[opendtv] Re: IETF mboned working group on (TV) content distribution
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
- Date: Sat, 18 Jan 2014 01:32:38 +0000
Craig Birkmaier wrote:
> This is informative. I will admit that it is not clear to me why IP
> multicasts cannot be relied upon from large portals through the WAN
> to the ISPs.
Until now, with IPv4, one problem is address space. Multicast (Class D)
addresses are subdivided into different categories, so there aren't that many
available for global distribution to anyone who wants to use multicast. So, it
becomes more of a network-by-network structure. If an ISP wants to create the
same multicast in many of his local networks, i.e. in multiple "markets," the
multicasts are typically tunneled through the WAN, and then the extra overhead
stripped off and the multicast transmitted as a multicast, but only within the
confines of each local network run by that ISP.
Another problem is that multicast is inherently, per its original design
concept, unable keep track of individual multicast users. That is the advantage
of multicast, after all, that you can send the same packets to any number of
devices, without the source having to know much of anything. Much like TV
transmitters, in this regard.
Even from the receiver side, receivers joining multicast groups aren't even
supposed to announce themselves, unless they are the first to do so in a given
IP subnet. All of this to make the scheme efficient, keeping background traffic
at a minimum, and also keeping as little state information in the network as
possible. (That's been IP's huge advantage over other schemes such as ATM.)
So network operators felt they couldn't manage this well enough, and have
stayed away from using multicast. I've seen more than one scheme proposed in an
Internet Draft, and then disappear after the Draft expired. There is one active
IP Multicast Receiver Access Control Draft document out there, as of now. It's
not an RFC yet. And different ISP nets have also been "rolling their own"
schemes. (Or just staying away from multicast.)
> It is also obvious that the mboned group has been tasked with making
> all of this work with full access control by the content providers
> who colocate servers. Whether this is intended to continue leveraging
> the MVPD bundles for authorization, or will lead to smaller bundles
> of programming controlled by paid apps remains to be seen...
Yup. For multicast, organizing the permissions in bundles is probably as
advantageous as it is now in MVPD nets. But I really think that the "by
appointment" nature of IP multicast programming will keep it restricted mostly
to live news and sports. For unicast streams, which you use in VOD, of course
the server can and must keep track of each client.
Bert
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