In this paper, a new algorithm introduced to save RAM Memory when ip address looked up this method is called bit-shued trie. About this we discuss in later section to describe this, which diereent bits are rearranged to create new index table. The Momory cost for a 474K prex IPv4 routing table is only 1.1 MB and the momory cost for a 215 K 64-Bit Prexes IPv6 routing table. For this purpose FGPA device is used. A eld-programmable gate array (FPGA) is an integrated circuit (IC) that can be programmed in the eld after manufacture.

1. A Review of
IP Address lookup using bit-shuffled trie
October 14, 2015
Submitted By:
Name: Sunawar Khan
Reg No. : 813-MSCS-F14
Research Paper Authors:
Author 1: Derek Pao
Author 2: Zian Lu
Author 3: yat Hang Poon
About Research Paper:
Volume No: 47
Cited: 3
1 What This Paper Tells Us?
In this paper, a new algorithm introduced to save RAM Memory when ip
address looked up this method is called bit-shuffled trie. About this we
discuss in later section to describe this, which differeent bits are rearranged
to create new index table. The Momory cost for a 474K prefix IPv4 routing
table is only 1.1 MB and the momory cost for a 215 K 64-Bit Prefixes IPv6
routing table. For this purpose FGPA device is used. A field-programmable
gate array (FPGA) is an integrated circuit (IC) that can be programmed in
the field after manufacture.
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2. 2 Motivtion
The IP Lookup problem can be build upon on the basis over Binary-Trie.
Multibit-trie is ussed where mutliple bits of the input address are processed.
the number of bits processed in a sterp is called Stride width.
There are differnt casses for LMP of an input address against a set of
prefixes.
1. Prefix inthe rouring table are divided into 6 groups. and it can be
eliminated, and no reference pointers are required in the bitmap structures.
2. All prefixes in a group have a minimun length of Lmin bits.
3. separate hardware pipelines are used to seach 6 groups of prefixs in
parallel.
Bit Shuffled trie is motivated by multibit trie on the basis of folow-
ing reasons.
1. In the conventional multibit-trie, bits of the input address are processed
from left to right. in bit-shuffled in some other order.
2. In the conventional multibit trie, where prefixes are expanded to some
predefined are divided into several lenghts.
3. Prefix expansion require in multibit-trie, where prefixes are expanded
to some predefined discrete length.
3 Approach
There are three algortihm propoed for this approach named as IP Lookup,
other is trie-based approach and the third approach is range search approach.
IP lookup is essential because routing table size mantain the order of half
million devices entries. Memorey is primary resource required. FGPA more
or less fully used. here we discuss memory cost methods.
i. Trie-Based Approach As we discuss above searching problem mod-
eled over a binary trie. some of the well know trie-based methods have very
compact data structures e.g. LC-Trie. and the shape shifting trie. Processing
of a node may require iterative operations.
Other design constraints in hardware implementations for example com-
plexity of hardware circut. here are some reasons for desirable for hardware
IP Lookup engine:
i. the method use simple data structure that are ease to interpret
ii. simple operations are involved.
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3. iii. the method gurantees to finish in a fixed number of steps.
Lim et al. proposed a variant of trie-based method called priority-trie.
In this empty nodes are replace on the basis of priority prefixes.
Hsieh and yang proposed a method called classified multisuffix trie which
is a varient of multi-bit trie.
ii. Range-search approach. A prefix corresponds to a range on the
number line. To find the longest matching prefix for an input address is
equivalent to finding the most specify range that encloses the input value.
iii.Hashing-based approachUsing hash tables to solve the IP lookup
problem, a hash function operates on fixed-length keys, there is one hash
table for each possible prefix length in the basic scheme.
4 Techniquer Enhanced
Bit-shuffled trieDifferent table are use to get result.
The shortest prefix length is 8 bits, and the longest prefix length is 32
bits. In the proposed method, prefixes in the routing table are divided into
6 groups by length
Bits 1 to 21 constitute the fixed-length portion, and bits 22 to 24 are
called the extension bits.
The hardware pipeline contains 4 stages, and the data fields. In the first
two pipeline stages, a certain number of bits are extracted from the input
bit-vector to form the address for accessing the internal index table, and the
remaining bits are packed before passing onto the next pipeline stage. We
call this operation bit-shuffling.
i. Bit-Shuffle and bit extract circuir, and the subtree processing
module. In this approach two basic operations, bit-shuffle and bit-extract.
A common first stage bit-shuffle operation is applied to all prefixes in a
length-group. Hence, the first stage bit-shuffle circuit can be implemented
using multiplexors (MUXs).
ii. Dimension of lookup tables and selection of bitsMultiple pre-
fixes may share common leading 21-bit values.The procedure to determine
the selected bits.
Block overlaying and block compactionThe bit-shuffling and index-
ing operations effectively divide the group of prefixes into subsets, where
each subset has a small number of items. The items in a subset can then be
further distinguished by selecting a few bits from the residue prefix.
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4. 5 Performance Evaluation
i. Hardware Implement Cost We evaluate the memory cost of the pro-
posed method.
ii. Incremental update to the routing tableA few studies have
focused on the incremental update issue of IP lookup.In this section we study
dynamic updates to the bit-shuffled trie. There can be three types of updates
to the routing table, i. modification of the next-hop value associated with a
prefix, ii. insertion of a new prefix, iii. deletion of an existing prefix.
Extension to the IPv6 lookup.The 128-bit IPv6 address is logically
divided into 2 parts, the leading 64 bits correspond to the network address
and the remaining 64 bits correspond to the host ID.In principle we can
divide the prefixes into 12 length-groups where each length-group covers a
range of 4 bits as in the case for IPv4.
6 What We Get
.A simple and elegant pipelined architecture for IPv4 and IPv6 lookup is
presented. When the size of the IPv4 table is further increased, the density
of the 21 to 24 bits prefixes will become higher and we can expect to have
more prefixes encoded in a ST-vector. As a result, the memory efficiency
of the bit-shuffled trie method in terms of bits per prefix may be further
improved.
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