Thuesday, December 10th, 37th ietf (San
Jose, California, US)
Reported by:
Walid
Dabbous - Thanks to Jean Bolot for taking notes.
Made up of four presentations:
-Experimentation at INRIA with modified RIP.
The INRIA solution is based on modifying routing daemons. Receivers detect dynamically the presence of feeds and send routing messages to them via regular connections.
There were a question from the AD whether there might be a bootstrapping problem in the general case, i.e if there were more than one unidirectional link. This is the general case, and will not be addressed by the UDLR group.
Jon Crowcroft: one way around that is to use OSPF instead of distance vector-like RIP. Or let the receiver mcast the information.
Steve Deering: also there is an implosion problem because if there are N receivers, then N flows on the return path would overload links back and the source as well.
-Modifications to DVMRP:
Regarding implementation of DVMRP, Steve Deering pointed to Tom Puisetiari's draft (available for 6 months).
INRIA is currently implementing the modification to DVMRP but these modifications are not working yet.
-DVB interface:
Description of the DVB interface at INRIA and of the European MERCI testbed.
Defines 2 UDLR models:
Mentions bootstrapping problem in general case, seems like no answer available.
Hugues' solution to pb 1, is based on the use of tunneling. They implemented it in linux. Hugues says their problem translates into the asymmetric link metric.
This is true in general, unidirectional links are just a special case of non symmetric links, with one metric being infinity.
Short discussion about whether INRIA and Hughes solution allow autodiscovery.
Their approach is not based on dynamic routing. Solutions:
- For the backbone application (equivalent to INRIA's subnetwork access), the solution is similar to Hughes' (called VIF, Virtual InterFace message). The unidirectional link is hiden at level 2 by using a VIF. Does not require a change in RIP current implementation. OSPF in debugging mode
- For the home application, the solution is based on Network Address Translation (NAT) (select return path depending on application).
Problems of the approach:
Scalability
Lack of transparency
MAC address of satellite network.
Ongoing work:
- VIF: finish OSPF, experiments in larger environments
- NAT: implementation and evaluation
- Support of multicast
Multicast tree construction in directed networks
A presentation about ongoing theory work on the more general case of links with non symmetric metrics.
They assume an underlying routing protocol (so udlr overlay, same as case 1 above)
In fact, amounts to adding/deleting senders and receivers using a CBT like architecture (with core/RV points)
Part C was a discussion, the goal of which was to decide:
do we need a WG, and if so what are the goals?
Walid presented the proposed WG charter. (See below) Emphasizes that WG would not consider impact on higher level (RSVP)
Discussion:
-Somebody says that the work should not be restricted to satellite unidir links, but to unidir links in general
- Steve D: VIF/Hughes does not need modification to routing protocols whereas INRIA does, so what is the advantage of INRIA's approach?
- Walid D: At this point, no claim from INRIA about which one is better. Scalability and transparency issues should be considered in the comparison.
- Steve D: Regardless of solution, need to look at routing specific solutions to non-symm links. So maybe the WG should be asymetric link routing, not unidir link routing.
- Joel says no, need to stay focused (and if everything's done in 2 meetings, then fine)
- Question about ADSL. What's the relation with IP over other non symmetric links like ip over cable, issll?
- If the answer is a tunnel, then please take one that already exsits, and that works. Joel: Note that what we are talking here is a control tunnel.
- Question about link state. No work yet on LS routing, yet needs to be looked at (for commercial reasons) and suspects there might be pbs.
- Steve D: how much do you expect to learn from implementation of your schemes? He suspects whatever implementation results are found by Hughes/INRIA will not help in deciding which scheme to pick.
- Walid D: back to having a focused WG. And shows goals/milestones (see proposed charter below).
- Again mention ip over cable etc, wgs that look like they have stuff in common. In fact, does not seem like we know what the cable model is.
- Joel: all milestones need some kind of output (draft or whatever) for the charter.
- Walid and Yongguang are willing to co-chair the group.
- Joel says continue on mailing list.
W. Dabbous slides are ftp://ftp-sop.inria.fr/rodeo/udlr/slides/general37.ps.gz
INRIA slides are
ftp://ftp-sop.inria.fr/rodeo/udlr/slides/inria37-s1.ps.gz
ftp://ftp-sop.inria.fr/rodeo/udlr/slides/inria37-s2.ps.gz
ftp://ftp-sop.inria.fr/rodeo/udlr/slides/inria37-s3.ps.gz