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Documentation: NullNet

Simon Duquennoy edited this page Oct 27, 2017 · 8 revisions

Contiki-NG provides NullNet, a network layer that does nothing. NullNet is most useful for testing of lower layer protocols, or for IPv6-less networking in general. NullNet is enabled via the MAKE_NET variable, see doc:configuration.

With NullNet, network-layer packets are created directly by the application, and sent as-is to the MAC layer. On the receiver side, the MAC layer will pass the packet up to NullNet, which will in turn call the application with a callback.

Sending with NullNet

To send a packet with NullNet, first point nullnet_buf (declared in nullnet.h) to your buffer, and set nullnet_len to your payload length. Then, call NETSTACK_NETWORK.output, with the destination link-layer address as parameter. Use NULL or linkaddr_null to send a broadcast. For instance:

#include "net/nullnet/nullnet.h"
...
uint8_t payload[64] = { 0 };
nullnet_buf = payload; /* Point NullNet buffer to 'payload' */
nullnet_len = 2; /* Tell NullNet that the payload length is two bytes */
NETSTACK_NETWORK.output(NULL); /* Send as broadcast */

NullNet will send your payload as-is. No header added. There isn't even a notion of port, which means that NullNet does not segregate multiple connections for you.

Receiving with NullNet

To receive, set the NullNet application callback to a function of your own. This is done with nullnet_set_input_callback. The function must be of type nullnet_input_callback. For instance:

#include "net/nullnet/nullnet.h"
...
void input_callback(const void *data, uint16_t len,
  const linkaddr_t *src, const linkaddr_t *dest)
{
...
}
...
/* At process initialization */
nullnet_set_input_callback(input_callback);

The function input_callback will be called by NullNet upon every packet reception, both unicast or broadcast. The function arguments provide a pointer to the payload, the payload length, and the link-layer addresses of the source and destination. For broadcast, dest is set to linkaddr_null.

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