Subject: [manet] Comment on NHDP

From: "Teco Boot" <[email-masked]>
Date: Mon, 28 Jul 2008 19:15:17 +0200

All,

Let me repeat an older comment on NHDP (and OLSRv2).

The current document mandates exchange of ALL addresses on ALL interfaces of
the MANET Router.
E.g. page 11:
   o  A 2-Hop Set, which records the existence of bidirectional links
      between symmetric 1-hop neighbors of this MANET interface and
      other nodes (symmetric 2-hop neighbors).  The 2-Hop Set consists
      of 2-Hop Tuples, each of which records an interface address of a
      symmetric 2-hop neighbor, and all interface addresses of the
                                    =======================
      corresponding symmetric 1-hop neighbor.  The 2-Hop Set is updated
      by the signaling of this protocol, but is not itself reported in
      that signaling.

I prefer reducing overhead where we can, as bandwidth in the MANET can be
scarce and improvements on efficiency helps scalability.
IMHO a MANET router could advertize a single summary prefix into the MANET
protocol. For NHDP, a RouterID or alternative approach could be used for
identifying a MANET Router. Therefore I want to have removed specifications
that **all interface addresses** are exchanged.

Please respond on this opinion.

Regards, Teco

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From: "SATOH, Hiroki (HitachiSDL)" <[email-masked]>
Date: Wed, 30 Jul 2008 14:44:55 +0900

All,

I don't understand the merit of link metric routing calculation. I think 
if OLSRv2 have to support link metric calculation, control message 
overhead increase.

In our experience we have much effective to optimize neighbor 
connectivity locally more than link metric. Optimized neighbor 
connectivity method is checking the link quality; check link quality 
then if the link quality is bad, the link doesn't use.

In real world if we run 30 OLSRv2 nodes, which move around or not move, 
with link metric routing calculation, we have few effective compare to 
judging local link connectivity.

Regards,
Hiroki

------------------------------------------------
  SATOH, Hiroki (佐藤 弘起)
  Hitachi, Ltd., Systems Development Laboratory
  E-Mail:[email-masked]
------------------------------------------------
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From: Philip Levis <[email-masked]>
Date: Wed, 30 Jul 2008 07:55:16 +0100

On Jul 30, 2008, at 6:44 AM, SATOH, Hiroki (HitachiSDL) wrote:

> All,
>
> I don't understand the merit of link metric routing calculation. I  
> think if OLSRv2 have to support link metric calculation, control  
> message overhead increase.
>

You can think of your approach above as a binary link quality: good or  
bad. In practice, more bits of information are useful if you want to  
have good performance. I.e., a link with a 90% PRR and a link with a  
60% PRR are not equally good.

Phil

---

From: "Teco Boot" <[email-masked]>
Date: Wed, 30 Jul 2008 10:37:01 +0200

All,

My (well known) opinion: link metrics are important if links have very
different characteristics. The topologies I am working on are a mix of
radios and wired links. Data rates vary between 1Gbps (or more) and 2400bps
(or less). Moreover, the lower data rates are found on radios, where the
medium is shared. Also media access can have high overhead here and packet
delivery ratio may be less optimal. It is obvious a routing protocol without
metrics is not applicable here.
Note that state of the art radios have dynamic data rates, e.g. WiFi can
have 200Mbps down to 1Mbps.

The dearlove-olsrv2-metrics draft suggest a default metric, to be used in
environments where the overhead of metric exchange is to be eliminated. In
this case, the only disadvantage is the somewhat more complex coding and spf
calculation. IMHO this is minor and acceptable.
Please come up with real disadvantages, if exists, as I do not see any.

For the ones that prefer a more complex metric, please post on this, as I
cannot see how we can implement this on a short term. Also, there must be a
mechanism for a default routing table anyway and the dearlove-olsrv2-metrics
provides just that. I am not against enhancing the OLSRv2 protocol after we
have completed the basics.

Regards, Teco

> -----Oorspronkelijk bericht-----
> Van: [email-masked] [mailto:[email-masked]] Namens
> Philip Levis
> Verzonden: woensdag 30 juli 2008 8:55
> Aan: SATOH, Hiroki (HitachiSDL)
> CC: [email-masked]
> Onderwerp: Re: [manet] Comment on Link Metric routing calculation
> 
>

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From: Philippe Jacquet <[email-masked]>
Date: Wed, 30 Jul 2008 12:22:21 +0200

Dear Hiroki,

The overhead should not increase (at least not very much) since the 
topology reduction works similarly with general metric as with hop-count 
metric (default value).

I see your point about focusing on local link quality, but this would 
not work with multiple topologies. For example a high capacity link may 
have a bad energy balance and vice-versa.

You have also cases where local link admission control based on quality 
may be unstable and using link metric instead would give more stable 
routes, in particular when the network is very large (eg .Freifunk).

Best regards,
Philippe

---

From: Rex Buddenberg <[email-masked]>
Date: Wed, 30 Jul 2008 09:01:27 -0700

> metrics is not applicable here.

Teco's observations are on target.  The US Defense Department's internet
infrastructure is pretty representative: the terrestrial internet
(called Defense Information System Network) has OC192 backbones (10G).
And all of our Navy ships have ethernets with at least 100BaseT
backbones (and easily upgraded).  But the connectivity between these
'islands of wired' is in the 10k-and-less territory.  
	The four order of magnitude break here is a fairly constant ratio.
When I was a comms officer for the first time, the shoreside
connectivity was 64K and the ship-shore circuits were 75 baud.

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From: "SATOH, Hiroki (HitachiSDL)" <[email-masked]>
Date: Thu, 31 Jul 2008 16:04:14 +0900

All,

Thanks comments. I know Link Metric routing calculation is effective in 
theory and when we build mesh networking.

Here is paper[1] as consideration link metric on mesh networking with 
rate-switching control. This methods based on authors experiment in 
their test bed, so that it is very useful and practical, I think.

I still wonder effectiveness when we build mobile adhoc network or not 
so large static network (under 30 nodes include some mobile nodes). It's 
simple scenario on using MANET.

Regards,
Hiroki

[1]K. Mase, Y. Owada, H. Okada, T. Imai, "A Testbed-based Approach to 
Develop Layer 3 Wireless Mesh Network Protocols," International 
Conference on Testbeds and Research Infrastructures for the Development 
of Networks & Communications, 2008
------------------------------------------------
  SATOH, Hiroki (佐藤 弘起)
  Hitachi, Ltd., Systems Development Laboratory
  E-Mail:[email-masked]
------------------------------------------------
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