:TEP: 119
:Group: Net2 Working Group
:Type: Documentary
-:Status: Draft
-:TinyOS-Version: 2.x
+:Status: Final
+:TinyOS-Version: > 2.1
:Author: Rodrigo Fonseca, Omprakash Gnawali, Kyle Jamieson, and Philip Levis
:Draft-Created: 09-Feb-2006
====================================================================
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 a tree. There may be
-multiple tree roots in a network, and in this case the semantics
-are *anycast* delivery to at least one of the roots. A node sending
-a packet does not specify which root the packet is destined to.
+the collection protocols in TinyOS 2.x. Collection provides
+best-effort, multihop delivery of packets to one of a set of
+collection points. There may be multiple collection points in a
+network, and in this case the semantics are *anycast* delivery to at
+least one of the collection points. A node sending a packet does not
+specify which of the collection points the packet is destined to. The
+union of the paths from each node to one or more of the collection
+points forms a set of trees, and in this document we assume that
+collection points are the roots of these trees.
1. Introduction
====================================================================
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 *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.
-
-When a network has multiple base stations that act as *root* nodes,
-rather than one tree, it has a *forest* 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 *anycast* 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.
-
-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:
-
- * Loop detection, detecting when a node selects one of its
- descendants as a new parent.
-
- * Duplicate suppression, detecting and dealing with when lost
- acknowledgments are causing packets to replicate in the
- network, wasting bandwidth.
+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.
+
+Collection provides best-effort, multihop delivery of packets to one
+of a network's tree roots: it is an *anycast* protocol. The
+semantics are 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 node implementing the 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 or real-time guarantees, although
+specific implementations may extend the basic functionality to do
+so.
+
+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:
+
+ * Loop detection, for when a node selects one of its descendants as
+ a next hop.
+
+ * Duplicate suppression, detecting and dealing with lost
+ acknowledgments that can cause packets to replicate in the
+ network, wasting capacity.
* Link estimation, evaluating the link quality to single-hop
neighbors.
2. Collection interfaces
====================================================================
-A node can perform four different roles in collection: producer,
-snooper, in-network processor, and consumer. Depending on their role,
-the nodes use different interfaces to interact with the collection
-component.
+A node can perform four different roles in collection: sender (or
+source), snooper, in-network processor, and receiver (or
+root). Depending on their role, the nodes use different interfaces to
+interact with the collection component.
The collection infrastructure can be multiplexed among independent
-applications, by means of a *collection identifier*. It is important
-to note that the *data* traffic in the protocol is multiplexed,
-while the *control* traffic is not.
-
-The nodes that generate data to be sent to the root are *producers*.
-The producers use the Send interface [1_] to send data to the root
-of the collection tree. The collection identifier is specified as a
+applications, by means of a collection identifier. The collection
+identifier is used to identify different data traffic at the sender,
+intermediate-nodes, or the receiver, much like port number in TCP. All
+data traffic, regardless of the collection identifier, use the same
+routing topology.
+
+The nodes that generate data to be sent to the root are *senders*.
+Senders use the Send interface [1_] to send data to the root of
+the collection tree. The collection identifier is specified as a
parameter to Send during instantiation.
The nodes that overhear messages in transit are *snoopers*. The
message. The collection identifier is specified as a parameter
to Receive during instantiation.
-The nodes can process a packet that are in transit. These in-network
-*processors* 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::
+The nodes can process a packet that is in transit. These in-network
+*processors* 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::
interface Intercept {
event bool forward(message_t* msg, void* payload, uint8_t len);
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. This interface allows a higher layer
-to inspect the internals of a packet and possibly suppress it if
-it is unnecessary or if its contents can be aggregated into an
-existing packet.
-
-Root nodes that receive data from the network are *consumers*. The
-consumers use the Receive interface [1_] to receive a message
-delivered by collection. The collection identifier is specified
-as a parameter to Receive during instantiation.
-
-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, *i.e.*, all roots in this
-set active at the same time are part of the same infrastructure.
+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.
+
+Root nodes that receive data from the network are *receivers*. Roots
+use the Receive interface [1_] to receive a message delivered by
+collection. The collection identifier is specified as a parameter to
+Receive during instantiation.
+
+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, *i.e.*, all roots in this set active at the
+same time are part of the same infrastructure.
The RootControl interface configures whether a node is a
root::
command bool isRoot();
}
-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
+The first two 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.
+to isRoot() MUST return TRUE. If unsetRoot() returns SUCCESS, then a
+subsequent call to isRoot() MUST return FALSE.
3 Collection Services
====================================================================
}
-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.
+CollectionC MAY have additional interfaces. All outgoing invocations
+(commands for uses, events for provides) of those interfaces MUST have
+default functions. Those default functions enable CollectionC to
+operate properly even when the additional interfaces are not wired.
Components SHOULD NOT wire to CollectionC.Send. The generic
component CollectionSenderC (described in section 3.1) provides
protocol operating on top of collection, in the same way that
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.
+collection_id_t generally SHOULD have the same payload format, so that
+snoopers, intercepters, and receivers can parse them properly.
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.
-
-If CollectionC receives a data packet to forward and it is not a
-root node, it MAY signal Intercept.forward.
-
-If CollectionC receives a data packet that a different node
-is supposed to forward, it MAY signal Snoop.receive.
+nodes. CollectionC MUST signal Receive.receive on a root node when a
+unique (non-duplicate) data packet successfully arrives at that
+node. It MAY signal Receive.receive when a duplicate data packet
+successfully arrives. 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.
+
+If CollectionC receives a data packet to forward and it is not a root
+node, it MAY signal Intercept.forward. CollectionC MAY signal
+Snoop.receive when it hears a packet which a different node is
+supposed to forward. For any given packet it receives, CollectionC
+MUST NOT signal more than one of the Snoop.receive, Receive.receive,
+and Intercept.forward events.
RootControl allows a node to be made a collection tree root.
CollectionC SHOULD NOT configure a node as a root by default.
AMSenderC [1_], except that it is parameterized by a collection_id_t
rather than an am_id_t. As with am_id_t, every collection_id_t SHOULD
have a single packet format, so that receivers can parse a packet
-based on its collection ID and contents.
+based on its collection ID and contents.
-4 Implementation
+4. Implementation
====================================================================
-An implementation of this TEP can be found in
-``tinyos-2.x/tos/lib/net/ctp`` and ``tinyos-2.x/tos/lib/net/4bitle``, 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 [2_]. 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, CtpRoutingEngineP, and
-CtpForwardingEngineP.
-
-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.
-
-4.1 LinkEstimatorP
---------------------------------------------------------------------
-
-LinkEstimatorP estimates the quality of link to or from each
-neighbor. In this TEP, we briefly describe the reference
-implementation in ''tinyos-2.x/tos/lib/4bitle'' and refer the readers
-to [3]_ for a detailed description of the estimator.
-
-Link estimation is decoupled from the establishment of routes. There
-is a narrow interface -- LinkEstimator and CompareBit -- between the
-link estimator and the routing engine. A smaller return value from
-LinkEstimator.getLinkQuality() implies that the link to the neighbor
-is estimated to be of a higher quality than the one that results in a
-larger return value. 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. LinkEstimatorP
-returns (ETX-1)*10 as the link quality. The routing engine instructs
-LinkEstimatorP to insert the neighbor, through which a high quality
-path to the root can be constructed, into the neighbor table by
-returning TRUE when LinkEstimatorP signals Comparebit.shouldInsert()
-for the newly discovered neighbor.
-
-LinkEstimatorP does not generate its own control messages to compute
-link qualities. When a user of LinkEstimatorP (CtpRoutingEngineP, for
-example) sends a packet using the Send interface provided by
-LinkEstimatorP, link estimation information is also sent with the
-packet as described in an upcoming TEP [4_]. LinkEstimatorP provides
-calls (txAck(), txNoAck(), and clearDLQ()) to update the link
-estimates based on successful or unsuccessful data transmission to the
-neighbors. LinkEstimatorP uses the LinkPacketMetadata interface to
-determine if the channel was of high quality when a packet is received
-from a neighbor to consider the link to that neighbor for insertion
-into the neighbor table.
-
-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::
-
- typedef uint16_t neighbor_table_entry_t
-
- LinkEstimatorP {
- provides {
- interface StdControl;
- interface AMSend as Send;
- interface Receive;
- interface LinkEstimator;
- interface Init;
- interface Packet;
- interface CompareBit;
- }
- uses {
- interface AMSend;
- interface AMPacket as SubAMPacket;
- interface Packet as SubPacket;
- interface Receive as SubReceive;
- interface LinkPacketMetadata;
- interface Random;
- }
- }
-
- interface CompareBit {
- event bool shouldInsert(message_t *msg, void* payload, uint8_t len, bool white_bit);
- }
-
- interface LinkEstimator {
- command uint16_t getLinkQuality(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);
- }
-
-
-
-4.2 CtpRoutingEngineP
---------------------------------------------------------------------
-
-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 CtpForwardingEngineP.
-The main interface between the two is UnicastNameFreeRouting.
-
-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 computes a routing tree 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::
-
- 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 SplitControl as RadioControl;
- interface Timer<TMilli> as BeaconTimer;
- interface Timer<TMilli> as RouteTimer;
- interface Random;
- interface CollectionDebug;
- interface CtpCongestion;
- interface Comparebit;
- }
- }
-
-
-::
-
- interface UnicastNameFreeRouting {
- command am_addr_t nextHop();
-
- command bool hasRoute();
- event void routeFound();
- event void noRoute();
- }
-
-
-
-4.3 CtpForwardingEngineP
---------------------------------------------------------------------
-
-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.::
-
- 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;
- }
- }
-
-
-CtpForwardingEngineP uses a large number of interfaces, which can be
-broken up into a few groups of functionality:
-
- * Single hop communication: SubSend, SubReceive, SubSnoop,
- SubPacket, PacketAcknowledgments, AMPacket
- * Routing: UnicastNameFreeRouting, RootControl, CtpInfo,
- CollectionId, SentCache
- * Queue and buffer management: SendQueue, MessagePool,
- QEntryPool
- * Packet timing: Random, RetxmitTimer
-
-4.4 MultihopLqi
-====================================================================
-
-There is another implementation of collection in ``tos/lib/net/lqi``.
-Its software structure is similar, with the exception that it does
-not have a separate link estimator. MultihopLqi only works on
-platforms that have a CC2420 radio, as it uses a special piece
-of physical layer data the radio provides (the LQI value).
-The three major components of the MultihopLqi implementation
-are the modules LqiForwardingEngineP and LqiRoutingEngineP, as
-well as the configuration MultihopLqiP.
-
+Implementations of collection can be found in
+``tinyos-2.x/tos/lib/net/ctp`` and ``tinyos-2.x/tos/lib/net/lqi``.
+The former is the Collection Tree Protocol (CTP), described in TEP 123
+[2_]. The latter is a TinyOS 2.x port of MultihopLqi, a
+CC2420-specific collection protocol in TinyOS 1.x.
5. Author Addresses
====================================================================
6. Citations
====================================================================
-.. [1] TEP 116: Packet Protocols
-
-.. [2] TEP 123: The Collection Tree Protocol (CTP)
+.. [1] TEP 116: Packet Protocols.
-.. [3] 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
+.. [2] TEP 123: The Collection Tree Protocol (CTP).
-.. [4] TEP 124: The Link Estimation Exchange Protocol (LEEP)
projects / tinyos-2.x.git / blobdiff