Subject: [PCN] regarding consensus on selection encoding options

From: "Georgios Karagiannis" <[email-masked]>
Date: Wed, 12 Mar 2008 13:02:53 +0000

Hi all

Regarding the selection of the encoding option that is pending I would
like to propose the following.

In order to compare Option 1 and Option 3 presented by Toby yesterday 
during the PCN meeting (see uploaded slides), I think that it will be
usefull if certain clear comparison criteria are used, see below:

(1) Fullfils requirements imposed by RFC4774

(2) Minimum number of required DSCPs

(3) Minimum number of DSCPs required to be standardized

(4) Minimum number of DSCPs required as experimental

(5) Additional complexity required at the interior nodes

(6) Additional complexity required at edges (ingress + egress)

Below I will try to do this comparison.

Before doing this comparison I consider that in the most cases a
combination of CL-PHB for admission control and SM for flow termination
will be used.
Considering the above observation, then the comparison of Option 1 and
Option 3 using the criteria listed above could be as follows:

(1) Fullfils requirements imposed by RFC4774

Both Options (1 and 3) fullfil the requirements imposed by RFC4774.

2) Minimum number of required DSCPs
Option 1 requires 3 DSCPs;
Option 3 requires 2 DSCPs

(3) Minimum number of DSCPs required to be standardized

Both option 1 and option 3 require only one DSCP to be standardized,
i.e., the DSCP that identifies the new PCN PHB.

(4) Minimum number of DSCPs required as experimental

Option 1 requires two additional experimental DSCPs.
Option 3 requires one additional experimental DSCP.

(5) Additional complexity required at the interior nodes

Compared to Option 1, Option 3 requires more complexity at the interior
nodes because it requires to monitor and interchange values between the
DSCP and ECN fields. Option 1 needs only to monitor and change DSCP
values.

6) Additional complexity required at edges (ingress + egress)

Related to this criterion, note that Option 3 can fulfill the
requirements imposed by RFC 4774 only by Ip over Ip tunelling of the end
to end ECN traffic.

Option 3 requires Ip over Ip tunelling that is provided by the ingress
and egress edges. Therefore, compared to Option 1, Option 3 requires
more complexity at the ingress and egress edges.

Best regards,
Georgios
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