Subject: A few concerns about diff-services

From: Shivkumar Kalyanaraman <[email-masked]>
Date: Sat, 22 Nov 1997 15:08:23 -0500 (EST)

Folks,

Here are some concerns I have about diff-servs, esp the proposal of 
Clark/Wroclawski. Pardon me if I am stating things which have already been
taken care of.

- implementation of the "in"/"out" feature inside the network. 
  A: Have one FIFO Queue for both "in" and "out" packets but handle the
     drop etc prefentially using RIO. 
	My concern is: how to you do the buffer allocation/dropping so
        that "in" packets are not affected by "out" packets. Do you
	keep a count of "in" and "out" packets and perform RIO based on these
	counts (i.e dropping the next "in" or "out" packet coming inside
	the queue ?)

	Qn: is there a performance comparison between these two
            approaches ?

  B: Have two FIFO queues. 
	Concern: How do you schedule between queues, esp due to the fact
                 that if more than 3 packets arrive out of order, TCP
                 will retransmit ? 
	{These out-of-order packets would most likely be "out" packets
         anyway. But does this additional performance penalty does not
         seem to be warranted }

	Qn: Is there a performance comparison between different scheduling
            schemes studying the impact on TCP performance ?

- The "fairness" of the approach (if it is a goal) is unclear to me, esp
if all sources declare that they want zero-guaranteed rate and rest best
effort. I would suppose that it will be easy to construct a case when 
the "in" queues are empty and the traffic is in the "out" queues. The
question then arises - why the profile meter for these sources ?

- For interoperability between int-serv and diff-serv:
  If you bunch the "in" packets of all profiles into one FIFO, won't the 
  delay parameters be affected ?

- Use of "profile meters":
  The user negotiates a profile with the ISP and the ISPs negotiate
  profiles with each other. Can/should these profiles be (re)negotiated 
  dynamically ? Does the user choose a separate profile per group of
  applications (audio/video apps vs data apps) ?

- I find it extremely difficult to do simulations with 1000s and miilions
  of sources. Could folks point me to techniques/simulators which can
  do this ?

-Regards
Shiv
===
Shivkumar Kalyanaraman   
Assistant Professor, Dept of Electrical, Computer and Systems Engg,
Rensselaer Polytechnic Institute (RPI)
110, 8th Street, Rm JEC 6042, Troy NY 12180-3590
Ph: 518 276 8979  Secy (6313)	 Fax: 518 276 2433
Email: [email-masked]
Internet: http://www.ecse.rpi.edu/Homepages/shivkuma

---

From: [email-masked] (Hyogon Kim)
Date: Sat, 22 Nov 1997 17:08:34 -0500 (EST)

Shiv,

I do think some of your concerns are dealt with in Clark/Wroclawski and
the discussions in the list so far touched them as well. To summerize,

- it's better to have a single queue in Clark/Wroclawski to prevent
	packet reordering
- by setting maxth(out) <= minth(in) for instance, you can protect
	"in" packets - don't need to count them
- yes, it will increase the queueing delay, since you have a full RED
	buffer for "out" packets and more i.e. for "in" packets
	cf. mentioned in Clark/Wroclawski draft
- yes, profiles can be richer than just source address

Hyogon

>Internet: http://www.ecse.rpi.edu/Homepages/shivkuma

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