[Tinyos-2-commits] CVS: tinyos-2.x/doc/html tep124.html,NONE,1.1
Phil Levis
scipio at users.sourceforge.net
Fri Feb 9 13:01:09 PST 2007
Update of /cvsroot/tinyos/tinyos-2.x/doc/html
In directory sc8-pr-cvs10.sourceforge.net:/tmp/cvs-serv15709/html
Added Files:
tep124.html
Log Message:
LEEP
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<div class="document" id="the-link-estimation-exchange-protocol-leep">
<h1 class="title">The Link Estimation Exchange Protocol (LEEP)</h1>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<col class="docinfo-content" />
<tbody valign="top">
<tr class="field"><th class="docinfo-name">TEP:</th><td class="field-body">124</td>
</tr>
<tr class="field"><th class="docinfo-name">Group:</th><td class="field-body">Network Protocol Working Group</td>
</tr>
<tr class="field"><th class="docinfo-name">Type:</th><td class="field-body">Documentary</td>
</tr>
<tr><th class="docinfo-name">Status:</th>
<td>Draft</td></tr>
<tr class="field"><th class="docinfo-name">TinyOS-Version:</th><td class="field-body">2.x</td>
</tr>
<tr><th class="docinfo-name">Author:</th>
<td>Omprakash Gnawali</td></tr>
<tr class="field"><th class="docinfo-name">Draft-Created:</th><td class="field-body">05-Feb-2006</td>
</tr>
<tr class="field"><th class="docinfo-name">Draft-Version:</th><td class="field-body">1.2</td>
</tr>
<tr class="field"><th class="docinfo-name">Draft-Modified:</th><td class="field-body">2007-02-09</td>
</tr>
<tr class="field"><th class="docinfo-name">Draft-Discuss:</th><td class="field-body">TinyOS Developer List <tinyos-devel at mail.millennium.berkeley.edu></td>
</tr>
</tbody>
</table>
<div class="note">
<p class="first admonition-title">Note</p>
<p class="last">This memo documents a part of TinyOS for the TinyOS Community, and
requests discussion and suggestions for improvements. Distribution
of this memo is unlimited. This memo is in full compliance with
TEP 1.</p>
</div>
<div class="section">
<h1><a id="abstract" name="abstract">Abstract</a></h1>
<p>The memo documents the Link Estimation Exchange Protocol (LEEP). Nodes
use LEEP to estimate and exchange information about the quality of
links to the neighbors.</p>
</div>
<div class="section">
<h1><a id="introduction" name="introduction">1. Introduction</a></h1>
<p>Routing protocols often require bi-directional link qualities to
compute the routes. Nodes can estimate the quality of the in-bound
link from a neighbor by estimating the ratio of successfully received
messages and the total transmitted messages. These in-bound link
qualities are exchanged among the neighbors using LEEP to determine
the out-bound link qualities. Bi-directional link quality is computed
using thus learned in-bound and out-bound link qualities.</p>
</div>
<div class="section">
<h1><a id="definitions" name="definitions">2. Definitions</a></h1>
<div class="section">
<h2><a id="link-quality" name="link-quality">2.1 Link Quality</a></h2>
<p>Quality of the link between any two nodes describes the probability
with which data link layer packets can be received without any
error. This definition assumes uncorrelated link losses. The link
between the nodes A and B may have different quality in A to B and B
to A directions.</p>
</div>
<div class="section">
<h2><a id="in-bound-link-quality" name="in-bound-link-quality">2.2 In-bound Link Quality</a></h2>
<p>In a node pair (A,B), with B as the node of reference, in-bound link
quality is a value in the range of 0 to 255 that describes the quality
of the link from A to B estimated by B by counting the successfully
received packets from A among all the transmitted packets or using
link quality indicators such as LQI and RSSI provided by the radio on
the node B, or some other methods.</p>
</div>
<div class="section">
<h2><a id="out-bound-link-quality" name="out-bound-link-quality">2.3 Out-bound Link Quality</a></h2>
<p>In a node pair (A,B), with B as the node of reference, out-bound link
quality is defined as the quality of the link from B to A. B can
determine the out-bound link quality if A advertises its in-bound link
qualities. LEEP is the protocol that is used to exchange the in-bound
link qualities.</p>
</div>
<div class="section">
<h2><a id="link-information-entry" name="link-information-entry">2.4 Link Information Entry</a></h2>
<p>Link Information Entry created by node k is a tuple (n,q) where q is
the in-bound link quality from node n to k.</p>
</div>
</div>
<div class="section">
<h1><a id="id1" name="id1">3. The Link Estimation Exchange Protocol (LEEP)</a></h1>
<div class="section">
<h2><a id="assumptions" name="assumptions">3.1 Assumptions</a></h2>
<p>Following are the assumptions made by LEEP:</p>
<p>3.1.1. The data link frame has a single-hop source field.
3.1.2. The data link layer provides a broadcast address.
3.1.3. The data link layer provides the length of the LEEP frame.</p>
</div>
<div class="section">
<h2><a id="the-protocol" name="the-protocol">3.2 The Protocol</a></h2>
<p>To compute the bi-directional link quality, in-bound link quality must
be exchanged among the neighbors. LEEP maintains a sequence number
that is incremented by one for each outgoing LEEP frame. The sequence
number in the LEEP frame MUST be incremented by one even if the data
link layer retransmits the LEEP frame. The LEEP sequence number MAY be
used to count the number of missing packets to estimate the in-bound
link quality from the transmitter. LEEP MUST transmit Link Information
entries describing the in-bound link qualities for a subset of its
neighbors. The Link Information entry on the LEEP frame allows the
receiver node to find the out-bound link quality to the transmitter
node identified by the data link source address.</p>
</div>
<div class="section">
<h2><a id="leep-frame" name="leep-frame">3.3 LEEP Frame</a></h2>
<p>A LEEP frame has a header, the payload, and a footer with the Link
Information (LI) entries as shown in this diagram:</p>
<pre class="literal-block">
-------------------------------------------------------------
| LEEP | Payload | LI Entry | LI Entry | ... | LI Entry |
| Header | | 1 | 2 | | n |
-------------------------------------------------------------
</pre>
<p>The number of Link Information entries can be different in each
outgoing LEEP frame. The number of Link Information entries MUST not
increase the size of the LEEP frame beyond the maximum payload length
allowed by the data link layer. A LEEP frame can have 0 Link
Information entry.</p>
</div>
<div class="section">
<h2><a id="leep-header" name="leep-header">3.3.1 LEEP header</a></h2>
<p>The following diagram shows the LEEP header format:</p>
<pre class="literal-block">
1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|nentry | rsrvd | seqno |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</pre>
<p>Field definitions:</p>
<blockquote>
<ul class="simple">
<li>nentry - Number of Link Information entries in the footer</li>
<li>seqno - LEEP sequence number.</li>
<li>rsrvd - Reserved and must be set to 0.</li>
</ul>
</blockquote>
</div>
<div class="section">
<h2><a id="id2" name="id2">3.3.2 Link Information Entry</a></h2>
<p>The following diagram shows the Link Information Entry format:</p>
<pre class="literal-block">
1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| node id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| link quality |
+-+-+-+-+-+-+-+-+
</pre>
<p>Field definitions:</p>
<blockquote>
<ul class="simple">
<li>node id: the link layer address of the neighbor</li>
<li>link quality: The in-bound link quality from the node identified by node id
to the node that transmits this Link Information entry</li>
</ul>
</blockquote>
</div>
</div>
<div class="section">
<h1><a id="implementation" name="implementation">4. Implementation</a></h1>
<p>The following files in <tt class="docutils literal"><span class="pre">tinyos-2.x/tos/lib/net/le</span></tt> provide a
reference implementation of LEEP described in this TEP.</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">LinkEstimator.h</span></tt> and <tt class="docutils literal"><span class="pre">LinkEstimatorP.nc</span></tt></li>
</ul>
</blockquote>
<p>The reference implementation uses the LEEP sequence number to count
the number of missing packets to estimate the in-bound link
quality. The implementation tries to append Link Information entry for
all the neighbors in its neighbor table by sending the largest
possible data link frame. If there is still not enough room to fit all
the Link Information entries, it uses a round-robin policy to select
the entries to be exchanged that could not fit in the previous LEEP
frame. The LEEP frames are transmitted whenever the CTP <a class="footnote-reference" href="#id4" id="id3" name="id3">[1]</a> beacons,
sent as a LEEP payload, are sent.</p>
</div>
<div class="section">
<h1><a id="author-s-address" name="author-s-address">5. Author's Address</a></h1>
<div class="line-block">
<div class="line">Omprakash Gnawali</div>
<div class="line">Ronald Tutor Hall (RTH) 418</div>
<div class="line">3710 S. McClintock Avenue</div>
<div class="line">Los Angeles, CA 90089</div>
<div class="line"><br /></div>
<div class="line">phone - +1 213 821-5627</div>
<div class="line">email - <a class="reference" href="mailto:gnawali@usc.edu">gnawali@usc.edu</a></div>
<div class="line"><br /></div>
</div>
</div>
<div class="section">
<h1><a id="citations" name="citations">6. Citations</a></h1>
<table class="docutils footnote" frame="void" id="id4" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id3" name="id4">[1]</a></td><td>TEP 123: The Collection Tree Protocol.</td></tr>
</tbody>
</table>
</div>
</div>
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