2.5.8 UniDirectional Link Routing (udlr)

NOTE: This charter is a snapshot of the 51st IETF Meeting in London, England. It may now be out-of-date. Last Modified: 31-Jul-01


Walid Dabbous <dabbous@sophia.inria.fr>
Yongguang Zhang <ygz@hrl.com>

Routing Area Director(s):

Rob Coltun <rcoltun@redback.com>
Abha Ahuja <ahuja@wibh.net>

Routing Area Advisor:

Rob Coltun <rcoltun@redback.com>

Mailing Lists:

General Discussion:udlr@sophia.inria.fr
To Subscribe: udlr-(un)subscribe@sophia.inria.fr
Archive: http://www-sop.inria.fr/rodeo/udlr/archive/threads.html

Description of Working Group:

Note: An alternate site for UDLR's files is: ftp://irl.cs.ucla.edu/pub/udlr

High bandwidth, unidirectional transmission to low cost, receiver-only hardware is becoming an emerging network fabric, e.g. broadcast satellite links or some cable links.

Two cases for unidirectional links support may be envisaged:

1. unidirectional links on top of bidirectional underlying network (wired Internet) 2. bidirectional islands connected via unidirectional links.

In both cases, the integration of unidirectional links may require changes to the routing protocols in order to preserve dynamic routing across these links. A short term solution (i.e. to solve the first case) is to adopt current protocols with possible modifications. A long term solution (i.e. for the second case) is to propose, design and implement protocols that remove assumed link symmetry (e.g. by supporting 2-way metrics).

There have been several proposed approaches for the short term case. The first is based on the modification of the common routing protocols (RIP, OSPF, DVMRP) in order to support unidirectional links. The second is to add a layer between the network interface and the routing software to emulate bi-directional links through tunnels.

The purpose of the UDLR Working Group, therefore, is to study these approaches and suggest a short term solution to provide dynamic routing (including multicast) in the presence of unidirectional links.

Goals and Milestones:

Apr 97


Meet at IETF. Finish discussion of the general solution.

Apr 97


Post the description of the proposed solutions and the issues for the short term solution as I-D(s).

Aug 97


Preliminary experiments results of the short term solution.

Aug 97


Post the description of the short term solution as an I-D.

Dec 97


Produce Informational RFC on the proposed approach.

Dec 97


End WG.

No Current Internet-Drafts
Request For Comments:






A Link Layer Tunneling Mechanism for Unidirectional Links

Current Meeting Report

UDLR WG at the 51st IETF meeting in London.


Agenda bashing 5 min

New charter 5 min

UDLR general presentation - Emmanuel Duros (UDcast) 15 min

DVMRP over UDLR - Yann Guinamand (Alcatel) 15 min

PPPoE over UDLR - Virginie Faineant (France Telecom) 15 min

IPv6 over UDLR (WIDE) - Hidetaka Izumiyama (JSAT) 15 min

Approach for scalable multicast (HITACHI-IT) - Hidetaka Izumiyama (JSAT) 15 min

Identifying security holes - Emmanuel Duros (UDcast) 10 min

Open issues / Discussions


* Agenda Bashing: Emmanuel Duros (UDcast)

* New Charter: Walid Dabbous (Inria)
Walid informs the group that two new co-chairs are candidate: Emmanuel Duros and Hidetaka Izumiyama
No comments from the group

* UDLR Presentation: Emmanuel Duros (UDcast)

General presentation on UDLR: history of the WG, description the Link-Layer Tunneling mechanism (LLTM) [rfc 3077], network topologies/hardware which benefit of this mechanism, open issues

* Configuration of DVMRP over LLTM: Yann Guinamand (Alcatel Space)

Presentation and characteristics of a satellite network topology using LLTM. Configuration of dynamic Multicast routing (DVMRP) on a feed and receivers
- Question by Walid Dabbous: will you be moving from DVMRP to another protocol ?
- Answer: yes, we are starting to consider PIM-DM

* PPPoE over LLTM: Valerie Faineant (FT R&D)

Presentation of a satellite network using LLTM. Interest in using the same techno used to deploy ADSL services in a satellite environment. PPPoE works fine over LLTM. Easy to provide satellite connectivity re-using known protocols and administration tools.

* IPv6 over LLTM: Izu (JSAT)

Presentation of an IPv6 satellite network connecting remote IPv6 network.

- Question Walid Dabbous: is the solution described already deployed
- Answer: yes, this is solution is currently used within the wide project
- Question ???: what about the quality of video/voice due to the narrow bandwidth of the return channel?
- Answer Izu: The receivers send back text or low bandwidth voice
- Answer Emmanuel: This is common practice, there is now problem to return voice with GSM quality on a 64Kbps link
- Question: The solution described brings IPv6 connectivity to IPv4 only domains, is it possible to do the opposite ?
- Answer: Yes, there is no problem to do so with UDLR.

* Experiment of scalable multicast: Izu (for Hitachi)
deployment of a satellite network using LLTM. Use of IGMP proxy protocol in order to provide dynamic multicast routing over remote sites. Use of exponential timers to provide scalable routing.

* Security holes: Emmanuel Duros

Identify a list of security holes within the LLTM: HELLO msg (sensitive information), stateless tunneling (authentication), and routing protocols (authentication).

The group agrees to produce informational RFCs:

Yann Guinamand: configuration of DVMRP over a UDL
Valerie Faineant: Use of PPPoE over UDLR
Izu: IPv6
Emmanuel Duros: Identifying security holes

Comment from Jun Murai:
terrestrial bandwidth is increasing, and satellite bandwidth is rather stable around 40Mbps. Is the group going to think about the potential bottlenecks regarding the difference of bandwidth between the two medias ?

There was an off-line discussion between Abha Ahuja, Rob Coltun and Emmanuel Duros: This question is related to a more general problem and is out of scope of the WG.


None received.