:TEP: 124
:Group: Network Protocol Working Group
:Type: Documentary
-:Status: Draft
-:TinyOS-Version: 2.x
+:Status: Final
+:TinyOS-Version: > 2.1
:Author: Omprakash Gnawali
:Draft-Created: 05-Feb-2006
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. LEEP appends in-bound
+messages to the total transmitted messages. LEEP appends in-bound
packet reception rate (PRR) estimates to packets. Other nodes hearing
these packets can combine the in-bound PRR values with their own
in-bound values to compute bi-directional link quality. Thus, LEEP is
a discovery and link table bootstrapping mechanism. The link quality
is often fine-tuned using different mechanisms.
-Link quality estimates obtained using LEEP are often used as a
+Link quality estimates obtained using LEEP are often used as
bootstrapping values in the link quality table; data transmission
statistics can later be used to make these estimates more accurate.
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 packets transmitted by B.
+of the link from A to B estimated by B as the ratio of successfully
+received to all packets transmitted by A. Thus, in-bound link quality
+is the empirical probability that a packet will be successfully
+received on a given link. A value of 255 represents a probability of 1
+and a value of 0 represents a probability of 0 of successfully
+receiving a packet on a given link.
2.2 Out-bound Link Quality
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qualities. LEEP is the protocol that is used to exchange the in-bound
link qualities.
-2.3 Link Quality
+2.3 Bi-directional Link Quality
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-The link quality between a directed node pair (A,B) is the probability
-that a packet transmitted by A will be successfully received and
-acknowledged by B. The bidirectional link quality of an undirected
-node pair (A,B) is the product of the link quality of (A,B) and
-(B,A). This definition assumes independent link losses. It also
-includes the case when the link quality of (A,B) and (B,A) are
-different; this can occur due to local interference or noise.
+LEEP does not define or compute bi-directional link quality. LEEP
+provides a way to exchange sufficient information to compute in-bound
+and out-bound link qualities. These two link qualities can be used to
+compute the bi-directional link quality. Routing protocols often
+compute the bi-directional link quality of a node pair (A,B) as a
+function (product, min, etc.) of the link quality of (A,B) and (B,A).
+
2.4 Link Information Entry
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