Re: [PWE3] comments and questions to draft-stein-pwe3-ethpwcong-00.txt

Greg, Linda and all,
IMHO the data plane of S-PEs is not different (in any way) from that of any other LSR: they terminate (pop) all the labels above the PW label, then swap and forward based on the PW label. They are not expected to look a the CW; this is only possible for T-PEs which understand the CW structure (which is specific per PW type).

And of course drop eligibility indicators can be encoded in the EXP bits of the label stack, thus allowing any LST (including S-PE) to differentiate between PW packets carrying drop-eligible ("yellow")and not drop drop eligible ("green") frames.

My 2c,
     Sasha

________________________________
From: pwe3-bounces@ietf.org [mailto:pwe3-bounces@ietf.org] On Behalf Of Greg Mirsky
Sent: Wednesday, February 10, 2010 7:49 PM
To: Linda Dunbar
Cc: pwe3@ietf.org
Subject: Re: [PWE3] comments and questions to draft-stein-pwe3-ethpwcong-00.txt

Dear Linda and Yaakov,
I see more value of carrying Drop Eligibility in a PW CW for MS PW case. Then S-PE can check the encoded value and drop packets accordingly. I don't think that intermediate LSR, whether on SS-PW or MS-PW, can look up the Control Word and make any decision based on its value. For that Drop Eligibility must be encoded into outmost label, similar to mapping 802.1p bits into TC field.

Regards,
Greg

On Wed, Feb 10, 2010 at 9:04 AM, Linda Dunbar <ldunbar@huawei.com<mailto:ldunbar@huawei.com>> wrote:

Yaakov,

I have some questions on your draft:

Section 3 Drop Eligibility Indication: your draft indicates that Ingress PE will encode the Drop Eligibility bit in the Control word and the Egress node will drop those frames if congestion occurs. I am a little puzzled on this.
The Egress node will put the original Ethernet frame back to the Ethernet link. So the Drop Eligibility bit is in the Ethernet frame. Why need the PW's Control word to pass the information?

I see one useful application of encoding Drop Eligibility bit in the PW's Control Word: the intermediate node along the PW path can drop those frames should congestion occur along the way. Will it be possible?

Regards, Linda Dunbar

Advanced Technology Dept, Wireline Networks,
Huawei Technologies, Inc.

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