Tetrys

2014-07-16T15:09:51Z

Adaptive Tetrys Demo

LOCHIN Emmanuel — 2013-04-17T16:25:21Z

The big picture ...

Our paper that presents the adaptive on-the-fly coding scheme is avaliable on Arxiv

More experiment results to justify the statement in Section IV of our article can be found here

Time (s)	Loss pattern	Frame range
0 - 10	no losses	0 - 300
10 - 20	Gilbert-Elliott PLR=2%, mean burst size = 2	301 - 600
20 - 30	Gilbert-Elliott PLR=2%, mean burst size = 3	601 - 900
30 - 40	Gilbert-Elliott PLR=3%, mean burst size = 2	901 - 1200
40 - 50	Gilbert-Elliott PLR=3%, mean burst size = 3	1201 - 1500

The video below illustrates the PSNR and video obtained by Tetrys with redundancy adaptation algorithm against the ones obtained by Tetrys without redundancy adaptation algorithm. The packet loss pattern is shown in the table above. The video should be played in 720p format for better subjective evaluation.

the video below illustrates the PSNR and video obtained by Tetrys with redundancy adaptation algorithm against the ones obtained without Tetrys protection

	PSNR (dB)	BW occupation (kb/s)
Tetrys with redundancy adaptation algorithm	35.3 ± 2.6	773.8 ± 138.1
Tetrys without redundancy adaptation algorithm	34.1 ± 5.0	740.3 ± 137.6
Without Tetrys protection	31.9 ± 6.2	774.1 ± 174.8

Detail subjective evaluation with videos can be found here

More videos can be found here

Projects and Partners

LOCHIN Emmanuel — 2012-11-09T10:43:48Z

This page provides some projects and research studies where Tetrys is involved.

ARSSO

ARSSO project focuses on robustness and dynamic adaptation mechanisms for multimedia content communication systems over internet, characterized by more or less strict real-time communication constraints, within highly
heterogeneous networks and terminals.

See: http://open-innovation.alcatel-lucent.com/www/arsso/ for futher details about this french ministry project

CNES project: integration of Tetrys inside the DTN architecture

This project aims at studying the possibility to integrate Tetrys inside the DTN architecture.
Founded in 1961, the Centre National d'Etudes Spatiales (CNES) is the government agency responsible for shaping and implementing France's space policy in Europe.

See: CNES

La Région Midi-Pyrénées, FEDER European Funding and Toulouse Tech Transfer provides a support to promote, develop and raise funds for the Tetrys project.

Partners

Demo

LOCHIN Emmanuel — 2012-07-24T14:27:40Z

The big picture: Tetrys coding scheme with 5% of losses streaming HD video

The first video illustrates the PSNR obtained by Tetrys coding scheme against a FEC code over a Bernoulli erasure channel: PLR of 15%; redundancy ratio of 25%:

On the left FEC and on the right Tetrys ...

... and the resulting PSNR obtained compared to the original sequence.

The second illustrates the PSNR obtained by Tetrys coding scheme against a FEC code over a Gilbert Elliot erasure channel: mean average burst of 3; PLR of 15%; redundancy ratio of 25%:

On the left FEC and on the right Tetrys ...

... and the resulting PSNR obtained compared to the original sequence.

Publications

LOCHIN Emmanuel — 2012-07-24T14:26:58Z

IETF/IRTF work

Tetrys, an On-the-Fly Network Coding protocol (IETF working progess draft) draft-detchart-nwcrg-tetrys
Erasure Coding and Congestion Control for Interactive Real-Time Communication position paper presented at IAB/IRTF Workshop on Congestion Control for Interactive Real-Time Communication, 28 July 2012, Vancouver, Canada

Journals

Conferences

PhD

A Novel On-the-Fly Coding Scheme for Real-Time Applications Pierre-Ugo Tounoux PhD Thesis (November 2010)

Tea m

LOCHIN Emmanuel — 2012-07-24T14:26:07Z

Jonathan Detchart ISAE Engineer
Jérôme Lacan ISAE Professor
Emmanuel Lochin ISAE Professor

External collaborators & alumni

Vincent Roca INRIA
Pierre-Ugo Tournoux Université de La Réunion Assistant Professor
Tuan Tran Thai Expway

Tetrys

LOCHIN Emmanuel — 2010-09-13T15:33:49Z

Thanks to its "on-the-fly encoding" approach, Tetrys enables a fully or partially reliable delivery of contents, potentially with real-time constraints, better and faster than the TCP protocol or than traditional block FEC solutions would enable.

How to deal with packet losses?

Reliable transmissions over lossy channels are often either a must (e.g. in case of a file transfer) or a highly desired feature, even if a limited amount of losses may be tolerated (e.g. in case of video streaming). The origin of losses does not matter: it may be caused by bad reception conditions in case of wireless networks, or by IP datagram erasures in congested link. The result is the same and a certain number of data packets are missing.

Retransmitting lost packets is a solution. TCP, the dominant protocol over the Internet, heavily relies on TCP, even for video streaming (e.g. with the various “adaptive streaming over HTTP” techniques heavily used in video over the Internet services). However retransmitting requires both that a feedback channel exists (to know what is lost) and that data arrive in due time (it's not necessarily the case with real-time video transmissions).

Adding redundancy to the flow of data sent, thanks to an FEC code, is another solution. This FEC code is a smart component that can calculate redundant packets from a set of data packets at a sender, and reciprocally that uses redundant packets to recover the missing data packets in case of losses. However the usual approach consists in calculating redundant packets from a predetermined set of packets. The number of redundant packets can be either fixed or can depend on reception feedbacks. That's efficient and can be used even if the feedback channel is limited and in case of real-time content.

Tetrys is a solution that goes beyond these two techniques, taking the best of them, thanks to a unified encoding approach.

What about Tetrys and "On-the-Fly coding"?

TETRYS enables a new reliability algorithm that we call “on-the-fly encoding”. In the figure below, the sender periodically adds a redundant packet (noted R(..), in red) after two data packets (noted P.., in black). We assume that a feedback channel exists, also prone to losses.
The key innovation of Tetrys is the way encoding is performed: only non-acknowledged but useful packets are considered during encoding, using a sliding window over the data packets. This sliding window contains a number of packets that varies over the time, depending on what packets have been received or decoded so far at the receiver, and on the arrival of acknowledgements at the sender (they may be lost too).

In this example, R(1,2) is a redundant packet calculated with the two packets of the encoding window, P1 and P2. Since the acknowledgment of P1 has been lost, the encoding window grows and encompasses packets P1 to P4 the next time a redundant packet is calculated, R(1,4). In the absence of acknowledgment, the encoding window keeps on growing… until an acknowledgment of packets P1 to P8 arrives at the sender. Then the encoding window is updated to contain only P9 and P10,and the R(9,10) redundant packet is then calculated.

"On the fly encoding" is the key technology of Tetrys: only non-acknowledged and useful data packets are protected.

Full or partial reliability?

Usually, full reliability is only feasible if data is acknowledged by the receiver (or all the receivers with multicast transmissions), even lately. Applied to Tetrys, it means that a data packet stays in the encoding window until it is acknowledged.

But full reliability is not necessarily what an application is looking for. Indeed, a data packet may be useful only for a given time span. Think about a video frame. If this frame arrives after the moment it should have been displayed, it's of no use. In that case it's wiser to drop it anyway. Applied to Tetrys, it means that a data packet should stay in the “sliding encoding window” at most for a certain predefined time that depends on its real-time validity period. A data packet is either removed from the encoding window once acknowledged or upon reaching its maximum validity period.

Why is Tetrys a "must have"?

Tetrys is both an FEC coding scheme (e.g. it heavily relies on random linear FEC codes) and a transport protocol (it defines packets formats and protocol rules). As such it can be applied in several different places in a protocol stack:

below an application generating RTP packets for real-time video content, because of Tetrys exceptional benefits in terms of timely delivery of contents;
below TCP where it can help recovering from losses in wireless channels. Here poor reception conditions heavily hinder TCP connections since TCP assumes losses are caused by congestions and backs off, which is of no benefit in case of bad signal/noise issues;
in Delay Tolerant Network (DTN) systems, where feedbacks are not necessarily timely, nor necessarily feasible. In that case Tetrys offers a robust delivery even in presence of poor packet and feedback transmissions.

Tetrys provides a unified content delivery service that ensures a faster data availability to the receiving application compared to traditional techniques.

Contacts: Emmanuel Lochin and Jérôme Lacan