Re: [mpls-linux-general] about LDP code documentation

[James R. L. <jl...@mi...>]

On Thu, Nov 01, 2001 at 09:48:32PM -0800, Mouli T wrote:
> Hai,

Hello,

>    I am doing code study of LDP. I got the flow but
> i can not able to find the relation between data
> structures 
> 
>            particularly for
> Session <->  fs  <->  inlabel  <-> outlabel <-> fec

Heh heh, good to see someone actually looks at that document :-)

>                                           -----
>                                  in      |     |      
>                       .------------------| Fec |-out
>                      |             |     |     |
>                      |             |      -----
>                   ------         ------
>                  |  FS  |-------|  FS  |
>                   ------         ------
>                      |             |
>                  ---------
>            .----| session |----.
>           |      ---------      |
>        ------     ------     ------
>       | Attr |---| Attr |---| Attr |
>        ------     ------     ------
>          |           |          |
>       in label    in label   in label
> 
> Could someone please help me,is there any document
> for the above and for "LDP code".

The problem is that there is a N:M relationship between a FEC and the
sessions.  For each FEC in the database, LDP can hear info about it from
multiple sessions.  Each session can will hear info about many FECs.  The
info being stored for each FEC,session pair is the FEC attributes.

There are many ways to store this type of info, I choose to build
a tree based on the FECs and store a list of sessions that have heard info
about this FEC.  Each session also keeps track of the full list of FECs that
it has received info about.  So the one thing missing from the picture
above is a line between a FS and an Attr.  Each FS has a link to the session
and the attr that the session has learne for the FEC in question.

                          -----
                         |     |      
               .---------| Fec |---------.
               |         |     |         |
               |          -----          |
               |    Downstream FS list   |
               |  ------         ------  |
               '-|  FS  |-------|  FS  |-'
                  ------\        ------
                    |    `-------------------.
                    |                         \---------
    .--------------------------------.        | session |
    |                                |         ---------
    |  ------     ------     ------  |
    `-| Attr |---| Attr |---| Attr |-'
       ------     ------     ------

This piture is a more accurate picture of the FEC <-> Attr relationship.
Each FEC has multiple FS.  Each FE represents one session that has learned
info about this FEC.  More then one piece of info can be learned by a session
for a particular FEC, so each FS can have a list of Attr, which is all of the
info learned about this FEC by this session.  Take note that each FEC entry
has a list of FS for upstream and downstream sessions.


>    
> regards
> Mouli
> 
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-- 
James R. Leu