thanks to the authors for the well written draft!
Some comments below.
///Reiner
1. The subnetwork's retransmission persistency:
A subnetwork's retransmission persistency, i.e., for how long should a link
layer delay (e.g., in terms of milliseconds) an IP packet in an attempt to
transmit it over the link before it discards the packet, is an important
issue for subnetwork designers. However, I feel that the draft is too fague
on this matter:
"It is important to recognize that a
subnetwork can go too far in attempting to provide error recovery
services in the Internet environment. Subnet reliability should be
"lightweight", i.e., it only has to be "good enough", *not* perfect."
A more concrete alternative would be to say something along the following
lines:
Subnets that do not distinguish between delay sensitive (e.g., real-time or
streaming multimedia) and reliable flows (e.g., TCP, Reliable Multicast)
should implement a low retransmission persistency (on the order of a few 10
milliseconds) [IS95] [GSM]. This is necessary to not interfere with the
delay requirements of delay sensitive flows. On the other hand, subnetworks
that are capable of separating reliable flows should implement a high
retransmission persistency for such flows. However, a single IP packet may
never be delayed by more than the Maximum Segment Lifetime (MSL) of 240
seconds defined for TCP [RFC1122].
2. Minor detail in the section on "How TCP Works":
There is says: "Queues provide output-buffering on links that are
momentarily oversubscribed."
However, queues also provide input-buffering on links and in fact packets
can get dropped there, too, when the host/router is at high processor load.
3. Recovery from Subnetwork Outages:
To the sentence: "If it cannot
do this, then the subnetwork should hold onto at least some of the
packets it accepts during an outage and attempt to deliver them when
the subnetwork comes back up.", I propose to add the following sentence:
However, none of such packet may be held for more than the Maximum Segment
Lifetime (MSL) of 240 seconds defined for TCP [RFC1122].
Instead of the sentence: " Note that it is *not* necessary to avoid any and
all packet drops during an outage.", I propose the following refinement:
As long as the queue management policy allows (never queue packets without
reasonable bounds, e.g., not more than a common bandwidth*delay product)
the subnetwork should avoid dropping any packets. Beyond that it should
start dropping from front to give an early congestion signal to the TCP sender.
4. The "Quality of Service, ..." section
Although, I very much like the section and wish we could really implement
it that way, I don't understand the discussion about the TOS field [RFC1349].
The definitions of the TOS field are obsolete and have been replaced by the
definition of the differentiated service field [RFC2474 (proposed standard)] :-(
This archive was generated by hypermail 2b29 : Mon Jan 28 2002 - 09:12:24 EST