Hi Urs, I used a testbed of 15 IRIS sensor nodes which are placed in communication range of the reference broadcaster. I constructed a line topology by configuring each node such that it will accept incoming messages from the nodes with id one more or one less of the id of the current node. Packets from all other nodes are ignored. I attached a base station node to a PC to log logical clock values broadcasted by the nodes. At the end of each interval which are uniformly distributed between 5 and 8 seconds, the reference broadcaster node broadcasts a message. The corresponding message is received approximately at the same time by all nodes. This message is timestamped by the receiving nodes. After that, the nodes broadcast their logical clock values and a base station node transfers these messages to the serial port of the PC. An application listening the serial port logs these messages.
For the sample result, just disgard the left-side column. The right-side column is the logical clock values of the nodes at a time instant. 1287678021203: *[nodeid=0x1] [clock=0x1f3fc724]* 1287678021250: *[nodeid=0x2] [clock=0x1f3fc76a]* 1287678021294: *[nodeid=0x3] [clock=0x1f3fc75d]* 1287678021350: *[nodeid=0x4] [clock=0x1f3fc6ae]* 1287678021398: *[nodeid=0x5] [clock=0x1f3fc47d]* Sinan. 2010/10/21 Urs Hunkeler <urs.hunke...@epfl.ch> > Hi, > > As an interested outside observer of the conversation (I have no experience > with FTSP), how do you measure the clock skews? What do the values in the > different columns mean? > > Thanks, > Urs > > > On 10/21/2010 06:17 PM, Sinan Yildirim wrote: > >> Hi Janos, >> >> I have done the modifications as you have said and also used the >> NoSleepC component of your implementation in tinyos-2.x-contrib >> repository. But I don't get tight skew values on a line of 5 iris sensor >> nodes. >> >> Here are the results after a 15 minute run: >> >> 1287678021203: [nodeid=0x1] [clock=0x1f3fc724] >> 1287678021250: [nodeid=0x2] [clock=0x1f3fc76a] >> 1287678021294: [nodeid=0x3] [clock=0x1f3fc75d] >> 1287678021350: [nodeid=0x4] [clock=0x1f3fc6ae] >> 1287678021398: [nodeid=0x5] [clock=0x1f3fc47d] >> >> Why am I measuring such big clock skew in this small network?? Any >> suggestions? >> >>
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