Re: Clarifications with RFC 3077

Hello William,

On Tue, 2002-10-29 at 12:01, William StanisLaus wrote:
> Hi all,
> 
>     I am a newbee to UDLR technology. I have few clarifications with RFC 3077.
> 
> Can you help me in understanding the concept.
> here we go.....
> 
> 1)
> 
> In Section 7
> "The number of feeds is expected to be relatively small (Section 3),
> so at every feed the list of all feeds is configured manually."
> 
> In Section 7.1
> When Feed multicasts the DTCP Hello Message, it passes the Feed Type
> 
> i.e.
>    F (1 bit): bit indicating the type of feed:
>       0 = Send-only feed
>       1 = Receive-capable feed
> 
> 
> So the Reciever can maintain the Feed type in the DTCP routing table.
> In Such cases, 
> for Scenario 2: "A receiver can send a broadcast/multicast packet on the
> link to all nodes (point-to-multipoint)"
> 
> Section 6.2.2 (3)
> As of now, Receiver sends packets to be broadcasted/multicasted to the default 
> feed and the default feed broadcast/multicast the packet to the other Feed & 
> Receivers.
> 
> 
> Clarification :-
> 
> When the Receiver maintains the Feed types, which is dynamic at any moment, 
> why Receiver is not multicasting to all the Feeds which are Send only?

The main reason I see is that it would be costly in term of bandwidth
for the receiving site. A copy of every multicast packet would have to
be tunneled from the receiver to each Send-only feed. It can get really
bad for the receiver if it has a low speed return link such as GSM or
RTC.

It is easier for the operator to set up high speed links between the
feeds and let them make the duplication of packets...

> It can also have a default Feed which forwards the packet to all receivers and 
> receive capable Feeds.
> 
> 
> The clarification is because, we have the overhead of encapulation at the 
> receiver side and sending to the default feed which decapulate and again 
> encapulate to send to Send only Feeds. Also in the Feeds the list of
> other feeds are manually configured i.e. Static. Might be broken at any time.
> 
> 
> 2)
> 
> In the RFC 3077 which explaines about the Feeds , i.e. Send only and Recieve 
> capable Feeds. But for receivers it is always targeted as Receive only. Just 
> imagine a RCST with send capable receivers i.e. which has both Tx and Rx port.
> 
> What are the configurations in the UDLR if the receiver happens to be send 
> capable.
> 

The receiver you are describing is pretty much similar to a receiver
whose return link is unidirectional. Am I right ? It seems the TX and RX
are 2 differents interfaces...

This situation can be handled by UDLR although RFC 3077 says the
receiver needs a bidirectional interface to send GRE to the feed. In
fact, as long as the return link can carry IP datagrams from the
receiver to the feed, the UDLR protocol will work. We've been using some
DVB-RCS systems with UDLR and it works pretty well.


> 
> 
> Thanks and Best Regards,
> William StanisLaus.
> 
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Regards,
> 
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