Ipolite best effort local broadcast
[The Rime communication stack]

The ipolite module sends one local area broadcast packet within one time interval. More...

Data Structures
struct	ipolite_callbacks
	A structure with callback functions for an ipolite connection. More...
struct	ipolite_conn
	An opaque structure with no user-visible elements that holds the state of an ipolite connection,. More...
Files
file	ipolite.c
	Ipolite Anonymous best effort local area BroadCast (ipolite).
file	ipolite.h
	Header file for Ipolite best effort local Broadcast (ipolite).
Functions
void	ipolite_open (struct ipolite_conn *c, uint16_t channel, uint8_t maxdups, const struct ipolite_callbacks *cb)
	Open an ipolite connection.
void	ipolite_close (struct ipolite_conn *c)
	Close an ipolite connection.
int	ipolite_send (struct ipolite_conn *c, clock_time_t interval, uint8_t hdrsize)
	Send a packet on an ipolite connection.
void	ipolite_cancel (struct ipolite_conn *c)
	Cancel a pending packet.

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Detailed Description

The ipolite 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 ipolite module uses 1 channel.

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Function Documentation

void ipolite_cancel

(

struct ipolite_conn *

c

)

Cancel a pending packet.

Parameters:

c

A pointer to a struct ipolite_conn that has previously been opened with ipolite_open().

This function cancels a pending transmission that has previously been started with ipolite_send().

void ipolite_close

(

struct ipolite_conn *

c

)

Close an ipolite connection.

Parameters:

c

A pointer to a struct ipolite_conn that has previously been opened with ipolite_open().

This function closes an ipolite connection that has previously been opened with ipolite_open().

void ipolite_open	(	struct ipolite_conn *	c,
		uint16_t	channel,
		uint8_t	maxdups,
		const struct ipolite_callbacks *	cb
	)

Open an ipolite connection.

Parameters:

	c	A pointer to a struct ipolite_conn.
	channel	The channel number to be used for this connection
	maxdups	The number of duplicates that are allowed to be heard before suppressing
	cb	A pointer to the callbacks used for this connection

This function opens an ipolite connection on the specified channel. The callbacks are called when a packet is received, or when another event occurs on the connection (see "struct ipolite_callbacks").

int ipolite_send	(	struct ipolite_conn *	c,
		clock_time_t	interval,
		uint8_t	hdrsize
	)

Send a packet on an ipolite connection.

Parameters:

	c	A pointer to a struct ipolite_conn that has previously been opened with ipolite_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 ipolite connection. The packet is sent some time during the time interval, but only if no other packet is received with the same header.