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The relation between implementation variables and the graph abstraction is
given by the following relations:
- A bridge portal is the prime portal iff
*prime* is equal to
its unique 64-bit identity and *alpha* is true.
- A bridge represents a directed edge in the net tree iff for both
portals,
*mute* is false, and for one of the portals *alpha* is false
or it is the prime portal, and for the other portal *alpha* is true and it
is not the prime portal.
The directed bridge is an outgoing edge on the bus where the adjacent portal's
*alpha* is true and it is not the prime portal, and it is an incoming edge
on the other bus.
- A bridge represents an undirected edge in the net tree iff for both
portals,
*mute* is true and each portal's *alpha* is false.
- A bridge represents a directed edge in the bus tree for bus id
iff it is a directed edge in the net tree, and
*route map*[] is forward
for one portal, and valid for the other portal.
The directed bridge is an outgoing edge on the bus with the forward entry,
and it is an incoming edge on the other bus.
- A bridge represents an undirected edge in the bus tree for bus id
iff it is a undirected edge in the net tree, and
*route map*[] is valid
for both portals.
- A bridge does not represent an edge in the bus tree for bus id
iff for both portals,
*route map*[] is clean or dirty.
The value dirty represents a bus id for which the bus tree is being destroyed,
it is a temporary value that only occurs during net update.

Any bridge state that is not covered by the above possibilities is an
inconsistent state and cannot occur in the net update protocol, except the
`half-directed' edge in a bus tree, where *route map*[] is valid for
one portal and dirty for its co-portal. This is treated as an incoming edge
as well on the bus with the valid entry.

** Next:** Net update algorithm
** Up:** IEEE FireWire and Net
** Previous:** How?
Wieger Wesselink
2004-05-24