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Transitions in Live Video Streaming Services
Björn RicherzhagenTU Darmstadt, Germany
Stefan WilkTU Darmstadt, [email protected]
darmstadt.de
Julius RückertTU Darmstadt, Germany
Denny StohrTU Darmstadt, [email protected]
darmstadt.de
Wolfgang EffelsbergTU Darmstadt, Germany
ABSTRACTThis work shows a demonstration on the work of the Col-laborative Research Center 1053 pursuing Multi-MechanismAdaptation for the Future Internet. Our prototype showsa live video streaming system on mobile devices featuringPeer-to-Peer (P2P) and Client/Server delivery concepts. Thefocus is to showcase seamless transitions between those mech-anisms, depending on the monitored system state. For this,our system streams video from a central server to mobiledevices connected by a WiFi Access Point. The system exe-cutes transitions between client/server delivery and a P2Pstreaming overlay based on the number of clients streamingthe video. For demonstration purposes, transitions can betriggered either automatically or manually. The transitionsbetween both delivery schemes and the clients’ states aremonitored and visualized on a central UI.
Categories and Subject DescriptorsC.2.4 [Computer-Communication Networks]: DistributedSystems
KeywordsP2P; transitions; Client-Server; Monitoring
1. INTRODUCTIONToday, a variety of events attract large numbers of live
streaming viewers. For some of these live streams access ratescan be predicted up-front, others show a more spontaneousbut fast increase in the number of parallel viewers. Ourresearch demonstration and the research project addressesthose spontaneous and rarely predictable events. In suchscenarios, delivering high quality video streams in time cannotbe guaranteed – especially when considering mobile networks.
We propose an adaptive streaming system, that showcasesa set of mechanisms to mitigate these limitations. The
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system is composed of Peer-to-Peer (P2P) and Client/Server(C/S) delivery mechanisms that can be switched at run-time. We refer to the replacement of whole networkingmechanisms during runtime, such as streaming mechanisms,as transitions. Those transitions enable the streaming systemto adapt to a large range of scenarios and conditions suchas a sudden increase or decrease in the number of users.Our demonstration illustrates that the replacement of awhole delivery mechanism can be achieved seamlessly withoutdegrading the user experience.
2. STREAMING OVERLAYModern streaming services have to handle high scalability
demands. In most cases, a simple C/S-based system offers theresources required by streaming users but is not scalable tothousands of parallel views. The P2P dissemination paradigmon the other hand offers promising scalability properties,as every client contributes resources to keep the systemworking. However, P2P systems are expensive in terms ofoverhead and control based on the number of concurrentaccesses. In contrast to existing hybrid P2P-based videodissemination services such as ToMo [1] or mTreebone [2]this demonstration shows a transition-enabled framework fornetworking mechanisms on the basis of a live video streamingservice. Transition-enabled means in this context that C/S aswell as different P2P-based video dissemination protocols cancoexist and are used when environmental conditions favortheir selection. The framework is not limited to an exchangeof topologies such as it is demonstrated in this work, butallows to switch arbitrary networking mechanisms if theycomply to specified interfaces.
This demonstration implements an adaptation mechanismto seamlessly switch between two content dissemination mech-anisms: a central C/S and a decentralized P2P-based dissemi-nation scheme. With this it circumvents issues resulting fromsignificantly varying environmental conditions. Streamingshould be continued in a consistent quality for all users eventhough the operations on the network change. The used P2Psystem is based on Wichtlhuber et al.’s TRANSIT [3]. TheC/S system follows a classical star topology, where joiningnodes contact a server and are provided with small videosegments, so called chunks by only this central source. TheP2P-based mechanism allows clients to retrieve video chunksfrom the server but additionally from each available othernode. Therefore, a tracking functionality is hosted on thecentral server to provide node contacts used for the initial
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neighborhoods in the P2P topology, while the exchange ofmedia chunks is then done completely decentralized. As [3]has shown in live streaming scenarios: a tree topology isbeneficial to reduce delay between streaming nodes due tothe push-based delivery of chunks. Thus, the system aims toarrange clients in a tree, but allows an hybrid video chunkexchange in cases of high churn or if chunks are dropped dueto unreliable UDP transmissions. In such cases, the clientcan request chunks in a pull-based, mesh-like manner fromeach other node currently in its neighborhood. Transitionsand mechanism reconfigurations are shown between C/S andP2P, but the P2P-based system allows further replacementsof tree and mesh-topologies.
3. PLANNING AND EXECUTIONBesides the streaming overlays and mechanisms the demon-
stration prototype of the research project includes a moni-toring, planning, and execution framework allowing sounddecisions on when to transition between networking mech-anisms. Therefore, the prototype implements a centralizedmonitoring approach. It allows to gather metrics from eachstreaming device on the number of nodes involved in stream-ing one specific live video, the throughput on the up- anddownlink, available energy of each client and the streamingquality assessed by the number of stalls. The data is thenused by the central video server to visualize the topology andassociated metrics. Based on the measured metrics, tran-sition rules can be defined to execute transitions betweenindividual networking mechanisms automatically. In a P2P-based video streaming system, this involves topology and itsmanagement, scheduling, or neighborhood management.
4. SCENARIO AND DEMONSTRATIONThe demonstration software of the Collaborative Research
Centre 1053 illustrates the rising need for efficient, self-adaptive distributed systems, using the case-study of videodelivery to mobile devices. It offers a toy model includingthe central video streaming server represented by a laptop,the wireless network depicted by the WiFi Access Point andfive Nexus 7 tablets accessing video from the central server.The central, resource-limited video streaming server offersa continuous video stream. Depending on the interest inthe content nodes join the system to watch the stream. Thefirst clients joining the streaming system retrieve the videoin a continuously high quality. As more and more nodesare joining the network, the available resources (uplink ca-pacity of the server) are depleted. The system as explainedin Section 2 is designed to replace whole mechanisms andstreaming approaches without interfering with the applica-tion layer – in this case the video playback. As the systemis centrally monitored, it can identify a resource bottleneck.When detecting such a bottleneck, it selects an appropriatemechanism for highly scalable video streaming - in this casea P2P overlay - and switches to the new mechanism. Dur-ing this switch, continuous playback is ensured even thoughthe underlying streaming mechanism is replaced. In onedemonstration setting the automatic execution of transitionsis disabled initially. Based on a toggle button users can en-or disable the automatic execution of transitions. If the tran-sition capabilities are disabled, the user will see reoccurringstalling as the central server’s upload capacities are limited.A central visualization as depicted in Figure 1b illustrates
(a) Demonstration setup
(b) Overview of the streamingtopology
metrics of each device as well as aggregated up- and downloadcapacities. Additionally, the current streaming topology isdepicted allowing users to easily identify whether the systemis currently streaming in C/S or P2P mode. An overviewof the setup, consisting of a laptop representing the centralstreaming server and the Nexus 7 tablets representing themobile streaming nodes is given in Figure 1a.
AcknowledgementThis work has been funded by the DFG as part of the CRC1053 MAKI.
5. REFERENCES[1] S. Awiphan, Z. Su, and J. Katto. ToMo: A Two-Layer
Mesh/Tree Structure for Live Streaming in P2P OverlayNetwork. In 2010 7th IEEE Consumer Communicationsand Networking Conference, pages 1–5, 2010.
[2] F. Wang, Y. Xiong, and J. Liu. mTreebone: A HybridTree/Mesh Overlay for Application-Layer Live VideoMulticast. In IEEE 27th International Conference onDistributed Computing Systems (ICDCS ’07), 2007.
[3] M. Wichtlhuber, B. Richerzhagen, J. Ruckert, andD. Hausheer. TRANSIT: Supporting transitions inPeer-to-Peer live video streaming. In 2014 IFIPNetworking Conference, pages 1–9, 2014.
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