Re: [Int-area] whither multicast?

[Dirk Trossen <[e-mail]>]

Hi John,

Thanks for the comments. Please see inline.

Best,

Dirk

-----Original Message-----
From: Int-area <[e-mail]> On Behalf Of John Gilmore
Sent: 30 November 2022 03:16
To: Luigi Iannone <[e-mail]>
Cc: int-area <[e-mail]>; [e-mail]
Subject: Re: [Int-area] whither multicast?

> https://arxiv.org/pdf/2211.09029.pdf

The paper is a useful high level review of what multicast promised and why IP multicast has failed so far.  As it says, "The takeaway here is that the woes of previous multicast deployments can be overcome by observing the lessons learned from those deployments..."
[DOT] Glad to see that you saw useful messages in the paper. 

But its cheerful-charlie outlook about its "proposed new multicast semantic" (which exact semantic, isn't clear) 
[DOT] Being called 'cheerful' as a cynical German is quite unusual to me 😉 The attempt was to outline the view that multicast isn't dead or not useful anymore, on the contrary (see other drivers, even outside of where IP multicast would be applied, in Section V). That may count as cheerful already for some though, I admit. 

doesn't seem to address any of three major issues in how today's Internet relates to IP
Multicast:

  *  Should the allocation of hundreds of millions of IPv4 addresses to
     native multicast be reconsidered?  Only a tiny fraction of them are
     in use, while unicast is the clear success story of the Internet.
     Unicast address demand continues to rise, while multicast demand is
     invisibly small.  IANA has never allocated roughly half of all
     multicast addresses to anyone for any use (225-231/8 and
     235-238/8).  The vast bulk, of the tiny fraction that were
     allocated, are for services now considered obsolete (all but LAN
     use, e.g. for Neighbor Discovery or MDNS; and all but
     Source-Specific Multicast, which is limited to 232/8).
[DOT] To me, this question is a consequence of what is being discussed. If a multicast semantic was to separate WHAT from HOW, questioning the allocation of routing identifiers is indeed valid. 

  *  For end-users seeking access to nonlocal IP multicast, over the last
     few decades, one issue at ISPs continued to get in the way.  Large
     backbone unicast routers could not reliably be used to forward
     native multicast traffic, because enabling multicast on those
     routers tended to make them crash (more often).  When seeking
     99.9999% uptime for the unicast traffic that pays all the bills,
     and seeking low network debugging and support costs, having a
     backbone router crash for even ten minutes a year from running a
     niche service, caused ISPs too much trouble.  So when multicast was
     supported at all, it tended to be supported on side-machines that
     were not in the main pipelines of the ISP, were not as highly
     capable as the mainline routers, and required custom tunnel
     configuration from each end-user -- a non-starter for mass market
     use.

  *  And with few or no ISPs supporting multicast by default, no end-user
     applications that tried to use it ever caught on.  So there was
     very little demand encouraging other ISPs to enable multicast.
[DOT] Both of these last two issues  are part of the chicken-and-egg problem that often exists in technology. If demand was sufficient, striving for matching the supply would usually happen (and being fortified in realization, so without crashing of parts of the supply chain), while the lacking and inadequate supply of course hampers demand. 

[DOT] This raises the question on what may break this vicious cycle. We largely approached this from the 'more and new demand' angle. One may think of multicast efficiencies (and the possible impact on the environmental impact of unicast proliferation), which is outlined towards the end of Section V with some example work; I would welcome more thoughts and contributions for this angle, which may also relate to the soon-to-happen IAB workshop on environmental impact. 
 

The paper does not seem to address any of those issues.
[DOT] Not directly indeed - see above - but it's positioned as a working paper in the hope to incorporate wider thinking into a revision, so your comments are certainly useful achieving that hopefully.

	John Gilmore
	

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