Subject: [rmcat] SCReAM implemenation aspects

From: Ingemar Johansson S <[email-masked]>
Date: Thu, 7 Apr 2016 06:26:43 +0000

Hi

As there is some interest to experiment with the CC candidates, here some
notes on how to integrate SCReAM into your platform.

The SCReAM source code can be fetched from
https://github.com/EricssonResearch/scream , it is written in C++. A good
first start is to read the description
(https://github.com/EricssonResearch/scream/blob/master/SCReAM-description.p
df ) first. In particular it is important to understand when the various
methods in the ScreamTx and ScreamRx class are called.

The C++ implementation lacks the following components.

+ Transmit queue : It is assumed that you implement a function that queues
up the RTP packets from the video coder (one queue per SSRC). The OpenWebRTC
code
(https://github.com/EricssonResearch/openwebrtc-gst-plugins/blob/master/gst/
scream/gstscreamqueue.c ) has an example how this can be done, search for
GstScreamDataQueueRtpItem

+ RTCP generation : Code for generation and parsing of the SCReAM feedback
elements is needed, code for this can be found in
https://github.com/EricssonResearch/openwebrtc/blob/master/transport/owr_tra
nsport_agent.c 

RTCP feedback generation code is found on lines 2991 to 3018

RTCP feedback parsing code is found on lines 4191 to 4205

The timestamp clock is currently assumed to be 1000Hz. 

Note that the code use the old feedback format from
(https://tools.ietf.org/html/draft-ietf-rmcat-scream-cc-00 ), this is
however not something that will affect performance as long as the packet
reordering depth in the network is below 5. 

A change to the use of RTC3611 requires some changes to the code (in
ScreamTx), given time and general interest I will try to fix this in a
reasonable near future.

Please don’t hesitate to ask questions if something is unclear (which is
very likely) 

/Ingemar

==================================

Ingemar Johansson  M.Sc. 

Master Researcher

Ericsson AB

Wireless Access Networks

Labratoriegränd 11

971 28, Luleå, Sweden

Phone +46-1071 43042

SMS/MMS +46-73 078 3289

 <mailto:[email-masked]> [email-masked]

www.ericsson.com

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