Subject: [Tsvwg] PPS: influence of route changes

From: "Geib, Ruediger" <[email-masked]>
Date: Thu, 22 Jan 2004 09:57:57 +0100

Dear Naotaka,

accounting for the influence of route changes to me is an 
open issue with respect to PPS. What happens after a route 
change is that some routers recognise a sudden increase in 
High Subclass traffic without prior Middle Subclass traffic 
(others notice a sudden decrease).

If service quality should not suffer from this effect, 
resources must be overprovisioned prior to its occurence.
If resources are to be re-provisioned as a consequence of a 
route change, a rather fast signaling protocol is required. 
This protocol must further accurately determine the 
resources required. That sounds complex and it may 
spoil the "state free" benefits of pps.

Assuming overprovisioned High Subclass resources as a solution, 
which value is added by an information on route change 
occurences? It doesn't decrease the load, it only helps to 
distinguish the effect of a route change from a DoS attack or 
other kinds of misuse. I'm not sure whether PPS is a reasonable 
architecture if it allows for DoS attacks and other kinds of 
misuse. So excluding this cause for a spontaneous load increase, 
the load increase itself indicates a route change. A 
node will discard Middle Subclass traffic for a while. What it 
further may do is marking High Subclass Traffic by something 
as ECN. Many voice and video codecs are able to decrease 
sending rate. After a while, "normal" operation is resumed and
these ECN marks dissapear.

What are your thoughts about how to deal with route changes in 
a PPS network?

Regards, Rudiger

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From: "Geib, Ruediger" <[email-masked]>
Date: Thu, 22 Jan 2004 12:20:29 +0100

Naotaka,

thanks for your fast reply. I think we agree on the best way 
to deal with route changes in a pps architecture. Some 
comments and a clarification in line.

Regards, Rudiger

----snip----

|In the above example, the link would be 100Mbps and
|up to 40Mbps can be used in normal operation.
|In the case of route change,
|the link can tolerate upto 80Mbps with High class.
|The values of 40Mbps and 80Mbps are configured and no 
|signalling is necessary.
|Off course, it can not tolerate more than double traffic,
|but it is a matter of network engineering.
|If I carefully design the network, it is not a problem I believe.

I fully agree.

|This concept can easilly be exteded when MF-PHB is applied to 
|MPLS network.

Yes. Another benefit of pps.

------snip--------------

The following section just should say that DoS attacks and 
other misuse aren't expected to be an issue for PPS. To 
clarify this, I've argued from an opposite viewpoint: if 
attacks and misuse were an issue for pps, nobody would 
deploy it.

| >. I'm not sure whether PPS is a reasonable
| >architecture if it allows for DoS attacks and other kinds of
|*************
| >misuse. So excluding this cause for a spontaneous load increase,
| >the load increase itself indicates a route change. A
|************
| >node will discard Middle Subclass traffic for a while. What it
| >further may do is marking High Subclass Traffic by something
| >as ECN. Many voice and video codecs are able to decrease
| >sending rate. After a while, "normal" operation is resumed and
| >these ECN marks dissapear.
|I sorry but I do not understand the two lines between *****.
|
|Yes, DoS is an issue of PPS, but as is described in the 
|framework draft, I assume two protecting point: edge router and 
|media monitor server.