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====== MPRTP (Multipath Realtime Transport Protocol) ======

We propose the use of MPRTP (MultiPath Real-time Transport Protocol) [1] to support multimedia high-bandwidth applications. The core idea is quite simple: multiple physical links (pool) are used at the same time to deliver the multimedia content to a remote destination. In a similar way to RAID (Redundant Array of Independent Disks) storage technology, multiple low-cost links can be aggregated, in order to provide an efficient, reliable and cost-effective high-bandwidth logical channel, composed of several physical channels. Having more than one channels available at any time, the better performing channel (or subset of channels) can be used, excluding (or limiting the use of) bad performing ones. Our implementation of the MPRTP protocol aims at removing some of the existing limitations of [2], providing the possibility to //schedule// the transmission of the multimedia flow over multiple links, according to implemented policies. For instance, such as the use of a subset of channels within the pool that are reliable, or a subset showing the lowest aggregated RTT.

In the following, we show the preliminary results provided by our modified scheduler, in a scenario involving the use of an Unmanned Aerial Vehicle (UAV) with an on-board camera, delivering the stream to a terrestrial fixed station.

===== Scheduler Implementation =====
The scheduler implementation available at [2] estimates the overall available bandwidth, and splits the multimedia flow accordingly. The source video bitrate is then set, in order to provide the maximum achievable video quality, according to the available bandwidth. Anyway, [2] does not provide a way to reduce the load fraction on lossy and/or high-delay sub-links, thus causing corrupted video at the receiver. As analysed in [3], the scheduler should be able to quickly adapt to bandwidth changes, to overcome the packet skew due to the different RTTs, and to choose an optimal subset of sub-links, in order to provide the desired Quality of Service (QoS) and Quality of Experience (QoE).

==== ORIGINAL SCHEDULER [2] ====
{{:ncmprtp:original_scheduler.mp4|}}

//Corruption on even a single link within the pool makes the whole multimedia stream unusable.//


==== PROPOSED MODIFIED SCHEDULER ====
In order to reduce the impact of links showing bad channel statistics, we modified the scheduler available at [2], in order to only use the links within the pool that can deliver the multimedia stream in a usable way. Read the current advancements in [4,5,6,7].

{{:ncmprtp:intermediate_scheduler.mp4|}}

//Corruption on a single link does not make the whole stream unusable, because the former is excluded from the subset of the links in use.
//




== REFERENCES ==
[1] An IETF draft is available at https://tools.ietf.org/html/draft-ietf-avtcore-mprtp-03, which describes MPRTP protocol.

[2] MP-RTP implementation: https://github.com/balazskreith/gst-mprtp

[3] Singh V, Ahsan S, Ott J. //MPRTP: multipath considerations for real-time media//. Proceedings of the 4th ACM Multimedia Systems Conference 2013 Feb 28 (pp. 190-201).

[4] Bacco, Manlio, Pietro Cassarà, Alberto Gotta, and Massimo Puddu. "A Simulation Framework for QoE-Aware Real-Time Video Streaming in Multipath Scenarios." In International Conference on Ad-Hoc Networks and Wireless, pp. 114-121. Springer, Cham, 2020. https://link.springer.com/chapter/10.1007/978-3-030-61746-2_9

[5] Bacco, Manlio, Pietro Cassarà, Alberto Gotta, and Vincenzo Pellegrini. "Real-time multipath multimedia traffic in cellular networks for command and control applications." In 2019 IEEE 90th Vehicular Technology Conference (VTC2019-Fall), pp. 1-5. IEEE, 2019. https://ieeexplore.ieee.org/abstract/document/8891090

[6] Bacco, Manlio, Pietro Cassarà, and Alberto Gotta. "Air-to-ground real-time multimedia delivery: A multipath testbed." Vehicular Communications 33 (2022) https://doi.org/10.1016/j.vehcom.2021.100443

[7] Machumilane, Achilles, Alberto Gotta, Pietro Cassara, and Manlio Bacco. "A Path-Aware Scheduler for Air-to-Ground Multipath Multimedia Delivery in Real Time." IEEE Communications Magazine (2022) https://doi.org/10.1109/MCOM.001.2100904
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