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Re: IPv6 MTU issues in FTTH applications

2002-02-25 10:30:02
Stephen M. Bellovin wrote:

If you're doing 
uncompressed voice (compression makes this effect worse), a 1500 byte 
packet holds 214 ms of voice at the (U.S.) standard rate of 56K bps. 
That's already beyond the delay budget, just for that one hop,

On the other hand, that's assuming POTS-grade audio quality.  Some people 
could have use for higher-quality audio.  For example, radio stations 
prefer to use high-quality audio when doing interviews with people in 
remote locations.  Musicians could use CD-quality audioconferencing to 
practice together remotely (for example, if Big Stars from different 
continents are preparing for a live show together); at 176K bytes/second, 
a 1500-byte MTU is less than a single millisecond, meaning you'd have to 
route more than 1000 packets per second.  (And that's just for stereo; 

And then there's video; given FTTH, it could be practical for a TV news 
program to do an IP-based videoconference when it needs to interview 
somebody remotely.  Since by then we'd be talking about HDTV, they'd need 
a huge bit rate; individual frames could easily turn out to overflow the 
1500-byte MTU.

I know this is stuff that's been talked about for a long time, and has 
remained impractical (I used to work in videoconferencing); but the 
biggest part that makes it impractical has been bandwidth.  FTTH would 
increase that bandwidth, so it does seem like something for a body working 
on FTTH to consider.

/========================================================\
|John Stracke                    |Principal Engineer     |
|jstracke(_at_)incentivesystems(_dot_)com   |Incentive Systems, Inc.|
|http://www.incentivesystems.com |My opinions are my own.|
|========================================================|
|Cogito ergo Spud. (I think, therefore I yam.)           |
\========================================================/