Subject: Proposed BoF on Unidirectional Link Routing

From: Walid Dabbous <[email-masked]>
Date: Mon, 27 May 1996 16:26:02 +0200

Dear all,

We are working at INRIA on the problem of Unidirectional
Link Routing. We would like to have a BoF session during 
the next IETF in Montreal to discuss this problem.
A request has been sent to [email-masked]
to reserve a slot for the BoF session.

If you are not interested in the problem, sorry to bother
you with this mail!

If you are interested, here follows a description of the
problem and related information.

---------------
Today, all the routing protocols assume that communication is
bidirectional between directly-connected routers. Links may be
asymmetric, e.g., have different delays and throughputs in different
directions, but they have to be duplex.

With the emergence of satellite networks, communication can be
unidirectional. Feeds transmit information to satellites which is
broadcast to a set of receivers. In that configuration, there is no
possibility for receivers to communicate with feeds since there is no
up-link.

In that particular configuration routing protocols are not
operational. Indeed, routers exchange protocol messages only with their
neighbors. A feed will never receive protocol messages from a receiver
since communication is unidirectional. For instance, a feed that uses
RIP (Routing Information Protocol), will never advertise routes via
satellite links because it never processes responses that come from
receivers. Therefore, IP datagrams will not be sent over the satellite
network.

Routing is based on the exchange of routing information to discover the
topology of the network. Feeds must in somehow get this information from
receivers. This might be feasible if feeds and receivers can also
communicate via regular connections. Receivers will send protocol
messages to the unicast address of each feed instead of sending
broadcast messages. 

This lead us at INRIA to propose some modification to standard routing 
protocols in order to handle unidirectional links.  We propose three drafts 
that presents the modifications which can be applied to common routing 
protocols (RIP, OSPF, DVMRP). These drafts can be obtained from:
ftp://zenon.inria.fr/rodeo/udlr/
A more detailed description of the problem, and a proposed
charter for the (possible) WG will be put soon in this
ftp area.

A mailing list: <[email-masked]>
has been established to start discussing this problem.
to join the list please send an e-mail to [email-masked]

We are implementing the proposed modifications in a version
of gated, and we will experiment the modified protocols
on a satellite link for multicast video distribution over IP.
We would like to exchange views, and discuss the problem
with the experts in the routing area.

If you are interested in this problem, please join
the mailing list. If in addition you want to attend 
the BoF session and/or you have suggestions for the
agenda items for this session, please indicate this.

For general questions about the documents please send
e-mail to the udlr list.

For any further information, you can contact
[email-masked]
and/or
[email-masked]

Thank you,

Walid Dabbous

---

From: [email-masked]
Date: Thu, 30 May 96 16:49:19 -0400

> messages to the unicast address of each feed instead of sending
The use of routing protocols indeed makes sense at both islands that
are interconnected by a unidirectional link, but there is little
beyond a static route that needs to be applied to that link.

This entire subject (and BOF) might better be called 
   Handling of unidirectional alternate links with [OSPF|RIP]
                              ^^^^^^^^^
The papers offer nothing for sites that have only unidirectional
connectivity...they *demand* a bi-directional link in addition to the
unidirectional link.   While this is a useful addition to the protocols
in question, it does not offer anything to the sites with only
unidirectional linkage.  This ought to be made clearer.

	Walt