The MPLS WG Archive

["wu min" <made_in__china@hotmail.com>]

Hi,

I found out the terms used to describe the label distribution are very 
confusing especially between 'label binding' and 'label distribution 
control'. They seems to be more or less describing one another. Here I try 
to re-state the meaning of the terms and please correct me if I am wrong or 
miss any important stuffs.

I assume 'label binding' and 'label distribution method' refer to the same 
thing. In fact, it should be 'label binding and distribution method' since 
it involve label binding and label distribution (I am not sure whether I am 
right here.)

Label Bindings/Label Distributions Methods
==========================================
1. Downstream label binding
     - Unsolicited Downstream label binding
     - Downstream on demand label binding
2. Upstream label binding

These modes define who (upstream or downstream) responsible for 'generating' 
a label for binding an FEC that is to be 'advertised' to the neighboring 
peers.

A) In unsolicited downstream mode, a downstream LSR locally generates a 
label for binding an FEC and advertises its label binding information to its 
neigbouring peers without being requested.

B) In downstream mode on demand mode, the downstream LSR only distributes a 
label when explicitly requested from an upstream LSR for label binding for 
an FEC.

C) In upstream mode, an upstream LSR loacally assigns a label to an FEC and 
advertises to its neighbouring peers.


Label Distribution Controls
===========================
1. Independent control
2. Ordered control

These distribution controls define the 'decision' of an LSR with respect to 
other LSRs in establishing an LSP path.

A) For the independent control, the decision of an LSR to assign a label to 
an FEC and to advertise that label binding to its neighbouring peers are 
made independently with respect to other LSRs. It is used in support of 
destination-based routing. It uses unsolicited downstream label binding in 
achieving path setup.

B) For the ordered control, label assignment proceeds in orderly fashion 
from one end of LSR to the other. The LSP establishment may be iniated by 
the infgress or egress end of the LSP. It uses downstream on demand label 
binding to obtain labels for binding to form the path.


Questions:
----------
1. Is it possible for the independent control form of path establishment 
accomplish its task through downstream on demand label bindings?

2. Is it possible for the ordered control to setup path using downstream 
label bindings?

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.

Anyone can help me?


Thank you in advance.

-Tze Ven


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