Re: hierarchical, multicast routing etc

[Polly Huang <huang@catarina.usc.edu>]

> On Wed, 30 Sep 1998, Padmaparna Haldar wrote:
> 
> > On Wed, 30 Sep 1998, Polly Huang wrote:
> > 
> > > It seems to me that the following error is due to the change in 
> > > link/node indexing for hierarchical routings. Am I right, Padma?
> > 
> > Hierarchical rotuing uses the same link indexing (using node ids) as does
> > flat rtg.
> 
> I shouldn't be using hierarchical routing; that only kicks in when you 
> have more than one routing level, yes? Not with:
> 
> $ns set-address-format hierarchical 1 9
> 
> or similar. In any case, since they use the same link indexing, it's
> a moot point.
> 
> 
> > looks like either the link_ array was not created completely or
> > CtrMcast is trying to use a non-existing link?
> 
> CtrMcast encountered a simplex link, and apparently didn't know what
> to do with it. Is CtrMcast assuming that links are duplex even when
> they're not?

Now, I see what you are saying. Yes, CtrMcast assumes links are all
bi-directional.  I.e., if two nodes are connected, they must be
connected with a duplex link or 2 simplex links with different bw and
delay.  Padma is right. The error is due to that CtrMcast is trying to
acess a non-existing link.

CtrMcast sets up reversed shortest paths. I.e., the mcast forwarding
entries are established along the shortest path from members to
srouces/RPs. Even if there are routes from members to sources/RPs, when
links are uni-directional, there might not be routes from sources/RPs to
group members. 

The above problem occurs in setting up mcast forwarding entries, CtrMcast
is trying to find the incoming interface of the data stream which is
determined by looking at the interface object at the tail of the link from
the 1-hop upstream node to the current node.

-Polly

> 
> thanks,
> 
> L.
> 
> and the IETF UDLR group is addressing similar problems in RL.
> 
>  
> > --Padma.
> > 
> > > -Polly
> > > 
> > > > As for simplex errors with CtrMcast:
> > > > 
> > > > ns: _o3116 join-group _o5342 0x8000: can't read "link_(6:5)": no such
> > > > element in array
> > > >     while executing
> > > > "return $link_($from:$to)"
> > > >     (procedure "_o4" line 6)
> > > >     (Simulator RPF-link line 6)
> > > >     invoked from within
> > > > "$ns RPF-link $target [$upstreamtmp id] $tmp"
> > > >     (procedure "_o4827" line 33)
> > > >     (CtrMcastComp compute-branch line 33)
> > > >     invoked from within
> > > > "$Agent compute-branch $s $group [$Node id]"
> > > >     (procedure "_o4970" line 27)
> > > >     (CtrMcast join-group line 27)
> > > >     invoked from within
> > > > "$proto join-group $group"
> > > >     (procedure "_o3120" line 4)
> > > >     (McastProtoArbiter join-group line 4)
> > > >     invoked from within
> > > > "$mcastproto_ join-group $group"
> > > >     (procedure "_o3116" line 5)
> > > >     (Node join-group line 5)
> > > >     invoked from within
> > > > "_o3116 join-group _o5342 0x8000"
> 
> <http://www.ee.surrey.ac.uk/Personal/L.Wood/>PGP<L.Wood@surrey.ac.uk>
> 
>