From: gnawali Date: Fri, 21 Nov 2008 06:54:40 +0000 (+0000) Subject: phils comments X-Git-Tag: rc_6_tinyos_2_1_1~564 X-Git-Url: https://oss.titaniummirror.com/gitweb/?p=tinyos-2.x.git;a=commitdiff_plain;h=22c456730fc9d645403869ac2ba2b872f8382959 phils comments --- diff --git a/doc/txt/tep123.txt b/doc/txt/tep123.txt index 942a24f9..55c85930 100644 --- a/doc/txt/tep123.txt +++ b/doc/txt/tep123.txt @@ -66,13 +66,17 @@ neighbors. These provide an estimate of the number of transmissions it takes for the node to send a unicast packet whose acknowledgment is successfully received. -CTP has several mechanisms in order to improve delivery reliability, -but it does not promise 100\% reliable delivery. It is best effort, but -a best effort that *tries very hard.* +CTP has several mechanisms in order to achieve high delivery +reliability, but it does not promise 100\% reliable delivery. It is a +best effort protocol. -CTP is designed for relatively low traffic rates. Bandwidth-limited systems -might benefit from a different protocol, which can, for example, pack -multiple small frames into a single data-link packet. +CTP is designed for relatively low traffic rates such that there is +enough space in the channel to transmit and receive routing frames +even when the network is forwarding collection data +frames. Bandwidth-limited systems or high data rate applications might +benefit from a different protocol, which can, for example, pack +multiple small frames into a single data-link packet or employ rate +control mechanisms. 3. Collection and CTP @@ -163,7 +167,7 @@ distinction is important for duplicate suppression in the presence of routing loops. If a node suppresses origin packets, then if asked to forward the same packet twice due to a routing loop, it will drop the packet. However, if it suppresses packet instances, then it -will route succesfully in the presence of transient loops unless the +will route successfully in the presence of transient loops unless the THL happens to wrap around to a forwarded packet instance. A node MUST send CTP data frames as unicast messages with link-layer @@ -237,12 +241,12 @@ increasing randomized timer. The implementation resets the timer to a small value when one or more of the following conditions are met: 1) The routing table is empty (this also sets the P bit) - 2) The node's routing ETX increases by >= 1 trasmission + 2) The node's routing ETX increases by >= 1 transmission 3) The node hears a packet with the P bit set The implementation augments the LEEP link estimates with data transmissions. This is a direct measure of ETX. Whenever the data path -transmits a packet, it tells the link estimator the destimation and +transmits a packet, it tells the link estimator the destination and whether it was successfully acknowledged. The estimator produces an ETX estimate every 5 such transmissions, where 0 successes has an ETX of 6. @@ -256,8 +260,9 @@ the rate at which CTP collects data estimates is proportional to the transmission rate, then it can quickly detect a broken link and switch to another candidate neighbor. -The component ``tos/lib/net/le/LinkEstimatorP`` implements the -link estimator. It couples LEEP-based and data-based estimates. +The component ``tos/lib/net/4bitle/LinkEstimatorP`` implements the +link estimator. It couples LEEP-based and data-based estimates as +described in [4]_. 6.2 Routing Engine ------------------------------------------------------------------------------ @@ -274,7 +279,7 @@ implements the routing engine. ------------------------------------------------------------------------------ The component ``tos/lib/net/ctp/CtpForwardingEngineP`` implements the -forwarding engine. It has five repsonsibilities: +forwarding engine. It has five responsibilities: 1) Transmitting packets to the next hop, retransmitting when necessary, and passing acknowledgment based information to the link estimator @@ -360,3 +365,6 @@ along the path. in Wireless Sensor Networks." In Proceedings of the First USENIX Conference on Networked Systems Design and Implementation (NSDI), 2004. .. [3] TEP 119: Collection. +.. [4] Rodrigo Fonseca, Omprakash Gnawali, Kyle Jamieson, and Philip Levis. + "Four Bit Wireless Link Estimation." In Proceedings of the Sixth Workshop + on Hot Topics in Networks (HotNets VI), November 2007. diff --git a/doc/txt/tep124.txt b/doc/txt/tep124.txt index 3a16cfe9..24024230 100644 --- a/doc/txt/tep124.txt +++ b/doc/txt/tep124.txt @@ -35,9 +35,15 @@ 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 -packet reception rate (PRR) estimates to packets. Other nodes hearing +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. +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 +bootstrapping values in the link quality table; data transmission +statistics are later used to make these estimates more accurate. 2. Definitions ============================================================================ @@ -103,7 +109,17 @@ 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. +node identified by the data link source address. Thus, LEEP is also a +way for nodes to discover new nodes and links in the network. + +Link quality estimation is inherently imperfect - data transmission +and link quality estimation might be done at different timescales. The +PRR for LEEP frames (broadcast) and data frames (unicast) might be +different. So LEEP is better used as a link quality bootstrapping +mechanism. The link quality estimate can be made more accurate later +using data transmission statistics. + + 3.3 LEEP Frame -------------------------------------------------------------------- @@ -179,6 +195,10 @@ the entries to be exchanged that could not fit in the previous LEEP frame. The LEEP frames are transmitted whenever the CTP [1]_ beacons, sent as a LEEP payload, are sent. +Another reference implementation resides in +``tinyos-2.x/tos/lib/net/le``. This implementation is described in +detail in [2]_. + 5. Author's Address ============================================================================ @@ -195,3 +215,6 @@ sent as a LEEP payload, are sent. ============================================================================ .. [1] TEP 123: The Collection Tree Protocol. +.. [2] Rodrigo Fonseca, Omprakash Gnawali, Kyle Jamieson, and Philip Levis. + "Four Bit Wireless Link Estimation." In Proceedings of the Sixth Workshop + on Hot Topics in Networks (HotNets VI), November 2007.