[zeromq-dev] why PGM is not a complete multicast protocol?

[Doron Somech]

I'm not 100% sure with my answer but I will try.

Q#1 - I think it is related to multicast communication between routers, PGM
cannot travel between networks (at least not without another protocol).

Q#2 - take a look at the RFC (https://tools.ietf.org/html/rfc3208),  in
general PGM works on NACKS, so when a receiver miss a message it multicast
every X second a request for the missing packets until received.

On Thu, Nov 5, 2015 at 1:53 AM, Noh, Jangho <jangho.noh at wustl.edu> wrote:

> Hello,
>
>
>
> I have questions about PGM.
>
>
>
> Question#1.
>
> According to Juniper Networks, PGM is not a complete multicast protocol.
> Why is that?
>
> How PGM makes distribution path???
>
>
>
> PGM adds reliability to multicast traffic streams. *It is not a complete
> multicast protocol* like the Distance Vector Routing Multicast Protocol
> (DVMRP) or Protocol Independent Multicast (PIM). Adding PGM to a router
> does not enable the router to perform multicast functions. Instead, a PGM
> router with multicast capabilities and a preconfigured multicast protocol
> such as PIM can offer more reliable multicast services to PGM sources and
> receivers. PGM is not an alternative to multicast routing protocols, but an
> enhancement of the multicast capabilities already present and configured on
> the router.
>
>
> http://www.juniper.net/documentation/en_US/junos13.2/topics/topic-map/mcast-pgm.html
>
>
>
> Question#2.
>
> How PGM receivers handle out of order packets?? (related to sliding window)
>
> Suppose a PGM receiver expects to get packet#1 but it received packet#3.
> And later on, the receiver got packet#1 and packet#2.
>
> Is there any specified document for this scenario?
>
>
>
> Any comments are welcome.
>
> Appreciate.
>
>
>
> Sincerely,
>
> Jangho Noh
>
>
>
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>
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