The polite module sends one local area broadcast packet within one time interval.
If a packet with the same header is received from a neighbor within the interval, the packet is not sent.
The polite primitive is a generalization of the polite gossip algorithm from Trickle (Levis et al, NSDI 2004). The polite gossip algorithm is designed to reduce the total amount of packet transmissions by not repeating a message that other nodes have already sent. The purpose of the polite broadcast primitive is to avoid that multiple copies of a specific set of packet attributes is sent on a specified logical channel in the local neighborhood during a time interval.
The polite broadcast primitive is useful for implementing broadcast protocols that use, e.g., negative acknowledgements. If many nodes need to send the negative acknowledgement to a sender, it is enough if only a single message is delivered to the sender.
The upper layer protocol or application that uses the polite broadcast primitive provides an interval time, and message along with a list of packet attributes for which multiple copies should be avoided. The polite broadcast primitive stores the outgoing message in a queue buffer, stores the list of packet attributes, and sets up a timer. The timer is set to a random time during the second half of the interval time.
During the first half of the time interval, the sender listens for other transmissions. If it hears a packet that matches the attributes provided by the upper layer protocol or application, the sender drops the packet. The send timer has been set to a random time some time during the second half of the interval. When the timer fires, and the sender has not yet heard a transmission of the same packet attributes, the sender broadcasts its packet to all its neighbors.
The polite broadcast module does not add any packet attributes to outgoing packets apart from those added by the upper layer.
Channels
The polite module uses 1 channel.
|
struct | polite_callbacks |
| A structure with callback functions for a polite connection. More...
|
|
struct | polite_conn |
| An opaque structure with no user-visible elements that holds the state of a polite connection,. More...
|
|
|
file | polite.h |
| Header file for Polite Anonymous best effort local Broadcast (polite)
|
|
Cancel a pending packet.
- Parameters
-
c | A pointer to a struct polite_conn that has previously been opened with polite_open(). This function cancels a pending transmission that has
previously been started with polite_send(). |
Close a polite connection.
- Parameters
-
c | A pointer to a struct polite_conn that has previously been opened with polite_open(). This function closes a polite connection that has
previously been opened with polite_open(). |
Open a polite connection.
- Parameters
-
c | A pointer to a struct polite_conn. |
channel | The channel number to be used for this connection |
cb | A pointer to the callbacks used for this connection This function opens a polite connection on the
specified channel. The callbacks are called when a
packet is received, or when another event occurs on the
connection (see \ref "struct polite_callbacks"). |
int polite_send |
( |
struct polite_conn * |
c, |
|
|
clock_time_t |
interval, |
|
|
uint8_t |
hdrsize |
|
) |
| |
Send a packet on a polite connection.
- Parameters
-
c | A pointer to a struct polite_conn that has previously been opened with polite_open(). |
interval | The timer interval in which the packet should be sent. |
hdrsize | The size of the header that should be unique within the time interval. This function sends a packet from the packetbuf on the
polite connection. The packet is sent some time during
the time interval, but only if no other packet is
received with the same header. |