Subject: [magma] IGMPv3 question

From: [email-masked]
Date: 28 Oct 2006 15:43:19 +0200

Hello, 
I would like kindly ask to answer my question.  Section 6.4.1 of RFC 3376 contains the following description of a router behavior in response to Current-State Record:

Router State   Report Rec'd  New Router State         Actions
   ------------   ------------  ----------------         -------

   INCLUDE (A)    IS_IN (B)     INCLUDE (A+B)            (B)=GMI

   INCLUDE (A)    IS_EX (B)     EXCLUDE (A*B,B-A)        (B-A)=0
                                                         Delete (A-B)
                                                         Group Timer=GMI

   EXCLUDE (X,Y)  IS_IN (A)     EXCLUDE (X+A,Y-A)        (A)=GMI

   EXCLUDE (X,Y)  IS_EX (A)     EXCLUDE (A-Y,Y*A)        (A-X-Y)=GMI
                                                         Delete (X-A)
                                                         Delete (Y-A)
                                                         Group Timer=GMI
Entry Exclude(X,Y) means that all sources in set Y will not be forwarded by a router. Entries in set X are all sources that were requested by some hosts to be excluded, but router also received from other hosts Include report for the same souurces X. It means that there is a conflict because some receivers wish to receive data form sources X and some not. 
In the light of those facts case number two in the cited text is clear. Router is in state Include(A), gets request to exclude B so it transits to state Exclude (A*B, B-A).
However I do not understand intention of case 3. Router is in state Exclude(X,Y) and gets report IS_IN(A). The result is Exclude(X+A,Y-A). Set Y-A is straightforward, some of sources in set A required to be forwarded can also be in set Y. Though, I do not understand meaning of X+A. This set should contain only the conflicting sources. So it seems to be that it should be X + (common part of A and Y). In order words it should be X + (A*Y). Can you please explain that to me?
Thank you in advance for your help
Tomasz Bartczak

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From: "Ashish Yadav" <[email-masked]>
Date: Mon, 30 Oct 2006 10:16:19 +0530

Hi,

In the case EXCLUDE( X, Y ),  Y are the sources from where router has
explicitly got an exclude report.

Router has received include report from some host(s) for sources in X
while exclude reports from some other host(s) for the sources in X.

So, X has been added in conflicting list.

The sources from which no request has been received are assumed to be
excluded implicitly.

On receiving IS_IN ( A ), include report has been received for sources
in A, that means they should be put into the conflicting list, i.e. ( X
+ A ).

The ( X + A) comes from the implicit EXCLUDE for the sources for which
no report has been received.

If exclude reports had ever been received for the sources in A, the
sources should be removed from exclude list Y, i.e. ( Y - A ).

Warm Regards,

Ashish Yadav

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] 
Sent: Saturday, October 28, 2006 7:13 PM
To: [email-masked]
Subject: [magma] IGMPv3 question

Hello, 

I would like kindly ask to answer my question.  Section 6.4.1 of RFC
3376 contains the following description of a router behavior in response
to Current-State Record:

                                                         Delete (A-B)

                                                         Group Timer=GMI

                                                         Delete (X-A)

                                                         Delete (Y-A)

                                                         Group Timer=GMI

Entry Exclude(X,Y) means that all sources in set Y will not be forwarded
by a router. Entries in set X are all sources that were requested by
some hosts to be excluded, but router also received from other hosts
Include report for the same souurces X. It means that there is a
conflict because some receivers wish to receive data form sources X and
some not. 

In the light of those facts case number two in the cited text is clear.
Router is in state Include(A), gets request to exclude B so it transits
to state Exclude (A*B, B-A).

However I do not understand intention of case 3. Router is in state
Exclude(X,Y) and gets report IS_IN(A). The result is Exclude(X+A,Y-A).
Set Y-A is straightforward, some of sources in set A required to be
forwarded can also be in set Y. Though, I do not understand meaning of
X+A. This set should contain only the conflicting sources. So it seems
to be that it should be X + (common part of A and Y). In order words it
should be X + (A*Y). Can you please explain that to me?

Tomasz Bartczak

 

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