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Re: Comments on draft-ietf-multi6-v4-multihoming-02

On 18-nov-04, at 20:31, Joe Touch wrote:

|> Persistent connections are the kind of TCP connections that might go
|> idle for extended periods;

| Actually I believe they are closed after a relatively short time when
| they aren't used. And very few sessions use persistent connections last
| time I checked. 

TCP connections are not closed just because they are idle, and idle
means no packets exchanged at all.


I was talking about HTTP connections, not about TCP in general.

|> Such as? I was thinking 300ms-500ms as a ballpark.

| I was thinking along the lines of 10 - 15 seconds for non-TCP stuff. I
| heaven't really looked in detail, but I'm pretty sure transports for AV
| streaming don't generate ACKs every 500 ms. 

Anything that doesn't generate ACKs every couple-hundred ms when the
stream is active is asking for trouble ;-)


Any particular reason why? I think so many ACKs are excessive.

|> I'd like it to do something - to keep verifying that reachability is
|> still possible for exactly the period that an idle TCP 'expects' there
|> not to be a substantial change in the channel. 

| Wouldn't an outage happening right after a session goes idle and a
| keepalive has been exchanged be such a corner case that we can safely
| ignore it as a special case?

I don't like ignoring corner cases, esp. where TCP is concerned.

There is ignoring and then there is ignoring. Obviously when such a corner case happens our mechanisms must be able to deal with it in a reasonably way. What I'm saying is that not having code to specifically handle this case and thus potentially incurring a retransmit before the multihoming layer does its thing is ok here.

Don't forget that outages are relatively rare. I don't find the situation where there is a significant hiccup when one happens problematic, as long as such a hiccup is short enough for sessions to recover and for users to wait for this. (I.e., recovering after 239 wouldn't do, but after 5 - 10 seconds would be just fine.)