Subject: RE: [mobile-ip] Times for Low-Latency IPv6 Handoff

From: James Kempf <[email-masked]>
Date: Tue, 5 Jun 2001 14:50:33 -0700 (PDT)

>
>First, shouldn't you include the propagation delay from the oldAR to
>the MN and back into the calculation?
>Speed of light is 1 ns/foot=3ns/meter=3ms/km, so
>in a CDMA cell of about 3Km in radius, you have 10 ms
>propagation delay in each direction, which mean 20 ms total.
>

I assume that is built into the user level bit rate figures Holma
and Toskala give for WCDMA.

>Also, I don't know what WCDMA does these days, but don't they add
>some padding to the layer 3 signal (maybe that is not too big :) )
>

Typically, radio frames are much smaller than IP packets (on the
order of 40 bytes). It is possible that there may be padding
if a packet won't fit into an even number of frames, but, again,
I was using the user level throughput figures.

>Now, my question isn't HI/HACK between oldAR/ newAR included in stateful
>case, aren't
>those messages in critical path? I saw your comment about Mobile
>determined case (that HI/HACK should be included). Doesn't the same 
>apply to Network determined stateful?
>
>Again the HI/HACK has both transmission delay and propagation delay.
>

Signalling across the wired backbone is typically less than 10 ms. 
I believe I calculated something in the submillisecond range for
T1 on the HI/HACK. So it's basically in the noise, as far as
the radio link is concerned.

		jak

---

From: Arthur Ross <[email-masked]>
Date: Tue, 5 Jun 2001 15:22:08 -0700

>>propagation delay in each direction, which mean 20 ms total.
Shame on you Madjid - A slap of the ol' grammar school teachers ruler!
That's 3 MICROseconds (roughly) per km. [C=299.792458 m/microsec]
>the radio link is concerned.
Typically a LOT less than 10 ms, I would guess. Old BTL measurements of the
REAL prop delay (i.e. group delay in the 300-3000 Hz band) in the voice
network showed, IIRC, typically about 25% of C, calculated using the
airline distance between the endpoints, which winds up being circa 50 ms
for a transit of the entire US of A. The 25% accounted for all the PCM
sample buffering, analog group delays, etc. ... everything - it was a
pretty good, statistically sound measurement.

Seconding Jim's comments, the major contributions to the signaling will be
the L2-ish things - framing (if used), interleaving, coding, transmission
time, decoding, etc - most of which are proportional to message length, not
the EM prop delay.

I haven't been paying much attention to this lately, but I think it's time
to get caught up ....

   -- Best, ahmr