Subject: [manet] MANET protocol stacks

From: <[email-masked]>
Date: Mon, 8 May 2006 12:43:03 -0500

Joe Carey wrote on 7 May 06

> In a traditional OSI network model, there's the PHY layer, the LINK
> layer and the NETWORK layer.
>
> It appears from my limited exposure that the 802.11s protocol - and
> many vendors proprietary implementations of mesh - that they are
> attempting to implement multi-hop mesh networks at the LINK layer. 
> This seems to be exactly the wrong way to partition the problem; it 
> would seem that the store-and-forward nature of mesh networking,
> including multiple links, should remain at layer 3 (the IP layer), 
> where most current implementations have it.  However, these are 
> smart people with a lot of experience.  So what is motivating this?

Two comments:

1.  Actually, the OSI and Internet networking efforts have always 
considered hierarchical layering of networks, where one multi-hop routing 
network provides what looks like a link (via tunneling or routing through 
the lower network) to the higher network.

ISO 8648 "Internal Organization of the Network Layer" breaks the Network 
Layer into 3 sublayers:  SubNetwork Independent Convergence Protocol 
(SNICP), SubNetwork Dependent Convergence Protocol (SNDCP), and SubNetwork 
Access Protocol (SNAcP). 

IEN 48, "The Catanet Model for Internetworking" by Vint Cerf talks about 
the Internet as being a collection of gateways with interfaces to local 
networks.  The local networks in turn provide the higher layer with what 
looks like an IP link (even if it is tunneled through the lower layer). 
And, discussions of internet protocols in the 1970s and 1980s (before the 
7-layer OSI model became the de facto protocol model) talked about four 
layers:  a Host/Application Layer, a Transport Layer, an Internet Layer, 
and a Subnetwork/Local Networks Layer.  (For example, look at figure 1 in 
RFC 791 "Internet Protocol" where 4 protocol layers are shown.)  The 
subnet layer basically subsumes the OSI Physical, Data Link, and SNAcP 
functionality.  It was back then that we started talking about layers 3A 
and 3B.  Most say 3A = Subnet and 3B = Internet (although others say the 
opposite: 3A = Internet and 3B = Subnet).

Anyway, the point is that both the traditional OSI and the Internet 
protocol architectures assume that routing may occur at multiple layers.

And, when we think about wireline networks, I never see/hear arguments 
that MPLS/VPLS violates layering because routing is performed below IP. So 
why do we argue about it in wireless networks.

2.  I believe an appropriate architecture for MANETs includes two 
networking layers.  The two layers are the Internet Protocol layer and a 
wireless MANET layer.

The Internet Protocol layer provides networking where neighbors and links 
look nice and graph-like.  In other words, the links are independent(i.e. 
what happens on one link does not affect other links contrary to wireless 
networks where transmissions on one link can interfere or congest other 
links) and links are fairly reliable and stable.  And, the concept of a 
neighbor is straight forward.  In addition, the protocol suite is 
standardized and predicted to be stable on the scale of decades.

The wireless MANET layer provides networking where neighbors and links are 
fuzzy and less graph-like.  In other words, the performance of one link 
may be dependent on that of other links (i.e. what happens on one link can 
affect what happens on other links) and links can operate in all manner of 
dynamic, and possibly poorly predictable ways.  And, the concept of a 
neighbor is more complicated. In addition, the protocol suite may change 
as wireless technologies change - although the protocol suite should 
provide a standard interface and service to the upper IP layer.

Thus, I believe that the MANET work should focus on multiple layers like 
the original Internet model - namely the Internet layer (which may have 
different routing hierarchical domains, but links basically look nice and 
graph-theoretic-like) and Wireless Subnets that may be just a star-like 
WLAN based around APs or may be full-blown mesh subnetworks. 

In the MANETs that I am involved with, we do subnet routing to (a) hide 
the link dynamics in the wireless subnets from the Internet so that 
changes in subnet routes are hidden from the Internet, (b) we found it 
more efficient (from a throughput, spectrum usage, and responsiveness to 
RF dynamics) to adapt to the dynamics at the subnet - analogous to how 
MPLS is more efficient than IP routing for wireline subnets, (c) it allows 
us to do some nice information assurance defense in depth protection 
mechanisms tailored to the particular wireless environment we are 
operating in, and (d) it hides the evolving wireless technologies and 
their cross-layer solutions from the more static IP networking.

Jim Stevens

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
James A. Stevens, PhD
Chief Network Architect
Rockwell Collins Government Systems
_______________________________________________
manet mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/manet

---

From: "Paul Ward" <[email-masked]>
Date: Sat, 13 May 2006 18:06:23 -0400

How do you model ExOR as having "nice and graph-theoretic-like" links?

On 5/8/06, [email-masked] <[email-masked]>
wrote:
> graph-theoretic-like) and Wireless Subnets that may be just a star-like WLAN
> based around APs or may be full-blown mesh subnetworks.
>

---

From: <[email-masked]>
Date: Mon, 15 May 2006 09:10:24 -0500

Paul,

When you asked on 5/13/06 about how to model ExOR as having "nice and 
graph-theoretic-like" links, I think that your email implies that we are 
in agreement that wireless mesh networks have lots of interactions and 
effects that make it important to have merged cross-layer aware protocols 
rather than segregated cross-layer unaware protocols.

So, I recommend that we perform this cross-layer MAC/networking in the 
subnet below the Internet Protocol - leaving the Internet Protocol to 
operate with "nice and graph-theoretic-like" links.  So I would think that 
things like ExOR should be performed at a subnet (merged layer 3A/2) below 
IP rather than at a layer 3B.

Jim Stevens