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Interoperability between RAMA and non RAMA

Motivation ~ migration to RAMA

Note there will be constraints since RAMA has a larger address space,
not all non RAMA addresses are mappable to the RAMA address space
 
Interoperability 
i) between RAMA host and non RAMA routers
- tunnel through

ii) between non RAMA host and RAMA routers
- manual configuration of root address at RAMA DRs.
- download (possibly from a well-known service) and cache configuration
database of root address to RAMA DRs 

iii) between RAMA domain and non RAMA domain.

Constraint
~ a root is either in the RAMA or non RAMA domain, but not both
~ if the M part of the RAMA address <R,M> is already used in a non RAMA
domain, users in the non RAMA domain cannot join other <Rx,M> groups.
Otherwise a mapping function between RAMA and non RAMA is required.

- extend the current Interop rules to allow non RAMA domain to
pass/accept the root address as well. 
- add rules for RAMA Border Router to pass/accept root address to/from
non RAMA BR
- devise mechanisms for a non RAMA domain to learn root addresses from a
RAMA domain
(Note that a RAMA domain can easily be provided the root address by a
non RAMA domain, see 1st bullet in this para ).