Re: [core] group-comm comments

"weigengyu" <weigengyu@bupt.edu.cn> Wed, 06 November 2013 03:25 UTC

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From: weigengyu <weigengyu@bupt.edu.cn>
To: Carsten Bormann <cabo@tzi.org>, consultancy@vanderstok.org
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Cc: core <core@ietf.org>
Subject: Re: [core] group-comm comments
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Hi, Carsten,

Thank you for the information.

> Because of the complexity of the subject, CoRE is explicitly chartered not 
> to attempt work on Reliable Multicast:
> »The working group will not develop a reliable multicast solution, 
> […]«.https://datatracker.ietf.org/wg/core/charter/

Regards,

Gengyu

Network Technology Center,
School of Computer
Beijing University of Posts & Telecommunications


-----原始邮件----- 
From: Carsten Bormann
Sent: Wednesday, November 06, 2013 12:12 AM
To: consultancy@vanderstok.org
Cc: weigengyu ; core
Subject: Re: [core] group-comm comments

On 05 Nov 2013, at 07:34, peter van der Stok <stokcons@xs4all.nl> wrote:

> As far as I know algorithms exist, but I don't know about standardization.

Reliable multicast has a long history in the IETF.
It is not an easy problem, so there even was an IRTF research group for it:
http://irtf.org/concluded/rmrg
The RMT (reliable multicast transport) working group has concluded in 2006:
http://tools.ietf.org/wg/rmt/

The main standards document to look at is RFC5401 in conjunction with RFC 
5740 (NORM).
Another output of the RMRG, RFC 3208 (PGM) has never been advanced to the 
standards track, but enjoys some deployment.  Other approaches such as RFC 
6726 (FLUTE, File Delivery over Unidirectional Transport) are more oriented 
towards content distribution.

None of these attempt to achieve group-wide consistency.  RFC 1301 did, as 
did follow-on proposals such as draft-bormann-mtp-so, but there are strong 
limitations.  If you really need this, you are looking for algorithms such 
as Paxos:
http://en.wikipedia.org/wiki/Paxos_(computer_science)

More generally speaking, the CAP theorem applies:
http://en.wikipedia.org/wiki/CAP_theorem
I.e., you only get at most two out of the three:

• Consistency (all nodes see the same data at the same time)
• Availability (a guarantee that every request receives a response about 
whether it was successful or failed)
• Partition tolerance (the system continues to operate despite arbitrary 
message loss or failure of part of the system)

Because of the complexity of the subject, CoRE is explicitly chartered not 
to attempt work on Reliable Multicast: »The working group will not develop a 
reliable multicast solution, […]«.
https://datatracker.ietf.org/wg/core/charter/

Grüße, Carsten