, user-delegates and provider-delegates forward to a storage-agent guarantees more for consideration. We recall that the provider-agent creates a provider-delegate according to the devices to which they will be sent for execution. Initially, these the user-delegate has informed the storage-agent of that storage server about agent for notication purposes. Notications are then forw arded to device-agent Provider-delegate resides in the MI; it acts on behalf of provider-agent. In our regarding the m-services it oers. In addition, it interacts with its providerand transfers it to the MI. the m-services it will receive (cf. Table 3). Double-checking the information that Device-agent resides in provider’s site. Its responsibility is to wrap m-services the contact details of the storage-server to the device agent. We recall that security to our system. m-services are sent to storage servers. The provider-agent has already submitted eral responsibilities: it supervises the operations that occur in the MI; it medidelegates the storage server to be used.
MI-oriented components Supervisor-agent resides in the MI and has sevuser-delegates and assigns them to user-agents (cf. Table 1); it checks providerdelegates identity when they arrive from provider sites; and it suggests to userUser-delegate and provider-delegate are explained above. ates in case of conicts bet ween user-delegates and provider-delegates; it sets-up the m-services one at a time (cf. Table 6). These m-services are ready for execution. The deletion of m-services from the storage-servers as well as from wireless Based on the requests it receives from user-agent, the storage-agent pushes devices follows specic reliabilit y rules (cf. Figure 3). 3 This is not a shortcoming of our system. It is part of our current work to consider 1:N negotiation.
Meeting infrastructure UseUr-saegren1t.aNeeds 2.aSCure3pa.teiIornnvteirsaocrti-oangsent 2.b Migration 1.b Creation
User-delegate Provider-delegate Pdreolevgidaeter Provider-agent 7t.reaMxne-scsfueetrrivofioncres 4.naoMtif-csaetrivoinces 4n.botCifocnattriaocnts 5n.oCtiofinctartaicotns
6. M-services Storage-agen1t transfer
Storage server1
Device-agent Provider Bank of m-services user-agent sends an acknowledgement message to the storage-agent so it deletes that follows the one it has received. For the last m-service of a sequence, the that m-service (cf. Figure 3). of this service at its level. It deletes it when the user-agent asks for the m-service a storage-agent sends an m-service to a user-agent, the storage-agent keeps a copy approach considers a storage-server as a back up server for the m-services. When In the realization phase, reliability aspect has been taken into account. Our a/ a/ Provider-delegates are targeted in advance. Supervisor-agent becomes a bottleneck. the MI content. delegates and provider-delegates. not satisfy completely user-delegates.
User-delegates have a narrow perception of the MI content. delegates oer. b/ b/ User-delegates have a wide perception of More messages to discover what providerMore freedom is given to user-delegates.
Less interaction messages between user- Supervisor-agent’s recommendations could the m-services that are involved and the storage-server that is used. Among the actions the device-agent undertakes we cite submitting the m-services to the storage-agent of the storage-server. provider-agent forwards them to the device-agent. This information concerns Based on the information it has received from its provider-delegate, the agent about the m-services it will receive from device-agents (cf. Table 3). Before of this stage. We recall that the user-delegate has already informed the storageRealization stage purpose is to execute the sequence of m-services that the user-delegate has designed. User-agent and storage-agent are the participants the user-agent starts asking the storage-agent for the m-services it has, it waits is ready to be submitted for execution. for a notication message from the storage-agen t mentioning that the sequence Advantages Disadvantages Table8. Advantages and disadvantages of searching for provider-delegates approaches Notic ation stage purpose is to inform dieren t agents about user-delegates’ and provider-delegates’ agreements. upon the m-services to use, notications are sen t to dieren t recipients. This will be explained in the notication stage.
Regarding the provider-delegate, it noties the provider-agent about its agreements with a user-delegate (cf. Table 4). We recall that provider-agents do not reject any agreements. of services it will receive from dieren t device-agents (cf. Table 3).
Regarding the user-delegate, it is in charge of the following operations: informs the user-agent about the sequence of m-services it has established to satisfy its user’s request (cf. Table 2); and informs the storage-agent about the sequence ment and consulting module supports the subscription process to user-delegates. agement and installation, which is responsible for receiving delegates from their which is a Java edition that runs on wireless handheld devices with constrained communications that take place between user-delegates and provider-delegates. network. services that are required for satisfying specic needs. In addition, the adv ertisein this module. The second module is the interaction module that supports the ing Voyager [14]. Regarding the user-agent, it is mainly an interface-agent that For instance, if a user-delegates is interested in a specic ev ent, then it can be [8] that provides a simple, fast, and a unied mec hanism for sharing, coordinatstock m-service that can be used to simulate stock operations. Once the stock can enter the m-services he requires. In this example, the user is requesting a notied when this ev ent occurs. JavaSpaces provides this notication operation.
The MI is implemented as a set of three modules. The rst module is the manis supported by JavaSpaces, deals with advertising services and identifying the Provider-agents and their delegates and user-delegates are implemented usproviders’ m-services advertisement. JavaSpaces is an implementation of Linda type uses SUN’s JavaSpaces technology [5] to implement a repository that holds At this stage of our implementation, we simulate the situation where a user ing, and communicating distributed resources, services, and objects across the feeds the user-delegate with requests. This agent is implemented using J2ME [4], resources. A snapshot of the user-agent prototype is shown in Figure 4.
An implementation of the MI has already been undertaken in [9]. The protoFinally, the third module is the advertisement and consulting module, which original systems and installing them. All the security operations are undertaken User-agent Interactions Storage-agent Actions Sequence: m-servic1e,2,3 Actions
To-make-ready: seq1. prepare: message prepare: request Request: ?m-servic1e
Push: m-service1 save: m-service1 run: m-service delete: m-service11 Request: ?m-servic2e
delete: m-service1
Push: m-service2 save: m-service2 wait: m-service2 Request: ?m-servic2e
Push: m-service2 run: m-service delete: m-service22 Request: ?m-servic3e
delete: m-service2
Push: m-service3 save: m-service3 run: m-service delete: m-service33 Request: ok delete:m-service3 m-service has been downloaded the user will be notied, as sho wn in Figure 4, so that she can start using it as shown in Figure 5. way of doing business [1,10,11,13]. In HP Laboratories, [10] worked on delivering for mobile and adaptive applications. It denes a platform for adaptiv e mobile services from storage agents according to the resources that are available on for Pervasive Services Infrastructure (PSI). The vision is "any service to according to the wireless devices’ characteristics; and user-agents request mof applications to mid-point servers can enable and enhance service execution on Furthermore, we are interested in supporting users in their search for m-services is to adjust the quality of accessed data to match available resources. In our their users’ devices. any client (anytime, anywhere)". The project investigated how ooading parts player, and a speech recognition, could run on top. The Odyssey’s approach There exist several projects that study how wireless devices could change our a resource-constrained device. In our work, we are interested in the same issues. system, we considered adaptability at two dieren t levels: m-services are wrapped Internet services to wireless users. This work was conducted under the project in an open environment. In [11] the Odyssey project provides system support data access on which dieren t applications, such as a web browser, a video 7 Conclusion its previous experiences, the user-agent could entrust to this storage-agent its less devices to complete their daily operations. Therefore, new facilities should anisms will be applied to all m-services despite their origin (i.e. device-agent) on wireless devices should be used in a rationale way, our future work is based on the opportunity to deal with the same storage-agent several times and based on heterogeneous services implemented and provided by dier ent providers available trust between user-agents and storage-agents. For instance, if a user-agent had dier ent networks, and from dier ent terminals". m-services and the storage-servers can be replicated across the network. This in Figure 1 is highly scalable. The system can be extended, at a reasonable cost, specic securit y procedures. to handle all client requests. scalability. Our suggestion for security consists of enhancing the storage-agent adding more meeting infrastructures to a wireless carrier network. The bank of Several aspects are still under investigation, among them security [7] and Regarding scalability, the architecture of the m-services system we suggested as the demand for the m-services it provides increases. This can be achieved by allows us to avoid the performance bottleneck that would arise if a single MI has and destination (i.e. user-agent). Specic securit y procedures that answer each user’s priorities should be done at the wireless device level. Since the resources be provided. Our work aims at achieving "anywhere and anytime" paradigm. with security mechanisms that could be generic; in the sense that these mechfor roaming users as an integrated package, with the same "look and feel" across This paradigm could be summarized by [2] who stated "How to make a set of In this paper, we presented our work on m-services. M-services are considered as an extension to e-services. Users are more and more relying on their wireComparable to our sequence of m-services, a path is an abstraction through tional intermediaries put between devices and services to shield them from each a Service Discovery Service (SDS) for two reasons: enable services to announce meet the requirements of an emerging class of extremely heterogeneous devices which units, services, and active proxies are composed. Proxies are transformaAnother related project to our work is Ninja [13]. It aimed at suggesting new types of robust and scalable distributed Internet services. Ninja’s objective is to architecture considered four elements: bases, units, active proxies, and paths.
Similar to the SDS, the MI has a brokering role. Moreover, the MI facilitates the direct interactions between providers and users. In fact, the MI avoids bottleneck their presence and enable users and programs to locate these announced services. situations and ensures a better security. that would access these services in a transparent way. In Ninja, the proposed other. Ninja proxies are similar to our device-agents. In addition, Ninja suggested