[vlc-devel] Re: Streaming HOWTO update suggestions

Marian Durkovic md at bts.sk
Tue Dec 12 08:40:16 CET 2006

Hi Jean-Paul,

> >  as VLC-0.8.6 was recently released, I think it's a good opportunity to
> >also make some updates for Streaming HOWTO reflecting the preference
> >of TS/RTP over TS/rawUDP. Here are the proposed changes:
> I suggest to take a slightly different approach, because for both of 
> them there are good reasons to support them. Please, describe it in such 
> a way that TS/RTP is prefered when doing Internet streaming.

I have initially thought about taking this route, but after considering all
the arguments I came to conclusion that stronger and more explicit message
is needed.

The RTP stuff is in fact a kind of "bugfix" for deficiencies found in the
original raw UDP approach. Although IP network was *never* supposed to 
guarantee delivery of packets in correct order, raw UDP relies on this flawed
assumption. RTP also fixes other problems, like distinct identification of
payload (wild guesses and black magic is all we can do with raw UDP).

Those problems are not specific to Internet-wide streaming - for example if
you happen to have a certain type of ethernet switch which has parallelism
inside, packet reordering will happen even on a LAN. Wireless LANs often
suffer from duplicate packets which breaks with raw UDP as well.

Thus in my opinion, the only reason to support raw UDP is backwards
compatibility with devices from vendors, which were lazy or unwilling 
to provide SW upgrade to fix those bugs. (When one of our ISPs talked 
to Amino about this, they responded that they'll do it only if he
orders >10000 units). If all vendors were so reluctant to implement
new standards, we'd still have to live with e.g. IGMPv1...

So the message I'd like to deliver to VLC users is the following:
- the standard, proper and state-of-the-art way is to use RTP
- raw UDP is legacy approach which has serious bugs, so we don't recommend
  to use it unless absolutely necessary (and ask your STB vendor why they
  still haven't implemented RTP after ~11 years since RFC1889 went out!)

	With kind regards,


----                                                                  ----
----   Marian Durkovic                       network  manager         ----
----                                                                  ----
----   Slovak Technical University           Tel: +421 2 524 51 301   ----
----   Computer Centre, Nam. Slobody 17      Fax: +421 2 524 94 351   ----
----   812 43 Bratislava, Slovak Republic    E-mail/sip: md at bts.sk    ----
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