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Vers un environnement collaboratifmulti-utilisateurs

An Ubiquitous Shared Environment to work Together

Laurent Lucas, Hervé Deleau, Benjamin Battin & Julien Lehuraux

English Abstract—Ubiquitous is one of the essential features of what should be the desktop of the future. In practice, thisconcept covers several issues related to multi-users collaboration, remote applications control or remote display and secureaccess over IP networks. With its standards and capabilities, WebRTC provides a new vision of real-time communicationsservices that can raise these challenges. This paper presents a WebRTC-based middleware solution for real-time multi-usersremote collaboration. It allows a full desktop setup where everyone can see what other users are doing and where they positionthemselves in the shared workspace. In contrast to standard WebRTC’s Peer-to-Peer architecture, our system supports asynchronous communication model through a star topology. It also improves network bandwidth efficiency by using hardwarevideo compression when the GPU resource is available, though assuring a very low latency streaming. In this way, we canmaintain awareness and sense of presence without changing the usual practices of the users in front of a desktop. Several usecases are provided and a comparison of advantages and drawbacks of this solution is also presented to guide users in applyingthis technology under real-life conditions.

Index Terms—WebRTC, Remote Display, Multi-Users Collaborative Environment

F

1 INTRODUCTION

The requirements related to teamwork and mobilityespecially in corporate environments as well as inscience and academic environments are becomingincreasingly requested. This new way of working onspatially and temporally [2] distributed systems hasbecome a more commonplace practice especially withthe emergence of remote collaboration tools allowinga group of people to share their resources or to createin a common effort. In this sense and for a growingrange of devices, the availability of these tools hasto be ensured particularly in terms of security andaccessibility, for instance, from traditional computer aswell as from mobile devices like smartphones and/ortablets. Web technologies through modern capabilitiesof browsers enable today the development of cross-platform software systems as capable and powerfulas desktop applications [18]. From this point of view,the Web has opened a new way for the developmentof cloud hosted Internet-based collaboration apps [12]and other means of interaction. Online collaborationtools can be classified in two categories: synchronousvs. asynchronous communication tools. Unlike asyn-

• Laurent Lucas: Université de Reims Champagne-Ardenne, CReSTICEA3804, FranceE-mail: laurent.lucas@univ-reims.fr.

• Hervé Deleau: Université de Reims Champagne-Ardenne, CReSTICEA3804 & Maison de la Simulation de Champagne-Ardenne, FranceE-mail: herve.deleau@univ-reims.fr.

• Benjamin Battin: OPEXMedia, FranceE-mail: bbattin@opexmedia.com.

• Julien Lehuraux: OPEXMedia, FranceE-mail: jlehuraux@opexmedia.com.

chronous communication, synchronous communica-tion involves an ongoing real time character and cantake place face-to-face irrespective of distance.Although this distinction tends to fade, the feelingof presence has become crucial in all collaborativeenvironments [7], [9] especially with the recent de-velopment of immersive collaborative solutions [4],[21]. This observation has been partly achieved by thewidespread use of both HPC and graphics virtualiza-tion that has brought significant changes to corporatenetworks by delivering for instance an immersive,high-quality user experience for everyone [10], fromdesigners [5] to engineers [16] and other mobile pro-fessionals or simple office workers. This technologicalinnovation used widely in many industrial sectors isone of the most disruptive of our time.However, if current software solutions partially andspecifically address – e.g. in terms of online collab-orative work, video conferencing, multi-users remotecontrol or remote display – the issues raised by the“desktop of the future” [15], it must be noted that:

1) there is no integrated environment today aroundall of these elements and

2) data privacy is not always guaranteed whichcan be a serious problem of sovereignty for allstrategic institutions.

Whether they are research projects as well as com-mercial systems, there are many collaborative onlinesolutions used today in areas such as health [8], col-laborative visualization [5], [7], [9] and learning [13],[19] with specific software developments related towhiteboarding collaboration [14], [17], [20] for in-

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stance.Regarding commercial products, software market canbe segmented into three fields:

1) online collaborative solutions first such as thoseoffered by Cisco with Spark1 or Amazon withChime2.

2) multi-users remote control next with Screen-hero3.

3) remote visualization after all through solutionslike Citrix HDX 3D Pro4, HP RGS5 or NiceDCV6.

In this paper we present our solution called USETogether1. This middleware is a secure multi-usercollaborative system allowing professionals to sharetheir applications and data in real time, accessiblefrom any device, over any network. It enhances yourcommunications in terms of i) user QoE by deliveringHD in real time with low latency, ii) simplicity ofuse based on standards such as WebRTC and HTML5with zero-client deployment iii) security without datatransmission but only pixel on a Peer-to-Peer archi-tecture with encrypted streams and iv) flexibility ofuse by supporting both SaaS, on-premises and host-to-host deployment modes.The reminder of this paper is organized as follows:in section 2 we propose a brief overview of themain functionalities of WebRTC before introducing,in section 3, our contribution USE Together and itsarchitecture. Then we present and discuss in section 4some use cases. Finally, conclusion and future worksare given in section 5.

2 WEBRTC

WebRTC (Web Real Time Communication) [6] is atechnology that allows real-time Peer-to-Peer commu-nication between browsers without the use of addi-tional plugins. WebRTC is designed “to enable rich,high-quality RTC applications to be developed forthe browser, mobile platforms, and IoT devices, andallow them all to communicate via a common set ofprotocols” [1]. WebRTC was open-sourced by Googlein 2011 and after that an ongoing work started tostandardize the protocols associated with it by IETFand its browser APIs by W3C. Interest and support forWebRTC has been since growing steadily. Today, themost advanced WebRTC implementation is offeredby Mozilla Firefox and Google Chrome and includesthree APIs:

1. https://www.ciscospark.com/2. http://www.hp.com/go/rgs3. https://screenhero.com/4. https://www.citrix.fr/products/xenapp-xendesktop/hdx-3d-

pro.html5. http://www.hp.com/go/rgs6. http://www.nice-software.com/home1. Ubiquitous Shared Environment Together

1) MediaStream, which allows an application tostream media from the user’s web camera andmicrophone or from a screen capturing.

2) DataChannel, which allows to share arbitrarydata between peers. This layer is an importantfeature of WebRTC allowing the development ofall kind of Peer-to-Peer applications and collab-orative solutions.

3) PeerConnection, which represents the glue be-tween MediaStream and DataChannel by pro-viding a handshake mechanism for two ma-chines to exchange necessary information so aPeer-to-Peer connection can be set up.

The architecture of WebRTC including the signalingserver is shown in schematic 1. Although WebRTC as-pires to enable Peer-to-Peer communication betweenbrowsers without relaying data through any interme-diary, the use of a server is still required for two rea-sons: the first reason is the obvious one, a web serveris needed to “serve” the actual web application thatutilizes WebRTC. The second reason is less obvious.A server is required in order to initialize sessionsbetween the clients that need to communicate. Thisprocess is known as “Signaling” and is responsiblefor the exchange of the initial (meta) data of sessiondescriptions (using SDP and ICE framework) whichcontain details on the form and nature of the datawhich will be transmitted [24]. These information caninclude network data, such as IP addresses and ports,media metadata such as codecs and codec settings,bandwidth and media types, error messages or userand room information. PeerConnection API is used toachieve this process.

3 USE TOGETHERTMOVERVIEW AND IM-PLEMENTATION

Based on the native C++ APIs implementation of We-bRTC by Google, USE Together is structured aroundtwo modules: USE Signaling and USE Engine. Theimplemented and developed solution with all its ele-ments with respect to the architecture is illustrated inFigure 1.a. In the two following subsections, to givea better understanding of the overall architecture tothe reader, we will illustrate the description of eachmodule with a typical usage scenario: a user A startsa collaborative working session S on his desktop anda user B wants to join S.

3.1 USE Engine

The USE Engine module consists in two major sub-systems: the former, called ‘USE Engine Core’, actsas the central point of communication between thehost (which initiates the collaborative session) and theremote users who join it. In terms of network topology(cf. Figure 1.b), one can see a collaborative sessionas a star where the host is located in the center and

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Fig. 1. a) WebRTC system architecture and b) peers connection topology – star – where a callee (noted Ce)sends captured media to each caller (noted Cr) which, in turn, transmit their inputs with transactions of controlmessages in both cases.

each remote user resides in a branch. Thus, the ‘USEEngine Core’ part is essentially dedicated to receivingand delivering data to each branch over WebRTCchannels: video and audio streaming (resp. input andcontrol messages) over Media Channels (resp. DataChannel). The latter sub-system, named ‘USE EngineGUI’, is an application responsible for the followingtasks:

• capturing an entire desktop or a specific window.• capturing local video and/or audio data (eg. from

a webcam).• encoding the resulting streams and transmitting

it to ‘USE Engine Core’.• injecting keyboard and mouse input events from

remote peers.• specifying multiple settings to configure the ses-

sion.

When the user A wants to start a collaborative work-ing session, he just starts USE Engine, which automat-ically creates a working session S and registers it onUSE Signaling (described below). The session is nowactive and can be reachable by any remote user whoknows the session name and the session password.In order to provide the best possible experience tothe user, USE Engine especially focuses on addressingtwo typical issues related to collaborative softwares:latency and multiple user inputs management. Withtraditional remote desktop visualization tools, theuser generally has to deal with high latency whichcould be annoying while using real time applicationsremotely. USE Engine exploits the latest technologiesin terms of screen capturing and video encodingrespectively with the use of the NVIDIA’s GRID andNVENC APIs. The first one, (GRID), provides directaccess to video memory while NVENC makes use ofa hardware H.264 encoding chip, integrated since therelease of Kepler NVIDIA GPUs, to produce a lowlatency H.264 video stream. Obviously, if the desktopis not equipped with such hardware, a fallback mode

provides a desktop capture system based on OS APIsand a CPU encoding framework delivering eitheran H.264 (still with a low latency profile) or a VP8video stream. The last issue lies in the input eventshandling of each connected user on an operatingsystem natively thought for a single usage. To thatend, USE Engine includes two interaction modes: asynchronized one, where a user can seamlessly takethe control anytime he does a specific action (mouseclicks or keyboard usage) and if nobody already did,ignoring the other users input events for the durationof those actions, and a token-based one where a userhas the control as long as he keeps the token (set bythe session administrator).

3.2 USE Signaling

As mentioned in section 2, an auxiliary server, whichacts both as a web server and as a signaling server,is required to set up the Peer-to-Peer communicationbetween user A and user B. Firstly, user B has tolog himself, then specify the session name and theassociated password. USE Signaling is then able, fromthe session name, to identify the user who initiatesthe collaborative session (in our case, user A) andto relay messages between A and B during the sig-naling stage. Signaling can be defined as a classichandshaking phase during which the two users ex-change network information (to find the best networkroute between them) and their session descriptions(a data structure containing streaming capabilities ofa specific machine/browser couple) to negotiate acompatible way to exchange data. As soon as thenegotiation is done, the peer connection (and theassociated communication channels) can be createdbetween A and B. At this point, B is now connectedto S and can work collaboratively with user A.

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Fig. 2. Example CAD viewer application. The actual image shown on screen is being rendered remotely. Thefour users connected to their browsers can interact simultaneously on the 3D model.

4 USE CASES DESCRIPTION AND DISCUS-SION

Two kind of use cases have been realized with a com-mon objective to stay focused on what is essential toapplication area by centralizing data and applicationsfor a remote multi-peer collaborative access.For manufacturing industries case first, USE Togetherhas been used as a project management tool to en-able its users to work remotely with different CADapplications. Project review, synchronous co-design,simulation and visualization are the main functionstested in a multi-user collaborative framework. As wecan see in Figure 2, four users interact synchronouslyon a same 3D model during a project review phase.The second use case was carried out within a biomed-ical environment with different softwares visualiza-tion. Mainly based on GPU-accelerated direct volumerendering algorithms, these tests confirmed the com-patibility of the system with GPU-intensive resourcesapplications without altering facility to encode theoutput video stream in real time. Several scenarioshave been designed to work remotely with differentpartners on a collegial basis in order i) to jointlyannotate and navigate in a set of biological data ob-tained through a slide scanner and ii) to engage HPCresources to visualize and interact with simulationsremotely.In both cases, USE Together has received a largeendorsement by:

• increasing users’ productivity on load-intensiveapplications and complex data through remoteaccess on centralized resources.

• enhancing performance of teams with a real time

collaborative solution running on a same appli-cation instance.

With its usage of the latest NVIDIA GPU-basedstreaming technologies (accelerated desktop framegrabbing and encoding), USE Together has achievedto bring a smooth experience on both of the use casesover any network, from 3G/4G to wifi and ethernet,with a bitrate about as low as 1.5 mbps for a full HDremote display.

5 CONCLUSION AND FUTURE WORKS

This paper proposed a WebRTC-based collaborativemulti-user solution enhancing communications of agroup by enabling them to share their applicationsand data in real time over any network. This solu-tion called USE Together can be deployed on var-ious hardware environments in a secure way andbe accessed through a simple web browser withoutusing any additional software nor plugin. Composedof two modules allowing i) to connect two peersand ii) to exchange encrypted streams between peers,USE Together is able to address many challenges inrelation to pervasive computing like capabilities tooffer interactive shared workspaces in a collaborativeway and to maintain calculation accessibility through“invisible” resources while guaranteeing a good levelof confidentiality during exchanges.Exclusively based on a web implementation today,this solution should also evolve to provide end-pointdevices support like specific 3D displays [3] andVR/AR devices [11].

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ACKNOWLEDGMENT

This work is supported by the French national funds(PIA2’program) under contract No. P112331-3422142(3DNS project). We would like to thank the threeclusters (Cap Digital, Systematic and Medicen) thatsupport this project.

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