Subject: [manet] manet-arch-00 Terminology #2

From: "Ian Chakeres" <[email-masked]>
Date: Tue, 1 Aug 2006 12:57:14 -0700

A link is commonly defined as a communication facility between which
nodes can pass IP packets without IP forwarding. Here is the current
definition from draft-chakeres-manet-arch-00.txt:

Link
      A communication facility on a layer below IP, over which nodes
      exchange IP packets.  In a MANET, links may change quality on
      short time scales, present unique views of their local
      neighborhood, and have other challenging properties.

MANETs might use a link that is slightly different from existing like
types (e.g. non-broadcast (NBMA) and broadcast).

With NBMA, broadcast is not available. In a broadcast network all
devices are assumed to be able to broadcast to each other; a
completely connected set.

In MANET (see Section 3 in arch-00) you can have something in between
NBMA & full-broadcast. That is, a node can broadcast to a reachable
set of nodes (not necessarily bi-directionally) and each nodes'
reachable set is not necessarily the same.

I propose we term this link type as partial-broadcast multiple access
(PBMA - thanks to Fred Templin for the suggestion), as only a part the
set is reachable. NBMA < PBMA <= full-broadcast.

Using this type of link, existing definitions for link, neighbor, and
interface need not be modified. Regarding the draft arch-00, link,
neighbor, BI, & WBI might be revised given discussion on this topic.

Ian Chakeres

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From: David Young <[email-masked]>
Date: Tue, 1 Aug 2006 17:58:23 -0500

> set is reachable. NBMA < PBMA <= full-broadcast.

Now and then I have heard this link type called more succinctly (IMO)
"semi-broadcast."

Dave

-- 
David Young             OJC Technologies
[email-masked]      Urbana, IL * (217) 278-3933

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From: "Templin, Fred L" <[email-masked]>
Date: Thu, 3 Aug 2006 09:40:25 -0700

> Now and then I have heard this link type called more succinctly (IMO)

I don't mind "semi-broadcast". An alternative would be "Semi-Broadcast,
Multiple Access (SBMA)" (or even "Restricted-Broadcast, Multiple Access
(RBMA)") as a way of coining a familiar-sounding acronym. Here is a
proposed definition:

  semi-broadcast/Semi-Broadcast, Multiple Access (SBMA)/etc.
    a broadcast-capable link type over which a node's transmission
    coverage may be restricted and/or time-varying due to range
    limitations, terrain features, signal interference, etc.
    Ad-hoc wireless networks are the most commonly-cited example,
    but traditional link types such as Ethernet, point-to-point,
    etc. are also examples.

Fred
[email-masked]

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From: "Yi, Seung" <[email-masked]>
Date: Thu, 3 Aug 2006 11:29:10 -0700

I'm not quite sure if I buy this new type of link. It seems to me SBMA
or RBMA is simply a broadcast link that shows much less predictable
behavior. For example, if one uses a very low-quality coax cable to
deploy an Ethernet segment that has much higher loss rate than usual,
does that qualify as a SBMA/RBMA link or is it simply a broadcast link
implemented poorly? I can see the qualitative difference between an NBMA
link and a broadcast link. Does one exist (between NBMA and SBMA/RBMA)
and/or (between SBMA/RBMA and broadcast interfaces)?

- Seung

-----Original Message-----
From: Templin, Fred L 
Sent: Thursday, August 03, 2006 9:40 AM
To: David Young; manet
Subject: RE: [manet] manet-arch-00 Terminology #2

Fred

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From: "Templin, Fred L" <[email-masked]>
Date: Thu, 3 Aug 2006 11:56:25 -0700

Hi Seung, 

> I'm not quite sure if I buy this new type of link. It seems to
> me SBMA or RBMA is simply a broadcast link that shows much less
> predictable behavior.

If by "much less predictable" you mean "may be restricted and/or
time-varying" I agree. :^}

> For example, if one uses a very low-quality
> coax cable to deploy an Ethernet segment that has much higher
> loss rate than usual, does that qualify as a SBMA/RBMA link or
> is it simply a broadcast link implemented poorly?

That would be pretty much the same thing as an ad-hoc wireless
network in which some neigbhors experience signal intermittence,
fading, etc. A MANET routing protocol will run just fine on an
Ethernet just as for an ad-hoc wireless network, and if QoS
metrics are available it can route around such trouble spots.   

> I can see the qualitative difference between an NBMA link and
> a broadcast link. Does one exist (between NBMA and SBMA/RBMA)

Well, as I understand NBMA there is no L2 multicast/broadcast
capability and L3 multicast/broadcast is supported by unicast
emulation, e.g., MARS. So, a MANET routing protocol could still
run over NBMA but it would have to send NDISC messages to the
unicast addresses of neighbors which would have to be discovered
through some means other than multicast/broadcast transmissions.

For SBMA/RBMA, a node could send L2 multicasts/broadcasts and
could discover the existence of neighbors by listening their
(range-limited) multicasts/broadcasts.

> and/or (between SBMA/RBMA and broadcast interfaces)?

A broadcast link is just an SBMA/RBMA link that has the property
that all nodes hear the transmissions of all other nodes, i.e.,
its connectivity graph is a full mesh.

- Seung

-----Original Message-----
From: Templin, Fred L 
Sent: Thursday, August 03, 2006 9:40 AM
To: David Young; manet
Subject: RE: [manet] manet-arch-00 Terminology #2

Fred

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From: "NI, BIN" <[email-masked]>
Date: Thu, 3 Aug 2006 15:20:18 -0400

Dear all:

   Does anybody have the code of DSR simulation for NS2?  
   I would like to implement some variation based on the basic DSR protocl.
   Thanks very much!

Bin Ni