Subject: [nwcrg] Management of network/erasure coding schemes to carry and protect data application flows

From: "LOCHIN Emmanuel" <[email-masked]>
Date: Fri, 13 Jan 2017 17:43:49 +0100

Hello everybody,

I wish to start a discussion concerning the management of network/erasure coding schemes to carry and protect data application flows.
We are all users/developers of such schemes and we certainly use different ways to benefit/demonstrate their capabilities.
One common option is to use a tunnel or a proxy to encapsulate the data flow (this could be either a single flow or an aggregate).
Such context of use raises several questions from both transport and coding areas and I would be interested in exchanging views and discussing on the following items:

1. tunneling an aggregate:
Let's consider a tunnel that protects an aggregate of several flows. One possibility is to not distinguish flows between them and to protect the whole traffic as a single flow with a network coding scheme. As a matter of fact, this could have an impact at the microflow level depending on the rate of each encapsulated flow and each application type. For instance, combining indifferently bulk data traffic with VoIP traffic might not be the best way to perform. Obviously, there is an overhead cost to analyze the semantic of each flows;

2. managing single data flows :
For instance, let's consider either a connexion establishment or the termination of a connexion. There are cases where the application source does not have any more data to send. So, the transfer might stall because the decoder (from an erasure coding scheme) at the destination is still waiting for repair packets to rebuild missing packets and deliver them to the application. Without "seeing" the FIN flag, and thus analyzing packets, the decoder is not aware that no more packets will be sent by the source. So what to do during silence? Of course, some protocols (such as TCP) would recover by a retransmission timeout (considering that the retransmitted packet won't be lost... crossing fingers) but this won't be the case for several others protocols such as UDP reliable, DCCP, ...

In brief, the use of network coding scheme as a transport scheme raises several questions that I feel, are worth to debate.

Emmanuel

-- 
Emmanuel LOCHIN
Professeur ISAE
ISAE SUPAERO - Institut Supérieur de l'Aéronautique et de l'Espace
10 avenue Edouard Belin - BP 54032
31055 TOULOUSE CEDEX 4 FRANCE 
http://www.isae-supaero.fr
Tel +33 5 61 33 84 85 - Fax (+33) 5 61 33 83 30