Re: Multicast Data

Adding to that that has been said:
-yes, you can loose first, second, third... any, cause Mcast runs
over UDP and there are no L4 delivery warranties. Actually, there
are very few L7 protocols that have assured delivery over mcast.

-registration does not stop when S (source router) receives join from
RP, so there can be many packets going unicast to RP.
RP tells S to stop registration after it receives direct mcast from S,
so no packets lost in between.

-sending can start before receivers have joined the RP, in which case
the RP will stop registration w/o joining the source. Then you it will
start a slow "flapping", trying to register every 3 mins, and being
call to silence untill a receiver shows up.

I guess you can loose up to 3 minutes of the show if nobody was
listening and you are late to the start :)

-Carlos

Kambiz Agahian @ 9/04/2010 3:44 -0300 dixit:
> Hi Tharin,
>
> Good point!
> First off, I'm hoping that my interpretation of your question is correct
> anyway correct me if your question if not exactly this but actually the
> problem is that almost all resources (including most pages on cisco.com and
> juniper.com as well as the RFC!) focus on the "second" action taken by the RP
> after receiving the registration request! and the first (but the less
> important action) is somehow ignored (or underestimated)....
>
> Here is the process (briefly):
>
> Your Windows 2003 Media server starts sending the Multicast packets of (analog
> term : broadcasting) "The Family guy". The first Mcast packets hit their
> gateway and the DR of that segment tries to get a hold of the RP to kick off
> the registration process. You know the encapsulation process (the actual mcast
> content inside a unicast packet - right?) so the RP gets the first capsule and
> "extracts" the multicast content. At this stage the RP has to take two
> actions:
>
> 1- It sends the extracted Multicast packet down the tree based on the (*,G).
> Where did you get that from? my Visa client had talked to his DR and his DR to
> his upstream then to his upstream...all the way up to the RP to indicate his
> interest. So before getting the first packet (the capsule) as you mentioned
> the RP does know that I'm waiting to watch Quagmire (there is a receiver down
> there). In fact the (*,G) is on the RP waiting for the source to come up.
>
> 2- The RP then tries to join the group and now everyone knows what's gonna
> happen afterwards...I save some key strokes.
>
> Well, as you see (the first action), even the first packet (probably the first
> frame of the Fox ad!) is delivered by the RP to (*,G) to ensure nothing's
> going to be missed.
>
> HTH
>
>
>
>
> Kambiz Agahian
> CCIE (R&S)
> CCSI, WAASSE, RSSSE
> Technical Instructor
> CCBOOTCAMP - Cisco Learning Solutions Partner (CLSP)
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>
> -----Original Message-----
> From: nobody_at_groupstudy.com on behalf of Tharindu Rukshan Bamunuarachchi
> Sent: Thu 4/8/2010 10:04 PM
> To: ccielab_at_groupstudy.com
> Subject: Multicast Data
>
> hi Experts,
>
> In sparse-mode, AFAIK first packet is forwarded to RP as unicast. (In
> Register Unicast process).
>
> Is there any possibility to lose first packet without being delivered to
> destination. (assuming destination is already subcribed to multicast tree)?
>
>
> __
> btharindu.blogspot.com
>
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-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net