SDfR - Service Discovery for Robots Stefan-Gabriel Chitic1, Julien Ponge2 and Olivier Simonin1 1Universite´ de Lyon, INSA-Lyon, INRIA, CITI, F-69621, Villeurbanne, France 2Universite´ de Lyon, INSA-Lyon, CITI, F-69621, Villeurbanne, France Keywords: Robotic Fleet, Service Discovery, Service Oriented Architecture. Abstract: Multi-robots systems require dedicated tools and models for their design and the deployment. Our approach proposes service-oriented architecture that can simplify the development and deployment. In order to solve the problem of neighbors and service discovery in an ad-hoc network, the fleet robot needs a protocol that is able to constantly discover new robots in its coverage area. To this end we propose a robotic middleware, SDfR, that is able to provide service discovery. This protocol is an extension of the Simple Service Discovery Protocol (SSDP) used in Universal Plug and Play (UPnP) to dynamic networks generated by the mobility of the robots. Even if SDfR is platform independent, we propose a ROS (ROS, 2014) integration in order to facilitate the usage. We evaluate a series of overhead benchmarking across static and dynamic scenarios. We also present some use-cases where our proposal was successfully tested. 1 INTRODUCTION cover reachable neighbors and their services. We also provide a ROS integration node, simplifying the us- Nowadays more and more robotic systems tend to be age of SDfR. composed of several robots moving and cooperating, The paper is structured as follows: Section 2 generally called fleets of robots. They are able to per- presents the background of service orientated archi- form one or multiple tasks together and to share in- tecture and discovery in multi-robot systems, Sec- formation about complex missions. tion 3 discusses the service discovery approaches in One of the problems in developing multi-robot ap- middleware for robotics, Section 4 presents our pro- plications is the communication inside the fleet. The posal for service discovery in a fleet context, Section robots need to know the reachable peers in any type 5 presents the arhitecture and the implementation of of communication infrastructure. In an ad-hoc net- SDfR, Section 6 presents the main results of over- work, this problem becomes challenging because the head benchmarking and Section 7 describes a couple robots are highly mobile. A fleet can easily partition of use-cases. Section 8 concludes the paper. or merge with another fleet. Also single robots can become isolated or join an existing fleet. There is a great need of having a suitable middle- 2 MOTIVATION ware that can abstract the neighbor and service dis- covery layer and offer high-level application inter- One problem of robotic fleets is how functionalities faces (APIs) to robotic applications. The challenge can be applied to make the collaboration between is to provide an adapted system that can offer a suit- peers easier. Robots in fleet system that perform able mechanism for network configuration. Second, a mission together need to communicate with other this mechanism needs to maintain a list of connected peers. The communication can be done using a cen- peers and their services in a highly mobile scenario. tralized node or directly using an ad-hoc network. In this paper we propose a new service discov- ery middleware, called SDfR (Service Discovery for Robots), an extension of the Simple Service Discov- Robotic Applications as Services. In our vision, ery Protocol (SSDP) used in Universal Plug and Play robots need to advertise their functionalities as ser- (UPnP). SDfR is able to make an auto-configuration vices in order to allow other members of the fleet to for the connectivity to the fleet ad-hoc network, dis- interact with them. In network based applications, 236 Chitic, S-G., Ponge, J. and Simonin, O. SDfR - Service Discovery for Robots. DOI: 10.5220/0005755202360243 In Proceedings of the 8th International Conference on Agents and Artificial Intelligence (ICAART 2016) - Volume 1, pages 236-243 ISBN: 978-989-758-172-4 Copyright c 2016 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved SDfR - Service Discovery for Robots service-oriented programming is now a largely ac- designed for mono-robot with little applicability in cepted principle (Issarny et al., 2011). multi-robot systems. Service-oriented architecture greatly simplifies One of the first middleware that emerged for the implementation of highly-adaptive, constantly- robotics is Player/Stage (Kranz et al., 2006) project evolving applications (Frenot´ et al., 2010). It also re- which is designed to provide an infrastructure, drivers duces the process of developing and deploying new and a collection of dynamically loaded device-shared robotic applications. This architecture is very suit- libraries for robotic applications. It neither offers a able to quickly cope with new developing models and service orientated architecture, nor a discovery for requirements. neighbors services system. In order to increase the mobility of the robots and Another highly used middleware for robotics is to distribute the communication without having a cen- ROS (Robot operating system). It is a recent flexi- tral node, there is a need for the communication to be ble middleware for robot applications (Quigley et al., decentralized using ad-hoc networks. In this case, the 2009; Cousins et al., 2010; ROS, 2014). It is a col- robots do not have any image of their neighbors. Fur- lection of tools, libraries, and conventions that aim to thermore, the communication across peers is suscep- simplify the task of creating complex and robust robot tible to route change and different peers can be used behavior across a wide variety of robotic platforms. It to relay a data package. The ad-hoc network becomes provides hardware abstraction, device drivers, visual- the sum of peer to peer network with 2 robots at least. izers, message-passing, package management. ROS (ROS, 2014) seems to be the emerging mid- dleware for mono-robot with the most potential to Fleet Service Discovery. In order to solve the prob- become the most used framework for robotic fleets. lem of neighbors and service discovery in an ad-hoc However, it has no multi-robot coordination system network, a fleet robot needs a protocol that is able to and no automated testing environment, but it has al- constantly discover new robots in its coverage area, ready the advantage of having a large community that while maintaining a neighbor connectivity quality in- develops new packages for it. dicator. Since there is not any central node that can manage IP address allocation, the protocol should be To the best of our knowledge, none of the existing able to negotiate an IP address inside the network middleware for robots provides a service discovery and to have a conflict management tool in case of mechanism. ROS internal repository is represented an IP collision. Our work focuses on ad-hoc multi- as an internal node designed for internal service dis- robot systems communication, especially on a family covery, but it does not support neighbors discovery. of middleware that accelerates the development and the deployment of new robotic applications. 3.2 Service Discovery and Robotics Classical protocols and middlewares for service dis- covery in distributed environments like data-grids, 3 RELATED WORK clouds or even smart environments have a central- ized or decentralized registry that manages service In this section we present some of the major middle- description. Decentralized systems (e.g UPnP (Ahn wares in robotics as well as some of existing service et al., 2005), Jini (Pereira et al., 2011) or SLP discovery protocols used in the field. (Romero et al., 2010)) can be a purely distributed so- lution where each node stores its own service repos- 3.1 Middleware for Robotics itories or a hybrid solution that includes super-nodes that aggregate information from other peers. All aspects of communication, application deploy- Another way to see a fleet of robots is like a ment and configuration can be facilitated using a service-oriented multi-agent system. Such environ- proper middleware. The biggest difference between ments like Peer-to-Peer (P2P), Multi-Agent Systems a classical middleware that runs in a cloud central- (MAS) or Service-Oriented Environments (SOE) tend ized infrastructure and a robotic one, is the mobility to approach the problem of service discovery in a cen- of the fleet and the decentralization of its components. tralized, distributed or decentralized way. Central- An exhaustive survey of the existing middlewares for ized mechanisms like super-peers (Gummadi et al., robot contexts is clearly impossible because of the 2002), middle-agents (Klusch et al., 2006) or cen- large number of existing middleware and frequent re- tral registries (Rompothong and Senivongse, 2003) leases of new ones. A detailed survey can be found are limited in number of agents in the system and in (Chitic et al., 2014). Most of the middlewares are in terms of the number of requests. They also use 237 ICAART 2016 - 8th International Conference on Agents and Artificial Intelligence a centralized node which can have serious impact if tive is to propose a network configuration negotiation the central point becomes unreachable. Distributed protocol. Due to the mobility of robots, classical peer approaches such as Distributed Hash Tables (DHT) to peer network configuration techniques are not suit- (Maymounkov and Mazieres, 2002) offer more scal- able. ability and robustness by having multiple specific In this section we present the general description nodes that can manage the resources. Decentralized of our service discovery protocol for robotic applica- systems consider all the nodes to be equal. This ap- tions, called SDfR (Service Discovery for Robots). proach provides more flexibility, but it has its down- sides, since each node has only a partial view of the 4.1 SDfR vs SSDP entire system.