On Oct 18, 2005, at 6:14 PM, Soohong Daniel Park wrote:
I couldn't find an easy way to search the archive
for prior discussions on this topic but the
datagram tag size of 7 bits seems too low to me.
The max data rate for 802.15.4 is 250kbps.
Of this, lets assume that one only achieves about
128kbps or 16KBps. At this rate, an application could
potentially be pumping out 128-byte packets (this
is long enough to cause each packet to be fragmented)
at the rate of 128 packets per second and cause the
tag field to rollover every second. So to avoid any
potential of confusion due to tag reuse, one would
have to assume that packets do not stay in the
multihop network for more than a second or so. This
expectation seems unreasonable (especially
for a reactive routing protocol where route discovery
alone might take this long).
thoughts/comments?
Interesting point, but I am really not sure how often the tag field
reuse happen in 6lowpan scenarios. The major applicable connectivity
amongst 6lowpan nodes are simple control. Anything else ?
You are certainly correct in the assumption that many applications
are unlikely to involve high data rates (at least not all the time).
However, there are several applications (e.g. structural monitoring
etc.) where an application keeps collecting sensor readings until
some application specific buffer is full and then turns on the radio
and to send data back to a central collection site.
In such "bursty traffic" scenarios, tag rollover could be an issue
even though the "average" data rate is very low.
vipul
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