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proposed modification of Add_Undirected_Links() to better deal with p…
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…arallel link originating from a block root
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@cbowers
cbowers committed Jun 17, 2015
1 parent 6a92a3f commit 5d5e5c9
Showing 1 changed file with 133 additions and 70 deletions.
203 changes: 133 additions & 70 deletions draft-ietf-rtgwg-mrt-frr-algorithm.xml
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Expand Up @@ -1341,84 +1341,147 @@ GADAGs.</t>
<t>To convert a GADAG to a DAG, it is necessary to remove all links
that point to a root of block from within that block. That provides
the necessary conversion to a DAG and then a topological sort can be
done. Finally, all UNDIRECTED links are assigned a direction based
upon the total ordering. Any UNDIRECTED links that connect to a root
of a block from within that block are assigned a direction INCOMING to
that root. The exact details of this whole process are captured in
<xref target="topo_sort_links"/></t>
done. When adding undirected links to the GADAG, links connecting the
block root to other nodes in that block need special handling because
the topological order will not always give the right answer for those
links. There are three cases to consider. If the undirected link in
question has another parallel link between the same two nodes that is
already directed, then the direction of the undirected link can be
inherited from the previously directed link. In the case of parallel
cut links, we set all of the parallel links to both INCOMING and
OUTGOING. Otherwise, the undirected link in question is set to
OUTGOING from the block root node. A cut-link can then be identified
by the fact that it will be directed both INCOMING and OUTGOING in the
GADAG. The exact details of this whole process are captured in <xref
target="topo_sort_links"/></t>

<figure anchor="topo_sort_links" align="center"
title="Assigning direction to UNDIRECTED links">
<artwork align="center"><![CDATA[
Set_Block_Root_Incoming_Links(topo, gadag_root, mark_or_clear)
foreach node x in topo
if node x is a cut-vertex or gadag_root
foreach interface i of x
if (i.remote_node.localroot is x)
if i.UNDIRECTED
i.OUTGOING = true
i.remote_intf.INCOMING = true
i.UNDIRECTED = false
i.remote_intf.UNDIRECTED = false
if i.INCOMING
if mark_or_clear is MARK
if i.OUTGOING // a cut-link
i.STORE_INCOMING = true
Add_Undirected_Block_Root_Links(topo, gadag_root):
foreach node x in topo
if x.IS_CUT_VERTEX or x is gadag_root
foreach interface i of x
if (i.remote_node.localroot is not x
or i.PROCESSED )
continue
Initialize bundle_list to empty
bundle.UNDIRECTED = true
bundle.OUTGOING = false
bundle.INCOMING = false
foreach interface i2 in x
if i2.remote_node is i.remote_node
add_to_list_end(bundle_list, i2)
if not i2.UNDIRECTED:
bundle.UNDIRECTED = false
if i2.INCOMING:
bundle.INCOMING = true
if i2.OUTGOING:
bundle.OUTGOING = true
if bundle.UNDIRECTED
foreach interface i3 in bundle_list
i3.UNDIRECTED = false
i3.remote_intf.UNDIRECTED = false
i3.PROCESSED = true
i3.remote_intf.PROCESSED = true
i3.OUTGOING = true
i3.remote_intf.INCOMING = true
else
if (bundle.OUTGOING and bundle.INCOMING)
foreach interface i3 in bundle_list
i3.UNDIRECTED = false
i3.remote_intf.UNDIRECTED = false
i3.PROCESSED = true
i3.remote_intf.PROCESSED = true
i3.OUTGOING = true
i3.INCOMING = true
i3.remote_intf.INCOMING = true
i3.remote_intf.OUTGOING = true
else if bundle.OUTGOING
foreach interface i3 in bundle_list
i3.UNDIRECTED = false
i3.remote_intf.UNDIRECTED = false
i3.PROCESSED = true
i3.remote_intf.PROCESSED = true
i3.OUTGOING = true
i3.remote_intf.INCOMING = true
else if bundle.INCOMING
foreach interface i3 in bundle_list
i3.UNDIRECTED = false
i3.remote_intf.UNDIRECTED = false
i3.PROCESSED = true
i3.remote_intf.PROCESSED = true
i3.INCOMING = true
i3.remote_intf.OUTGOING = true
Modify_Block_Root_Incoming_Links(topo, gadag_root):
foreach node x in topo
if x.IS_CUT_VERTEX or x is gadag_root
foreach interface i of x
if i.remote_node.localroot is x
if i.INCOMING:
i.INCOMING = false
i.remote_intf.STORE_OUTGOING = true
i.INCOMING_STORED = true
i.remote_intf.OUTGOING = false
i.TEMP_UNUSABLE = true
i.remote_intf.TEMP_UNUSABLE = true
else
i.TEMP_UNUSABLE = false
i.remote_intf.TEMP_UNUSABLE = false
if i.STORE_INCOMING and (mark_or_clear is CLEAR)
i.INCOMING = true
i.STORE_INCOMING = false
i.remote_intf.OUTGOING = true
i.remote_intf.STORE_OUTGOING = false
Run_Topological_Sort_GADAG(topo, gadag_root)
Set_Block_Root_Incoming_Links(topo, gadag_root, MARK)
foreach node x
set x.unvisited to the count of x's incoming interfaces
that aren't marked TEMP_UNUSABLE
Initialize working_list to empty
Initialize topo_order_list to empty
add_to_list_end(working_list, gadag_root)
while working_list is not empty
y = remove_start_item_from_list(working_list)
add_to_list_end(topo_order_list, y)
foreach ordered_interface i of y
if (i.OUTGOING) and (not i.TEMP_UNUSABLE)
i.remote_node.unvisited -= 1
if i.remote_node.unvisited is 0
add_to_list_end(working_list, i.remote_node)
next_topo_order = 1
while topo_order_list is not empty
y = remove_start_item_from_list(topo_order_list)
y.topo_order = next_topo_order
next_topo_order += 1
Set_Block_Root_Incoming_Links(topo, gadag_root, CLEAR)
Add_Undirected_Links(topo, gadag_root)
Run_Topological_Sort_GADAG(topo, gadag_root)
foreach node x in topo
foreach interface i of x
if i.UNDIRECTED
if x.topo_order < i.remote_node.topo_order
i.OUTGOING = true
i.UNDIRECTED = false
i.remote_intf.INCOMING = true
i.remote_intf.UNDIRECTED = false
else
i.INCOMING = true
i.UNDIRECTED = false
i.remote_intf.OUTGOING = true
i.remote_intf.UNDIRECTED = false
i.remote_intf.OUTGOING_STORED = true
Revert_Block_Root_Incoming_Links(topo, gadag_root):
foreach node x in topo
if x.IS_CUT_VERTEX or x is gadag_root
foreach interface i of x
if i.remote_node.localroot is x
if i.INCOMING_STORED:
i.INCOMING = true
i.remote_intf.OUTGOING = true
i.INCOMING_STORED = false
i.remote_intf.OUTGOING_STORED = false
Run_Topological_Sort_GADAG(topo, gadag_root):
Modify_Block_Root_Incoming_Links(topo, gadag_root)
foreach node x in topo:
node.unvisited = 0
foreach interface i of x:
if (i.INCOMING):
node.unvisited += 1
Initialize working_list to empty
Initialize topo_order_list to empty
add_to_list_end(working_list, gadag_root)
while working_list is not empty
y = remove_start_item_from_list(working_list)
add_to_list_end(topo_order_list, y)
foreach ordered_interface i of y
if intf.OUTGOING
i.remote_node.unvisited -= 1
if i.remote_node.unvisited is 0
add_to_list_end(working_list, i.remote_node)
next_topo_order = 1
while topo_order_list is not empty
y = remove_start_item_from_list(topo_order_list)
y.topo_order = next_topo_order
next_topo_order += 1
Revert_Block_Root_Incoming_Links(topo, gadag_root)
def Set_Other_Undirected_Links_Based_On_Topo_Order(topo):
foreach node x in topo
foreach interface i of x
if i.UNDIRECTED:
if x.topo_order < i.remote_node.topo_order
i.OUTGOING = true
i.UNDIRECTED = false
i.remote_intf.INCOMING = true
i.remote_intf.UNDIRECTED = false
else
i.INCOMING = true
i.UNDIRECTED = false
i.remote_intf.OUTGOING = true
i.remote_intf.UNDIRECTED = false
Add_Undirected_Links(topo, gadag_root)
Add_Undirected_Block_Root_Links(topo, gadag_root)
Run_Topological_Sort_GADAG(topo, gadag_root)
Set_Other_Undirected_Links_Based_On_Topo_Order(topo)
Add_Undirected_Links(topo, gadag_root)
]]></artwork>
</figure>

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