Re: [IMRG] Requirements for IMP

[jon bennett <jcrb@yahoo.com>]

Maurizio,

when discussing measuring a sampling of routers you said

>  or using a very few bits (an IPMP can write a paket only if the TLL ends 
> with the same bit pattern).
to do this you would need two things, you would need a mask of the bit 
pattern, and a mask (or a count which would wind up being used by the 
router to make a mask) of which bits out of the 8 in the TTL you wanted to 
match against the pattern.

in the interests of simplicity, would it suffice to have the packet be 
stamped only if the TTL was some even multiple of 2? In other words there 
would be for example the IMP packet would have a 3 bit field (N) and only 
if the last N bits of the TTL were 1 (or 0?) would the packet be stamped. 
this would let you test every 2nd, 4th, 8th, 16th, etc router. By altering 
the initial TTL value you would be able to change where the series started. 
for example if you had set N to 2 then a packet sent with TTL=255 would measure

TTL                     stamp   router
255=11111111            NO      1
254=11111110            NO      2
253=11111101            NO      3
252=11111100            YES     4
251=11111011            NO      5
250=11111010            NO      6
249=11111001            NO      7
248=11111000            YES     8
etc
yielding stamps by routers
4,8,12,16,20,etc

but if instead you sent it with a TTL=253 you would get

TTL                     stamp   router
253=11111101            NO      1
252=11111100            YES     2
251=11111011            NO      3
250=11111010            NO      4
249=11111001            NO      5
248=11111000            YES     6
247=11110111            NO      7
246=11110110            NO      8
etc
yielding stamps by routers
2,6,10,14,18,etc




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