David Culler, Jason Hill, Robert Szewczyk, and Alec Woo - PowerPoint PPT Presentation

1 / 31
About This Presentation
Title:

David Culler, Jason Hill, Robert Szewczyk, and Alec Woo

Description:

TOS Boot Camp. 15. A Simple Ad Hoc Routing Example (II) ... TOS Boot Camp. 16. Packet Forwarding. Node receives a packet destined to it will ... – PowerPoint PPT presentation

Number of Views:23
Avg rating:3.0/5.0
Slides: 32
Provided by: david3084
Category:
Tags: alec | camp | culler | david | hill | jason | robert | szewczyk | woo

less

Transcript and Presenter's Notes

Title: David Culler, Jason Hill, Robert Szewczyk, and Alec Woo


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

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)

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

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

6
CSMA in TOS Network Stack
Application
AM_SEND_MSG fails
AM
VAR(state) ! 0
PACKET
RADIO BYTE
Backpressure
Channel is busy
RFM
7
One CSMA Example
  • In each RADIO_BYTE components
  • Random listening period

Busy
Transmission Request
Listen for Random Period
Transmit
Idle
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
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
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) gtgt 1
  • bit ((VAR(shift_reg) 0x4000) gtgt 14)
  • bit ((VAR(shift_reg) 0x8000) gtgt 15)
  • VAR(shift_reg) gtgt1
  • if (bit 0x1) VAR(shift_reg) 0x8000
  • VAR(wait_amount) (VAR(shift_reg)
    0x3f)12
  • if(VAR(waiting) gt VAR(wait_amount))
  • Prepare for transmission

Channel is busy. Starts again
16 bit LFSR
Listening period ? 12,75
11
CSMA Evaluation
Channel Utilization 70
Throughput per node is fair
12
Outline
  • Media Access Control
  • Ad Hoc Routing Mechanism
  • Hands on Exercise

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

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

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 childrens broadcasts
  • has an effect in lowering the number of messages
    in broadcasting to the entire network
  • Broadcast becomes unidirectional (from BS
    outward)

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

17
Packet Format
  • Defined in system/include/MSG.h
  • define DATA_LENGTH 30
  • struct MSG_VALS
  • char addr
  • char type
  • char group
  • char dataDATA_LENGTH
  • Special Address (addr)
  • Broadcast 0xff (TOS_BCAST_ADDR)
  • Send to UART 0x7e (TOS_UART_ADDR)

Application Data Unit
18
Routing Data Unit
  • data0 number of hops from the base station
  • Each node appends its address to data indexed
    by number of hops (data(int)data0)

BS (12)
Node 33
Node 56
Node 33s data unit
2
12
33
1
2
0
3
19
Ad Hoc Routing Code in AM_ROUTE.c
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).data0 1
  • VAR(data_buf).data1 TOS_LOCAL_ADDRESS

Tick every 2 seconds
Set route to UART
BS is 1 hop away
Append my ID
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
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_AD
    DR,AM_MSG(ROUTE_UPDATE),VAR(buf))
  • else
  • if(VAR(set) gt 0) VAR(set) --
  • endif

Base stations periodic broadcast
Nodes count down to expire its route
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)data0
  • VAR(set) 8
  • //create an update packet to be sent out.
  • data0
  • data(int)data0 TOS_LOCAL_ADDRESS
  • TOS_CALL_COMMAND(ROUTE_SUB_SEND_MSG)
  • (TOS_BCAST_ADDR,AM_MSG(ROUTE_UPDATE),msg)

Set route to parents 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
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.
25
Packet Forwarding Code in AM_ROUTE.c
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.
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.
28
AM_ROUTE.c (DATA_MSG)
  • TOS_MsgPtrTOS_MSG_EVENT(DATA_MSG) (TOS_MsgPtr
    msg)
  • if(VAR(route) ! 0)
  • //update the packet.
  • data5 data4
  • data4 data3
  • data3 data2
  • data2 data1
  • data1 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.
29
Outline
  • Media Access Control
  • Ad Hoc Routing Mechanism
  • Hands on Exercise

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

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
  • data0 already tells you number of hops from the
    base station of the sender of the packet
  • and the corresponding node id
    data(int)data0
  • 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
Write a Comment
User Comments (0)
About PowerShow.com