Subject: Re: [MPLS-OPS]: Confusing Terms

From: "wu min" <[email-masked]>
Date: Tue, 02 Apr 2002 07:40:53 +0000

Hi,

Thank you for answering my questions.

Okay now I am sure that the 'distribution' is a separate process from 
'binding'. I was confused since I read "MPLS: Technology and Applications" 
by Davie & Rekhter. They introduced the terms local binding and remote 
binding. And of course these do not involve any distribution, just purely 
the origin of label binding occurance. Immediately after that, they 
described upstream/downstream bindings as way of populating the forwarding 
table with labels that are of local/remote bindings. In their description, 
they also mentioned the direction of label distribution. And that has caused 
me to confuse the true meaning of 'distribution' and 'binding' used in MPLS. 
Probably they mentioned the flow of label binding information just for the 
sake of making their statement complete. To end this paragraph, 
upstream/downstream binding is orthogonal to upstream/downstream 
distribution. Full stop.

Unfortunately I am still confuse with 'distribution' terms. The downstream 
on demand and unsolicted downstream label distributions define how and when 
label is being distributed. However, independent and ordered controls also 
describe similar label distribution processes. And since you said ordered 
control can only be achieved by downstream on demand label distribution, the 
question is, what are their differences to warrant them with different 
terms? Or does ordered control mean downstream on demand? (the same is true 
for independent control if it can only be achieved by unsolicted downstream 
label distribution.)

> > 3. Given the following control-driven scenario:
> >
> > ------a           __________
> >        \         /          \
> >         c---d---|  142.23.5  |
> >        /         \__________/
> > ------b
> >
> > The diagram above shows a portion of a network. Let a, b, c and d be the
> > LSRs. Let LSR d attached to network 142.23.5. At any moment LSR d 
>assigns a
> > label #30 to an FEC which describes the address prefix 142.23.5 and
> > advertises the binding to c. LSR c determines that it will use LSR d as 
>its
> > next hop to deliver packets to 142.23.5 thus assigns label #56 and #21 
>for
> > that FEC and advertises to its upstream neighbours a and b respectively.
> > Both upstream LSRs accept the binding information and perform the same
> > binding procedures. Obviously the path establishment here uses 
>unsolicited
> > downstream label binding. The question is, what form of distribution 
>control
> > is this? My bet is that it should be ordered control.
>
>Using two different labels suggests to me you're thinking about doing this
>over ATM. There you should be doing downstream on demand ordered control.
>So I would be surprised to see c independently assigning labels.
>If the same label were advertised to both neighbors, then MPLS over frame
>is probably in place doing unsolicited unordered control.

My example does not favour for any specific architecture. My question is 
plain; is it an ordered control or independent control label distribution?

Your answer I believe is unsolicited independent control and you are the 
second person to give this answer after Rick Gallaher. However, I have doubt 
with the answer. In my example, notice that the label distribution is 
control-driven triggered by routing information and it starts from the 
egress up to the rest of the LSR in an orderly manner (it was my mistake not 
to clearly state this earlier but it should be obvious from my statement.) 
Both RFC3031 and the book "MPLS: Technology and Applications" state that if 
the label distribution is done in orderly fashion from any one end to 
another, it is an ordered control label distribution. If this is true that 
the example is an ordered control, then I have answer my own previous 
question -- ordered control does not mean downstream on demand.

In Rick's reply to my questions, he pointed out that independent control can 
be achieved by downstream on demand but he has never seen this kind of 
combination before in practice. Anyone can give an example of this, please?

-Tze Ven

_________________________________________________________________
Send and receive Hotmail on your mobile device: http://mobile.msn.com

---

From: "wu min" <[email-masked]>
Date: Tue, 02 Apr 2002 07:40:53 +0000

Hi,

-Tze Ven