Re: Purpose of terminology I-D

[Steve Deering <deering@cisco.com>]

At 3:22 AM -0700 7/25/97, Walid Dabbous wrote:
> do you think that two way nodes attached to a non-trans
> link require specific treatment? or is it just for
> complete terminology purpose/

There exist satellite communication systems in which every groundstation
has both send and receive capabilities, and which therefore act like a
normal multi-access, bidirectional links.  There also exist satellite
communication systems in which there are one or more send-only ground
stations and many receive-only ground stations, e.g., DBS TV systems.
I imagine that there are, or will be, hybrid systems, in which there
are multiple groundstations capable of both send and receive, plus
other groundstations that are receive-only (and perhaps also some send-
only stations).  For communication between those nodes with send-and-rcv
capability, the satellite channel is bidirectional, whereas for
communication between other pairs of nodes, it is unidirectional.

For designing IP routing schemes for satellite networks, I thought it
might be helpful to keep the more general non-transitive case in mind.
In particular, a subset of nodes with both send-and-rcv capability can
use the satellite channel to exchange routing information, rather than
resorting to a terrestrial backchannel, and there might be good reasons
to exploit that capability.

Alternatively, one could split such a hybrid network into two virtual
networks, one unidirectional and one bidirectional, and ignore the more
general non-transitive case.  But I suggest that it would be worth at
least thinking about the pros and cons of those two different approaches.

Steve