Subject: RE: [Tsvwg] Proposed FEC Streaming Framework

From: "Mark Watson" <[email-masked]>
Date: Mon, 18 Jul 2005 11:52:21 -0400

Jeremy,

You asked:

"Is there any particular reason why FEC shouldn't be
implemented in a first-class transport layer immediately
above IP, apart from ease of research?"

A good questions. There are two reasons that I can see:
1) Backwards compatibility: by defining the FEC layer above UDP then FEC
Schemes can be designed within the framework which do not modify the
source packets at all. In this case, then existing receivers can still
process the source packets, even if they do not support FEC. Even in the
case that the source packets are modified by appending the FEC Payload
ID, then all that is required of receivers which do not support the FEC
code is to remove this field.

2) A new transport protocol is not necessary. What we want to achieve is
purely additive to the functions of UDP, so defining new transport layer
would be unnecessary work from an implementation perspective. It would
also introduce a whole bunch of issues around signaling and NATs etc.
Those problems could be tackled but it would be a lot of effort for no
gain.

...Mark

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