The uip_ds6_nbr_t structure is a data structure used in Contiki OS to represent information associated with neighboring nodes in an IPv6 network. The definition of this structure is as follows:
/** \brief The default nbr_table entry (when
* UIP_DS6_NBR_MULTI_IPV6_ADDRS is disabled), that implements nbr
* cache */
typedef struct uip_ds6_nbr {
#if UIP_DS6_NBR_MULTI_IPV6_ADDRS
struct uip_ds6_nbr *next;
uip_ds6_nbr_entry_t *nbr_entry;
#endif /* UIP_DS6_NBR_MULTI_IPV6_ADDRS */
uip_ipaddr_t ipaddr;
uint8_t isrouter;
uint8_t state;
#if UIP_ND6_SEND_NS || UIP_ND6_SEND_RA
struct stimer reachable;
struct stimer sendns;
uint8_t nscount;
#endif /* UIP_ND6_SEND_NS || UIP_ND6_SEND_RA */
#if UIP_CONF_IPV6_QUEUE_PKT
struct uip_packetqueue_handle packethandle;
#define UIP_DS6_NBR_PACKET_LIFETIME CLOCK_SECOND * 4
#endif /*UIP_CONF_QUEUE_PKT */
} uip_ds6_nbr_t;
This structure represents the IPv6 neighbor node table entry in Contiki OS. Descriptions of the areas within the building are as follows:
next: Holds a pointer to the next neighbor node in the neighbor node table.
nbr_entry: Pointer to the neighbor table entry. This is used to support multiple IPv6 addresses.
ipaddr: Keeps the IPv6 address of the neighbor node.
isrouter: A byte that indicates whether the neighboring node is a router.
state: A byte that indicates the state of the neighboring node.
reachable: Reachability timer. This timer is used to determine the reachability of the neighboring node.
sendns: NS (Neighbor Solicitation) send scheduler. This scheduler controls the sending of NS messages to the neighboring node.
nscount: NS (Neighbor Solicitation) counter. This counter is used to keep track of the number of NS messages sent.
packethandle: Packet queue pointer. This is used to hold packets to be sent to the neighboring node.
This structure stores information about neighboring nodes in the IPv6 network and is used in the operation of routing protocols.
The uip_lladdr_t type represents the link-layer addresses of nodes in the IPv6 network in Contiki OS. The expression const uip_lladdr_t *current_nbr creates a pointer named current_nbr, which points to a constant of type uip_lladdr_t. Link layer addresses depend on physical or cable network technologies that enable direct communication between nodes.
For example, in an Ethernet network, the link layer address is known as the MAC (Media Access Control) address. Using this expression, the current_nbr pointer provides access to the link layer address of a neighbor node in the IPv6 network. Appropriate methods or fields can be used to access the link layer address via the current_nbr pointer. This will depend on the specific application context. This type of pointer can be used, for example, to communicate directly with a neighbor node in an IPv6 network or to provide access to other nodes in the network. Link layer addresses play an important role for addressing and routing in data communication between nodes.
The current_nbr_link_stats expression creates a pointer to a structure of type struct link_stats. This pointer provides access to all statistics of a particular link.
The “struct link_stats” structure represents the statistical information of a link. Its content is as follows:
struct link_stats {
clock_time_t last_tx_time; // Son gönderim zaman damgası
clock_time_t last_rx_time; // Son alım zaman damgası
uint16_t etx; // ETX (Expected Transmission Count)
int16_t rssi; // RSSI (received signal strength indicator)
uint8_t freshness; // İstatistiklerin tazeliği
#if LINK_STATS_ETX_FROM_PACKET_COUNT
uint8_t tx_count; // Gönderim sayısı, ETX hesaplaması için kullanılır
uint8_t ack_count; // ACK sayısı, ETX hesaplaması için kullanılır
#endif /* LINK_STATS_ETX_FROM_PACKET_COUNT */
#if LINK_STATS_PACKET_COUNTERS
struct link_packet_counter cnt_current; // Mevcut dönemdeki paket sayısı
struct link_packet_counter cnt_total; // Toplam paket sayısı
#endif
};
This structure stores statistical information used to evaluate the performance and quality of a link. Descriptions of the fields inside are as follows:
- last_tx_time: The last send timestamp represents the time of the last transmission.
- last_rx_time: The last reception timestamp represents the time of the last reception.
- etx: ETX (Expected Transmission Count) represents the expected transmission count of the transmission. ETX is used to measure communication quality in wireless networks.
- rssi: RSSI (received signal strength indicator) represents the received signal strength. RSSI is used to measure the received signal strength. freshness: It is a value that expresses the freshness of the statistics.
- tx_count and ack_count: The number of transmissions and the number of ACKs used for ETX calculation. These numbers are used in the ETX calculation algorithm.
- cnt_current and cnt_total: These are structures containing packet counts. cnt_current represents the number of packages in the current period, while cnt_total represents the total number of packages.
This structure provides statistical information used to measure the performance of a link and make decisions of network protocols. For example, it contains information such as transmission power, received signal quality, and transmission stability.
while(uip_nbr != NULL) {
current_nbr = uip_ds6_nbr_lladdr_from_ipaddr((const uip_ipaddr_t *)&uip_nbr->ipaddr);
current_nbr_link_stats = link_stats_from_lladdr((const linkaddr_t *)current_nbr);
current_nbr_id = uip_nbr->ipaddr.u16[7];
if(n != NULL)
{
n->current_nbr_id = current_nbr_id;
rpl_parent_t *current_nbr_t = nbr_table_get_from_lladdr(rpl_parents, (const linkaddr_t *)current_nbr);
}
else
{
n = memb_alloc(&vrt_reward_list_mem);
if(n != NULL)
{
list_add(reward_list, n);
n->current_nbr_id = current_nbr_id;
rpl_parent_t *current_nbr_t = nbr_table_get_from_lladdr(rpl_parents, (const linkaddr_t *)current_nbr);
}
}
uip_nbr = uip_ds6_nbr_next(uip_nbr);
}
This piece of code performs a series of operations that run in a loop. Operations focus on obtaining information about neighboring nodes in an IPv6 network and performing some operations using this information. Let’s explain the functioning of the code snippet step by step:
- The loop continues as long as the uip_nbr pointer is not NULL.
- The current_nbr pointer accesses the link layer address of the neighbor node using the uip_ds6_nbr_lladdr_from_ipaddr function via the uip_nbr pointer.
- The current_nbr_link_stats pointer accesses the statistics of the corresponding neighbor node via the current_nbr pointer using the link_stats_from_lladdr function.
- current_nbr_id retrieves the 7th component of the IPv6 address (uip_nbr->ipaddr.u16[7]) via the uip_nbr pointer.
- If pointer n is not NULL, it updates the current_nbr_id field of structure n.
- The current_nbr_t pointer retrieves a reference to an entry matching the current_nbr pointer from the rpl_parents table using the nbr_table_get_from_lladdr function.
- If pointer n is NULL, vrt_reward_list_mem allocates an item (n) from the memory pool and adds it to the reward_list list.
- Updates the current_nbr_id field of structure n.
- The current_nbr_t pointer retrieves a reference to an entry matching the current_nbr pointer from the rpl_parents table using the nbr_table_get_from_lladdr function.
- The uip_nbr pointer moves to the next neighboring node’s reference using the uip_ds6_nbr_next function.
This piece of code retrieves information about neighboring nodes in the IPv6 network, performs some operations using this information, and finally passes on the information of the next neighboring node. The function of the code can be clearer if the relevant network structures and functions are fully understood.
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