Fast Incremental updates on TernaryCAMs for routing lookups and packet classification

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Fast Incremental updates on Ternary-CAMs for
routing lookups and packet classification
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Ternary-CAM (TCAM)

• TCAM is a special type of fully associative
  memory
• Each cell in a TCAM can takes three logic states
  0, 1, X
• X allows the TCAM to store wildcards
• Fully parallel search

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Longest Prefix match and Packet classification

• The need to maintain a sorted list makes
  incremental update slow
• Adding a new entry result in the need to move
  O(N) TCAM entries
• ( N the total number of prefixes/rules)

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Longest Prefix matching using TCAM
Empty space
General configuration of a TCM
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Prefix-length ordering constraint

• P j the set of all prefixes length j
• Prefix-length ordering constraint
• If jgtk, all prefixes in the set P j must appear
  before P k, but prefixes within P j may appear in
  any order

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L-algorithm

• L the width of the destination address field

The prefix-length ordering constraint enables an
empty memory location to be found in at most L
32 memory shifts.
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PLO_OPT algorithm

• The worse case number of memory operations is at
  least L/2
• PLO_OPT is optimal on-line algorithm under the
  prefix-length ordering constraint

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Chain-ancestor ordering constraint

• If all prefixes were to be stored in a trie, data
  structure, only prefixes that lie on the same
  chain need to be ordered.
• Only considering overlapping prefixes

• Q3, Q2, Q1 must be in order
• Q4 can be stored anywhere with respect to Q2 and
  Q3
• Q4 must be stored at a lower location than Q1

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Chain-ancestor ordering constraint

• LC(p) the longest chain comprising prefix p
• rootpath(p) the path from the trie root node to
  node p
• hcld(p) highest prefix-child of p i.e.,
  among the children of p, the node which has the
  highest memory location in the TCAM
• HCN(p) the chain comprising ancestors of p,
  prefix p itself, hcld(p), hcld(hcld(p)) and so on
  i.e., a descendant node of p is inHCN(p) if it
  is the highest prefix-child of its ancestor

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CAO_OPT algorithm
Every prefix, p, is at a distance less than or
equal to D/2 prefixes from the free space pool,
where D len(LC(p))
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Auxiliary trie data structure

• The information to be keep in a trie node p
• wt(p)
• 1 if p is a leaf
• max(wt(lchild(p),rchild(p))) if p is not a leaf
  and not a prefix
• 1 max(wt(lchild(p),rchild(p))) otherwise
• wt_ptr(p)
• Keeps a pointer to the prefix-child has the
  highest weight
• hcld_ptr(p)
• Keeps a pointer to the prefix-child appears at
  the highest memory location in TCAM

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Insertion in CAO_OPT
the prefix to be inserted is above the free space
pool
the prefix to be inserted is below the free
space pool
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Deletion in CAO_OPT