One document matched: draft-perkins-manet-tdpb-00.xml
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<rfc ipr="trust200902" docName='draft-perkins-manet-tdpb-00.txt' >
<front>
<title abbrev="TDPB Cost Metric">
Transmission Duration Per Bit Cost Metric</title>
<author fullname="Charles E. Perkins" initials="C.E." surname="Perkins">
<organization abbrev="Futurewei">Futurewei Inc. </organization>
<address>
<postal>
<street>2330 Central Expressway</street>
<city>Santa Clara</city>
<code>95050</code>
<region>CA</region>
<country>USA</country>
</postal>
<phone>+1-408-330-4586</phone>
<email>charliep@computer.org</email>
</address>
</author>
<date/> <!-- day="25" month="October" year="2010" /> -->
<area>Routing</area>
<workgroup>Mobile Ad Hoc Networks [manet]</workgroup>
<keyword>Mobility</keyword>
<keyword>Metric</keyword>
<abstract>
<t>
The Transmission Duration Per Bit metric is a simple cost metric that
enables selection of a route with the highest end-to-end bandwidth.
</t>
</abstract>
</front>
<middle>
<section anchor='intro' title='Introduction'>
<t>
It is often desirable to identify which of several available routes
offers the highest bandwidth for data transmission, regardless of
other considerations such as number of hops. However, bandwidth is
in certain ways less suitable for use as a routing metric; in
particular, the bandwidth of a path with several hops is not
as easy to calculate as cost metrics such as hop count.
</t>
<t>
Instead of bandwidth, we specify the transmission duration as a cost
metric. The route with the lowest total transmission duration per
bit is the same as the route with the highest bandwidth, and yet the
end-to-end transmission duration per bit is simple to calculate.
The total transmission duration per bit for a route is the sum of
the transmission durations at each hop, so that the TDPB cost
metric is additive, monotonic, and easy to calculate.
</t>
</section>
<section anchor='def'
title='Total Transmission Duration Per Bit'>
<t>
The bandwidth between two neighboring nodes determines the
transmission duration per bit (TDPB) between those two nodes.
If bandwidth = B bits/second, then we define TDPB = 1 / bandwidth.
</t>
<t>
For a route R as follows composed of links between nodes N_1 ... N_k:
<list style="empty">
<t>N_1 <--> N_2 <--> N_3 <--> .... <--> N_k</t>
</list>
denote the link between
N_{i} and N_{i+1} by L_{i,i+1} and the bandwidth over link L_{i,i+1}
by B_{i,i+1}. Then the TDPB over link L_{i,i+1} is 1 / B_{i,i+1},
which we denote as TDPB(L_{i,i+1}). The TDPB cost for route R is the
sum of the TDPB costs for each link, or in other words
TDPB(R) = SUM TDPB(L_{i,i+1}) [i == 1..k-1].
</t>
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http://www.gs1.org/gsmp/kc/epcglobal/tds/tds_1_1_rev_1_27-standard-20050510.pdf
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</section>
<section anchor='funcs'
title='Cost() and Loop_Free() functions for the TDPB metric'>
<t>
To be useful with AODVv2 <xref target="I-D.ietf-manet-aodvv2"/>,
it is helpful to define
functions Cost() and Loop_Free() for the TDPB metric.
</t>
<t>
The definition of the Cost() function for TDPB is exactly
the same as the TDPB itself. In other words, using TDPB,
Cost(L) = TDPB(L) and Cost(R) = TDPB(R) for a link L and a route R.
</t>
<t>
For routes R1 and R2, Loop_Free(R1, R2) for TDPB is defined
as follows:
<list style="empty">
<t> LoopFree(R1,R2) := TDPB(R1) < TDPB(R2) </t>
</list>
or, in other words, LoopFree(R1,R2) returns TRUE if the cost of R1
is less than the cost of R2 (cost as measured by the TDPB metric).
</t>
</section>
<section anchor='units'
title='Units for TDPB metric'>
<t>
Transmission times per bit for modern wireless media are tiny. For a
slow link operating at only 1 Mb/sec, the transmission time for a
single bit is 1 microsecond. Faster links commercially available
today for personal computers are able to transmit one bit in less than
1 nanosecond. Already, terabit wireless transmission is available,
for instance with satellite communications. In order to lengthen the
time for which the TDPB metric may be useful for route selection in
wireless networks, it is necessary to pick an extremely unit of
measurement.
</t>
<t>
For the purposes of this initial draft, it is proposed to use
units of 0.001 picosecond, and for the value of metric to be 16 bits
long, with substructure as follows.
<figure anchor="figTDPB"
title="Structure of Value Field for TDBP metric">
<artwork><![CDATA[
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Exponent | Significant Digits |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
<!-- <postamble></postamble> -->
</figure>
From the figure, it is seen that the range of values for the
TDBP metric will be 2^31 * [0..2^11]. This will enable measurements
of TDBP for links as slow as 4 milliseconds, with accuracy of better
than one part in a thousand. For routes of length up to 64 hops,
the average link speed would need to be faster, perhaps no worse
than 64 microseconds/bit; this enables route selection in foreseeable
networks with that many hops.
</t>
<t>
However, should this be insufficient, either more bits of resolution
could be added (i.e., metric value of 24 bits instead of 16), or
the exponent field could be made into 6 bits or longer. Also see
RFC 7185 <xref target="RFC7185"/> for related discussion.
</t>
</section>
<section anchor='sec'
title='Security Considerations'>
<t>
This document does not introduce any security mechanisms,
and does not have any impact on existing security mechanisms.
</t>
</section>
<section anchor='iana' title='IANA Considerations'>
<t>
The routing metric defined in the document should
be assigned a value from the "Routing Metric/Constraint Type"
registry <xref target="RFC6551"/>.
</t>
</section>
</middle>
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<title>
EPC(TM) Generation 1 Tag Data Standards Version 1.1 Rev.1.27
http://www.gs1.org/gsmp/kc/epcglobal/tds/tds_1_1_rev_1_27-standard-20050510.pdf
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<date day='10' month="January" year="2005"/>
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<title>United States Department of Defense Suppliers Passive RFID
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<author surname="Department of Defense">
<organization>
</organization>
</author>
<date month="January" year="2010"/>
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<title>IEEE Std 802: IEEE Standards for Local and
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<author surname="IEEE">
<organization>
</organization>
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<date year="2001"/>
</front>
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