Subject: RE: [PCN] Simplicity, Scalability, Robustness

From: <[email-masked]>
Date: Fri, 13 Oct 2006 20:30:37 +0100

Michael
 Thanks for this as well. I'm basically proposing to include it in the
new version of the cl-architecture draft.

Suggesting instead of the bullet "Networks are dimensioned ..." (which
I'm not completely comfortable with), a bullet about PCN controlling the
load dynamically:-

o	The admitted load is controlled dynamically. Therefore it adapts
as the traffic matrix changes, and also if the network topology changes
(eg after a link failure). Hence an operator can be less conservative
when deploying network capacity, and less accurate in their prediction
of the traffic matrix. Also, controlling the load using statically
provisioned capacity per ingress (regardless of the egress of a flow),
as is typical in the DiffServ architecture [RFC2475], can lead to
focussed overload: many flows happen to focus on a particular link and
then all flows through the congested link fail catastrophically (Section
6.2).

thanks
phil
-----Original Message-----
From: Michael Menth [mailto:[email-masked]] 
Sent: 22 September 2006 14:42
To: [email-masked]
Subject: [PCN] Simplicity, Scalability, Robustness

The proposed network admission control (NAC) method is simple, scalable,

and robust because

- Per flow states are only required at the ingress routers to prevent 
non-admitted CL traffic from entering the CL region, other network 
entities are not aware of individual flows.
- Each router has a separate admission saturation and excess traffic 
marker for each of its links. These markers operate on the overall CL 
traffic of the respective link. Therefore, there are no scalability 
concerns.
- The information of these measurements is implicitly signaled to the 
respective egress routers by the marks in the packet headers and no 
protocol actions are required.
- The egress routers measure the rates of all received, admission 
saturation marked, and excess traffic marked packets separately for each

ingress router.  These meters operate on the overall CL traffic of the 
respective link. Therefore, there are no scalability concerns as long as

the number of ingress routers is sufficiently small (or at least not 
overwhelmingly large).
- Feedback signaling is required between all pairs of ingress and egress

routers and the signaled information is on the basis of the 
corresponding b2b CL aggregate, i.e., it is also unaware of individual 
flows.
- The admissible link rates can be chosen small enough and the 
supportable link rates can be chosen large enough that admitted traffic 
can be carried after a rerouting in failure cases. This is an important 
feature as QoS violations in core networks due to link failures are more

likely than QoS violations due to increased traffic volume.
- Networks are dimensioned in such a way that packet delay and loss or 
excessive call blocking are unlikely. Thus, the effect of admission 
control is usually not visible. It can be viewed as an insurance to 
prevent congestion in exceptional scenarios such as excessive user load 
or redirected traffic due to single link failures (see point above).
- The preemption function complements AC to recover from sudden 
unexpected surges of already admitted CL traffic on the links. Such 
scenarios are very unlikely but not impossible. They can be caused by 
large network failures that redirect lots of admitted CL traffic to 
other links, by malfunction of the measurement-based AC in the presence 
of a flash crowd of new admission requests, or by malfunction of the 
measurement-based AC in the presence of admitted flows that send for a 
while with an atypically low rate and increase their rates in a 
concerted way.

-- 
Dr. Michael Menth, Assistant Professor
University of Wuerzburg, Institute of Computer Science
Am Hubland, D-97074 Wuerzburg, Germany, room B206
phone: (+49)-931/888-6644, fax: (+49)-931/888-6632
mailto:[email-masked]
http://www3.informatik.uni-wuerzburg.de/research/ngn

_______________________________________________
PCN mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/pcn

_______________________________________________
PCN mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/pcn