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

From: Linda Dunbar <[email-masked]>
Date: Wed, 10 Feb 2010 11:04:53 -0600

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.

---

From: Greg Mirsky <[email-masked]>
Date: Wed, 10 Feb 2010 09:48:48 -0800

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 <[email-masked]> wrote:

> PW’s Control word to pass the information?
>
>
>
> I see one useful application of encoding Drop Eligibility bit in the PW’s
> _______________________________________________
> pwe3 mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/pwe3
>
>

---

From: Alexander Vainshtein <[email-masked]>
Date: Wed, 10 Feb 2010 20:17:44 +0200

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: [email-masked] [mailto:[email-masked]] On Behalf Of Greg Mirsky
Sent: Wednesday, February 10, 2010 7:49 PM
To: Linda Dunbar
Cc: [email-masked]
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 <[email-masked]<mailto:[email-masked]>> wrote:

Yaakov,

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

_______________________________________________
pwe3 mailing list
[email-masked]<mailto:[email-masked]>
https://www.ietf.org/mailman/listinfo/pwe3

---

From: Linda Dunbar <[email-masked]>
Date: Wed, 10 Feb 2010 14:28:54 -0600

Greg, 

Thanks for pointing out that MS-PW could use the bit in Control word as
criteria of dropping packets. I think it is a good application. 

Sasha: 

Do you mean that switching PE for MS-PW will not understand CW of PW? 

Encoding "drop eligibility" to the EXP bits is possible. But most service
providers have used up all bits in EXP to represent 8 levels of DiffServ.
There is no bit left in EXP field to represent the "drop eligibility" bit. 

Linda

  _____  

From: Alexander Vainshtein [mailto:[email-masked]] 
Sent: Wednesday, February 10, 2010 12:18 PM
To: Greg Mirsky; Linda Dunbar
Cc: [email-masked]
Subject: 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: [email-masked] [mailto:[email-masked]] On Behalf Of Greg
Mirsky
Sent: Wednesday, February 10, 2010 7:49 PM
To: Linda Dunbar
Cc: [email-masked]
Subject: Re: [PWE3] comments and questions to
draft-stein-pwe3-ethpwcong-00.txt

Dear Linda and Yaakov,

Regards,
Greg

Yaakov, 

Regards, Linda Dunbar

---

From: Alexander Vainshtein <[email-masked]>
Date: Thu, 11 Feb 2010 07:20:31 +0200

Linda,
Quoting from RFC 5659, Section 6:
The receiving S-PE swaps the existing PW demultiplexer for the demultiplexer of the next segment and then sends the PDU over transport tunnel in PSN2.  Where the ingress and egress PSN domains of the S-PE are of the same type, e.g., they are both MPLS PSNs, a simple label swap operation is performed, as described in Section 3.13 of RFC 3031.
This document also states that
Native service PDUs from the CE are passed through an Encapsulation Layer and a PW demultiplexer is added at the sending T-PE
But processing at the Encapsulation layer  (i.e., at the layer that deals with the CW) is not mentioned as part of the S-PE functionality.  For MPLS MS-PWs this is fully consistent with the normal LSR behavior as defined in 3031.

IMO this confirms that CW processing is "out of bounds" for T-PEs.

Regards,
     Sasha

________________________________
From: Linda Dunbar [[email-masked]]
Sent: Wednesday, February 10, 2010 10:28 PM
To: Alexander Vainshtein; 'Greg Mirsky'
Cc: [email-masked]
Subject: RE: [PWE3] comments and questions to draft-stein-pwe3-ethpwcong-00.txt

Greg,
Thanks for pointing out that MS-PW could use the bit in Control word as criteria of dropping packets. I think it is a good application.

Sasha:

Encoding “drop eligibility” to the EXP bits is possible. But most service providers have used up all bits in EXP to represent 8 levels of DiffServ. There is no bit left in EXP field to represent the “drop eligibility” bit.

Linda

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

Greg, Linda and all,

My 2c,
     Sasha

Regards,
Greg

Yaakov,

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

---

From: Alexander Vainshtein <[email-masked]>
Date: Thu, 11 Feb 2010 08:41:07 +0200

Linda, and all,
On the second thought:
If T-PE could use the drop eligibility indicator (DEI) in the CW, this would, IMHO and FWIW, result in an operational mess, since different DEI  would be looked at by the T-PE and P routers (of course, P routers only look at the top label stack entry, including the label and EXP bits).
E.g., if DE cannot be encoded into the EXP bits, congested P routers would drop packets indiscriminately, while congested T-PEs would respect DEI... there is no reason to expect that congestion only occurs in S-PEs, right?
Regards,
     Sasha

________________________________
From: [email-masked] [mailto:[email-masked]] On Behalf Of Alexander Vainshtein
Sent: Thursday, February 11, 2010 7:21 AM
To: Linda Dunbar
Cc: [email-masked]
Subject: Re: [PWE3] comments and questions to draft-stein-pwe3-ethpwcong-00.txt

Linda,

Regards,
     Sasha

Greg,

Sasha:

Encoding "drop eligibility" to the EXP bits is possible. But most service providers have used up all bits in EXP to represent 8 levels of DiffServ. There is no bit left in EXP field to represent the "drop eligibility" bit.

Linda

Greg, Linda and all,

My 2c,
     Sasha

Regards,
Greg

Yaakov,

Regards, Linda Dunbar

---

From: Linda Dunbar <[email-masked]>
Date: Thu, 11 Feb 2010 10:58:55 -0600

Sasha and all, 

I totally agree with you that DEI should be processed by both P routers and
S-PEs. 

Therefore, a better way is to encode the DEI into EXP bits. Since EXP field
has 3 bits which can only represent 8 levels, some encoding is needed to map
8 priorities and 1 DEI into the 3 bits. IEEE802.1Q has already specified the
recommended encoding table. It is specified by IEEE802.1Q Section 6.9.3
Priority Code Point encoding:

Linda Dunbar

  _____  

From: Alexander Vainshtein [mailto:[email-masked]] 
Sent: Thursday, February 11, 2010 12:41 AM
To: Linda Dunbar
Cc: [email-masked]
Subject: RE: [PWE3] comments and questions to
draft-stein-pwe3-ethpwcong-00.txt

Linda, and all,

On the second thought:

If T-PE could use the drop eligibility indicator (DEI) in the CW, this
would, IMHO and FWIW, result in an operational mess, since different DEI
would be looked at by the T-PE and P routers (of course, P routers only look
at the top label stack entry, including the label and EXP bits).

E.g., if DE cannot be encoded into the EXP bits, congested P routers would
drop packets indiscriminately, while congested T-PEs would respect DEI...
there is no reason to expect that congestion only occurs in S-PEs, right?

Regards,

     Sasha  

  _____  

From: [email-masked] [mailto:[email-masked]] On Behalf Of
Alexander Vainshtein
Sent: Thursday, February 11, 2010 7:21 AM
To: Linda Dunbar
Cc: [email-masked]
Subject: Re: [PWE3] comments and questions to
draft-stein-pwe3-ethpwcong-00.txt

Linda,

The receiving S-PE swaps the existing PW demultiplexer for the demultiplexer
of the next segment and then sends the PDU over transport tunnel in PSN2.
Where the ingress and egress PSN domains of the S-PE are of the same type,
e.g., they are both MPLS PSNs, a simple label swap operation is performed,
as described in Section 3.13 of RFC 3031.

Native service PDUs from the CE are passed through an Encapsulation Layer
and a PW demultiplexer is added at the sending T-PE

But processing at the Encapsulation layer  (i.e., at the layer that deals
with the CW) is not mentioned as part of the S-PE functionality.  For MPLS
MS-PWs this is fully consistent with the normal LSR behavior as defined in
3031.

Regards,

     Sasha

  _____  

Greg, 

Sasha: 

Linda

  _____  

Greg, Linda and all,

My 2c,

     Sasha

  _____  

Dear Linda and Yaakov,

Regards,
Greg

Yaakov, 

Regards, Linda Dunbar