The memo documents the interfaces used by packet protocol components in
TinyOS 2.x as well as the structure and implementation of ActiveMessageC,
the basic data-link HIL component. It also documents the virtualized
-active message interfaces AMSender and AMReceiver.
+active message interfaces AMSenderC and AMReceiverC.
1. Introduction
============================================================================
The command address() returns the local AM address of the
node. AMPacket provides accessors for its two fields, destination and
-type. It does not provide commands to set these fields, as they are
-set in the sending call path (see Section 2.3). The ``setDestination``
-and ``setType`` commands fulfill a similar purpose to
-``Packet.setLength``.
+type. It also provides commands to set these fields, for the same
+reason that Packet allows a caller to set the payload length.
2.2 Sending interfaces
--------------------------------------------------------------------
}
//Case 3
- message_t* ptr;
+ message_t buf;
+ message_t* ptr = &buf;
message_t* Receive.receive(message_t* msg, void* payload, uint8_t len) {
message_t* tmp = ptr;
ptr = msg;
can be passed to another data link layer (e.g., the UART) without
shifting the data payload. This means that the ``message_header_t`` must
include all data needed for AM fields, which might introduce headers
-in addition to those of the data link. For example, this is the
-structure of the CC2420 header::
+in addition to those of the data link. For example, this is an example
+structure for a CC2420 (802.15.4) header::
typedef nx_struct cc2420_header_t {
nx_uint8_t length;
1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- |C|P| reserved | THL |
+ |P|C| reserved | THL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ETX |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Field definitions are as follows:
- * C: Congestion notification. If a node drops a CTP data frame, it MUST set the C field on the next data frame it transmits.
* P: Routing pull. The P bit allows nodes to request routing information from other nodes. If a node with a valid route hears a packet with the P bit set, it SHOULD transmit a routing frame in the near future.
+ * C: Congestion notification. If a node drops a CTP data frame, it MUST set the C field on the next data frame it transmits.
* THL: Time Has Lived. When a node generates a CTP data frame, it MUST set THL to 0. When a node receives a CTP data frame, it MUST increment the THL. If a node receives a THL of 255, it increments it to 0.
* ETX: The ETX routing metric of the single-hop sender. When a node transmits a CTP data frame, it MUST put the ETX value of its route through the single-hop destination in the ETX field. If a node receives a packet with a lower gradient than its own, then it MUST schedule a routing frame in the near future.
* origin: The originating address of the packet. A node forwarding a data frame MUST NOT modify the origin field.
1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- |C|P| reserved | parent |
+ |P|C| reserved | parent |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| parent | ETX |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields are as follows:
- * C: Congestion notification. If a node drops a CTP data frame, it MUST set the C field on the next routing frame it transmits.
* P: Same as data frame.
+ * C: Congestion notification. If a node drops a CTP data frame, it MUST set the C field on the next routing frame it transmits.
* parent: The node's current parent.
* metric: The node's current routing metric value.
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.
+messages and 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.
2. Definitions
============================================================================
2.1 Link Quality
--------------------------------------------------------------------
-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.
+The link quality between a directed node pair (A,B) is the probability
+that a packet transmitted by A will be successfully received 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.
2.2 In-bound Link Quality
--------------------------------------------------------------------
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