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TinyOS Programming Boot Camp (V) Communication

TinyOS Programming Boot Camp (V) Communication. David Culler, Jason Hill, Robert Szewczyk, and Alec Woo U.C. Berkeley 2/9/2001. Outline. Media Access Control Ad Hoc Routing Mechanism Hands on Exercise. Mote Characteristics. Hardware: single channel RF radio

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TinyOS Programming Boot Camp (V) Communication

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  1. TinyOS Programming Boot Camp (V) Communication David Culler, Jason Hill, Robert Szewczyk, and Alec Woo U.C. Berkeley 2/9/2001

  2. Outline • Media Access Control • Ad Hoc Routing Mechanism • Hands on Exercise TOS Boot Camp

  3. Mote Characteristics • Hardware: single channel RF radio • Nodes contend for the same wireless channel • Traffic is likely • Periodic : nature of sensor networks applications • Correlated : detection of common events • Collision detection mechanism is not available • Carrier Sense Multiple Access (CSMA) TOS Boot Camp

  4. CSMA in TOS Framework • Channel capacity ~25 packet/s • High amount of traffic due to • High node density • High transmission rate of each node • Application layer lacks information about the channel • Place CSMA at RADIO_BYTE level in between application layer and RFM radio component TOS Boot Camp

  5. CSMA Design • Basic mechanism • Listen on the channel before transmit • Only transmit if channel is idle • If the channel is busy, “wait” until channel becomes idle again • Correlated periodic traffic may lead to repeated collisions • Introduce random delay in MAC layer • If channel becomes busy, MAC backpressures to application to drop further transmissions TOS Boot Camp

  6. CSMA in TOS Network Stack Application AM_SEND_MSG fails AM VAR(state) != 0 PACKET RADIO BYTE Backpressure Channel is busy RFM TOS Boot Camp

  7. One CSMA Example • In each RADIO_BYTE components • Random listening period Busy Transmission Request Listen for Random Period Transmit Idle TOS Boot Camp

  8. FOUR_B_RADIO_BYTE.c (RADIO_BYTE_INIT) • 16 bit Linear Feedback Shift Register (LFSR) as Pseudo Random Number Generator • Initialization char TOS_COMMAND(RADIO_BYTE_INIT)(){ TOS_CALL_COMMAND(RADIO_SUB_INIT)(); VAR(wait_amount) = 12; VAR(shift_reg) = 119 * LOCAL_ADDR_BYTE_2; return 1; } Minimum number of bits to listen (Encoding Dependent) Seed for LFSR TOS Boot Camp

  9. FOUR_B_RADIO_BYTE.c(RADIO_BYTE_TX_BYTES) char TOS_COMMAND(RADIO_BYTE_TX_BYTES)(char data){ … if(VAR(state) == 0){ //if currently in idle mode, then switch over to transmit mode //and set state to waiting to transmit first byte. VAR(third) = data; VAR(state) = 10; return 1; } … Goes to CSMA TOS Boot Camp

  10. FOUR_B_RADIO_BYTE.c (RADIO_BYTE_RX_BIT_EVENT) else if(VAR(state) == 10){ if(data){ VAR(waiting) = 0; }else{ if (++VAR(waiting) == 11){ bit = (VAR(shift_reg) & 0x2) >> 1; bit ^= ((VAR(shift_reg) & 0x4000) >> 14); bit ^= ((VAR(shift_reg) & 0x8000) >> 15); VAR(shift_reg) >>=1; if (bit & 0x1) VAR(shift_reg) |= 0x8000; VAR(wait_amount) = (VAR(shift_reg) & 0x3f)+12; } if(VAR(waiting) > VAR(wait_amount)){ … Prepare for transmission } } Channel is busy. Starts again 16 bit LFSR Listening period  [12,75] TOS Boot Camp

  11. CSMA Evaluation Channel Utilization ~70% Throughput per node is fair TOS Boot Camp

  12. Outline • Media Access Control • Ad Hoc Routing Mechanism • Hands on Exercise TOS Boot Camp

  13. Ad Hoc Routing Goal • Nodes should self organize into a multi-hop network topology • Each node can discover a route to deliver packets to the base station • uni-directional towards the base station • Simple, robust, local algorithm • Works in an ad hoc, spontaneously changing network • Assume bi-directional connectivity in general TOS Boot Camp

  14. A Simple Ad Hoc Routing Example (I) • AM_ROUTE.c • A route is simply knowing a neighboring node (or parent) that can send to the base station • Base station broadcasts itself as a route • Node gets the route and retransmits the broadcast with itself as the route TOS Boot Camp

  15. A Simple Ad Hoc Routing Example (II) • Base station refreshes route with periodic broadcast • Nodes expire the old route and wait for base station next route refreshment • Nodes only broadcast once for each route update it gets • Prevent rebroadcast of children’s broadcasts • has an effect in lowering the number of messages in broadcasting to the entire network • Broadcast becomes unidirectional (from BS outward) TOS Boot Camp

  16. Packet Forwarding • Node receives a packet destined to it will • forward it to the next hop • Base station receives a packet destined to it will • forwards it to the UART TOS Boot Camp

  17. Packet Format • Defined in system/include/MSG.h #define DATA_LENGTH 30 struct MSG_VALS{ char addr char type char group; char data[DATA_LENGTH]; }; • Special Address (addr) • Broadcast 0xff (TOS_BCAST_ADDR) • Send to UART 0x7e (TOS_UART_ADDR) Application Data Unit TOS Boot Camp

  18. 1 12 BS’s data unit Node 56’s data unit 3 12 33 56 Routing Data Unit • data[0] = number of hops from the base station • Each node appends its address to data[] indexed by number of hops (data[(int)data[0]]) BS (12) Node 33 Node 56 Node 33’s data unit 2 12 33 1 2 0 3 TOS Boot Camp

  19. Ad Hoc Routing Code in AM_ROUTE.c TOS Boot Camp

  20. AM_ROUTE.c (AM_ROUTE_INIT) (Base Station) char TOS_COMMAND(AM_ROUTE_INIT)(){ … //set beacon rate for route updates to be sent TOS_COMMAND(CONNECT_SUB_CLOCK_INIT)(255, 0x06); //route to base station is over UART. VAR(route) = TOS_UART_ADDR; VAR(set) = 1; VAR(place) = 0; VAR(data_buf).data[0] = 1; VAR(data_buf).data[1] = TOS_LOCAL_ADDRESS; … } Tick every 2 seconds Set route to UART BS is 1 hop away Append my ID TOS Boot Camp

  21. AM_ROUTE.c (AM_ROUTE_INIT) (NOT Base Station) char TOS_COMMAND(AM_ROUTE_INIT)(){ … //set rate of sampling TOS_COMMAND(CONNECT_SUB_CLOCK_INIT)(255, 0x03); VAR(set) = 0; VAR(route) = 0; VAR(count) = 0; return 1; } Tick every 0.25 seconds Route is not set initially TOS Boot Camp

  22. AM_ROUTE.c (AM_ROUTE_SUB_CLOCK) void TOS_EVENT(AM_ROUTE_SUB_CLOCK)(){ #ifdef BASE_STATION … TOS_CALL_COMMAND(ROUTE_SUB_SEND_MSG)(TOS_BCAST_ADDR,AM_MSG(ROUTE_UPDATE),&VAR(buf)); … #else … if(VAR(set) > 0) VAR(set) --; … #endif } Base station’s periodic broadcast Nodes count down to expire its route TOS Boot Camp

  23. AM_ROUTE.c (ROUTE_UPDATE) • TOS_MsgPtr TOS_MSG_EVENT(ROUTE_UPDATE)(TOS_MsgPtr msg){ … //if route hasn't already been set this period... if(VAR(set) == 0){ //record route VAR(route) = data[(int)data[0]]; VAR(set) = 8; //create an update packet to be sent out. data[0]++; data[(int)data[0]] = TOS_LOCAL_ADDRESS; … TOS_CALL_COMMAND(ROUTE_SUB_SEND_MSG) (TOS_BCAST_ADDR,AM_MSG(ROUTE_UPDATE),msg); …} Set route to parent’s ID Set to expire the route after 8 ticks I am 1 more hop away from the BS Append my ID to the buffer Broadcast the message TOS Boot Camp

  24. AM_ROUTE.c (ROUTE_UPDATE cont.) TOS_MsgPtr TOS_MSG_EVENT(ROUTE_UPDATE)(TOS_MsgPtr msg){ … If (VAR(set) == 0){ … }else{ return msg; } … Only broadcast once for each new route; otherwise, do nothing. TOS Boot Camp

  25. Packet Forwarding Code in AM_ROUTE.c TOS Boot Camp

  26. AM_ROUTE.c (ROUTE_SUB_DATA_READY) • Data source char TOS_EVENT(ROUTE_SUB_DATA_READY)(int data){ … if(VAR(route) != 0 && other App. Specific conditions){ … TOS_CALL_COMMAND(ROUTE_SUB_SEND_MSG) (VAR(route),AM_MSG(DATA_MSG), &VAR(data_buf)); … } } Send out a data packet if a node has a route. TOS Boot Camp

  27. AM_ROUTE.c (DATA_MSG) TOS_MsgPtrTOS_MSG_EVENT(DATA_MSG) (TOS_MsgPtr msg){ … if(VAR(route) != 0){ Application Specific Modification of the forwarding packet … TOS_CALL_COMMAND(ROUTE_SUB_SEND_MSG) (VAR(route),AM_MSG(DATA_MSG),msg); … } … } Node has a route Forward message if you have a route. TOS Boot Camp

  28. AM_ROUTE.c (DATA_MSG) TOS_MsgPtrTOS_MSG_EVENT(DATA_MSG) (TOS_MsgPtr msg){ … if(VAR(route) != 0){ //update the packet. data[5] = data[4]; data[4] = data[3]; data[3] = data[2]; data[2] = data[1]; data[1] = TOS_LOCAL_ADDRESS; … TOS_CALL_COMMAND(ROUTE_SUB_SEND_MSG) (VAR(route),AM_MSG(DATA_MSG),msg); … } … } Modify the forwarding packet to stores the hops taken. TOS Boot Camp

  29. Outline • Media Access Control • Ad Hoc Routing Mechanism • Hands on Exercise TOS Boot Camp

  30. Hands on Exercise (I) • Run the “apps/router.desc” application • Set it to your own LOCAL GROUP in Makefile • Default is 0x13 • Goes to tools directory • Run listen.c TOS Boot Camp

  31. Hands on Exercise (II) • Modify ROUTE_UPDATE in AM_ROUTE.c • GOAL: pick route based on depth of the tree • Pick the route with the smallest number of hops from the base station • Can use the same data unit format • data[0]already tells you number of hops from the base station of the sender of the packet • and the corresponding node id = data[(int)data[0]] • If a better route (smaller number of hops) is received, use that as the new route. • You may need to introduce a new variable (e.g. myLevel) to remember your current depth TOS Boot Camp

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