In einer eMail vom 13.07.2008 18:50:57 Westeuropäische Normalzeit schreibt
bonomi@mail.r-bonomi.com:
Unidirectional elements -- in a multiple-source, multiple-destination,
network -- also allow for better handling of assymetric load levels among
particular station 'pairs' -- i.e., A->B is much higher/lower than
B->A,
by whatever metric is employed.
And, of course, when
networks have multiple points of inter-connection, the
'preference' of
which inter-connect point ot use may well be different,
depending on
"where, on which network" one is starting from.
Many years ago, in
metro Chicago, I had a wonderful real-world example
of this.
Two systems, less than 3 miles apart, on networks without any
direct
peering, or regional inter-connect. 'Preferred' path from A to
B was
via MAE-EAST, but the preferred path from B to A was via
MAE-WEST.
'traceroute' clearly identified where the preference changed --
one could
clearly see the discontinuity in RTT when packets reached the
node where
the 'return' preference changed.
Thanks for your response.
Certainly, the computation of a different path from B to A than from A to B
may not only be enforced by some link which is only usable in one
direction, but as well by the per link and per direction assigned
weight values.
In summary, there are many good reasons for replacing a link by either
one or two directed arrows.
Heiner
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