Unequal Erasure Protection and Object Bundle Protection with the Generalized Object Encoding Approach

When a data ow contains information of di erent priority levels, it is natural to try to o er an unequal protection where the high priority data bene ts from a higher protection than the rest of data. In this work we focus on the erasure channel", for instance the Internet where the UDP/IP datagram integrity is guaranteed by the physical layer FCS (or CRC) and the UDP checksum. In this context UEP refers to an Unequal Erasure Protection (rather than Error) and the FEC code being used is one of the various ApplicationLayer Forward Erasure Correction (AL-FEC) codes that have been designed and standardized in the past years, like Reed-Solomon, one of the LDPC variants, or Raptor(Q) codes. O ering an unequal protection in this context can be achieved by one of the following three general approaches: by using dedicated UEP-aware FEC codes, by using a dedicated UEP-aware packetization scheme, or by using an UEP-aware signaling scheme. In this work we ignore the rst approach as we want to reuse existing AL-FEC codes. Instead we focus on and compare the last two approaches and more precisely the well known Priority Encoding Transmission (PET) scheme that belongs to the UEP-aware packetization category and a Generalized Object Encoding (GOE) scheme, we propose, that belongs to the UEP-aware signaling category. We compare them both from an analytical point of view (we use an N-truncated negative binomial distribution to that purpose) and from an experimental, simulation based, point of view. Since we want to derive practical recommendations, we consider erasure recovery metrics, but also processing load and peak memory requirements metrics that can be of high importance. We show that the GOE approach, by the exibility it o ers, its simplicity, its backward compatibility and its good recovery capabilities, is highly recommendable for practical systems requiring UEP. ∗ INRIA, France, { rstname.name}@inria.fr † Alcatel Lucent Bell Labs, France, { rstname.name}@inria.fr ‡ Alcatel Lucent Bell Labs, France, { rstname.name}@inria.fr § Alcatel Lucent Bell Labs, France, { rstname.name}@inria.fr in ria -0 06 12 58 3, v er si on 1 29 J ul 2 01 1 UEP and Object Bundle Protection with the GOE approach 2 In a second part of the paper we consider the use of PET, more precisely an extension called Universal Object Delivery (UOD), and GOE in situations where one needs to send a bundle of small object (e.g. les). If both solutions can address this need, we show that once again the GOE scheme is highly recommendable for practical realizations. Key-words: Application-Layer Forward Erasure correction code, Unequal Erasure Protection RR n° 7699 in ria -0 06 12 58 3, v er si on 1 29 J ul 2 01 1 Protection inégale aux e acements et protection de fagots d'objets par l'approche Generalized Object Encoding Résumé : Nous proposons une nouvelle méthode qui permet à la fois de protéger des objets di érents de manière inégale aux e acements mais qui peut aussi regrouper des objets en un fagot a n de fournir à chacun des objets du fagot, le même niveau de protection. Cette technique est apppelée Generalized Object Encoding (GOE). Nous la détaillons et l'analysons dans ce rapport. Mots-clés : Application-Layer Forward Erasure correction code, Unequal Erasure Protection in ria -0 06 12 58 3, v er si on 1 29 J ul 2 01 1 UEP and Object Bundle Protection with the GOE approach 4