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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
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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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