/* * Copyright (C) 2015 Daniel Krebs * 2016 INRIA * * This file is subject to the terms and conditions of the GNU Lesser * General Public License v2.1. See the file LICENSE in the top level * directory for more details. */ /** * @defgroup net_gnrc_lwmac Simplest possible MAC layer * @ingroup net_gnrc * @brief Lightweight MAC protocol that allows for duty cycling to save * energy. * * ## LWMAC implementation * * ## Radio duty cycling * LWMAC adopts the radio duty-cycle scheme to conserve power. Namely, in each * cycle period (MAC superframe), a node device wakes up for a short period of * time (called listen period or wake-up period) for receiving possible incoming * packets from other devices. Outside the listen period, the node device turns * off its radio to conserve power. * * ## Phase-lock scheme * LWMAC adopts the phase-lock scheme to further reduce power consumption. Each * node device in LWMAC will try to record/track its Tx-neighbor's wake-up phase. * This is called phase-lock. After phase-locking, the sender node will (likely) * spend less preamble packets (also called WR packet, i.e., wake-up-request, in * LWMAC) for initiating a hand-shaking procedure for transmitting a data packet, * compared to the first time it talks to the receiver. * * ## Burst transmission * LWMAC adopts pending-bit technique to enhance its throughput. Namely, in case * of having multi packets for the receiver, a sender uses the pending-bit flag * embedded in the MAC header to instruct this situation, and the buffered packets * will be transmitted in a continuous sequence, back to back, to the receiver in * one shot. * * ## Auto wake-up extension * LWMAC adopts auto wake-up extension scheme based on timeout (like T-MAC). In short, * when a packet is successfully received at the receiver side, the receiver will * reset the wake-up timeout to extend its wake-up period for receiving more potential * incoming packets. This is to be compatible with the pending-bit technique to allow * the receiver to absorb more packets when needed, thus boosts the throughput. * * ## Simple retransmission scheme * LWMAC adopts a simple retransmission scheme to enhance link reliability. The data * packet will only be dropped in case the retransmission counter gets larger than * @ref GNRC_LWMAC_MAX_DATA_TX_RETRIES. * * ## Automatic phase backoff scheme * LWMAC adopts an automatic phase backoff scheme to reduce WR (preamble) collision * probability. In multi-hop scenarios, let's say, nodes A <---B <----C (which is * common in multi-hop data collection networks), in which B has packets for A, and * C has packets for B. In case A and B's wake-up phases are too close (overlapping). * Then, especially in high traffic conditions, B and C may initiate transmissions * at the same time (B sends to A, and C sends to B), a link of either will be * definitely interfered, leading to collisions and link throughput reduction. To * this end, by using the automatic phase backoff scheme, if a sender finds its * receiver's phase is too close to its own phase, it will run a backoff scheme to * randomly reselect a new wake-up phase for itself. * * @{ * * @file * @brief Interface definition for the LWMAC protocol * * @author Daniel Krebs * @author Shuguo Zhuo */ #ifndef NET_GNRC_LWMAC_LWMAC_H #define NET_GNRC_LWMAC_LWMAC_H #include "kernel_types.h" #include "net/gnrc/netdev.h" #ifdef __cplusplus extern "C" { #endif /** * @brief Time between consecutive wake-ups. * * This macro governs power consumption, latency and throughput! * In LWMAC, devices adopt duty-cycle scheme to conserve power. That is, * time is divided into repeated cycles (or, superframes), and in each * cycle, a node only wakes up for a period of time for receiving potential * incoming packets for itself. This macro defines the wake-up interval, or, * in other words, defines the cycle duration used in LWMAC. If the wake-up interval * is short, nodes will wake up more frequently, which also increases * the chances for receiving packets from neighbors (i.e., leads to higher * throughput), but also results in higher power consumption. * In LWMAC, by default, we regard the wake-up period as the beginning of a cycle. */ #ifndef GNRC_LWMAC_WAKEUP_INTERVAL_US #define GNRC_LWMAC_WAKEUP_INTERVAL_US (100LU * US_PER_MS) #endif /** * @brief The Maximum WR (preamble packet @ref gnrc_lwmac_frame_wr_t) duration time. * * Since LWMAC adopts duty-cycle scheme, a node only wakes up for a short * period in each cycle. Thus, to probe where is the wake-up period of the * receiver, a sender sends WR (preamble) packets to notice the receiver for * communication. To ensure that the receiver will catch at least one WR * packet in one cycle, the sender repeatedly broadcasts a stream of WR packets * with the broadcast duration (preamble duration) slightly longer period than * @ref GNRC_LWMAC_WAKEUP_INTERVAL_US. */ #ifndef GNRC_LWMAC_PREAMBLE_DURATION_US #define GNRC_LWMAC_PREAMBLE_DURATION_US ((13LU * GNRC_LWMAC_WAKEUP_INTERVAL_US) / 10) #endif /** * @brief Timeout to send the next WR in case no WA has been received during that * time. * * In LWMAC, when a sender initiates a transmission to a receiver, it starts with * sending a stream of repeated WR packets with @ref GNRC_LWMAC_TIME_BETWEEN_WR_US interval * between two consecutive WRs. After sending one WR (preamble) packet, the sender turns * to the listen mode to receive the potential incoming WA (preamble-ACK) packet with * a timeout of @ref GNRC_LWMAC_TIME_BETWEEN_WR_US. If no WA is received during * @ref GNRC_LWMAC_TIME_BETWEEN_WR_US, the sender starts sending the next WR. * It is referenced to the beginning of both WRs, but due to internal * overhead, the exact spacing is slightly higher. * The minimum possible value depends on the time it takes to completely * send a WR with the given hardware (including processor) and data rate. */ #ifndef GNRC_LWMAC_TIME_BETWEEN_WR_US #define GNRC_LWMAC_TIME_BETWEEN_WR_US (5U * US_PER_MS) #endif /** * @brief How long a node in LWMAC should keep awake and listen on the channel in one cycle. * * LWMAC adopts the duty-cycle scheme that a node only wakes up for a short * period of @ref GNRC_LWMAC_WAKEUP_DURATION_US in each cycle. In the rest of the cycle, the node * turns off the radio to conserve power. @ref GNRC_LWMAC_WAKEUP_DURATION_US is set to twice the * duration of @ref GNRC_LWMAC_TIME_BETWEEN_WR_US, to guarantee that the wake-up period is long * enough that receiver will not miss the WR (preamble) packet. * Receiver needs to support @ref NETDEV_EVENT_RX_STARTED event in order to use time-between-WR * as a sensible default here. Otherwise the duration of WRs as well as longest * possible data broadcasts need to be taken into account. */ #ifndef GNRC_LWMAC_WAKEUP_DURATION_US #define GNRC_LWMAC_WAKEUP_DURATION_US (GNRC_LWMAC_TIME_BETWEEN_WR_US * 2) #endif /** * @brief How long broadcast packets @ref gnrc_lwmac_frame_broadcast_t will be sent to make sure * every participant has received at least one copy. * * Since LWMAC adopts duty-cycle scheme, a node only wakes up for a short period in * each cycle. Thus, when a node wants to broadcast a packet, it repeatedly broadcasts the * packet for one @ref GNRC_LWMAC_BROADCAST_DURATION_US duration which is slightly longer * than @ref GNRC_LWMAC_WAKEUP_INTERVAL_US. This is to ensure that all neighbors will not miss * the broadcast procedure of the sender and catch at least one copy of the broadcast packet. */ #ifndef GNRC_LWMAC_BROADCAST_DURATION_US #define GNRC_LWMAC_BROADCAST_DURATION_US ((GNRC_LWMAC_WAKEUP_INTERVAL_US * 11) / 10) #endif /** * @brief Time to idle between two successive broadcast packets, referenced to the * start of the packet. * * The same limitation as for @ref GNRC_LWMAC_TIME_BETWEEN_WR_US apply here. * In LWMAC, when a sender initiates a broadcast, it starts with sending a stream of * repeated broadcast packets with @ref GNRC_LWMAC_TIME_BETWEEN_BROADCAST_US interval * between two consecutive broadcast packets. After sending one broadcast packet, the sender * turns to the listen mode with a timeout of @ref GNRC_LWMAC_TIME_BETWEEN_BROADCAST_US. When this * timeout expires, the sender sends the next broadcast packet until reaching the maximum * broadcast duration of @ref GNRC_LWMAC_BROADCAST_DURATION_US. */ #ifndef GNRC_LWMAC_TIME_BETWEEN_BROADCAST_US #define GNRC_LWMAC_TIME_BETWEEN_BROADCAST_US (GNRC_LWMAC_TIME_BETWEEN_WR_US) #endif /** * @brief WR preparation overhead before it can be sent (higher with debugging output). * * In LWMAC, when a sender wants to send a data packet to the receiver, it starts * sending the WR stream a little bit earlier (advance) to the beginning edge * of destination's wake-up phase over time. The idea is not to miss the wake-up * period of the receiver, otherwise will lead to a long WR procedure. */ #ifndef GNRC_LWMAC_WR_PREPARATION_US #define GNRC_LWMAC_WR_PREPARATION_US ((3U * US_PER_MS)) #endif /** * @brief How long to wait after a WA for data to come in. * * When a node in LWMAC gets a WR during its wake-up period, it immediately * replies a WA packet to the sender for acknowledging the sender's transmission * request. After sending the WA, the receiver waits for the data packet from the * sender, with a timeout of @ref GNRC_LWMAC_DATA_DELAY_US duration. In case no data will be * received in this period, the receiver regards reception failed and go back to * normal listen mode. However, in case the receiver receives other unintended packets, * like WR/WA packets from other neighbor communication pairs, the receiver resets * this timeout and continues to wait for the data packet, with the consideration that * the sender's data transmission might be delayed due to other ongoing transmissions * (the data packet is transmitted with CSMA/CA). * This data timeout is long enough to catch the beginning of the packet if the transceiver * supports @ref NETDEV_EVENT_RX_STARTED event (this can be important for big packets). */ #ifndef GNRC_LWMAC_DATA_DELAY_US #define GNRC_LWMAC_DATA_DELAY_US (10U * US_PER_MS) #endif /** * @brief CSMA retries for DATA packet after WR->WA was successful. * * After receiving the WA packet @ref gnrc_lwmac_frame_wa_t from the receiver, the sender * starts sending the data packet using CSMA/CA. This macro defines how many CSMA retries * a sender will be allowed to execute for sending its data, before the data is successfully * sent (gets data ACK from the receiver). */ #ifndef GNRC_LWMAC_DATA_CSMA_RETRIES #define GNRC_LWMAC_DATA_CSMA_RETRIES (3U) #endif /** * @brief Maximum TX transmission retries for DATA packet in case of no response from the receiver. * * When a data packet is scheduled for transmission, i.e., pushed into TX for sending, * LWMAC defines a maximum of @ref GNRC_LWMAC_MAX_DATA_TX_RETRIES retries for transmission of the * packet. That is, in case of transmission failure in TX due to no WA from the receiver, * the sender will not drop the packet, but keeps it and retries to send the data packet * in the following cycles, until the sender reaches the maximum retries limit defined here. * Then, the packet will be dropped. */ #ifndef GNRC_LWMAC_MAX_DATA_TX_RETRIES #define GNRC_LWMAC_MAX_DATA_TX_RETRIES (3U) #endif /** * @brief MAX burst transmission packet number in one shot. * * LWMAC supports burst transmission based on the pending-bit technique, and this macro * here defines the largest number of packets allowed to be sent in one consecutive * sequence. In case a sender has multi packets for one receiver,the burst transmission * procedure is as follow: * 1. The sender first uses WR stream to locate the receiver's wake-up period (if the * sender has already phase-locked the receiver's phase, normally the sender only cost * one WR to get the first WA from the receiver) and then sends its first data. * 2. After the transmission of the first data, the sender immediately sends a WR to * the receiver for starting the second round of transmission of the second data. The * receiver should also immediately reply WA for continue receiving data packets. In * case the sender doesn't receive WA during @ref GNRC_LWMAC_TIME_BETWEEN_WR_US, it regards the * consecutive (burst) transmission failed and quits TX procedure (the data will be queued * back to the transmission queue for normal transmission attempt in following cycles). * 3. In case the second transmission succeeds, the sender repeats step (2) to send all the * following pending packets. * In short, in burst transmission mode, the sender doesn't tolerate no-WA event. ALl the * pending data packets should be sent with only one WR cost for leading the transmission. */ #ifndef GNRC_LWMAC_MAX_TX_BURST_PKT_NUM #define GNRC_LWMAC_MAX_TX_BURST_PKT_NUM (GNRC_LWMAC_WAKEUP_INTERVAL_US / GNRC_LWMAC_WAKEUP_DURATION_US) #endif /** * @brief MAX bad Listen period extensions a node can tolerate. * * In LWMAC, to allow burst transmissions, when in the wake-up period and by default, a node * will extend its wake-up period to another @ref GNRC_LWMAC_WAKEUP_DURATION_US after each packet * reception (except for broadcast packet). However, in some cases, a receiver may * overhear other unintended packets, e.g., WR or WA packets for other nodes, these are * called bad extensions for the receiver. If a receiver reaches the maximum bad listen * extension limit defined here, it goes to sleep mode with the consideration that the * channel is currently unavailable/busy. */ #ifndef GNRC_LWMAC_MAX_RX_EXTENSION_NUM #define GNRC_LWMAC_MAX_RX_EXTENSION_NUM (3U) #endif /** * @brief CSMA retries for broadcast packet. * * Currently, each broadcast packet is sent with CSMA/CA for collision avoidance. * Too many CSMA retries may lead to running out of destinations wake-up period. */ #ifndef GNRC_LWMAC_BROADCAST_CSMA_RETRIES #define GNRC_LWMAC_BROADCAST_CSMA_RETRIES (3U) #endif /** * @brief Default message queue size to use for the LWMAC thread. * * The value of this macro should be enough for supporting the manipulation of * LWMAC. * */ #ifndef GNRC_LWMAC_IPC_MSG_QUEUE_SIZE #define GNRC_LWMAC_IPC_MSG_QUEUE_SIZE (8U) #endif /** * @brief Initialize an instance of the LWMAC layer * * The initialization starts a new thread that connects to the given netdev * device and starts a link layer event loop. * * @param[in] stack stack for the control thread * @param[in] stacksize size of *stack* * @param[in] priority priority for the thread housing the LWMAC instance * @param[in] name name of the thread housing the LWMAC instance * @param[in] dev netdev device, needs to be already initialized * * @return PID of LWMAC thread on success * @return -EINVAL if creation of thread fails * @return -ENODEV if *dev* is invalid */ kernel_pid_t gnrc_lwmac_init(char *stack, int stacksize, char priority, const char *name, gnrc_netdev_t *dev); #ifdef __cplusplus } #endif #endif /* NET_GNRC_LWMAC_LWMAC_H */ /** @} */