Transport protocols and bulk file transfer

["Lawrence D. Dunn" <>]

Stas, (& others)

  (This was one of my action items from last time.
  Stas, Steven and I did go over most of this at I2 joint-techs
  meeting. But I had scribbled this stuff on paper, and promised
  Stas I'd type it up).

  Per our conversation at joint-techs, here's the text starter-questions
  from our (1/p) formalization discussion.

 1. Is the information metric correct? We discuss the error rate "p",
   but what about the information contained in the ACK's. Since the
   algorithm takes action on each ACK reception, it is deriving some 
information
   per-packet from the received ACKs.
   Also, are we correctly characterizing "p" for both congestive and 
non-congestive
  loss?  It's pretty easy to think about small "p" for non-congestive loss.
  But if there is congestion then the number of dup-ACKs will go up until
  the sender backs off.  So during that time, the experienced "p" would
  be possibly higher, and the backoff-signals more frequent.
  I'm not sure that behavior is modelled in the Shannon formula.
  (i.e. "p" is time-varying around the loss event, etc)

2. alpha ("a") <1 or >1? text has examples of <1 (.5, .82), but formalization
    slips in a>1 as basic assumption.  If you're trying to make a point that
   a>1 is the key factor that makes things degrade, and therefore 
cannot be used,
   should highlight that assertion.  As written, there's no hint to 
believe that a>1 is
   any more/less important than c>0.  They seem like they're just
   boundary-condition constants, rather than critical "I'm about to show that
   for a>1 things fall apart" components.

3. Does p^(a-1) / log2 (p) --> infinity? Seems like maybe not.
    Top term -> 0, bottom term -> large_negative.
    (other side issue- lost a "-" sign on first page).

4. meta-issue: Does it matter if precision degrades with low-loss?
   (It may be that some constant-number of bits of accuracy is sufficient).

4.1 What *should* rate be with zero congestive loss (i.e. all loss is
  non-congestive)?  Compare examples when Tx interface is
  less_than or greater_than bottleneck rate.

5. "Bottleneck router needs to communicate...". Really? If it's non-congestive
  loss, then routers never signal anything.  There is a confusing mix 
of discussion
  the centers on congestive loss, versus other parts of the text 
where non-congestive
  loss seems to be the focus.  So is the discussion about congestive, or
  non-congestive loss?  Or both equally, etc.

Larry
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