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<title>Collection</title>
<meta name="author" content="Rodrigo Fonseca, Omprakash Gnawali, Kyle Jamieson, and Philip Levis" />
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<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 class="field"><th class="docinfo-name">TinyOS-Version:</th><td class="field-body">> 2.1</td>
</tr>
<tr><th class="docinfo-name">Author:</th>
<td>Rodrigo Fonseca, Omprakash Gnawali, Kyle Jamieson, and Philip Levis</td></tr>
<h1><a id="abstract" name="abstract">Abstract</a></h1>
<p>The memo documents the interfaces, components, and semantics used by
collection protocol in TinyOS 2.x. Collection provides a best-effort,
-multihop delivery of packets to the root of <em>a</em> tree. There may be
-multiple roots in a network, and in this case the semantics implemented
-are of <em>anycast</em> delivery to at least one of the roots. A node sending
+multihop delivery of packets to the root of a tree. There may be
+multiple tree roots in a network, and in this case the semantics
+are <em>anycast</em> delivery to at least one of the roots. A node sending
a packet does not specify which root the packet is destined to.</p>
</div>
<div class="section">
<h1><a id="introduction" name="introduction">1. Introduction</a></h1>
<p>Collecting data at a base station is a common requirement of sensor
-network applications. The general approach used is to build one
-or more collection <em>trees</em>, each of which is rooted at a base
-station. When a node has data which needs to be collected, it
-sends the data up the tree, and it forwards collection data that
-other nodes send to it. Sometimes, depending on the form of data
-collection, systems need to be able to inspect packets as they go
-by, either to gather statistics, compute aggregates, or suppress
-redundant transmissions.</p>
-<p>When a network has multiple base stations that act as <em>root</em> nodes,
-rather than one tree, it has a <em>forest</em> of trees. By picking a
-parent node, a collection protocol implicitly joins one of these
-trees. Collection provides a best-effort,
-multihop delivery of packets to one of a network's tree roots:
-it is an <em>anycast</em> protocol. The semantics is that the protocol
-will make a reasonable effort to deliver the message to at least
-one of the roots in the network. There are however no guarantees of
-delivery, and there can be duplicates delivered to one or more
-roots. There is also no ordering guarantees.</p>
-<p>Given the limited state that nodes can store and a general need
-for distributed tree building algorithms, simple collection protocols
-encounter several challenges. These challenges are not unique to
-collection protocols. Instead, they represent a subset of common
-networking algorithmic edge cases that occur in this protocol
-family:</p>
+network applications. The general approach used is to build one or
+more collection trees, each of which is rooted at a base station. When
+a node has data which needs to be collected, it sends the data up the
+tree, and it forwards collection data that other nodes send to
+it. Sometimes, depending on the form of data collection, systems need
+to be able to inspect packets as they go by, either to gather
+statistics, compute aggregates, or suppress redundant transmissions.</p>
+<p>Collection provides a best-effort, multihop delivery of packets to one
+of a network's tree roots: it is an <em>anycast</em> protocol. The semantics
+is that the protocol will make a reasonable effort to deliver the
+message to at least one of the roots in the network. By picking a
+parent node, a collection protocol inductively joins the tree its
+parent has joined. Delivery is best effort, and there can be
+duplicates delivered to one or more roots. Collection provides no
+ordering guarantees. Collection does not provide real-time guarantees,
+although specific implementations may extend the basic functionality
+to do so.</p>
+<p>Given the limited state that nodes can store and a general need for
+distributed tree building algorithms, collection protocols encounter
+several challenges. These challenges are not unique to collection
+protocols. Instead, they represent a subset of common networking
+algorithmic edge cases that generally occur in wireless routing:</p>
<blockquote>
<ul class="simple">
-<li>Loop detection, detecting when a node selects one of its
-descendants as a new parent.</li>
-<li>Duplicate suppression, detecting and dealing with when lost
-acknowledgments are causing packets to replicate in the
-network, wasting bandwidth.</li>
+<li>Loop detection, for when a node selects one of its descendants as
+a next hop.</li>
+<li>Duplicate suppression, detecting and dealing with lost
+acknowledgments causing packets to replicate in the network,
+wasting capacity.</li>
<li>Link estimation, evaluating the link quality to single-hop
neighbors.</li>
<li>Self-interference, preventing forwarding packets along the route
from introducing interference for subsequent packets.</li>
</ul>
</blockquote>
-<p>The rest of this document describes a set of components and interfaces
-for a collection service outlined above.</p>
+<p>While collection protocols can take a wide range of approaches to
+address these challenges, the programming interface they provide is
+typically independent of these details. The rest of this document
+describes a set of components and interfaces for collection services.</p>
</div>
<div class="section">
<h1><a id="collection-interfaces" name="collection-interfaces">2. Collection interfaces</a></h1>
-<p>A node can perform four different roles in collection: producer,
-consumer, snooper, and in-network processor. Depending on their role,
-the nodes use different interfaces to interact with the collection
-component.</p>
-<p>A consumer is a root of a tree. The set of all roots and the paths that
+<p>A node can perform four different roles in collection: sender,
+snooper, in-network processor, and receiver/root. Depending on their
+role, the nodes use different interfaces to interact with the
+collection component.</p>
+<p>The collection infrastructure can be multiplexed among independent
+applications, by means of a collection identifier. While data traffic
+in the protocol is multiplexed through these identifiers, control
+traffic is not: all data traffic uses the same routing topology.</p>
+<p>The nodes that generate data to be sent to the root are <em>senders</em>.
+Senders use the Send interface [<a class="reference" href="#id1">1</a>] to send data to the root of
+the collection tree. The collection identifier is specified as a
+parameter to Send during instantiation.</p>
+<p>The nodes that overhear messages in transit are <em>snoopers</em>. The
+snoopers use the Receive interface [<a class="reference" href="#id1">1</a>] to receive a snooped
+message. The collection identifier is specified as a parameter
+to Receive during instantiation.</p>
+<p>The nodes can process a packet that are in transit. These in-network
+<em>processors</em> use the Intercept interface to receive and update a
+packet. The collection identifier is specified as a parameter to
+Intercept during instantiation. The Intercept interface has this
+signature:</p>
+<pre class="literal-block">
+interface Intercept {
+ event bool forward(message_t* msg, void* payload, uint8_t len);
+}
+</pre>
+<p>Intercept has a single event, Intercept.forward(). A collection
+service SHOULD signal this event when it receives a packet to forward.
+If the return value of the event is FALSE, then the collection layer
+MUST NOT forward the packet. The Intercept interface allows a higher
+layer to inspect the internals of a packet and suppress it if needed.
+Intercept can be used for duplicate suppression, aggregation, and
+other higher-level services. As the handler of Intercept.forward()
+does not receive ownership of the packet, it MUST NOT modify the
+packet and MUST copy data out of the packet which it wishes to use
+after the event returns.</p>
+<p>Root nodes that receive data from the network are <em>receivers</em>. Roots
+use the Receive interface [<a class="reference" href="#id1">1</a>] to receive a message delivered by
+collection. The collection identifier is specified as a parameter to
+Receive during instantiation.</p>
+<p>The set of all roots and the paths that
lead to them form the collection routing infrastructure in the network.
For any connected set of nodes implementing the collection protocol
there is only one collection infrastructure, <em>i.e.</em>, all roots in this
set active at the same time are part of the same infrastructure.</p>
-<p>A node is configured to become a root by using the RootControl
-interface. RootControl.setRoot() MUST make the current node a root of
-the the collection infrastructure. RootControl.unsetRoot() MUST
-make the current root no longer a root in the collection infrastructure.
-Both calls are idempotent.
-RootControl.setRoot() MAY be called on a node that is already a root, to
-no effect. RootControl.unsetRoot() MAY be called on a node that is
-not a root:</p>
+<p>The RootControl interface configures whether a node is a
+root:</p>
<pre class="literal-block">
interface RootControl {
command error_t setRoot();
command bool isRoot();
}
</pre>
-<p>The collection infrastructure can be multiplexed among independent
-applications, by means of a <em>collection identifier</em>. It is important
-to note that the <em>data</em> traffic in the protocol is multiplexed,
-while the <em>control</em> traffic is not.</p>
-<p>The nodes that generate data to be sent to the root are <em>producers</em>.
-The producers use the Send interface [<a class="reference" href="#id1">1</a>] to send data to the root
-of the collection tree. The collection identifier is specified as a
-parameter to Send during instantiation.</p>
-<p>Root nodes that receive data from the network are <em>consumers</em>. The
-consumers use the Receive interface [<a class="reference" href="#id1">1</a>] to receive a message
-delivered by collection. The collection identifier is specified
-as a parameter to Receive during instantiation.</p>
-<p>The nodes that overhear messages in transit are <em>snoopers</em>. The
-snoopers use the Receive interface [<a class="reference" href="#id1">1</a>] to receive a snooped
-message. The collection identifier is specified as a parameter
-to Receive during instantiation.</p>
-<p>The nodes can process a packet that are in transit. These in-network
-<em>processors</em> use the Intercept interface [<a class="reference" href="#id1">1</a>] to receive and update
-a packet. The collection identifier is specified as a parameter
-to Intercept during instantiation.</p>
+<p>Both commands MUST return SUCCESS if the node is now in the specified
+state, and FAIL otherwise. For example, if a node is already a root
+and an application calls RootControl.setRoot(), the call will
+return SUCCESS. If setRoot() returns SUCCESS, then a subsequent call
+to isRoot() MUST return TRUE. If unsetRoot() returns SUCCESS, then
+a subsequent call to isRoot() MUST return FALSE.</p>
</div>
<div class="section">
<h1><a id="collection-services" name="collection-services">3 Collection Services</a></h1>
}
}
</pre>
-<p>CollectionC MAY have additional interfaces, but they MUST have
-default functions on all outgoing invocations (commands for uses,
-events for provides) of those interfaces so that it can operate
-properly if they are not wired.</p>
+<p>CollectionC MAY have additional interfaces. These additional
+interfaces MUST have default functions on all outgoing invocations
+(commands for uses, events for provides) of those interfaces so that
+it can operate properly if they are not wired.</p>
<p>Components SHOULD NOT wire to CollectionC.Send. The generic
component CollectionSenderC (described in section 3.1) provides
a virtualized sending interface.</p>
different am_id_t values represent different protocols operating on
top of active messages. All packets sent with a particular
collection_id_t generally have the same payload format, so that
-snoopers, intercepters, and receivers can parse it properly.</p>
-<p>Receive.receive MUST NOT be signaled on non-root
-nodes. CollectionC MAY signal Receive.receive on a root node when
-a data packet successfully arrives at that node. If a root node calls
-Send, CollectionC MUST treat it as it if were a received packet.
-Note that the buffer swapping semantics of Receive.receive, when
-combined with the pass semantics of Send, require that CollectionC
-make a copy of the buffer if it signals Receive.receive.</p>
-<p>If CollectionC receives a data packet to forward and it is not a
-root node, it MAY signal Intercept.forward.</p>
+snoopers, intercepters, and receivers can parse them properly.</p>
+<p>ColletionC MUST NOT signal Receive.receive on non-root
+nodes. CollectionC MAY signal Receive.receive on a root node when a
+data packet successfully arrives at that node. If a root node calls
+Send, CollectionC MUST treat it as it if were a received packet. Note
+that the buffer swapping semantics of Receive.receive, when combined
+with the pass semantics of Send, require that CollectionC make a copy
+of the buffer if it signals Receive.receive.</p>
+<p>If CollectionC receives a data packet to forward and it is not a root
+node, it MAY signal Intercept.forward.</p>
<p>If CollectionC receives a data packet that a different node
is supposed to forward, it MAY signal Snoop.receive.</p>
<p>RootControl allows a node to be made a collection tree root.
</div>
</div>
<div class="section">
-<h1><a id="implementation" name="implementation">4 Implementation</a></h1>
-<p>An implementation of this TEP can be found in
-<tt class="docutils literal"><span class="pre">tinyos-2.x/tos/lib/net/ctp</span></tt> and <tt class="docutils literal"><span class="pre">tinyos-2.x/tos/lib/net/le</span></tt>, in
-the CTP protocol. It is beyond the scope of this document to fully
-describe CTP, but we outline its main components. CTP will be
-described in an upcoming TEP [<a class="reference" href="#id2">2</a>]. This implementation is a
-reference implementation, and is not the only possibility. It
-consists of three major components, which are wired together to form
-a CollectionC: LinkEstimatorP, CtpTreeRoutingEngineP, and
-CtpForwardingEngineP.</p>
-<p>This decomposition tries to encourage evolution of components and
-ease of use through modularization. Neighbor management and link
-estimation are decoupled from the routing protocol. Furthermore, the
-routing protocol and route selection are decoupled from the
-forwarding policies, such as queueing and timing.</p>
-<div class="section">
-<h2><a id="linkestimatorp" name="linkestimatorp">4.1 LinkEstimatorP</a></h2>
-<p>LinkEstimatorP estimates the quality of link to or from each
-neighbor. Link estimation can be done in a variety of ways, and we
-do not impose one here. It is decoupled from the establishment of
-routes. There is a narrow interface -- LinkEstimator -- between the
-link estimator and the routing engine. The one requirement is that
-the quality returned is standardized. A smaller return value from
-LinkEstimator.getQuality(), LinkEstimator.getforwardQuality(),
-LinkEstimator.getReverseQuality() MUST imply that the link to the
-neighbor is estimated to be of a higher quality than the one that
-results in a larger return value. The range of value SHOULD be
-[0,255] and the variation in link quality in that range SHOULD be
-linear. Radio provided values such as LQI or RSI, beacon based link
-estimation to compute ETX, or their combination are some possible
-approaches to estimating link qualities.</p>
-<p>LinkEstimatorP MAY have its own control messages to compute
-bi-directional link qualities. LinkEstimatorP provides calls
-(txAck(), txNoAck(), and clearDLQ()) to update the link estimates
-based on successful or unsuccessful data transmission to the
-neighbors.</p>
-<p>The user of LinkEstimatorP can call insertNeighbor() to manually
-insert a node in the neighbor table, pinNeighbor() to prevent a
-neighbor from being evicted, and unpinNeighbor() to restore eviction
-policy:</p>
-<pre class="literal-block">
-typedef uint16_t neighbor_table_entry_t
-
-LinkEstimatorP {
- provides {
- interface StdControl;
- interface AMSend as Send;
- interface Receive;
- interface LinkEstimator;
- interface Init;
- interface Packet;
- interface LinkSrcPacket;
- }
-}
-
-interface LinkEstimator {
- command uint8_t getLinkQuality(uint16_t neighbor);
- command uint8_t getReverseQuality(uint16_t neighbor);
- command uint8_t getForwardQuality(uint16_t neighbor);
- command error_t insertNeighbor(am_addr_t neighbor);
- command error_t pinNeighbor(am_addr_t neighbor);
- command error_t unpinNeighbor(am_addr_t neighbor);
- command error_t txAck(am_addr_t neighbor);
- command error_t txNoAck(am_addr_t neighbor);
- command error_t clearDLQ(am_addr_t neighbor);
- event void evicted(am_addr_t neighbor);
-}
-</pre>
-</div>
-<div class="section">
-<h2><a id="ctproutingenginep" name="ctproutingenginep">4.2 CtpRoutingEngineP</a></h2>
-<p>CtpRoutingEngineP is responsible for computing routes to the roots of a
-tree. In traditional networking terminology, this is part of the
-control plane of the network, and is does not directly forward any
-data packets, which is the responsibility of CtpForwardingEngine.
-The main interface between the two is UnicastNameFreeRouting.</p>
-<p>CtpRoutingEngineP uses the LinkEstimator interface to learn
-about the nodes in the neighbor table maintained by LinkEstimatorP and
-the quality of links to and from the neighbors. The routing protocol
-on which collection is implemented MUST be a tree-based routing
-protocol with a single or multiple roots. CtpRoutingEngineP
-allows a node to be configured as a root or a non-root node
-dynamically. CtpRoutingEngineP maintains multiple candidate next hops:</p>
-<pre class="literal-block">
-generic module CtpRoutingEngineP(uint8_t routingTableSize,
- uint16_t minInterval,
- uint16_t maxInterval) {
- provides {
- interface UnicastNameFreeRouting as Routing;
- interface RootControl;
- interface CtpInfo;
- interface StdControl;
- interface CtpRoutingPacket;
- interface Init;
- }
- uses {
- interface AMSend as BeaconSend;
- interface Receive as BeaconReceive;
- interface LinkEstimator;
- interface AMPacket;
- interface LinkSrcPacket;
- interface SplitControl as RadioControl;
- interface Timer<TMilli> as BeaconTimer;
- interface Timer<TMilli> as RouteTimer;
- interface Random;
- interface CollectionDebug;
- interface CtpCongestion;
- }
-}
-</pre>
-<pre class="literal-block">
-interface UnicastNameFreeRouting {
- command am_addr_t nextHop();
-
- command bool hasRoute();
- event void routeFound();
- event void noRoute();
-}
-</pre>
-</div>
-<div class="section">
-<h2><a id="ctpforwardingenginep" name="ctpforwardingenginep">4.3 CtpForwardingEngineP</a></h2>
-<p>The CtpForwardingEngineP component provides all the top level interfaces
-(except RootControl) which CollectionC provides and an application
-uses. It deals with retransmissions, duplicate suppression, packet
-timing, loop detection, and also informs the LinkEstimator of the
-outcome of attempted transmissions.:</p>
-<pre class="literal-block">
-generic module CtpForwardingEngineP() {
- provides {
- interface Init;
- interface StdControl;
- interface Send[uint8_t client];
- interface Receive[collection_id_t id];
- interface Receive as Snoop[collection_id_t id];
- interface Intercept[collection_id_t id];
- interface Packet;
- interface CollectionPacket;
- interface CtpPacket;
- interface CtpCongestion;
- }
- uses {
- interface SplitControl as RadioControl;
- interface AMSend as SubSend;
- interface Receive as SubReceive;
- interface Receive as SubSnoop;
- interface Packet as SubPacket;
- interface UnicastNameFreeRouting;
- interface Queue<fe_queue_entry_t*> as SendQueue;
- interface Pool<fe_queue_entry_t> as QEntryPool;
- interface Pool<message_t> as MessagePool;
- interface Timer<TMilli> as RetxmitTimer;
- interface LinkEstimator;
- interface Timer<TMilli> as CongestionTimer;
- interface Cache<message_t*> as SentCache;
- interface CtpInfo;
- interface PacketAcknowledgements;
- interface Random;
- interface RootControl;
- interface CollectionId[uint8_t client];
- interface AMPacket;
- interface CollectionDebug;
- }
-}
-</pre>
-<p>CtpForwardingEngineP uses a large number of interfaces, which can be
-broken up into a few groups of functionality:</p>
-<blockquote>
-<ul class="simple">
-<li>Single hop communication: SubSend, SubReceive, SubSnoop,
-SubPacket, PacketAcknowledgments, AMPacket</li>
-<li>Routing: UnicastNameFreeRouting, RootControl, CtpInfo,
-CollectionId, SentCache</li>
-<li>Queue and buffer management: SendQueue, MessagePool,
-QEntryPool</li>
-<li>Packet timing: Random, RetxmitTimer</li>
-</ul>
-</blockquote>
-</div>
+<h1><a id="implementation" name="implementation">4. Implementation</a></h1>
+<p>Implementations of collection can be found in
+<tt class="docutils literal"><span class="pre">tinyos-2.x/tos/lib/net/ctp</span></tt> and <tt class="docutils literal"><span class="pre">tinyos-2.x/tos/lib/net/lqi</span></tt>.
+The former is the Collection Tree Protocol (CTP), described in TEP 123
+[<a class="reference" href="#id2">2</a>]. The latter is a TinyOS 2.x port of MultihopLqi, a
+CC2420-specific collection protocol in TinyOS 1.x.</p>
</div>
<div class="section">
<h1><a id="author-addresses" name="author-addresses">5. Author Addresses</a></h1>
<table class="docutils footnote" frame="void" id="id1" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
-<tr><td class="label"><a name="id1">[1]</a></td><td>TEP 116: Packet Protocols</td></tr>
+<tr><td class="label"><a name="id1">[1]</a></td><td>TEP 116: Packet Protocols.</td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="id2" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
-<tr><td class="label"><a name="id2">[2]</a></td><td>TEP 123: The Collection Tree Protocol (CTP)</td></tr>
+<tr><td class="label"><a name="id2">[2]</a></td><td>TEP 123: The Collection Tree Protocol (CTP).</td></tr>
</tbody>
</table>
</div>
projects / tinyos-2.x.git / blobdiff