All things related to multicast

["Richard Mavrogeanes" <>]

Minute duration setup is also common (from the viewer's perspective)
when unicast rollover occurs. Some clients try multicast for this long,
give up, then play via unicast.  The user may think they are viewing a
multicast but they are not...just a thought.

Rich
 

-----Original Message-----
From: Marshall Eubanks 
[mailto:]
 
Sent: Tuesday, October 25, 2005 9:29 AM
To: Russ Hobby; 

Subject: Re: Is Multicast a Real Service?

On Tue, 25 Oct 2005 06:01:25 -0700
 Russ Hobby 
<>
 wrote:
> Hi All,
> 
> I have been asked a question from a researcher who's project has been 
> trying to use multicast for some time with many problems, and she 
> asked me "Are we trying to do the impossible?"
> 
> Their particular use of multicast relies on multiple multicast 
> connections and for them to be set up in a timely fashion.  It is the 
> setup time for a connection with which they have been having trouble.

> Connections can take up to several minutes to be established.  They 
> have worked the problem out with a couple of campuses and a gigapop to

> get it to work (which had to wait for new router codes to be installed

> in several places).  However every time they go to a new site, they 
> are likely to have the problem again and they have to work it through
those network engineers.
> 
> So the researcher is asking if they should give up on multicast and 
> redesign their application.  What do you think?

I think that you are not giving enough information to get a useful
answer.

What exactly are they trying to do ? How many connections ? One to many
or many to many ? ASM or SSM ?

Why, exactly, is it taking so long ? What code (to do what) has to be
changed ?

The long-term problems that  I have seen with multicast tend to be along
the lines of having some sites silently black-holed, not excessive
delays. 
Minute-duration set up times seem very  strange (unless the packet loss
is in the  50% range, in which case you have other problems). Multicast
setup should be in the one second or less range, generally comparable to
or less than player buffers and other systemic delays.

But, no, based on the information given, this does not seem usual.

Regards
Marshall Eubanks

> 
> Russ
>