Draft: draft-irtf-nwcrg-network-coding-satellites-05

Commentary: A first sentence says quasi - error - free is usually guarranteed thanks to redundancy , while the following sentence tends to say the opposite . Not very clear . The intro fails to clarify the targets . Among them there is " coding to recover from packet losses " ( to avoid confusion with bit - error corrections ) , but also " coding to improve the usage of radio resource " . You should also clarify better what is meant by coding : it 's not a content coding ( e.g. , to compress a video flow ) but rather a computation of linear combination of packets . Say since the begining you 'll rely on RFC8406 whenever possible . Parts of the text currently in section 3 ( 1st paragraph ) deserve to be moved here . Typo : s / to cope from / to cope with/ 
 We have updated the introduction structure and changed the usage of coding in the whole document . We hope this is better . cf PR and PR 
 this is cherrypicking , not discussing link / channel FEC ( Error ) or ACK . the heading should really be ' of network coding schemes ' . " to cover cases where where " ? At the physical layer , FEC mechanisms can be exploited.-- Erasure or Error ? " Based on public information , coding does not seem to be widely used at higher layers . " it is n't , and that section can be reduced to just that sentence . 
 Vincent in item X1 , 1st sentence , it suggests QUIC is a video streaming application . Change it .  . 2 raises a general question : it refers to upper applications that are by nature on the end - hosts . Everything is imaginable here and this is not specific to a SATCOM system . Why do n't you limit yourself to the communication layers + middleware ? I 'm a bit confused . When you say : " Based on public information , coding does not seem to be widely used at higher layers . " I guess you limit yourself to the " packetization UDP / IP + middleware " but do not consider upper applications . It 's also confusing . 
 We think that these comments have been assessed with PR 
 " In this context , this document aims at identifying opportunities for further usage of coding in these systems . " again , network coding . this pretending that link and channel FEC do n't exist and that " coding " , i.e. network coding , is somehow new is irksome . 
 Closed by PR
This memo details a multi-gateway satellite system to identify
multiple opportunities on how network coding techniques could be
deployed at a wider scale.
This memo details a multi-gateway satellite system to identify
multiple opportunities on how coding techniques could be deployed at
a wider scale.
exploiting coding schemes at application or transport layers is an
opportunity for releasing constraints on the physical layer and
improving the performance of SATCOM systems.
The notations used in this document are based on the taxonomy
document RFC8406: End-to-End Coding (E2E), Network Coding (NC),
Intra-Flow Coding (IntraF), Inter-Flow Coding (InterF), Single-Path
Coding (SPC) and Multi-Path Coding (MPC).  Following the taxonomy
document RFC8406, channel and link codings are gathered in the PHY
layer coding and are out of the scope of this document.  This
document considers FEC as coding mechanisms above the network layer
only.
X1 embodies the source coding that could be used at application
level for instance within QUIC or other video streaming
applications.  This is not specific to SATCOM systems since such
deployment can be relevant for broadband Internet access
discussions.
X2 embodies the physical-layer to optimize the satellite capacity
usage.  At the physical layer, other coding mechanisms can be
exploited.
We notice an active research activity on coding and SATCOM.  That
being said, not much has actually made it to industrial developments.
In this context, this document aims at identifying opportunities for
further usage of coding in these systems.
exploiting coding techniques at application or transport layers is an
opportunity for releasing constraints on the physical layer and
improving the performance of SATCOM systems.
Channel and link codings are gathered in the PHY layer coding and
are out of the scope of this document.
FEC (also called Application-Level FEC) operate above the network
layer.
This document considers coding (or coding techniques or coding
schemes) as a linear combination and not as a content coding
(e.g., to compress a video flow).
X1 embodies the source coding techniques that could be used at
application level for instance within QUIC or other video
streaming applications.  This is not specific to SATCOM systems
since such deployment can be relevant for broadband Internet
access discussions.
X2 embodies the physical-layer techniques exploited in SATCOM
systems (note that other coding techniques can be exploited).
This is out of the scope of the document.
We notice an active research activity on coding techniques and
SATCOM.  That being said, not much has actually made it to industrial
developments.  In this context, this document aims at identifying
opportunities for further usage of coding in these systems.
Some functional blocks aggregate the traffic of multiple users.
Coding schemes could be applied on both single and aggregated
traffic.
This section details use-cases where coding schemes could improve the
overall performance of a SATCOM system (e.g. considering a more
efficient usage of the satellite resource, delivery delay, delivery
ratio).
Some functional blocks aggregate the traffic of multiple users.
Coding techniques could be applied on both single and aggregated
traffic.
This section details use-cases where coding techniques could improve
the overall performance of a SATCOM system (e.g. considering a more
efficient usage of the satellite resource, delivery delay, delivery
ratio).
To cope with packet loss (due to either end-user mobility or
physical-layer impairments), coding could be introduced in both the
CPE and at the concentrator.
This use-case considers the usage of coding to cope with cases where
channel condition can change in less than a second and where the
physical-layer codes could not guarantee a Quasi-Error-Free (QEF)
transmission.
To cope with packet loss (due to either end-user mobility or
physical-layer impairments), coding techniques could be introduced
both at the CPE and at the concentrator.
This use-case considers the usage of coding techniques to cope with
cases where channel condition can change in less than a second and
where the physical-layer codes could not guarantee a Quasi-Error-Free
(QEF) transmission.
This use-case is mostly relevant for when mobile users are considered
or when the chosen band induce a required physical-layer coding that
may change over time (Q/V bands, Ka band, etc.).  Depending on the
use-case (e.g. very high frequency bands, mobile users) or depending
on the deployment use-cases (e.g. performance of the network between
each individual block), the relevance of adding coding is different.
This use-case is mostly relevant for when mobile users are considered
or when the chosen band induce a required physical-layer coding that
may change over time (Q/V bands, Ka band, etc.).  Depending on the
use-case (e.g. very high frequency bands, mobile users) or depending
on the deployment use-cases (e.g. performance of the network between
each individual block), the relevance of adding coding techniques is
different.
SATCOM systems typically feature Performance Enhancement Proxy (PEP)
RFC3135.  PEP usually split TCP end-to-end connections and forward
TCP packets to the satellite baseband gateway that deals with layer-2
and layer-1 encapsulations.  PEP could host coding mechanisms and
thus support the use-cases that have been discussed in this document.
SATCOM systems typically feature Performance Enhancement Proxy (PEP)
RFC3135.  PEP usually split TCP end-to-end connections and forward
TCP packets to the satellite baseband gateway that deals with layer-2
and layer-1 encapsulations.  PEP could host coding techniques and
thus support the use-cases that have been discussed in this document.
Related to the foreseen virtualized network infrastructure, coding
schemes could be easily deployed as VNF.  Next generation of SATCOM
ground segments could rely on a virtualized environment.  This trend
can also be seen in cellular networks, making these discussions
extendable to other deployment scenarios I-D.chin-nfvrg-cloud-5g-
core-structure-yang.  As one example, the coding VNF functions
deployment in a virtualized environment is presented in I-D.vazquez-
nfvrg-netcod-function-virtualization.
Related to the foreseen virtualized network infrastructure, coding
techniques could be easily deployed as VNF.  Next generation of
SATCOM ground segments could rely on a virtualized environment.  This
trend can also be seen in cellular networks, making these discussions
extendable to other deployment scenarios I-D.chin-nfvrg-cloud-5g-
core-structure-yang.  As one example, the coding VNF functions
deployment in a virtualized environment is presented in I-D.vazquez-
nfvrg-netcod-function-virtualization.
Coding enables E2E reliable communication over DTN with adaptive re-
encoding, as proposed in THAI15.  In this case, the use-cases
proposed in subsec:varying would legitimize the usage of coding
within the DTN stack to improve the channel utilization and the E2E
transmission delay.  In this context, the use of erasure coding
inside a Consultative Committee for Space Data Systems (CCSDS)
architecture has been specified in CCSDS-131.5-O-1.  A research
challenge would be on how such coding can be integrated in the IETF
DTN stack.
Coding enables E2E reliable communication over DTN with adaptive re-
encoding, as proposed in THAI15.  In this case, the use-cases
proposed in subsec:varying would legitimize the usage of coding
within the DTN stack to improve the channel utilization and the E2E
transmission delay.  In this context, the use of erasure coding
techniques inside a Consultative Committee for Space Data Systems
(CCSDS) architecture has been specified in CCSDS-131.5-O-1.  A
research challenge would be on how such coding can be integrated in
the IETF DTN stack.