CS199 Notes for 9/14/2004
Topic: TinyOS Networking
Scribe: Xin Yang
==================

Internet:  
	- every client and server works independently
	- End to End traffic
	- very low loss
	- lowes 1% packet loss

	* ----- *
	* ----- *

Sensor Network:
	- nodes collaborate
	- variety of traffic networks

	* >>>>
	^	*
	* <<<<

	- no wires (in wireless space, not really a graph)
	- every one can hear each other, so interference issues
	- Hidden Terminal 
	A	B	C
		- A doesn't kno C, C doesn't know B, then A and C can both transmit without knowing 

	- High loss
		- possibly more than 30-40% loss

Active Message:
	- its a field in the packet
	- 256 fields (possible values)

	Example:

	interface ReceieveMsg {
		event TOS.MsgPtr receieve(TOS_MsgPtr);

	}

	GenericComm {
		provides interface ReceieveMSG[uint8_t];
		provides interface Send[uint8_t];
	}

	implementation {
		command result_t send(uint8_t addr, uint8_t len, Tos.MsgPtr prt);
		event result_t SendDone (TOS_MsgPtr ptr, result_t success);
	}


	TosMsg:
	- generic message format, struct
	
	Receieve:
	- must return a pointer for buffer for the next buffer
	- you swap buffers each time you get a message
        - does not assume unlimited allocation on receive: keeps limited
          resources in mind
	- common source of confusion
		- 	receieve(Tos_MsgPtr ptr)
			send(m)
			return m;
          - the send and receieve buffer are the same so it might get over written if a new packet arrives before send
	

	!!!! Radio stack will idle and drop packets untill this event returns with new pointer
	!!!! Thus if your handler takes a long time, you will drastically reduce performance

	- pervious only does point to point stuff
	- what about Tree Base collection?

	- Need to Build layer on top of this point-point stuff
	- Modules who build ontop of generic comm will implement the following interfaces

	I Send {
		C result_t Send(TOS_MsgPtr msg, uint16_t len)
		C void	getBuffer(Tos_MsgPtr, uint16_t len)		
		C result_t sendDone( .. )
	}

	I Receive {
		E Tos.MsgPtr receieve (TOSMsgPtr ptr, void payload, uint len);
	}
	
	getBuffer:
		- returns a pointer to where the previous layer can put stuff
		- just a convenience
		- still has to know how big headers in the stack are and how much space that takes in the payload of the tosMsg packet
		

	Generic Comm can only keep 1 packet at a time
	- single component not a problem
	- multiple component a problem
	- Queued Sends (tos lib queue) - library compoenet that does this