Subject: How to use the "Source Control Flag" in GVPLS

From: lidefeng <[email-masked]>
Date: Mon, 28 Apr 2003 16:51:51 +0800

Hi,all,

In section "5.4 Information Model entities" of
draft-radoaca-ppvpn-gvpls-01.txt,there is a concept of "Source Control
Flag",I don't know how to use it in implementation,and what this field is
composed of ? And it states in the draft that"The VC-Labels calculation and
the MAC source learning process are dependent on this flag.", I don't know
how the VC-label calculation and MAC source learning process depend on this
flag,could you please explain it in detail? Thank you!

Li Defeng

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From: "Vasile Radoaca" <[email-masked]>
Date: Mon, 28 Apr 2003 11:58:04 -0400

Li,

In the original definition of the PW, the VC-Label was suppose to represent
the destination of the outgoing port [physical or virtual]. However, in the
VPLS scope, in order to emulate a LAN in the VPLS core,  the N-PE/U-PE needs
to learn the source of the originating packets. There are different ways to
provide such mechanism: 
 - to overload the VC-Label semantic, with the source indication. For
example this is the case of the  vkompella-lasserre-vpls draft. Because the
MAC learning is done entirely in the N-PE device, the VC-Label needs to
represent both the Source and the Destination N-PE. This model doesn't scale
from both MAC learning perspective and for the number of VC-Labels.  In
order to resolve the VC_Labels issue, the vpls model propose to extend with
an access network [via Hub-and Spoke model, or via Q-in-Q]. The MAC learning
accumulation is still not solved, instead is increasing pretty well if you
consider that now you aggregate a larger access network. The other problem
that Q-in-Q/Spoke model added is the granularity of the end-to end circuit.
Because the source is indicated only from the N-PE device, there is no way
to check a circuit from end-to-end Spoke. 
   If the overload solution is used in the distributed model, then the
number of VC-Labels would increase with an order of magnitude [O(N2)].
 
 - to leave the VC-Label semantic as defined in the PWE3 and to represent
the SRC in the Control Word. The solution solve both the non-distributed
model and also the distributed model. The number of VC-Labels would stay
relative low, regardless of the number of U-PE/ N-PE devices. Also, the
issue of the circuit granularity end-to-end would no be  a problem - the SRC
can indicate the U-PE or N-PE device.

Now, because GVPLS is built on top of vpls, the solution tries to preserve
the overload model of the VC-Label, and in the same time to offer an
alternative for performance and scalability, by using the Control Word
model. The Source Control Flag [SRC-Flag] indicates such options - and it is
provisioned and signaled in the control plan.
If the SRC-Flag indicates the overload model, then a VC-Label is calculated
for each pair (local U-PE[N-PE] and remote U-PE[N-PE]).
If the SRC-Flag indicates the Control word model, then a VC-Label is
calculated only for the local U-PE[N-PE] device as per PWE3 model.

Cheers 
  Vasile 

-----Original Message-----
From: lidefeng [mailto:[email-masked]] 
Sent: Monday, April 28, 2003 4:52 AM
To: [email-masked]
Subject: How to use the "Source Control Flag" in GVPLS

Hi,all,

Li Defeng