Subject: RE: Silent Packet Loss & Header Compression

From: "Shriver, John" <[email-masked]>
Date: Thu, 24 May 2001 05:39:39 -0700

> -----Original Message-----
> From: James Carlson [mailto:[email-masked]]
> 
> Ramana Gollamudi writes:
> > Agreed. However, most of internet seems to work reasonably 
> well without
> > intermediate nodes doing providing any support for ensuring ordered
> > delivery.
> 
> That assumption is false.  Well-designed routers take a great deal of
> care to avoid reordering IP packets within a flow.  This is a
> substantial concern even at high speeds with (presumably) high levels
> of traffic aggregation.
> 
> It's true that reordering does sometimes occur, but it should be quite
> rare and due to transient problems at the network level (i.e., route
> flaps) and not due to design flaws.

Try telling that to the Digital Gigaswitch at MAE-East.  Reordering is
routine, along with 25% packet drop rates.

Reference:
Jon C. R. Bennett, Craig Partridge, and Nicholas Shectman, "Packet
Reordering is Not Pathological Network Behavior," IEEE/ACM TRANSACTIONS ON
NETWORKING, VOL. 7, NO. 6, DECEMBER 1999.

(Of course, the Gigaswitch and FDDI should be replaced by a Gigabit Ethernet
switch and Gigabit Ethernet, but that's a political issue with the major
transit ISPs, not a technical or financial one...)

Also, the negotiation sequences of PPP Control Protocols do depend on a lack
of re-ordering.

---

From: James Carlson <[email-masked]>
Date: Thu, 24 May 2001 08:44:18 -0400 (EDT)

> routine, along with 25% packet drop rates.

Thus the "well-designed" adjective in my message.  I know that some
routers do reorder as a matter of course.  They're broken.

> Also, the negotiation sequences of PPP Control Protocols do depend on a lack

True.  That's why I quoted section 1 of RFC 1661.

-- 
James Carlson, Internet Engineering       <[email-masked]>
SUN Microsystems / 1 Network Drive         71.234W   Vox +1 781 442 2084
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