The MPLS WG Archive

[Wang Yu <wangyu7707@263.net>]

Eric Gray,

thanks a lot!    
-----------------
01-4-26 10:37:00 You wrote:
>Yu,
>
>    In this answer, I will use the following shorthand:
>
>        NHCB = Next Hop Control Block
>        NHCBP = Next Hop Control Block Pointer
>        NHTCB = Next Hop Trigger Control Block
>        NHTCBP = Next Hop Trigger Control Block Pointer
>        JPLIG = Just Plain Lazy I Guess
>
>    On page 6, you should see a statement that the NHCBP
>"points to the control block which is used for switching over
>to a better LSP."
>
>    In section 3.2.6.1 Next Hop Trigger Control Block, on page
>24, you should find that the NHTCB contains two pointers -
>one to the original downstream LSP control block and one to a
>new Next Hop LSP Control Block.  I confess that - in at least
>this case - I'm guilty of not quite catching every inconsistency
>in the terminology used.  In this definition,
>
>         NHCB also equals Next Hop LSP Control Block, and
>         NHCBP also equals Next Hop LSP Control Block Pointer
>

>I believe this is vestigial since LSP is redundant and should
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>have been removed.
~~~~~~~~~~~~~~~~~~~
Do you mean Next Hop LSP Control Block and Next Hop LSP Control Block is useless and should have been removed? 
If the answer is no, what is the function of Next Hop LSP Control Block Pointer in LSP Control Block?
>
>    Does this help?
>
>--
>Eric Gray
>

In 3.2.1, LSP Control Block contains NHCBP (Next Hop LSP Control Block Pointer).
But it seems that NHCBP is not useless. 
It is NHTCBP that is used for switching over to a better LSP.
Certainly, NHCBP is useful in Next Hop Trigger Control Block.


 
             +-----------------------+
             | LSP Control Block     |
             | (original LSP)        |
             +-----------------------+
          (LSP      ^  |
           Control  |  | (Next Hop Trigger Control Block Pointer)
           Block    |  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
           Pointer) |  v
             +--------------------------------+
             | Next Hop Trigger Control Block |
             +--------------------------------+
                    ^  |
          (Trigger  |  | (New Next Hop LSP Control Block Pointer)
            Control |  |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
            Block   |  |
            Pointer)|  |
                    |  v
             +------------------------+
             | LSP Control Block      |
             | (for LSP: LSR-B, LSR-E,|
             |   LSR-D)               |
             +------------------------+




Wang Yu